Plug-flow reactor for volatile fatty acid production from the organic fraction of municipal solid waste: Influence of organic loading rate

This work experimentally assessed the production of total and specific volatile fatty acids (VFAs) by dry thermophilic anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW) in a semi-continuous pilot-scale plug-flow reactor (PFR). The experimental test compared the two organic loading rates (OLR) of 7.5 and 14 gVS/(L d) for an overall duration of 150 days. The results revealed that OLR positively affects the production of total VFAs, since their overall concentration reached a maximum of 12136 mg/L with OLR of 14 gVS/(L d). In addition, the productivity increased by 150.9% and the yield increased by 49.2% compared to the lowest OLR tested. Propionate dominated during the whole experimental period ranging between 86.2% and 64.4% of total VFAs. As the OLR increased, the concentration of iso-valeric and butyric acids increased as well, accounting for 15.7% and 9.6% of total VFAs, respectively. Meanwhile, the specific biogas production (SGP) decreased from 280.8 +/- 72.8-196.3 +/- 24.4 NLbiogas/kgVS diminishing by 30.6%, and the oxygen uptake rate (OUR) raised from 46.4 +/- 0.6-124.8 +/- 10.9 mmolO(2)/(kgVS h) increasing by 169.1%.