Combining submerged membrane technology with anaerobic and ...

Impact of a methanogenic pre-treatment on the performance of an aerobic MBR systemhighest value corresponded to period III (0.036 kgCOD·kgMLVSS -1·d -1 ). During periods II,IV, VI and VII the F/M was around 0.025 kgCOD·kgMLVSS -1·d -1 . Regarding SRT, thevalues calculated in periods II, IV, V and VII, during which aerobic MLVSS were notrecycled to the UASB system, were very similar (between 12 and 16 d). In periods I, IIIand VI (with suspended biomass recirculation from the MBR to the UASB system) it wasdifficult to define a SRT, since a fraction of aerobic biomass was continually recirculatedbetween the UASB and MBR systems. Nevertheless, the amount of aerobic biomasspurged from the system was similar to that in periods without recirculation. Thus, variationsof SRT or F/M could be discharged to be the main cause of the observed MBR behaviour.Recovery cleanings were performed in periods I and III where recirculation was usedand also at the beginning of period VI, as a consequence of severe permeability loss at theend of period V. This confirmed the impact of plastic support and hydrolysis of aerobicbiomass in the methanogenic stage over membrane fouling. Moreover, membrane criticalflux was 20.2 ± 2.8 L·m -2·h -1 during the periods I, III, V and VI. . The highest critical fluxvalues were obtained during the periods II and IV, reaching 28.0 L·m -2·h -1 , with no aerobicsludge recycling and the presence of the plastic support in the aerobic biofilm chamber.5.4.3. Fouling indicatorsThe carbohydrate fraction of soluble microbial products (SMPc), transparentexopolymers (TEP) and biopolymer clusters (BPC) has been reported as possible foulingindicators (Rosenberger et al., 2006; Drews, 2010; Sun et al., 2008; de la Torre et al.,2008). In this study, these parameters were measured in order to establish a relationshipwith fouling rate and membrane performance. As can be observed in figure 5.3, certainlinear relationships between these indicators and fouling rate can be established. Thehigher was the concentration of each one of these parameters, the higher was the foulingrate. A linear correlation between SMPc and fouling rate has been reported previously bysome authors (Rosenberger et al., 2006) but not in the case of cBPC and TEP.BPC have been defined as a pool of non-filterable organic matter in the liquid phaseof the MBR sludge mixture much larger than SMP, being an important factor in theformation of the sludge fouling layer on the membrane surface and responsible for theincrease of fouling potential (Sun et al., 2008). TEP are very sticky particles that exhibit thecharacteristics of gels, and consist predominantly of acidic polysaccharides (Passow,2002). TEP has been recently reported as a useful tool for MBR investigation that mayhelp understanding the complex phenomenon of membrane fouling.139