Sewage sludge ash-based thermo-responsive hydrogel as a novel draw agent towards high performance of water flux and recovery for forward-osmosis

This work made use of the sewage sludge ash (SSA) to enhance thermo-responsive hydrogel for driving forward-osmosis (FO) process. Results showed that owing to the porous structure and intermolecular interactions between the ionized groups of monomers and the chemical surface of silica , the SSA-based thermo-responsive hydrogel (SSA2.5H) had increased swelling capacity and osmotic pressure , resulting in an average water flux (2.33 LMH) twice as high as the hydrogel without adding SSA (1.18 LMH) during 24 h FO with DI water or different concentrations (2000–8000 ppm) of NaCl as feed solution. More importantly, SSA2.5H can maintain good thermo-responsive dehydration performance in spite of an enhancement to its swelling ability. 93.8% of the adsorbed water can be retrieved from SSA2.5H in water bath of moderate temperature (60 °C) for 10 min and water flux can be recovered to 94.4% of the initial value after 4 times of hydrogel regeneration during FO as draw agent. Therefore, this work showed that SSA was an excellent modifier to enhance the thermo-responsive hydrogel for improving permeation performance in FO and lowering down the actual energy requirement for water recovery and draw agent regeneration.