Thickened waste activated sludge (TWAS) from biological treatment processes is less amenable to anaerobic digestion than primary sludge. This is due to TWAS being composed mostly of cellular material and extracellular polymeric substances (EPS) instead of more easily digestible carbohydrates and fats that are typically found in primary sludge. In an attempt to improve TWAS digestion performance, a process for pretreating TWAS before digestion, known as the MicroSludge TM process, was tested at the Los Angeles County Sanitation Districts' (Districts) Joint Water Pollution Control Plant (JWPCP) in Carson, CA. The MicroSludge process is a chemical/mechanical system that uses caustic soaking to weaken cell walls and EPS, and a high-pressure shearing valve to lyse the cell walls and break down EPS to increase the overall solubility of the TWAS.The MicroSludge process was evaluated using both full-scale and bench-scale mesophilic anaerobic digesters operated at various conditions. In most of the tests, the TWAS was digested with primary sludge. Pure TWAS was digested in some of the bench-scale tests. Digestion performance was determined by volatile solids destruction (VSD) and gas production. In addition to digestion performance, the effects of the MicroSludge process on dewatering performance and odor generation were examined.The results from the study indicate that the MicroSludge system significantly increased the solublization of TWAS. Under the operating conditions at JWPCP, VSD increased from 54 to 57%, and gas production increased by less than 5%. The MicroSludge process may have slightly improved dewatering performance with a small increase in cake solids content, and dewatered cake from the test digester was approximately 40% less odorous than cake from a control digester. Despite the minor improvement in digestion, odor control and dewatering performance, the Districts determined that the MicroSludge treatment process was not cost effective for treating TWAS at the JWPCP.
The Sanitation Districts of Los Angeles County (Districts) have been using ferrous chloride (FeCl 2 ) to control the hydrogen sulfide (H 2 S) concentration in digester gas at the Joint Water Pollution Control Plant (JWPCP) for over 30 years. Although FeCl 2 has been very effective in controlling digester H 2 S levels, the cost of this chemical has increased significantly in the last few years. Consequently, the Districts initiated a study to investigate the use of biotrickling filters (BTFs) to control digester gas H 2 S. Two pilot-scale biotrickling filters were tested under slightly aerobic and anoxic conditions. Two types of filter media, lava rock and plastic rings, were tested in the aerobic filter, and lava rock was tested in the anoxic filter. Concentrated H 2 S was spiked into the digester gas to simulate elevated H 2 S levels characteristic of lower FeCl 2 doses. For H 2 S levels between 200 and 400 ppm, the aerobic BTF with a plastic ring media was able to reduce H 2 S to below the regulatory limit of 40 ppm at empty bed retention times (EBRT) of 20 to 37 seconds. The aerobic lava rock BTF experienced a clogging problem, and the anoxic lava rock BTF was not able to reduce 200 ppm of H 2 S to below the regulatory limit at an EBRT of 50 seconds.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.