COMPLETE ANAEROBIC-DIGESTION OF ACTIVATED-SLUDGE BY COMBINING MEMBRANE SEPARATION AND ALKALINE HEAT POSTTREATMENT

The objective of this laboratory study was to improve the particulate solids decomposition of activated sludge by combining solids-liquid se paration and post-treatment to anaerobic digestion. The application of membrane. separation has been shown to enhance the anaerobic biodegra dability of sewage sludge. In this study, an anaerobic membrane digest er with a volume of 51 and UF membrane of 177 cm(2) was operated at 35 degrees C and a HRT of 30 days without considerable sludge wastage. F or the first 83 days, the membrane digester was operated without post- treatment. For the succeeding 41 days the membrane digester was combin ed with alkaline heat post-treatment. This was done by taking out 50 m i per day of the digester sludge, post-treating it under the condition of 0.1M NaOH and 175 degrees C for 1hr, and returning it to the diges ter. The particulate solids decomposition percentage averaged for each operating phase was 61% without the post-treatment and about 100% wit h the post-treatment. These results indicate that the post-treatment w as able to selectively destroy unbiodegradable components of the lab-c ultivated activated sludge. In addition, because the feed activated sl udge can be concentrated in the membrane digester, the post-treatment requires less volume to be treated than pretreatment On the other hand s, the operation and application of this post-treatment combined proce ss are limited by the allowable digester sludge level imposed by the m embrane separation. The problem to be solved is the deterioration of m embrane permeate quality and methane production efficiency. Copyright (C) 1996 IAWQ.