Flush It Back to the Farm...
an essay
by Tony Ryals
Treating agriculture and sewage recycling (or the lack of it), as if they were two different processes is truly schizophrenic. The two are inseparable because to complete a nutrient cycle human and domestic animal waste must be recycled back to farmland. In fad, the more productive an agricultural system is, the more it takes nutrients from the soil.
In both rural and urban environments, flush toilets can be used to a greater advantage as a means of returning sewage nutrients (fertilizers) back to the farmland than the dry composting toilets such as a Clivus Multrum. This is true because dry fertilizer requires the addition of adequate water through irrigation to be effective for plant absorption of nutrients - besides the fact that 90% of Ecotopians already have flush toilets.
When water is directly combined with human wastes, as in flush toilets, the most practical means of separating water from sewage-fertilizer is by means of transpiration and the nutrient absorption of plants. The water used by flush toilets for conventional irrigation projects and various forms of hydroponics also serves to deliver fertilizer to an agricultural system.
Recycling sewage or removing nutrients from water is called tertiary treatment. Biological systems, particularly harvestable plants, are the only logical means of tertiary treatment for an environmentally stable community. The reason is that both energy use and non-renewable resources (petrochemicals) are required for present urban-industrial sewage treatment systems - as well as the foreseeable world fertilizer crisis - as fossil fuels become scarce.
Modern sewage treatment besides consuming large quantities of chemicals and energy, does not recycle sewage fertilizer or water. The quantity of this wasted fertilizer added to rivers, lakes, and oceans through these conventional sewage treatment systems upsets water ecology, and represents a form of erosion (or nutrient loss) unequalled in history. Our present agriculture would surely collapse if fossil fuels were not used to replace these lost nutrients.
Before raw sewage is recycled to edible crops or other harvested plants, it is advisable to insure some form of microbial decomposition. The action of microbes on sewage releases and makes available the basic plant nutrients, while substantially decreasing the population of pathogenic microbes associated with human waste.
The most common method of microbial decomposition of water-logged human waste (fertilizer) is through retention in a pond or series of ponds. Microbial action within these sewage ponds can be aerobic or anaerobic, but is generally a combination of both. After a period of retention within a sewage pond system nutrient-rich liquid should be released to fertilize plants but, at present, is used only to pollute local watersheds.
The Max Planck Institute of Germany has developed a process which is basically organic hydroponics in which reeds and bull-rushes are grown in beds or trenches containing sand and gravel. This well aerated system helps speed the decomposition of waste water organics. The reeds contribute to aeration while aiding the bullrush in nutrient uptake and thus, water purification.
The amount of surface area or land required for biological tertiary sewage treatment is dependent upon the population of a community, the climate, and the growth rates of the organisms being grown in the sewage. Virtually any usable plant will grow and indeed thrive in the "sewage farm conditions. And of course many different plants should be grown for the sake of diversity and in accordance with the bioregion.
Past experience has shown that irrigation of crops with liquefied decomposed sewage can improve yields. The use of human wastes in the rice fields of Asia is one of the most famous historic examples of this method of nutrient recycling. As recently as last century, the human wastes of major European cities were recycled to farm crops through the use of holding ponds and trenches. Statistics of the time showed that those people living and working on sewage farms were often healthier than their urban counter-parts.
While past experience with sewage irrigation has been successful, cheap chemical fertilizers from petroleum and simplistic "industrial solutions" to sewage problems have prevented biological recycling from reaching it's potential.
Leonard Stevens in his book Clean Water states "fewer than two dozen persons supply enough nitrogen, phosphorus and potash annually to meet the fertilizer requirements for growing one acre of high-quality mixed crops."
Experiments have shown that forestland can more effectively absorb large quantities of sewage water than cultivated field crops. However, plants
used for fiber (clothing, paper, building material, fuel) am not easily recycled. Therefore, communities should probably use sewage nutrients for food producing plants in order to maintain a more complete and continual nutrient recycling system.
Aquatic plants, particularly tropical ones, are capable of removing much greater quantities of nutrients from water and producing much greater bio-mass (fertilizer, mulch, food, energy) than conventional crops. A National Academy of Sciences report, "Making Aquatic Weeds Useful", states that under favorable conditions (warmth, water, nutrients) one hectare or 2.2 acres of water hyacinths can be used to remove the nitrogenous waste of over 2000 people and the phosphorus waste of over 800 people.
The rapid growth of these plants makes them of considerable value for recycling nutrients in tropical or sub-tropical regions, or in enclosed ponds, in temperate regions.
This form of hydroponic aquaculture could be applied to recycling animal wastes as is done in parts of Southeast Asia. Manure wastes from a poultry operation, for example, could be hydroponically fed to corn, alfalfa, and other conventional feed crops, or even to the more productive aquatic plants like duckweed (indigenous to Ecotopia) and the water fern, Azolla. Under ideal conditions, duckweed can produce several times the protein of soybeans on the same amount of surface to be fed directly to chickens or livestock.
Another method of producing a nutrient-rich liquid fertilizer from sewage is through strictly anaerobic fermentation in an airtight container, which also produces methane gas as a by-product. New Alchemy's Newsletter No. 3 on Methane Digesters suggests growing grasses for animal feed hydroponically on the nitrogen rich fertilizer produced with methane. In cooler temperate regions the methane can be burned to produce heat, carbon dioxide, and water for greenhouse agricultural systems. However, additional water must later be added to this fertilizer for direct application to plants through irrigation.
A common septic tank also produced similar liquid fertilizer. This could be used effectively to grow a wide variety of useable plants rather than purposely losing the nutrients to a leach line.
A different method of reclaiming sewage nutrients involves the seawater-enriched irrigation of conventional crops grown hydroponically in a sand or gravel medium instead of soil. The airspaces between the particles prevent the accumulation of salt, which would normally occur in soil. Seawater contains the necessary nutrients for plant growth except nitrogen and phosphorus, which could be provided by sewage. In fact, Emmanuel Epstein of the University of California at Davis has already developed and grown a variety of barley using this method.
Saltwater plants, such as seaweed, marsh grasses, and marine algae could also be used to purify sewage water and provide animal feed and human food. At Woods Hole Oceanographic Institute, a sewage treatment recycling system was developed and tested in 1975 which mixed human wastes with salt water, fed that to marine algae which in turn were fed to oysters and other mollusks and their wastes used to feed flounder, lobster, and seaweed. From this pilot plant it was determined that on 48 acres, 183 tons of oysters, 3,000 tons of seaweed, and an undetermined amount of flounder and lobster along with complete nitrogen removal could be accomplished for 10,000
people annually.
Conceivably, coastal communities could use seawater to flush toilets and then irrigate and fertilize crops.
One reason for my optimism with sewage hydroponics is a modest experiment I did in which I grew com in two inches of vermiculite, watered and fed daily with septic tank waste headed for a leach line. This corn grew short but produced good edible ears, and there wasn't much scientific about it. This sort of small scale recycling experiment for small farms and homesteads is certainly useful, but eventually every city in Ecotopia will have to seriously consider how best to recycle the valuable agricultural nutrients now being flushed out to sea. A Clivus is not the only answer.
