Abstract

Two continuous stirred tank reactors (CSTRs) each fed with palm oil mill effluent (POME), operated at 37°C and 55°C, respectively, were investigated for their performance under varies organic loading rates (OLRs). The 37°C reactor operated successfully at a maximum OLR of 12.25 g[COD]/L/day and a hydraulic retention time (HRT) of 7 days. The 55°C reactor operated successfully at the higher loading rate of 17.01 g[COD]/L/day and had a HRT of 5 days. The 37°C reactor achieved a 71.10% reduction of chemical oxygen demand (COD), a biogas production rate of 3.73 L of gas/L[reactor]/day containing 71.04% methane, whereas the 55°C reactor achieved a 70.32% reduction of COD, a biogas production rate of 4.66 L of gas/L[reactor]/day containing 69.53% methane. An OLR of 9.68 g[COD]/L/day, at a HRT of 7 days, was used to study the effects of changing the temperature by 3°C increments. The reactor processes were reasonably stable during the increase from 37°C to 43°C and the decrease from 55°C to 43°C. When the temperature was increased from 37°C to 46°C, the total volatile fatty acid (TVFA) concentration and biogas production was 2,059 mg as acetic acid/L and 1.49 L of gas/L[reactor]/day at day 56, respectively. When the temperature was reduced from 55°C to 40°C, the TVFA concentration and biogas production was 2,368 mg as acetic acid/L and 2.01 L of gas/L[reactor]/day at day 102, respectively. By first reducing the OLR to 4.20 g[COD]/L/day then slowly increasing the OLR back to 9.68 g[COD]/L/day, both reactors were restored to stable conditions at 49°C and 37°C respectively. The initial 37°C reactor became fully acclimatized at 55°C with an efficiency similar to that when operated at the initial 37°C whereas the 55°C reactor also achieved stability at 37°C but with a lower efficiency. © 2007 by Pontificia Universidad Católica de Valparaíso.