Combining submerged membrane technology with anaerobic and ...

colloidal BPC (mg·L -1 )Impact of a methanogenic pre-treatment on the performance of an aerobic MBR system5.4.5. Effect of external MLVSS source on membrane foulingIn order to study the impact of biopolymers release in the anaerobic digester, sludgefrom a municipal WWTP was fed to the UASB reactor in the period VII. As shown in figure5.6, colloidal BPC concentration increased remarkably when the addition of sludge started,confirming that the release of biopolymers took place due to the hydrolysis of this complexsubstrate in anaerobic conditions. Nevertheless, the same impact over membraneperformance that the one reported on periods I to VI was not observed. It has to be takeninto account that at the beginning of the periods I, III and VI (in which recirculation wasturned on), the effect of recirculation not only led to an increase of cBPC concentration butalso a rapid decrease of MLVSS concentration in both aerobic biofilm and membranefiltration chambers (0.5-2.0 g·L -1 ). Therefore, the membrane fouling observed could beexplained as a combined effect of both factors. The assumption is that with a high MLVSSconcentration, the membrane would be protected and the influence of the biopolymersreleased during the hydrolysis of aerobic biomass could be lower.After stopping the addition of external sludge on day 841, cBPC concentrationremained in high values due to the slow degradation of this complex substrateaccumulated in the UASB reactor (figure 5.6).160140120100806040200700 725 750 775 800 825 850 875Time (d)Figure 5.6. Evolution of cBPC concentration during period VI. In grey the period in whichexternal sludge from a WWTP was fed to the system.During the days in which the external addition of sludge to the methanogenic stagetook place, MLVSS concentration in the membrane filtration chamber was manipulated inorder to check the influence of this parameter on membrane fouling. The results presented143