Microbial Removal from Secondary Treated Wastewater Using a Hybrid System of Ultrafiltration and Reverse Osmosis

The efficiency of advanced membranes wastewater treatment plant towards removal of general and specific microbes was investigated. The unit operation of the plant includes activated sludge, ultrafiltration (hollow fibre membranes with 100 kD cutoff, and spiral wound membrane with 20 kD cutoff), and reverse osmosis (RO). The removal evaluation of screened microbes present in wastewater under study showed that hollow fibre membrane rejected only one log (90% rejection) of the total microbial count (TPC), total coliforms (TC), and faecal coliforms (FC). On the other hand, a much more efficient removal was observed with spiral wound, 2-3 logs (99 - 99.9%) for TPC. In addition, this last filter was able to completely eliminate TC and FC. Rejection of all received bacteria by RO was complete. The removal evaluation of inoculated specific types of bacteria showed that the UF hollow membrane removed 2 logs (99%) of inoculated E. coli (107 – 108 cfu/mL inoculum), 2-3 logs (99-99.9%) of Enterococus spp. (107 – 1010 cfu/mL inoculum), 1-2 logs (90-99%) of Salmonella (108 – 1010 cfu/mL inoculum) and 1-2 logs (90-99%) of Shigella (105 – 106 cfu/mL inoculum). The spiral wound was significantly efficient in rejecting 3 logs of E. coli, 5 logs of Enterococus spp., 4 logs of Salmonella, and 1-3 logs of Shigella that were received from the UF hollow fibre membrane. The results indicate that gram positive bacteria were removed much more efficiently compared to the gram negative ones and the rationale behind of such a behaviour is based on cell walls elasticity