Effect of reseeding and pH control on the performance of a two-stage mesophilic anaerobic digester operating on acid cheese whey

The effects of reseeding and using sodium bicarbonate to control the pH of the second chamber of a two-stage, 150 L anaerobic digester, operating on acid cheese whey on the quality and quantity of biogas, and the pollution potential reduction were investigated. The digester was operated at a temperature of 35 degreesC and a hydraulic retention time of 15 days under three conditions (no pH control, pH control with no reseeding, and pH control with reseeding). The results indicated that operating the digester without pH control resulted in a low pH (3.3) which inhibited the methanogenic bacteria. The inhibition was irreversible and the digester did not recover (no methane production) when the pH was restored to 7.0 (without reseeding). When the system was reseeded and the pH was controlled, the biogas production was 1.63 m(3) m(-3) d(-1) and the methane content was 52.0%. Reductions of 55.0, 79.0, 58.6, 65.2, and 27.1% in the total solids, volatile solids, chemical oxygen demand, soluble chemical oxygen demand, and total Kjeldahl nitrogen were obtained, respectively. The ammonium nitrogen and the fixed solids increased by 27.6 and 162.7%, respectively. The addition of base resulted in a total alkalinity of 8230 mg/L as CaCO3.