What community wouldn't give its right arm for an annual grant of that amount? The environmental philosophy is helping to disseminate an understanding of sewage treatment. It is being perceived as a separation process. There are a whole array of alternatives that can be used to separate. One approach is conventional technology. It contains three steps. The first one is called primary treatment, which is, by and large, mechanical. Skimming, screening and settling are used to remove material from the wastewater.
The primary step generally doesn't malfunction, since it's physical. The second step provides biological treatment, or secondary. A colony of bacteria feeds on the organic matter. Because it depends on living cells, it is subject to periodic biological upsets. The third stage--"tertiary" or advanced waste treatment- seeks to remove nutrients through a range of physical, chemical and ecological processes.
In any extent, anything removed must be taken someplace. The more effective the treatment, the more material that has to be taken someplace else. The conventional approach is what an economist would call non-productive. It's not producing goods and services that can be marketed. Therefore, we need tax money to construct, operate and maintain such systems. And as construction costs go up, we need more money. Federal and state participation is a subsidy helping local units of government to construct these systems.
It involves agriculture; it involves open space; you can't do it on asphalt. You have to have land and you have to have growing crops or trees. Therefore, it has the good air quality implications. It has implications with respect to urban sprawl. The first one is pre- treatment. You do not irrigate with raw sewage. How you pre-treat is going to be determined by local conditions. I prefer a pre-treatment system that minimizes sludge production, because it's difficult to handle and get rid of. The pre-treatment avoids nuisance conditions. To beneficially use the pre-treated wastewater, storage must be provided.
Crops don't need to be irrigated during the non-growing season and you don't want to be irrigating when you're trying to plant or harvest the crop. So you need a means of storing. Incidentally, that's a U. Many people say, "Well, there were sewage farms in Germany, Australia, Paris. When it was raining eight inches during the day, they had still to irrigate.
When the ground was covered with snow and a mess, they still had to irrigate. Those of us in America, and I think it's an American contribution, we said, "Hey, we can store it, and irrigate it when the crops need it. A contribution which made land treatment work, one which made Muskegon quite different from any other land treatment system in the world.
We select the storage to fit the area we are in. The amount of storage is obviously dictated by the climate. After storage, we irrigate. The irrigation of the pre-treated, nutrient-rich stored water takes place at an appropriate site on selected crops. Wastewater with a high concentration of cadmium should not be used to irrigate leafy crops, like lettuce. Cadmium will be accumulated in the leaves. There is a wide range of crops to consider. There is a wide range of wastewater char- acteristics. What happens when wastewater is put on the land?
Some of the nutrients are recycled by the plants. The organic matter is added to the soil to enrich it and improve its tilth. Pollutants not recycled generally are confined and contained. Some are not. Salts which are dissolved in the wastewater may flow through the soil. Therefore, any properly designed land treatment system is going to have an under-drainage system that is going to collect this material so that we can avoid two problems: salt build-up [in underground water] and water-logging [of the soil]. Heavy metals are primarily confined.
A few of them will migrate or be taken up by the plants. That's why I used cadmium as an example. That's the most difficult one to deal with. Therefore, we have to plant crops, if we have a cadmium-rich wastewater, that aren't going to be affected adversely by the cadmium. With the under-drainage system we come out with reclaimed, purified water and crops. We have a productive system, one which has the potential to increase our production of food and fiber.
The federal and state participation can be viewed as an investment in the production of future food and fiber. The justification is that federal money in innovative and alternative systems such as land treatment is an investment in the production of future food and fiber. There are working examples of large-scale land treatment systems.
Muskegon has had problems. It was a first. Irrespective of the problems, it's gone through its second year with essentially a million-dollar crop return on the County's wastewater. I don't think there's any other system that can claim that. Muskegon was a very poor agricultural area prior to it. It is now one of the leading agricultural counties in Michi- gan.
Sales of fishing licenses, particularly 3-day out of state licenses, increased drastically in Muskegon. New plants were located there. Existing plants were expanded. All the so-called good things to a Chamber of Commerce took place in Muskegon. Yet, the staff at the National Chamber of Commerce has not been encouraging efforts to allow communities to recycle their wastewaters.
I believe the economic issue is resolved. There are enough examples of land treatment systems to show that large systems are viable, both in the humid and the arid parts of our nation. Legislation is changing. I refer to the Amendments. Dave Zwick [of the Clean Water Action Project] would agree with me, when the law was passed, we thought we had solved the problem. When Senator Muskie went on the floor of the Senate and said the Federal Water Pollution Control Act Amendments of mean one simple thing: "streams are no longer a part of the sewage treat- ment process," it appeared that we were on the road to clean water.
Little time elapsed, how- ever, before pollution administrators were trying to figure out the assimilative capacity of streams. They were working out waste load allocations, sophisticated models to see how much pollution we can put in the stream before we break its back. That showed me that legislation probably would never solve the problem. There is encouraging action. If land treatment is not recommended, the community Is to explan why it could not do it.
State water pollution control commissions are approving recycling systems, sometimes against the recommendations of their technical staff. The Northglenn, Colorado system is proceedinq. Northqlenn said there are better ways for cities than to condemn farmers' water and to put farmers out of business.
A better way is to borrow the water. This approach, incidentally mitigates flood problems downstream. There are many private actions taking place in the U. Lubbock Christian College has signed a contract with the city of Lubbock, Texas. For 20 years they're going to take the effluent from Lubbock and they're going to irrigate farm land which was donated to the College. El Reno, Oklahoma will be selling its effluent to a private farmer. Because it is the most economical way. Arguments that it costs too much to go to land treatment certainly are paling in the light of such evidence.
The private sector selects the most efficient systems, because they have to pay for them without federal or state grants. Self-contained wastewater urban systems are being more and more frequently articulated as the goals of new urban development. What does this all mean? We're going to clean up our water. We can't afford to pollute our streams.
We need the nitrogen, we need the phosphorus, we need the organic matter. Pollutants, or displaced resources, will be used rather than discharged in the water. The only conjecture is, when? Properly informed citizens are getting the upper hand. The management of wastewater as a resource in a comprehensive program is an idea whose time has come. Now is the time to get involved. I'm striving to break the shackles of polluted water, confrontation politics, technical distortions, inflation, frustration, and negative attitudes about waste.
I'm looking forward to clean water! I'm not too fond of a couple of them, although they have their applications. I'll discuss the three methods in order of their increasing ability in pol- lution control performance, which is also the order of the degree to which they accomplish recycling. I really do believe, as Jack Sheaffer mentioned, that everything's got to be some- where. And I think it's got to be recycled or spread back out, not accumulated.
The first type of land application system which is the least effective at removal of pollutants and the least effective at accomplishing recycling, is known as infiltration-percolation. With this technique, a wastewater that has had primary or secondary treatment, is simply percolated into the ground and groundwater. It doesn't take much land, as hydraulic loading rates are high.
A typical system would use from 10 to 25 acres of ground per million gallons a day of wastewater or roughly 10 to 25 acres per 10, population. Obviously, this accomplishes high recharge to the groundwater table. It may not discharge the best of water, but it does have that benefit of high rate of recharge to the groundwater. It does not recycle contained nutrients.
So it's low on my list of technologies that are applicable today. This system is called overland flow. With this technique, primary or secondary treated wastewater is spread on the ground through sprinklers or other distributing devices. The ground receiving the wastewater slopes very gently, at maybe two or four feet per hundred feet.
This system will treat a relatively raw wastewater. For example, a wastewater that has been settled in a tank for maybe 10 or 30 minutes. Now, strangely enough, various grasses can be grown on those slopes. And strangely enough, this is most applicable where the soil is very tight, like clay, which will not accept much water. A little further down, a reduction of nitrates is accomplished nitrogen goes off into the air as a gas. Overland flow does not contribute to groundwater recharge, but it does discharge an effluent better than many of the older conventional secondary treatment process and it is con- siderably cheaper.
There are several of these systems around the country which are quite suc- cessful. These systems have to some extent been made famous by the Campbell Soup Company who had good results with this type of system. The third and best type of land application system is irrigation with pre-treated wastewater. Roswell, New Mexico, for example, uses this technique. At Roswell, the wastewater undergoes conventional secondary treatment before it is sold to farmers for use in the irrigation and fertilization of forage crops.
It's actually rather a shame to spend the money to treat the wastewater in a conventional secondary treatment plant prior to irrigating forage crops, because the secondary treatment is expensive and removes some of the goodies which would be a benefit on the field. While there may be some application where that would make sense, usually it would not be warranted. The degree of pre-treatment depends on the soil and type of crop to be irrigated.
Too much pre-treatment increases cost and reduces benefits. For an extreme example, one would not design tertiary treatment in a system to irrigate hay. The irrigation technique accomplishes very high removals of suspended solids, BOD, phosphorus, nitrogen and the heavy metals. Further, research produced at Muskegon by EPA shows good removals of most of the feared toxic organics. The irrigation technique is best, over- land flow is next best, and direct infiltration is the lowest on the ladder of land application techniques.
That is designed for 44 million gallons a day. It's in operation now at something like 25 to 30 million gallons a day. Melbourne, Australia is the largest. There, an irrigation system has been in operation since the turn of the century. There is a two-and-a-quarter million population whose wastes are treated by irrigation of a 20, acre beef ranch. Part of the area is irrigated with raw wastewater and part with secondary effluent. There is a guest house in the middle of the farm.
The recycling program is really considered a use of the resource for the benefit of the public, and they grow beef there and have for years and years. A significant wastewater irrigation project is under construction at El Reno, Oklahoma. The system is designed for a 25, population. It will be completed in December The plan- ning was begun in , so accomplishing this recycling project has been a lengthy process. El Reno is on the North Canadian River, in a three or four mile wide river alluvial valley. This alluvial valley is filled with sand, gravel, silt and clay to a depth of around 50 feet.
Two reservoirs are located on the river, about twenty miles downstream. The reservoirs supply water for Oklahoma City. Water wells adjacent to the river supply water to Yukon, Oklahoma, about ten miles downstream. This river, like so many rivers, has been receiving the wastewater, treated or untreated, depending on the situation, from various towns for years and years. The permeable alluvial valley is saturated with groundwater. Much of the land in the flat valley is irrigated. There is a very strong, competing demand for the limited amount of water in the Canadian River valley.
The irrigators need and use it. But likewise, the municipalities need water. The cities also use groundwater, and then discharge the wastewater into the stream to fertilize, and therefore pollute, the river and downstream reservoirs. This competition and pollution con- dition set the stage for an exciting project. Now the city will get the groundwater from the farmers and the farmers will use the nutrient-rich wastewater to irrigate and fertilize the crops instead of fertilizing the river.
The system consists of simplified lagoon pre-treatment and conventional center-pivot irrigation. The simple lagoons function as storage reservoirs also, allowing the water to be used only when it's beneficial to do so--that is, the crops will be irrigated only when they can utilize the nutrients. They will not be irrigated during freezing or wet weather.
A significant thing is that in the development of the project, an objective was to get the farmers involved in the project, and to establish an air of competition for the wastewater. For sure, that wastewater is very valuable. It contains the water and the nutrients. So early in the project, we met with seven different groups of farmers, some near the proposed lagoons, some across the river, some upstream and some out of the valley, and talked with them about this con- cept.
They seemed to like it. We held those meetings a couple of times during the planning and design process. It's hard for a civil and sanitary engineer to talk with farmers because engi- neers are not noted for their knowledge about agriculture. So at first it was difficult to gain their respect, although I could tell they thought this system would work.
So we called in Mr. Frank Gray from Texas. He is a farmer who has used wastewater for years. He helped to gain the confidence of the farm community. And after competitive proposals from the farmers were reviewed, we signed a contract with one of the farmers to use the wastewater on his land. We did not have to buy the land. The farmer is paying the city a significant sum of money for the wastewater, nutrients, and use of the equipment.
In addition, the farmer operates the irri- gation activities. And, most importantly, the farmer has transferred to the city his ground- water rights in an acreage equal to the acreage that is irrigated. The cost for this system handling 2. Abney works with local agencies in dealing with prohibitive health regula- tions for implementation of on-site disposal systems. Planned the Fountain Run Kentucky facility plan, one of the first in the nation to consider on- site and cluster disposal systems.
Emphasis on favorable ecomomia and environrrtental impacts for users. Specializes in appropriate technologies. Consultant and specialist in water and sewer issues, Strasburg, Virginia. An engineer who has specialised in composting, Lindstrom was responsible for research on waste treatment technologies at Sweden's Environmental Protec- tion Agency, before becoming the Environmental Attache to the Swedish Embassy. Clivus Multrum manufactures the oldest Swedish waste composting system. It is just nonsense that we do it that way. Some of us have seen that our traditional centralized urban approach to the wastewater planning problem has not solved the problems in all communities in the manner in which we had hoped.
This basic urban approach could be stated in two basic concepts: the primary concept is that the ultimate goal of wastewater planning should be regionalization of all wastewater collection and treatment. And this has resulted in extension of sewers through undeveloped land, construction of treatment plants which replace other treatment plants, and regionalization of these systems. And increasing costs for wastewater management. Part of this concept included the oft-repeated statement that septic tanks and other on-site systems should be judged as only temporary, until sewers could be provided.
In addition, it was felt very strongly that all good systems were scale versions of centralized urban systems, even in very small towns. Economic and environmental costs of centralized systems were considered inevitable, if considered at all. In fact, before the Clean Water Act and the resulting facilities planning guidelines were published, the consultant often merely wrote a feasibility study and presented one alternative with no consideration of an environmental impact at all. This was a very common practice and was part of the reason that consultants resisted the facil- ities planning guidelines.
There are some disadvantages to this urban approach, as we are now beginning to realize. First, the economic cost was found to be a disadvantage in many areas. Economic costs became dispro- portionate where certain key social and environmental conditions departed from the typical urban model by more than certain amounts, and we have begun to recognize some rough rules of thumb.
Well, we find that the costs of a centralized system are high where population density is less than 10 persons per acre. Where the topography is flat or rolling, costs are increased. Where the depth of bedrock is less than six feet, and where unstable soil conditions exist, the costs of centralized systems are greatly increased.
These often stem from the plant's failure to meet the design effluent criteria or perhaps failure of operation, such as through neglect. Other negative primary impacts may, in some areas, include: exfiltration, which is seldom considered by consultants; overflows due to storm water or other overloads; and pump failures. Secondary impacts would include unplanned growth resulting from a sewer construction project, which perhaps would have an impact on air quality in some areas. Now, there are changes occurring in wastewater planning.
We are beginning to realize that on- site systems may in many places have a proper role in community wastewater planning. Advantages of on-site treatment and disposal systems may include: lower monetary cost to users; reduced primary and secondary environmental impacts as compared to sewers, of course ; the possible development of marginal land with on-site systems, where sewers would be too costly to install. On-site systems may permit the development of residential lots of a large size, such as one acre or more, where this is desired by the community or the people.
Remember, the persons utilizing on-site disposal are taxpayers, and they may not have been getting an equitable return on their tax dollars under previous policies. Bosly, in Indiana, analyzed the assessed evalua- tion of sewered versus unsewered properties in that state.
He found that there were approximately 6. On the other hand, there was 5. According to the wastewater needs survey, those properties had no wastewater needs, at least not officially. Populations using on-site wastewater disposal were virtually ignored in the needs survey. But some recent policy decisions have begun to change the traditional concepts about wastewater planning.
Primary among these would be U. EPA program guidance memorandum which was issued June 21, It established requirements for considering on-site disposal in a commun- ity's wastewater plans. It stated that future collection systems must show that there's an adequate capacity for treatment, that there's an adequate population density for sewering, that there's documentation of any claimed health or groundwater problems caused by existing on-site systems.
It stated that if it is claimed that there are site restrictions against the use of on- site disposal, these must be carefully documented. The planner wishing to install collection must also identify the nature, number and location of malfunctioning on-site systems. And fin- ally, it's required that any sewers proposed be shown to be clearly more cost-effective than on- site systems.
Particularly where population density is low. Alternatives which were required to be considered by this memorandum include: improved operation and maintenance of on-site systems; new septic tanks; holding tanks; truck transport; mounds or other designs for overcoming site limitations; clustered systems; water conservation systems; and partial sewering, as of a simple small business district in a small town. The Clean Water Act of also contains provisions which should enhance the consideration of on-site disposal, as you'll learn later in this conference.
Some states have taken positive actions, independently of the federal EPA, to encourage the con- sideration of on-site wastewater treatment and disposal. Chief among these would be the Illinois EPA. Guidelines used there parallel the new federal guidelines, and they also provide screening criteria for planners and engineers.
There's increasing activity related to the development of technical manuals. Design manuals are considering on-site wastewater alternatives. These have been funded byttie EPA. A new manual for on-site wastewater system design should be available in about a year. What are some examples of on-site wastewater planning? There are some on-site services provided by local governments, mostly in California.
These would include county health departments, which may design and provide some maintenance, or at least maintenance inspections, to all on-site systems, and perhaps order the pumping of septic tanks, or the repair of leaking absorption fields after this annual inspection.
In some counties, there may be established specific sub- divisions which have public maintenance of on-site wastewater systems. Some special districts have been established. These include the Santa Cruz Countywide District in California and the Georgetown Divine Utility District in California, which was established to provide on-site systems design, construction inspection, and operating assistance to a large sub-division develop- ment.
One community, Bolinas, California formed a utility district to manage on-site systems to avoid the extention of sewers, which they felt would change the nature of their community. Other plans are probably being developed under the impetus of the new criteria published by EPA. The community of Fountain Run, Kentucky, was one where we considered four basic alternatives.
Fountain Run is at present an unsewered community. There are no sewers, except for house to septic tank sewers, in the entire small town. There are about people living there. They have a water district which provides public water services. But they have no wastewater services, other than those provided by private contractors and perhaps the county health department in a regulatory sense.
The second alternative was for the installing of septic tanks, or upgrading septic tanks in each home and carrying the septic tank effluent to a central system. The final alternative, complete on-site disposal at each individual business and residence, was rejected by the local people because they felt that it would not be that much different from what they already had; they did not recognize the advantages of properly designed and maintained on-site wastewater systems.
This decision was the result of a public hearing and much discussion. It consists basically of 22 subservice disposal areas in the community which would serve the majority of the potential customers. There would be an additional 20 or so individual on-site systems which would also be publically managed, if the residents desired that type of management system.
It can be seen that the subservice disposal alternative, although very unconventional and not providing the growth potential that a conventional sewer may have provided, was clearly the most desirable alternative in this small community. Application of this concept is hindered by several factors. They include the growth psychology which is prevalent in some areas, prejudice against septic tanks and against four-inch sewers which would not have any manholes, and a lack of profit incentive for change agents such as con- sultants and developers.
Some persons have expressed strong concern about the possible groundwater contamination resulting from on-site disposal by subservice application. There have been several studies of groundwater which did not show significant impact from subservice disposal of septic tank effluents. These include a University of Michigan study at Travis City, Michigan, where sandy soils and high groundwater combined to provide conditions which would normally be thought of as conducive to groundwater contamination.
But the researchers in that study could find no correlation between any parameters related to septic tank effluent except nitrate. They predicted that by , if growth continued in the Travis City area, that nitrate as nitrogen might rise to about 2. This is approximately one-fourth the drinking water standard.
Therefore, no serious result or affect on groundwater could be predicted in that area. There's another study by the U. Geological Survey in Dade County, Florida, where , septic tanks existed. The U. Geological Survey could not find a correlation between groundwater quality and subservice disposal or septic tank effluents. I've often heard it said that the average septic tank system only lasts about seven years.
Some studies have found this to be untrue. The Connecticut Agricultural Experiment Station in published a report which summarized their findings in one Connecticut town. They found that in dense glacial till, the least permeable of the soils studied, that the half life of septic tanks equals 38 years. That is, in 38 years, one half of the systems could be expected to fail. So we can summarize by saying that traditional sewers and centralized treatment of wastewater has not been a very successful means of wastewater management in many places.
Also recent federal, state and local actions have enhanced the viability of on-site wastewater management alternatives, including septic tanks and subservice absorption.https://spacbodisthora.gq
And finally, the use of on-site alternatives, may result in lowered monetary and environmental and land use impacts. Our wastes have been returning with a vengeance. We have to connect our plumbing with the natural cycles for the greatest benefit and the lowest cost to us all. We have to treat nature as an ally and not as an adversary. Thomas Elliot said: "The end of all exploring is to return where you started and know the place for the first time. One adversary that can be an ally is the hyacinth. Millions and millions of dollars have been spent trying to poison it in Florida because it literally takes over the waterways.
One day they discovered it might be a benefit. They fed some of this plant, literally, some raw sewage. It started to grow at a very, very fast rate. So fast, in fact, that it was completely taking over the very small lagoon that the raw sewage was going into.
The uptake of nutrients produces roughly anywhere from 8 to 16 tons per acre of green material per day feeding on raw sewage. A single acre of sewage growing hyacinths can produce enough biomass to generate 3, to 7, cubic feet of methane gas daily, which, in a sense, is cogeneration.
The by-products, of course, can be used for feed stock because it is very high in protein. Greenhouses can be added to the pond treatment system, increasing the temperature and boosting the process. This is an aquaculture system. The city of Hercules, California is currently planning a waste treatment plant utilizing water hyacinths and other aquatic polycultures. This is followed by sun filtration and then disinfection. I know of places where ozone is used rather than chlorine, because ozone doesn't have the propensity to form substances with carcinogenic properties that may be attributed to chlorine.
The treated wastewater could then be sent into a reservoir where it is reclaimed for agricultural and industrial uses. The treatment ponds vary from six to eight feet in depth, which seems to be the ideal depth for the polyculture. Fish can be used along with plants to eat the sewage. The fish are harvested.
The plants are also harvested daily and put into a methane generator and the methane provides the fuel to heat the'solar ponds. There are on-site systems that get away from the flush toilet entirely, which I'll leave to other speakers. Generally on-site treatment refers to privately owned and operated septic systems comprised of a septic tank and leach field.
There are variations to the standard septic system, which I will describe later. The Clean Water Act of gave all these on-site systems a boost by making them eligible for federal funding under certain circumstances, even when they are privately owned. The purpose of on-site wastewater treatment is no different than any other kind of wastewater management.
The intention is to provide for safe disposal of all wastes in a way that prevents the contamination of surface water, groundwater, land, and air. What distinguishes on-site systems from other sewerage systems is the wastes are treated at the same location where they were produced. This singular aspect of on-site treatment has both advantages and dis- advantages.
The advantages include less monetary and energy costs for conveyance of wastes to the treatment site, direct recycling of wastewater to replenish the groundwater or to be reused in ponds or irrigation, and simpler treatment technology due to the lack of toxic materials in wastes. The disadvantages of on-site systems stem primarily from poor design, poor construction, and poor maintenance, all of which result in inadequate treatment with possible public health con- sequences and groundwater contamination.
Additionally, many planning agencies view septic systems as a threat to good land use planning because on-site treatment allows decentralized development apart from the restrictions set by the central water and sewer services. A bias against septic systems is seen everywhere, starting on the first page of the Public Health Service's Manual for Septic Tank Practice, and filtering into most branches of the govern- ment, into engineering schools, throughout public health departments, and most particularly among consulting engineers.
Septic systems generally are viewed as health hazards, leading to water pollution and shallow well contamination. It's no wonder: most of these systems were designed according to the outdated Manual of Septic Tank Practices which is largely responsible for the "creeping progressive failure," seen in many failing systems. But most importantly, there just isn't much profit in these systems, because any competent backhoe operator can put one in, they work uery well, and they use very little energy to operate.
For all these reasons, the general tendency has been to discontinue use of septic systems, even if they are operating well. Between and , 10 million homes with on-site treatment were connected with sewers. No one knows how many of these were done needlessly. Today this trend has reversed somewhat, as the shift to the rural countryside increases. We can only hope that what we are doing now will help reverse the poor record of on-site treatment. Good engineering is available today to make these systems work even better at lower costs and more environmental protection.
Nearly one-third of the U. These systems are good reliable equipment which have already been paid for, and short of the improper maintenance given to most, they are one of the cheapest, most reliable, and stable wastewater management systems there are. Many people do not realize that on-site systems actually have been utilized for many decades and that they can per- form reliably often for the life of the home they serve.
Some soils are more porous and biologically active than others. Poor soils may not be suitable at all. Generally, the poorer the soil, the more it will cost. A lot of people are getting sewer bills like that every month these days to pay for advanced waste treatment plants. A leach field can cost considerably more, again depending on the amount of wastewater and the local soil conditions. Even so it is the least costly of all systems.
It requires little maintenance and it may not use any energy. I am reluctant to stress this aspect of low maintenance because people say, "Well a little maintenance: that means every five, six or seven years I need to get the honey dipper in here and in between I can just forget about it. A septic system gives very effective treatment. One of the nice things about it is that it doesn't act up if you go away for a weekend, a month, or even a year.
In fact, it's really good for it if you go away for awhile, to let the soil dry out and rejuvenate its good filtering capacities. It is reliable for surge flows; if you have 20 people in for the weekend, it can handle that too. It's very dependable in highly variable situations.
And no power and moving parts means there's no energy cost, unless of course a pump is needed to pump the waters uphill to the leach field. It also has a self-stabilizing mechanism, characteristic of biological systems. There are also some disadvantages. Obviously, adequate space is needed and good soils are nec- essary. This simple design for the leach field cannot be used in shallow bedrock because drain- age is poor. Similarly, a high water table will interfere with good treatment because treatment is dependent on the stability of the biological community in the soil.
If the water table fluc- tuates rapidly or is generally high, then the biological integrity of the field is going to be impaired somewhat. Such conditions require changes in the leach field design, which I'll get into later. The soils in the leach field are the most sensitive component of the whole system.
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It is critically important to protect them, both in the construction process and throughout its life. Oftentimes the system gets dug in wet seasons when it's easier to dig. That is fine, but they never should be completed then. Wet soil compacts very easily. What happens is that the sides and the bottom of the leach field are smeared, effectively limiting the amount of porous openings in the soil.
The water does not pass as easily against compacted surfaces and the biological degradation of the wastes is impaired. This kind of smearing or clogging often begins in the construction phase, producing a system that is prone to progressive failure. What is actually happening is that a good bit of your treatment capacity is eliminated from the outset. The soil in the leach field can also be compacted by machinery, cars, or motorbikes over it. My recommendation is that you should never take anything over a leach field heavier than a hand- pushed lawn mower or maybe a roto tiller, at the maximum.
Even this will compact it some, but the effect is marginal. All homes should be accompanied with a map of the leach field, so that this rule can be respected. Figure 3 shows a diagram of how the water enters the pipes in the leach field. In normal gravity feed, a whole stream of water enters in a surge. Obviously it's going to take the course of least resistance so most of it will percolate downward at the beginning of the line with less and less as it moves down the line.
This slowly builds up a condition of clogging at the begin- ning of the line and as the system is used longer, you'd have what is called "creeping progres- sive failure. This can be achieved with pressure distribution using a simple one- third horse power pump. An additional benefit of this system is that all the water is distri- buted at once rather than being allowed to trickle out. This gives the soil a chance to dry out, allowing the aerobic bacteria to breathe. The aerobes take over when the soil is not engulfed with water and the anaerobes thrive when the field is inundated.
This teamwork between the two kinds of microbes gives excellent treatment. Pressure distribution, dosing the absorption trenches, or alternating leach fields will maximize this teamwork arrangement between the aerobes and the anaerobes. They have found these methods result in much longer life of the absorption fields. October In systems where conventional leach fields do not work well because of poor drainage or poor top soil, there are other ways of dealing with wastewater on-site. In a mound, water is pumped uphill to a leach field constructed a few feet above the normal grade see Figure 4.
Additional soil and sand are brought to the site and mounded over the area to be used for the leach field. The sand is laid down on the grade, followed by the gravel, the drain pipes, more gravel, and finally covered over with good soil. These can be expensive because of the site-specific design, the transportation costs, and the fill itself.
They also have regular operating costs for the electricity to pump the septic tank effluent to the leach lines, but these expenses are worth it to many who could not build on their site with some special design as this. Evapotranspiration beds see Figure 5 are similar to mounds except that they rely on evapora- tion and transpiration for water disposal.
However, unlike mounds, an impermeable liner is placed underneath the mound. This is particularly valuable where the groundwater is very high because it should prevent contamination. The surface vegetation utilize the nutrients and evaporate the water through its leaves in a process called transpiration.
These ET beds are more likely to work in Southern climates that are not quite as harsh or in summer homes in Northern climates. It bubbles air into the tank in order to maintain an aerated effluent. These aerated units cost a good bit more than regular septic tanks and they have high energy costs for operation. Maintenance has caused many owners to discontinue using them. The manufacturers often recommend them in cases where the leach field is ponding, with stinky septic soup flooding lawns. They do help for a year or so to clear up the symptoms, but since the problems began in the leach field, the ponding will return.
When a leach field is misdesigned, misconstructed, and mismanaged, a remedial solution for the septic tank will not do the job. It is much better to let the field dry out by itself and put in a new one to use alternately. Sand filters are now being suggested by the Wisconsin people as a follow-up treatment for the septic tank, before the water flows into the leach field.
They are useful in cases where the leach field is quite close to a stream. Sand is a fairly effective medium to filter out bac- teria and there is also some nutrient removal. Before I conclude my remarks on on-site treat- ment, I want to acquaint you with some innovative work being done by Dr. He is feeding sanitary wastes from pigs directly to fish ponds. A grouping of eight different species of fish, primarily some Chinese carp, perform the treatment and most of them can be used for a harvestable cash crop. The resul- tant water quality is good, the crop is of high quality, and the environmental impact appears to be negligible.
These systems are operating throughout the Midwest now, with one of the most interesting applications being a state hospital in Arkansas. Aquaculture appears to offer much promise for small communities, and it suggests that the thousands of lagoons we have all over the country might offer a means of recycling the nutrient value of our wastes directly into harvestable crops used for feed instead of needing to further treat them on the land. Concluding Remarks The work of people like Tim Winneberger in California, Dick Otis and Bill Boyle in Wisconsin, Jack Abney in Kentucky, Rein Laak in Connecticut and others, coupled with renewed interest in on-site systems at the federal level, has shown that today the future of on-site is brighter than ever.
New engineering developments, along with a tested model of on-site management have significantly advanced the field of on-site treatment and disposal. For the public to benefit from this technology, its use must be permitted and encouraged. The advantages of on-site systems are too numerous to overlook. Today, these systems can be engineered to reduce ground- water pollution, provide greater service life and lower annual energy costs, and recycling of nutrients and water.
The problem of toxics in the environment can be dealt with in different ways. One choice is trying to stop the proliferation of petrol chemicals, that in general, show up as statistics. We can't see the harm. It's coming out at us as increases in cancer, allergies, and things like that. The other thing we can do is to at least stop their spreading into the environment. That's why we have to be considering the idea of segregating waste treatment in such a way that we at least don't invite the mixing of things that belong in our food cycle with those that do not belong there.
Once they are mixed, we'll eventually need energy or work, one way or another, to achieve this separation again. So we might as well try to keep them segregated from the start. It will be immensely easier. I will try to give at least some idea why. Sweden had a very rapid development of advanced sewage treatment in the early 's. The main experience from that is that we have, all of a sudden, a new product that we don't know how to deal with, which is sludge.
You can't dump it in the water, which should be self-evident. And the farmers are often not very happy about taking it, because the better you do with the wastewater purifi- cation, the worse the sludge. From the farmer's point of view, receiving sludge as a fertilizer is a very risky proposition. As soon as it's on the market, it's going to be in the sludge. If you have a small municipality and a smaller collection system, you run into different problems, because now you probably will not have a consistent type or a consistent level of these elements.
But you run into the lack of predictability of when it's there and when it's not there. You may run into something that you don't know about. Then you look back and your soil has a concentra- tion of something that is not easy to rectify. This has been happening repeatedly in Sweden. You need to keep these toxic organics, as much as possible, out of the whole chain, so that you can retrieve the valuable nutrients. Greywater has several differences from sewage that I want to talk about. Greywater can be land treated on-site successfully because, first, it's less volume to deal with than sewage.
There is less nitrogen in it, which is an important thing. Nitrogen, when it is being transformed into mtrates, is very easily leaked through all soils and could show up rapidly in the groundwater. But there is another interesting difference as It relates to land treatment and that is that its biological characteristic is different. It is a much more rapidly stabilizing liquid from the biological point of view. It consumes oxygen more quickly. Compared to sewage, you have a very quick decomposition process in the beginning with greywater and then it pretty much levels out So you let the water percolate through the soil; it stabilizes relatively fast and you have a better buffer, so that when the water eventually hits the groundwater table, there is a very good chance that it is in a stable biological form.
We'll first review what separated treatment is, the principles at work in separated on- site treatment and what happens with one particular process, and the barriers to widespread use of on-site treatment. First, why bother making two problems out of one by treating the "black" kitchen and toilet wastes one way, and the "grey" wastes washwater another? The answer to the second half of the question has three parts: 1 conventional on-site subsurface systems receiving the combined load of organic wastes and washwater are only capable, by anyone's standards, of treating those materials in a certain per- centage of the soils in this country; a significant percentage of the land in the U.
The new criteria include protection of the groundwater; making the effluent percolate into the ground at a certain rate is no longer con- sidered good enough. What then does separated on-site treatment of domestic wastes involve to effectively work? This, in turn, means keeping them near or at the surface of the soil. This second point needs elaboration.
About two-thirds of the total organic pollution based on the ultimate biological oxygen demand in domestic sewage is from the toilet wastes. This is not to show that greywater can be directly discharged into bodies of water. On the con- trary, the pollution concentration based on is about the same as in combined sewage. There is no question but that it must receive treatment in the soil, the best medium known for puri- fying organically polluted water. But, the character of the organic content in greywater is different from that of combined sewage in an important way: its constituents are more readily available to oxidation by bacteria than are toilet wastes Olsson, This means that, if greywater is discharged untreated into water, the effects of the pollution e.
On the other hand, if it is discharged into soil, as it should be, the consequence of this characteristic is that purification takes place sooner that is, higher up in the soil profile. Thus, the effects of the absolute reduction in pollution in greywater unburdened by kitchen and toilet wastes, the rapid stabilization of its remaining organic content and its higher tempera- ture, altogether benefit the groundwater below by keeping the nutrients out and the plants above by making them accessible. It's the oldest Swedish com- posting toilet. It is designed to treat all food, as well as toilet, wastes without the aid of water, chemicals or externally supplied energy, since these wastes are transported in most cases by gravity, and converted by the metabolic energy of microorganisms to a stable, highly mineralized compost.
Nor does one have to put food wastes in the trash the other conventional recipient where a Multrum is installed This is as important to the management of solid wastes as keeping toilet wastes out of the water is to the management of wastewater. The remaining solid wastes cans, bottles, paper, plastics, etc. We should also remember that, in ten years, half of the cities will run out of landfill space. The Multrum process is an effectively aerobic one because of its ventilation system which affords a continuous airflow through and over the decomposing wastes.
This means that, although there may be pockets of anaerobic activity, the end product cannot, because of the baffle and airduct design, be removed before it has been subjected to aeration. Odors are prevented from entering the house by the same air flow serving the decomposition process: the negative pressure in the tank causes air to be drawn into it, through either the toilet or kitchen waste depository, whenever either of these lids is opened. The system relies on time and microbial competition and predation, rather than on high tempera- tures, to achieve safety of the end product.
Incrementally introduced, the metabolically generated heat is incrementally released, and therefore never reaches the thermophilic levels characteristic of forced composting. Now, we would like here to emphasize the importance of size of the composting chamber. Many attempts have been made to "do the same thing" with a little box, in order to avoid the incon- venience of installing the large system.
However, we're convinced that such small units cannot accomplish the same thing; that is, they cannot, without a lot of attention, achieve a regularly safe end product relying on decomposition alone. Nor can they withstand peak loads, since their tolerance with respect to urine build-up is very limited.
These dehydration toilets have in common the problem of trying to compensate for their small size by striking an all-but-impossible balance between adding enough heat electrically supplied to drive off the liquid, and, at the same time, not so much that the excrement is baked, making it difficult to remove. These units have their place where use is low and without sudden peak loads chiefly in vacation homes. But it should be noted that the trade-off at issue is their small size plus high maintenance and an unpredictably stable end product, versus the large, compost-heap sized decomposition chamber plus low maintenance and assurance of an immediately usable end product, such as the Multram has.
Given the benefits of separated on-site treatment, and the availability of a range of technologi- cal devices, what are the barriers to widespread implementation of such treatment? The first is the fact of greywater. Phase One of the Project on the Predicament of Mankind took definite shape at meetings held in the summer of in Bern, Switzerland, and Cambridge, Massachusetts. At a two—week conference in Cambridge, Professor Jay Forrester of the Massachusetts Institute of Technology MIT presented a global model that permitted clear identification of many specific components of the problematique and suggested a technique for analyzing the behavior and relationships of the most important of those components.
This presentation led to initiation of Phase One at MIT, where the pioneering work of Professor Forrester and others in the field of System Dynamics had created a body of expertise uniquely suited to the research demands. The Phase One study was conducted by an international team, under the direction of Professor Dennis Meadows, with financial support from the Volkswagen Foundation. The team examined the five basic factors that determine, and therefore, ultimately limit, growth on this planet—population, agricultural production, natural resources, industrial production, [ Page 12 ].
We, like The Club of Rome, are a young organization, and we believe the Club's goals are very close to our own. Our purpose is to bring new ideas, new analyses, and new approaches to persistent problems—both national and international—to the attention of all those who care about and help determine the quality and direction of our life. We are delighted therefore to be able to make this bold and impressive work available through our book program. We hope that The Limits to Growth will command critical attention and spark debate in all societies.
We hope that it will encourage each reader to think through the consequences of continuing to equate growth with progress. And we hope that it will lead thoughtful men and women in all fields of endeavor to consider the need for concerted action now if we are to preserve the habitability of this planet for ourselves and our children. T he problems U Thant mentions— the arms race, environmental deterioration, the population explosion, and economic stagnation—are often cited as the central, long—term problems of modern man.
Many people believe that the future course of human society, perhaps even the survival of human society, depends on the speed and effectiveness with which the world responds to these issues. And yet only a small fraction of the world's population is actively concerned with understanding these problems or seeking their solutions. Every person in the world faces a series of pressures and problems that require his attention and action.
These problems [ Page 18 ]. These very different levels of human concern can be represented on a graph like that in figure 1. The graph has two dimensions, space and time. Every human concern can be located at some point on the graph, depending on how much geographical space it includes and how far it extends in time. Most people's worries are concentrated in the lower left—hand corner of the graph. Life for these people is difficult, and they must devote nearly all of their efforts to providing for themselves and their families, day by day.
Other people think about and act on problems farther out on the space or time axes. The pressures they perceive involve not only themselves, but the community with which they identify. The actions they take extend not only days, but weeks or years into the future. A person's time and space perspectives depend on his culture, his past experience, and the immediacy of the problems confronting him on each level. Most people must have successfully solved the problems in a smaller area before they move their concerns to a larger one.
In general the larger the space and the longer the time associated with a problem, the smaller the number of people who are actually concerned with its solution. There can be disappointments and dangers in limiting one's view to an area that is too small.
There are many examples of a person striving with all his might to solve some immediate, local problem, only to find his efforts defeated by events occurring in a larger context. A farmer's carefully maintained [ Page 19 ]. Are the implications of these global trends actually so threatening that their resolution should take precedence over local, short—term concerns?
Is it true, as U Thant suggested, that there remains less than a decade to bring these trends under control? If they are not brought under control, what will the consequences be? What methods does mankind have for solving global problems, and what will be the results and the costs of employing each of them? These are the questions that we have been investigating in the first phase of The Club of Rome's Project on the Predicament of Mankind. Our concerns thus fall in the upper right—hand corner of the space—time graph. Every person approaches his problems, wherever they occur on the space—time graph, with the help of models.
A model is simply an ordered set of assumptions about a complex system. It is an attempt to understand some aspect of the infinitely varied world by selecting from perceptions and past experience a set of general observations applicable to the problem at hand. A farmer uses a mental model of his land, his assets, market prospects, and past weather conditions to decide which crops to plant each year.
A surveyor constructs a physical model—a map—to help in planning a road. An economist uses mathematical models to understand and predict the flow of international trade. Decision—makers at every level unconsciously use mental models to choose among policies that will shape our future world. These mental models are, of necessity, very simple when [ Page 21 ].
We, too, have used a model. Ours is a formal, written model of the world. Our world model was built specifically to investigate five major trends of global concern—accelerating industrialization, rapid population growth, widespread malnutrition, depletion of nonrenewable resources, and a deteriorating environment. These trends are all interconnected in many ways, and their development is measured in decades or centuries, rather than in months or years. With the model we are seeking to understand the causes of these trends, their interrelationships, and their implications as much as one hundred years in the future.
The model we have constructed is, like every other model, imperfect, oversimplified, and unfinished. We are well aware of its shortcomings, but we believe that it is the most useful model now available for dealing with problems far out on the space—time graph. Since ours is a formal, or mathematical, model it also has two important advantages over mental models. First, every assumption we make is written in a precise form so that it is open to inspection and criticism by all. Second, after the assumptions have been scrutinized, discussed, and revised to agree with our best current knowledge, their implications for the future behavior of the world system can be traced without error by a computer, no matter how complicated they become.
We feel that the advantages listed above make this model unique among all mathematical and mental world models available to us today. But there is no reason to be satisfied with it in its present form. We intend to alter, expand, and improve it as our own knowledge and the world data base gradually improve.
In spite of the preliminary state of our work, we believe it is important to publish the model and our findings now. Decisions are being made every day, in every part of the world, that will affect the physical, economic, and social conditions of the world system for decades to come. These decisions cannot wait for perfect models and total understanding.
They will be made on the basis of some model, mental or written, in any case. We feel that the model described here is already sufficiently developed to be of some use to decision—makers. Furthermore, the basic behavior modes we have already observed in this model appear to be so fundamental and general that we do not expect our broad conclusions to be substantially altered by further revisions.
It is not the purpose of this book to give a complete, scientific description of all the data and mathematical equations included in the world model. Such a description can be found in the final technical report of our project Rather, in The Limits to Growth we summarize the main features of the model and our findings in a brief, nontechnical way. The emphasis is meant to be not on the equations or the intricacies of the model, but on what it tells us about the world.
We have used a computer as a tool to aid our own understanding of the causes and consequences of the accelerating trends that characterize the modern world, but familiarity with computers is by no means necessary to comprehend or to discuss our conclusions. The implications of those accelerating trends raise issues that go far beyond the proper domain of a purely scientific document. They must be debated by a wider community than that of scientists alone.
Our purpose here is to open that debate. The following conclusions have emerged from our work so far. We are by no means the first group to have stated them. For the past several decades, people who have looked at the world with a global, long—term perspective have reached similar conclusions. Nevertheless, the vast majority of policymakers seems to be actively pursuing goals that are inconsistent with these results. These conclusions are so far—reaching and raise so many questions for further study that we are quite frankly overwhelmed by the enormity of the job that must be done.
We hope that this book will serve to interest other people, in many fields of study and in many countries of the world, to raise the space and time horizons of their concerns and to join us in understanding and preparing for a period of great transition— the transition from growth to global equilibrium. A ll five elements basic to the study reported here—population, food production, industrialization, pollution, and consumption of nonrenewable natural resources—are increasing. The amount of their increase each year follows a pattern that mathematicians call exponential growth.
Nearly all of mankind's current activities, from use of fertilizer to expansion of cities, can be represented by exponential growth curves see figures 2 and 3. Since much of this book deals with the causes and implications of exponential growth curves, it is important to begin with an understanding of their general characteristics. A quantity is growing linearly when it increases by a.
For example, a child who becomes one inch taller each year is growing linearly. The amount of increase each year is obviously not affected by the size of the child nor the amount of money already under the mattress. A quantity exhibits exponential growth when it increases by a constant percentage of the whole in a constant time period. A colony of yeast cells in which each cell divides into two cells every 10 minutes is growing exponentially. For each single cell, after 10 minutes there will be two cells, an increase. After the next 10 minutes there will be four cells, then eight, then sixteen.
The amount added each year to a bank account or each 10 minutes to a yeast colony is not constant.
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It continually increases, as the total accumulated amount increases. Such exponential growth is a common process in biological, financial, and many other systems of the world. Common as it is, exponential growth can yield surprising results—results that have fascinated mankind for centuries. There is an old Persian legend about a clever courtier who presented a beautiful chessboard to his king and requested that the king give him in return 1 grain of rice for the first square on the board, 2 grains for the second square, 4 grains for the third, and so forth.
The king readily agreed and ordered rice to be brought from his stores. The fourth square of the chessboard required 8 grains, the tenth square took grains, the fifteenth required 16,, and the twenty-first square gave the courtier more than a million grains of rice. By the fortieth square a million million rice grains had to be brought from the storerooms.
The king's entire rice supply was exhausted long before he reached the sixty-fourth square. Exponential increase is deceptive because it generates immense numbers very quickly. A French riddle for children illustrates another aspect of exponential growth—the apparent suddenness with which it approaches a fixed limit. Suppose you own a pond on which a water lily is growing. The lily plant doubles in size each day.
If the lily were allowed to grow unchecked, it would completely cover the pond in 30 days, choking off the other forms of life in the water. For a long time the lily plant seems small, and so you decide not to worry about cutting it back until it covers half the pond. On what day will that be? On the twenty—ninth day, of course. You have one day to save your pond. It is useful to think of exponential growth in terms of doubling time , or the time it takes a growing quantity to.
In the case of the lily plant described above, the doubling time is 1 day. A sum of money left in a bank at 7 percent interest will double in 10 years. There is a simple mathematical relationship between the interest rate, or rate of growth, and the time it will take a quantity to double in size. The doubling time is approximately equal to 70 divided by the growth rate, as illustrated in table 1. In simple systems, like the bank account or the lily pond, the cause of exponential growth and its future course are relatively easy to understand.
When many different quantities are growing simultaneously in a system, however, and when all the quantities are interrelated in a complicated way, analysis of the causes of growth and of the future behavior of the system becomes very difficult indeed. Does population growth cause industrialization or does industrialization cause population growth?
Is either one singly responsible for increasing pol—. Will more food production result in more population? If any one of these elements grows slower or faster, what will happen to the growth rates of all the others? These very questions are being debated in many parts of the world today. The answers can be found through a better understanding of the entire complex system that unites all of these important elements. Over the course of the last 30 years there has evolved at the Massachusetts Institute of Technology a new method for understanding the dynamic behavior of complex systems.
The method is called System Dynamics. The world model described in this book is a System Dynamics model. Dynamic modeling theory indicates that any exponentially growing quantity is somehow involved with a positive feedback loop. A positive feedback loop is sometimes called a "vicious circle. In a positive feedback loop a chain of cause—and—effect relationships closes on itself, so that increasing any one element in the loop will start a sequence of changes that will result in the originally changed element being increased even more.
The positive feedback loop that accounts for exponential increase of money in a bank account can be represented like this:. The more money there is in the account, the more money will be added each year in interest.
The more is added, the more there will be in the account the next year causing even more to be added in interest. And so on. As we go around and around the loop, the accumulated money in the account grows exponentially. The rate of interest constant at 7 percent determines the gain around the loop, or the rate at which the bank account grows. We can begin our dynamic analysis of the long-term world situation by looking for the positive feedback loops underlying the exponential growth in the five physical quantities we have already mentioned.
In particular, the growth rates of two of these elements—population and industrialization—are of interest, since the goal of many development policies is to encourage the growth of the latter relative to the former. We will describe their basic structures in the next few pages. The many interconnections between these two positive feedback loops act to amplify or to diminish the action of the loops, to couple or uncouple the growth rates of population and of industry.
These interconnections constitute the rest of the world model and their description will occupy much of the rest of this book. The exponential growth curve of world population is shown in figure 5. In the population numbered about 0. In the population totaled 3. Thus, not only has the population been growing exponentially, but the rate of growth has also been growing. We might say that population growth has been "super"—exponential; the population curve is rising even faster than it would if growth were strictly exponential.
The feedback loop structure that represents the dynamic behavior of population growth is shown below. On the left is the positive feedback loop that accounts for the observed exponential growth. In a population with constant average fertility, the larger the population, the more babies will be born each year. The more babies, the larger the popula-. After a delay to allow those babies to grow up and become parents, even more babies will be born, swelling the population still further.
Steady growth will continue as long as average fertility remains constant. If, in addition to sons, each woman has on the average two female children, for example, and each of them grows up to have two more female children, the population will double each generation. The growth rate will depend on both the average fertility and the length of the delay between generation's.
Fertility is not necessarily constant, of course, and in chapter III we will discuss some of the factors that cause it to vary. There is another feedback loop governing population growth, shown on the right side of the diagram above. It is a negative feedback loop. Whereas positive feedback loops generate runaway growth, negative feedback loops tend to regulate growth and to hold a system in some stable state.
They behave much as a thermostat does in controlling the temperature of a room. If the temperature falls, the thermostat activates the heating system, which causes the temperature to rise again. When the temperature reaches its limit, the thermostat cuts off the heating system, and the temperature begins to fall again. In a negative feedback loop a change in one element is propagated around the circle until it comes back to change that element in a direction opposite to the initial change. The negative feedback loop controlling population is based upon average mortality, a reflection of the general health of the population.
The number of deaths each year is equal to the total population times the average mortality which we might think of as the average probability of death at any age. An increase in the size of a population with constant average mortality will result in more deaths per year. More deaths will leave fewer people in the population, and so there will be fewer deaths the next year. If on the average 5 percent of the population dies each year, there will be deaths in a population of 10, in one year. Assuming no births for the moment, that would leave 9, people the next year.
If the probability of death is still 5 percent, there will be only deaths in this smaller population, leaving 9, people. The next year there will be only deaths. Again, there is a delay in this feedback loop because the mortality rate is a function of the average age of the population. Also, of course, mortality even at a given age is not necessarily constant. If there were no deaths in a population, it would grow exponentially by the positive feedback loop of births, as shown below.
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If there were no births, the population would decline. Since every real population experiences both. What has caused the recent super—exponential rise in world population? Before the industrial revolution both fertility and mortality were comparatively high and irregular. The birth rate generally exceeded the death rate only slightly, and population grew exponentially, but at a very slow and uneven rate.
In the average lifetime of most populations in the world was only about 30 years. Since then, mankind has developed many practices that have had profound effects on the population growth system, especially on mortality rates. With the spread of modern medicine, public health techniques, and new methods of growing and distributing foods, death rates have fallen around the world. World average life expectancy is currently about 53 years 3 and still rising. On a world average the gain around the positive feedback loop fertility has decreased only slightly while the gain around the negative feedback loop mortality is decreasing.
The result is an increasing dominance of the positive feedback loop and the sharp exponential rise in population pictured in figure 5. What about the population of the future? How might we extend the population curve of figure 5 into the twenty-first century? For the moment we can safely conclude that because of the delays in the controlling feedback loops, especially the positive loop of births, there is no possibility of leveling off the population growth curve before the year , even with the most optimistic assumption of decreasing fertility.
Most of the prospective parents of the year have already been born. Unless there is a sharp rise in mortality,. And if we continue to succeed in lowering mortality with no better success in lowering fertility than we have accomplished in the past, in 60 years there will be four people in the world for every one person living today. Figure 6. The average growth rate from to was 7 percent per year, or 5 percent per year on a per capita basis.
What is the positive feedback loop that accounts for exponential growth of industrial output? The dynamic structure, diagramed below, is actually very similar to the one we have already described for the population system. With a given amount of industrial capital factories, trucks, tools, machines, etc.
The output actually produced is also dependent on labor, raw materials, and other inputs. For the moment we will assume that these other inputs are sufficient, so that capital is the limiting factor in production. The world model does include these other inputs. Much of each year's output is consumable goods, such as textiles, automobiles, and houses, that leave the industrial system.
But some fraction of the production is more capital—looms, steel mills, lathes—which is an investment to increase the capital stock. Here we have another positive feedback loop. More capital creates more. The new, larger capital stock generates even more output, and so on. There are also delays in this feedback loop, since the production of a major piece of industrial capital, such as an electrical generating plant or a refinery, can take several years. Capital stock is not permanent. As capital wears out or becomes obsolete, it is discarded.
To model this situation we must introduce into the capital system a negative feedback loop accounting for capital depreciation. The more capital there is, the more wears out on the average each year; and the more that wears out, the less there will be the next year. This negative feedback loop is exactly analogous to the death rate loop in the population system. As in the population system, the positive loop is strongly dominant in the world today, and the world's industrial capital stock is growing exponentially. Since industrial output is growing at 7 percent per year and population only at 2 percent per year, it might appear that dominant positive feedback loops are a cause for rejoicing.
Simple extrapolation of those growth rates would suggest that the material standard of living of the world's people will double within the next 14 years. Such a conclusion, however, often includes the implicit assumption that the world's growing industrial output is evenly distributed among the world's citizens. The fallacy of this assumption can be appreciated when the per capita economic growth rates of some individual nations are examined see figure 7.
Most of the world's industrial growth plotted in figure 6 is actually taking place in the already industrialized countries, where the rate of population growth is comparatively low. The most revealing possible illustration of that fact is a simple table listing the economic and population growth rates of the ten most populous nations of the world, where 64 percent of the world's population currently lives. Table 2 makes very clear the basis for the saying, "The rich get richer and the poor get children.
It is unlikely that the rates of growth listed in table 2 will continue unchanged even until the end of this century. The end of civil disturbance in Nigeria, for example, will probably increase the economic growth rate there, while the onset of civil disturbance and then war in Pakistan has already interfered with economic growth there. Let us recognize, however, that the growth rates listed above are the products of a complicated social and economic system that is essentially stable and that is likely to change slowly rather than quickly, except in cases of severe social disruption.
It is a simple matter of arithmetic to calculate extrapolated values for gross national product GNP per capita from now until the year on the assumption that relative growth rates of population and GNP will remain roughly the same in these ten countries. The result of such a calculation appears in table 3. The values shown there will almost certainly not actually be realized. They are not predictions. The values merely indicate the general direction our system, as it is currently structured, is taking us.
They demonstrate that the process of. Most people intuitively and correctly reject extrapolations like those shown in table 3, because the results appear ridiculous. It must be recognized, however, that in rejecting extrapolated values, one is also rejecting the assumption that there will be no change in the system.
If the extrapolations in table 3 do not actually come to pass, it will be because the balance between the positive and negative feedback loops determining the growth rates of population and capital in each nation has been altered.
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Fertility, mortality, the capital investment rate, the capital depreciation rate—any or all may change. In postulating any different outcome from the one shown in table 3, one must specify which of these factors is likely to change, by how much, and when. These are exactly the questions we are addressing with our model, not on a national basis, but on an aggregated global one. To speculate with any degree of realism on future growth rates of population and industrial capital, we must know something more about the other factors in the world that interact with the population-capital system.
We shall begin by asking a very basic set of questions. Can the growth rates of population and capital presented in table 3 be physically sustained in the world? How many people can be provided for on this earth, at what level of wealth, and for how long? To answer these questions, we must look in detail at those systems in the world which provide the physical support for population and economic growth.
W hat will be needed to sustain world economic and population growth until, and perhaps even beyond, the year ? The list of necessary ingredients is long, but it can be divided roughly into two main categories. The first category includes the physical necessities that support all physiological and industrial activity—food, raw materials, fossil and nuclear fuels, and the ecological systems of the planet which absorb wastes and recycle important basic chemical substances.
These ingredients are in principle tangible, countable items, such as arable land, fresh water, metals, forests, the oceans. In this chapter we will assess the world's stocks of these physical resources, since they are the ultimate determinants of the limits to growth on this earth. The second category of necessary ingredients for growth consists of the social necessities.
Even if the earth's physical systems are capable of supporting a much larger, more econom—. These factors are much more difficult to assess or to predict. Neither this book nor our world model at this stage in its development can deal explicitly with these social factors, except insofar as our information about the quantity and distribution of physical supplies can indicate possible future social problems.
Food, resources, and a healthy environment are necessary but not sufficient conditions for growth. Even if they are abundant, growth may be stopped by social problems. Let us assume for the moment, however, that the best possible social conditions will prevail. How much growth will the physical system then support?
The answer we obtain will give us some estimate of the upper limits to population and capital growth, but no guarantee that growth will actually proceed that far. In India and Pakistan the ratio is of every thousand; in Colombia it is Many more die before they reach school age; others during the early school years. Where death certificates are issued for preschool infants in the poor countries, death is generally attributed to measles, pneumonia, dysentery, or some other disease.
In fact these children are more likely to be the victims of malnutrition. No one knows exactly how many of the world's people are inadequately nourished today, but there is general agreement that the number is large—perhaps 50 to 60 percent of the population of the less industrialized countries, 5 which means one-third of the population of the world. Estimates by the. UN Food and Agriculture Organization FAO indicate that in most of the developing countries basic caloric requirements, and particularly protein requirements, are not being supplied see figure 8.
Furthermore, although total world agricultural production is increasing, food production per capita in the nonindustrialized countries is barely holding constant at its present inadequate level see figure 9. Do these rather dismal statistics mean that the limits of food production on the earth have already been reached? The primary resource necessary for producing food is land.
Recent studies indicate that there are, at most, about 3. The remaining land will require immense capital inputs to reach, clear, irrigate, or fertilize before it is ready to produce food. In Southern Asia In the dryer regions it will even be necessary to return to permanent pasture the land which is marginal or submarginal for cultivation. In most of Latin America and Africa South of the Sahara there are still considerable possibilities for expanding cultivated area, but the costs of development are high and it will be often more economical to intensify utilization of the areas already settled.
If the world's people did decide to pay the high capital costs, to cultivate all possible arable land, and to produce as much food as possible, how many people could theoretically be fed? The lower curve in figure 10 shows the amount of land needed to feed the growing world population, assuming that the present world average of 0. To feed the entire world population at present US standards, 0. The upper curve in figure 10 shows the actual amount of arable land available over time.
This line, slopes downward because each additional person requires a certain amount of land 0. Land loss through erosion is not shown here, but it is by no means negligible. Figure 10 shows that, even with the optimistic assumption that all possible land is utilized, there will still be a desperate land shortage before the year if per capita land requirements and population growth rates remain as they are today. Figure 10 also illustrates some very important general facts about exponential growth within a limited space.
First, it shows how one can move within a very few years from a situation of great abundance to one of great scarcity. There has been an overwhelming excess of potentially arable land for all of history, and now, within 30 years or about one population doubling time , there may be a sudden and serious shortage. Like the owner of the lily pond in our example in chapter I, the human race may have very little time to react to a crisis resulting from exponential growth in a finite space.
A second lesson to be learned from figure 10 is that precise numerical assumptions about the limits of the earth are unimportant when viewed against the inexorable progress of exponential growth. We might assume, for example, that no arable land is taken for cities, roads, or other nonagricultural uses. In that case, the land available is constant, as shown by the horizontal dashed line. The point at which the two curves cross is delayed by about 10 years. Or we can suppose that it is possible to double, or even quadruple, the productivity of the land through advances in agricultural technology and in—.
The effects of two different assumptions about increased productivity are shown by the dotted lines in figure Each doubling of productivity gains about 30 years, or less than one population doubling time. Of course, society will not be suddenly surprised by the "crisis point" at which the amount of land needed becomes greater than that available. Symptoms of the crisis will begin to appear long before the crisis point is reached. Food prices will rise so high that some people will starve; others will be forced to decrease the effective amount of land they use and shift to lower quality diets.
These symptoms are already apparent in many parts of the world. Although only half the land shown in figure 10 is now under cultivation, perhaps 10 to 20 million deaths each year can be attributed directly or indirectly to malnutrition. There is no question that many of these deaths are due to the world's social limitations rather than its physical ones. Yet there is clearly a link between these two kinds of limitations in the food-producing system. If good fertile land were still easily reached and brought under cultivation, there would be no economic barrier to feeding the hungry, and no difficult social choices to make.
The best half of the world's potentially arable land is already cultivated, however, and opening new land is already so costly that society has judged it "uneconomic. Even if society did decide to pay the necessary costs to gain new land or to increase productivity of the land already cultivated, figure 10 shows how quickly rising population would bring about another "crisis point. Each doubling of yield. We might call this phenomenon the law of increasing costs. The best and most sobering example of that law comes from an assessment of the cost of past agricultural gains. To achieve a 34 percent increase in world food production from to , agriculturalists increased yearly expenditures on tractors by 63 percent, annual investment in nitrate fertilizers by percent, and annual use of pesticides by percent.
How many people can be fed on this earth? There is, of course, no simple answer to this question. The answer depends on the choices society makes among various available alternatives. There is a direct trade—off between producing more food and producing other goods and services needed or desired by mankind. The demand for these other goods and services is also increasing as population grows, and therefore the trade—off becomes continuously more apparent and more difficult to resolve.
Even if the choice were consistently to produce food as the first priority, however, continued population growth and the law of increasing costs could rapidly drive the system to the point where all available resources were devoted to producing food, leaving no further possibility of expansion. In this section we have discussed only one possible limit to food production—arable land. There are other possible limits, but space does not permit us to discuss them in detail here. The most obvious one, second in importance only to land, is the availability of fresh water.
There is an upper limit to the fresh water runoff from the land areas of the earth each year, and there is also an exponentially increasing demand for that water. We could draw a graph exactly analogous to figure In some areas of the world, this limit will be reached long before the land limit becomes apparent. It is also possible to avoid or extend these limits by technological advances that remove dependence on the land synthetic food or that create new sources of fresh water desalinization of sea water.
We shall discuss such innovations further in chapter IV. For the moment it is sufficient to recognize that no new technology is spontaneous or without cost. The factories and raw materials to produce synthetic food, the equipment and energy to purify sea water must all come from the physical world system.
The exponential growth of demand for food results directly from the positive feedback loop that is now determining the growth of human population. The supply of food to be expected in the future is dependent on land and fresh water and also on agricultural capital, which depends in turn on the other dominant positive feedback loop in the system—the capital investment loop.
Opening new land, farming the sea, or expanding use of fertilizers and pesticides will require an increase of the capital stock devoted to food production. The resources that permit growth of that capital stock tend not to be renewable resources, like land or water, but nonrenewable resources, like fuels or metals. Thus the expansion of food production in the future is very much dependent on the availability of nonrenewable resources. Are there limits to the earth's supply of these resources?
At the present rate of expansion. By the year , several more minerals may be exhausted if the current rate of consumption continues. Despite spectacular recent discoveries, there are only a limited number of places left to search for most minerals. Geologists disagree about the prospects for finding large, new, rich ore deposits.
Reliance on such discoveries would seem unwise in the long term. Table 4 lists some of the more important mineral and fuel resources, the vital raw materials for today's major industrial processes. The number following each resource in column 3 is the static reserve index, or the number of years present known reserves of that resource listed in column 2 will last at the current rate of usage.
This static index is the measure normally used to express future resource availability. Underlying the static index are several assumptions, one of which is that the usage rate will remain constant. But column 4 in table 4 shows that the world usage rate of every natural resource is growing exponentially.
For many resources the usage rate is growing even faster than the population, indicating both that more people are consuming resources each year and also that the average consumption per person is increasing each year. In other words, the exponential growth curve of resource consumption is driven by both the positive feedback loops of population growth and of capital growth. We have already seen in figure 10 that an exponential increase in land use can very quickly run up against the fixed amount of land available.
An exponential increase in resource consumption can rapidly diminish a fixed store of resources in the same way. Figure 11, which is similar to figure 10, illus—. Africa 40 Rep. Germany 11 25 Rep. Calculated from the above formula with 5s in place of s. Flawn, Mineral Resources Skokie, Ill. The example in this case is chromium ore, chosen because it has one of the longest static reserve indices of all the resources listed in table 4. We could draw a similar graph for each of the resources listed in the table.
The time scales for the resources would vary, but the general shape of the curves would be the same. The world's known reserves of chromium are about million metric tons, of which about 1. The dashed line in figure 11 illustrates the linear depletion of chromium reserves that would be expected under the assumption of constant use. The actual world consumption of chromium is increasing, however, at the rate of 2. If we suppose that reserves yet undiscovered could increase present known reserves by a factor of five, as shown by the dotted line, this fivefold increase would extend the lifetime of the reserves only from 95 to years.
Even if it were possible from onward to recycle percent of the chromium the horizontal line so that none of the initial reserves were lost, the demand would exceed the supply in years. Figure 11 shows that under conditions of exponential growth in resource consumption, the static reserve index years for chromium is a rather misleading measure of resource availability.
We might define a new index, an exponential reserve index," which gives the probable lifetime of each resource, assuming that the current growth rate in consumption will. We have included this index in column 5 of table 4. We have also calculated an exponential index on the assumption that our present known reserves of each resource can be expanded fivefold by new discoveries. This index is shown in column 6. The effect of exponential growth is to reduce the probable period of availability of aluminum, for example, from years to 31 years 55 years with a fivefold increase in reserves.
Copper, with a 36—year lifetime at the present usage. It is clear that the present exponentially growing usage rates greatly diminish the length of time that wide—scale economic growth can be based on these raw materials. Of course the actual nonrenewable resource availability in the next few decades will be determined by factors much more complicated than can be expressed by either the simple static reserve index or the exponential reserve index.
We have studied this problem with a detailed model that takes into account the many interrelationships among such factors as varying grades of ore, production costs, new mining technology, the elasticity of consumer demand, and substitution of other resources. Figure 12 is a computer plot indicating the future availability of a resource with a —year static reserve index in the year , such as chromium.
At first the annual consumption of chromium grows exponentially, and the stock of the resource is rapidly depleted. The price of chromium remains low and constant because new developments in mining technology allow efficient use of lower. As demand continues to increase, however, the advance of technology is not fast enough to counteract the rising costs of discovery, extraction, processing,. Price begins to rise, slowly at first and then very rapidly.
The higher price causes consumers to use chromium more efficiently and to substitute other metals for chromium whenever possible. After years, the remaining chromium, about 5 percent of the original supply, is available. This more realistic dynamic assumption about the future use of chromium yields a probable lifetime of years, which is considerably shorter than the lifetime calculated from the static assumption years , but longer than the lifetime calculated from the assumption of constant exponential growth 95 years.
The usage rate in the dynamic model is neither constant nor continuously increasing, but bell-shaped, with a growth phase and a phase of decline. The computer run shown in figure 13 illustrates the effect of a discovery in that doubles the remaining known chromium reserves. The static reserve index in becomes years instead of As a result of this discovery, costs remain low somewhat longer, so that exponential growth can continue longer than it did in figure The period during which use of the resource is economically feasible is increased from years to years.
In other words, a doubling of the reserves increases the actual period of use by only 20 years. The earth's crust contains vast amounts of those raw materials which man has learned to mine and to transform into useful things. However vast those amounts may be, they are not infinite. Now that we have seen how suddenly an exponentially growing quantity approaches a fixed upper limit, the following statement should not come as a surprise.
Given present resource consumption rates and the projected increase in these rates, the great majority of the currently important nonrenewable resources will be extremely costly ioo years from now. The above statement remains true regardless of the most optimistic assumptions about undiscovered reserves, technological advances, substitution, or recycling, as long as the.
The prices of those resources with the shortest static reserve indices have already begun to increase. The price of mercury, for example, has gone up percent in the last 20 years; the price of lead has increased percent in the last 30 years. The simple conclusions we have drawn by considering total world reserves of resources are further complicated by the fact that neither resource reserves nor resource consumption are distributed evenly about the globe. The last four columns of table 4 show clearly that the industrialized, consuming countries are heavily dependent on a network of international agreements with the producing countries for the supply of raw materials essential to their industrial base.
Added to the difficult economic question of the fate of various industries as resource after resource becomes prohibitively expensive is the imponderable political question of the relationships between producer and consumer nations as the remaining resources become concentrated in more limited geographical areas. Recent nationalization of South American mines and successful Middle Eastern pressures to raise oil prices suggest that the political question may arise long before the ultimate economic one.
Are there enough resources to allow the economic development of the 7 billion people expected by the year to a reasonably high standard of living? Once again the answer must be a conditional one. It depends on how the major resource—consuming societies handle some important decisions ahead. They might continue to increase resource consumption according to the present pattern. They might learn to reclaim and recycle discarded materials. They might develop new designs to increase the durability of products made from scarce. They might encourage social and economic patterns that would satisfy the needs of a person while minimizing, rather than maximizing, the irreplaceable substances he possesses and disperses.
All of these possible courses involve trade—offs. The trade—offs are particularly difficult in this case because they involve choosing between present benefits and future benefits. In order to guarantee the availability of adequate resources in the future, policies must be adopted that will decrease resource use in the present. Most of these policies operate by raising resource costs.
Recycling and better product design are expensive; in most parts of the world today they are considered "uneconomic. What happens to the metals and fuels extracted from the earth after they have been used and discarded? In one sense they are never lost. Their constituent atoms are rearranged and eventually dispersed in a diluted and unusable form into the air, the soil, and the waters of our planet.
The natural ecological systems can absorb many of the effluents of human activity and reprocess them into substances that are usable by, or at least harmless to, other forms of life. When any effluent is released on a large enough scale, however, the natural absorptive mechanisms can become saturated. The wastes of human civilization can build up in the environment until they become visible, annoying, and even harmful.
Mercury in ocean fish, lead particles in city air, mountains of urban trash, oil slicks on beaches—these are the results of the increasing flow of. It is little wonder, then, that another exponentially increasing quantity in the world system is pollution. This is entirely the fault of our own species.
Man's concern for the effect of his activities on the natural environment is only very recent. Scientific attempts to measure this effect are even more recent and still very incomplete. We are certainly not able, at this time, to come to any final conclusion about the earth's capacity to absorb pollution. We can, however, make four basic points in this section, which illustrate, from a dynamic, global perspective, how difficult it will be to understand and control the future state of our ecological systems.
These points are:. It is not possible to illustrate each of these four points for each type of pollutant, both because of the space limitations. Therefore we shall discuss each point using as examples those pollutants which have been most completely studied to date.
It is not necessarily true that the pollutants mentioned here are the ones of greatest concern although they are all of some concern. They are, rather, the ones we understand best. Exponentially increasing pollution Virtually every pollutant that has been measured as a function of time appears to be increasing exponentially.
The rates of increase of the various examples shown below vary greatly, but most are growing faster than the population. Some pollutants are obviously directly related to population growth or agricultural activity, which is related to population growth.
Others are more closely related to the growth of industry and advances in technology.