Performance analysis of the combined plug-flow anaerobic digester (PFAD) and upflow anaerobic sludge blanket (UASB) for treating swine wastewater in Thailand

Abstract

The objective of this research was to analyze the overall performance, especially the removal efficiency, of the combined plug-flow anaerobic digester (PFAD) and upflow anaerobic sludge blanket (UASB) system, at a large swine farm in Thailand. Eighty-four wastewater samples from the digester were collected during the observation period of 302 days. Appropriate influent and effluent regions were selected for wastewater collection. Treatment efficiencies of the system were evaluated by key parameters such as chemical oxygen demand (COD), soluble chemical oxygen demand (SCOD), total solids (TS), total suspended solids (TSS) and total Kjeldahl nitrogen (TKN). In addition, microbiological parameters such as E. coli and Salmonella spp. were measured. These parameters were analyzed according to the Standard Method for Examination of Water and Wastewater. The average removal efficiencies of COD, SCOD, TS, TSS and TKN were 80.6%, 85.6%, 58.7%, 82.7% and 33.9%, respectively. For the COD removal, the solid part was removed by sedimentation process while the soluble part was stabilized anaerobically. The TSS removal efficiency was quite high, indicating that the system could separate suspended solid from wastewater. The effluent had dramatically lower amount of E. coli compared with the influent. The most common Salmonella serovars in the influent samples were Stanley, Rissen, and Anatum, respectively. Biogas production rates fluctuated due to variable organic inputs to the system. These results clearly indicate that the system of PFAD and UASB is capable of treating both solid and soluble portions of swine wastewater as well as reducing pathogenic bacteria to a certain extent. However, a polishing step is required to reduce organic content of the effluent in order to meet the limit set by the regulatory agency of Thailand.