Membrane Fouling Alleviation by Chemically Enhanced Backwashing in Treating Algae-Containing Surface Water: From Bench-Scale to Full-Scale Application

Ultrafiltration (UF) has been increasingly implemented in drinking water treatment plants; however, algae and their secretions can cause severe membrane fouling and pose great challenges to UF in practice. In this study, a simple and practical chemically enhanced backwashing (CEB) process was developed to address such issues using various cleaning reagents, including sodium hypochlorite (NaClO), sodium chloride (NaCl), sodium hydroxide (NaOH), sodium citrate, and their combinations. The results indicate that the type of chemical played a fundamental role in alleviating the hydraulically irreversible mem-brane fouling (HIMF), with NaClO as the best-performing reagent, followed by NaCl. Furthermore, a CEB process using a combination of NaClO with NaCl, NaOH, or sodium citrate delivered little improve-ment in the alleviation of membrane fouling compared with NaClO alone. The optimized dosage and dos-ing frequency of NaClO were 10 mg center dot L-1 two times per day. Long-term pilot-scale and full-scale experiments further verified the feasibility of the CEB process in relieving algae-derived membrane foul-ing. Compared with the conventional hydraulic backwashing without chemical involvement, the CEB pro-cess can effectively remove the organic foulants including biopolymers, humic substances, and protein -like substances by means of oxidization, thereby weakening the cohesive forces between the organic fou-lants and the membrane surface. Therefore, the CEB process can efficiently alleviate the algae-related membrane fouling with lower chemical consumption, and is proposed as an alternative to control mem-brane fouling in treating the algae-containing surface water.(c) 2021 THE AUTHORS. Published by Elsevier LTD on behalf of Chinese Academy of Engineering and Higher Education Press Limited Company. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

A chemically enhanced backwashing (CEB) process was developed using different cleaning reagents to alleviate the membrane fouling caused by algae in ultrafiltration (UF) for drinking water treatment. The study found that sodium hypochlorite (NaClO) was the most effective reagent in alleviating membrane fouling, followed by sodium chloride (NaCl). Combining NaClO with NaCl, sodium hydroxide (NaOH), or sodium citrate did not significantly improve the alleviation of membrane fouling compared to NaClO alone. The optimized dosage and dosing frequency of NaClO were determined to be 10 mg/L, used twice per day. Long-term pilot-scale and full-scale experiments confirmed the feasibility of the CEB process in relieving algae-derived membrane fouling. The CEB process effectively removed organic foulants through oxidization, weakening the cohesive forces between the foulants and the membrane surface.