Biogas sparging to control fouling and enhance resource recovery from anaerobically digested sludge centrate by forward osmosis

Abstract This study demonstrates the proof-of-concept of biogas sparging to control membrane fouling during sludge centrate pre-concentration by forward osmosis (FO). Sludge centrate sparging by biogas reduced membrane fouling (measured by flux decline) and filtration time by two and eight times, respectively compared to FO operation without biogas sparging at the same water recovery of 60%. In addition, the water flux was almost fully recovered by physical flushing when biogas sparging was applied. Biogas sparging also resulted in a significant improvement in the enrichment of organic, ammonia, and phosphate to close to the theoretical value based on mass balance calculation. In other words, organic matter and nutrients were retained in the bulk solution for subsequent recovery. Fouling mitigation and nutrient enrichment improvement by biogas sparging could be attributed to carbonate buffering to maintain a near neutral pH for preventing calcium phosphate precipitation on the membrane surface and ammonia volatilisation.