EFFECTS OF NITROGEN-SOURCE ON CRUDE-OIL BIODEGRADATION

The effects of NH4Cl and KNO3 on biodegradation of light Arabian crude oil by an oil-degrading enrichment culture were studied in respiromet ers. In poorly buffered sea salts medium, the pH decreased dramaticall y in cultures that contained NH4Cl, but not in those supplied with KNO 3. The ammonia-associated pH decline was severe enough to completely s top oil biodegradation as measured by oxygen uptake. Regular adjustmen t of the culture pH allowed oil biodegradation to proceed normally. A small amount of nitrate accumulated in all cultures that contained amm onia, but nitrification accounted for less than 5% of the acid that wa s observed. The nitrification inhibitor, nitrapyrin, had no effect on the production of nitrate or acid in ammonia-containing cultures. When the culture pH was controlled, either by regular adjustment of the cu lture pH or by supplying adequate buffering capacity in the growth med ium, the rate and extent of oil biodegradation were similar in NH4Cl- and KNO3-containing cultures. The lag time was shorter in pH-controlle d cultures supplied with ammonia than in nitrate-containing cultures.