Pilot scale comparison of single and double-stage thermophilic anaerobic digestion of food waste

This study compared the performances of single and two-stage anaerobic digestion processes of food waste. The processes were monitored by taking into account both the steady state process performances and the transient conditions. In addition to a conventional univariate analysis, a multivariate analysis to increase the validity of the results of the comparison study was also performed. The transient states caused peaks due to a high organic loading rate, simulating possible overloading events and the recovery capacity of both processes (resilience). The specific gas production of the methanogenic reactor of the two-stage process was higher (0.88 m3 biogas/kgVS) than for the single-stage process (0.75 m3 biogas/kgVS). This finding was related to the increase in the removal efficiency (of 17%). Considering the pilot-scale results, a comparison of mass and energy balance, and costs (assuming the upgrading of the biogas produced) was also discussed.