Application of forward osmosis (FO) under ultrasonication on sludge thickening of waste activated sludge

Abstract

Forward osmosis (FO) is an emerging process for dewatering solid-liquid stream which has the potential to be innovative and sustainable. However, the applications have still been hindered by low water flux and membrane fouling when activated sludge is used as the feed solution due to bound water from microbial cells. Hence, a novel strategy was designed to increase sludge thickening and reduce membrane fouling in the FO process under ultrasonic condition. The results from the ultrasound/FO hybrid system showed that the sludge concentration reached up to 20,400 and 28,400 mg/L from initial sludge concentrations of 3000 and 8000 mg/L with frequency of 40 kHz after 22 hours, while the system without ultrasound had to spend 26 hours to achieve the same sludge concentration. This identifies that the presence of ultrasound strongly affected sludge structure as well as sludge thickening of the FO process. Furthermore, the ultrasound/FO hybrid system could achieve NH4+-N removal efficiency of 96%, PO4(3-)-P of 98% and dissolved organic carbon (DOC) of 99%. The overall performance demonstrates that the proposed ultrasound/FO system using seawater as a draw solution is promising for sludge thickening application.

Physical cleaning techniques to control fouling during the pre-concentration of high suspended-solid content solutions for resource recovery by forward osmosis

“…Ultrasonic application also reduced the extent of concentration polarisation by rapidly mixing both the feed and draw solutions close to the membrane surface, and thus improving the water flux dynamics [50]. Our results are consistent with previous studies on membrane cleaning using ultrasonication [42,43,51].…”

“…FO membrane fouling can be controlled via either a physical or chemical cleaning process [38,39]. Physical cleaning techniques such as cross-flow velocity increase or pulsated crossflow, membrane flushing, air-scouring, osmotic backwashing, and ultrasonication have been studied for different applications and FO configurations [40][41][42][43]. These techniques provide vigorous hydrodynamic conditions to prevent or remove the fouling cake layer from the membrane surface [30,40].…”

“…In this context, ultrasonication is a promising technique to complement other physical cleaning techniques. Indeed, the potential of ultrasonication as a robust but chemical free FO cleaning technique has recently been demonstrated for calcium sulfate scaling [43] and supernatant from waste activated sludge thickening [42].…”

Performance of a seawater-driven forward osmosis process for pre-concentrating digested sludge centrate: organic enrichment and membrane fouling

“…In recent years, the potential of FO to treat many complex feed solutions has been demonstrated in the literature. These complex solutions include drilling and fracking fluids from oil and gas exploration [6][7][8][9] , sludge 10,11 , digested sludge centrate 2,12,13 , and municipal wastewater 4,14,15 .…”

“…Ansari et al 12 has recently demonstrated a seawater-driven FO process for phosphorus recovery from digested sludge centrate with a specific focus on evaluating the efficiency of nutrient recovery. Results from previous studies suggest that identifying the most suitable membrane type and orientation is necessary to ensure the best performance of seawaterdriven FO process for pre-concentrating sludge centrate 2,[10][11][12] . More importantly, understanding of the fouling process and developing strategies to control fouling need to be discussed to guarantee the long-term operation of the FO system.…”