Treatment of phenolic wastewater by sequencing batch reactors with aerated and unaerated fills

This paper presents the experimental results of a sequencing batch reactor (SBR) with aerated fill and an SBR with unaerated fill treating synthetic phenolic wastewater under identical conditions of influent phenol concentration and aeration time. The performance of the two reactors was evaluated according to substrate removal efficiency, phenol profiles, sludge settleability and effluent suspended solids concentration. At low influent phenol concentrations (e.g, <400 mg/l), the SBR with unaerated fill performed better than the SBR with aerated fill, in which there was a tendency for filamentous bacteria to develop. However, when the influent phenol concentration was high (e.g, >800 mg/l), phenol accumulated during the fill period in the SBR with unaerated fill became inhibitory to micro-organisms, This led to a reduction in substrate removal efficiency and the growth of dispersed biomass. The selection of fill strategies for the SBR were dependent not only on the wastewater composition and biodegradability, but also on the concentration of toxic organic matters in wastewaters. (C) 1997 Elsevier Science Ltd.