Enhancement of anaerobic digestion of waste activated sludge by chemical pretreatment

Abstract

In this study, the effects of alkaline (pH 10) and acidic (pH 2–5) chemical pretreatment on dissolution of organic matters and biochemical methane potential (BMP) at waste activated sludge (WAS). For each pretreatment methods at different temperature (25, 40, 50 and 60 °C) and operating time (5, 15, 30, 45 min) are the two factors. In the first step, the feasibility of chemical pretreatment in anaerobic digestion was investigated. Increases in soluble chemical oxygen demand (sCOD)/total chemical oxygen demand (tCOD) were determined in all chemical pretreatments. In the second step, the sCOD/tCOD ratio was used to determine the effects on the pretreatment and BMP assay was used to examine the enhanced anaerobic digestion. The pretreatment study conditions were determined due to the highest sCOD/tCOD ratios. These highest ratios were obtained at different pH values, operational times and temperatures. The highest cumulative BMP values were taken at pH 10, 10 min, 60 °C and pH 5, 15 min, 40 °C. Under these pretreatment conditions, the cumulative BMP values were 47.7 mL CH4/g VSS and 12.3 mL CH4/g VSS at conditions pH 10, 10 min, 60 °C and pH 5, 15 min, 40 °C (the control BMP value was extracted). The methane yield values were 43.61% and 12.34% at alkaline acidic conditions (pH 10 and 5). In the pH 2 study results indicated that the cumulative BMP values were 105.1 and 90.5 mL CH4/g VSS for 50–60 °C. These values were exactly the same or lower than the control BMP value.