Enhancing Industrial Water Security through Reverse Osmosis Concentrate Reuse: Water-Energy Trade-offs in Pharmaceutical Cooling Systems

Industrial cooling systems can represent a substantial share of water and energy demand in manufacturing facilities, making technology selection particularly relevant to industrial water security. This study evaluated the reuse of reverse osmosis (RO) concentrate as cooling-tower make-up water and the associated water-energy trade-offs in a pharmaceutical manufacturing facility in São Paulo, Brazil. Three cooling configurations were compared: water-cooled chillers without reuse, water-cooled chillers with RO concentrate reuse, and air-cooled chillers.

The assessment integrated cooling-water quality, cycles of concentration, water and wastewater balances, electricity demand, and operating costs. RO concentrate reuse was technically feasible, although the increased silica concentration in the blended make-up water reduced the allowable cycles of concentration from 7.4 to 4.3 and increased cooling-tower blowdown from 1.51 to 2.97 m³ h⁻¹. Consequently, reuse of 3.51 m³ h⁻¹ of RO concentrate resulted in a net potable water saving of 2.06 m³ h⁻¹.

At the system level, concentrate reuse reduced potable water consumption by 16% and wastewater generation by 41%, with virtually no additional electricity demand. The air-cooled configuration eliminated cooling-tower water consumption but required approximately 29% more electricity, corresponding to an additional 1.7 GWh year⁻¹ compared with the water-cooled alternatives. Under the adopted utility tariffs, annual operating costs were R$ 5.39, 5.01, and 5.13 million for the water-cooled system without reuse, with reuse, and the air-cooled system, respectively.

Overall, RO concentrate reuse provided the most balanced water-energy performance under the evaluated conditions, whereas air cooling maximized direct water savings at the expense of higher electricity demand. These findings demonstrate that industrial water-security strategies should assess water reuse and cooling technology jointly, considering the trade-offs among freshwater dependence, wastewater generation, energy demand, and operating costs.