High-salinity Organic Wastewater Research Articles

Asymmetric Ba0.7Sr0.3CoO3-δ/MXene solar evaporators for enhanced treatment of high salinity organic wastewater: Improving salt deposition control and pollutant removal

Solar-driven interfacial evaporation (SIE) utilizes solar thermal energy to produce clean water, addressing the water-energy paradox. However, challenges like photothermal conversion performance and salt deposition limit its adoption. Additionally, when SIE is applied to organic wastewater treatment, volatile organic compounds (VOCs) in the distilled water can diminish water purification efficiency. In this study, we developed a Ba0.7Sr0.3CoO3-δ/MXene composite solar evaporator capable of simultaneous removal of organic matters (93.70 % removal of 4-chlorophenol) with high evaporation performance (1.50 kg m−2 h−1) during the evaporation of salt-containing organic wastewater. The incorporation of Ba0.7Sr0.3CoO3-δ into the composite significantly enhanced the photothermal conversion capacity, improving the evaporation efficiency. The organic pollutant removal activity of Ba0.7Sr0.3CoO3-δ stemmed from lattice oxygen, which was activated by photothermal conversion heat. The incorporation of Ba0.7Sr0.3CoO3-δ and MXene in the solar evaporator significantly enhances the photothermal conversion performance. Additionally, the innovative asymmetric edge structure effectively addresses the salt deposition issue and enables the removal of organic pollutants through in situ utilization of heat generated from photothermal conversion. This approach offers a subtle yet effective strategy for mitigating pollutant accumulation in the solar interfacial evaporation process, ensuring long-term water purification and clean water production.

Study on the Removal Effect of 3DEPs on Microplastics in Groundwater and Desalination Mechanism

Owing to water scarcity, groundwater quality has become an important constraint on sustainable regional development, especially in coastal areas. Coastal groundwater is subject to natural conditions and intense human activities, and the evolution of water quality is extremely complex, with the possibility of seawater intrusion into the groundwater, leading to the salinisation of freshwater aquifers. At present, the commonly used methods for removing groundwater pollution include coagulation, adsorption, biological method, membrane technology, etc., among which the coagulation method is more commonly used. At present, three-dimensional electrode electrochemical technology is widely used in high salinity organic wastewater and many organic wastewaters, but there are few studies related to microplastic removal by three-dimensional electrode electrochemical technology using metallic aluminium particles as particle electrodes. The treatment of microplastics in coastal groundwater is a relatively novel issue, and with the increasing application of three-dimensional electrochemical technology in the study of desalination, the three-dimensional electrode electrochemical technology will be promising due to the high salinity of coastal groundwater, the increasingly serious pollution of microplastics, and the fluctuation of water quality and quantity.

Simultaneous purification of salt and condensate by collaborated evaporation-peroxodisulfate treatment of high salinity organic wastewater

High salinity organic wastewater is commonly treated by evaporation, which produces a large amount of waste salts and condensed water containing organic compounds. The waste salts are typical classified as hazardous waste and the condensed water often requires advanced oxidation treatment before it can be biochemically treated. In this study, a synergistic treatment process combining evaporation with thermal activation of peroxodisulfate (PDS) was developed for the treatment of wastewater containing tetrabromobisphenol S (TBBPS) and Na2SO4 to reduce the content of organics in the crystal salt and condensed water. Compared with evaporation alone, the synergistic treatment process allows the complete removal of TBBPS from the crystal salt with an increase of TOC removal from 4.48 % to 94.44 %. Meanwhile, in the condensed water, TBBPS can also be completely removed with a decrease of the average TOC content from 25.56 mg/L to 4.97 mg/L. EPR detection reveals that the dominant reactive species are •OH, SO4-•, and 1O2. Moreover, the presence of SO42- can enhance the conversion of •OH to SO4-•, thereby improving the utilization of reactive species by increasing the contribution of SO4-•. The degradation intermediates of TBBPS were detected by IC and LC-MS, based on which the possible degradation mechanism of TBBPS was proposed. The synergistic treatment process can not only promote the resource utilization of waste salt and reduce the difficulty of condensed water treatment but also improve the stability of the evaporation system.

MgMnxOy-GAC particle electrode for effective peroxone oxidation: High salinity organic wastewater treatment with synergistic electrocatalytic ozonation

A three-dimensional electro-peroxone (3D-EP) system achieved efficient degradation of high salinity organic wastewater and showed significant implications for potential application. Herein, an MgMn-granule-activated carbon (GAC) particle electrode was developed through impregnation calcination and applied in multipollutant removal. The integration of electrolysis, ozone application, and MgMn-GAC in the 3D-EP system manifested strong synergy, leading to successful elimination of all phenol within 30 min due to ample hydroxyl radical production. The energy consumption of MgMn-GAC was 1.86 kWh·m−3 and the specific energy consumption was 0.033 kWh·g−1 COD, exhibiting high electrical energy utilization efficiency under low applied current and low O3 exposure conditions. After six consecutive reaction experiments, COD removal reached 95.6 %, demonstrating remarkable catalytic activity and cycling stability. The study findings indicate that this material could be used as a low-cost particle electrode for practical wastewater treatment.

Enhancing membrane distillation efficiency in treating high salinity organic wastewater: A pressure-driven membrane electrochemical reactor approach

Fouling of membranes continues to be a prominent challenge in the membrane distillation (MD) treatment of high salinity organic wastewater (HSOW). Although membrane electrochemical reactor (MER) can effectively inhibit the membrane fouling of MD, the high cost of the proton exchange membrane (PEM) used in MER limits its widespread application. In this study, cost-effective pressure-driven membranes were employed as a substitute for PEM to establish pressure-driven membrane electrochemical reactors for HSOW pre-treatment. By using ultrafiltration membrane (UFM) and reverse osmosis membrane (ROM), UFMER and ROMER were developed, respectively. Due to the superior electrochemical performance of UFM, UFMER saved 43 % of energy compared to PEMER with the highest removal rate of organics (~85 %) in the simulated HSOW treatment. In practical applications, using UFMER significantly reduced the amount and size of complexes in the real nanofiltration concentrate (NC) of landfill leachate. This contributed to the superior specific flux maintenance (97 %) with a salt rejection (>99 %) and the highest recovered specific water flux (99.6 %) in MD cases. UFMER reduced ~27 % of energy compared to PEMER in MER pre-treatment, and saved the most energy (~39.6 %) in MD post-treatment. Hence, this strategy is potential for forthcoming applications, notably in lowering the membrane cost of MER and energy consumption of both MER and MD.

Study on regeneration characteristics of granular activated carbon using ultrasonic and thermal methods.

Dye wastewater is a type of high-concentration, high chromaticity, and high salinity organic wastewater, which is generally treated with activated carbon adsorbent. The effective regeneration of granular activated carbon (GAC) is the key to reducing the operating cost of GAC in the wastewater treatment process. The regeneration characteristics of saturated GAC adsorbed on 288 orange dye wastewater were studied by using the ultrasonic coupled thermal regeneration method. The results showed that the regeneration efficiency of GAC adsorbed on 288 orange dye wastewater increased with the increase of ultrasound power. The optimal ultrasound frequency and regeneration temperature were determined to be 45kHz and 60 ℃, and the relationship between regeneration times and carbon loss rate was explored. The combination of ultrasound and high-temperature heating methods has successfully improved the regeneration efficiency of GAC and significantly reduced the high-temperature thermal regeneration time of GAC, thereby reducing the mass loss rate of GAC. The performance changes of fresh activated carbon (FAC), saturated activated carbon (SAC), ultrasonic regeneration of activated carbon (UAC), and thermal regeneration of activated carbon (TAC) during the combined regeneration process were explored by characterizing the regenerated GAC. Infrared characterization showed that the C-O group of GAC was significantly weakened after coupling treatment, indicating that ultrasonic treatment can significantly enhance the desorption effect of thermal regeneration. The microjet, shock wave, and cavitation effects generated by ultrasonic treatment restore the specific surface area of GAC, mainly increasing the micropore volume and pore size of GAC, and enhancing the treatment effect of thermal regeneration.

Feasibility of replacing proton exchange membranes with pressure-driven membranes in membrane electrochemical reactors for high salinity organic wastewater treatment

Membrane electrochemical reactor (MER) shows superiority to electrochemical oxidation (EO) in high salinity organic wastewater (HSOW) treatment, but requirement of proton exchange membranes (PEM) increases investment and maintenance cost. In this work, the feasibility of using low-cost pressure-driven membranes as the separation membrane in MER system was systematically investigated. Commonly used pressure-driven membranes, including loose membranes such as microfiltration (MF) and ultrafiltration (UF), as well as dense membranes like nanofiltration (NF) and reverse osmosis (RO), were employed in the study. When tested in a contamination-free solution, MF and UF exhibited superior electrochemical performance compared to PEM, with comparable pH regulation capabilities in the short term. When foulant (humic acid, Ca2+ and Mg2+) presented in the feed, UF saved the most energy (43 %) compared to PEM with similar removal rate of UV254 (∼85 %). In practical applications of MER for treating nanofiltration concentrate (NC) of landfill leachate, UF saved 27 % energy compared to PEM per cycle with the least Ca2+ and Mg2+ retention in membrane and none obvious organics permeation. For fouled RO and PEM with ion transport impediment, water splitting was exacerbated, which decreased the percentage of oxidation for organics. Overall, replacing of PEM with UF significantly reduce the costs associated with both the investment and operation of MER, which is expected to broaden the practical application for treating HSOW.

Mechanism insights into salt tolerance strengthened by CoCe encapsulated N-doped CNTs cathode in microbial fuel cell

To address the challenges of bioanode deactivation and instability of cathode catalysts in the treatment of high-salt organic wastewater using microbial fuel cells (MFCs), a series of CoCe catalysts encapsulated within nitrogen-doped carbon nanotubes (CoCe@NCNTs) was synthesized using a one-pot calcination method. Among the synthesized catalysts, CoCe0.5@NCNTs demonstrated outstanding and stable electrochemical performance in a high-salt environment with 600 mM NaCl, achieving a power density of 144.29 mW m−2, which was 2.7 times higher than that of Co@NCNTs. Notably, the characterization of the catalyst revealed that the addition of Ce element enhanced the stability of the Co crystal structure, mitigated Co leaching, and facilitated the retention of a higher valence state of the Co species after the reaction under high salt conditions. Specifically, the Co3+/(Co2+ + Co3+) ratio in CoCe0.5@NCNTs was 2.82 times larger than that of Co@NCNTs, signifying the favorable influence of the mutual electron conversion between the bimetallic Ce and Co on the performance and stability of catalyst in a high-salt environment. Furthermore, the study assessed the removal efficiency of norfloxacin (NOR), NAD+/NADH ratios, and microbial diversity in conjunction with the stability of cathode electrochemical performance, demonstrating the interconnection between cathode and anode. By considering the practical challenges in treating high-salinity wastewater and the principles of bioelectrochemistry, this paper proposes a mechanism for enhancing anode performance through cathode linkage, thereby providing a novel strategy for MFCs to treat high-salinity organic wastewater treatment.

Wastewater from natural gas Cansolv desulfurization process: Comprehensive characterization and effective removal of organic compounds

The wastewater generated by the solvent amine desulfurization process in natural gas purification plants is characterized by its recalcitrant organic compounds and high salinity. Without effective treatment, it has the potential to inflict severe environmental harm. The composition of organic matter, however, exerts a profound influence on the outcomes of oxidation processes. To rectify the limitations associated with indiscriminate oxidation that yields suboptimal results, this investigation meticulously performed a molecular-level analysis of organic matter. Based on the organic matter composition in the influent, this study compared the treatment efficacy of three oxidation processes and determined O3/H2O2-Fenton as the optimal joint approach. After O3/H2O2 oxidation, long-chain unsaturated organic compounds (C > 40,DBE > 20) underwent degradation into short-chain aldehydes and low-molecular-weight fatty acids, with priority given to reactions involving CC, CO, and OH over CH reactions. Subsequent Fenton oxidation effectively removed the refractory organics (CHOS, CHONS) and significantly reduced the diversity of organic matter (from 7730 to 4237). The carboxylation, demethylation, and dehydrogenation reactions further facilitated the removal of recalcitrant organic compounds. In light of these findings, this study substantiates that the conversion of extended-chain unsaturated compounds into abbreviated-chain saturated compounds within the system through O3/H2O2 oxidation significantly enhances the subsequent efficacy of Fenton oxidation in organic matter removal. These insights offer valuable perspectives for the efficient remediation of analogous high-salinity organic wastewater scenarios.

In-situ Cu-loaded sludge biochar catalysts for oxidative degradation of bisphenol A from high-salinity wastewater

Safe disposal of excess sewage sludge (SS) produced from chemical/biochemical water treatment processes has been a worldwide concern. In this work, sewage sludge biochar-based Cu-loaded catalysts (CSBC) were synthesized by a simple impregnation-pyrolysis method. The impregnated Cu2+ in SS was converted to Cu0/CuI species after pyrolysis, which greatly improved the removal efficiency of bisphenol A (BPA). BPA (100 mg/L) could be completely removed within 130 min in CSBC/Peroxydisulfate (PDS) system, compared to 77.8% in sewage sludge biochar/PDS system. Meanwhile, CSBC performed well over a wide pH range of 3∼9. In CSBC/PDS system, singlet oxygen (1O2) dominated non-radical pathway had been proved to play an essential role in BPA degradation, boosting the oxidative treatment of phenolic wastewater under high-salinity. Results showed that the removal efficiency of BPA reached 93.6%, 91.0% and 84.6% in high-salinity wastewater with salinities of 16, 80, and 160 g/L, respectively. The total estimated cost of CSBC (1 kg) was $5.053 and the cost of BPA-containing wastewater (100 mg/L) treatment was estimated approximately 0.02 $/L, indicating its cost-effectively potential in practical applications. This study not only provides a new value-added reuse method for sewage sludge treatment and disposal, but also a new strategy for the effective treatment of high-salinity organic wastewater.

Insight into the effect of rice-straw ash on enhancing the anaerobic digestion performance of high salinity organic wastewater

Anaerobic digestion is an economic method for treating high salinity organic wastewater (HSOW), but performance enhancement is needed because of the inhibitory effect of high salinity. In this study, rice-straw ash (RSA) was applied to alleviate the inhibitory effect during HSOW anaerobic digestion. The results showed that, when the NaCl content increased from 0% to 3.0%, the methane production decreased by 87.35%, and the TOC removal rate decreased to 34.12%. As a K+ and alkalinity source, RSA addition enhanced the anaerobic digestion performance, and the optimal dosage was 0.88 g/L. Under this dosage, the methane production increased by 221.60%, and TOC removal rate reached 66.42% at 3.0% salinity. The addition of RSA increased the proportion of living cells in the high salinity environment, and enhanced the activity of key enzymes and electron transfer efficiency in the anaerobic digestion process. The addition of RSA with a dosage of 0.88 g/L promoted the accumulation of acetoclastic methanogen Methanothrix. The abundance of substrate transporters, ion transporters and electron transfer related functional genes were enriched, which might be key for promoting HSOW anaerobic digestion performance. The results also showed that RSA addition played an important role in maintaining the stability of the anaerobic digestion system, and it could be a potential strategy for enhancing the anaerobic digestion performance under high salinity conditions.

Rapid start-up of anaerobic digestion reactor with rice-straw ash addition for treating high salinity organic wastewater

Anaerobic digestion is an economic method to treat high-salinity organic wastewater (HSOW). However, due to the inhibitory effect of high salinity, the start-up of the anaerobic digestion reactor is slow and easy to fail. In this study, as a potassium source, rice-straw ash (RSA) was used to enhance the HSOW treatment performance and shorten the start-up time of anaerobic digestion reactor under 3.0% NaCl content and high loading rate. The results showed that RSA could provide adequate potassium ion (K+) for alleviating the inhibitory effect of high salinity on anaerobic microorganisms. The rapid start-up of the anaerobic digestion reactor was realized, and the TOC removal rate reached 81.65%. In the reactor with RSA addition, the activities of dehydrogenase, acetic kinase and coenzyme F420 were 25.67%− 89.81%, 19.03%− 50.93% and 35.83%− 944% higher than that of the control reactor, respectively. The addition of RSA promoted the accumulation of acetoclastic methanogen Methanothrix, and changed the methanogenic pathway from hydrogenotrophic methanogenesis in the beginning stage of anaerobic digestion to acetoclastic methanogenesis under high salinity condition. After stopping the addition of RSA, the performance of the anaerobic digestion reactor remained stable, indicating that RSA was only needed at the start-up stage. This study could provide a feasible method for rapid start-up of anaerobic digestion reactor treating HSOW in practice.

Mn(VII) enhanced by CaSO3 to remove trace organic pollutants in high salt organic wastewater: Further enhancement of salinity

The high concentration of salt in organic wastewater has a strong inhibitory effect on the removal of pollutants. A method for the efficient removal of trace pollutants in high-salinity organic wastewater was developed. This study investigated the effect of the combination of permanganate [Mn(VII)] and calcium sulfite [S(IV)] on pollutant removal in hypersaline wastewater. The Mn(VII)-CaSO3 system removed more pollutants from high-salinity organic wastewater than from normal-salinity wastewater. Chloride (increasing from 1 M to 5 M) and low concentration of sulfate (increasing from 0.05 M to 0.5 M) significantly enhanced the system's resistance to pollutants under neutral conditions. Despite the fact that Cl− can combine with the free radicals in the system and reduce their efficiency in removing pollutants, the presence of chloride ions greatly enhances the electron transfer rate in the system, promoting the conversion of Mn(VII) to Mn(III) and significantly increasing the reaction rate of Mn(III) as the primary active species. Therefore, chloride salts can greatly enhance the removal of organic pollutants by Mn(VII)-CaSO3. Although sulfate does not react with free radicals, a high concentration of sulfate (1 M) will affect the formation of Mn(III), which greatly weakens the removal effect of the entire system on pollutants. The system can still have a good pollutant removal effect with mixed salt. Altogether, this study demonstrates that the Mn(VII)-CaSO3 system offers new possibilities for the treatment of organic pollutants in hypersaline wastewater.

Pilot-scale study and biochemical verification of salt-tolerant catalyst Fe-Bi@γ-Al2O3 for catalytic ozonation of high-salinity wastewater

In this study, Fe-Bi@ γ-Al2O3 was used as a catalyst to construct a heterogeneous catalytic ozonation system for the treatment of high-salinity organic wastewater and its biochemical verification was studied. The optimum operating conditions and degradation mechanism of Fe-Bi@ γ-Al2O3 catalytic ozonation of high salinity wastewater were systematically investigated. The biodegradability of wastewater before and after treatment was also studied. Under the optimum operating conditions of ozone dosage of 160 mg/L, catalyst filling rate of 15%, ratio of height to diameter of 15, hydraulic retention time of 210 min and recycle ratio of 500%, the removal rate of COD is 45.13%. The mechanical strength of Fe-Bi@ γ-Al2O3 catalyst is almost unchanged after being reused for 20 times. The results of Ultraviolet and visible spectrophotometry (UV-Vis), 3D (Three-Dimensional)-fluorescence and Gas Chromatography-Mass Spectrometer (GC-MS)showed that humus, fulvic acid and undissolved microbial organic matter were degraded. In the biochemical verification experiment, after the high salinity wastewater was used to impact the bio-reactor, the mixed liquor suspended solids (MLSS) was basically stable at 9597 mg/L, 8856 mg/L, 9414 mg/L and 8741 mg/L, and the mixed liquor volatile suspended solids (MLVSS) was basically stable at 7042 mg/L, 6940 mg/L, 6949 mg/L and 6519 mg/L. The dissolved oxygen (DO) in the four reactors were 2.9 mg/L, 3.48 mg/L, 3.6 mg/L and 2.92 mg/L respectively, and the sludge Volume Index (SVI30) were 93 mL/g, 98 mL/g, 93 mL/g and 91 mL/g respectively. After two cycles (20d) of 30% high salinity wastewater, the chemical oxygen demand (COD) removal rates of the four reactors were 78%, 84%, 86% and 91%, respectively. When the reaction time is 40 min, the BOD5/COD (B/C) value of the high-salinity wastewater reaches 0.91, and the biodegradability of the wastewater is improved significantly. Scanning electron microscope (SEM) showed that the granular sludge in the reactor had compact structure and smooth surface, and there were a lot of fungi and filamentous microorganisms on the sludge surface.in that condition of salinity stress, the microbial community in the activate sludge changed to a great extent, and Proteobacteria and Bacteroidetes became the main phylum. The Fe-Bi@ γγ-Al2O3 catalyst has good catalytic performance and can be used for deep treatment of high-salt organic wastewater.

Removal of chemical oxygen demand and ammonia nitrogen from high salinity tungsten smelting wastewater by one-step electrochemical oxidation: From bench-scale test, pilot-scale test, to industrial test

In recent years, electrochemical oxidation (EO) shows the characteristics of green and high efficiency in removing chemical oxygen demand (COD) and ammonia nitrogen (NH3–N) from wastewater, which has been favored by researchers. However, at present, most of current studies on EO remain in laboratory stage, reports about pilot-scale or even industrial tests with large treatment capacity are few, which slowing down the use of the advanced technology to practical application. In this study, bench-scale tests, pilot-scale tests (treatment capacity 200–500 L/h), and industrial tests (treatment capacity 100 m3/h) were carried out by EO technology in view of the characteristics of tungsten smelting wastewater (TSW) with high salinity (NaCl), COD, and NH3–N. Results showed that the removal of COD and NH3–N was a competitive reaction in the EO process, and COD could be removed more preferentially than NH3–N. When NH3–N content was low, the influent pH had a minimal effect on its removal, and when NH3–N content was high, increasing the influent pH was beneficial to its removal. Industrial tests showed that the one-step removal of COD and NH3–N in TSW met the standard, and the power consumption per cubic meter of wastewater was only 4.2 kW h, and the treatment cost was much lower than the two-step process of “breaking point chlorination to remove NH3–N and adding oxidant to remove COD”. This study has successfully realized industrial application of EO technology in TSW treatment for the first time and provided a successful case, which is helpful to accelerate the popularization and application of this technology in the field of high salinity organic ammonia nitrogen wastewater treatment.

Research Progress of High-Salinity Wastewater Treatment Technology

With the continuous expansion of industrial enterprises, a large amount of high-salt wastewater with complex components is produced. Direct discharge will cause great harm to the ecosystem and waste a large amount of potential salt resources. This paper summarizes the source, water quality characteristics, and environmental impact of high-salinity wastewater, and introduces the desalination and treatment technologies of high-salinity wastewater. The desalination technology of high-salinity wastewater mainly includes two processes: concentration and crystallization, obtaining concentrated solution through membrane concentration or thermal concentration and then carrying out crystallization treatment on the concentrated solution, thereby realizing the recovery of salt. The advanced treatment technologies of high-salinity wastewater were analyzed, including physicochemical treatment, biological treatment, and coupling treatment. Catalytic ozonation is one of the most widely used physicochemical technologies for the advanced treatment of high-salinity wastewater. Biological treatment processes operating in the presence of halotolerant bacteria show excellent performance at high salinity. High salinity has a negative impact on the performance of various physicochemical processes and biological treatment technologies. However, high salinity has little effect on the performance of a coupled system designed to treat high-salinity wastewater. In this review, the effect of salinity on the scaling and corrosion of equipment is also illustrated. It is suggested that the research direction of high-salinity wastewater should be to develop new membrane materials and catalysts, develop salt-tolerant microorganisms, explore high-efficiency and energy-saving physico–chemical–biochemical combination processes, improve the treatment efficiency of high-salinity organic wastewater, and reduce treatment costs.

Enhancement of methane production in anaerobic digestion of high salinity organic wastewater: The synergistic effect of nano-magnetite and potassium ions

During high salinity organic wastewater (HSOW) anaerobic digestion treatment, the process of methanogenesis can be severely inhibited in the high salinity environment, and the accumulation of volatile organic acids (VFAs) leads to failure of the anaerobic reaction. In this study, nano-magnetite and KCl were adopted to alleviate the inhibitory effect of high salinity and enhance the HSOW anaerobic digestion performance. The result showed that, under the optimal dosage of 200 mg/L, nano-magnetite addition promoted the anaerobic digestion performance, and the methane production increased by 11.06%. When KCl was added with a dosage of 0.174%, the methane production increased by 98.37%. The simultaneous addition of nano-magnetite (200 mg/L) and KCl showed a synergistic effect on enhancing HSOW anaerobic digestion performance, and the methane production increased by 124.85%. The addition of nano-magnetite and KCl promoted the conversion of VFAs, especially accelerated the degradation of propionic acid and butyric acid, also it promoted the activity of acetate kinase, dehydrogenase and F420, and thereby enhanced the methanogenesis process. This study could provide a new method for enhancing the anaerobic digestion of HSOW.

Solidification/stabilization of organic matter and ammonium in high-salinity landfill leachate concentrate using one-part fly ash-based geopolymers

Landfill leachate concentrate (LLC) is a high-salinity organic wastewater produced in the process of membrane separation and has become an urgent problem because of its complex composition and high biological toxicity. Solidification/stabilization (S/S) technology using geopolymers provides a feasible and economical zero-discharge LLC treatment method. This study developed one-part fly ash-based geopolymers using LLC as the only solvent. The results showed that the solid alkali activator significantly increased the LLC treatment capacity with a high liquid−solid ratio of 0.55. The high-salinity LLC significantly promoted the substitution of Al for Si and improved the compressive strength of the geopolymers. Three leaching experiments showed that the prepared geopolymers had excellent stability, high S/S rates for organic matter (92.9%) and NH3-N (91.4%), and a high contaminant removal rate to reduce acute biological toxicity. Microscopy tests showed that sodium aluminosilicate hydrate (N-A-S-H) gel was the main component of the fly ash-based geopolymers after the addition of LLC. Cl− attached to the surface of the geopolymer gels through exchange with OH−, while SO42− was bound within the geopolymer structure in the form of Na2SO4 crystals. There was no evidence that organic matter and NH3-N were chemically combined with the geopolymer material, rather, they were physically encapsulated within the geopolymer structure. This study proposes a technical strategy for LLC S/S using fly ash-based geopolymer. The geopolymer can be used as a new building material, which provides a new perspective for the treatment of LLC and the utilization of fly ash resources.

Fabrication of S-PBI cation exchange membrane with excellent anti-fouling property for enhanced performance in electrodialysis

A novel anti-fouling cation exchange membrane (CEM) of sulfonated polybenzimidazole (S-PBI) was fabricated by the polymer bulk grafting modification of poly (4,4′-diphenyl ether-5,5′-bibenzimidazole) with sodium styrene sulfonate. FTIR, TGA, XPS, SEM and AFM were used to characterize membrane properties and the results showed that the ion exchange capacity and hydrophilicity of S-PBI increased with increased degrees of grafting and the electric resistance decreased accordingly. When the mass ratio of O-PBI/SSS was 1:4, the electric resistance of S-PBI-4.0 was 4.5 Ω·cm2, while the ion exchange capacity was 2.3 meq/g. The ED experiment with the S-PBI-4.0 membrane exhibited good desalination rate (>96 %), high current efficiency (80.73 %) and low energy consumption (1.13 kW·h/kg), which were very close to the results of a commercial CEM (Neosepta CMX). What's more, because of its good hydrophilicity, the S-PBI-4.0 membrane had better anti-fouling ability than Neosepta CMX, which was manifested as less resistance increase after membrane fouled by bovine serum albumin and smaller resistance after membrane cleaned by deionized water. These results demonstrate that the S-PBI-4.0 membrane is an appropriate candidate CEM and helpful to expand the application of ED in high-salinity organic industrial wastewater treatment.

Dye mineralization under UV/H2O2 promoted by chloride ion at high concentration and the generation of chlorinated byproducts.

Chloride ion (Cl-) may promote or inhibit the oxidation of specific organic compounds treated by hydroxyl radical based advanced oxidation processes (HR-AOPs) depending on the reactivity of chlorine radicals towards the organics. However, the effects of high contents of Cl- on the removal of total organic compounds (TOC) in high salinity organic wastewater treated by HR-AOPs were unclear. The removal and mineralization of azo dye Orange II (OrgII) by UV/H2O2 process with Cl- at high contents under various pH conditions were investigated. As the pH conditions increased higher than pH 5, TOC removal rates increased slightly possibly related to the increase of O2- production and the reduce of futile decomposition of H2O2 into O2. Cl- at relative high concentration (1000 and 2000 mM) significantly promoted the mineralization of dyes with TOC removal increasing by 10 %-40 % under both acid and alkaline conditions. The proposed mechanism is that the reaction of Cl- with OH would decline the decomposition of H2O2 into O2 by inhibiting the reaction between OH and H2O2, and the generated chlorine species (Cl and Cl2-) could further promote the oxidation of dye molecules into intermediates and be helpful for the subsequent mineralization process. In addition, H2O2 and Cl- can slowly react to give HClO and ClO-, which may partly contribute to the decolorization and mineralization of OrgII. Meanwhile, an appropriate relative proportion between Cl2- and OH depending on Cl- contents and pH conditions is important to enhance the TOC removal. However, the formation of various chlorinated byproducts especially under alkaline condition may increase the risk of environmental pollution accidents. The results demonstrate the promotion of TOC removal by UV/H2O2 under certain high contents of Cl- and provide new insight into the application of HR-AOPs to the pretreatment of high salinity organic wastewater.