Treatment of anaerobically treated domestic wastewater using rotating biological contactor

A small-scalp pilot plant consisting of a three-stage RBC has been investigated for the removal of E. coli, COD fractions and ammonia from the effluent of an UASB reactor treating domestic wastewater. The results obtained reveal that a three-stage system operated at a HRT of 3.0 h represents an effective post-treatment process. The remaining COD in the final effluent was only 51 ( 7) mgl(-1). Ammonia concentration was reduced by 67 (+/- 7.6) %. The overall E coli reduction was 1.39 log(10),at an influent count of 6.5 log(10) corresponding to an overall removal efficiency of 95.8(+/- 4.7)%. However, according to prevailing standards, residual E coli counts are still high for unrestricted reuse for irrigation purposes. When the system was operated at a HRT of 10 h, overall E. coli removal and ammonia reduction were 99.9 (+/- 0.05) % and 92 ( 6.5) % respectively. At a HRT of 10 h, recirculation of the 3rd stage effluent to the 1 st stage reduced the residual of E. coli in the final effluent from 2 x 10(3) to 9.8 X 10(2)/100ml. Moreover, the recirculation of nitrified effluent from the 3rd stage to the 1 st stage increased ammonia removal in the stage 1 from 23,to 43%. This relatively high ammonia removal likely can be attributed to the supply of nitrifiers from 3rd stage to the 1 st one.