Pilot study of circle sequence reverse osmosis for high-recovery water reuse in industry using tertiary effluent

Water reuse has recently been emphasized to ensure a sustainable water supply in response to water scarcity challenges. Reverse osmosis (RO) is widely adopted in water reuse to produce high-quality water from wastewater. However, RO needs to achieve further improvements in recovery and reduce fouling formation, particularly in brackish water reuse conditions. The circle-sequence reverse osmosis (CSRO) system provides a novel solution to the limitations of conventional RO systems in water reuse applications, enabling high recovery while mitigating scaling and organic fouling. Although the benefits of CSRO have been explored in modeling studies, its performance in practice still needs to be evaluated. Therefore, this study examined the performance of a 40 m3/ d CSRO pilot plant to explore its implications for high-recovery water reuse in industry ( e.g., ultrapure water) using tertiary effluent from a sewage treatment plant. The CSRO system achieved a high recovery of up to 97.2 %, with a critical recovery rate of 93.2 %. The CSRO pilot plant operated for four weeks at a recovery of 79.1 % without chemical cleaning in place, exhibiting specific energy consumption (SEC) of 0.71 +/- 0.03 kWh/m3 and permeate conductivity of 33 +/- 2 mu S/cm. Operating parameters were further investigated to provide insights into CSRO performance and highlight its operational features. Lastly, the SEC of CSRO was compared to that of a two stage RO system, with CSRO achieving a reduction of approximately 12-14 % in SEC. The advantages of CSRO highlight its potential for high-recovery and high-quality water reuse with innovative RO technology.