Recycling water from municipal wastewater offers a reliable and sustainable solution to cities and regions facing shortage of water supply. Places including California and Singapore have developed ...advanced water reuse programs as an integral part of their water management strategy. Membrane technology, particularly reverse osmosis, has been playing a key role in producing high quality recycled water. This feature paper highlights the current status and future perspectives of advanced membrane processes to meet potable water reuse. Recent advances in membrane materials and process configurations are presented and opportunities and challenges are identified in the context of water reuse.
Wastewater treatment plants in many countries use anaerobic digesters for biosolids management and biogas generation. Opportunities exist to utilise the spare capacity of these digesters to co-digest ...food waste and sludge for energy recovery and a range of other economic and environmental benefits. This paper provides a critical perspective for full-scale implementation of co-digestion of food waste and wastewater sludge. Data compiled from full-scale facilities and the peer-reviewed literature revealed several key bottlenecks hindering full-scale implementation of co-digestion. Indeed, co-digestion applications remain concentrated mostly in countries or regions with favourable energy and waste management policies. Not all environmental benefits from waste diversion and resource recovery can be readily monetarised into revenue to support co-digestion projects. Our field surveys also revealed the important issue of inert impurities in food waste with significant implication to the planning, design, and operation of food waste processing and co-digestion plants. Other pertinent issues include regulatory uncertainty regarding gate fee, the lack of viable options for biogas utilisation, food waste collection and processing, impacts of co-digestion on biosolids reuse and downstream biogas utilisation, and lack of design and operation experience. Effort to address these bottlenecks and promote co-digestion requires a multi-disciplinary approach.
Fundamental understanding of membrane fouling in osmosis-driven membrane processes is important for further deployment of this emerging technology in desalination and wastewater reuse. In this study, ...we investigated the role of pressure in organic fouling and reversibility in forward osmosis (FO) and reverse osmosis (RO) using alginate as a model organic foulant. Varying contributions of pressure (i.e., osmotic versus hydraulic) to the overall driving force were realized in forward osmosis (FO), pressure-assisted FO (PFO), and reverse osmosis (RO) experiments, while the same total driving force for water permeation was applied. Confocal laser scanning microscopy was used to examine alginate fouling layer structure in the hydrated state, which informed two key parameters: fouling layer thickness and foulant volume. We observed that the resulting fouling layer became increasingly more compact in the order of FO, PFO, and RO experiments. Fouling layer reversibility followed the same trend, with the highest and lowest reversibility observed for the FO and RO fouling experiments, respectively. Possible mechanisms for fouling layer compaction in RO were discussed, including permeate drag force and foulant compressibility, as opposed to FO where only permeate drag force applies. Our findings suggest that pressure mechanistically alters the membrane fouling layer structure and fouling reversibility, leading to higher fouling reversibility in FO, where the driving force is osmotic pressure, than RO, where the driving force is hydraulic pressure.
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•We examined the role of pressure in organic fouling reversibility in FO and RO.•We examined the alginate fouling layer in the hydrated state with confocal microscopy.•We observed a denser and more compact alginate fouling layer in RO than FO.•We observed higher alginate fouling layer reversibility in FO than RO.•We proposed possible mechanisms for fouling layer compaction under pressure.
This article discusses the potential ramifications of the COVID-19 pandemic on waste and wastewater services, focusing on critical points where alternative operating procedures or additional ...mitigation measures may be advisable. Key concerns are (i) the long half-life of the virus on materials such as waste containers, bags, and in wastewater, and (ii) possible transmission via contaminated waste surfaces and aerosols from wastewater systems. There are opportunities to further the science of wastewater-based epidemiology by monitoring viral RNA in wastewater to assess disease prevalence and spread in defined populations, which may prove beneficial for informing COVID-19 related public health policy.
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•Free ammonia pretreatment is assessed for the first time by semi-continuous anaerobic digester.•Free ammonia pretreatment enhances VS destruction in anaerobic digestion.•Free ammonia pretreatment ...improves digestate dewaterability.•Free ammonia pretreatment increases pathogen removal in anaerobic digestion.•This study is significant in promoting application of FA pretreatment in the real world.
Our previous work has reported the pretreatment of secondary sludge with free ammonia (NH3, FA) enhanced the methane production in batch biochemical methane potential tests. However, the batch biochemical methane potential test could only provide conservative results compared to continuous/semi-continuous anaerobic digestion. Also, the impacts of FA pretreatment on the key anaerobic digestion parameters, including volatile solids (VS) destruction, sludge dewaterability and pathogen removal, are still unknown. This study for the first time investigated these impacts using semi-continuous anaerobic digestion systems for 130 days. Pretreatment of secondary sludge for 24 h at an FA concentration of 560 mg NH3-N/L improved VS destruction by 26.4% (from 22.0 to 27.8%), supported by a similar increase of 28.6% in methane production (from 126.7 to 162.9 ml CH4/g VSfed). Model based analysis revealed that FA pretreatment improved the sludge degradability extent, which may be the reason for the enhanced VS destruction. Equally importantly, the dewaterability of the digested sludge with FA pretreatment was also enhanced by 9.2% (from 12.0 to 13.1% in solids content of the dewatered digested sludge), which could be partly attributed to the increased zeta potential from -16.7 to -14.5 mV. Anaerobic digestion with FA pretreatment enhanced the removals of Fecal Coliform and E. Coli by 1.3 and 1.4 log MPN/g TS (MPN: Most Probable Number; TS: Total Solids), indicating FA pretreatment was effective in enhancing pathogen removal. With inorganic solids representing 21% of the sludge used, the volume of dewatered sludge to be disposed of was reduced by 14.5% via FA pretreatment. This will substantially decrease the cost as evaluated by economic analysis. In brief, this study provides a promising strategy to enhance sludge reduction in anaerobic digestion and is of great significance in promoting the application of FA pretreatment strategy in the real world.
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Anaerobic mono-digestion and co-digestion of primary sludge and two organic wastes (namely food waste or paper pulp reject) were evaluated by biomethane potential assessment and kinetics modelling to ...elucidate the synergistic effect. The specific methane yields were 159, 652 and 157 mL/g VS added during mono-digestion of primary sludge, food waste and paper pulp reject, respectively. Co-digestion of primary sludge with either food waste or paper pulp reject resulted in much higher specific methane yields of 799 and 368 mL/g VS, respectively. pH and intermediate inhibitions (e.g. volatile fatty acids and ammonium-N) were not observed. The synergistic effect was also confirmed by examining the VS and COD removals. COD balance also identified and validated the enhanced specific methane yields from both primary sludge and organic waste (i.e. additional 32 and 19% of COD was converted to biogas during co-digestion of primary sludge with food waste or paper pulp reject, respectively). The apparent first order rate constant derived from kinetics modelling increased from 0.18 to 0.63 d−1 during mono-digestion of paper pulp reject and co-digestion of primary sludge with paper pulp reject, which can be attributed to the initial high soluble biodegradable fraction in primary sludge.
•Synergistic effect of co-digestion of primary sludge & organic waste was observed.•COD balance showed an increase in ultimate substrate biodegradability.•Kinetics modelling further verified the synergistic effect of co-digestion.•Co-digestion increased reactions kinetics for paper pulp reject but not food waste.
This study demonstrates the robustness and treatment capacity of a forward osmosis (FO)–membrane distillation (MD) hybrid system for small-scale decentralized sewer mining. A stable water flux was ...realized using a laboratory-scale FO–MD hybrid system operating continuously with raw sewage as the feed at water recovery up to 80%. The hybrid system also showed an excellent capacity for the removal of trace organic contaminants (TrOCs), with removal rates ranging from 91 to 98%. The results suggest that TrOC transport through the FO membrane is governed by “solute–membrane” interaction, whereas that through the MD membrane is strongly correlated to TrOC volatility. Concentrations of organic matter and TrOCs in the draw solution increased substantially as the water recovery increased. This accumulation of some contaminants in the draw solution is attributed to the difference in their rejection by the FO and MD systems. We demonstrate that granular activated carbon adsorption or ultraviolet oxidation could be used to prevent contaminant accumulation in the draw solution, resulting in near complete rejection (>99.5%) of TrOCs.
•Membrane-confined catalysis for water purification is reviewed for the first time.•Fundamental understanding of nanoconfinement effect is provided.•Membrane-based nanoconfined catalysis (MNC) has ...unique properties.•The fabrication methods and effect of operating conditions are discussed.•A roadmap for the future research of MNC is proposed.
Progress in heterogeneous advanced oxidation processes (AOPs) is hampered by several issues including mass transfer limitation, limited diffusion of short-lived reactive oxygen species (ROS), aggregation of nanocatalysts, and loss of nanocatalysts to treated water. These issues have been addressed in recent studies by executing the heterogeneous AOPs in confinement, especially in the nanopores of catalytic membranes. Under nanoconfinement (preferably at the length of less than 25 nm), the oxidant-nanocatalyst interaction, ROS-micropollutant interaction and diffusion of ROS have been observed to significantly improve, which results in enhanced ROS yield and mass transfer, improved reaction kinetics and reduced matrix effect as compared to conventional heterogenous AOP configuration. Given the significance of nanoconfinement effect, this study presents a critical review of the current status of membrane-based nanoconfined heterogeneous catalysis system for the first time. A succinct overview of the nanoconfinement concept in the context of membrane-based nanofluidic platforms is provided to elucidate the theoretical and experimental findings related to reaction kinetics, reaction mechanisms and molecule transport in membrane-based nanoconfined AOPs vs. conventional AOPs. In addition, strategies to construct membrane-based nanoconfined catalytic systems are explained along with conflicting arguments/opinions, which provides critical information on the viability of these strategies and future research directions. To show the desirability and applicability of membrane-based nanoconfined catalysis systems, performance governing factors including operating conditions and water matrix effect are particularly focused. Finally, this review presents a systematic account of the opportunities and technological constraints in the development of membrane-based nanoconfined catalytic platform to realize effective micropollutant elimination in water treatment.
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Antimicrobial resistance (AMR) is a growing threat to human and animal health. Progress in molecular biology has revealed new and significant challenges for AMR mitigation given the immense diversity ...of antibiotic resistance genes (ARGs), the complexity of ARG transfer, and the broad range of omnipresent factors contributing to AMR. Municipal, hospital and abattoir wastewater are collected and treated in wastewater treatment plants (WWTPs), where the presence of diverse selection pressures together with a highly concentrated consortium of pathogenic/commensal microbes create favourable conditions for the transfer of ARGs and proliferation of antibiotic resistant bacteria (ARB). The rapid emergence of antibiotic resistant pathogens of clinical and veterinary significance over the past 80 years has re-defined the role of WWTPs as a focal point in the fight against AMR. By reviewing the occurrence of ARGs in wastewater and sludge and the current technologies used to quantify ARGs and identify ARB, this paper provides a research roadmap to address existing challenges in AMR control via wastewater treatment. Wastewater treatment is a double-edged sword that can act as either a pathway for AMR spread or as a barrier to reduce the environmental release of anthropogenic AMR. State of the art ARB identification technologies, such as metagenomic sequencing and fluorescence-activated cell sorting, have enriched ARG/ARB databases, unveiled keystone species in AMR networks, and improved the resolution of AMR dissemination models. Data and information provided in this review highlight significant knowledge gaps. These include inconsistencies in ARG reporting units, lack of ARG/ARB monitoring surrogates, lack of a standardised protocol for determining ARG removal via wastewater treatments, and the inability to support appropriate risk assessment. This is due to a lack of standard monitoring targets and agreed threshold values, and paucity of information on the ARG-pathogen host relationship and risk management. These research gaps need to be addressed and research findings need to be transformed into practical guidance for WWTP operators to enable effective progress towards mitigating the evolution and spread of AMR.
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•Wastewater treatment plays a crucial role in controlling AMR.•Molecular biology techniques can quantify ARG and identify ARB in wastewater system.•Keystone species of the AMR network and contributing factors can be mapped.•Revealing ARG-pathogen host relationships is essential to assess and monitor risk.•Future work to focus on ARG/ARB surrogates, thresholds and reporting units
The effects of feed and draw solution temperature and transmembrane temperature difference on the rejection of 12 trace organic contaminants (TrOCs) by two forward osmosis (FO) membranes were ...investigated. The membrane structure parameter (S) and the reverse salt (NaCl) flux selectivity (RSFS) were constant over the temperature range of 20–40°C, suggesting that within this range, the solution temperature did not significantly influence the membrane polymeric structure. Draw solution properties, including diffusivity, viscosity, and osmotic pressure, played an important role in water and reverse salt (NaCl) flux behaviour and TrOC rejection. Pure water and salt (NaCl) permeability coefficients of the two forward osmosis membranes increased as both the feed and draw solution temperatures increased from 20 to 40°C due to an increase in solute diffusivity and a decrease in water viscosity. Rejection of charged TrOCs was higher than that of neutral TrOCs and their rejection was insensitive to temperature variation. On the other hand, rejection of neutral TrOCs decreased significantly when the feed and draw solution temperatures were 40 and 20°C, respectively, due to the increase in their diffusivity at an elevated temperature. By contrast, rejection of neutral TrOCs increased when the feed and draw solution temperatures were 20 and 40°C, respectively. The reverse salt (NaCl) flux increased due to an increase in the draw solute diffusivity. In addition, at a higher draw solution temperature, the dilution effect induced by higher water flux and the hindrance effect enhanced by a higher reverse salt (NaCl) flux led to the increase in the rejection of neutral TrOCs.
•Negligible thermally-induced changes in membrane polymer structure were observed.•Draw solution properties controlled flux and TrOC rejection.•Rejection of charged TrOCs was insensitive to temperature variation.•Rejection of neutral TrOCs decreased with increasing feed temperature.•Rejection of neutral TrOCs increased with increasing draw solution temperature.
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