OPTIMIZATION OF BIOGAS PRODUCTION FROM CO-DIGESTION OF WASTE ACTIVATED SLUDGE AND MODIFIED TAPIOCA STARCH SLUDGE

Abstract

Waste activated sludge (WAS) obtained from a modified tapioca starch wastewater treatment plant
has potential for use as feedstock for biogas production. However, it has a very low C/N ratio of 4.3, leading to a
low methane yield. Co-digestion of WAS with starch sludge (SS) can potentially provide balanced nutrients and
can enhance biogas production. The results from a biochemical methane potential (BMP) test showed that using
WAS as a single feed stock provided a low biogas production at 80 L/kg TVSadded. In co-digestion, the addition of
30% and 50% SS increase the biogas yields by as much as 150 and 209 L/kg TVSadded, respectively. However, the
addition of 70% SS reduces the biogas yield to as low as 117 L/kg TVSadded. The result also showed that the
optimum condition for biogas production is achieved at 2% TVSadded of mixed WAS and SS (1:1) with a desired
C/N ratio of 23.56. The increase in % TVSadded of the mixed feedstock resulted in a reduction of the biogas yield.
The co-digestion of WAS and SS (1:1) also improved the rate of digestion and enhanced the system stability. TVS
removal efficiency of the mixed WAS and SS was 41.44% higher than the efficiency when using WAS alone.
Moreover, the result of continuous stirred tank reactor (CSTR) confirmed that the co-digestion ratio of WAS:SS
(1:1) can enhance biogas yield and methane yield at 301 and 142 L/kg TVSadded, respectively at retention time of
11 days.