Combining submerged membrane technology with anaerobic and ...

COD removal (%)Chapter 3120100Period I II III IVV8060400 50 100 150 200 250 300 350Time (d)Figure 3.4. Overall COD removal efficiency for the F-SBR (▲) and G-SBR () systems.The evolution of soluble COD in the effluent of the biological reactors is depicted infigure 3.5a. In figure 3.5b, the evolution of soluble COD in the permeates of the twofiltration chambers is shown. The ratio between soluble and total COD in the fedwastewater was 0.81 ± 0.09 g·g -1 , except during period IV when the wastewater fed to thesystem was filtered. The behaviour of both SBRs was similar during period I, with solubleCOD concentrations ranging between 10 and 80 mg·L -1 . The increase on the soluble CODconcentration of both SBRs observed at the beginning of period II was due to higher OLRapplied between days 111 and 133 (figure 3.3).During period II, similar soluble COD concentrations were observed in the effluentsof the SBRs and in the permeates of both tertiary filtration chambers. The CODconcentration in the SBR effluents gradually decreased from 140 mg·L -1 to 20 mg·L -1(figure 3.5a). A similar trend was observed for the filtration chamber permeates. Duringperiods III, IV and V, the COD concentration in the permeate of the granular system washigher than that observed in the flocculent system because the former system was fed withwater with a higher COD concentration. It was also observed that COD in the permeatewas higher than the SBR effluent for the G-SBR system. A possible reason of suchbehaviour is presented in section 3.4.2.94