Low-maintenance anti-scaling of nanofiltration pretreated by bipolar-induced electrolysis for decentralized water supply

Abstract

Nanofiltration (NF) offers an effective solution to ensure a decentralized water supply. However, its reliance on dosing for pre-precipitation and anti-scaling severely complicates its maintenance, adding to its cost and limiting its application, especially in rural areas. In this study, a bipolar-induced electrolysis (BIE) pretreatment method was developed to reduce the NF membrane scaling potential without the need for additional reagents. The water flux of the BIE-NF increased by 24.2 ± 6.5 % compared to traditional NF. This benefits from the synergistic effects of electrocoagulation (EC) and electro-precipitation (EP) of BIE to remove hardness ions (36.8 ± 0.7 g CaCO3 m−2 h−1), 26.2 ± 2.6 % and 16.1 ± 4.7 % faster than that of traditional EP and EC, respectively, exhibiting robust resistance to the interfering ions and organics. The unit energy consumption of BIE was only 18.9 ± 1.0 kWh/(kg CaCO3), 11.8 ± 1.9 % and 67.0 ± 1.4 % lower than that of EP and EC, respectively. After BIE electrolysis, the Ca, humic acid, and Mg contents were dramatically reduced, and a uniformly loose fouling layer formed on the NF membrane, demonstrating alleviated membrane scaling. Remarkably, BIE softening demonstrated its stability and feasibility in sustaining 120.0 m3/d of drinking water to rural populations without requiring additional reagents or manual maintenance, minimizing the operation and maintenance cost to 5.1 US cents/m3 water, 29.0 % lower than the cost of conventional dosing pretreatment. This study offers a low-cost and sustainable method for water supply through decentralized membrane purification.