Estimation of Nitrate and Phosphate Leaching from Lysimeter Simulation of Rice Straw Landfill Bioreactor and Evaluation of Fertilizer Quality of Resulting Compost

Rice is the staple food in Sri Lanka where more than 40% of the farmers are engaged in paddy cultivation producing approximately 4.1 million metric tons of paddies. Cultivation of paddy results in almost the same quantity of rice straw annually out of which a very high proportion is wasted. Hence, there is an enormous potential of utilizing paddy straw for the production of quality compost using landfill bioreactors. In this context, the main objectives of the study were to design a lysimeter simulation of a landfill bioreactor to produce compost from anaerobic digestion using rice straw, animal and green manure and evaluate the quality of the resulting compost. A secondary objective was to minimize possible groundwater pollution with nitrate nitrogen, phosphate and reduce the BOD and COD levels resulting from direct dumping of straw. The lysimeter consisted of a liner made of claypolythene- clay, gas collection system, leachate recirculation system, and main reactor. Altogether 431 kg of straw, 26 kg of cow dung and 32kg of Gliricidia were added to the main reactor. The lysimeter performances were evaluated by estimating pH, nitrate nitrogen, phosphate contents, BOD and COD of both leachate and the permeate. After 200 days of operation, nitrate nitrogen and phosphate of the leak were 1.23 mg/L and 0.03 mg/L, respectively. BOD increased during the first 14 days and it gradually decreased after 200 days. Quality of the compost is tallying with the Sri Lanka standards (SLS) guidelines. The study shows that there is a high potential of producing compost from landfill bioreactor using rice straw. It also revealed that the ground water pollution resulting from nitrate nitrogen and phosphate can significantly be mitigated. Further, it was observed that the levels of BOD and COD can also be reduced. Key words: Bioreactor; BOD; COD; Compost; Lysimeter; Mitigation. DOI: 10.4038/tar.v22i2.2831 Tropical Agricultural Research Vol. 22 (2): 220-228 (2011)