Water reclamation from municipal wastewater using combined microfiltration reverse osmosis (ME-RO): Preliminary performance data and microbiological aspects of system operation

Hollow fibre microfiltration (MF) was used as a pretreatment to reverse osmosis (RO) for evaluation of the production of high-quality water from secondary effluent. Four different low operating pressure RO membranes (PVD, CTA, TFCL and NF45) produced a target flux of 20 L/m(2) h at the relatively low operating pressures of 230 kPa, 750 kPa, 550 kPa and 360 kPa, respectively. Conductivity measurements revealed rejections of ionic species of 99.2% and 41% for TFCL and NF45, respectively. TFCL and NF45 totally removed orthophosphates from microfiltered secondary effluent, but nitrite/nitrate were only partially removed. PVD and NF 45 were exposed to microfiltered secondary effluent in stirred cells for up to 4 d for detailed evaluation of bioadhesion. Bacteria rapidly attached and grew on these membranes and produced significant amounts of extracellular polymers. Adhesion of these organisms was random on some membranes, but aggregates were observed on others. The numbers of bacteria on the surfaces of the RO membranes began to diminish after 72 h incubation in microfiltered secondary effluent. Three different primary colonizing microbes were isolated from membrane surfaces, two of which were tentatively assigned to the genus Pseudomonas.