Tuning nanofiltration membrane performance: OH-MoS2 nanosheet engineering and divalent cation influence on fouling and organic removal.

Natural organic matter (NOM) present in surface water causes severe organic fouling of nanofiltration (NF) membranes employed for the production of potable water. Calcium (Ca2+) and magnesium (Mg2+) are alkaline earth metals present in natural surface water and severely exacerbate organic fouling owing to their ability to cause charge neutralization, complexation, and bridging of NOM and the membrane surface. Hence, it is of practical significance to engineer membranes with properties suitable for addressing organic fouling in the presence of these cations. This study employed OH-functionalized molybdenum disulphide (OH-MoS2) nanosheets as nanofillers via the interfacial polymerization reaction to engineer NF membranes for enhanced removal of NOM and fouling mitigation performance. At an optimized concentration of 0.010 wt.% of OH-MoS2 nanosheet, the membrane was endowed with higher hydrophilicity, negative charge and rougher membrane morphology which enhanced the pure water permeance by 46.33% from 11.2 to 16.39 L m-2 h-1 bar-1 while bridging the trade-off between permeance and salt selectivity. The fouling performance was evaluated using humic acid (HA) and sodium alginate (SA), which represent the hydrophobic and hydrophilic components of NOM in the presence of 0, 0.5, and 1 mM Ca2+ and Mg2+, respectively, and the performance was benchmarked with control and commercial membranes. The modified membrane exhibited normalized fluxes of 95.09% and 93.26% for HA and SA, respectively, at the end of the 6 h filtration experiments, compared to the control membrane at 89.71% and 74.25%, respectively. This study also revealed that Ca2+ has a more detrimental effect than Mg2+ on organic fouling and NOM removal. The engineered membrane outperformed the commercial and the pristine membranes during fouling tests in the presence of 1 mM Ca2+ and Mg2+ in the feed solution. In summary, this study has shown that incorporating OH-MoS2 nanosheets into membranes is a promising strategy for producing potable water from alternative water sources with high salt and NOM contents.

Phosphorus adsorption and organic release from dried and thermally treated water treatment sludge.

The study investigated water treatment sludge (WTS) as a phosphorus (P) adsorbent and examined the release of organic matter during the P adsorption process. Previous studies indicated that WTS is an effective adsorbent for P but also releases organic matter, which may affect the organoleptic properties of treated water, but no study has characterised organic release and conducted an in-depth study on its behaviours. This study characterised the organic release during the P adsorption process from four different WTS samples. This study also offers results from a 60-day column experiment that indicate that WTS columns effectively removed the majority of P from the 2 mg/L feed solution. The total organic carbon (TOC) release was gradually reduced from 24.9 mg/L on day 1 to stable levels of 4.4 mg/L to 4.1 mg/L from day 22 onwards. After 60 days, when the organic matter was nearly exhausted, WTS columns were still effective in P adsorption from the solution. In addition, the thermal treatment of WTS at different temperatures was investigated to reduce TOC release and increase P adsorption. The results showed that thermal treatment not only minimized TOC release but also enhanced the P adsorption capacity of the sludge. In a 24-h batch experiment, WTS treated at 600 °C showed the highest P adsorption (1.7 mg/g) with negligible TOC release when compared to sludge treated at 500 °C WTS (1.2 mg/g), 700 °C WTS (1.5 mg/g) and dried WTS (0.75 mg/g). However, the release of inorganic compounds slightly increased after thermal treatment. Future studies could focus on determining whether the thermal processing of WTS which can enhance the WTS's adsorption to emerging pollutants like per- and poly-fluoroalkyl substances and other contaminants. The findings of this study could influence the management practices of water authorities and contribute to the water sector's sustainability objectives.

Removal of natural organic matter from surface water sources by nanofiltration and surface engineering membranes for fouling mitigation - A review.

Given that surface water is the primary supply of drinking water worldwide, the presence of natural organic matter (NOM) in surface water presents difficulties for water treatment facilities. During the disinfection phase of the drinking water treatment process, NOM aids in the creation of toxic disinfection by-products (DBPs). This problem can be effectively solved using the nanofiltration (NF) membrane method, however NOM can significantly foul NF membranes, degrading separation performance and membrane integrity, necessitating the development of fouling-resistant membranes. This review offers a thorough analysis of the removal of NOM by NF along with insights into the operation, mechanisms, fouling, and its controlling variables. In light of engineering materials with distinctive features, the potential of surface-engineered NF membranes is here critically assessed for the impact on the membrane surface, separation, and antifouling qualities. Case studies on surface-engineered NF membranes are critically evaluated, and properties-to-performance connections are established, as well as challenges, trends, and predictions for the field's future. The effect of alteration on surface properties, interactions with solutes and foulants, and applications in water treatment are all examined in detail. Engineered NF membranes containing zwitterionic polymers have the greatest potential to improve membrane permeance, selectivity, stability, and antifouling performance. To support commercial applications, however, difficulties related to material production, modification techniques, and long-term stability must be solved promptly. Fouling resistant NF membrane development would be critical not only for the water treatment industry, but also for a wide range of developing applications in gas and liquid separations.