Combining submerged membrane technology with anaerobic and ...

IntroductionFigure 1.8. Posible relation between polymer fractions (Drews, 2010)The characteristics of mixed liquor are directly related with the characteristics of thewastewater and the operating conditions applied to the biomass. Some parameters, suchas SRT and F/M ratio should be controlled in order to limit membrane fouling. SRTbetween 15 and 50 d (Meng et al., 2009) and are recommended in MBRs. Regarding F/Mit is important to prevent higher ratios but also to assure a minimum F/M relationship inorder to guarantee a proper development of the biomass. Typical values for aerobic MBRtreating municipal wastewaters are in the range of 0.1-0.3 kgCOD·kgMLVSS -1·d -1 (Brepols,2006; Judd, 2011).Another common rules applied to MBR operation are to operate with a flux awayfrom the critical flux, to avoid working with high TMP, to maintain the membrane modulesaerated and avoid operating with too low dissolved oxygen concentrations in order toprevent the proliferation of filamentous bacteria or sludge deflocculation.A relatively recent concept in fouling minimization is the use of coagulants/flocculantssuch as aluminium sulphate, ferric chloride, poly-aluminum chloride or poly-ferric sulphate(Ji et al., 2008; Zhang et al., 2008; Teli et al., 2012). The addition or adsorbents such aspowdered activated carbon (PAC) and granular activated carbon (GAC) have been alsoreported to improve membrane filtration performance through the adsorption of biopolymerfoulants and the increase on sludge particle size (Hu and Stuckey, 2007; Akram andStuckey, 2008; Remy et al., 2010) . Moreover, in the case of AnMBR, the addition of PACcould be also beneficial in case of shock load event since volatile fatty acids would beadsorbed.45