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Modelling aerobic 4-chlorophenol and 2,4-dichlorophenol biodegradation-effect of biogenic substrate concentration

Şahinkaya, Erkan
Aerobic biodegradation kinetics of 4-Chlorophenol (4-CP) and 2,4-Dichlorophenol (2,4-DCP) by acclimated mixed cultures were examined separately and in mixture using batch and sequencing batch reactors (SBRs). Biodegradation abilities of acclimated mixed cultures were also compared with those of isolated pure species. Complete degradation of chlorophenols and high COD removal efficiencies were observed throughout the SBRs operation. During the degradation of 4-CP, 5-chloro-2-hydroxymuconic semialdehyde, (the -meta cleavage product of 4-CP), accumulated but was subsequently removed completely. Chlorophenol degradation rates increased with increasing chlorophenols concentration in the feed of the SBRs. Gradually decreasing feed peptone concentration did not adversely affect chlorophenol degradation profiles in SBRs. Only competent biomass was thought to be responsible for chlorophenol degradation due to required unique metabolic pathways. It was assumed that the fraction of competent biomass (specialist biomass) is equal to COD basis fraction of chlorophenols in the feed of the reactors as competent biomass grows on chlorophenols only. Models developed using this assumption agreed well with experimental data. The performance of a two stage rotating biological contactor (RBC) was also evaluated for the treatment of synthetic wastewater containing peptone, 4-CP and 2,4-DCP at 5 rpm. High chlorophenols (>98%) and COD (>94%) removals were achieved throughout the reactor operation up to 1000 mg/L 4-CP and 500 mg/L 2,4-DCP in the feed. Results showed that RBC is more resistant than suspended growth reactors to high chlorophenols load. The change of dominant species during the operation of SBRs and RBC was also followed using API 20NE identification kits.