Biogas Production from Activated Sludge Using Anaerobic Digestion

Abstract


This thesis discusses the influence of pretreatment and microbial inoculums on sludge. The pretreatments include sterilization, frozen/thawed, acidification, and alkalization. The microbial inoculums include clostridium and K8 inoculums. Based on the HPLC results we analyzed, the digestion pathway of pathway and biotechnology experiments (PCR&DGGE) assisted to show the microbial society change.

The results show that the pretreated sludge increases digestion rate. The sample accumulates hydrogen initially, but was consumed fast. The volatile acid accumulates for a period of time, then the acetic acid was consumed ollowed by propionic acid. The methane was also produced at the same time.

The original sludge, which was added clostridium inoculums, increases anaerobic digestion rate. The rate is almost the same with the alkalized sludge, and both of the samples accumulates methane faster after 168 hours of digestion. The frozen/thawed sludge accumulates methane after 240 hrs. Therefore the avail is not very clear by pretreatment in this case.

The avail is very clear when added the K8 into the sludge. The pretreatments help hydrolysis, and the sludge added K8 produces methane faster than the original sludge. This result proves that the pretreatments and sludge added K8 can make the anaerobic digest faster.

The DGGE results show that the pretreatment will influence the growth of bacteria. In the hydrolysis pretreatments (sterilization, alkalization), the bacterium grew very well; and the destructive pretreatments (like acidification, sterilization) kills the bacterium. When the initial sludge digestion, the bacteria are mainly acidgenic bacterium, like clostridium sp., and lactobacillus sp.