Denitrification in presence of benzene, toluene, and m-xylene: kinetics, mass balance, and yields.

Denitrification of the electron donors toluene-C (15-100 mg/L), m-xylene-C (15-70 mg/L), benzene-C (5-25 mg/L), and acetate-C as experimental reference (50-140 mg/L) was carried out in batch culture. An initial concentration of 1.1 +/- 0.15 g of volatile suspended solids/L of denitrifying sludge without previous exposure to aromatic compounds was used as inoculum. The results showed toluene and nitrate consumption efficiency (ET and EN, respectively) of 100%. Toluene was completely mineralized (oxidized) to CO2. In all cases, the N2 (YN2) and HCO3-yields (YHCO3) were 0.97 +/- 0.01 and 0.8 +/- 0.05, respectively. The consumption efficiency (EX) of m-xylene (53 +/- 5.7%) was partial. The YN2 and YHCO3 were 0.96 +/- 0.01 and 0.86 +/- 0.02, respectively. Benzene was not consumed under denitrifying conditions. The specific consumption rates of toluene (qT) and m-xylene (qX) were lower than that of acetate (qA). The differences in specific consumption rates were probably owing to the negative effect of benzene, toluene, and isomers of xylene on the cell membrane.