Sewage treatment in an up-flow anaerobic sponge reactor followed by moving bed biofilm reactor based on polyurethane carrier material

Comparison of the performance of an up-flow anaerobic sponge reactor (UASR) versus a classical up-flow anaerobic sludge blanket (UASB) reactor for sewage treatment was investigated. Both reactors were operated at a hydraulic retention time (HRT) of 6.0 h and organic loading rate (OLR) of 2.3 kg COD m(-3)/d. The results obtained revealed that the UASR produced better effluent quality as compared to the UASB reactor. Residual values of CODtotal, CODsoluble and CODparticulate in the treated effluent of UASR were 170 +/- 54, 88 +/- 36 and 82 +/- 41 mg/l, respectively. Corresponding values in the UASB reactor effluent were 247 +/- 69, 120 +/- 40 and 127 +/- 74 mg/l respectively. Furthermore, residual values of VFA-COD, oil and grease were quite less in the effluent of UASR. The removal efficiencies of faecal coliform (FC) and faecal streptococci (FS), in both reactors did not exceed one log(10). However, the geometric mean of residual bacterial count was less in case of UASR. Moreover; excess sludge production from UASR reactor was almost half that produced from the UASB reactor. Although, the UASR showed a better performance for COD fractions removal than the UASB reactor, the effluent quality still exceeds the limits for discharge and /or reuse in irrigation purposes. Therefore, moving bed biofilm reactor (MBBR) based on polyurethane carrier material was investigated as a post-treatment unit. The MBBR was operated at an OLR of 7.0 g COD m(-2)/d and a HRT of 3.6 h. The reactor achieved a substantial reduction of CODtotal, CODparticulate and CODsoluble resulting in an average effluent concentration of 63 +/- 27, 19 +/- 15 and 44 +/- 27 mg/l respectively. Nitrate and nitrite data reveal that 68% of the ammonia removed occurred through nitrification. Moreover, the system achieved 70 +/- 13% for TKj-N removal resulting an average value of 9.3 +/- 3.9 mg/l in the treated effluent. The MBBR system provided an effluent quality of 2.9 x 10(4) MPN100 ml(-1) for FC and 1.8 x 10(3) MPN 100 ml(-1) for FS corresponding to the removal efficiencies of 99.87 and 99.85% respectively.