Combining submerged membrane technology with anaerobic and ...

Chapter 33.1. IntroductionIn recent years, granular sludge has been proposed as an alternative for highcapacity SBR wastewater treatment systems. G-SBR systems can be operated at higherOLR than F-SBR systems. Arrojo et al. (2004) reported organic and nitrogen loading ratesof 7 gCOD·L -1·d-1 and 0.7 gN·L -1·d-1 , respectively, in a G-SBR. The OLR valuesrecommended for flocculent SBRs in the literature range from 0.5 to 2.0 gCOD·L-1·d-1(Beun et al., 1999).The basis of granulation is the continuous selection of sludge particles that occurinside a reactor. The part of the biomass that does not settle quickly enough is washed outwith the effluent (Beun et al., 1999). However, a main drawback of G-SBR systems is thepresence of suspended solids that are washed out with the treated effluent. Therefore, asuitable post-treatment process may be required to fulfil local requirements for the amountof total suspended solids (TSS) in the effluent, which can be accomplished usingmembrane filtration units, depth filters, surface filters or external settlers (Arrojo et al.,2004).Tertiary filtration, especially depth filtration, has been used to remove suspendedsolids from secondary treated waters. However, in recent years, the use of tertiarymembrane filtration (TMF) systems is becoming more common. Low-pressure tertiarymembranes have been proved to meet stringent standards. Membranes are a physicalbarrier to suspended solids that are larger than the membrane pore size. Micro- andultrafiltration membranes (MF/UF) have been used since the early 1990s for drinking waterproduction. They can also be used to remove particulate and colloidal matter from settledsecondary effluents, which increases the effectiveness of disinfection with either ultravioletradiation or ozone for reuse applications (Tchobanoglous et al., 1998; Lubello et al., 2003).Thus, compared to depth filtration, tertiary MF or UF membrane treatments produce waterof better microbiological quality that is also free of suspended solids. This should be takeninto account when water will be reused or discharged into sensible areas.Fouling is the main drawback associated with the application of membranetechnology for wastewater treatment (Kimura et al., 2005; Meng et al., 2009; Drews, 2010).Fouling decreases the permeability of a membrane, limits flux and shortens the life ofmembrane modules, thus increasing both the capital and the operating costs of filtrationsystems. Membrane fouling is the result of complex phenomena that are not yetcompletely understood.86