Effects of anaerobic and aerobic sequentials in the treatment of Polyaromatic Hydrocarbons(PAHs)from a petrochemical industry wastewater

The aerobic and sequential anaerobic/aerobic treatment of fifteen PAHs [acenaphthene (ACT), fluorene (FLN), phenanthrene (PHE), anthracene (ANT), carbazole (CRB), fluoranthene (FL), pyrene (PY), benz[a]anthracene (BaA), chrysene (CHR), benz[b]fluoranthene (BbF), benz[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IcdP), dibenz[a,h]anthracene (DahA), benzo[g,h,i]perylene (BghiP)] were studied in the aerobic continuous stirred tank reactor (CSTR) and sequential anaerobic inverse turbulent bed reactor (ITBR)/aerobic CSTR system from the real petrochemical industry wastewater. Among the biosurfactants [(Rhamnolipid (RD, Emulsan (EM) and Surfactin (SR)] used it was found that the maximum PAH yields were obtained with RD biosurfactant at optimum sludge retention times (SRTs) and hydraulic retention times (HRTs). RD decreased significantly the inert chemical oxygen demand (COD) and the slowly degradable COD concentrations in the effluent of CSTR at optimum SRT and HRT. The main removal mechanism of the total PAHs was biodegradation. The maximum total PAH yields were observed with RD biosurfactant in the anaerobic ITBR system at optimum HRTs. The contribution of aerobic reactor to the removal of PAH in the sequential system was the biodegradation of the PAHs, of the PAH metabolites and of the dissolved COD remaining from the anaerobic reactor. The PAHs were mainly biodegraded according to the Monod and to the Modified Stover Kincannon in aerobic and anaerobic reactors, respectively. The PAHs exhibited inhibitions according to the competitive kinetic at high biosurfactant concentrations. High acute toxicity removals were observed in sequential reactor at optimum HRT and RD concentration using the Daphnia magna and Vibrio fischeri. The electric energy obtained from the methane in the anaerobic reactor can be used to recover partly the total electricity expenses for the sequential reactor.Keywords: anaerobic inverse turbulent bed reactor, aerobic continuous stirred tank reactor, biosurfactant, polycyclic aromatic hydrocarbons, petrochemical industry wastewater, toxicity