Renewable energy powered membrane technology: Energy consumption analysis of ultrafiltration backwash configurations

Abstract

In the field of ultrafiltration (UF) membranes for water treatment, fouling is a severe problem that limits the potential of the technology UF membranes and results in increased energy consumption. In this study, a small-scale photovoltaic-powered membrane system was employed to investigate the energy consumption of two UF backwashing configurations – a bladder tank and a backwash (BW) pump powered by supercapacitors – under varied solar irradiance conditions. Fouling was induced via the addition of bentonite, and then examined at varied BW intervals using the bladder tank to optimize the total specific energy consumption (TSEC) – determined for both UF BW and reverse osmosis (RO) desalination processes. Simulated fouling – realized via a pressure drop across a ball valve – was proposed to induce inorganic fouling without requiring the addition of foulants. The TSEC of both bentonite and simulated fouling was compared. Under simulated fouling and constant solar irradiance operating conditions, the bladder tank exhibits a BW SEC of 0.3 Wh/L, while the BW pump exhibits SEC of 0.09Wh/L. The TSEC is maintained at ∼ 4 Wh/L under varied real “solar days” with the bladder tank, indicating that the energetic penalty for implementing one BW cycle every 90 min is small. A BW interval of 60 min exhibited a TSEC of 3.7 Wh/L and provided a good compromise between TSEC and the mitigation of membrane fouling. The concept of using a valve to simulate fouling in the system can assist with the UF membrane fouling studies without inducing irreversible fouling to the membrane. Despite its higher BW SEC, the bladder tank was a more robust setup and is recommended for adding BW functionality to renewable-energy powered membrane filtration systems.