Transport and accumulation of organic matter in forward osmosis-reverse osmosis hybrid system: Mechanism and implications

Improving biological removal of pharmaceutical active compounds and estrogenic activity in a mesophilic anaerobic osmotic membrane bioreactor treating municipal sewage

The contamination of water sources by pharmaceutically active compounds (PhACs) and their effect on aquatic communities and human health have become an environmental concern worldwide. Membrane bioreactors (MBRs) are an alternative to improve biological removal of recalcitrant organic compounds from municipal sewage. Their efficiency can be increased by using high retention membranes such as forward osmosis (FO) and membrane distillation (MD). Thus, this research aimed to evaluate the performance of an anaerobic osmotic MBR coupled with MD (OMBR-MD) in the treatment of municipal sewage containing PhACs and estrogenic activity. A submerged hybrid FO-MD module was integrated into the bioreactor. PhACs removal was higher than 96% due to biological degradation, biosorption and membrane retention. Biological removal of the PhACs was affected by the salinity build-up in the bioreactor, with reduction in biodegradation after 32 d. However, salinity increment had little or no effect on biosorption removal. The anaerobic OMBR-MD removed >99.9% of estrogenic activity, resulting in a distillate with 0.14 ng L^-1 E2-eq, after 22 d, and 0.04 ng L^-1 E2-eq, after 32 d. OMBR-MD treatment promoted reduction in environmental and human health risks from high to low, except for ketoprofen, which led to medium acute environmental and human health risks. Carcinogenic risks were reduced from unacceptable to negligible, regarding estrogenic activity. Thus, the hybrid anaerobic OMBR-MD demonstrated strong performance in reducing risks, even when human health is considered.

Effect of organic micropollutants on biofouling in a forward osmosis process integrating seawater desalination and wastewater reclamation

This study systematically investigated the effect of organic micropollutants (OMPs) on biofouling in forward osmosis (FO) integrating wastewater treatment and seawater dilution. Synthetic seawater (0.6 M sodium chloride) was used as a draw solution and synthetic municipal wastewater as a feed solution. To evaluate the impact of OMPs in a replicate parallel study, wastewater was supplemented with a mixture of 7 OMPs (OMPs-feed) and without OMPs (control) during 8 batch filtration cycles with feed and draw solution replacement after each filtration. The FO performance (water flux), development and microbial composition properties of biofilm layers on the wastewater side of the FO membrane were studied. Compared to the control without OMPs, the FO fed with OMPs containing wastewater showed (i) initially the same water flux and flux decline during the first filtration cycle, (ii) with increasing filtration cycle a lower flux decline and (iii) lower concentrations for the total cells, ATP, EPS carbohydrates and proteins in biofilm layers, and (iv) a lower diversity of the biofilm microbial community composition (indicating selective pressure) and (v) increasing rejection of 6 of the 7 OMPs. In essence, biofouling on the FO membrane showed (i) a lower flux decline in the presence of OMPs in the feed water and (ii) a higher OMPs rejection, both illustrating better membrane performance. This study has a significant implication for optimizing osmotic dilution in terms of FO operation and OMPs rejection.

Characteristics and influencing factors of organic fouling in forward osmosis operation for wastewater applications: A comprehensive review

Wastewater reuse is considered one of the most promising practices for the achievement of sustainable water management on a global scale. In the context of the safe reuse of water, membrane filtration is a competitive technique due to its superior efficiency in several processes. However, membrane fouling by organics is an inevitable challenge that is encountered during the practical application of membrane processes. The resolution of the membrane fouling challenge requires an in-depth understanding of many complex interactions between organic foulants and the membrane. In the last few decades, the forward osmosis (FO) membrane process, which exploits osmosis as a driving force, has emerged as an effective technology for water production with low energy consumption, thus leveraging the water-energy nexus. However, their successful application is severely hampered by membrane fouling, which is caused by such complex fouling mechanisms as cake enhanced osmotic pressure (CEOP), reverse salt diffusion (RSD), internal, and external concentration polarization as well as by the traditional fouling processes encompassing colloids, microbial (biofouling), inorganic, and organic fouling. Of these fouling types, the fouling potential of organic matter in FO has not been given sufficient attention, in particular, when FO is applied to wastewater treatment. This paper aims to provide a comprehensive overview of FO membrane fouling for wastewater applications with a special focus on the identification of the major factors that lead to the unique properties of organic fouling in this filtration process. Based on the critical assessment of organic fouling formation and the governing mechanisms, proposals were advanced for future research aimed at the mitigation of FO membrane fouling to enhance process efficiency in wastewater applications.

Comparison of performance and biofouling resistance of thin-film composite forward osmosis membranes with substrate/active layer modified by graphene oxide

In this study, the influence mechanisms of graphene oxide (GO) on the membrane substrate/active layer for improving the water flux and anti-biofouling ability of thin-film composite (TFC) membranes in forward osmosis (FO) were systematically investigated. We fabricated a pristine TFC membrane, a TFC membrane in which the substrate or polyamide active layer was modified by GO (TFN-S membrane or TFN-A membrane), and a TFC membrane in which both the substrate and active layer were functionalized by GO (TFN-S + A membrane). Our results showed that the TFN-S membrane possesses a higher water flux (∼27.2%) than the TFN-A because the substrate that contained GO could improve the porous structure and porosity, while the TFN-A membrane exhibited a lower reverse salt flux and higher salt rejection than the TFN-S membrane, indicating that the surface properties played a more important role than the substrate for the salt rejection. Regarding the biofouling experiment, the TFN-A and TFN-S + A membranes facilitated a higher antifouling performance than the TFN-S and TFC membranes after 72 h of operation because of the greater hydrophilicity, lower roughness and facilitated higher bactericidal activity on the GO-modified surface. In addition, the biovolume and biofilm thickness of the TFN-A and TFN-S + A membranes were found to follow the same trend as flux decline performance. In conclusion, the substrate modified by GO could greatly improve the water flux, whereas the GO-functionalized active layer is favorable for salt rejection and biofouling mitigation. The advantage of TFN-A in biofouling mitigation suggests that the antibacterial effect of GO has a stronger influence on biofouling control than the changes of hydrophilicity and roughness.

The substrate modified by GO could greatly improve water flux, whereas the GO-functionalized active layer is favorable for biofouling mitigation.

Manure digestate storage under different conditions: Chemical characteristics and contaminant residuals

In this study, chemical characteristics and contaminant residuals in livestock manure digestate were investigated during storage under different conditions. Results show that storing digestate openly under the mesophilic condition (30 ± 1 °C) led to water evaporation and thus considerable mass reduction. As a result, concentrative effect occurred to increase the contents of organic matter, nutrients, and heavy metals during digestate storage. By contrast, ammonium (NH₄⁺) concentration in digestate decreased over storage period. The concentrative effect and NH₄⁺ reduction could be mitigated by storing digestate with coverage and/or under psychrophilic conditions (e.g. 15 ± 1 °C). Regardless of storage conditions, organic matter was further biodegraded, thereby reducing the residuals of antibiotics in digestate. Antibiotic removal was more notable when digestate was stored under mesophilic conditions. Nevertheless, additional processes to control heavy metals and antibiotics in digestate are still necessary before agricultural applications.

Seeing is believing: Insights from synchrotron infrared mapping for membrane fouling in osmotic membrane bioreactors

We employed synchrotron infrared (IR) mapping to resolve forward osmosis (FO) membrane fouling in osmotic membrane bioreactor (OMBR). Synchrotron IR mapping offers a unique perspective to elucidate the fouling mechanisms and associated consequences in OMBR operation. We demonstrated the spatial distribution and relative intensity of carbohydrate and protein longitudinally along of the fouled FO membrane at the conclusion of OMBR operation. Both transmission and attenuated total reflection (ATR) modes were used to map the cross-section and surface of the fouled FO membrane. Micro X-ray computed tomography revealed patchy, "sand-dune" features on the membrane surface at the conclusion of OMBR operation. Synchrotron IR-ATR mapping demonstrated that the development of membrane fouling layer in OMBR operation was initiated by polysaccharide-like carbohydrate, followed by layering with protein-like substance, resulting in a characteristic "sand-dune" three dimensional feature. Synchrotron FTIR mapping shed light on foulant occurrence and accumulation in the draw solution. Strong penetration of protein-like substance into membrane matrix was visualised, resulting the detection of protein adsorption in the region of membrane supporting layer.

Osmotic versus conventional membrane bioreactors integrated with reverse osmosis for water reuse: Biological stability, membrane fouling, and contaminant removal

This study systematically compares the performance of osmotic membrane bioreactor - reverse osmosis (OMBR-RO) and conventional membrane bioreactor - reverse osmosis (MBR-RO) for advanced wastewater treatment and water reuse. Both systems achieved effective removal of bulk organic matter and nutrients, and almost complete removal of all 31 trace organic contaminants investigated. They both could produce high quality water suitable for recycling applications. During OMBR-RO operation, salinity build-up in the bioreactor reduced the water flux and negatively impacted the system biological treatment by altering biomass characteristics and microbial community structure. In addition, the elevated salinity also increased soluble microbial products and extracellular polymeric substances in the mixed liquor, which induced fouling of the forward osmosis (FO) membrane. Nevertheless, microbial analysis indicated that salinity stress resulted in the development of halotolerant bacteria, consequently sustaining biodegradation in the OMBR system. By contrast, biological performance was relatively stable throughout conventional MBR-RO operation. Compared to conventional MBR-RO, the FO process effectively prevented foulants from permeating into the draw solution, thereby significantly reducing fouling of the downstream RO membrane in OMBR-RO operation. Accumulation of organic matter, including humic- and protein-like substances, as well as inorganic salts in the MBR effluent resulted in severe RO membrane fouling in conventional MBR-RO operation.