Performance of a Pilot Scale AnMBR Digesting WAS

This research was conducted to assess the feasibility of using AnMBRs for WAS treatment by evaluating the performance of the membrane when subjected to conventional versus higher loading conditions, identifying changes in sludge characteristics with process conditions and assessing their influence on membrane performance. Under normal loading conditions (15 day HRT and 30 day SRT), stable membrane operation at an average flux of 40±3.6 LMH was observed when the digester was fed with polymer-dosed TWAS and digester TSS concentrations were maintained less than 15 g/L. Above this solids concentration a decline in flux to 24.1±2.0 LMH was observed even with polymer-dosed TWAS. During this period the introduction of a fouling control strategy that was new to tubular membranes, an intermittent mode of operation (i.e. 5 minutes permeation and 1 minute relaxation) significantly increased the flux from 24.1±2.0 to 37.9±3.8 LMH for a neutral membrane and from 27.5±1.9 to 50.5±3.8 LMH for a negatively charged membrane. As the process was shifted into the higher loading condition (7 day HRT and 30 day SRT), the concentrations of TSS, filtered COD, filtered protein and filtered carbohydrates increased by 50, 70, 64, and 70% respectively. This resulted in reduction of the membrane's critical flux by 60% from the normal loading conditions. The study clearly indicates that it is technically feasible to employ AnMBRs for concurrent WAS digestion and thickening.