Zhihui Pan,Xiongrui Yang,Yilun Liang,Mengze Lyu,Yingru Huang,Hong Zhou,Gang Wen,Huarong Yu,Junguo He
A temperature-sensitive hydrogel modified with sewage sludge ash (SSA) was used as an advanced draw agent for forward osmosis (FO) application in treating chromium-containing wastewater. The performance of the modified hydrogel (SSA-TSH) was measured in terms of the swelling and deswelling properties, as well as adsorption and desorption effects on Cr(VI), chemical oxygen demand (COD), total phosphorous (TP) and ammonium (NH 4 + -N) in chromium-containing wastewater. Furthermore, the efficiencies of wastewater treatment , water flux , and the reusability of the SSA-TSH as draw agent in the FO process (FO-SSA-TSH) using a commercially available thin-film composite membrane (Sterlitech) were also investigated. The results indicated that FO-SSA-TSH achieved high removal rates of pollutants (Cr(VI): 96.9 %–97.4 %, COD: 97.1 %–97.4 %, TP: 97.7 %–99.6 %, and NH 4 + -N: 76.8 %–77.9 %) in various Cr(VI) concentrations (0– 40 mg/L) due to the high rejection rate of FO membrane and notable adsorption capacity of the hydrogel. Moreover, the average water flux of FO-SSA-TSH (1.95– 2.02 LMH) was nearly twice as much as that of the FO with pure temperature-sensitive hydrogel as draw agent (FO-TSH, 1.33– 1.42 LMH) in 24 h chromium-containing wastewater treatment . In addition, SSA-TSH with excellent deswelling property exhibited high water recovery performance and good reusability in low cost and energy consumption after the FO permeation process for wastewater treatment.
Zhihui Pan,Haoyong Guo,Huarong Yu,Gang Wen,Fangshu Qu,Tingjian Huang,Junguo He
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.
Huayong Luo,Shiyin Li,Zirong Xu,Hongwei Rong,Qingwu Long
To explore a simple and energy-efficient approach to regenerate draw agent is a key challenge for forward osmosis (FO) desalination. Electro-responsive hydrogels have attracted great attention due to their reversible swelling-shrinking behaviors under an electric stimulus. However, the developed electro-sensitive hydrogels based on 2-acrylamido-2-methyl-l-propanesulfonic acid (AMPS) so far exhibit low reusability due to their unstable electro-sensitive properties and poor degradability with potential environmental impact. This study explored the use of an electro-responsive superabsorbent hydrogel as a draw agent by grafting acrylic acid (AA) and acrylamide (AM) onto sodium carboxymethyl cellulose (CMC). The grafted hydrogel’s morphology and structure were investigated by FTIR and SEM. The swelling behaviors and deswelling properties in an electrode contact system were examined. The swelling kinetics of the hydrogel could be well described by the Schott's pseudo-second-order model with a theoretical swelling ratio of 452.5 g/g. The grafted hydrogel exhibited stable electro-sensitive characteristics with a decrease of 7.3 % in the equilibrium swelling ratio after undergoing three cycles of deswelling and swelling. During the FO test, the dry hydrogel particles produced a water flux of 1.55 L·m −2 ·h −1 within the first hour, surpassing the performance of other carboxylic acid-based hydrogels used as draw agents. Significantly, it exhibited encouraging water recovery capabilities in the five recycling FO processes, retaining around 84 % of its initial water recovery ratio after 40 min of exposure to a voltage of 15 V. This indicated that the grafted hydrogel could be considered as an effective and sustainable draw agent for FO desalination.
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