The Anaerobic Digestion Of High-solid And High-nitrogen Sludge

With the improving of environmental quality standards, the sewage treatmentrate has gradually increased and sludge production increased dramatically as well.Turning waste sludge into bio-energy has become a hot issue. Anaerobic digestiontechnology is being used more and more widely with the advantage of its lowerenergy consumption and higher reducing quantity, what’s more, the biogas itproduced can be reused to generate electricity. At present, the anaerobic digestionprocess has become a more mature technology to treat sludge treatment but there arestill many difficulties. For example, stirring condition is difficult to control, as well ashigh concentration ammonia nitrogen and heavy metals can inhibit activity, etc.The sludge of aquatic products processing plant belongs to high-solid andhigh-nitrogen sludge. The paper studied on different influential factors(total solid,C/N, inoculation concentration and the stirring frequency) in anaerobic digestion ofhigh-solid sludge. Via analyzing the variation of the volatile fatty acids, volatile solid,ammonia concentration, total organic carbon, biogas output and the characteristics ofmicrobial communities, we can explore the feasibility of quick start for the high-solidand high-nitrogen anaerobic digestion system, and obtain the differentperformances and biogas production with different conditions.In spite of the ammonia concentration higher than the inhibition concentration,the high-solid anaerobic digestion system could start within10ds without acidinhibition in inoculation concentration of20%.The concentration of VFA increased in10days, but didn’t reach the inhibition concentration. The digestion periods variedfrom70days to90days which was longer than the normal anaerobic digestion.The analysis of the microbial community analyzed after anaerobic systemoperating steadily indicated that the lower nitrogen content of the sludge, the lesstypes of bacteria in the system. The dominant bacterial communities were differentwith different C/N, and the higher C/N, the less dominant bacterial communities, andthe lower density of shared dominant bacterial communities.At the beginning of mesophilic digestion, the ammonia concentration was1439mg/L while the total solid was10%,the ammonia concentration went upgradually until reaching3420mg/L during the digestion period, and the change of biogas production had same pattern with low-nitrogen sludge.All of this declared thatthe increasing ammonia concentration didn’t affect the biogas production, and themethane bacteria had adapt to the high ammonia concentration during the systemstarting process. Biogas generated steadily in the anaerobic digestion system. Theconcentration of total nitrogen didn’t vary obviously in the digestion, so we canconsider that most of the ammonia nitrogen existed in the digestion system withoutnitrogen loss.Since the differences of biogas production and TOC removal rate between theinoculation concentration of20%and30%were not too much, we take theinoculation concentration of20%for economic benefit considering improving theunit volume capacity and gas production. The results of contrast experiments indifferent conditions indicted that the digestion operated well and can achieve highergas production (572mL/g VS) and better digestive efficiency (VS removal rate of34%) when adopting constant stirring at the sludge TS of10%,C/N of12andinoculation concentration of20%.