BIODEGRADATION OF VOLATILE FATTY-ACIDS BY 3 SPECIES OF NITRATE-REDUCING BACTERIA

The rates of consumption of volatile fatty acids (VFA), of nitrate red uction and of nitrite production rates are evaluated for three selecte d bacterial strains from a mixed population of denitrifying bacteria ( 21 strains isolated). This population was perfectly adapted to grow on VFA (acetate, propionate, butyrate and valerate) under anoxic conditi ons. The three isolated species were able to metabolize nitrate. The f our VFA tested and the nitrate are consumed at different rates by the three species tested. When acetate is used as the only source of carbo n, there is a transient accumulation of nitrite with Alcaligenes denit rificans and, even more so with Pseudomonas mendocina. The third speci es, Comamonas testosteroni reduced nitrate only to nitrite when grown on the VFA. Alcaligenes denitrificans, the dominant species in the mix ed population, consumed the four VFA fastest (18-28 mg C g(-1) suspend ed solids h(-1)), but surprisingly the nitrate reduction rates were th e same (approximate to 18 NO3--N g(-1) suspended solids h(-1)). The ca rbon and nitrate consumption rates were explained by the fact that the biomass production is highest with valerate, then decreases with buty rate, propionate and acetate.