A pilot study on recycling cooling tower blowdown water through ultrafiltra-tion and reverse osmosis

Recycling of blowdown water from cooling towers through ultrafiltration followed by reverse osmosis has seen progressive development in industrial applications over the years. Whereas published information from pilot studies on the subject has generally indicated favorable results in meeting a water quality acceptable for feed to the reverse osmosis membranes, full-scale applications have met operational challenges, primarily with regard to membrane fouling despite employing elaborate pretreatment schemes as compared to the pilot studies. This work presents the results of a pilot study carried out to recycle cooling tower blowdown water through ultrafiltration followed by reverse osmosis. Contrary to previous studies, it was found that reverse osmosis feed water was not consistently brought within the preferred silt density index value of <3.0 primarily due to the presence of dissolved organics in the water, necessitating more elaborate pretreatment than what is required for conventional groundwater and seawater streams. The present study focused on specific contaminant removal and demonstrated total iron removal of 85.7%, total organic carbon removal of 45.4%, and a total phosphate removal of up to 80.0% through coagulation-ultrafiltration. The study also presents important feedwater characterizations including diurnal cooling tower blowdown temperature profile, particle-size distribution analysis and ultrafiltration membrane flux decay that will help improve system design for recycling cooling tower blowdown water.