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Methane Production and Water Quality Improvements in Agricultural Biodigesters in Costa Rica

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  067014,  2006 ASAE Annual Meeting . (doi: 10.13031/2013.21009) @2006
Authors:   Stephanie L. Lansing, Jay F. Martin, Raúl Botero Botero
Keywords:   Biodigester, agricultural wastewater, methane, ammonium, organic matter, Costa Rica

In developing countries, water pollution and access to energy resources are interrelated challenges that encompass issues of human health, environmental protection, and economic development. Anaerobic biodigesters utilize on-site animal waste to simultaneously reduce water pollutants and produce methane gas for cooking or electricity generation. Seven low-cost biodigesters located in the Limon Province of Costa Rica on small-scale farms were studied to determine wastewater treatment ability and methane production potential of these systems. Twelve environmental parameters were studied for each biodigester to determine the quality of methane produced and improvements in water quality. The variability among wastewater at the seven biodigesters was examined to determine the influence of wastewater differences on methane production.

The biodigesters in this study consistently reduced organic matter and solids by 79% – 91%. Total kjeldahl nitrogen (TKN) was decreased by 46%. Ammonium (NH4-N) increased during the digestion process, which increased the usefulness of the effluent as an organic fertilizer. Methane concentrations in the biogas averaged 65%. Through principle component analysis and multivariate analysis of variance (MANOVA), chemical oxygen demand (COD), turbidity, NH4-N, TKN, and pH were determined to be the most useful parameters to characterize the wastewater. There were significant variations between the wastewater influent and effluent concentrations, but these variations did not significantly influence the methane concentrations produced within each biodigester. The biodigester outflow concentrations exhibited less variation than the inflow concentrations, which suggests that these systems are robust to fluctuations in influent wastewater concentration.