Dry thermophilic anaerobic digestion of the organic fraction of municipal solid wastes: Solid retention time optimization

The main results have showed that the process is feasible in SRTs lower that those found in literature. Probably the history of the reactor, joined to the lower organic content in the waste, can be a key factor and the progressive decreasing of SRT is a strategy that permits to maintain stable conditions for lower SRT. The best operating conditions for thermophilic semicontinuous systems ranged in 8-5 days, with a yield of 0.33-0.34 LCH4/gVSadded and a concentration of Volatile Fatty Acids (VFA) around 100 mg HAc/L. The process becomes unstable for SRTs lower than 4 days, showing a clear decrease in methane productivity (lower than 0.2 LCH4/gVSadded) and an accumulation of VFA (more than 500 mg HAc/L). In general, SRTs below 4 days were not suitable for single stage of dry AD of OFMSW.