Ute Arnold, Joachim Clemens:
Nutrient Fluxes in Waste Water in Farming Systems in the Mekong Delta


1University of Can Tho, Center of Environmental Engineering and Renewable Energy, Vietnam
2University of Bonn, Institute of Plant Nutrition, Germany

The Mekong Delta is strongly based on agriculture, 75% of the 40.000 km2 land is agricultural land. 85% of the population in the Delta (17 million) are farmers living in communities which are split into small parcels along the water ways.

Human organic sanitary waste as well as the excrements of about 2,9 mio pigs, 46 mio poultry and other livestock are disposed mostly directly into the surface water. While most of local farmers depend on the surface water for drinking, irrigating their crops, fishing, aquaculture, etc., protection of this water source is crucial. Their organic sanitary waste can be valuable when used for fertilising soil for cropping or growing fish but may harm the environment -- especially the water -- when spilled uncontrolled.

Within this project SANSED water quality shall be improved by developing site-adapted-systems that reduce the nutrient losses and produce effective fertilisers for agriculture.

To optimise the nutrient reuse quantitative nutrient fluxes through households and water treatment systems are required. Therefore nutrient concentrations within two typical small farming households in Can Tho Province using biogas systems in combination with fishponds have been monitored regularly for one year. Water and sludge samples have been taken and analysis include field parameter (pH, electric conductivity, dissolved oxygen), nutrients (nitrogen, phosphorus, potassium) Carbon, Heavy Metals, and characteristic waste water parameters BOD, COD, E. coli, Coliforms.

By passing the biogas system first and the fish pond second the concentrations of COD, BOD5 are reduced significantly i.e. COD concentrations in the inflow reach around [10,000]mgl, in the ponds it is usually below [50]mgl. Pond concentrations sometimes even reach the Vietnamese Standard for surface water (COD <[10]mgl).

Fluxes have been estimated out of these data. A flux model through the systems has been developed that may be used to optimise the process of waste water treatment and agricultural production.

Keywords: Biogas, nutrient fluxes, waste water


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Contact Address: Ute Arnold, University of Can Tho, Center of Environmental Engineering and Renewable EnergyVietnam, e-mail: utearnold@ctu.edu.vn
Andreas Deininger, September 2004