Critical solids residence time for phenolic wastewater treatment

The impact of solids residence time (SRT) on the aerobic treatment of phenol and o-cresolbearing wastewater by sequencing batch reactors (SBR) at loading rates of 800 g phenol.m^-3.day^-l and 600 g cresol.m^-3.day^-l and a hydraulic retention time (HRT) of 1.1 days was assessed. Solids residence times in the ranges of 3-20 days, and 5-20 days were employed for phenol, and o-cresolbearing wastes, respectively. A rapid breakthrough of phenolics occurred at 3 and 5-day SRT for phenol, and o-cresol, respectively, simultaneously with a breakthrough of total suspended solids (TSS). Rapid deterioration in effluent quality occurred at toxicant loadings of 0.7 mg phenol-mg MLVSS^-l and 0.6 mg cresol.mg MLVSS^-l. Reactors treating phenol and o-cresol at SRTs of 10 days and above maintained effluent phenol and cresol concentrations of 0.5 mg.l^-l as well as effluent BOD5 and TSS concentrations of 5, and 12 mg.l^-l, respectively.