4-Chlorophenol inhibition on flocculent and granular sludge sequencing batch reactors treating synthetic industrial wastewater

Abstract

Two laboratory-scale column-type sequencing batch reactors (SBRs) were used to investigate the inhibition of suspended flocs and aerobic granular biomass at COD4CP/CODTotal ratios ranging from 0 to 1. The inhibitory concentrations of 4-chlorophenol (4CP) were determined as a function of substrate consumption rate (qmax) and specific oxygen uptake rate (SOUR), as well as of chemical oxygen demand (COD) and 4CP removal efficiencies. Monoethylene glycol was used as a biogenic substrate to simulate industrial wastewater. Granular SBR (GSBR) showed high efficiency in both COD and 4CP removal, at concentrations of up to 620 mg/L; however, the process ceased at 200 and 550 mg-4CP/L in the suspended flocs SBR (FSBR). Other than dosing various concentrations of 4CP in the system, the lack of sufficient dedicated time led to the accumulation of inhibitory compounds over time. At inhibitory concentration levels, only partial degradation of 4CP occurred, which resulted in 5-chloro-2-hydroxymuconic semialdehyde accumulation in the system. Assimilatory removal of 4CP was negligible at the normal performance of FSBR, but reached considerable values in GSBR, or at the time of cessation of FSBR performance. The bulk liquid color evolution in the case of repeated feast and famine conditions, both after process cessation and in the absence of 4CP in the feed, emphasized the crucial role of the biodegradable organic compound to enhancement of 4CP removal. An increasing trend of qmax was not only observed at any definite concentration of 4CP as the cycles proceeded, but also with the feed ratio of 4CP/CODTotal in both reactors. In comparison with FSBR, higher qmax was observed in GSBR, as biomass completely adapted to 4CP, suggesting that the granular bioreactor is limited by diffusion rather than biomass.