Swine Wastewater Treatment in Anaerobic Digesters with Floating Medium

A 20–L attached–growth anaerobic system with floating plastic Ballast rings as a medium has been studied for swine wastewater [chemical oxygen demand (COD) = 1,925 to 2,033 mg/L; total suspended solids (TSS) = 1,051 to 1,184 mg/L] treatment at the mesophilic temperature of 353C. The plastic Ballast rings had a specific surface area of 108 m2/m3 and a density of 0.98 g/cm3 and filled the upper half of the anaerobic digesters. The porosity of the filled portion of the digesters was 0.86. Performance of the anaerobic digesters was evaluated for organics decomposition and methane production with two different hydraulic retention times (HRTs): 10 days and 5 days. When HRT was 10 days in the anaerobic digesters, removal of COD, total organic carbon (TOC), TSS, and volatile suspended solids (VSS) was 65%, 55%, 69%, and 70%, respectively. Methane yield was 0.23 m3 CH4 per kg COD removed. As the HRT was reduced to 5 days, the removal of COD, TOC, TSS, and VSS decreased to 55%, 48%, 57%, and 60%, respectively. Methane yield was 0.24 m3 CH4/kg CODrem. Higher HRT in the anaerobic digester resulted in higher organics degradation efficiency. However, higher rates of methane production and organics decomposition were obtained in the digester with lower HRT.