Electrically Redox-Active Membrane with Switchable Selectivity to Contaminants for Water Purification.

Membrane technology provides an attractive approach for water purification but faces significant challenges in separating small molecules due to its lack of satisfactory permselectivity. In this study, a polypyrrole-based active membrane with a switchable multi-affinity that simultaneously separates small ionic and organic contaminants from water was created. Unlike conventional passive membranes, the designed membrane exhibits a good single-pass filtration efficiency (>99%, taking 1-naphthylamine and Pb2+ as examples) and high permeability (227 L/m2/h). Applying a reversible potential can release the captured substances from the membrane, thus enabling membrane regeneration and self-cleaning without the need for additives. Advanced characterizations reveal that potential switching alters the orientation of the doped amphipathic molecules with the self-alignment of the hydrophobic alkyl chains or the disordered sulfonate anions to capture the target organic molecules or ions via hydrophobic or electrostatic interactions, respectively. The designed smart membrane holds great promise for controllable molecular separation and water purification.

Electrically Controlled Adsorptive Membranes with Tunable Affinity for Selective Chromium (VI) Separation from Water.

Ionic contaminants such as Cr(VI) pose a challenge for water purification using membrane-based processes. However, existing membranes have low permeability and selectivity for Cr(VI). Therefore, in this study, we prepared an electrically controlled adsorptive membrane (ECAM-L) by coating a loose Cl--doped polypyrrole layer on a carbon nanotube substrate, and we evaluated the performance of ECAM-L for Cr(VI) separation from water. We also used electrochemical quartz crystal microbalance measurements and molecular dynamics and density functional theory calculations to investigate the separation mechanisms. The adsorption and desorption of Cr(VI) could be modulated by varying the electrostatic interactions between ECAM-L and Cr(VI) via potential control, enabling the cyclic use of the ECAM-L without additional additives. Consequently, the oxidized ECAM-L showed high Cr(VI) removal performance (<50 µg/L) and treatment capacity (>3500 L/m2) at a high water flux (283 L/m2/h), as well as reusability after the application of a potential. Our study demonstrates an efficient membrane design for water decontamination that can selectively separate Cr(VI) through a short electric stimulus.

In situ regulation of selectivity and permeability by electrically tuning pore size in trans-membrane ion process.

Regulating ion transport behavior through pore size variation is greatly attractive for membrane to meet the need for precise separation, but fabricating nanofiltration (NF) membranes with tunable pore size remains a huge challenge. Herein, a NF membrane with electrically tunable pores was fabricated by intercalating polypyrrole into reduced graphene oxide interlayers. As the potential switches from reduction to oxidation, the membrane pore size shrinks by 11%, resulting in a 16.2% increase in salt rejection. The membrane pore size expands/contracts at redox potentials due to the polypyrrole volume swelling/shrinking caused by the insertion/desertion of cations, respectively. In terms of the inserted cation, Na+ and K+ induce larger pore-size stretching range for the membrane than Ca2+ due to greater binding energy and larger doping amount. Such an electrical response characteristic remained stable after multiple cycles and enabled application in ion selective separation; e.g., the Na+/Mg2+ separation factor in the reduced state is increased by 41% compared to that in the oxide state. This work provides electrically tunable nanochannels for high-precision separation applications such as valuable substance purification and resource recovery from wastewater.

Sequential Demulsification through the Hydrophobic-Hydrophilic-Hydrophobic Filtration Layer toward High-Performing Oil Recovery.

Demulsification using membranes is a promising method to coalesce highly stable emulsified oil droplets for oil recovery. Nevertheless, a structure of the current filtration medium that is not efficient for oil droplet coalescence impedes rapid permeability, thereby inevitably restricting their practical applications. Herein, we report a hydrophobic-hydrophilic-hydrophobic (3H) demulsification medium that exhibits a benchmark permeability of ∼2.1 × 104 L m-2 h-1 with a demulsification efficiency of >98.0%. Remarkably, this 3H demulsification medium maintains over 90% demulsification efficiency in the oil-in-water (O/W) emulsions with a wide range of surfactant concentrations, which shows excellent applicability. Based on the combined results of quasi situ microscope images and molecular dynamics simulations, we show that the polydimethylsiloxane-modified hydrophobic layer facilitates the capture and coalescence of oil droplets, the hydrophilic inner layer assists in squeezing the coalescence of enlarged droplets, and the third hydrophobic layer accelerates the discharge of demulsified oil to sustain permeability. The sequential demulsification mechanism between this 3H filtration layer provides a general guide for designing a demulsifying membrane with high demulsification efficiency and high flux toward oil recovery.

Can radicals-orientated chemical oxidation improve the reduction of antibiotic resistance genes (ARGs) by mesophilic anaerobic digestion of sludge?

The dissemination of antibiotic resistance genes (ARGs) increases risks towards human health and environmental safety. This work investigates the control of ARGs abundance and bacterial community evolution involved in waste activated sludge (WAS) treatment by chemical conditioning and subsequent mesophilic anaerobic digestion (MAD). The different chemical oxidation processes of ferrous iron-activated oxone and hydrogen peroxide (PMS-Fe2+ and H2O2-Fe2+) and thermal-activated oxone (PMS@80 â„ƒ) were investigated, and the ferric chloride (FeCl3) and inactivated oxone (PMS) were compared. PMS@80 â„ƒ decreased the absolute abundance of most ARGs by 10.6-99.3% and that of total ARGs by 66.3%. Interestingly, oxidation pretreatment increased rather than decreased the relative abundance of most ARGs. MAD with PMS@80 â„ƒ pretreatment increased the absolute abundance of total ARGs by 51.6%, and other MAD processes decreased it by 8.6-47.4%. PMS-Fe2+ and PMS@80 â„ƒ negatively inhibited methane production from 98.3 to 81.7 and 94.4 mL/g VSS in MAD. MAD effluent showed high abundance of Arcobacter genus in the range of 8.1-17.4% upon PMS-based pretreatment, possibly related to sulfur oxidation, nitrate reduction, and blaVEB enrichment. The radicals-orientated chemical oxidation can hardly improve the ARGs elimination by MAD due to the extremely high competitive organics in sludge.

Regulating Oriented Adsorption on Targeted Nickel Sites for Antibiotic Oxidation with Simultaneous Hydrogen Energy Recovery by a Direct Electrochemical Process.

The efficiency of antibiotic oxidation by direct electrochemical processes based on transition metal electrodes is largely restricted by the adsorption capacity for single molecules on targeted active sites. Inspired by density functional theory (DFT) calculations, we found that the adsorption energy of sulfanilamide molecules on Ni sites could be markedly changed by regulating the local atomic environment of the Ni atoms (for NiCo2O4 and NiCoP, ΔGNi = -0.11 and +0.47 eV, respectively). The high electronegativity of oxygen changed the electron cloud density around the Ni atoms, leading to an oriented adsorption of SA on Ni sites. Moreover, the oriented adsorption on Ni sites occurs not only on NiCo2O4 but on the in situ-generated NiIIIOOH (ΔGNi = -0.09 eV). Consequently, utilizing NiCo2O4 as the anode resulted in superior removal performance (97% vs 55% efficiency) for SA oxidation, with a kinetic constant ∼10 times higher than that of NiCoP (0.031 min-1 vs 0.0029 min-1). Meanwhile, non-oriented adsorption reduced the competition between SA molecules and H+ for active sites, which benefitted the activity of the hydrogen evolution reaction at the NiCoP cathode (68 mV at j = 10 mA·cm-2, 0.5 mmol·L-1 SA added in). Furthermore, the in situ Raman spectra and DFT calculations confirmed that NiIIIOOH dominated the oxidation process and terminated it at the p-benzoquinone stage. These findings provide a feasible strategy to combine electrochemical antibiotic oxidation by Ni-based electrodes with hydrogen energy recovery.

Potassium-Ion Recovery with a Polypyrrole Membrane Electrode in Novel Redox Transistor Electrodialysis.

Conductive polymers are potential selective ion-exchange membrane materials. In this study, a novel redox transistor electrodialyzer consisting of two chambers separated by a polypyrrole (PPy) membrane electrode was designed for potassium ion (K+) recovery from water. The PPy membrane electrode was fabricated by depositing PPy on a stainless-steel wire mesh through the electrochemical method. Based on ion-exchange results, the PPy membrane exhibited electrodialysis selectivity for K+ in the presence of Na+, with a K+/Na+ separation factor of 2.10. Adding modified active carbon to PPy provided a larger electroactive area and better conductivity, resulting in higher ion-exchange capacity (1.04 mmol/L) compared with the original PPy membrane. Even for seawater containing a very low concentration of K+ (16.18 mmol/L), the PPy membrane still demonstrated K+ selectivity (separation factor of 2.18). Energy consumption in the electrodialyzer was 3.80 kW h/kg K, which was 37% lower than that in traditional electrodialysis. Furthermore, the PPy membrane exhibited antiscaling/fouling ability with the help of a pulse voltage. These findings highlight a novel redox transistor electrodialysis process with great potential application in K+ recovery from wastewater with relatively low energy consumption.

A layered aluminum-based metal-organic framework as a superior trap for nitrobenzene capture via an intercalation role.

Layered materials with porous layers are of great interest due to their intriguing structural topologies and potential applications as new adsorbents. In this study, a layered aluminum-based metal-organic framework, i.e. Al-TCPP, was successfully synthesized via a facile method for the adsorptive removal of nitrobenzene (NB). The as-synthesized Al-TCPP exhibited a typical layered structure and can be stable in water at pH = 5-7. Batch experimental results showed a superior adsorption performance towards NB with a maximum adsorption capability of 1.85 mg mg-1, and an exceptionally rapid equilibrium within 1 min, yielding an overall adsorptive performance superior to the state-of-the-art NB adsorbents reported so far. The morphology and crystallinity of the Al-TCPP adsorbent basically retain the original status after the capture of NB. Importantly, X-ray diffraction patterns of the samples after the NB adsorption revealed that the possible NB intercalation took place in layered Al-TCPP and expanded the interlayer space during the adsorption, which greatly enriched the adsorption sites and thus achieved the outstanding performance. This work highlights new prospects in designing layered materials for use in environmental remediation.

Enhanced Stabilization and Effective Utilization of Atomic Hydrogen on Pd-In Nanoparticles in a Flow-through Electrode.

Surface-adsorbed active species are intermediates with strong activities in heterogeneous catalytic reactions. Effective stabilization of these intermediates is crucial to improve the catalytic performance. Here, we demonstrated highly active bimetallic palladium-indium (Pd-In) nanoparticles (NPs) that can stabilize atomic H* on the surface and show efficient electrocatalytic reduction performance toward bromate. The optimal atomic ratio of Pd to In was investigated with the aim of efficient formation and strong stabilization of H*, thus facilitating the reduction and decontamination of carcinogenic bromate. Pd2In3 was the most active catalyst, with a high rate constant of 0.029 min-1, whereas the rate constant for monometallic Pd NPs was only 0.009 min-1. Density functional theory calculations suggest that Pd2In3 NPs decrease the work function and provide strong H* stabilization ability. By employing a flow-through electrode coated with Pd2In3 NPs to enhance the mass transport, the utilization of H* could be boosted and the reduction kinetics increased up to 7.5 times.

Intercalation of Nanosized Fe3C in Iron/Carbon To Construct Multifunctional Interface with Reduction, Catalysis, Corrosion Resistance, and Immobilization Capabilities.

As a robust reducing system in industrial wastewater treatment, iron/carbon (Fe/C) microelectrolysis suffers from surface passivation and low utilization efficiency. Herein, we introduced Fe3C into the Fe/C system to develop a core-shell Fe0/Fe3C/C nanorod with a multifunctional interface (Fe3C/C) providing reduction, catalysis, adsorption, and corrosion resistance. The results proved that the fabricated Fe0/Fe3C/C possesses 5.6 times higher reduction capacity (220 mg/g) for Cr(VI) reduction but a relatively lower Fe leakage (2.7 mg/L) than Fe/C. On the basis of the results of electrochemical characterization (Tafel polarization curves and electrochemical impedance spectroscopy), the corrosion-resistant Fe3C/C shell can significantly prevent surface passivation of the Fe0 core, whereas Fe3C efficiently catalyzes electron transfer from the inner Fe0 to the external carbon surface. Moreover, the reductive species involved in Cr(VI) removal were identified as hydrogen atoms, adsorbed Fe(II) ions, and electrons tunneling from Fe0. STEM, XPS, and Mössbauer spectroscopies were further adopted to characterize the interface reaction of Fe0/Fe3C/C during the Cr(VI) removal process. Finally, the reaction mechanism for Cr(VI) reduction over Fe0/Fe3C/C was proposed, and the distribution of active sites was inferred.

Field-Enhanced Nanoconvection Accelerated Electrocatalytic Conversion of Water Contaminants and Electricity Generation.

The development of high-performance electrocatalytic systems for the extraction of energy from contaminants in wastewater are urgently needed in emerging renewable energy technologies. However, given that most of the contaminants are present in low concentrations, the heterogeneous catalytic reactions often suffer from slow kinetics due to mass transfer limitations. Here, we report that localized free convection induced by enthalpy change of the reaction can enhance interfacial mass transport. This phenomenon can be found around high-curvature nanosized tips. The finite-element numerical simulation shows that the heat of reactions can produce temperature gradients and subsequently lead to fluid motion at the interfaces, which facilitates the rate-limiting step (mass transfer). To demonstrate the effects of localized field-enhanced mass transport in electrocatalytic conversion of aqueous dilute species, a galvanic cell is constructed with a vertically aligned polyaniline array with sharp tips (as cathode) for the detoxification of a low concentration of carcinogenic chromate and synchronous electricity generation, which show lower overpotential (0.17 V decreased), higher reaction rate (increased by 28%), and power density (22.3 W m-2 in 2 mM chromate). The power output can be scaled up (open voltage of ∼3.7 V and volumetric power density of 840.1 W m-3) by using a continuous flow-through cell with stacked electrodes for further improve the mass transport.

Reactive, Self-Cleaning Ultrafiltration Membrane Functionalized with Iron Oxychloride Nanocatalysts.

Self-cleaning, antifouling ultrafiltration membranes are critically needed to mitigate organic fouling in water and wastewater treatment. In this study, we fabricated a novel polyvinylidene fluoride (PVDF) composite ultrafiltration membrane coated with FeOCl nanocatalysts (FeOCl/PVDF) via a facile, scalable thermal-treatment method, for the synergetic separation and degradation of organic pollutants. The structure, composition, and morphology of the FeOCl/PVDF membrane were extensively characterized. Results showed that the as-prepared FeOCl/PVDF membrane was uniformly covered with FeOCl nanoparticles with an average diameter of 1-5 nm, which greatly enhanced membrane hydrophilicity. The catalytic self-cleaning and antifouling properties of the FeOCl/PVDF membrane were evaluated in the presence of H2O2 at neutral pH. Using a facile H2O2 cleaning process, we showed that the FeOCl/PVDF membrane can achieve an excellent water flux recovery rate of ∼100%, following organic fouling with a model organic foulant (bovine serum albumin). Moreover, the in situ catalytic production of active hydroxyl radicals by the FeOCl/PVDF membrane was elucidated by electron spin resonance (ESR) and UV analysis. The catalytic performance of the FeOCl/PVDF membrane was further demonstrated by the complete degradation of bisphenol A when H2O2 was dosed in the feed solution at neutral pH. Our results demonstrate the promise of utilizing this novel membrane for the treatment of waters with complex organic pollutants.

Speciation matching mechanisms between orthophosphate and aluminum species during advanced P removal process.

Aluminum (Al) salts are widely used as coagulants to remove phosphorus (P) in water treatment. However, the relationship between P and Al species and the underlying coagulation mechanisms is rarely studied. Currently, water eutrophication is a serious issue, and therefore advanced P removal is extremely necessary. Herein, the orthophosphate removal behavior of Al coagulants with various species distributions was investigated. The results showed that AlCl3·6H2O (AC) had a more pronounced P removal efficiency than polyaluminum chloride (PACl). Medium (Alb or Al13) and high polymeric species (Alc) played a more significant role in removing P than monomeric species (Ala). During coagulation, adsorption onto flocs was the dominant P removal mechanism, which could be categorized as multilayer adsorption. Although the adsorption kinetics showed that physical adsorption best described the adsorption mechanism for AC and PACl, it is worth noting that chemical adsorption also occurred during P removal by AC because of the formation of the AlPO4 precipitate. This could be because of the strong complex adsorption between the in situ Al13 species and P. Based on the excellent P removal performance, we believe these findings will have a large potential for application in advanced P removal in water treatment.

Comparison of the effects of aluminum and iron(III) salts on ultrafiltration membrane biofouling in drinking water treatment.

Coagulation plays an important role in alleviating membrane fouling, and a noticeable problem is the development of microorganisms after long-time operation, which gradually secrete extracellular polymeric substances (EPS). To date, few studies have paid attention to the behavior of microorganisms in drinking water treatment with ultrafiltration (UF) membranes. Herein, the membrane biofouling was investigated with different aluminum and iron salts. We found that Al2(SO4)3·18H2O performed better in reducing membrane fouling due to the slower growth rate of microorganisms. In comparison to Al2(SO4)3·18H2O, more EPS were induced with Fe2(SO4)3·xH2O, both in the membrane tank and the sludge on the cake layer. We also found that bacteria were the major microorganisms, of which the concentration was much higher than those of fungi and archaea. Further analyses showed that Proteobacteria was dominant in bacterial communities, which caused severe membrane fouling by forming a biofilm, especially for Fe2(SO4)3·xH2O. Additionally, the abundances of Bacteroidetes and Verrucomicrobia were relatively higher in the presence of Al2(SO4)3·18H2O, resulting in less severe biofouling by effectively degrading the protein and polysaccharide in EPS. As a result, in terms of microorganism behaviors, Al-based salts should be given preference as coagulants during actual operations.

Deiodination of iopamidol by zero valent iron (ZVI) enhances formation of iodinated disinfection by-products during chloramination.

Iodinated X-ray contrast media (ICM) is considered as one of iodine sources for formation of toxic iodinated disinfection byproducts (I-DBPs) during disinfection. This study investigated transformation of a typical ICM, iopamidol (IPM) by zero valent iron (ZVI) and the effect of transformation on the formation of I-DBPs during chloramination. It was found that the presence of ZVI could deiodinate IPM into I- and the transformation of IPM exhibited a pseudo-first-order kinetics. Acidic circumstance, SO42-, Cl- and monochloramine could promote the transformation of IPM by ZVI, while SiO32- inhibited the transformation of IPM. Moreover, the transformation of IPM by ZVI changed both the formed species and amounts of I-DBPs during chloramination. During the chloramination of IPM-containing water, CHCl2I and iodoacetic acid were the predominant iodinated trihalomethanes (I-THMs) and iodinated haloacetic acids (I-HAAs), respectively in the absence of ZVI, while CHI3 and triiodoacetic acid became the predominant ones with 1.0 g L-1 ZVI. The addition of 5.0 g L-1 ZVI increased I-DBPs formation amounts by 6.0 folds after 72 h and maximum formation of I-DBPs occurred at pH 5.0. Enhanced I-DBPs formation was also observed with various real water sources. Given that ZVI ubiquitously exists in the unlined cast iron distribution pipes, the deiodination of IPM by ZVI during distribution may increase the formation of I-DBPs, which needs receive enough attention.

Impacts of water quality on the corrosion of cast iron pipes for water distribution and proposed source water switch strategy.

Switch of source water may induce "red water" episodes. This study investigated the impacts of water quality on iron release, dissolved oxygen consumption (ΔDO), corrosion scale evolution and bacterial community succession in cast iron pipes used for drinking water distribution at pilot scale, and proposed a source water switch strategy accordingly. Three sets of old cast iron pipe section (named BP, SP and GP) were excavated on site and assembled in a test base, which had historically transported blended water, surface water and groundwater, respectively. Results indicate that an increasing Cl- or SO42- concentration accelerated iron release, but alkalinity and calcium hardness exhibited an opposite tendency. Disinfectant shift from free chlorine to monochloramine slightly inhibited iron release, while the impact of peroxymonosulfate depended on the source water historically transported in the test pipes. The ΔDO was highly consistent with iron release in all three pipe systems. The mass ratio of magnetite to goethite in the corrosion scales of SP was higher than those of BP and GP and kept almost unchanged over the whole operation period. Siderite and calcite formation confirmed that an increasing alkalinity and hardness inhibited iron release. Iron-reducing bacteria decreased in the BP but increased in the SP and GP; meanwhile, sulfur-oxidizing, sulfate-reducing and iron oxidizing bacteria increased in all three pipe systems. To avoid the occurrence of "red water", a source water switch strategy was proposed based on the difference between local and foreign water qualities.

Simultaneous detection of chlorinated polycyclic aromatic hydrocarbons with polycyclic aromatic hydrocarbons by gas chromatography-mass spectrometry.

Chlorinated polycyclic aromatic hydrocarbons (ClPAHs), including polychlorinated naphthalenes (PCNs), are hazardous and widespread in the environment, but studies of these substances in the wastewater environment are lacking. In this study, five typical PCNs and five typical ClPAHs (other than PCNs) were simultaneously detected along with their parent polycyclic aromatic hydrocarbons in wastewater samples. All these compounds could be analyzed by gas chromatography- electron ionization mass spectrometry in selected ion monitoring mode and separated on a DB-17ms column. Calibration curves were created both in pure solvent and in wastewater matrix samples. The coefficients of determination for most compounds were greater than 0.99, indicating a satisfactory degree of linearity in the complex matrix samples. The influence of the matrix on the true concentrations of the environmental samples was corrected by use of the matrix calibration curve. The recoveries of all compounds were between 58% and 127%, with standard deviations lower than 20%. The method detection and quantification limits were less than 27.6 ng/L and less than 91.9 ng/L respectively in the aqueous phase, and less than 0.18 ng/L and less than 0.61 ng/L respectively in the solid phase of 4-L wastewater samples. This analytical method was successfully used to detect PCNs and ClPAHs in the water from a river receiving effluent from a wastewater treatment plant. The concentrations of each compound ranged from 3.1 to 29.6 ng/L. This method could also be used for detection of other polycyclic aromatic hydrocarbon derivatives with similar physical and chemical properties in different matrix samples. Graphical Abstract ᅟ.

An activated carbon fiber cathode for the degradation of glyphosate in aqueous solutions by the Electro-Fenton mode: Optimal operational conditions and the deposition of iron on cathode on electrode reusability.

An activated carbon fiber (ACF) cathode was fabricated and used to treat glyphosate containing wastewater by the Electro-Fenton (EF) process. The results showed that glyphosate was rapidly and efficiently degraded and the BOD5/COD ratio was increased to >0.3 implying the feasibility of subsequent treatment of the treated wastewater by biological methods. The results of ion chromatography and HPLC measurements indicated that glyphosate was completely decomposed. Effective OH generation and rapid recycling/recovery of the Fe2+ ions at the cathode were responsible primarily for the high performance of the ACF-EF process. Factors such as inlet oxygen gas flow rate, Fe2+ dosage, initial glyphosate concentration, applied current intensity, and solution pH that may affect the efficiency of the ACF-EF process were further studied and the optimum operation condition was established. Results of SEM/EDX, BET and XPS analysis showed the deposition of highly dispersed fine Fe2O3 particles on the ACF surface during the EF reaction. The possibility of using the Fe2O3-ACF as iron source in the EF process was assessed. Results showed that the Fe2O3-ACF electrode was effective in degrading glyphosate in the EF process. The deposition of Fe2O3 particles on the ACF electrode had no adverse effect on the reusability of the ACF cathode.

Probing Coagulation Behavior of Individual Aluminum Species for Removing Corresponding Disinfection Byproduct Precursors: The Role of Specific Ultraviolet Absorbance.

Coagulation behavior of aluminum chloride and polyaluminum chloride (PACl) for removing corresponding disinfection byproduct (DBP) precursors was discussed in this paper. CHCl3, bromine trihalomethanes (THM-Br), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) formation potential yields were correlated with specific ultraviolet absorbance (SUVA) values in different molecular weight (MW) fractions of humic substances (HS), respectively. Correlation analyses and principal component analysis were performed to examine the relationships between SUVA and different DBP precursors. To acquire more structural characters of DBP precursors and aluminum speciation, freeze-dried precipitates were analyzed by fourier transform infrared (FTIR) and C 1s, Al 2p X-ray photoelectron spectroscopy (XPS). The results indicated that TCAA precursors (no MW limits), DCAA and CHCl3 precursors in low MW fractions (MW<30 kDa) had a relatively good relations with SUVA values. These DBP precursors were coagulated more easily by in situ Al13 of AlCl3 at pH 5.0. Due to relatively low aromatic content and more aliphatic structures, THM-Br precursors (no MW limits) and CHCl3 precursors in high MW fractions (MW>30 kDa) were preferentially removed by PACl coagulation with preformed Al13 species at pH 5.0. Additionally, for DCAA precursors in high MW fractions (MW>30 kDa) with relatively low aromatic content and more carboxylic structures, the greatest removal occurred at pH 6.0 through PACl coagulation with aggregated Al13 species.

KMnO4-Fe(II) pretreatment to enhance Microcystis aeruginosa removal by aluminum coagulation: Does it work after long distance transportation?

KMnO4-Fe(II) pretreatment was proposed to enhance Microcystis aeruginosa (M. aeruginosa) removal by aluminum (Al) coagulation in drinking water treatment plants (DWTPs) in our previous study. This study aims to optimize this process and evaluate the feasibility of using the process at water sources, which are usually far away from DWTPs. The optimum molar ratio of KMnO4 to Fe(II) [Formula: see text] is observed to be 1:3 with respect to algae removal and residual manganese (Mn) control. As indicated from flow cytometer analysis, KMnO4 at <20 µM promisingly maintains cell integrity, with damaged cell ratios of below 10%. KMnO4 at 30 and 60 µM damages M. aeruginosa cells more significantly and the damaged cell ratios increase to 21% and 34% after 480 min. The intracellular organic matter (IOM) release can be controlled by the subsequent introduction of Fe(II) to quench residual KMnO4. KMnO4-Fe(II) pretreatment at the KMnO4 dose of 10 µM dramatically enhances the algae removal by over 70% compared to that by Al coagulation, even if KMnO4 and Fe(II) are introduced 480 min prior to the addition of Al2(SO4)3. The Al doses can be reduced by more than half to achieve the same algae removal. Furthermore, the deposition of the tiny Fe-Mn precipitates formed rarely occurs, as indicated by a settleability evaluation prior to Al addition. The KMnO4-Fe(II) process can be sequentially dosed at intake points in water sources to achieve moderate inactivation of algae cells and to enhance algae removal in DWTPs thereafter.