Electricity Production in Small-scale Swine and Dairy Digesters in Costa Rica

摘要

Methane production, electricity production, and wastewater transformations were quantified for a digestion system that combines biogas from a swine digester and dairy digester in Costa Rica. The low-cost, plug-flow digesters were not heated and operated in the lower portion of the mesophilic range (25 - 27 deg C). The dairy digester produced 27.5 m3/day of biogas with 62.6% methane and reduced organic matter (COD) by 86%. The swine digester produced 6.0 m3/day of biogas with 76.4% methane and reducedCOD by 92%. The digester effluent was treated to below treatment standards using constructed wetlands. The farm's 2-hour peak electricity demand (12.9 kW/day) was 81.8% met. The electricity was produced using manure equivalent to the quantity excreted by 5 dairy cows and 40 pigs. The recovery time of the 21,000 dollar digester project is 10 years through electricity savings and wastewater fines reductions. If the generator were more appropriately sized for the farm, the recovery time would be 7.6 years. The investigations proved that small-scale digesters produce enough biogas for cost-effective electricity generation and are ideal systems for rural farmers to treat livestock wastewater and obtain renewable energy from their waste product.