Renewable energy powered membrane technology: Impact of intermittency on membrane integrity

Abstract

Directly coupled photovoltaic-powered nanofiltration/reverse osmosis is a sustainable and cost-effective solution to brackish water desalination in remote areas. Intermittent operation of the system may cause physical membrane damage and loss of membrane integrity. The potential causes of integrity loss during intermittency include the sudden spontaneous restart process, frequent shut-down events, and osmotic backwash (OB) cleaning with controlled permeate backpressure. A bench-scale crossflow system powered by a solar array simulator was used to perform periodic fluctuation on filtration experiments that in this case cause intermittency. A wide range of feed pressure increase rates (0.17 to 2 bar/s) during the start-up process, up to 1000 shut-down events, and additional permeate backpressure up to 4 bar to enhance OB were applied. Results show that no significant membrane performance deterioration was observed at the highest feed pressure increase rate (2 bar/s), and when the shut-down event number increased to 1000 implying the robustness of NF/RO membranes and spontaneous OB cleaning. When increasing permeate backpressure to 2–4 bar to enhance the OB process, membrane integrity loss of both membranes was observed. This demonstrates the reliability and robustness towards fluctuations, intermittency, and spontaneous OB cleaning in a directly coupled photovoltaic-powered nanofiltration/reverse osmosis system if permeate backwash is avoided.