Comparison of cooling tower blowdown and enhanced make up water treatment to minimize cooling water footprint

When water supply restrictions increasingly escalate to water supply risks, developing strategies to minimize the water footprint of wet cooling systems becomes crucial. This study compares two water engineering approaches to minimize the water footprint of a recirculating evaporative cooling tower (CT): (1) reusing cooling tower blowdown and (2) producing demineralized water to increase the cycles of concentration (CoC) of the CT. Our techno-economic analysis across various scenarios and CT settings reveals that reusing blowdown (option 1) is the most feasible approach for an industrial cooling system currently operating at CoCs of > 3, discharging blowdown with a conductivity of 2 mS/cm and a total organic carbon (TOC) concentration of approximately 20 mg/L. Compared to enhanced make up treatment, blowdown reuse allows higher water savings (13 %) and involves lower implementation and operation costs. Pilot scale trials validated the feasibility of both approaches. Blowdown and enhanced make up treatment included biologically activated carbon filtration, ultrafiltration and reverse osmosis, producing high-quality permeate, suitable for (re)use as CT make up or within other processes. The blowdown treatment reached a product quality of 80 μS/cm conductivity and 70 μg/L TOC, make up treatment 20 μS/cm in conductivity and 60 μg/L TOC, respectively. The study's findings underscore the viability of blowdown reuse as a cost-effective and efficient strategy to minimize the water footprint of cooling systems under increasing water scarcity conditions.