Anaerobic biodegradation of high strength 2-chlorophenol-containing synthetic wastewater in a fixed bed reactor

In this study the continuous treatment of 2-chlorophenol (2-CP) containing synthetic wastewater at increasing concentrations up to 2600 mg L−1 in an anaerobic fixed bed reactor was achieved. As a source of microorganisms municipal sewage sludge was acclimatised to maximally 50 mg L−1 2-CP by 3 successive feedings within 1.5 months. Then, an anaerobic fixed bed reactor was inoculated with this sludge and was operated for 318 d, during which the 2-CP influent concentration was stepwise increased from 50 to 2600 mg L−1 within 265 d. At a hydraulic retention time (HRT) of 2.2 d the 2-CP loading rate was 2 g L−1 d−1 and the average 2-CP removal rate was 0.87 g L−1 d−1, accounting for 73% removal. This is the highest 2-CP removal rate ever reported. The negative effect of a 2-CP loading rate of 1.36 g L−1 d−1 on 2-CP removal was reversible within 2 wk when lower loading conditions (e.g. 0.76 g 2-CP L−1 d−1) were re-established. The median chloride ion release per unit 2-CP degraded was 0.24, which was reasonably close to the theoretically expected value of 0.28. In a batch assay, carried out with relatively clear reactor effluent, the highest removal rate of 2-CP was 175 mg L−1 d−1. At the time of reactor termination on day 318, the 2-CP removal rate by the biofilm in the reactor was 0.61 g L−1 d−1, corresponding to a HRT of 3.4 d and a 2-CP loading rate of 0.76 g L−1 d−1. At these very stable conditions removal of COD was 84% and of 2-CP 81%.