Combining submerged membrane technology with anaerobic and ...

Chapter 1fluxes typically reported, between 20 and 30 L·m -2·h -1 , in aerobic membrane bioreactorsoperating with similar membrane modules (Judd, 2002; Wen et al., 2004).Moreover, The BF-MBR is an alternative strategy to reduce the effect of membranefouling by high biomass concentrations, particularly under low loading rates.Many studies have pointed out that the main foulants for membrane fouling aresoluble organic polymers such as soluble microbial products (SMP) and extracellularpolymers (EPS) (Rosenberger et al., 2006). Attached biomass, such as biofilm can adsorbthese soluble organic polymers from the liquid, and therefore can decrease their effect onmembrane fouling (Li and Yang, 2007). This tends to explain the reason of the TMPdecrease under the assistance of the biomass on the suspended carriers reported in somestudies (Leikness and Ødegaard, 2007; Liu et al., 2010).Nevertheless, it was reported by Yang et al. (2009b) a rate of membrane fouling inMBMBR three times higher than conventional MBR, with higher carbohydrate and proteinconcentrations. Comparison of composing of suspended solids indicated that theovergrowth of filamentous bacteria resulted in a thick and compact cake layer in MBMBR,affecting negatively to membrane filtration. Therefore, further studies are still needed inorder to know best the implications and mechanisms of this technology regardingmembrane fouling.1.6.3. Hybrid biofilm-suspended biomass membrane bioreactorsHybrid reactors are those systems in which suspended and attached biomass growin the same system. These systems can achieve high biomass concentrations and solidretention time in comparison with conventional activated sludge systems. Hybrid systemshave been successfully used to upgrade the nitrifying capacity in conventional activatedsludge (Christensson and Welander, 2004). These systems have been constructed usingfixed carriers (Watanabe et al., 1994), suspended support (Christensson and Welander,2004), and even clay and powders materials. Recently membrane technology has beensuccessfully tested to improve hybrid systems efficiency (Oyanedel et al., 2003; Artiga etal., 2005). Hybrid biofilm-suspended biomass systems have been widely studied and theiradvantages, in comparison with conventional activated sludge, are well known. Adrawback of the above mentioned hybrid systems are those which can arise from theapplication of high organic load rates, as well as from the physicochemical features of thewaste water, which can negatively affect the settleability properties of the sludge which isgenerated in the biological systems and can therefore negatively affect the separation, by50