Efficiency and reliability of membrane processes in a water reclamation plant

Performance of a water reclamation plant using ultrafiltration (UF) and reverse osmosis (RO) treating 280,000 m3/d of wastewater was evaluated over 1 year. Statistical analyses were performed on flow rate, temperature, pH, total suspended solids (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD5) and total coliforms. Variations in flow rates coincided with those in temperature, both being seasonal, but plant performance was not highly influenced by such variations. The RO system recovered 85% of water flow. Data on process variables conform to a normal probability distribution and reveal the high process efficiency and reliability of UF and RO systems. Plant efficiencies were >99% for TSS, TDS, BOD5 and total coliforms. Efficiencies were the highest for TSS and total coliforms in the UF system, while they were the highest for TDS and BOD5 in the RO system. Cumulative frequency distribution analyses indicate that RO plays an important role in maintaining a stable plant performance and high quality reclaimed water. The UF system proved essential for complimenting successful performance of the RO system. Reclaimed water satisfies, at 99% frequency, the quality standards for potable water concerning TSS, TDS, BOD5 and total coliforms even though membranes have been operating continuously for 6 consecutive years.