Integrated Electrocoagulation, Ultrafiltration, Membrane Distillation, and Crystallization for Treating Produced Water

Produced water (PW) generated from hydraulic fracturing operations was treated using an integrated electrocoagulation, ultrafiltration, membrane distillation, and crystallization process (EC UF MDC). The aim was to determine the viability of this integrated process for maximizing water recovery. The results obtained here indicate that optimizing the various unit operations could lead to increased recovery of PW. Membrane fouling limits all membrane separation processes. A pretreatment step to suppress fouling is essential. Here, removal of total suspended solids (TSS) and total organic carbon (TOC) was achieved by electrocoagulation (EC) followed by ultrafiltration (UF). The hydrophobic membrane used in membrane distillation may be fouled by dissolved organic compounds. Reducing membrane fouling is essential to increase the long-term durability of the membrane distillation (MD) system. In addition, combining membrane distillation with crystallization (MDC) can help reduce scale formation. By inducing crystallization in the feed tank, scale formation on the MD membrane was suppressed. The integrated EC UF MDC process can impact Water Resources/Oil & Gas Companies. Conservation of surface and groundwater is possible by treating and reusing PW. Additionally, treating PW reduces the amount of PW disposed in Class II disposal wells and promotes more environmentally sustainable operations.

Pig Slurry Management Producing N Mineral Concentrates: A Full-Scale Case Study

Manure treatment to recover nutrients presents a great challenge to delocalize nutrients from overloaded areas to those needing such nutrients. To do this, approaches for the treatment of manure have been proposed, and currently, they are mostly under investigation before being upgraded to full scale. There are very few fully operating plants recovering nutrients and, therefore, very few data on which to base environmental and economic studies. In this work, a treatment plant carrying out full-scale membrane technology to treat manure to reduce its total volume and produce a nutrient-rich fraction, i.e., the concentrate, was studied. The concentrate fraction allowed the recovery of 46% of total N and 43% of total P. The high mineral N content, i.e., N-NH₄/total-N > 91%, allowed matching the REcovered Nitrogen from manURE (RENURE) criteria proposed by the European Commission to allow the potential substitution of synthetic chemical fertilizers in vulnerable areas characterized by nutrient overloading. Life cycle assessment (LCA) performed by using full-scale data indicated that nutrient recovery by the process studied, when compared with the production of synthetic mineral fertilizers, had a lower impact for the 12 categories studied. LCA also suggested precautions which might reduce environmental impacts even more, i.e., covering the slurry to reduce NH₃, N₂O, and CH₄ emissions and reducing energy consumption by promoting renewable production. The system studied presented a total cost of 4.3 € tons^-1 of slurry treated, which is relatively low compared to other similar technologies.

Circular Economy Approach in Treatment of Galvanic Wastewater Employing Membrane Processes

According to the idea of sustainable development, humanity should make every effort to care for the natural environment along with economic development. Decreasing water resources in the world makes it necessary to take action to reduce the consumption of this resource. This article presents the results of research conducted to improve the use of recyclable materials in line with the circular economy model. The research focused on the development of a technological solution for the recovery of raw materials from galvanic wastewater. The concept of a galvanic wastewater treatment system presented in the article includes wastewater pre-treatment in the ultrafiltration (UF) process and water recovery in the reverse osmosis (RO) process. In addition, the purpose of the work was to manage post-filtration waste (RO retentate) containing high concentrations of zinc in the process of galvanizing metal details. The obtained results indicate that it is possible to reduce the amount of sewage from the galvanizing industry by reusing the recovered water as technical water in the process line. The carried-out model tests of galvanizing confirmed the possibility of using RO retentate for the production of metal parts. The achieved results are a proposal to solve the problem of reducing the impact of galvanic wastewater on the environment and to improve the profitability of existing galvanizing technologies by reducing the consumption of water and raw materials.

Multistage Surface-Heated Vacuum Membrane Distillation Process Enables High Water Recovery and Excellent Heat Utilization: A Modeling Study

Surface-heated membrane distillation (MD) enhances the energy efficiency of desalination by mitigating temperature polarization (TP). However, systematic investigations of larger scale, multistage, surface-heated MD system with high water recovery and heat recycling are limited. Here, we explore the design and performance of a multistage surface-heated vacuum MD (SHVMD) with heat recovery through a comprehensive finite difference model. In this process, the latent heat of condensation is recovered through an internal heat exchanger (HX) using the retentate from one stage as the condensing fluid for the next stage and an external HX using the feed as the condensing fluid. Model results show that surface heating enhances the performance compared to conventional vacuum MD (VMD). Specifically, in a six-stage SHVMD process, 54.44% water recovery and a gained output ratio (GOR) of 3.28 are achieved with a surface heat density of 2000 W m^-2, whereas a similar six-stage VMD process only reaches 18.19% water recovery and a GOR of 2.15. Mass and energy balances suggest that by mitigating TP, surface heating increases the latent heat trapped in vapor. The internal and external HXs capture and reuse the additional heat, which enhances the GOR values. We show for SHVMD that the hybrid internal/external heat recovery design can have GOR value 1.44 times higher than that of systems with only internal or external heat recovery. Furthermore, by only increasing six stages to eight stages, a GOR value as high as 4.35 is achieved. The results further show that surface heating can reduce the energy consumption of MD for brine concentration. The multistage SHVMD technology exhibits a promising potential for the management of brine from industrial plants.

An Overview of the Modification Strategies in Developing Antifouling Nanofiltration Membranes

Freshwater deficiency has become a significant issue affecting many nations' social and economic development because of the fast-growing demand for water resources. Nanofiltration (NF) is one of the promising technologies for water reclamation application, particularly in desalination, water, and wastewater treatment fields. Nevertheless, membrane fouling remains a significant concern since it can reduce the NF membrane performance and increase operating expenses. Consequently, numerous studies have focused on improving the NF membrane's resistance to fouling. This review highlights the recent progress in NF modification strategies using three types of antifouling modifiers, i.e., nanoparticles, polymers, and composite polymer/nanoparticles. The correlation between antifouling performance and membrane properties such as hydrophilicity, surface chemistry, surface charge, and morphology are discussed. The challenges and perspectives regarding antifouling modifiers and modification strategies conclude this review.

The Impact of Salt Accumulation on the Growth of Duckweed in a Continuous System for Pig Manure Treatment

Duckweed (Lemna) is a possible solution for the treatment of aqueous waste streams and the simultaneous provision of protein-rich biomass. Nitrification-Denitrification effluent (NDNE) from pig manure treatment has been previously used as a growing medium for duckweed. This study investigated the use of a continuous duckweed cultivation system to treat NDNE as a stand-alone technology. For this purpose, a system with a continuous supply of waste streams from the pig manure treatment, continuous biomass production, and continuous discharge that meets the legal standards in Flanders (Belgium) was simulated for a 175-day growing season. In this simulation, salt accumulation was taken into account. To prevent accumulating salts from reaching a toxic concentration and consequently inhibiting growth, the cultivation system must be buffered, which can be achieved by altering the depth of the system. To determine the minimum depth of such a system, a tray experiment was set up. For that, salt accumulation data obtained from previous research were used for simulating systems with different pond depths. It was found that a depth of at least 1 m is needed to prevent a significant relative growth inhibition at the end of the growing season compared to the start. This implies a high water consumption (5-10 times more than maize). As a response, a second cultivation system was investigated for the use of more concentrated NDNE. For this purpose, salt tolerance experiments were conducted on synthetic and biological media. Surprisingly, it was observed that duckweed grows better on diluted NDNE (to 75% NDNE, or EC of 8 mS/cm) than on a synthetic medium (EC of 1.5 mS/cm), indicating the potential of such a system.

A Zero-Brine Discharge Seawater Desalination Using a Pilot-Scale Membrane Distillation System Integrated with Crystallizer

The management of brines generated from reverse osmosis operation remains a critical challenge requiring new approaches and processes to limit the impact of brine discharge onto ecosystems and to enhance both water and valuable resource recovery. The treatment of real seawater reverse osmosis (SWRO) brines (45,000 ppm TDS) obtained from a local Singaporean desalination plant with a crystallizer integrated pilot-scale membrane distillation unit (MDC) was studied. Commercial STOMATE® hollow fiber membranes were used in vacuum membrane distillation (VMD) configuration, leading to an average flux of around 3.7 L/m2-h at a permeate vacuum of 80 kPa and an average feed temperature of 65 °C. Consistent separation operations were achieved for the treatment of real SWRO brine over a period of 280 h; this led to a water recovery of >95% and to the collection of salt slurries, containing up to ~10−20 wt% of moisture, from the crystallizer. This approach demonstrates the potential of MDC systems to achieve zero brine discharge efficiently from seawater desalination systems, providing an environmentally friendly alternative to manage brines by increasing water recovery and generating salt slurries of economic value.

Co-Benefits of Pollutant Removal, Water, and Heat Recovery from Flue Gas through Phase Transition Enhanced by Corona Discharge

Pollutant removal and resource recovery from high-humidity flue gas after desulfurization in a thermal power plant are crucial for improving air quality and saving energy. This study developed a flue gas treatment method involving phase transition enhanced by corona discharge based on laboratory research and established a field-scale unit for demonstration. The results indicate that an adequate increase in size will improve the ease of particle capture. A wet electrostatic precipitator is applied before the condensing heat exchangers to enhance the particle growth and capture processes. This results in an increase of 58% in the particle median diameter in the heat exchanger and an emission concentration below 1 mg/m³. Other pollutants, such as SO₃ and Hg, can also be removed with emission concentrations of 0.13 mg/m³ and 1.10 μg/m³, respectively. Under the condensation enhancement of the method, it is possible to recover up to 3.26 t/h of water from 200 000 m³/h saturated flue gas (323 K), and the quality of the recovered water meets the standards stipulated in China. Additionally, charge-induced condensation is shown to improve heat recovery, resulting in the recovery of more than 43.34 kJ/h·m³ of heat from the flue gas. This method is expected to save 2628 t of standard coal and reduce carbon dioxide emission by 2% annually, contributing to environmental protection and global-warming mitigation.

Sustainability of Heating, Ventilation and Air-Conditioning (HVAC) Systems in Buildings-An Overview

Increasing demand on heating, ventilation, and air-conditioning (HVAC) systems and their importance, as the respiratory system of buildings, in developing and spreading various microbial contaminations and diseases with their huge global energy consumption share have forced researchers, industries, and policymakers to focus on improving the sustainability of HVAC systems. Understanding and considering various parameters related to the sustainability of new and existing HVAC systems as the respiratory system of buildings are vital to providing healthy, energy-efficient, and economical options for various building types. However, the greatest opportunities for improving the sustainability of HVAC systems exist at the design stage of new facilities and the retrofitting of existing equipment. Considering the high available percentage of existing HVAC systems globally reveals the importance of their retrofitting. The attempt has been made to gather all important parameters that affect decision-making to select the optimum HVAC system development considerations among the various opportunities that are available for sustainability improvement.

Membrane Distillation: Pre-Treatment Effects on Fouling Dynamics

In the research reported in this paper, membrane distillation was employed to recover water from a concentrated saline petrochemical effluent. According to the results, the use of membrane distillation is technically feasible when pre-treatments are employed to mitigate fouling. A mathematical model was used to evaluate the fouling mechanism, showing that the deposition of particulate and precipitated material occurred in all tests; however, the fouling dynamic depends on the pre-treatment employed (filtration, or filtration associated with a pH adjustment). The deposit layer formed by particles is not cohesive, allowing its entrainment to the bulk flow. The precipitate fouling showed a minimal tendency to entrainment. Also, precipitate fouling served as a coupling agent among adjacent particles, increasing the fouling layer cohesion.

An effective integrated system used in separating for anaerobic digestate and concentrating for biogas slurry

In this work, an integrated system was developed which achieves full-scale separation and valorization for anaerobic digestate of livestock manure, completes anaerobic digestate separation, biogas residue recovery, biogas slurry concentration and water recovery simultaneously. Compared with the centrifugal pretreatment, the particle size of the biogas slurry is reduced significantly via P/I pretreatment, the liquid recovery ratio is increased to 94.0%, this leads to the substantial increase of the entire system nutrients recovery ratio directly. What's even more valuable is the permeate flux of UF membrane is increased for 2.5 times via P/I pretreatment. The results showed that P/I pretreatment had much better effects in solid-liquid separation of biogas slurry, which reduced the load of the subsequent membrane separation unit and enhanced the UF membrane permeation flux greatly. That prolonged the cleaning cycle and service life of the UF membrane. The efficiency of system was validated according to the nutrients recovery ratios, the biogas slurry concentration efficiency, the recovery of water and the pollutants levels of discharged water. The results showed that the total nutrients recovery ratio was about 100%, the concentration ratios of biogas slurry were more than 3.7 (via UF) and 6.6 (via RO), total water recovery ratio was 46.9% (ratio of the discharged water volume to the digestate volume, the COD removal ratio of the discharged water was 99.9%, the contents of COD, TP and TN were 43.6 mg/L, 0.2 mg/L and 1.2 mg/L, which reached the nation integrated wastewater discharged standard class I.

Low- and High-Pressure Membrane Separation in the Production of Process Water for Coke Quenching

Although the time for operating mines and coking plants in many countries is coming to an end due to climate change, we must still ensure that the pollution generated by this source of the economy is minimized. Despite the several stages of treatment of the coke-oven effluent, completed with nitrification and denitrification processes preceding final sedimentation, the stream obtained does not meet the requirements of water for coke quenching. That is why the stream after biodegradation and sedimentation was treated on membrane units to ensure water reusing in the coking plant. As the subjected stream contained both solid and dissolved pollutants, a two-stage system was proposed: low- and high-pressure membrane filtration. Industrial modules were tested on pilot units operating under industrial plant conditions. In the case of the ultrafiltration process, all the tested ultrafiltration modules fulfilled the primary task. All of them separated almost completely the turbidities present in the stream, which would have disturbed the operation of the high-pressure plant. Considering the decrease in permeate flux and the possibility of cleaning, a PCI membrane made of PVDF tubes with a diameter of 12.5 mm and pore size of 20 μm was selected. Regarding the high-pressure membrane filtration, the reverse osmosis membrane was significantly better in the removal efficiency of both organic and inorganic dissolved substances. An operating pressure of 3 MPa was chosen for the system. Hence, membrane processes, which are not used as stand-alone treatment units for coke-oven effluents, function well as a final treatment stage.

Combining electro-bioremediation of nitrate in saline groundwater with concomitant chlorine production

Groundwater pollution and salinization have increased steadily over the years. As the balance between water demand and availability has reached a critical level in many world regions, a sustainable approach for the management (including recovery) of saline water resources has become essential. A 3-compartment cell configuration was tested for a new application based on the simultaneous denitrification and desalination of nitrate-contaminated saline groundwater and the recovery of value-added chemicals. The cells were initially operated in potentiostatic mode to promote autotrophic denitrification at the bio-cathode, and then switched to galvanostatic mode to improve the desalination of groundwater in the central compartment. The average nitrate removal rate achieved was 39±1 mgNO₃^--N L^-1 d^-1, and no intermediates (i.e., nitrite and nitrous oxide) were observed in the effluent. Groundwater salinity was considerably reduced (average chloride removal was 63±5%). Within a circular economy approach, part of the removed chloride was recovered in the anodic compartment and converted into chlorine, which reached a concentration of 26.8±3.4 mgCl₂ L^-1. The accumulated chlorine represents a value-added product, which could also be dosed for disinfection in water treatment plants. With this cell configuration, WHO and European legislation threshold limits for nitrate (11.3 mgNO₃^--N L^-1) and salinity (2.5 mS cm^-1) in drinking water were met, with low specific power consumptions (0.13±0.01 kWh g^-1NO₃^--N_removed). These results are promising and pave the ground for successfully developing a sustainable technology to tackle an urgent environmental issue.

State-of-the-Art and Opportunities for Forward Osmosis in Sewage Concentration and Wastewater Treatment

The application of membrane technologies for wastewater treatment to recover water and nutrients from different types of wastewater can be an effective strategy to mitigate the water shortage and provide resource recovery for sustainable development of industrialisation and urbanisation. Forward osmosis (FO), driven by the osmotic pressure difference between solutions divided by a semi-permeable membrane, has been recognised as a potential energy-efficient filtration process with a low tendency for fouling and a strong ability to filtrate highly polluted wastewater. The application of FO for wastewater treatment has received significant attention in research and attracted technological effort in recent years. In this review, we review the state-of-the-art application of FO technology for sewage concentration and wastewater treatment both as an independent treatment process and in combination with other treatment processes. We also provide an outlook of the future prospects and recommendations for the improvement of membrane performance, fouling control and system optimisation from the perspectives of membrane materials, operating condition optimisation, draw solution selection, and multiple technologies combination.

Theoretical Analysis of Constant Voltage Mode Membrane Capacitive Deionization for Water Softening

Water softening is desirable to reduce scaling in water infrastructure and to meet industrial water quality needs and consumer preferences. Membrane capacitive deionization (MCDI) can preferentially adsorb divalent ions including calcium and magnesium and thus may be an attractive water softening technology. In this work, a process model incorporating ion exclusion effects was applied to investigate water softening performance including ion selectivity, ion removal efficiency and energy consumption in a constant voltage (CV) mode MCDI. Trade-offs between the simulated Ca²⁺ selectivity and Ca²⁺ removal efficiency under varying applied voltage and varying initial concentration ratio of Na⁺ to Ca²⁺ were observed. A cut-off CV mode, which was operated to maximize Ca²⁺ removal efficiency per cycle, was found to lead to a specific energy consumption (SEC) of 0.061 kWh/mole removed Ca²⁺ for partially softening industrial water and 0.077 kWh/m³ removed Ca²⁺ for slightly softening tap water at a water recovery of 0.5. This is an order of magnitude less than reported values for other softening techniques. MCDI should be explored more fully as an energy efficient means of water softening.

Treatment of Olive Mill Wastewater through Integrated Pressure-Driven Membrane Processes

The disposal of wastewater resulting from olive oil production (olive mill wastewater, OMW) is a major issue for olive oil producers. This wastewater is among the most polluting due to the very high concentration of organic substances and the presence of hardly degradable phenolic compounds. The systems proposed for OMW treatment are essentially based either on conventional chemical-physical, biological and thermal processes, or on membrane processes. With respect to conventional methods, membrane processes allow to separate different species without the use of chemicals or heat. This work deals with the use of the integrated pressure-driven membrane processes for the treatment of OMW. They consist of a first stage (microfiltration, MF) in which a porous multichannel ceramic membrane retains suspended materials and produces a clarified permeate for a second stage (reverse osmosis, RO), in order to separate (and concentrate) dissolved substances from water. Laboratory scale experiments with different small flat sheet RO membranes were first carried out in order to select the most appropriate one for the successive bench scale tests with a spiral wound module having a large membrane surface. The aim of this test was to concentrate the dissolved substances and to produce water with low salinity, chemical oxygen demand (COD), and reduced phytotoxicity due to a low content of phenolic compounds. The trend of the permeate flux and membrane retention as a function of the volume concentration ratio was investigated. The influence of OMW origin and its aging on the membrane performance was also studied.

Study on the Preparation and Properties of Talcum-Fly Ash Based Ceramic Membrane Supports

Ceramic membrane method for moisture recovery from flue gas of thermal power plants is of considerable interest due to its excellent selection performance and corrosion resistance. However, manufacturing costs of commercial ceramic membranes are still relatively expensive, which promotes the development of new methods for preparing low-cost ceramic membranes. In this study, a method for the preparation of porous ceramic membrane supports is proposed. Low-cost fly ash from power plants is the main material of the membrane supports, and talcum is the additive. The fabrication process of the ceramic membrane supports is described in detail. The properties of the supports were fully characterized, including surface morphology, phase composition, pore diameter distribution, and porosity. The mechanical strength of the supports was measured. The obtained ceramic membrane supports displays a pore size of about 5 μm and porosity of 37.8%. Furthermore, the water recovery performance of the supports under different operating conditions was experimentally studied. The experimental results show that the recovered water flux varies with operating conditions. In the study, the maximum recovered water flux reaches 5.22 kg/(m²·h). The findings provide a guidance for the ceramic membrane supports application of water recovery from flue gas.

Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-Of-The-Art and Performance Analysis

Wastewater reuse as a sustainable, reliable and energy recovery concept is a promising approach to alleviate worldwide water scarcity. However, the water reuse market needs to be developed with long-term efforts because only less than 4% of the total wastewater worldwide has been treated for water reuse at present. In addition, the reclaimed water should fulfill the criteria of health safety, appearance, environmental acceptance and economic feasibility based on their local water reuse guidelines. Moreover, municipal wastewater as an alternative water resource for non-potable or potable reuse, has been widely treated by various membrane-based treatment processes for reuse applications. By collecting lab-scale and pilot-scale reuse cases as much as possible, this review aims to provide a comprehensive summary of the membrane-based treatment processes, mainly focused on the hydraulic filtration performance, contaminants removal capacity, reuse purpose, fouling resistance potential, resource recovery and energy consumption. The advances and limitations of different membrane-based processes alone or coupled with other possible processes such as disinfection processes and advanced oxidation processes, are also highlighted. Challenges still facing membrane-based technologies for water reuse applications, including institutional barriers, financial allocation and public perception, are stated as areas in need of further research and development.

Exploring the Operation Factors that Influence Performance of a Spiral-Wound Forward Osmosis Membrane Process for Scale-up Design

Forward osmosis (FO) technology has increasingly attracted attention owing to its low operational energy and low fouling propensity. Despite extensive investigations on FO, very few module-scale FO studies on the operation and design of the FO process have been conducted. In this paper, a simple and practical FO process design parameter called normalized membrane area is suggested based on a performance analysis of spiral-wound FO elements. The influence of operation factors on operating pressures and water recovery was investigated using 8-inch spiral wound elements in the continuous operation mode. The membrane area was adjusted by series connection of FO elements to a maximum value of 46 m² (three elements). The feed and draw flow rates were varied between 5 and 15 LPM under various feed (10, 20, and 30 g/L) and draw (58.4 and 233.8 g/L) concentration combinations. The analysis of flow rates (feed, draw, and permeate flow rates) indicated not only high flow channel resistance on the draw side but also high permeate flow rates can induce higher operating pressures owing to strong mutual interaction of the feed and the draw streams. Feed water recovery was focused on as a key performance index, and the experimental recovery (R_Exp) and theoretical maximum recovery (R_Th) values were compared. The results revealed the significance of the feed flow rate and the membrane area in terms of enhancing the water recovery performance. In addition, a clear relationship was observed between the membrane area normalized by the initial feed flow rates and the water recovery ratio (R_Exp/R_Th), even though the applied operation conditions were different. Finally, an empirical equation to estimate the required membrane area of spiral-wound FO was proposed for the FO process design. The equation can be used to predict water recovery of FO systems as well, for example, if an FO system is operated at 0.08 m²L⁻¹h of the normalized membrane area, the system is expected to offer 78% of the R_Th value.

Experimental Study on Water Recovery from Flue Gas Using Macroporous Ceramic Membrane

In this work, a ceramic membrane tube with a pore size of 1 μm was used to conduct experimental research on moisture and waste heat recovery from flue gas. The length, inner/outer diameter, and porosity were 800 mm, 8/12 mm, and 27.2%, respectively. In the experiments, the flue gas, which was artificially prepared, flowed on the shell side of membrane module. The water coolant passed through the membrane counter-currently with the gas. The effects of flue gas flow rate, flue gas temperature, water coolant flux, and water coolant temperature on the membrane recovery performance were analyzed. The results indicated that, upon increasing the flue gas flow rate and its temperature, both the amount of recycled water and the recovered heat increased. The amount of recycled water, recycled water rate, recovered heat, and heat recovery rate all decreased as the water coolant temperature increased. When the water coolant temperature exceeded 30 °C, the amount of recycled water dropped sharply. The maximum amounts of recycled water, recovered heat, and total heat transfer coefficient were 2.93 kg/(m²·h), 3.63 kW/m², and 224.3 W/(m²·K), respectively.

Hybrid Membrane Distillation and Wet Scrubber for Simultaneous Recovery of Heat and Water from Flue Gas

Flue gas contains high amount of low-grade heat and water vapor that are attractive for recovery. This study assesses performance of a hybrid of water scrubber and membrane distillation (MD) to recover both heat and water from a simulated flue gas. The former help to condense the water vapor to form a hot liquid flow which later used as the feed for the MD unit. The system simultaneously recovers water and heat through the MD permeate. Results show that the system performance is dictated by the MD performance since most heat and water can be recovered by the scrubber unit. The scrubber achieved nearly complete water and heat recovery because the flue gas flows were supersaturated with steam condensed in the water scrubber unit. The recovered water and heat in the scrubber contains in the hot liquid used as the feed for the MD unit. The MD performance is affected by both the temperature and the flow rate of the flue gas. The MD fluxes increases at higher flue gas temperatures and higher flow rates because of higher enthalpy of the flue gas inputs. The maximum obtained water and heat fluxes of 12 kg m⁻² h⁻¹ and 2505 kJm⁻² h⁻¹ respectively, obtained at flue gas temperature of 99 °C and at flow rate of 5.56 L min⁻¹. The MD flux was also found stable over the testing period at this optimum condition. Further study on assessing a more realistic flue gas composition is required to capture complexity of the process, particularly to address the impacts of particulates and acid gases.

A study on near zero liquid discharge approach for the treatment of reverse osmosis membrane concentrate by electrodialysis

A lab-scale electrodialysis (ED) which consisted of 11 pieces of cation-exchange membranes and 10 pieces of anion-exchange membranes was used to treat concentrated brine of Reverse osmosis (RO) membrane. The effect of operating parameters such as applied voltage, flowrate, and operating mode was investigated to measure the performance of a lab-scale ED. Three different voltages (5, 10, and 15 V) and flowrates (20, 30, and 40 L/h) were applied in order to optimize the operating conditions of the ED system. The maximum TDS removal efficiencies were 85%, 97%, and 98% for 5, 10, and 15 V, respectively. It was concluded that the desalination efficiencies were almost the same at flowrates values of 20, 30 and 40 L/h. The TDS concentration of the treated brine in the concentrate compartment rises to the highest value of 25,400 mg/L with desalination rate of 92.5% after five cycle operation. Moreover, the desalinated brine can be used as fresh water.

Implication of Non-electrostatic Contribution to Deionization in Flow-Electrode CDI: Case Study of Nitrate Removal From Contaminated Source Waters

While flow-electrode capacitive deionization (FCDI) operated in short-circuited closed cycle (SCC) mode appears to hold promise for removal of salt from brackish source waters, there has been limited investigation on the removal of other water constituents such as nitrate, fluoride or bromide in combination with salt removal. Of particular concern is the effectiveness of FCDI when ions, such as nitrate, are recognized to non-electrostatically adsorb strongly to activated carbon particles thereby potentially rendering it difficult to regenerate these particles. In this study, SCC FCDI was used to desalt source waters containing nitrate at different concentrations. Results indicate that nitrate can be removed from source waters using FCDI to concentrations <1 mg NO₃-N L^-1 though a lower quality target such as 10 mg L^-1 would be more cost-effective, particularly where the influent nitrate concentration is high (50 mg NO₃-N L^-1). Although studies of the fate of nitrate in the FCDI system show that physico-chemical adsorption of nitrate to the carbon initially plays a vital role in nitrate removal, the ongoing process of nitrate removal is not significantly affected by this phenomenon with this lack of effect most likely due to the continued formation of electrical double layers enabling capacitive nitrate removal. In contrast to conventional CDI systems, constant voltage mode is shown to be more favorable in maintaining stable effluent quality in SCC FCDI because the decrease in electrical potential that occurs in constant current operation leads to a reduction in the extent of salt removal from the brackish source waters. Through periodic replacement of the electrolyte at a water recovery of 91.4%, we show that the FCDI system can achieve a continuous desalting performance with the effluent NO₃-N concentration below 1 mg NO₃-N L^-1 at low energy consumption (~0.5 kWh m^-3) but high productivity.

Dual-Function Conductive Copper Hollow Fibers for Microfiltration and Anti-biofouling in Electrochemical Membrane Bioreactors

Membrane bioreactors (MBRs) with polymeric/ceramic microfiltration (MF) membranes have been commonly used for wastewater treatment today. However, membrane biofouling often results in a dramatically-reduced service life of MF membranes, which limits the application of this technology. In this study, Cu hollow fiber membranes (Cu-HFMs) with low resistivity (104.8-309.8 nΩ·m) and anti-biofouling properties were successfully synthesized. Further analysis demonstrated that Cu-HFMs reduced at 625°C achieved the bimodal pore size distribution of ~1 μm and a porosity of 46%, which enable high N₂ permeance (1.56 × 10^-5 mol/m² s pa) and pure water flux (5812 LMH/bar). The Cu-HFMs were further applied as the conductive cathodes, as well as MF membranes, in the electrochemical membrane bioreactor (EMBR) system that was enriched with domestic wastewater at an applied voltage of 0.9 V. Excellent permeate quality (Total suspended solids (TSS) = 11 mg/L) was achieved at a flux of 9.47 LMH after Cu-HFM filtration, with relatively stable transmembrane pressure (TMP) and low Cu²⁺ dissolvability (<25 μg/L). The anti-biofouling over time was demonstrated by SEM characterization of the rare biofilm formation on the Cu-HFM cathode surface. By using Cu-HFMs in EMBR systems, an effective strategy to control the membrane biofouling is developed in this study.

Recovery of real dye bath wastewater using integrated membrane process: considering water recovery, membrane fouling and reuse potential of membranes

It has been recognized by the whole world that textile industry which produce large amounts of wastewater with strong color and toxic organic compounds is a major problematical industry requiring effective treatment solutions. In this study, reverse osmosis (RO) membranes were tested on biologically treated real dye bath wastewater with and without pretreatment by nanofiltration (NF) membrane to recovery. Also membrane fouling and reuse potential of membranes were investigated by multiple filtrations. Obtained results showed that only NF is not suitable to produce enough quality to reuse the wastewater in a textile industry as process water while RO provide successfully enough permeate quality. The results recommend that integrated NF/RO membrane process is able to reduce membrane fouling and allow long-term operation for real dye bath wastewater.

Membrane treatment of alkaline bleaching effluents from elementary chlorine free kraft softwood cellulose production

This paper reports experimental results on the sequential use of ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) to fractionate alkaline extraction bleaching effluents from kraft cellulose production. The aim was to unveil the way key pollutants are distributed when subjected to sequential UF/NF/RO membrane separation processes. Alkaline bleaching effluents were obtained from a local pinewood-based mill, featuring elementary chlorine free bleaching to produce high-brightness cellulose. The experimental system was based on a laboratory-scale membrane system, DSS LabStak® M20 Alfa Laval, using Alfa Laval UF and NF/RO membranes, operated at a constant transmembrane pressure (6 bar for UF membranes and 32 bar for NF/RO membranes), at 25°C. Results show that 78% chemical oxygen demand (COD) and total phenols, 82% adsorbable organic halogens (AOX) and 98% colour were retained by UF membranes which have molecular weight cut-off (MWCO) above 10 kDa. In all, 16% of original COD, total phenols and AOX, and the remaining 2% colour were retained by UF membranes within the 1 to 10 kDa MWCO range. Chloride ions were significantly present in all UF permeates, and RO was required to obtain a high-quality permeate with a view to water reuse. It is concluded that UF/NF/RO membranes offer a feasible option for water and chemicals recovery from alkaline bleaching effluents in kraft pulp production.