Treatment of two industrial wastewaters in a submerged membrane bioreactor

A membrane biological reactor (MBR), Zenon ZW-10, with a 220 L volume, was used during 120 days for treating two different wastewaters with different characteristics. During the first 50 operating days the unit was fed with an influent similar to the streams generated in wineries. From day 50 on, the MBR treated a wastewater generated in a tannery factory. The major differences between both wastewaters were the absence of both suspended solids and particulate chemical oxygen demand (COD) in the winery stream and the presence of these compounds in the wastewater from the tannery. Efficiency of the MBR was high: COD removal efficiency above 97% was obtained with winery wastewater, and about 86% during the period in which the tannery wastewater was used. COD concentration in the permeate of the unit varied between 60-80 mg COD/L during the whole experimental period, despite the differences in both wastewater characteristics and the operating conditions applied. Biomass concentration, in terms of volatile suspended solids (VSS), ranged between 0.5 and 15 g VSS/L. Apparent biomass yield was estimated at 0.14 g VSS/g COD and 0.16 g VSS/g COD for winery and tannery wastewater, respectively. A drop in the oxygen transfer efficiency was observed when the system operated with biomass concentrations above 8 g VSS/L.