Organic acid consumption of phototrophic bacteria in a lighted upflow anaerobic sludge blanket reactor

It was previously suggested that a population of phototrophic bacteria, Rho dopseudomonas palustris strain RN1 and Blastochloris sulfoviridis strain GN 1 could be induced from granules in a lighted upflow anaerobic sludge blank et (LUASB) reactor. The present study showed that both strains RN1 and GN1 could use acetate, propionate, butyrate, and lactate as electron donors und er anaerobic light conditions. The composition of organic acids in the effl uent from the LUASB reactor was studied to investigate competitive consumpt ion between acetogenic bacteria, methanogens, and phototrophic bacteria in the reactor. When acetate, propionate and lactate were supplied to the reac tor, a small amount of acetate and propionate was observed in the effluent under light conditions. The concentrations of acetate and propionate increa sed under dark conditions compared with those under light conditions using organic acid and peptone media as the influent. When starch was supplied to the reactor, the concentrations of formate, acetate, propionate, butyrate, and lactate in the effluent were less than 0.5 mg C.l(-1) during operation under light and dark conditions. The concentrations of ammonium and phosph ate in the effluent under dark conditions were higher than those under Ligh t conditions. These results suggested that phototrophic bacteria in the LUA SB reactor consumed acetate and propionate as well as ammonium and phosphat e in competition with methanogens and acetogenic bacteria.