Integrated Bio-Systems : A Global Perspective

Integrated Bio-Systems : A Global Perspective

Jacky Foo,
Integrated Bio-Systems Network
International Organization on Biotechnology and Bioengineering
http://www.ias.unu.edu/proceedings/icibs/ibs/ibsnet
Email: foo@swipnet.se Fax: 46-8-5982 9229

Paper submitted to National Workshop on Integrated Food Production and Resource Management (InFoRM 2000), Brisbane, (9-10 November, 2000).

Summary

"Integrare" is the latin verb which means to make whole and complete by adding parts or to combine parts into a whole. To the biologists, an integrated biosystem contains at least two biological activities or subsystems where nutrients in by-products (waste) from one sub-system serve as resources or inputs for another. This can be represented in a schematic process flow chart for a simple integration of two sub-systems.

Traditional integrated biosystems often use labour-intensive bio-systems or technologies in low-input, organic farming that can provide a variety of products at a micro-level. They recycle nutrients in solids and liquids into biofertilisers, feeds, aquatic plants, fish and food. In the past century, access to chemical fertilisers, pesticides, herbicides and mechanization led to monoculture crop production. This replaced the practice of the traditional integrated farming systems in many countries. In the new millennium, we will continue to face challenges at a larger dimension in scales. They include : local shortages and/or need for more efficient use of natural resources (water, forest, energy, agricultural land), managing biodegradable wastes from cities and farms in an environmentally sound manner, ensuring food security, reducing poverty and creating sustainable livelihoods and human communities. Can integrated biosystems serve as the tools to reduce some of these problems?

Large-scale farming and intensification in small farms seem inevitable in the future if the estimated 50 % of the world's population who will live in urban areas by 2025 are to be fed. Some cities now grow food 10-70 % of the vegetables for local needs in urban and peri-urban areas and they can be enhanced using integrated bio-systems by integrating crop production with small livestock production and/or composting selected biodegradable municipal wastes. An example of a large livestock farm in Colombia is described in this paper.

Sewage is a major problem in cities. In Dar es Salaam, 70 % of the city population (3 million) live in an area of about 1350 km2 that is unplanned with marginal access to tap water, sewage systems, infrastructure or basic social services. Sewage can be a resource to provide employment and to produce food. It has been demonstrated in Bangladesh that 2.5 hectares are needed to use and treat the sewage from 3,000 inhabitants and at the same time to produce bananas and fish. Details of this case study will be provided.

The integrated bio-systems approach is a multi-purpose tool that can improve resource utilisation and minimise external inputs in production processes, strengthen the local economies for food production, enable productive solid and liquid waste management as well as create sustainable livelihoods and communities. This approach can be applied to Australia.

Introduction

The holistic approach to utilise fully a resource such as water is not a new concept or a new practice. It is common sense. In the ancient Egyptian painting of about 2000 BC old that was found from the Tomb of Thebaine, it seems to present an integrated bio-system for pond aquaculture where nutrients in pond water were used for cultivation of flowers, vegetables and fruits. Other early civilisations such as those in Mexico and China have also developed integrated farming systems that are unique to their regions, e.g. the Chinampa system (Foo, 2000) in Mexico that at one time provided food and flowers to Mexico city. Integrated bio-systems are still widely practised in China where there exists numerous types of systems for different scales for the production of food, fuel, biofertiliser and fibre (Ruddle et al. 1983, Ruddle & Zhong 1988, Li, 1993, Wang, 1998).

"Integrare" is the latin verb that means to make whole and complete by adding parts or to combine parts into a whole. To the biologists, an integrated biosystem would contain at least two biological activities or subsystems and a generic focus is on the balanced flow of materials and their nutrients as food from one sub-system to another. In Nature, there are many integrated biological systems that are often complexly interlinked with one another. Examples of systems such as those on the food chains for different animals are commonly presented in primary school education. To an industrialist and a farmer, these sub-systems would generate new products using by-products produced within in the factory or the farm. In the area of primary food production, the focus is on the flow of nutrients to the environment that supports the process of food production. This can be represented in a schematic process flow chart for a simple integration of two sub-systems, as shown above in the abstract.

Natural food production systems are limited by their low productivity per unit land or water space. There is an urgent need to produce more from a unit space to be able to feed more people because of the failure to control human population which has already led to disastrous consequences in many countries. In India, as an example, the human population between 1940 to 2000 increased from 400 million to more than 1200 million. Correspondingly, food grain production rose 4 times from 50 million tons to 200 million tonnes between 1950 and 2000. However, consumption on a per capita basis increased slightly to 435 gm cereals per day from 400 gm in 1950. The amount of pulses consumed actually decreased by more than 33 % (from 75 gms to below 50 gms) per day between 1950 and 2000 (Khosla, 2000). By 2025, 50 % of the world's population will live in cities and this will further aggravate the food and resource situation as the major portion of the world's population will be consumers rather than primary food producers. Many countries know that they need to produce or import 2 or 3 times more food in order to cope with their local needs and the poor will find it even more difficult to put food on their dinning table.

Agro-food processing industries and marketing of crop produce use a small fraction of the primary biomass generated. A major part is the crop residue or industrial by-products or wastes that need to be disposed of. Environmental pressures and costs in incineration or landfilling are major driving forces demanding change from the linear model for production and waste management to a more integrated approach with eco-restructuring so that wastes are used as resources to generate income or make savings. At the same time it should also contribute to sustainable development in a more environmentally sound manner. This challenge is paving the way to the renewal of traditional practices and new opportunities to apply the integrated bio-systems approach for household, commercial and large scale bio-systems.

The Integrated Bio-Systems Approach

The Integrated Bio-Systems (IBS) approach follow three basic principles. The first principle is to use all biologically organic materials and wastes instead of disposing it. The second principle is to obtain at least two products from a waste. The third principle is to close the loop for the material and nutrient flow in order to achieve total use of a resource and zero waste disposal. The IBS approach has its potentials as well as limitations. These principles originally developed from situations where natural resources were limited and when the full use of resources is crucially interlinked with their survival. Such situations still exists in many countries. Low-input and subsistence farming systems often used the IBS approach in livestock-crop integration or in livestock-aquaculture integration. The technology used in IBS is still limited and to composting, vermi-culture, mushroom and insect larvae cultivation and biogas technology. to enhance the efficiency in utilising nutrients and increasing productivity. IBS is often labour intensive but ideal for small farms that are operated by single households. Large farms that generate large volumes of material will need some form of mechanisation or workers. The socio-cultural taboos and modern lifestyles may not accept the use of certain waste materials is also an important factor, particularly when dealing with the use of animal and human excretement, animal offal and some organisms/animals.

The IBS approach has only been applied recently by industry for utilisation and management of agro-industrial wastes, e.g. from brewery in Fiji, (Foo, 1995), Samoa (Foo & Dalhammar, 2000) and Namibia (Foo, 1998). Detailed information from industries on their use of IBS is however still lacking. The approach can enhance sustainability of their businesses through savings by reducing the cost for disposal of wastes and income generation by conversion of by-products into new value-added products. The use of agro-industrial by-products is an area for future business opportunities by industry and small-scale entreprises and should be encourage by policy makers as it provides employment and reduces pollution at the same time.

This paper provides a global perspective of integrated bio-syetms in developing countries through a few selected examples of small and large scale operations. They are:
(1) the pig-biogas-duckweed-cassava IBS in Vietnam
(2) brewery wastes-duck-insect larvae-aquatic plants-earthworm IBS in Samoa
(3) compost toilet and graywater garden system in Fiji
(4) the St. Petersburg Eco-house, Russia
(5) Pozo Verde Farm in Colombia
(6) Sewage-duckweed-fish-banana IBS in Bangladesh
(7) Rice-Flower-fish IBS in China

Pig-biogas-duckweed-cassava IBS in Vietnam

Figure 2: Livestock-biogas-duckweed-cassava IBS in Vietnam

The schematic chart (Figure 2) shows an integrated livestock-biodigester-duckweed-cassava biosystem (Rodríguez, Preston & Nguyen, 1998) that requires only 108 m² land space to raise 4 Mong Cai sows and to produce supplementary feed. Each sow is fed with basal feed (400 g/day boiled whole soya bean seed with added lime and salt and 500 g/day water spinach) with sugar palm juice and any other vegetation or root crop that is available. Manure is fed to a 3m³ plastic biogas digester to produce biogas (used for boiling soya bean) and the effluent goes into eight duckweed ponds of 7m² each (total 56 m2). Duckweed yield (fresh weight) is 100 g/m2/day with about 6% of dry matter and 35% crude protein. 5.6 Kg Duckweed/day is therefore available daily. Live weight gains of pigs ranged from 350-450 g/day. The cassava trees grow on heavily fertilised with organic manure and sludge from the duckweed ponds and can produce about 1 kg of leaves/m² every 2 months. This amounts to an annual yield of up to 60 tonnes leaves/ha (Preston et al., 1998). The dry matter content is around 25% and the protein content of the dry matter is 25% (Nguyen & Rodriguez. 1998). Cassava leaf can contain a high content of HCN and is ensiled anaerobically with 5% of molasses using a plastic bag (Nguyen et al 1998) for 6 weeks and then fed directly to the pigs.

The system was more profitable and provides better nutrition to the family than sugar production from sugar palm which also leads to deforestation because firewood is needed to concentrate the juice. Except for the plastic and PVC pipes for the digester, all other construction materials (bamboo, roofing materials) needed are locally available at site.

Photo 1: Livestock-plastic biodigester- Duckweed system in UTA-Vietnam. Picture by Lylian Rodriguez	Photo 2: Biogas-Duckweed-Cassava in UTA-Vietnam. Picture by Lylian Rodriguez
Photo 3 : A mixture of Duckweed-Rice Bran feed to laying hens in UTA-Vietnam. Picture by Lylian Rodriguez	Photo 4: Farmer taking the sap from the sugar palm. Picture by Khieu Borin

Use of Agro-Industrial wastes at a household level in Samoa
Breweries and vegetable oil industries generate high-protein residues and pressed cakes that can be used directly as animal feed. Yet in some locations as in Apia, Samoa, these residues are not fully used and part of these by-products are dumped. Brewery spent grains is given away free of charge while coconut meal is sold at US$ 2.00 per bag (using recycled 40kg-flour bag) at the factory site which is located in the city. The reasons for the lack of use of these by-products in Apia is high transportation costs and lack of local distribution system for the sale of the by-products. In July 2000, a project with a local NGO called METI in Apia, was launched to use fresh and stale brewery spent grains either directly as duck feed or to grow insect larvae. Duck manure from 20 ducks is washed into ponds to grow aquatic plants (Salvinia and duckweed) and mosquito fish. Feed residues are buried into the ground to grow earthworms which are dug out periodically to feed the ducks.

Figure 3: Schemctic diagram of IBS for raisning ducks using agro-industrial wastes.

Data on the material flow is not available yet but there is a potential of producing 3-5 kg (fresh weight) of aquatic plants per day from about 100 m2 pond area using duck manure. The project will provide information on the economical feasibility of using brewery spent grains and yeasts as duck feed at a household level. The IBS can provide new business opportunities to households around the brewery site as they can collect spent grain and yeast free of charge or the development of a business venture for raising ducks in Samoa. Such activities will help the brewery to reduce transportation costs to the dump site.

Photo 5 : Picture of ducks in Spent grain-insect
larvae-duck-duckweed-Salvinia-mosquito fish
integrated bio-system in Samoa.
Copyright: IBSnet, 2000

Photo 6 : Picture showing play-pond in front with
duckweed pond on the back right and Salvinia
-mosquito fish pond on the left background.
Copyright: IBSnet, 2000

Compost Toilet and Graywater Garden System in Fiji

The compost toilet and washgarden system is used by the Lalati eco-resort on the island of Beqa in Fiji. The system is an on-site zero sewage discharge system with a strategy in creating beautiful gardens while preventing pollution with ecological integrity. The system has a micro-flush toilet and the flushwater is led into a modified rollaway trash container serving as the composter. The composter is fitted with a hanging net to catch solids and allows flushwater to flow into a concrete trench filled to stones with a top soil. Different varieties of broad-leaved gingers and canna lilies are used in this case to absorb and transpire the water into the air. Lalati Eco-Resort has won an award for this system from the WHO for best eco-tourism practices. The system below is designed for warm countries and offer an appropriate solution with ecological integration to provide a better quality of life where central sewage treatment plants are lacking. The design can be modified and applied in temperate and colder countries by using a greenhouse.

Photo 7 : General view showing washwater garden and bungalow at Lalati eco-resort. Below the vertical vent/exhaust chimney is the composter for the compost toilet.
Photo: Sustainable Strategies
and Affiliates

Photo 8 : Composter of toilet system with a hanging net to hold and separate solids from liquid. Liquid flows through pipe on right into wastwater garden.
Photo: Sustainable Strategies
and Affiliates

Photo 9 : Washgarden protected by transparent Lexan roof from rain and with different varieties of broad-leaved gingers and canna lilies to absorb and transpire water from concrete 1 m deep and 1.5. m wide trench.
Photo: Sustainable Strategies
and Affiliates

The St Petersburg's EcoHouse

The Eco-house is an example of sustainable urban community development (Yemelin & Mehlmann, 2000). Among the massive standard apartment blocks in the Moskovsky district of St Petersburg, Russia, an average nine-stories building was chosen as the site. It has 267 apartments with 500 residents (60% senior citizens) in cramped apartments built in 1966. It had 1700 m2 of flat roof and 600 m2 unusable wet basement that was infested with rats and breeding mosquitoes. After 3 years, 50 people from 25 apartments are now involved in the project to (a) separate inorganic garbage, including selling some for recycling (b) process in-house organic waste into compost, using worm culture in the basement (c) produce organic food, flowers and plantlets on the roof-top. Monthly the compost process 200 kg of food garbage in winter and 300 kg in summer. The roof-top garden is 25 m above ground and has better air quality. As access to the rooftop is controlled, theft is nil. Two greenhouses are between chimney stacks to extend the growing season using heat from the chimneys. Roof-top grown food reduced cost of food purchases which represents a significant savings especially for the elderly. Products for sale are: currant berry bushes grown from cuttings, flowers and biohumus product of worm composting. Socio-psychological effects of the project, such as empowerment of residents, bettering of psychological climate, development of participatory grass-roots democracy cannot be overestimated.

Photo 11 : Vermi-composting in the basement Photo: Valentin Yemelin	Photo 12 : Harvesting Tomatoes from the roof-top greenhouse Photo: Valentin Yemelin
Photo 13 : Watering roof-top lawn/nursery with plantlets Photo: Valentin Yemelin	Photo 14 : Inside view of roof-top greenhouse Photo: Valentin Yemelin

Pozo Verde Farm in Colombia

Pozo Verde Farm is a livestock farm of 50 ha in size, of which 2 ha is used for for buildings and the rest for forage (42 ha, sugar cane, taro, grass, forage trees, aquatic plants) and about 5 ha wetlands. It buys ingredients and formulated feed for the sows, growing and fattening pigs and broilers. All manure (920 tons/yr) is used in an integrated biosystem (Figure 4, Table 1) to produce energy (19,200 m3 biogas), vermi-compost (160 tons), feed additives (52.6 tons as chicken manure) and forage (6,323 tons) for cattle and pigs.

Figure 4: Integrated Bio-System at Pozo Verde Farm, Colombia.(Chara, J.D. et. al. 2000)

Table 1 : Material flow at the Pozo Verde Farm, Colombia (modified after Chara, J.D. et al. 2000)

SUBSYSTEM	INPUTS (purchased or produced in Farm)	PRODUCTS (To the market)	BYPRODUCTS (To other subsystems)
Pigs - 73 breeding sows - 595 growing & fattening	Formulated feed: 384 ton Aquatic plants: 109 ton Giant taro: 5.6 ton	Pork meat: 107.4 ton	Wastewater: 10,477m3 Pig manure: 48.1 ton
166 Dual Purpose Cattle	Chicken litter: 52.6 ton Pizamo foliage: 46 ton Star grass: 5,920 ton Sugarcane tops: 340 ton Molasses : 23.2 ton Vinaza : 15.5 tons Rice bran: 6.9 tons Calcium Carbonate: 0.7	Milk: 159,200 litres. Weaned calves: 6.25 ton	Manure: 230 ton Wastewater: 2,883 m3
52 Buffaloes		Milk: 13,600 Cheese: 2.2 ton "Kumis": 4,160 liters Six trained draught buffaloes	Manure: 37 ton Animal draught: 657 Kwh
Poultry (29,000 broilers kept in 41 day cycles)	Formulated feed: 579 ton	Broilers: 303 ton	Chicken litter: 600 ton
Forage production (42 hectares and 1 ha pond)	Biodigester effluent: 15,000 m3 Chicken litter: 450 ton Earthworm compost: 80 ton		Foliage biomass: 6,323 ton
Earthworms (300 m2 area)	Cattle dung: 230 ton Buffalo dung: 37 ton	Worm compost: 80 ton	Worm compost: 80 ton
Wastewater Decontamination systems (4 digesters with total 178 m3 digester volume, 1 ha pond)	Wastewater: 13,360 m3 Pig manure: 48.1 ton		digester effluent: 15,000 m3 Biogás: 19,200 m3 aquatic plants: 109 tons

Sewage-duckweed-fish-banana IBS in Bangladesh
The Mirzapur Farm Complex (Iqbal, 1999) is more than 11 hectares in size and grows duckweed (Leng, 1999) using chemical fertiliser to raise fish. The Sewage-duckweed-fish-banana integrated biosystem is a demonstration unit to use nutrients from wastes (rather than purchasing inorganic fertiliser) on a 2.5 ha site. Community waste water of 2000-3000 inhabitants from a school, residences and a hospital (125-270 m3 / day) flows into a 0.2 ha duckweed covered sedimentation pond (0.2 ha in size, retention time=16-7 days) and is then pumped into a 500 m plug-flow lagoon (width=12.6 -13 m, depth=0.4 m at inflow point, 0.9 m at outflow point, retention time=about 20 days). Duckweed is manually harvested to feed fish that is raised on 3 ponds of 0.2 ha each). Duckweed harvest average 656+-177 kg ww/ha/day (Feb93-Mar94) while in the wet season it is 1000-1200 kg/ha/day. This is extrapolated to about 17 tons (dw)/ha/yr. Stocking of carps (18,000-20,000 fish/ha) is done in July and harvested after 10-12 months. The feed is duckweed (60% dw), and mustard oil cake (40% dw). Fish yield in 1994 was 10.58 t/ha/yr (FCR=2.8) and in 1995 - 12.62 t/ha/yr (FCR=3.3). 60 % harvest is sold to the hospital while the remainder is sold at local market. Bananas is grown on the dikes and yield about 100 tons per year.

Figure 5 : Diagram showing overview of Sewage-duckweed-fish-banana integrated bio-system. (Sascha Iqbal. 1999)	Photo 15 : Plug-flow lagoon for cultivation of duckweed. Photo: Gregory Rose (1999)
Photo 16 : Harvesting duckweed. Photo: Gregory Rose (1999)	Photo 17 : Harvesting Fish Photo: Gregory Rose (1999)

Table 2 : Typical wastewater parameters of a duckweed-covered plug
flow lagoon during dry/winter season in Bangladesh. (Sascha Iqbal, 1999)

Parameter	Loading rate (kg/ha/day)	Influent (mg/l)	Effluent (mg/l)	Reduction in concen- tration (%)
BOD₅	48-60	125 (80-160)	5 (8)	96 (90-95)
Kjeldahl-N	4.2	10.5	2.7	74
Total P	0.8	1.95	0.4	77
o-PO₄^3-	---	0.95 (0.5-2.5)	0.05 (0.05-1)	95 (90-95)
NH₄⁺	---	8 (3-20)	0.03 (0.1-1)	99 (90-99)
NO₃^-	---	0.03 (0.05-1)	0.05 (0.05-1)	---

The values in paratheses are based on a 4-year monitoring (1990.1994). Influent data was corrected for dilution effect caused by groundwater supply. Concentration of NH₄⁺ and NO₃^- are expressed in mg N/l. The concentration of o-PO₄^3- is given in mg P/l. Values were corrected for a leakage-free lagoon.

Faecal coliforms in the influent has 45,700 cfu/ml while the effluent contains less than 100 cfu/ml which is within the maximum WHO standard for wastewater discharge. Kabir 1995, Islam et al 1996 and Edwards et al 1987 considered the water quality as safe. Krishnan & Smith (1987) reported acceptable levels of heavy metals and pesticides but as duckweed can tolerate and accumulate high concentrations of heavy metals and organic compounds, monitoring of heavy metal content in the influent is advised.

Rice-Flower-fish IBS in China
Terrestrial plants can be planted on floating-platforms in lakes and integrated with aquaculture. The application of surface aquaponics was developed in China since 1989 (Song et al 1991, Song et al 1996) because of decreasing area of arable land and to fully use inland water surface. In 1996 the area of pond culture alone was 1.96 million ha in China with the fish production of 8.11 million tons (Chinese Agricultural Almanac 1997). Eutrophication in fishponds and deterioration of the water quality of fishponds is resulting in increase occurrence of fish diseases and fish mortality. Discharge of nutrient rich pond water further accelerates eutrophication in rivers or lakes. The strategy with the application of surface aquaponics is to clean the pond water by absorbing the nutrients and at the same time generate products of economic value. Rice and flower cultivation have proven as economically useful crops. The integration of crop-aquculture using less than 25 % coverage of the water surface is beneficial. Rice yield reached 7.92 t/ha and to the fish yield of 5,638 kg/ha and at the same time a higher water quality of pond water can be obtained.

Photo 18 : Cultivation of rice on floating bed in lake in a rice-fish integrated bio-system Photo: Kangmin Li (2000)	Photo 19 : Flowers and sedge grass on floating beds Photo: Kangmin Li (2000)
Photo 20 : Canna and money plant on floating beds Photo: Kangmin Li (2000)	Photo 21 : Comparison of the water from outside and inside the test area Photo: Kangmin Li (2000)

Conclusion

Much of the practice related to integrated bio-systems is still traditional and thus there is much room for research and improvement in productivity of the sub-systems at the household and farm level with technology and controlled of the biological processes. The biogas technology is an example and has become an important sub-system to provide energy and to provide nutrients and better hygienic quality of effluent. There is also a need to integrated renewable energy programmes that use biogas technology

References

Bakker, N. et al . 2000. Growing Cities, Growing Food - Urban agriculture on the policy agenda. Deutsche Stiftung fur internationale Entwicklung (DSE), Zentralstelle fur Ernährung und Landwirtschaft, Feldfing. Germany. Email: zel@dse.de

Chara, Julián David; Pulido, Elkin Dario; & Cuellar, Piedad. 2000. Material Flow in "Pozo Verde" Integrated Farm in Cauca Valley Province, Colombia. http://www.ias.unu.edu/proceedings/icibs/ic-mfa/index-proc.html . In: Foo, E.L. Della Senta, T. and Sakamoto, K. (Eds). 2000. Material Flow Analysis of Integrated Bio-Systems. Proceedings of the Internet Conference on Material Flow Analysis of Integrated Bio-Systems, March-Oct 2000. http://www.ias.unu.edu/proceedings/icibs/ic-mfa/index-proc.html

Chinese Agricultural Almanac, 1997.

Edwards, P. C. Polprasert & K.L. Wee. 1987. Resource recovery and health aspects of sanitation. AIT Research Report no. 205, pp 324.

Foo, E.L. 1995. UNU/IAS Integrated Bio-system Project at Montfort Boys Town, Suva, Fiji. http://www.ias.unu.edu/proceedings/icibs/ibs/info/fiji

Foo, E.L. 1998. IBS at Tunweni Brewery, Tsumeb, Namibia. http://www.ias.unu.edu/proceedings/icibs/ibs/info/namibia

Foo, E.L. (1999). Proceedings of the Electronic Seminar on "Community-Based Technologies for Domestic Wastewater Treatment and Reuse: options for urban agriculture" presented by Mr. Gregory D. Rose, (4-29 Oct. 1999). http://www.ias.unu.edu/proceedings/icibs/ibs/ibsnet/e-sem-rose.html

Foo, E.L. 2000. Chinampa Integrated Bio-System in Mexico. http://www.ias.unu.edu/proceedings/icibs/ibs/info/mexico

Foo, E.L. and Dalhammar, 2000. Biotechnological approach in the utilisation and treatment of wastes from a brewery via an integrated bio-system. http://www.ias.unu.edu/proceedings/icibs/ibs/info/samoa/sida-kth

Foo, E.L. & Della Senta, T. (eds). 1998.Integrated Bio-Systems in Zero Emissions Applications. Proceedings of the Internet Conference on Integrated Bio-Systems. http://www.ias.unu.edu/proceedings/icibs

ICLARM and GTZ. 1991. The context of small-scale integrated agriculture-aquaculture systems in Africa: a case study of Malawi. ICLARM Stud. Rev. 18. 302 p. ISBN 971-1022-65-6.

Iqbal, Sascha. 1999. Duckweed Aquaculture: Potentials, possibilities and limitations for combined wastewater treatment and aniumal feed production in developing countries. SANDEC Report No.6/99. Document contact: EAWAG/SANDEC, Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland. email: hauser@eawag.ch

Islam, M.S., et al. 1996. Faecal contamination of a fish culture farm where duckweed, grown in hospital wastewater are used as fish feed. Proceedings of the 5th Annual Sci Conf. ASCON V. Dhaka, Bangladesh. pp. 49.

Kabir, M.S. 1995. The duckweed-based sewage treatment and fish culture with special reference to Vibrio cholerae 0139. M.Sc. thesis. Dept fo Microbiology, University of Dhaka, Bangladesh. pp. 1-84.

Khosla, Ashok. 2000. Lecture presented at the Seminar on "The Value of Facts in the World of Change". Organized by the Biofocus Foundation, Stockholm.

Krishnan, S.B. & J.E: Smith. 1987. Public health issues of aquatic systems used for wastewater treatment. In: Aquatic plants for water treatment and resource recovery. Eds: Reddy K.R: & W.H. Smith. Magnolia, Orlando, FL. pp. 855-878.

Leng, R.A. 1999. Duckweed - A tiny aquatic plant with enormous potential for agriculture and environment. FAO-UTA Publication.

Li, Wenhua. 1993. Integrated farming systems in China. Veröffentlichungen des Geobotanischen Institutes der ETH, Zurich. 88 pages.

Mehlmann, M. & Yemelin, V. 2000. The St Petersburg EcoHouse – an example of sustainable urban community development. Status report, April 2000. http://www.ias.unu.edu/proceedings/icibs/ibs/info/russia
see also http://spb.ecology.net.ru/ecohouse/ or http://geocities.com/RainForest/Andes/2803/

Nguyen, Van Lai and Rodriguez, Lylian. 1998 Digestion and N metabolism in Mong Cai and Large White pigs having free access to sugar cane juice or ensiled cassava root supplemented with duckweed or ensiled cassava leaves Livestock Research for Rural Development. Volume 10, Number 2

Preston, T R, Rodríguez L , Nguyen Van Lai and Le Ha Chau 1998 El follaje de la yuca (Manihot esculenta Cranz) como fuente de proteína para la producción animal en sistemas agroforestales., Articulo presentado en La conferencia electrónica de FAO "Agroforestería Para La Producción Animal En Latinoamérica" April to Sept .In Spanish.

Rodríguez J. L., Thomas R Preston and Nguyen Van Lai. 1998. Integrated farming systems for efficient use of local resources. http://www.ias.unu.edu/proceedings/icibs/rodriguez/ In: Editors: Eng-Leong Foo & Tarcisio Della Senta. Integrated Bio-Systems in Zero Emissions Applications. Proceedings of the Internet Conference on Integrated Bio-Systems. http://www.ias.unu.edu/proceedings/icibs/wang

Ruddle K., Furtado J.I., Zhong G.F., and Deng H.Z.. 1983. The mulberry dike carp pond resource system of the Zhujiang (Pearl River) Delta, P.R. of China. 1. Environmental context and system overview. Applied Geography. 3,45-62.

Ruddle, K. & Zhong G.F. 1988. Integrated agriculture-aquaculture in South China. Cambridge Univ Press. 3-68.

Song Xiangfu, et al. 2000. Study of Agriculture-Aquaculture Ecological Economic System With Nutrient Flow Analysis. In: Foo, E.L. Della Senta, T. and Sakamoto, K. (Eds). 2000. Material Flow Analysis of Integrated Bio-Systems. Proceedings of the Internet Conference on Material Flow Analysis of Integrated Bio-Systems, March-Oct 2000. http://www.ias.unu.edu/proceedings/icibs/ic-mfa/index-proc.html

Song Xiangfu, et al. 1991. Study on rice cultivation on floating-beds in natural waters. Scientia Agricultura Sinica, 1991,24 (4): 8-13

Sustainable Strategies and Affiliates, 50 Beharrell Street, Concord, Massachusetts USA 01742-2973
E-mail: David Del Porto <daviddelporto@ecological-engineering.com> http://www.ecological-engineering.com/

Wang Rusong, Yan Jingsong, Lu Bingyou and Hu Dan. 1998. The Practice of Integrated Bio-Systems in China. http://www.ias.unu.edu/proceedings/icibs/wang Eds: Eng-Leong Foo & Tarcisio Della Senta. Integrated Bio-Systems in Zero Emissions Applications. Proceedings of the Internet Conference on Integrated Bio-Systems. http://www.ias.unu.edu/proceedings/icibs/wang