Aerobic biodegradation and inhibition kinetics of poly-aromatic hydrocarbons (PAHs) in a petrochemical industry wastewater in the presence of biosurfactants

BACKROUND: In Izmir, Turkey, wastewaters from the petrochemical industry are treated using conventional activated sludge systems. A significant proportion of poly-aromatic hydrocarbons (PAHs) with high-molecular weights remains in this treatment system and inhibits the biological activity. Biosurfactants increase PAHs degradation by enhancing the solubility of the petroleum components. The aerobic inhibition kinetics of PAHs has not previously been investigated in the presence of biosurfactants for a real petrochemical industry wastewater. RESULTS: Among the kinetic models used (Monod-type, zero, first-order and second-order) it was found that the Monod kinetic was effective for describing the biodegradation of PAHs in petrochemcal industry wastewater in the presence of three biosurfactants, namely Rhamnolipid (RD), Surfactine (SR) and Emulsan (EM) in an aerobic activated sludge reactor (AASR). The maximum PAH removal rate (Rmax) and specific growth rate of PAH degrading bacteria (mu max) increased, while the half saturation concentration of PAH (Ks) decreased at 15 mg L-1 RD concentration compared with the control without biosurfactant at a sludge retention time (SRT) of 25 days. CONCLUSION: PAH oxidation is typified by competitive inhibition at RD concentrations > 15 mg L-1 resulting in increases in Ks values with PAH accumulation. Low inhibition constant (KID) values reflect difficulties in the metabolizability of PAHs. Metabolite production decreased at RD = 25 mg L-1 in the PAHs indeno (1,2,3-cd) pyrene (IcdP), flourene (FLN), phenanthrene (PHE) and benzo(a) pyrene (BaP). (C) 2012 Society of Chemical Industry