A recirculated upflow anaerobic sludge blanket (RUASB) reactor was operated with three effluent recirculation ratios (5:1, 4:1, and 3:1) to evaluate the influence of hydraulic loading rate on the RUASB treatment of concentrated phenolic wastewater. The results indicate that following an adjustment of the recirculation ratio, a 2- or 3-week lag in methane production occurred, and the effluent concentrations of volatile suspended solid and phenol apparently increased. The results obtained emphasize that the sludge loading rate of 1.40 g phenol-chemical oxygen demand/g volatile suspended solid per day was a threshold limit for the methanogens to generate methane. A substrate metabolic activity experiment was carried out to measure the biogas converting capacity of the phenol-consuming granular sludge. A modified Gompertz equation then was applied to evaluate the biogas production potential and rate. The phenolic biodegradation characteristics were described using the Haldane relationship. The half-saturation constant (Ks) decreased with a decrease in the recirculation ratio, indicating that the granules inside the RUASB reactor had a higher substrate affinity under a low hydraulic loading rate than at a high hydraulic loading rate.
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Lay et al. (1998) studied this question.
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