Microbial Community Shifts during Biogas Production from Biowaste and/or Propionate

Propionate is the most delicate intermediate during anaerobic digestion as its degradation is thermodynamically unfavorable. To determine its maximum possible degradation rates during anaerobic digestion, a reactor was fed Monday to Friday with an organic loading rate (OLR) of 12/14 kg COD_biowaste·m^-3·d^-1 plus propionate up to a final OLR of 18 kg COD·m^-3·d^-1. No feed was supplied on weekends as it was the case in full-scale. To maintain permanently high propionate oxidizing activity (POA), a basic OLR of 3 kg COD_propionate·m^-3·d^-1 all week + 11 kg COD_biowaste·m^-3·d^-1 from Monday to Friday was supplied. Finally a reactor was operated with an OLR of 12 kg COD_biowaste·m^-3·d^-1 from Monday to Friday and 5 kg COD_propionate·m^-3·d^-1 from Friday night to Monday morning to maintain a constant gas production for permanent operation of a gas engine. The propionate degradation rates (PDRs) were determined for biowaste + propionate feeding. Decreasing PDRs during starvation were analyzed. The POA was higher after propionate supply than after biowaste feeding and decreased faster during starvation of a propionate-fed rather than a biowaste-fed inoculum. Shifts of the propionate-oxidizing and methanogenic community were determined.