Actual Surface Water Research Articles

Nano-Fe3O4/FeCO3 modified red soil-based biofilter for simultaneous removal of nitrate, phosphate and heavy metals: Optimization, microbial community and possible mechanism

The pollution of nitrogen, phosphorus and heavy metals in surface water is becoming more and more serious, affecting the safety of water quality. In this study, three biofilters were constructed using iron-modified red soil-based filler carriers (RSC, nano-Fe3O4@RSC, and FeCO3@RSC) combined with strain Zoogloea sp. ZP7 to simultaneously remove nitrate (NO3--N), phosphate (PO43--P), copper (Cu2+), and zinc (Zn2+). The long-term operation results showed that the three groups of biofilters could remove 85.0, 90.0, and 89.8% of NO3--N, respectively. Furthermore, the addition of iron compounds enhanced the removal of PO43--P and the resistance to the stress of Cu2+ and Zn2+ in the biofilter. The analysis illustrated that iron modification improved the redox activity and zeta potential of RSC surface. The secondary structure analysis of the protein showed that the microbial secreted proteins were more compact on the surface of the iron-modified RSC, which facilitated the formation of biofilm on the carrier surface. In addition, the iron-modified RSC-based biofilter also showed excellent NO3--N and PO43--P removal efficiency in the treatment of actual surface water. The microbial community analysis results showed that Zoogloea became the dominant species in the biofilter. On the other hand, the presence of iron-reducing bacteria and the expression iron cycle-related genes may contribute to denitrification under low nutrient conditions.

Electro-assisted carbon nanotube dual catalytic membrane system for high-efficiency and energy-efficient water treatment

Improving performance of peroxymonosulfate (PMS) catalytic membrane via electrochemical assistance renders an effective way for water decontamination. However, the current cathodic or anodic membrane based electro-assisted PMS catalytic single-membrane systems (EPSM) usually suffer from their inherent deficiencies. Herein, a novel electro-assisted PMS catalytic dual-membrane system (EPDM) was constructed by employing two electro-conductive carbon nanotube membranes as the anodic and cathodic membranes, in order to couple the advantages of anodic and cathodic catalytic membranes for enhanced water treatment. Moreover, the filtration sequence (anode–cathode (A-C) or cathode–anode (C-A)) was varied to explore its effect on EPDM performance. Results showed the EPDM operated in C-A mode achieved ultrafast (0.95 s−1) and energy-efficient (0.008 kWh m−3) removal towards sulfamethoxazole (SMX), and its SMX mineralization rate was 1.7 times higher than that of EPDM operated in A-C mode and 5.1 or 2.4 times higher than that of cathodic or anodic membrane based EPSM. Meanwhile, the EPDM also displayed efficient fouling mitigation on both membrane surface and pores. Furthermore, EPDM can maintain high performance and good stability in long-term actual surface water treatment. The outstanding performance of EPDM operated in C-A mode was attributed to the collaboration of cathodic and anodic membranes: For one thing, cathodic and anodic membranes sequentially activated PMS to produce radicals (OH and SO4−) and non-radicals (1O2 and electron transfer) for enhanced pollutant oxidation; for another, both membranes in C-A mode effectively resisted coexisting interferents in real water.

Novel Zn-based Metal Coordination Polymer for Ultrafast Capture and Electrochemical Sensing of Hg(Ⅱ)

The electrochemical sensor shows great promise in the detection of trace Hg(Ⅱ), of which the performance could be significantly enhanced by the functionalized material with the merits of effective and ultrafast capture for Hg(Ⅱ). In this study, the novel metal coordination polymers (MCPs) was synthesized by the 2-thio-barbituric acid as the organic ligand to modify the electrochemical sensor to address this issue. The as-prepared material was composed of regular flakes with a polyhedral and well-defined crystal structure, the successful loading of the abundant sulfurous group (7.49% of the total mass) endowed the Zn-TBA with the capability to efficiently uptake (97.4-99.9%) Hg(Ⅱ) at 500mg/L under a wider pHs as well as the high content of coexisting cations and anions, highlighted the excellent capacity, strong environmental adaptability, and selectivity. Notably, the superfast mass transfer was revealed in the adsorption kinetics test, in which the Hg(Ⅱ) content was effectively reduced from 50mg/L to 14 μg/L within 20s to meet the national emission standards. Based on this, Zn-TBA modified the carbon cloth (Zn-TBA/CC) and the glass carbon electrode (Zn-TBA/GCE) was prepared, thereinto, the current response of Zn-TBA/CC was approximately 60 times that of the pristine electrode. A strong positive correlation (R2=0.998) relationship could be attained across the content of 0.25-3μM, achieving the detection limit to be 0.29μM. The impressive performance was maintained in the complex matrices and regeneration test. In addition, Zn-TBA/CC exhibited better physical properties, charge transfer ability, and sensing properties than Zn-TBA/GCE, highlighting the advantages of CC as a flexible sensor substrate. Finally, the stable recovery (90-98.5%) in the spiked actual surface water confirmed that the two established methods possessed a promising application potential in capturing and detecting the trace Hg(Ⅱ) with high accuracy and precision. This study extended the application of MCPs in the electrochemical sensor and provided an available analysis method to trap and determine the metal content.

Surface engineered waterworks sludge embedded PAN electrospun membrane for efficient and selective removal of phosphate in actual surface water

Advanced adsorbents for selective removal of excessive phosphorus in actual surface water bodies and safe disposal of waterworks sludge are essential due to environmental risks and resource wastes. Herein, a strategy of killing two birds with one stone was proposed to design a La(OH)3/iron-based waterworks sludge/polyacrylonitrile (La(OH)3/IS/PAN) membrane for selective removal of phosphate. In this strategy, nano-La(OH)3 was well-dispersed on IS surface to realize functionalization of IS, and PAN electrospun nanofibers prevented powdered La(OH)3/IS from loss. The membrane showed a maximum adsorption capacity of 19.89 mg/L at 25 °C and remained relatively stable phosphate adsorption capacity under various anions interference. More importantly, after adsorption, the total phosphorus (TP) of the actual surface water from Yudai river was reduced to meet the requirement of the surface water standard of China, Ⅱ (GB 3838–2002). The work provides a novel way to overcome the challenges posed by eutrophication and sludge problems for industrial applications.

C3N4-interlayer-mediated interfacial polymerization of homopolymer nanofiltration membranes for efficient water purification

Interlayered thin film composite (TFNi) membranes have been shown to achieve high-quality polyamide (PA) skin layers with enhanced permeability and selectivity. Herein, we demonstrate the construction of a hydrophilic interlayer by polymeric graphitic carbon nitride (g-C3N4) for optimizing the interfacial polymerization of the nanofiltration membrane. Due to the effective enrichment and the slowed diffuse rate of amine monomer solutions, g-C3N4 modification decreases the thickness of the PA skin layer and increases the electronegativity of membranes. The best TFNi membrane exhibits a high water permeance of 31.82 L m−2 h−1 bar−1, nearly twice as high as that of the membrane without g-C3N4 interlayer, while maintaining a comparably Na2SO4 rejection efficiency. The stronger hydrophilicity and more negatively charged surface of the TFNi membrane effectively retarded membrane fouling, contributing to the high-efficiency removal of harmful drugs from actual surface water, with more than two times higher water flux that of commercialized NF270 membrane. This work provides a facile strategy to synthesize TFNi membranes with great application potential for high-performance nanofiltration.

Estimation of stability constants of Fe(III) with antibiotics and dissolved organic matter using a novel UV–vis spectroscopy method

Determining conditional stability constant (Kcond) is paramount in assessing complex stability, particularly in Fe(III) complexes that are prevalent in actual surface water and wastewater matrices. In this study, existing methods of Kcond determination were evaluated and a novel UV–Vis spectroscopy method was proposed based on the evaluation of these approaches. Model ligands (ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and oxalic acid (OA)), as well as common antibiotics (kanamycin (Kana) and tetracycline (TTC)), were employed to determine the Kcond of the Fe(III)-ligand complexes under neutral conditions (pH 6.5). The obtained fitting results revealed that the logKcond were in the order of Fe(III)-EDTA (7.08) > Fe(III)-NTA (4.67) > Fe(III)-OA (4.32) > Fe(III)-TTC (4.28) > Fe(III)-Kana (3.07). In addition to these single ligands, the methodology was extended to the Fe(III) complexation with humic acid (HA), a complex mixture of organic components, where the fitting result indicated a logKcond of 5.02 M−1. The method's application domain was analyzed by numerical analysis and combined with experimental results. The findings demonstrate that the proposed methodology possesses satisfactory measurement capability for Kcond ranging from 103 to 107 M−1, suggesting its broad applicability to the majority of complexes. This method can provide valuable insights into the impact of Fe(III) complexes within the water matrix.

Adsorption of lead ions by activated carbon doped sodium alginate/sodium polyacrylate hydrogel beads and their in-situ recycle as sustainable photocatalysts

In this study, sodium alginate (SA), sodium polyacrylate (PAAS) and powdered activated carbon (PAC) were cross-linked by calcium ions [(Ca(II)] to form SA/PAAS/PAC (SPP) hydrogel beads. The hydrogel-lead sulfide (SPP-PbS) nanocomposites were successfully synthesized by in-situ vulcanization after the lead ions [(Pb(II)] adsorption. SPP showed an optimal swelling ratio (600% at the pH value of 5.0) and superior thermal stability (206 °C of heat-resistance index). The adsorption data of Pb(II) was compatible with the Langmuir model, and the maximum adsorption capacity of SPP was 391.65 mg/g after optimizing the mass ratio of SA to PAAS (3:1). The addition of PAC not only enhanced the adsorption capacity and stability, but also promoted photodegradation. The significant dispersive capacity of PAC and PAAS resulted in PbS nanoparticles with particle sizes of around 20 nm. SPP-PbS showed good photocatalysis and reusability. The degradation rate of RhB (200 mL, 10 mg/L) was 94% within 2 h and maintained above 80% after 5 cycles. The treatment efficiency of SPP was more than 80% in actual surface water. The results of quenching experiments and electron spin resonance (ESR) experiments revealed that the superoxide radicals (O2–) and holes (h+) were the main active species in the photocatalytic process.

Ascorbic acid promoted sulfamethoxazole degradation in MIL-88B(Fe)/H2O2 Fenton-like system

In this work, the presence of ascorbic acid (AsA) in MIL-88B(Fe)/H2O2 system was demonstrated to significantly increase the sulfamethoxazole (SMX) degradation efficiency. The SMX degradation rate in AsA/MIL-88B(Fe)/H2O2 system was 0.177 L/(mg∙min), which was 60 times that of the MIL-88B(Fe)/H2O2 system. Moreover, the study shows that AsA not only promotes SMX degradation in Fenton-like systems but also expands its pH application range. The effect of coexisting anions on the catalytic performance of the AsA/MIL-88B(Fe)/H2O2 system was also investigated. Then, reactive species were detected via quenching experiments, which indicated •OH as the dominant free radical contributing to SMX degradation. Meanwhile, ESR determinations confirmed the existence of •OH and O2 − • in AsA/MIL-88B(Fe)/H2O2 system. The high activity of the AsA/MIL-88B(Fe)/H2O2 system was attributed to the effective surface Fe(III)/Fe(II) cycle promoted by AsA, and a possible mechanism of the AsA/MIL-88B(Fe)/H2O2 system is proposed. The possible pathways for SMX and AsA degradation in the AsA/MIL-88B(Fe)/H2O2 system are proposed based on the identified intermediates and the ecotoxicity analysis was conducted by ECOSAR. Finally, experimental results using the actual surface water and groundwater revealed the excellent availability of AsA/MIL-88B(Fe)/H2O2 system in remediating SMX contaminated water. This study presents a novel, efficient Fenton-like system using AsA and iron-based metal-organic frameworks for sulfonamide removal from water.

Simultaneous phosphorus removal and adsorbents recovery with Ca-PAC assisted adsorption dynamic membrane system: Removal performance and influencing factors

Ca(OH)2 treated powdered activated carbon (Ca-PAC) assisted adsorption dynamic membrane system was proposed for simultaneous phosphorus adsorption and micrometer scale adsorbent recovery. In Ca-PAC assisted adsorption dynamic membrane system, adsorption and dynamic membrane separation acted as the key roles for pollutants removal. At first, the effect of Ca(OH)2 concentration in Ca-PAC preparation was evaluated. Phosphorus removal rate increased from 3.79% to 98.01% when added Ca(OH)2 concentration was increased from 0 to 2 M in PAC treatment. Effect of initial phosphorus concentration, reaction temperature, and solution pH on phosphorus removal with Ca-PAC was explored in this study. And then, adsorption isotherms, adsorption kinetics, SEM, XRD, and FTIR were conducted to explain the phosphorus adsorption. Ligand exchange between hydroxyl on Ca-PAC and phosphate was confirmed to be the main phosphorus removal mechanism, with little Ca–P precipitation verified in X-ray diffraction (XRD) analysis. At last, integrated adsorption dynamic membrane system was operated with Ca-PAC, showing more than 90% phosphorus adsorbed in 1 min and 63.25%–87.65% micrometer scale Ca-PAC recovered. Overall, adsorption-dynamic membrane system presents to be stable and applicable in deep phosphorus removal and micrometer scale adsorbent recovery, which presents a new route for micrometer scale adsorbent application and recovery in actual surface water and wastewater treatment.

Efficient electrocatalytic nitrate reduction in neutral medium by Cu/CoP/NF composite cathode coupled with Ir-Ru/Ti anode

In this work, a three-dimensional self-supporting copper/cobalt phosphide/nickel foam (Co/CoP/NF) composite was fabricated and employed as the cathode for electrochemical nitrate removal from surface water with the assistance of a commercial Ir-Ru/Ti anode. The experimental results demonstrate that the introduction of Cu nanoparticles on CoP nanosheets is favorable for the electrocatalytic nitrate reduction. The influences of operating parameters (pH value, current density and initial nitrate concentration) on the nitrate reduction were assessed with the presence of Cl−. At the optimized conditions, the removal of nitrate exhibits an efficiency ca. 100% via the coupling electrochemical reduction and oxidation processes. Moreover, the nitrogen selectivity is found to be as high as 98.8% within 210 min, accompanied with a promising test endurance (>94.0% for total nitrogen (TN) and NO3− removal efficiencies after an electrochemical run of 24.5 h). Importantly, as for the treated actual surface water, the concentration of TN is smaller than 1.5 mg L−1, in accordance with the limit of Ⅳ-level standard of the surface water environmental quality in China (GB 3838-2002). The efficient removal of nitrate can be attributed to the synergistic effect of Cu and CoP microparticles to enhance the reduction activity, as well as the subsequent chloride oxidation for the major intermediate of ammonium.

Layered metal oxides loaded ceramic membrane activating peroxymonosulfate for mitigation of NOM membrane fouling

Catalytic membrane can achieve sieving separation and advanced oxidation simultaneously, which can improve the effluent water quality while reducing membrane fouling. In this study, the catalytic membranes (M2+Al@AM) were fabricated by loading different binary layered metal oxides (M2+Al-LMO: MnAl-LMO, CuAl-LMO and CoAl-LMO) on alumina ceramic substrate membranes (AM) via vacuum filtration followed by calcination process. The performance of the catalytic membranes was investigated by filtering actual surface water. It was found that the presence of peroxymonosulfate (PMS) could mitigate membrane fouling effectively, as evidenced by the increase of normalized flux from 0.28 to 0.62 in CoAl@AM/PMS system, from 0.25 to 0.52 in CuAl@AM/PMS system, and from 0.22 to 0.31 in MnAl@AM/PMS system, respectively. Correspondingly, the CoAl@AM exhibited the highest removal for UV254, TOC and fluorescent components in the surface water, followed by CuAl@AM and MnAl@AM. Quenching effect of phenol and furfuryl alcohol proposed the surface-bound radicals and singlet oxygen were the major reactive oxygen species in the M2+Al@AM/PMS systems. Interface free energy calculations confirmed the in-situ PMS activation could enhance the repulsive interactions between NOM and the membranes, thus mitigating membrane fouling. This work provides an original but simple strategy for catalytic ceramic membrane preparation and new insights into the mechanism of membrane fouling mitigation in catalytic membrane system.

Application of α-Fe2O3 nanoparticles in controlling antibiotic resistance gene transport and interception in porous media

Metal oxide nanoparticles (MONPs) with a large specific surface area are expected to bind with antibiotic resistance genes (ARGs), thereby controlling ARGs' contamination by reducing their concentration and mobilization. Here, adsorption experiments were carried out and it was found that α-Fe2O3 NPs could chemically bind with ARGs (tetM-carrying plasmids) in water with an adsorption rate of 0.04 min−1 and an adsorption capacity of 7.88 g/kg. Mixing α-Fe2O3 NPs into quartz sand column markedly increased the interceptive removal of ARGs from inflow water. The interception rate of 1.0 μg/mL ARGs in ultrapure water (25 mL, 5 pore volumes) through the sand column (plexiglass, length 8 cm, internal diameter 1.4 cm) with 1 g/kg α-Fe2O3 NPs was 1.73 times of that through the pure sand column; the interception rate overall increased with increasing addition of α-Fe2O3 NPs, reaching 68.8% with 20 g/kg α-Fe2O3 NPs. Coexisting Na+ (20 mM), Ca2+ (20 mM), and acidic condition (pH 4.0) could further increase the interception rate of ARGs by 1 g/kg α-Fe2O3 NPs from 21.1% to 86.2%, 90.7%, and 96.2%, respectively. The presence of PO43− and humic acid at environmentally relevant concentrations would not significantly affect the interception of ARGs. In the treatment groups with PO43− and humic acid, the removal rate decreased by only 1.8% and 0.1%, respectively. In addition, the interceptive removal of ARGs by α-Fe2O3 NPs-incorporated sand column was even better in actual surface water samples (87.2%) than that in the ultrapure water (21.1%). The findings provide a promising approach to treat ARGs-polluted water.

Efficient degradation of trimethoprim by catalytic ozonation coupled with Mn/FeOx-functionalized ceramic membrane: Synergic catalytic effect and enhanced anti-fouling performance

In this study, the flat microfiltration ceramic membrane (CM) was modified by wet impregnation method (Mn-Fe-CM) to catalyze ozone (O3) for the oxidative degradation of trimethoprim (TMP). The conventional characterization test showed that the Mn-Fe binary oxides (Mn/FeOx) with the crystal structure of FeMnO3 were successfully loaded on the membrane and the catalytic performance of Mn-Fe-CM for O3 was apparently enhanced as compared to CM. Consequently, compared with O3 oxidation alone, the degradation and mineralization efficiencies of TMP in the O3/Mn-Fe-CM system were both improved and 98.6% of TMP could be removed within 10 min. The degradation efficiency of TMP decreased with the increasing pH and the addition of Cl-、HCO3–、PO43-, while humic acid (HA) exhibited negative effect on the TMP removal. Radical scavenger experiment and electron paramagnetic resonance (EPR) analysis confirmed that direct oxidation by O3 played an important role in the degradation of TMP, while hydroxyl radical (·OH) and 1O2 also participated. Fe(II) could act as an intermediate to transfer electrons and accelerate the transformation of Mn(III) to Mn(II) and Mn(IV) to Mn(III) during the ozonation process, which definitely strengthened the synergic catalytic effect of Mn-Fe-CM. The proposed degradation mechanism of TMP mainly contained hydroxylation, carbonylation, demethoxylation and deamination. Due to the strong catalytic ozonation performance for organic pollutants degradation, the O3/Mn-Fe-CM system revealed better anti-membrane fouling ability, strong cyclic usage performance and high applicability for the actual surface water treatment.

Theoretical and experimental insights into electron-induced efficient defluorination of perfluorooctanoic acid and perfluorooctane sulfonate by mesoporous plasma

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are global environmental pollutants and pose significant threats to environmental safety and human health. Defluorination of PFOA and PFOS was investigated theoretically and practically in a mesoporous plasma system in this study. Rapid and highly efficient defluorination was realized, and 98% and 65% defluorination rate for PFOA and PFOS, respectively, were obtained within 60 min of treatment. Electrons generated in the mesoporous plasma system played a decisive role in PFOA and PFOS defluorination; other species, including 1O2 and ·OH, also contributed to defluorination. C-F, C-C, and C-S bonds were broken by plasma oxidation; various shorter-chain perfluorocarboxylic acids, polyfluoroalkyl substances, and alcohols were produced. PFOA and PFOS decomposition mechanisms involved electron transfer, defluorination, decarboxylation, and hydroxylation reactions. Desulfonation reactions were also involved in PFOS decomposition. Density functional theory calculations identified sites susceptible to be attacked and the main degradation pathways. Effective defluorination of PFOA and PFOS reduced their toxicities. Furthermore, its potential for actual surface water treatment was also determined.

Volcanic rock: A new type of particle electrode with excellent performance, which can efficiently degrade norfloxacin

In this work, volcanic rocks were used as particle electrodes to construct a volcanic rock three-dimensional (3D) electrode reactor. In a wide pH range (3 ~ 11), volcanic rocks can degrade norfloxacin (NOR) at low voltage (4 V) within 40 min. In acidic environment, the NOR removal was greater than 85%. Volcanic rock also showed excellent electrocatalytic activity when treating ofloxacin, methylene blue and other pollutants. After six cycles, the weight loss rate of volcanic rocks was 3.87%. Volcanic rocks had high mechanical strength stability. There were hydroxyl radicals (OH) and superoxide radical (O2−) produced in the volcanic rock 3D system. The volcanic rock surface was the main location of NOR degradation. The possible degradation mechanism and the degradation pathway of NOR were proposed. In addition, volcanic rock also showed excellent effects in actual surface water treatment.

Pd–O2 interaction and singlet oxygen formation in a novel reactive electrochemical membrane for ultrafast sulfamethoxazole oxidation

In this study, a novel reactive electrochemical membrane (REM) made of Pd-loaded porous Ti was prepared to achieve ultrafast and efficient oxidation of trace antibiotics sulfamethoxazole (SMX) under anodic polarization. At a current density of 0.5 mA/cm2, the percentage removal of SMX by the REM was 96.3% in flow-through mode, with the energy cost (i.e., the electrical energy per order of removal, 1.34 Wh/m3) being much lower than the flow-by mode (125.76 Wh/m3) under the same operating condition. Quenching experiments and electron spin resonance spectra demonstrated that singlet oxygen (1O2) was the main reactive oxygen species in the REM system, playing a vital role in SMX degradation. Results of this study indicated that 1O2 was mainly generated on the anode via Pd–O2 interaction that directly activated oxygen, rather than the evolution of 1O2 precursors (e.g., O2− and H2O2). The constantly high electrochemical removal of SMX (88.5–91.9%) from actual surface water demonstrated that the matrix effect on the process performance was minimal in realistic applications, highlighting this novel REM to be a viable way to remove trace organic contaminants from surface water.

Immobiling enzyme-like ligand in the ultrafiltration membrane to remove the micropollutant for the ultrafast water purification

Water security is one of the most pressing global challenges due to its effects on human health. To face the challenge of water pollution, membrane technology was widely applied for the removal of pollutants and desalination. In this work, an enzyme-like ligand, Iron (III)-tetraamidomacrocyclic ligand (Fe(III)-TAML), was for the first time immobilized into a polyethersulfone (PES) membrane for the catalytic oxidation removal of micropollutants during the ultrafiltration process. Through the introduction of graphene oxide-polyethyleneimine (GO-PEI), Fe(III)-TAML was successfully immobilized into the membrane. Results shown that porosity and hydrophilicity of the PES membrane were significantly enhanced after GO-PEI modification. Furthermore, about 100% of bisphenol A (BPA) in the feed water was removed after filtration using the Fe(III)-TAML immobilized membrane at a high flux of 192 L/m2 h, which was attributed to the generation of high valence Fe through activating Fe(III)-TAML by H2O2. Moreover, the Fe(III)-TAML in the membrane could be simply regenerated by a re-adsorption process, and the flux and removal efficiency of BPA were stabled during five cycles. Additionally, the TAML/GO-PEI/PES membrane maintained a high water flux and BPA removal efficiency for the filtration of actual surface water. Overall, these results highlight the potential of enzyme-like ligand catalytic oxidation coupled with ultrafiltration to remove micropollutants at a high flux for ensuring the water safety.

Sulfur-zinc modified kaolin/steel slag: A particle electrode that efficiently degrades norfloxacin in a neutral/alkaline environment

In this work, sulfur and zinc were used to modify the steel slag/kaolin particle electrodes. Sulfur-zinc modified kaolin/steel slag particle electrodes (S–Zn-KSPEs) was successfully prepared. In a wide pH range (pH 3–10), S–Zn-KSPEs could efficiently degrade norfloxacin at low voltage (4 V) within 90 min. The removal rate of NOR by S–Zn-KSPEs was about 100% in acidic environment, more than 90% in neutral environment, and more than 80% in alkaline environment. And S–Zn-KSPEs could also efficiently degrade methylene blue, diuron, levofloxacin and other refractory pollutants under neutral conditions. S–Zn-KSPEs showed good stability and recyclability, and could maintain high catalytic activity after 8 cycles in a neutral or alkaline environment. The possible degradation mechanism and the degradation pathway of norfloxacin are proposed. In addition, S–Zn-KSPEs also showed a higher treatment effect in the treatment of actual surface water bodies. And S–Zn-KSPEs had a strong acid-base buffering capacity, which could avoid some pretreatment measures of wastewater in practical applications.

Investigation of bromide removal and bromate minimization of membrane capacitive deionization for drinking water treatment

The ubiquitous bromide (Br−) poses a challenge to current drinking water treatment schemes due to the formation of brominated disinfection by-products, especially bromate (BrO3−). A cost-effective and energy-efficient technology to remove Br− before disinfection is highly desired. In this work, the application of membrane capacitive deionization (MCDI) for the removal of Br− and BrO3− minimization for drinking water treatment was systematically investigated. Results showed that the removal of Br− by MCDI followed the pseudo-second-order kinetics, in which kinetics was faster at lower Br− concentration. Additionally, Br− displayed a preferential electrosorption over Cl− in MCDI despite the relatively smaller amounts. Due to high removal performance of Br−, 99.49% of BrO3− minimization can be achieved. Moreover, the presence of humic acid (HA) had a negative effect on the removal of Br− and BrO3− minimization. However, Br− could be more preferentially removed than Cl− in the presence of HA due to the weak interaction with HA. Finally, by treating an actual surface water sample, it was found that the removal rate of Br− was 91.80%, and 83.97% of BrO3− minimization can be achieved. BrO3− concentration of effluent meets the control standard. Overall, these results prove the feasibility of MCDI for practical drinking water treatment.

The combination effect of preozonation and CNTs layer modification on low-pressure membrane fouling control in treating NOM and EfOM

In this study, the combination effect of preozonation and carbon nanotubes (CNTs) layer modification on low-pressure membrane (LPM) fouling control was systematically investigated. To understand the alleviation mechanism of the hybrid process, natural organic matter (NOM) from IHSS and effluent organic matter (EfOM) from actual sewage effluent were both selected as the typical organic foulants presented in actual surface water and wastewater. A dead-end continuous flow model combined with programmable logic control system was used to operate four membrane filtration units and their backwash processes. With a constant permeates flux, the fouling resistant of CNT modified LPM after preozonation could be evaluated according to the increase in transmembrane pressure (TMP). The results revealed that the hybrid approach of preozonation and CNTs modification could significantly improve the anti-fouling ability of LPM, reduce the backwash frequency, and improve the reversibility of membrane fouling. During the filtration of EfOM and NOM, preozonation improved the water treatment capacity of the CNTs modified membranes. The experiment of mass balance revealed that preozonation enhanced the recoverability of CNTs modified membrane and greatly increased its operation time in treating EfOM and NOM. The molecular weight distribution as well as EEM analysis demonstrated the dissimilar characteristics of EfOM and NOM, which caused the different treatment efficiency by preozonation and CNT modification. The mechanism of EfOM/NOM fouling on LPM was summarized as the primary blocking by medium-MW EfOM/NOM. CNTs modification had a better effect on the control of LPM fouling when treating EfOM, as it removed the medium-MW EfOM by adsorption and prevented the pores blockage of the original PVDF membrane. Preozonation had a better effect on the control of LPM fouling when treating NOM, as it greatly changed the MWD of NOM by removing medium-MW NOM. The combination effect of the hybrid preozonation and CNTs modification resulted in the most effective fouling control of LPM by both decreasing the medium-MW and large-MW EfOM/NOM. At the same time, it decreased irreversible fouling related with membrane pore blocking. The hybrid approach demonstrated its promising application for LPM fouling control in actual sewage water and surface water treatment process.