Physico-chemical factors affecting the E-coli removal in a rotating biological contactor (RBC) treating UASB effluent

The removal mechanism of E coli from UASB effluent using a Rotating Biological Contractor (RBC) has been investigated. Preliminary batch experiments in a RBC indicate a first-order removal kinetics. Variation in the dissolved oxygen concentration and E coli counts over the depth of the RBC has been recorded and indicates that the RBC is not a completely mixed reactor. Therefore batch experiments were carried out in a beaker where the different operating conditions can be controlled. Factors affecting the removal of E coli via a biofilm system as stirring, dissolved oxygen concentration, pH, and addition of cationic polymer were investigated, The results obtained indicated that the most important removal mechanism of E coli in the biofilm is the adsorption process, followed by sedimentation. Die-off is a relatively minor removal mechanism in an RBC system. Higher removal rate of E coli was observed in an aerobic compared to an anaerobic biofilm system. Variation of dissolved oxygen concentration (3.3-8.7 mg l(-1)) and pH-values between 6.5 and 9.3 did not exert any significant effect on the removal rate of the E coli by the heterotrophic biofilm. A rapid adsorption of E coli to the biofilm occurred during the first days after adding the cationic polymer, after which the adsorption slowed down. (C) 2003 Elsevier Ltd. All rights reserved.