Ammonia tolerance and microbial community in thermophilic co-digestion of sewage sludge initiated with lignocellulosic biomass

Rice straw is a useful lignocellulosic biomass for controlling ammonia inhibition in the thermophilic anaerobic digestion of sewage sludge. However, it is challenging to procure rice straw throughout the year because of its seasonal production. This study investigated methane production in a laboratory-scale digester by gradually decreasing rice straw addition to solid thermophilic sewage sludge digestion. The decrease in rice straw did not accumulate volatile fatty acids and stabilized methane production. Even with increased sludge concentration without rice straw, methane production continued under high ammonia conditions. Ammonia tolerance of the digested sludge of the experimental digester was higher than that of conventionally digested sludge. The cellulose-degrading bacteria Clostridia and high ammonia-resistant archaea Methanosarcina were dominant in the experimentally digested sludge. The community was maintained for over 200 days after discontinuing the rice straw supply. These findings suggest that anaerobic digestion initiation with rice straw is appropriate to facilitate ammonia-tolerant communities.

Automated summary

This study investigated the effect of gradually decreasing rice straw addition on methane production in the thermophilic anaerobic digestion of sewage sludge. The results showed that reducing rice straw addition did not lead to the accumulation of volatile fatty acids and resulted in stable methane production. Even without rice straw, methane production continued under high ammonia conditions. The digested sludge from the experimental digester exhibited higher ammonia tolerance and was dominated by cellulose-degrading bacteria Clostridia and high ammonia-resistant archaea Methanosarcina. The community remained stable for over 200 days after rice straw supply was discontinued.