Liquid Discharge Research Articles

Enhanced hydrogen production through cracking of ammonia water using liquid plasma on titanate-based perovskite catalysts

In this study, a mass production of hydrogen was studied through cracking of ammonia water using liquid plasma. A new FexNi1-xTiO3 perovskite composite with significantly improved visible-light sensitivity was synthesized to further improve the photochemical reaction activity. It is applied to hydrogen production from the decomposition of ammonia water using liquid plasma. In this reaction, a large amount of hydrogen is produced with a small amount of nitrogen gas; moreover, oxygen is produced by liquid plasma discharge and no CO2 byproduct is produced. Titanate-based perovskite catalysts have also been used in decomposition reactions. Titanate-based perovskite catalysts exhibiting high rates of hydrogen production during decomposition were obtained for the plasma and photocatalytic decomposition of aqueous ammonia. FexNi1-xTiO3, which is a newly synthesized ABTiO3-type titanate, showed a higher rate of hydrogen production (approximately 140 L/(g·h)) than other titanate-based perovskites. Furthermore, the FexNi1-xTiO3 exhibited the highest sensitivity to UV and visible light. Its high photosensitivity helped improve the photocatalytic activity in the decomposition of ammonia in water using plasma.

Unraveling the intricate fouling behaviors of landfill leachate components during membrane distillation concentration toward zero liquid discharge

Membrane distillation (MD) holds promise for cost-effectively concentrating wastewater toward zero liquid discharge (ZLD), while membrane fouling problems still hinder its practical application, especially for high-strength wastewater containing complex constituents. This study investigated the effects of different foulant components in actual landfill leachate (LFL) on MD deep concentration performances. The fouling behaviors of LFL components were revealed by comprehensively characterizing and analyzing the physicochemical properties of the fouling layers and membrane-foulant interactions. Results illustrated that suspended solids (SS) and macromolecular organics (MO) played significant yet distinct roles in fouling layer formation. SS (>0.45 μm, ∼24 % TOC) possessed strong adhesion energies with membrane surfaces and constructed the main skeleton of the fouling layer at the preliminary concentration stage; while MO (>20 kDa, 0.36 % TOC) deposition resulted in a densely packed fouling layer, influencing the salt crystallization potential and interfering with water and ammonia transport. In contrast, the low-molecular organics with the highest content (<20 kDa, ∼75 % TOC) were mainly electron-donor monopolar substances weakly adsorbed on the nonpolar membrane surface. Removing SS and MO from LFL notably prevented fouling layer formation and maintained high membrane efficacies (water flux decline mitigated from ∼50 % to ∼15 % and ammonia rejection increased from 71 % to 88 %), even as water recovery increased to 95 %. The findings of this work imply conventional anti-fouling strategies (e.g., complete removal or degradation of organic components) may have gone beyond what is necessary, and will inspire the development of simpler and greener methods to maintain membrane efficacy during high-strength wastewater treatment toward ZLD.

Anti-fouling rotating polymer-based heat exchanger for zero liquid discharge humidification-dehumidification desalination

The objective of this investigation is to assess the performance of various heat exchangers for application in a novel solar-powered zero liquid discharge humidification-dehumidification desalination system. In this study four heat exchangers (HX) having two different flow configurations namely counter flow (cf), cross flow (cr) made up of three different materials namely high-density polyethylene (HDPE), aluminum (Al), and Polypropelyne (PP) were compared in terms of their effectiveness and overall heat transfer coefficient under varying salinity levels (up to 10%) and mixing ratios (0.22–0.45). At a mixing ratio of 0.22 and 0% salinity, PP-HXcr and Al-HXcf exhibited similar effectiveness (∼85%), surpassing that of HDPE-HXcf (∼65%). Despite PP-HXcr's lower thermal conductivity in comparison to Al-HXcf, comparable effectiveness was achieved due to the superior flow distribution in PP-HXcr. Further investigations focused on the impact of salinity on heat exchanger performance. At 3.5% salinity, all heat exchangers experienced a decline in effectiveness and heat transfer coefficient (HTC), with Al-HXcf experiencing a more pronounced decrease compared to PP-HXcr. The higher thermal conductivity of Al-HXcf led to greater salt accumulation, while PP-HXcr demonstrated minimal fouling. As the experiment progressed, fouling increased for all heat exchangers, with the Al-HXcf being practically ineffective at 10% salinity with an effectiveness below 10%. To address the issue of fouling, a rotating cross-flow heat exchanger (RPP-HXcr) was introduced. While the effectiveness of the PP-HXcr drops from 85% to approximately 60% with increasing salinity from 0% to 10%, the RPP-HXcr demonstrates only a marginal decline in effectiveness with increasing salinity. For instance, at mixing ratio of 0.22 when the salinity is increased from 0% to 10%, the effectiveness of RPP-HXcr only drops from 83% to 77%. This exceptional performance was attributed to the continuous contact between the rotating tubes and the incoming feed, effectively preventing fouling and ensuring sustained efficiency. Rotating cross-flow heat exchanger (RPP-HXcr) is introduced and validated as a potentially reliable solution for mitigating fouling, as it demonstrates sustained efficiency and minimal performance degradation across different salinity conditions.

Characterization of arsenic species by liquid sampling-atmospheric pressure glow discharge ionization mass spectrometry

A liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source operating at a nominal power of 30 W and solution flow rate of 30 µL min−1 and supported in a He sheath gas flow rate of 500 mL min−1 was interfaced to an Orbitrap mass spectrometer and assessed for use in rapid identification of inorganic and organic arsenic species, including As(III), As(V), monomethylarsonic acid, dimethylarsinic acid, and arsenobetaine in a 2% (v/v) nitric acid medium. Mass spectral acquisition in low-resolution mode, using only the ion trap analyzer, provided detection of protonated molecular ions for AsBet (m/z 179), DMA (m/z 139), MMA (m/z 141), and As(V) (m/z 143). As(III) is oxidized to As(V), likely due to in-source processes. Typical fragmentation of these compounds resulted in the loss of either water or methyl groups, as appropriate, i.e., introducing DMA also generated ions corresponding to MMA and As(V) as dissociation products. Structure assignments were also confirmed by high-resolution Orbitrap measurements. Spectral fingerprint assignments were based on the introduction of solutions containing 5 µg mL−1 of each arsenic compound.

Electrified Solar Zero Liquid Discharge: Exploring the Potential of PV-ZLD in the US.

Current brine management strategies are based on the disposal of brine in nearby aquifers, representing a loss in potential water and mineral resources. Zero liquid discharge (ZLD) is a possible strategy to reduce brine rejection while increasing the resource recovery from desalination plants. However, ZLD substantially increases the energy consumption and carbon footprint of a desalination plant. The predominant strategy to reduce the energy consumption and carbon footprint of ZLD is through the use of a hybrid desalination technology that integrates renewable energy. Here, we built a computational thermodynamic model of the most mature electrified hybrid technology for ZLD powered by photovoltaic (PV). We examine the potential size and cost of ZLD plants in the US. This work explores the variables (geospatial and design) that most influence the levelized cost of water and the second law efficiency. There is a negative correlation between minimizing the LCOW and maximizing the second-law. And maximizing the second-law, the states that more brine produces, Texas is the location where the studied system achieves the lowest LCOW and high second-law efficiency, while California is the state where the studied system is less favorable. A multiobjective optimization study assesses the impact of considering a carbon tax in the cost of produced water and determines the best potential size for the studied plant.

A comprehensive assessment of the economic and technical viability of a zero liquid discharge (ZLD) hybrid desalination system for water and salt recovery

Brine, a by-product of desalination and industrial facilities, is becoming more and more of an environmental issue. This comprehensive techno-economic assessment (TEA), focusing on the technical and economic aspects, investigates the performance and viability of a novel hybrid desalination brine treatment system known as zero liquid discharge (ZLD). Notably, this research represents the first instance of evaluating the feasibility and effectiveness of integrating three distinct desalination processes, namely brine concentrator (BC), high-pressure reverse osmosis (HPRO), and membrane-promoted crystallization (MPC), within a ZLD framework. The findings of this study demonstrate an exceptional water recovery rate of 97.04%, while the energy requirements stand at a reasonable level of 17.53 kWh/m3. Financially, the ZLD system proves to be at least 3.28 times more cost-effective than conventional evaporation ponds and offers comparable cost efficiency to alternatives such as land application and deep-well injection. Moreover, the ZLD system exhibits profitability potential by marketing both drinking water and solid salt or solely desalinated water. The daily profit from the sale of generated water varies from US$194.08 to US$281.41, with Greece and Cyprus attaining the lowest and highest profit, respectively. When considering the sale of both salt and water, the profit rises by 8% across all locations.

Impact of industrial hotspots on Tamla nala and Nunia nala confluence - a tributary of the Damodar river.

Clean water is essential for drinking, household use, and agriculture. Researchers studied 39 sites near Tamla nala and Nunia nala channels in Durgapur and Asansol City (West Bengal) to assess the deterioration level of water due to industrial discharge. During the first phase out of three, the researchers conducted a spatial representation of various physicochemical parameters, such as temperature, pH, Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Total Hardness (TH), Electrical Conductivity (EC), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), significant anions such as chloride (Cl-), nitrate (NO3-), phosphate (PO4-3), sulfate (SO42-), cyanide (CN-1) and fluoride (F-), as well as heavy metals/metalloids such as lead (Pb), cadmium (Cd), chromium (Cr), iron (Fe), copper (Cu), nickel (Ni), mercury (Hg) and arsenic (As). As observed the parameters at various sites along the stream exceeded threshold limits majorly due to industrial discharge: highest pH, TDS, TH, EC, Cl-, SO42- at site 26; Fe at site 1, TSS, COD, CN- at site 33, 31, 2 respectively; Cd, Ni, Cu at site 19; Hg and Pb at site 3 and As at site 20. Contaminated areas were marked in red and secure areas in green. Additionally, the HMPI (Heavy metal pollution index) was estimated for eight locations to understand the impact of heavy metal pollution in the second phase of the study. An extremely high HMPI indicates heightened toxicity and health risks for both residents and outsiders. The Canadian Water Quality Index (1.0) was calculated for eight sites in the third phase based on seventeen parameters. The resulting WQI value was below 44, indicating poor water quality at the sites. Due to the poor quality and critical heavy metal toxicity, the authors recommended continuous monitoring, strict regulation enforcement, increased treatment capacity, Zero Liquid Discharge implementation, and raising awareness among residents.

Water reuse and resource recovery from greenhouse wastewater by capacitive electrodialysis at pilot scale

As food production dominates global freshwater consumption and nutrient discharge regulation tightens, the performance of novel technologies at applied scale needs to be studied to optimize water use and minimize environmental impact. Water reuse and the nutrient recovery from greenhouse wastewater were assessed utilizing one-pass capacitive electrodialysis (CED) at a pilot scale (19.32 m2 membrane area, 1–4 m3/day capacity), employing carbon-based electrodes. CED was optimized for key parameters, including applied voltage, cross-flow velocity, staging, water recovery, and varying feed concentrations. High-quality greenhouse irrigation water (conductivity<0.2 mS/cm and Na+ < 0.1 mmol/L) was produced, meeting specified guidelines. Na+ was retained less compared to Ca2+ and Mg2+ (86 % ± 4 %, 97 % ± 2 %, and 98 % ± 3 % removal, respectively) and nutrients concentration factors for K+, NO3− and PO43− reached up to 2.3 (596 ± 5 mg/L), 2.7 (1330 ± 20 mg/L), and 1.9 (130 ± 2 mg/L), respectively. There was no significant improvement in ion removal for all feed compositions beyond 12 V and 80 % water recovery. CED's specific energy consumption (SEC) with optimized parameters was 4-fold lower than the modeled RO system, and lower than previous electrodialysis studies. The highest SEC obtained was 0.24 kWh/m3. These findings suggest that CED is a promising technology for the greenhouse horticulture sector, aiding the move toward zero liquid discharge.

Contrasting mixed scaling patterns and mechanisms of nanofiltration and membrane distillation

Oriented towards the pressing needs for hypersaline wastewater desalination and zero liquid discharge (ZLD), the contrasting mixed scaling of thermal-driven vacuum membrane distillation (VMD) and pressure-driven nanofiltration (NF) were investigated in this work. Bulk crystallization was the main mechanism in VMD due to the high salinity and temperature, but the time-independent resistance by the adsorption of silicate and organic matter dominated the initial scaling process. Surface crystallization and the consequent pore-blocking were the main scaling mechanisms in NF, with the high permeate drag force, hydraulic pressure, and cross-flow rate resulting in the dense scaling layer mainly composed of magnesium-silica hydrate (MSH). Silicate enhanced NF scaling with a 75% higher initial flux decline rate attributed to the MSH formation and compression, but delayed bulk crystallization in VMD. Organic matter presented an anti-scaling effect by delaying bulk crystallization in both VMD and NF, but specifically promoted CaCO3 scaling in NF. Furthermore, the incipient scaling was intensified as silicate and organic matter coexisted. The scaling mechanism shifted from surface to bulk crystallization due to the membrane concentration in both VMD and NF. This work fills the research gaps on mixed scaling mechanisms in different membrane processes, which offers insights for scaling mitigation and thereby supports the application of ZLD.

Catalytic ozonation of reverse osmosis concentrate from coking wastewater reuse by surface oxidation over Mn-Ce/γ-Al2O3: Effluent organic matter transformation and its catalytic mechanism

Degradation of organics in high-salinity wastewater is beneficial to meeting the requirement of zero liquid discharge for coking wastewater treatment. Creating efficient and stable performance catalysts for high-salinity wastewater treatment is vital in catalytic ozonation process. Compared with ozonation alone, Mn and Ce co-doped γ-Al2O3 could remarkably enhance activities of catalytic ozonation for chemical oxygen demand (COD) removal (38.9%) of brine derived from a two-stage reverse osmosis treatment. Experimental and theoretical calculation results indicate that introducing Mn could increase the active points of catalyst surface, and introducing Ce could optimize d-band electronic structures and promote the electron transport capacity, enhancing HO• bound to the catalyst surface ([HO•]ads) generation. [HO•]ads plays key roles for degrading the intermediates and transfer them into low molecular weight organics, and further decrease COD, molecular weights and number of organics in reverse osmosis concentrate. Under the same reaction conditions, the presence of Mn/γ-Al2O3 catalyst can reduce ΔO3/ΔCOD by at least 37.6% compared to ozonation alone. Furthermore, Mn-Ce/γ-Al2O3 catalytic ozonation can reduce the ΔO3/ΔCOD from 2.6 of Mn/γ-Al2O3 catalytic ozonation to 0.9 in the case of achieving similar COD removal. Catalytic ozonation has the potential to treat reverse osmosis concentrate derived from bio-treated coking wastewater reclamation.

Efficient removal of Basic Violet 16 by a multistage oxygen enhanced liquid glow discharge plasma system: Mechanism and roles of reactive species quantified by machine learning

A multistage oxygen enhanced Liquid Glow Discharge Plasma reactor (LGDP/multistage oxygen, LGDP/M-O2) was designed to improve the removal efficiency of organic dyes in wastewater. As a result of the multistage oxygen system, the degradation rate constant of Basic Violet 16 (BV16) was enhanced by approximately 18 times, the decolorization rate of BV16 was 97.39 % in 4 min, and the removal rate of TOC was 33.32 % in 10 min. Detailed study of how the system works to help break down pollutants. The reactive species series of experiments showed that multistage oxygen injection strongly promoted reactive species production and utilization. Meanwhile, a machine learning model to quantify the contribution of reactants was proposed. Machine learning indicated the dominating contribution of reactive oxygen species (63.89 %) and reactive chlorine species (21.92 %) in the degradation of BV16. In addition, the transformation intermediates during the degradation of BV16 were monitored. Accordingly, three possible degradation pathways of BV16 in the LGDP/M-O2 system were proposed, i.e., benzene ring substitution of hydroxyl groups, hydroxyl addition of C=C double bond, and halogenation of benzene rings. This study demonstrates the importance of the LGDP/M-O2 system for organic dye removal from wastewater.

Highly efficient three‐dimensional solar evaporator for zero liquid discharge desalination of high‐salinity brine

AbstractSolar‐driven interfacial evaporation is a promising technology for freshwater production from seawater, but salt accumulation on the evaporator surface hinders its performance and sustainability. In this study, we report a simple and green strategy to fabricate a three‐dimensional porous graphene spiral roll (3GSR) that enables highly efficient solar evaporation, salt collection, and water production from near‐saturated brine with zero liquid discharge (ZLD). The 3GSR design facilitates energy recovery, radial brine transport, and directional salt crystallization, thereby resulting in an ultrahigh evaporation rate of 9.05 kg m−2 h−1 in 25 wt% brine under 1‐sun illumination for 48 h continuously. Remarkably, the directional salt crystallization on its outer surface not only enlarges the evaporation area but also achieves an ultrahigh salt collection rate of 2.92 kg m−2 h−1, thus enabling ZLD desalination. Additionally, 3GSR exhibits a record‐high water production rate of 3.14 kg m−2 h−1 in an outdoor test. This innovative solution offers a highly efficient and continuous solar desalination method for water production and ZLD brine treatment, which has great implications for addressing global water scarcity and environmental issues arising from brine disposal.

Techno-economic analysis (TEA) of zero liquid discharge (ZLD) systems for treatment and utilization of brine via resource recovery

The issue pertaining to brine disposal has generated considerable interest in advanced methodologies aimed at harnessing their potential for resource recovery (i.e., water and salts). This techno-economic analysis investigates the technical and economic outlooks of zero liquid discharge (ZLD) desalination systems, employing two distinct crystallization approaches: membrane-promoted crystallization (MPC) in case 1, and wind-aided intensified evaporation (WAIV) in case 2. The findings indicate that case 1 exhibits a higher drinking water recovery rate (96 %) compared to case 2 (84 %), as the crystallization technology adopted in case 2 (WAIV) does not facilitate freshwater recovery. In both systems, the water is extracted via the implementation of efficient technologies, leading to the attainment of ZLD conditions along with minimal brine volumes. In terms of energy and cost requirements, case 1 necessitates a greater total energy demand (19 kWh/m3) and cost (US$95/day) in contrast to case 2 (15 kWh/m3 & US$83/day). Both cases demonstrate feasibility, yielding profits varying from US$179.19/day to US$221.32/day, contingent upon the sale of solely water or both water and solid salt. The insights provided by this study are poised to facilitate viable utilization and management of brine originating from the seawater desalination industry as well as from diverse brine-generating sectors.

Multi-stage humidification–dehumidification system integrated with a crystallizer for zero liquid discharge of desalination brine

Desalination plants discharge a massive volume of brine every day, which negatively affects the ecosystem, particularly the subsurface ecology and marine life. To mitigate the brines' detrimental effects on the environment and facilitate the recovery of salt crystals and freshwater, the Zero Liquid Discharge (ZLD) approach was proposed. This study proposes four different configurations of multistage humidification dehumidification systems integrated with a crystallizer, exploring their energy and economic implications. Key findings from the study include the higher Gained Output Ratio (GOR) in series configurations due to lower temperature differences, resulting in lower heater energy consumption. The crystallizer significantly enhances water productivity, but it is a major consumer of both electricity (85%) and thermal energy (50.45–57.7%) in the system. Increasing the heat source temperature reduces the Specific Electrical Energy Consumption (SEEC) and the specific area while slightly increasing the Specific Thermal Energy Consumption (STEC). Elevated cooling water temperature raises SEEC and specific area but has negligible effects on STEC. Higher feed water flow rates increase SEEC but lower both STEC and specific area. Feed salinity elevation decreases productivity, SEEC, STEC, and specific area. The crystallizer constitutes 15.43–26.44% of the total capital cost, with series configurations incurring higher costs. Unit freshwater production costs, considering salt selling, range from 1.733 to 4.821 $.m−3. In a waste heat scenario, parallel configurations become profitable, where freshwater can be distributed at zero cost, while the produced salt crystals can be sold at an even lower price of $58.09 per tonne and $57.04 per tonne, respectively.

Towards a zero liquid discharge process from brine treatment: Water recovery, nitrate electrochemical elimination and potential valorization of hydrogen and salts

This research addresses the issues related with treatment and valorization of brines and nitrate decontamination of surface and ground waters. The objective was to approximate to zero liquid discharge (ZLD) minimizing the environmental impact of brines of an electrodialysis reversal water treatment plant (EDRWTP) as an example. The innovative in flow process was developed from lab to pre-industrial scale and joined several main concepts: ion-exchange equilibrium for softening or demineralization of brines; reversed osmosis to recover suitable water and to enrich the waste in nitrate for efficient electrochemical reduction of NO3− to N2; valorization of subproducts by direct use or by precipitation; and assessment of the whole process by measuring in-line several parameters. The achieved softening was around 98 % and the recovered water from this current by reversed osmosis was 75 %. The brine of this step (25 %) contained around 1500 mg/L of nitrate and it was treated by electrochemical reduction with a Bi/Sn cathode providing a gas current of 60 % of initial nitrate reduced to N2, O2, H2O, NH3 and at least 97 % of H2. The aqueous current contained around 40 % of initial nitrate as ammonium and nitrite lower than 50 and 5 mg/L, respectively. Hypochlorite was added to this last current for oxidizing ammonium and nitrite to N2 and nitrate, respectively, being nitrate and ammonium lower than 50 and 5 mg/L, respectively. After the obtained water was demineralized and conducted to the EDRWTP inlet. The recovery of insoluble salts as calcium carbonate, reuse of saline solutions for the regeneration of process resins and the potential use of hydrogen generated as a by-product during the electrochemical reduction are other possible utilities.

Advances in zero liquid discharge multigeneration plants: A novel approach for integrated power generation, supercritical desalination, and salt production

In light of the escalating worldwide demand for energy and water resources, the imperative for developing sustainable multigeneration systems has gained prominence in recent research and development. This study aims to investigate the feasibility and performance of a novel multigeneration plant operating at supercritical conditions to simultaneously generate freshwater, power, and dry salt as a by-product while eliminating liquid discharge. This approach offers a promising solution to address the interconnected challenges of energy and water sustainability. The theory contends that combining supercritical desalination with power generation increases energy efficiency and water production rates, surpassing conventional systems. Therefore, a model is developed employing a supercritical once-through boiler capable of supplying the necessary heat duty required for steam generation from the integrated desalination plant, producing power. Additionally, multiple heat exchangers and flash separators are implemented, enhancing freshwater productivity and obtaining dry salt, eliminating the need for brine waste disposal. A thorough sensitivity analysis is conducted utilizing a robust model developed on Aspen HYSYS to ascertain the optimal operational parameters of the proposed plant. The findings of this study underscore the potential of concurrent production of 1.65 million m3/year of freshwater, 302.5 GWh of electricity, and 64,845 ton/year of dry salt for 0.38 $/m3, 0.07 $/kWh, and 0.02 $/kg, respectively. In conclusion, this research highlights the prospects of revolutionary progress in multigeneration systems for sustainable development.

Nanosecond pulsed discharge with plasma-functionalized TiO2 for the high efficiency degradation of tetracycline

Non-thermal plasma coupling with photocatalyst is recognized as a promising technology for the degradation of antibiotics, and improving the photocatalyst performance is one of the most significant strategies to improve the efficiency of plasma-catalytic systems. This study employed a nanosecond pulsed gas–liquid discharge coupled with plasma-functionalized TiO2 to achieve a high efficiency of tetracycline degradation and clarify the synergistic mechanism of nanosecond pulse discharge coupling with functionalized TiO2. Results showed that the degradation efficiency with functionalized TiO2 increased by 20% compared to the untreated TiO2 for 4 min-plasma treatment. It is also suggested that the effect of photogenerated holes and electrons can be promoted in the functionalized TiO2, as evidenced by the radical quenching experiments. The plasma-modified TiO2 catalysts were proven to have a good stability and recyclability. This study provides a new sustainable approach to enhance the performance of photocatalysts in the plasma system for environmental remediation.

Pioneering minimum liquid discharge desalination: A pilot study in Lampedusa Island

Minimum Liquid Discharge (MLD) and Zero Liquid Discharge (ZLD) schemes have been widely proposed in the recent scientific literature not only as a possible solution to brine disposal but also as a non-conventional sustainable source of raw materials. Nevertheless, very few works have pushed the idea towards a real demonstration activity, and this somehow limits the reliability that such schemes have with respect to the real implementation potential at the industrial scale. In this work, for the first time in the literature, an integrated treatment chain for the sustainable production of freshwater and minerals has been demonstrated at a pre-industrial scale, in the island of Lampedusa (Italy). The treatment chain included a Nanofiltration (NF) step to separate monovalent and bivalent ions, followed by a Multi-Effect Distillation (MED) unit, powered by waste heat from a Thermal Power plant, generating high-quality water (<30 μS/cm) and an ultra-concentrated brine. The latter was treated in Evaporation Ponds (EPs) to generate high purity NaCl (>99 %). On the other side, the NF retentate was treated to selectively recover magnesium and calcium hydroxides (Mg(OH)2 purity up to 98 %) in a novel Multiple Feed-Plug Flow Reactor (MF-PFR). The resulting brine fed an ElectroDialysis with Bipolar Membranes unit (EDBM), generating in-situ alkaline and acidic solutions: chemicals needed for internal usage in the plant. All units were successfully tested, reaching satisfactory performance indicators. Furthermore, the stability of each unit during the daily operational run was assessed and successfully achieved, demonstrating not only the technical feasibility of the proposed demo plant, but also the feasibility of MLD as a sustainable alternative for minerals recovery.

Brine concentration using air gap diffusion distillation: A performance model and cost comparison with membrane distillation for high salinity desalination

Zero liquid discharge (ZLD) has emerged as a treatment process to address the challenges with brine disposal from desalination plants. To achieve ZLD, a brine concentrator is commonly used to extract water up to a high salinity approaching saturation. However, state-of-the-art brine concentrators are energy-intensive thermal evaporators comprising expensive metal alloys and complex maintenance. This study presents the design of a new brine concentrator referred to as air gap diffusion distillation (AGDD) that operates without a membrane up to a high salinity. A holistic analytical model is developed to evaluate the system performance in terms of its energy efficiency (gain output ratio, GOR) and water flux (represented as the recovery ratio, RR), as these metrics directly impact the levelized cost of water (LCOW). A multi-pass AGDD system achieves an overall water recovery of ~70 % and GOR of 7 (88 % latent heat recovery) with an initial feed salinity of 70 g/kg. A comparison is made to its thermodynamically similar counterpart, air gap membrane distillation (AGMD), which reveals that AGDD outperforms AGMD by eliminating heat and mass transport resistances associated with the membrane. The corresponding LCOW is 1.6× lower than AGMD, making it promising as a brine concentrator to achieve salinities >200 g/kg for minimal liquid discharge.

Current Status of Zero Liquid Discharge Technology for Desulfurization Wastewater

Desulfurization wastewater is industrial wastewater with a high salt content, high metal ions, and high hardness produced by flue gas desulfurization of the limestone-gypsum method in coal-fired power plants. This paper summarizes the source of desulfurization wastewater, water quality characteristics, water quality impacts, and other factors, combined with the current status of research worldwide to introduce the advantages and shortcomings of the existing desulfurization wastewater treatment technology. In addition, zero liquid discharge technology as a novel method to treat desulfurization wastewater is also summarized. It mainly includes evaporation and crystallization, flue gas evaporation, membrane distillation removal, etc. Finally, this manuscript looks forward to the future development direction of desulfurization wastewater based on its existing technology and emission standards.