Combining submerged membrane technology with anaerobic and ...

Chapter 55.1. IntroductionAnaerobic methanogenic technology is widely used, especially in warm climateregions, for treating low strength wastewaters at ambient temperature. Nevertheless,despite the advantages of anaerobic treatment, the final wastewater quality would not behigh enough for a direct discharge to a watercourse. Anaerobic biological treatmentsystems are typically not effective in removing residual levels of soluble and colloidalorganic contaminants (Berubé et al., 2006). Other concerns regarding the use of thistechnology, especially in temperate climate regions, are related with biomass loss in theeffluent. These problems related with anaerobic treatment have been overcome in the lastdecade by coupling a membrane to the bioreactor. However, one of the main drawbacks ofusing anaerobic membrane bioreactors (AnMBR) is related with membrane fouling and themaximum flux that can be achieved. Flux has a strong influence on both the capital andoperation costs of the process. For submerged membranes, most of the authors workingwith AnMBR reported fluxes in the range of 5-15 L·m -2·h -1 at temperatures above 30 °C(Zhang et al., 2005; Trzcinski and Stuckey, 2009). Jeison and van Lier (2006) obtainedcritical flux values in the range 16-23 L·m -2·h -1 under thermophilic (30 °C), and 5-21 L·m -2·h -1 under mesophilic (55 ºC) conditions. In the case of domestic wastewater treated atambient temperatures, fluxes are significantly lower. Robles et al. (2013) reported fluxesbetween 9 and 13 L·m -2·h -1 treating municipal wastewaters at temperatures between 15and 33 ºC. Lew et al. (2009) reported 11.25 L·m -2·h -1 at 25 ºC, while Wen et al. (1999),operating a laboratory scale anaerobic bioreactor coupled with a membrane filtrationworked with flux of 5 L·m -2·h -1 . Similar results were obtained by Ho and Sung (2010), whooperated with flux set on 5 L·m -2·h -1 and the temperature of 15-20 ºC. Moreover, Spagni etal. (2010) demonstrated that the applicable fluxes obtained in AnMBR ranged between 2and 5 L·m -2·h -1 depending strongly on operational conditions and rapid membrane foulingwas usually observed. Therefore, the fluxes obtained in AnMBR are lower than thoseobserved in aerobic MBR, typically being in the range between 20 and 30 L·m -2·h -1 (Judd,2002; Wen et al., 2004).Methanogenic reactors may be operated as a pre-treatment step, followed by anaerobic MBR system, for the treatment at ambient temperatures of domestic and industrialwastewaters (He et al., 2003; Buntner et al., 2011; Kushwaha et al., 2011). Additionally,the combination of both technologies might be an alternative to overcome problems relatedwith the operation of AnMBR (fouling) and aerobic MBR (high energy consumption andsludge production). The energy gained from the anaerobic plant can be equivalent to thatconsumed by the aerobic step (BREF, 2006). The treated wastewater could be suitable for130