Combining submerged membrane technology with anaerobic and ...

Chapter 7measured permeability of the new membrane module was 500 L·m -2·h -1·bar -1 , it can beassumed that the main membrane fouling mechanism was cake layer formation. This cakelayer acted like a shield, protecting the membrane from internal pore blocking. Therefore,the high MLTS concentration led to the formation of a dense sticky cake layer that cloggedthe membrane, and the SGD m applied, which was lower than the recommended value ofthe full scale module, did not help to alleviate its effect.Sludge properties, including biopolymer concentration, are the core parameters ingoverning sludge cake formation and membrane fouling in submerged AnMBR systems(Lin et al., 2009). The characteristics of the mixed liquor in an AnMBR are expected to varysignificantly based on the type of wastewater being treated (Kataoka et al., 1992). Inaddition, inorganic fouling should not be underestimated when treating complexwastewaters such as industrial herbal extraction wastewater since Inorganic species caninteract with biopolymers in the reactor and enhance the mechanical stability of the foulinglayer (Lin et al., 2009). The high COD concentration in the effluent led to increase MLTSconcentration in order to achieve higher removal capacities. However, COD removal wasonly slightly improved due to the poor anaerobic biodegradability of the wastewater butmembrane performance was seriously limited.The existence of a threshold value (30 g·L -1 ) above which the MLTS concentrationhas a negative influence on membrane filtration has been reported (Yamamoto et al. 1994;Lubbecke et al., 1995; Hong et al., 2002). In accordance with this studies, Robles et al.(2013) recently established a MLTS critical value between 28 and 31.5 g·L -1 for an AnMBRtreating municipal wastewater. Operation above this critical value would lead to lowerfluxes and shorter membrane lifespan. Therefore, the MLTS concentrations, between 38and 61 g·L -1 , achieved during the operation led to the severe fouling of the membrane andthe futility of PAC addition.In order to achieve higher membrane fluxes it would be recommended to diminishMLTS concentration below 25 g·L -1 . In this scenario, PAC addition might influence sludgefilterability and enhance membrane performance.Nevertheless, with the proposed treatment, COD values were much higher that theallowed threshold value for direct or indirect discharge. Therefore an aerobic treatmentstep has to be established. A combination of another high strength anaerobic system suchas an upflow anaerobic sludge blanket reactor (UASB) with an aerobic MBR would achievehigher COD removals, allowing to apply higher membrane fluxes as reported in Chapter 5(Sánchez et al., 2013).190