Effect of upflow velocity on the ultrafiltration resistance of UASB Effluents

Present work investigates the effect of upflow velocity on both biological removal efficiency and physicochemical characteristics of the effluent in a laboratory scale upflow anaerobic sludge blanket (UASB) reactor treating synthetic municipal wastewater. For this purpose, upflow velocities of 1.2 m/h, 0.6 m/h and 1.2 m/h were applied in four successive stages over a total operation period of 159 days. Filterability tests were carried out during each stage in order to assess the effect of upflow velocity on membrane performance. The results indicate that the increase in total chemical oxygen demand (COD) and turbidity at high upflow velocities were attributed to the washout of colloidal particles from the system. Moreover, particle size distribution (PSD) of the effluent showed a significant variation between different upflow velocities. Because of the observed PSD differences that obviously play an important role in membrane fouling, it was hypothesized that upflow velocity would be a critical parameter for the filterability of effluents in membrane coupled UASB reactors. This hypothesis was confirmed by the finding that the filterability of the effluent during the operation at 0.6 m/h was higher than that during the operation at 1.2 m/h.