Biodegradation of PCP enhanced by chemical oxidation pretreatment

Abstract

ABSTRACT: Biodegradation studies of 1 mM aqueous pentachlorophenol (PCP) solutions have been conducted in completely mixed batch reactors using a selected microbial consortium (SMC) and a stock culture of activated sludge (AS). Comparable biodegradation has also been carried out following chemical oxidation pretreatment by hydrogen peroxide alone and by Fenton's reagent (a solution of hydrogen peroxide with ferrous ion) in order to observe any enhancement of biodegradation. The microbial species isolated from the soil contaminated by PCP were gram‐negative, rod‐shaped bacteria, identified as Pseudomonas putida and Pseudomonas aeruginosa. The stock culture of activated sludge was developed from a wastewater treatment plant treating domestic wastewater only and maintained on tryptic soy broth substrate. Chemical oxidation pretreatment experiments were conducted in the absence of SMC and AS, and the chemical oxidation reaction was almost complete after four hours of reaction. The highest PCP removal by chemical oxidation tested in this study was 2.97% with Fenton's reagent at a molar ratio of 1:1 (H202 :PCP) and 50 mg/L iron. The biodegradation process was carried out on both pretreated and untreated PCP for 12 days, but the biodegradation was almost complete by the sixth day. Inoculation of SMC or AS into the aqueous PCP solutions following pretreatment by Fenton's reagent resulted in a higher PCP uptake rate than did the system treated by hydrogen peroxide alone. The enhanced biodegradation rate was highest when the system was pretreated by Fenton's reagent with the highest chemical oxidant dose, a 1:1 molar ratio of hydrogen peroxide to PCP and 50 mg/L iron. The biodegradation rates of untreated PCP, degraded by either SMC or AS, were each similar and much slower than for any of the pretreated systems. Comparison of the biodegradation rate of the un‐pretreated PCP with the rates of pretreated systems indicated that chemical oxidation by Fenton's reagent enhanced the biodegradability of PCP by both SMC and AS.