Combining submerged membrane technology with anaerobic and ...

Chapter 4recirculation from the MBR to the UASB system) it was difficult to define a real SRT, sincea fraction of aerobic biomass was continually recirculated between the MBR and UASBreactors. Nevertheless, the amount of aerobic biomass purged from the system wassimilar than that purged during period II (without recirculation).4.4.3. Membrane performanceThe main parameters regarding membrane performance are presented in table 4.1.The flux was maintained between 12 and 15 L·m -2·h -1 during most of the operationalperiods, being more variable on period I due to the higher fouling rate observed during thisperiod (figure 4.4b). During periods III and especially IV, the lower fluxes values wereobtained due to the extremely low MLVSS concentrations in the membrane filtrationchamber (table 4.1). Only in the period II, without recirculation between MBR and UASBreactor and a higher MLVSS concentration in membrane filtration chamber, stableoperation at 19 L·m -2·h -1 was achieved. The flux achieved was higher than those observedin AnMBR, with values between 5 and 10 L·m -2·h -1 (Spagni et al., 2010; Zhang et al., 2007;Lew et al., 2009; Ho and Sung, 2010), but lower than those typically reported in aerobicMBR operating with similar membrane modules, being between 20 and 25 L·m -2·h -1 (Judd,2002; Wen et al., 2004). On the other hand, the observed fluxes were much lower thanthose referred by Leikness et al. (2007), who worked with a biofilm membrane bioreactorwith a first moving bed bioreactor (MBBR) followed by a filtration chamber connected inseries and obtained fluxes of 50 L·m -2·h -1 .Table 4.1. Parameters related with membrane performance.Parameter Unit Period I Period II Period III Period IVMLVSS 1 g·L -1 1.3±0.7 3.3±0.7 0.8±0.3 0.9±0.4Flux L∙m -2·h -1 13.3±1.8 15.5±2.2 13.3 ± 2.8 11.0±1.5Permeability L∙m -2·h -1·bar -1 153±68 189±32 170 ± 42 148±47Fouling rate Pa·min -1 1.7±0.9 0.5±0.4 0.8±0.3 0.9±0.6SMP C mg·L -1 37.6±17.3 10.4±3.1 14.6±2.0 14.1±5.0Recirculation - yes (0.15) no yes (0.15) yes (0.075)1 In the membrane filtration chamber122