Biogas production performance and system stability monitoring in thermophilic anaerobic co-digestion of lipids and food waste

A thermophilic anaerobic co-digestion system treating lipids and food waste was demonstrated by a long-term operation (over 600 days) with different lipid/TS ratios (from 10 % to 80 %). The lipids degradation efficiency achieved 90 % in the system when the lipid/TS ratio was less than 70 %. Addition of lipids significantly enhanced methane production, as the lipid/TS ratio increased from 10% to 70 %, the biogas production rate increased from 2.36 g/L/d to 3.42 g/L/d with 59.7 % to 67.7 % of methane. From the view of system stability, the increase of lipid/TS ratio reduced the alkalinity of the system and eventually caused the system collapse. In order to avoid losses due to overload, the results suggested that the ratio of total ammonia nitrogen to alklinity-6.5 could be used as a monitoring indicator. And the system could maintain efficient operation when the indicator was less than 0.6.