Performance improvement and decolourization in the high‐solid thermophilic anaerobic digestion of thermally pretreated sewage sludge

Abstract

This laboratory-scale study attempted performance improvement and decolourization in the high-solid thermophilic anaerobic digestion of thermally pretreated sewage sludge, as it tends to be disturbed by ammonia inhibition and colour generation.Sewage sludge was adjusted to 7%-8% total solids (TS), and pretreated at 150 C for 1 h. The digesters were operated at 55 C and 20 days hydraulic retention time. An addition of powdered activated carbon (approximately 2% of the feed TS) significantly contributed to the removal of propionate and reduced the colour in digested sludge by about 27%. Microbial analysis detected less abundance of bacterial Synergistia and archaeal Methanosarcina and implied more hydrogenotrophic methanogenesis with the activated carbon addition. Conditioning with ferric chloride for dewatering digested sludge mitigated the colour of dewatered liquor by about 67%.Therefore, these methods were demonstrated to be effective and partly overcome the above-mentioned problems.