Science in Society Archive

Dream Farms

Abundantly productive farms with zero input and zero emission powered by waste-gobbling bugs and human ingenuity
Sustainable development is possible Dr. Mae-Wan Ho

Environmental engineer meets Chinese peasant farmers

Doesn't it sound like a dream to be able to produce a super-abundance of food with no fertilizers or pesticides and with little or no greenhouse gas emission? Not if you treat your farm wastes properly to mine the rich nutrients that can support the production of fish, crops livestock and more, get biogas energy as by-product, and perhaps most importantly, conserve and release pure potable water back to the aquifers.

That is what Professor George Chan has spent years perfecting; and he refers to it as the Integrated Food and Waste Management System (IFWMS) [1].

Chan was born in Mauritius and educated at Imperial College, London University in the United Kingdom, specializing in environmental engineering. He was appointed director of two important US federal programmes of the US Environmental Protection Agency and the US Department of Energy in the US Commonweath of the Northern Mariana Islands of the North Pacific. On his retirement, Chan spent 5 years in China among the Chinese peasants, and confessed he learned just as much there as he did in University.

What he learned was a system of farming and living that inspired him and many others including Gunter Pauli, the founder and director of the Zero Emissions Research Initiative (ZERI) (

Chan left China in 1989, and continued to work with Gunter and others in ZERI through consultancy services. This work has taken him to nearly 80 countries and territories, and contributed to evolving IFWMS into a compelling alternative to conventional farming.

The integrated farm typically consists of crops, livestock and fishponds. But the nutrients from farm wastes often spill over into supporting extra production of algae, chickens, earthworms, silkworms, mushrooms, and other valuables that bring additional income and benefits for the farmers and the local communities.

Treating wastes with respect

The secret is in treating wastes to minimize the loss of valuable nutrients that are used as feed to generate further nutrients from algae, fish, etc., that feed a variety of crops and livestock. At the same time, greenhouse gases emitted during the first phase of waste treatment are harvested for use as fuel, while the oxygen required in the second phase of waste treatment - which gets rid of toxins and pollutants - is generated by photosynthetic algae, so fish stocks are not suffocated through lack of dissolved oxygen in the nutrient-rich water entering the ponds.

Livestock wastes are first digested anaerobically (in the absence of air) to produce biogas (mainly methane). The partially digested wastes are then treated aerobically (in the presence of air) in shallow basins that support the growth of green algae. By means of photosynthesis, the algae produce all the oxygen needed to oxidise the wastes to make them safe for fish. This increases the fertilizer and feed value in the fishponds without robbing the fish of dissolved oxygen. All the extra nutrients, therefore, go to improve productivity. Biogas is used as a clean energy source for cooking, and also enables farmers to process their produce for preservation and added value, reducing spoilage and increasing the overall benefits.

IFWMS has revolutionized conventional farming of livestock, aquaculture, horticulture, agro-industry and allied activities in some countries, especially in non-arid tropical and subtropical regions. It has solved most of the existing economic and ecological problems and provided the means of production such as fuel, fertilizer and feed, increasing productivity many-fold.

"It can turn all those existing disastrous farming systems, especially in the poorest countries into economically viable and ecologically balanced systems that not only alleviate but eradicate poverty." Chan says [2].

Increasing the recycling of nutrients for greater productivity

The ancient practice of combining livestock and crop had helped farmers almost all over the world. Livestock manure is used as fertilizer, and crop residues are fed back to the livestock.

Chan points out, however, that most of the manure, when exposed to the atmosphere, lost up to half its nitrogen as ammonia and nitrogen oxides, before they can be turned into stable nitrate that plants use as fertilizer (see Box 1). The more recent integration of fish with livestock and crop has helped to reduce this loss [3].

The important addition of a second production cycle of nutrients from fish wastes has enhanced the integration process, and improved the livelihoods of many small farmers considerably. But too much untreated wastes dumped directly into the fishpond can rob the fish of oxygen, and end up killing the fish.

Box 1

How volatile nitrogen is turned into nutrient for plants [4]

Livestock manure contains large amounts of ammonia gas that must be turned back into stable nitrate before it can be absorbed as nutrient by plants. Nitrification is the process in which soil bacteria oxidize ammonia (NH3) sequentially into nitrite (NO2) and then nitrate (NO3). Ammonia is oxidized into nitrite by bacteria belonging mainly to the genus Nitrosomonas, but also Nitrosococcus, Nitrosospira, Nitrosolobus and Nitrosovibrio. Nitrite is then further oxidized into nitrate by bacteria belonging mainly to the genus Nitrobacter, but also by bacteria in other genera such as Nitrospina, Nitrococcus and Nitrospira.

In IFWMS, the anaerobically digested wastes from livestock are treated aerobically before the nutrients are delivered into the fishponds to fertilize the natural plankton that feed the fish without depleting oxygen, thereby increasing fish yield 3- to 4-fold, especially with the polyculture of many kinds of compatible fish feeding at different levels as practiced in China, Thailand, Vietnam, India and Bangladesh. The fish produce their own wastes that are converted naturally into nutrients for crops growing both on the water surface and on dykes surrounding the ponds.

The most significant innovation of IFWMS is thus the two-stage method of treating wastes; the anaerobic digester followed by the shallow aerobic basins containing green algae. Livestock waste contains very unstable organic matter that decomposes fast, consuming a lot of oxygen. So for any pond, the quantity of livestock wastes that can be added is limited, as any excess will deplete the oxygen and affect the fish population adversely, even killing them.

Chan is critical of "erratic proposals" of experts, both local and foreign, to spread livestock wastes on land to let them rot away and hope that the small amount of residual nutrients left after tremendous losses that damage the environment have taken place.

According to the US Environment Protection Agency, up to 70% of nitrous oxide, N2O, a powerful greenhouse gas with a global warming potential of 280 (i.e., 280 times that of carbon dioxide) comes from conventional agriculture [5]. Nitrous oxide is formed as an intermediate in denitrification, a process in which soil bacteria reduce nitrate ultimately back to nitrogen gas. Denitrifying bacteria belong to two main genera, Pseudomonas and Bacillus [6]. Animal manure could be responsible for nearly half of the N2O emission in agriculture in Europe, according to some estimates; the remainder coming from inorganic nitrate fertilizer [7]. Thus, anaerobic digestion not only prevents the loss of nutrients, it could also substantially reduce greenhouse gas emissions from agriculture.

Chan further dismisses the practice of composting nutrient-rich livestock wastes [8], for this ends up with a low-quality fertilizer that has lost ammonia and nitrite. Instead of mixing livestock wastes with household garbage in the compost, Chan recommends produce high-protein feeds such as earthworms from the garbage, and using worm castings and garbage residues as better soil conditioners. He is also critical of the outmoded practice of putting manure in septic tanks for not much financial or other benefits while the badly treated effluent is just as dangerous as the waste itself.

Instead, the livestock waste digested anaerobically followed by oxidation in open shallow basins with natural algae before letting the treated waste effluent flow into the fish pond, can convert almost 100% of the organic nutrients into inorganic nutrients that will not consume any oxygen to deprive the fish. So, theoretically, the quantity of waste input into the pond can increase 10-fold without the risk of pollution. But, Chan cautions, the nutrients in the waste must be totally used by both fish and crop culture, or the nutrients can create problems of eutrophication - over-enrichment of plankton - that uses up all the oxygen in the pond, thereby lowering productivity.

To close the circle, livestock should be fed with crops and processing residues, not wastes from restaurants and abattoirs. Earthworms, silkworms, fungi, insects and other organisms are also encouraged, as some of them produce high value goods such as silk and mushrooms.

The digester can be as simple as a couple of concentric plastic bags of 5m3 capacity or 200-litre drums for a small farm, or a complex reinforced concrete steel structure with an anaerobic sludge blanket to collect the biogas for a big farm or industrial enterprise.

As the fresh wastes enter the digester, the waste-eating bacteria transform the unstable ammonia (NH3) and nitrite (NO2) into stable nitrate (NO3), which is ready for use as fertilizer. As more wastes are added, the digester also produces an abundant and inexhaustible supply of biogas - 2/3 methane (CH4) and 1/3 carbon dioxide (CO2) - a convenient source of free and renewable energy for domestic, farming and industrial uses (see Box 2). Big farms, meat and fish-packing plants, distilleries, and various agro-industries are now self-sufficient in energy, besides having big volumes of nutrient-rich effluent for fertilizing fishponds, and 'fertigation' (fertilization and irrigation) of many kinds of crops.

Box 2

Formation of biogas [9]

Certain bacteria naturally present in manure produce a combustible gas (biogas) when they digest organic matter anaerobically (in the absence of oxygen). Biogas typically contains between 60 and 70 percent methane. Anaerobic digestion involves two groups of bacteria. The first group of ordinary bacteria produces organic acids such as acetic acid by fermentation. The second group of bacteria, the methanogens (methane makers), is special, it breaks down the organic acids and produces methane as a by-product.

Methanogens cannot tolerate oxygen and are killed when exposed to oxygen. Instead, they can use the dead end products of fermentation, carbon dioxide or organic acids such as acetic acid, to generate methane:

Methanogens are found wherever oxygen is depleted, such as wetland soils, aquatic sediments and in the digestive tracts of animals. Methane formation is the final step in the decay of organic matter when carbon dioxide and hydrogen accumulate, and all oxygen and other electron acceptors are used up.

Proliferating lifecycles for greater productivity

The aerobic treatment in the shallow basins depends on oxygen produced by the green alga Chlorella. Chlorella is very prolific and can be harvested as a high-protein feed for chickens, ducks and geese.

When the effluent from the Chlorella basins reaches the fishpond, little or no organic matter from the livestock waste will remain, and any residual organic matter will be instantly oxidized by some of the dissolved oxygen. The nutrients are now readily available for enhancing the prolific growth of different kinds of natural plankton that feed the polyculture of 5 to 6 species of compatible fish. No artificial feed is necessary, except locally grown grass for any herbivorous fish.

The fish waste, naturally treated in the big pond, gives nutrients that are used by crops growing in the pond water and on the dykes [10].

Fermented rice or other grain, used for producing alcoholic beverages, or silkworms and their wastes, can also be added to the ponds as further nutrients, resulting in higher fish and crop productivity, provided the water quality is not affected.

Trials are taking place with special diffusion pipes carrying compressed air from biogas-operated pumps to aerate the bottom part of the pond, to increase plankton and fish yields.

Apart from growing vine-type crops on the edges of the pond and letting them climb on trellises over the dykes and over the water, some countries grow aquatic vegetables floating on the water surfaces in lakes and rivers. Others grow grains, fruits and flowers on bamboo or long-lasting polyurethane floats over nearly half the surface of the fishpond water without interfering with the polyculture in the pond itself. Such aquaponic cultures have increased the crop yields by using half of the millions of hectares of fishponds and lakes in China. All this is possible because of the excess nutrients from the integrated farming systems.

Planting patterns have also improved. For example, rice is now transplanted into modules of 12 identical floats, one every week, and just left to grow in the pond without having to irrigate of fertilize separately, or to do any weeding, while it takes 12 weeks to mature. On the 13th week, the rice is harvested and the seedlings transplanted again to start a new cycle. It is possible to have 4 rice crops yearly in the warmer parts of the country, with almost total elimination of the back breaking work previously required.

Another example is hydroponic cultures of fruits and vegetables in a series of pipes. The final effluent from the hydroponic cultures is polished in earthen drains where plants such as Lemna, Azolla, Pistia and water hyacinth remove all traces of nutrients such as nitrate, phosphate and potassium before the purified water is released back into the aquifer.

Processing for added value and nutrient release

One big problem with agricultural produce is the drop in prices when farmers harvest the same crops at the same time. This is solved by the abundant supply of biogas energy, which enable simple processing to be done such as smoking, drying, salting, sugaring, and pickling.

Finally, the sludge from the anaerobic digester, the algae, macrophytes, crop and processing residues are put into plastic bags, sterilized in steam produced by biogas energy, and then injected with spores for high-priced mushroom culture.

The mushroom enzymes break down the ligno-cellulose to release the nutrients and enrich the residues, making them more digestible and more palatable for livestock. The remaining fibrous residues can still be used for culturing earthworms, which provide special protein feed for chickens. The final residues, including the worm casting, are composted and used for soil conditioning and aeration.

Sustainable development is possible

There has been a widespread misconception that the only alternative to the dominant model of infinite, unsustainable growth is to have no growth at all. I have heard some critics refer to sustainable development as a contradiction in terms. IFWMS, however, is a marvellous demonstration that sustainable development is possible.

The key is a balanced development and growth that's achieved by closing the overall production cycle, then using the surplus nutrients and energy to support as many different cycles of activities as possible while maintaining internal balance, rather like a developing organism [11]. The 'waste' from one production activity is resource for another, so productivity is maximised with the minimum of input and little or no waste is exported into the environment. It is possible to have sustainable development after all; the alternative to the dominant model of unlimited, unsustainable growth is balanced growth.

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Article first published 09/06/05


  1. Professor George Chan, oneVillage advisor and ecological design consultant, oneVillage Foundation
  2. George L. Chan. What does integrated farming system do? November 2003, reproduced in Sustainable Communities ZERI-NM.
  3. Prein M. ICLARM contribution No. 1611. Integration of Aquaculture into Crop-Animal Systems in Asia,. Agricultural Systems, 71pp127-146. Elsevier Science Ltd., Amsterdam The Netherlands, 2001.
  4. Nitrification. US Environment Protection Agency.
  5. Where does nitrous oxide come from? US Environment Protection Agency
  6. Hagedorn C. The nitrogen cycle: denitrification. Envionmental microbiology, Spring 2004
  7. Smith P, Goulding KW, Smith KA, Powlson DS, Smith JU, Falloon P and Coleman K. Enhancing the carbon sink in European agricultural soils: including trace gas fluxes in estimates of carbon mitigation potential. Nutrient Cycling in Agroecosystems 2001, 60, 237-252.
  8. Animal manure as a source of greenhouse gas. Transform Compost Systems Ltd.
  9. Methanogenesis. Wikipedia, the free encyclopedia June 2005.
  10. Zhong GF, Wan ZQ, Wu HS. Land-Water Interactions of the Dike-Pond System. Presses Universitaires de Namur and Eco-Technologie de Eaux Continentales, Belgium, 1997.
  11. Ho MW and Ulanowicz R. Sustainable systems as organisms? Biosystems 2005.

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