Synthesis and Characterization of Sewage Sludge Ash-Based Temperature-Sensitive Hydrogel as an Advanced Class of Forward Osmosis Desalination Draw Agent

Abstract

In this study, an advanced temperature-sensitive hydrogel with sewage sludge ash (SSA) was synthesized and employed as draw agent for forward osmosis (FO) desalination. The effects of the incineration temperature (700–1,000°C) of SSA obtention, particle size (20–300 meshes), and dosage (0–4.5 wt%) of SSA were investigated for optimally synthesizing the temperature-sensitive hydrogel to meet the requirement of FO. The resulting hydrogels were characterized in terms of crystal structure, surface morphology, surface functional groups, and lower critical solution temperature (LCST). It was shown that the dosage of SSA significantly influenced the swelling capacity (in different concentrations of NaCl solution) and deswelling property of hydrogels, whereas the other two factors only affected the swelling of hydrogel, but had no effect on the deswelling. In addition, as a result of higher reticulated pore structure, and the hydrogen-bonding interaction between the chemical surface of SSA and monomers of hydrogels, the best production D2.5H as a draw agent generated high average water flux of 2.22 LMH in FO desalination with 2,000 ppm NaCl as feed solution. Furthermore, despite a little higher LCST with the comparison of D0H (blank sample without SSA), the D2.5H as a draw agent can still maintain the prominent temperature-sensitive performance in that, most of the water can be recovered in 10 min of 60°C water bath, and the average water fluxes of FO with even three times regenerated hydrogels were similar to that with the initial.