Proceedings Biodigester Workshop March  2002

http://www.mekarn.org/procbiod/khang2.htm

Transferring the low cost plastic film biodigester technology to farmers

Duong Nguyen Khang and Le Minh Tuan^*

 

Department of Animal Physiology and Chemistry, University of Agriculture and Forestry,
Thu Duc district, Ho Chi Minh City, Viet Nam
khang@hcm.vnn.vn
^*Biogas centre, University of Agriculture and Forestry,
Thu Duc district, Ho Chi Minh City, Viet Nam

 

Abstract

The University of Agriculture and Forestry has been carrying out research, development and technology transfer of plastic film biodigesters for treating of animal wastes since 1990 with support from SidaSAREC, FAO and the Ministry of Education of Viet Nam. This paper summarises the technological and economical results from the installation of more than 15,000 plastic film biodigesters, most of them in the South of Viet Nam, especially the South-East area. The design of the biodigesters was based on experiences from Colombia combined with new ideas on using the local materials in Viet Nam for improving the technology. Assuming an interest rate of 6% the investment is recovered, on average, after 1.5 years by the saving on alternative fuel sources. The impacts of the technology and the constraints to be addressed in the future are discussed.

Key words: Low cost plastic film biodigester, technology transfer, development, socio-economic impact

Research and Development

The first plastic film biodigester in Viet Nam was established in 1992 at the University of Agriculture and Forestry, Thu Duc district, Ho Chi Minh City. The initiative was part of a project funded by SidaSAREC and FAO on strategies to promote sustainable use of local resources in livestock-based farming systems (Preston 1992). Tied up with this action plan, several plastic film biodigesters were constructed around Ho Chi Minh City and some districts belonging to Binh Duong province, such as Thuan An, Di An District.

The biogas yield of the plastic film biodigester reported in four sites (Table 1) was lower than that from a fixed dome concrete biodigester which was 340 litres/kg of OM according to Nguyen Van Thuan (1984). However, the biogas was enough for cooking at the householder level. The reason of the  lower biogas yield in the plastic film biodigesters was possibly because the ratio of manure to water was too low.

The COD (chemical oxygen demand) value if the manure was reduced significantly after being processed in the plastic film biodigesters (Table 2). Compared with the Viet Nam standard regulation for pollution caused by animal wastes of 100 to 400 mg COD/litre (1995), it appears that the plastic film biodigesters have the potential to reduce COD levels in raw manure to the accepted standard. E.coli density was reduced to between 7 x 10⁴ and 19 x 10⁴ MPN/ml by passing the manure through the plastic film biodigester system which is also within the accepted standard regulation of 5 x 10³ to 5 x 10⁴ MPN/ml.

Transfer of the technology

More than 40 provinces in Viet Nam have participated in the transfer of the plastic film biodigester system. The technology was also introduced to Cambodia, Lao, the Phillipines and Thailand (Photo 1). An efficient networking system involving representatives of the Government, Universities, Institutes, the Department of Environment, the Department of Agriculture and Rural Development, the Extension Agriculture Centre and farmers.

Photo 1: Transfer of the plastic film biodigester technology

More than 15,000 units have been set up in Vietnam during the past ten years, with numbers installed annually showing a consistent increase (Figure 1). There have been marked differences among regions. The numbers installed in the South-eastern part of Vietnam have been much greater than in the Mekong delta (Figure 2). This is probably because of the big increase in livestock production activities in the former region.

Figure 1: The numbers of biodigesters installed annually since 1992 (data for 2001 are not complete)

 

Figure 2: Numbers of biodigesters set up in the Mekong delta and in the South-Eastern region

 

 

Figure 3: Lifetime of plastic film biodigesters

A survey was made of 200 households having installed plastic film biodigesters since 1995 (Figure 3). Most of the units were still working up to five years after installation and some even longer, where there had been good protection.

Economic and environmental impact of the plastic biodigester technology

The cost of a 10m³ capacity biodigester (operating and capital costs) was estimated to be USD100.00. This is equivalent to a cost of USD6.00/month for the gas used for cooking. Therefore, with an interest rate of 6%, the payback period of the biogas system would be 1.5 years.  This does not take into account the positive effect of the technology on environmental parameters.   

The global advantages of the low-cost plastic biodigester technology

Economic advantages

• Produces cheap gas for poor farmers to replace industrial gas and wood.

• Creates new jobs, especially in the energy sector, and thereby decreases the unemployment rate in the country and stimulates the rural economy.

• Reducing work load for women to look for fuel in the field.

• It burns with a clean bluish flame thereby making it non-messy to cooking utensils and kitchens.

• The effluent is an excellent fertilizer for soil and water crops  and fish ponds

Environmental advantages

• Biogas does not contain toxic carbon monoxide so no danger to health and no offensive odour.

• Reduction in pollution as BOD and COD and fecal pathogens are considerably reduced.

Advantages and disadvantages of using plastic film biodigesters from the point of view of individual householders

Advantages:

• The plastic film biodigester is simple and easy to construct from readily available materials and its operation does not require special skills.

• Farmers can do the set up by themselves.

• Biodigester technology enhances energy supply decentralization, for instance rural communities having difficulties or no access to commercial fuels can produce biogas to meet their fuel needs, thereby increasing reliability of fuel supply and enhancing energy security to the rural areas.

• Plastic film biodigesters can be used for treating the waste water in live stock units

• Reducing the work of women in the household.

Disadvantages:

• The initial investment cost may be too high for poor families in rural areas.

• Plastic film biodigester could therefore be acquired only by the relatively richer farmers.

• Plastic film biodigesters are easily damaged physically and by sunlight

• Requires a considerable amount of residential space.

• Not enough high pressure for the flame (about 2 cm water column)

• Decrease of biogas production with drop in air temperature and in salt water areas.
   

Recommendations and policy implications:

Relatively high investment capital and maintenance cost is a major impediment to the adoption of plastic film biodigesters in the rural areas for poor farmers. Considering the long-term benefit of plastic film biodigester technology both economically and environmentally, it may be necessary to introduce some financial incentives to promote its penetration and diffusion into rural areas. The government agencies such as Department of Environment, Department of Agriculture and Rural Development, Agriculture Extension Center, and even private institutions could play a leading role by the issue of loans and subsidies. This could be implemented under government regulations and policies.

Research, development and demonstration are essential activities to overcome the technical obstacles and be well abreast of development in biogas technology. Government support will also be needed. Major research areas will include:

• Development and use of local materials for the construction of biogas plant,

• Improved fermentation process to obtain high biogas generation,

• Design specification for different plant sizes (plant construction techniques, effluent distribution, operation problems, gas appliances…),

• Development of effective and cheap appliances,

• Socio–cultural factors that affect the adoption of biogas technology,

• Evaluation of the technology.

• Intensification of networking activities in rural areas for poor farmers to understand how to protect the environment for development of suitable agriculture. 

References

Duong Nguyen Khang 1995 The low-cost plastic film biodigester technology. Training document. University of Agriculture and Forestry.

Nguyen Viet Lap 2001. Effects of loading rate and retention time on the rate of biogas production in plug-flow and liquid displacement biodigesters. Thesis. University of Agriculture and Forestry, Thu Duc, HCM city.

Pham Van Minh 1995 A survey on the technological developments of plastic film biodigester in East areas of the South of Viet Nam. Thesis. University of Agriculture and Forestry, Thu Duc, HCM city

Preston T R 1990 Livestock Production from Local Resources in an Integrated Farming System; a Sustainable Alternative for the Benefit of Small Scale Farmers and the Environment. Proceedings National Workshop-Seminar on Sustainable Livestock Production on Local Feed Resources. Ho Chi Minh City, Vietnam, January  18-20^th 2000.   

Nguyen Thanh Quoc 2000 Effect of loading rate of pig manure on the rate of biogas production in plastic film biodigesters. Thesis. University of Agriculture and Forestry, Thu Duc, HCM city.

Phan Duc Quy 1997  A survey on the usage and development of plastic film biodigester in East areas of the South of Viet Nam. Thesis. University of Agriculture and Forestry. Thu Duc, HCM city

Nguyen Van Thuan 1984  Guidance on the biogas production and usage. Journal of Dong Nai province.

Environmental Regulations of Viet Nam  1995 Volume 2. Quality Regulation Centre of Viet Nam.

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