Biokinetic modeling of in situ bioremediation of BTX compounds—impact of process variables and scaleup implications

The impact of three process parameters, i.e. ground water velocity, oxygen-to-BTX mass ratio, and benzene, toluene and xylene (BTX) concentrations on first-order biodegradation kinetics in a pilot-scale in situ bioremediation system was assessed. Generally, first-order biodegradation coefficients decreased with ground water velocity, and increased with hydrogen peroxide dose and BTX concentration. First-order biodegradation rate coefficients for benzene, toluene, and o-xylene varied from 0.3 to 0.81, 0.24 to 0.72, and 0.21 to 0.63 d^-1, respectively. Biomass-specific first-order rate coefficients were insensitive to ground water velocity, and decreased with increasing BTX concentrations. At 10 mg/l BTX concentration, the specific first-order coefficients increased with peroxide dose. However, at the 50 mg/l BTX concentration and a peroxide dose of 1020 mg/l, a 30–70% reduction in specific first-order biodegradation coefficients was observed. BTX biodegradation kinetics in this pilotscale system were approximately one-to-two orders of magnitude slower than in soil microcosms and mixed culture bioreactors, and about 200–300% higher than full-scale systems.