COMPARISON OF NANOFILTRATION AND REVERSE OSMOSIS MEMBRANE WATER TREATMENT SYSTEMS FOR COOLING TOWER BLOWDOWN IN A CO-GENERATION POWER PLANT

Abstract

Several power plants in Thailand are located in community area far from the natural sources of water and need to buy expensive tap water from private suppliers for use as a cooling water. This water is normally discharged without recycling back to the cooling processes. For this reason, the small size, low power consumption and effectiveness treatment methods like membrane processes for recycle blowdown water in the district power plant are interested. In this work, the performances for treatment blowdown water via two membrane treatment technologies, nanofiltration (NF) and reverse osmosis (RO) were investigated. Furthermore, attention was paid to ensuring that the pretreatment method could enhance the lifespan of the NF and RO membranes and decrease the membranes' fouling characteristics. Two different pretreatment methods, conventional and ultrafiltration (UF) were compared. For the conventional pretreatment, the results showed that the concentration of 150 mg/L of Polyaluminium chloride (PACl) in the presence of 1.0 ppm of anionic polyacrylamide (APAM) showed the best pretreatment performance in terms of silt density index (SDI) and turbidity. However, UF membrane showed a better pretreatment performance with lower SDI, and turbidity values, lower construction area, less chemical waste, and was selected to be appropriate pretreatment method for membrane treatment. For membrane treatment, NF showed the higher membrane permeability values (14.03 L/hr.m2.bar) but cannot be used as make up water because lower salts rejection (50%). Whereas RO showed the lower membrane permeability values (6.35 L/hr.m2.bar) but higher salts rejection (98%) and available for treatment blowdown water.