START-UP AND OPERATION OF A PROPIONATE-DEGRADING FLUIDIZED-BED REACTOR

A laboratory-scale fluidized-bed reactor was inoculated with a syntrophically propionate-degrading co-culture. After 24 days of batch operation with propionate and acetate in the medium, the reactor was operated for 8 months with propionate as the sole substrate. The loading rate was 8.5 kg chemical oxygen demand/m3.day, yielding a maximal gas production of 4.5 l/l.day at a removal efficiency of 94-99%. The degradation was not inhibited by up to 85 mM propionate in pulse experiments, but short-time changes in redox potential above -300 mV led to a drop in the propionate degradation rate. While Methanocorpusculum sp. and Methanospirillum sp. adhered to the sand in the early phase of the start-up, the consortium in the mature biofilm consisted of Desulfobulbus sp., Methanothrix soehngenii and species of at least three different genera of hydrogenotrophic methanogens. A syntrophic relationship between the sulphate-reducing Desulfobulbus sp. and hydrogenotrophic and acetotrophic methanogens is discussed.