Sweep flocculation and adsorption of viruses on aluminum flocs during electrochemical treatment prior to surface water microfiltration

Electrocoagulation technology for water purification: An update review on reactor design and some newly concerned pollutants removal

Water shortage and quality deterioration are plaguing people all over the world. Providing sustainable and affordable treatment solutions to these problems is a need of the hour. Electrocoagulation (EC) technology is a burgeoning alternative for effective water treatment, which offers the virtues such as compact equipment, easy operation, and low sludge production. Compared to other water purification technologies, EC shows excellent removal efficacy for a wide range of contaminants in water and has great potential for addressing limitations of conventional water purification technologies. This review summarizes the latest development of principle, characteristics, and reactor design of EC. The design of key parameters including reactor shape, power supply type, current density, as well as electrode configuration is further elaborated. In particular, typical water treatment systems powered by renewable energy (solar photovoltaic and wind turbine systems) are proposed. Further, this review provides an overview on expanded application of EC in the removal of some newly concerned pollutants in recent years, including arsenite, perfluorinated compounds, pharmaceuticals, oil, bacteria, and viruses. The removal efficiency and mechanisms of these pollutants are also discussed. Finally, future research trend and focus are further recommended. This review can bridge the large knowledge gap for the EC application that is beneficial for environmental researchers and engineers.

Virus Removal and Inactivation Mechanisms during Iron Electrocoagulation: Capsid and Genome Damages and Electro-Fenton Reactions

Virus destabilization and inactivation are critical considerations in providing safe drinking water. We demonstrate that iron electrocoagulation simultaneously removed (via sweep flocculation) and inactivated a non-enveloped virus surrogate (MS2 bacteriophage) under slightly acidic conditions, resulting in highly effective virus control (e.g., 5-logs at 20 mg Fe/L and pH 6.4 in 30 min). Electrocoagulation simultaneously generated H₂O₂ and Fe(II) that can potentially trigger electro-Fenton reactions to produce reactive oxygen species such as ^•OH and high valent oxoiron(IV) that are capable of inactivating viruses. To date, viral attenuation during water treatment has been largely probed by evaluating infective virions (as plaque forming units) or genomic damage (via the quantitative polymerase chain reaction). In addition to these existing means of assessing virus attenuation, a novel technique of correlating transmission electron micrographs of electrocoagulated MS2 with their computationally altered three-dimensional electron density maps was developed to provide direct visual evidence of capsid morphological damages during electrocoagulation. The majority of coliphages lost at least 10-60% of the capsid protein missing a minimum of one of the 5-fold and two of 3- and 2-fold regions upon electrocoagulation, revealing substantial localized capsid deformation. Attenuated total reflectance-Fourier transform infrared spectroscopy revealed potential oxidation of viral coat proteins and modification of their secondary structures that were attributed to reactive oxygen species. Iron electrocoagulation simultaneously disinfects and coagulates non-enveloped viruses (unlike conventional coagulation), adding to the robustness of multiple barriers necessary for public health protection and appears to be a promising technology for small-scale distributed water treatment.

The occurrence and control of waterborne viruses in drinking water treatment: A review

As the coronavirus disease 2019 continues to spread globally, its culprit, the severe acute respiratory syndrome coronavirus 2 has been brought under scrutiny. In addition to inhalation transmission, the possible fecal-oral viral transmission via water/wastewater has also been brought under the spotlight, necessitating a timely global review on the current knowledge about waterborne viruses in drinking water treatment system - the very barrier that intercepts waterborne pathogens to terminal water users. In this article we reviewed the occurrence, concentration methods, and control strategies, also, treatment performance on waterborne viruses during drinking water treatment were summarized. Additionally, we emphasized the potential of applying the quantitative microbial risk assessment to guide drinking water treatment to mitigate the viral exposure risks, especially when the unregulated novel viral pathogens are of concern. This review paves road for better control of viruses at drinking water treatment plants to protect public health.

Efficacy of electrochemical membrane bioreactor for virus removal from wastewater: Performance and mechanisms

Wastewater treatment facilities play pivotal roles in preventing the transmission of water-borne viruses and protecting human health. In this study, a new electrochemical membrane bioreactor (EMBR) was proposed to achieve a long-lasting and efficient removal of virus from wastewater. Results showed that applying a low electric field (2.0 V) in EMBR system could achieve ~100% removal efficiency at both batch tests and continuous flow experiments. In contrast, the control MBR, without the exertion of electric field, exhibited a very low removal efficiency (19.8% on average). Moreover, the fouling in EMBR was significantly mitigated, which enabled its operation duration almost 3 times longer than that of the control. Further explorations suggested that the reactive oxidants generated on electrodes in the EMBR system were mainly responsible for MS2 removal. This study demonstrated the potential of utilizing the EMBR process to achieve an enhanced virus disinfection efficiency during the wastewater treatment process.

Competitive co-adsorption of bacteriophage MS2 and natural organic matter onto multiwalled carbon nanotubes

A leading challenge in drinking water treatment is to remove small-sized viruses from the water in a simple and efficient manner. Multi-walled carbon nanotubes (MWCNT) are new generation adsorbents with previously demonstrated potential as filter media to improve virus removal. This study therefore aimed to evaluate the field applicability of MWCNT-filters for virus removal in water containing natural organic matter (NOM) as co-solute to viruses, using batch equilibrium experiments. Contrary to previous studies, our results showed with MS2 bacteriophages single-solute systems that the affinity of MWCNT for MS2 was low, since after 3 h of equilibration only 4 log₁₀ reduction value (LRV) of MS2 (20 mL at an initial concentration of 10⁶ PFU MS2/mL) were reached. Single solute experiments with Suwannee river NOM (SRNOM) performed with environmentally-relevant concentrations showed MWCNT surface saturation at initial SRNOM concentrations between 10 and 15 mgC/L, for water pH between 5.2 and 8.7. These results suggested that at NOM:virus ratios found in natural waters, the NOM would competitively suppress virus adsorption onto MWCNT, even at low NOM concentrations. We confirmed this expectation with SRNOM-MS2 co-solute experiments, which showed an exponential decrease of the MS2 LRV by MWCNT with an increase in the initial SRNOM concentration. More interestingly, we showed that pre-equilibrating MWCNT with a SRNOM solution at a concentration as low as 0.4 mgC/L resulted in a LRV decrease of 3 for MS2, due to the formation of a negatively charged SRNOM adlayer on the MWCNT surface. Complementary batch experiments with natural NOM-containing waters and competition experiments with SRNOM in the presence of CaCl₂ confirmed that the presence of NOM in waters challenges virus removal by MWCNT-filters, irrespective of the concentration and type of NOM and also in the presence of Ca²⁺. We therefore conclude that MWCNT-filters produced with commercially available pristine MWCNT cannot be considered as a viable technology for drinking water virus removal.

Mechanisms of virus mitigation and suitability of bacteriophages as surrogates in drinking water treatment by iron electrocoagulation

Emerging water treatment technologies using ferrous and zero-valent iron show promising virus mitigation by both inactivation and adsorption. In this study, iron electrocoagulation was investigated for virus mitigation in drinking water via bench-scale batch experiments. Relative contributions of physical removal and inactivation, as determined by recovery via pH 9.5 beef broth elution, were investigated for three mammalian viruses (adenovirus, echovirus, and feline calicivirus) and four bacteriophage surrogates (fr, MS2, P22, and ΦX174). Though no one bacteriophage exactly represented mitigation of the mammalian viruses in all water matrices, bacteriophage ΦX174 was the only surrogate that showed overall removal comparable to that of the mammalian viruses. Bacteriophages fr, MS2, and P22 were all more susceptible to inactivation than the three mammalian viruses, raising concerns about the suitability of these common surrogates as indicators of virus mitigation. To determine why some bacteriophages were particularly susceptible to inactivation, mechanisms of bacteriophage mitigation due to electrocoagulation were investigated. Physical removal was primarily due to inclusion in flocs, while inactivation was primarily due to ferrous iron oxidation. Greater electrostatic attraction, virus aggregation, and capsid durability were proposed as reasons for virus susceptibility to ferrous-based inactivation. Results suggest that overall treatment claims based on bacteriophage mitigation for any iron-based technology should be critically considered due to higher susceptibility of bacteriophages to inactivation via ferrous oxidation.

Critical evaluation of mechanism responsible for biomass abatement during electrochemical coagulation (EC) process: A critical review

This is a first review paper that delineates fundamental disinfection mechanism undergoes during the simple electrochemical coagulation (EC) process. The elucidation of detailed mechanistic phenomenon of EC process involved would help to enhance the disinfection efficiency. In this context, the biomass (bacteria, virus and algae) abatement mechanism by EC is critically reviewed and rationalized based on the experimental demonstration performed from the recent decade. Whereas, the effect of most significant abiotic operating parameters, dissolved contents and bacteria cell wall composition on biomass reduction are explored in detail. From these analyses, physical removal and chemical inactivation routes are identified for bacteria abatement mechanism during the EC process using sacrificial electrodes. Which includes (i) enmeshment of microbial contaminants by EC flocs, (ii) sweeping flocculation is preferentially for destabilization of negatively charged biomass, and (iii) inactivation/attenuation of micro-organism cell walls by electrochemically induced reactive oxygen species (ROS) or direct interaction of electric field. Perhaps, the overall abatement mechanism attributes due to the aforementioned phenomenon endures independently and/or synergistically during the EC process. Nonetheless, to obtain better understanding of virus and algae abatement mechanism, we require more experimental investigation on algae and virus removal. Eventually, more intensive research efforts on biomass attenuation by EC are most important to reinforce this claim.

Coagulant residues' influence on virus enumeration as shown in a study on virus removal using aluminium, zirconium and chitosan

Research on microorganism reduction by physicochemical water treatment is often carried out under the assumption that the microbiological enumeration techniques are not affected by the presence of coagulants. Data presented here indicate that bacteriophage enumeration by plaque assay and RT-qPCR (reverse transcription quantitative polymerase chain reaction) can be affected by these water treatment chemicals. Treatment of water samples with an alkaline protein-rich solution prior to plaque assay and optimization of RNA extraction for RT-qPCR were implemented to minimize the interference. The improved procedures were used in order to investigate reduction of three viral pathogens and the MS2 model virus in the presence of three coagulants. A conventional aluminium coagulant was compared to alternative agents (zirconium and chitosan) in a coagulation-filtration system. The highest virus reduction, i.e., 99.9-99.99%, was provided by chitosan, while aluminium and zirconium reduced virus by 99.9% in colour-rich water and by 90% in water with less colour, implying an effect of coagulant type and raw water quality on virus reduction. Although charge characteristics of viruses were associated with virus reduction, the results reveal that the MS2 phage is a suitable model for aggregation and retention of the selected pathogens.

Charge, size distribution and hydrophobicity of viruses: Effect of propagation and purification methods

Two virus propagation methods (in broth and on double agar overlay) and three purification procedures (PEG precipitation, centrifugal diafiltration and CsCl density gradient centrifugation) were comparatively evaluated using MS2 and P22 bacteriophages as model viruses. The prepared stocks were characterized in terms of electrophoretic mobility as a function of pH, particle size distribution, surface tension components and the overall hydrophobicity of the virus, as well as the percentage of infectious and total virus recovered. The obtained data were used to rank the purification methods according to six criteria of likely practical relevance. Regardless of the purification method applied, virus propagation in broth media resulted in higher purity virus stocks as the growth on double agar overlay introduced difficult-to-remove residual agar. CsCl density gradient centrifugation gave the highest quality bacteriophage suspensions, recovered infectious P22 at least as efficiently as the other two purification methods and selected for intact P22 virions over damaged ones. The impurities remaining in the virus suspension after PEG precipitation and centrifugal diafiltration broadened the size distribution and interfered with electrophoretic mobility measurements. The residual impurities had a major impact on the free energy of virus-virus interfacial interaction (the quantitative measure of virus hydrophobicity/hydrophilicity) leading to an incorrect determination of P22 bacteriophage as hydrophilic. The trends in measured physicochemical properties can be rationalized by considering impurity-coated virions as permeable soft particles.

Performance and Mechanisms of Ultrafiltration Membrane Fouling Mitigation by Coupling Coagulation and Applied Electric Field in a Novel Electrocoagulation Membrane Reactor

A novel electrocoagulation membrane reactor (ECMR) was developed, in which ultrafiltration (UF) membrane modules are placed between electrodes to improve effluent water quality and reduce membrane fouling. Experiments with feedwater containing clays (kaolinite) and natural organic matter (humic acid) revealed that the combined effect of coagulation and electric field mitigated membrane fouling in the ECMR, resulting in higher water flux than the conventional combination of electrocoagulation and UF in separate units (EC-UF). Higher current densities and weakly acidic pH in the EMCR favored faster generation of large flocs and effectively reduced membrane pore blocking. The hydraulic resistance of the formed cake layers on the membrane surface in ECMR was reduced due to an increase in cake layer porosity and polarity, induced by both coagulation and the applied electric field. The formation of a polarized cake layer was controlled by the applied current density and voltage, with cake layers formed under higher electric field strengths showing higher porosity and hydrophilicity. Compared to EC-UF, ECMR has a smaller footprint and could achieve significant energy savings due to improved fouling resistance and a more compact reactor design.

Integrated pretreatment and desalination by electrocoagulation (EC)-ion concentration polarization (ICP) hybrid

Conventional water treatment process is composed of multiple stages, including desalination (salt removal) and pre/post-treatment of desalination to remove particles, chemicals, and other potential foulants for desalination. In this work, we developed a microfluidic proof-of-concept for a single device water treatment system, which removes both salt ions and non-salt contaminants. Our system combines electrocoagulation (EC), a versatile contaminant removal process, and ion concentration polarization (ICP) desalination, which is an electromembrane desalination process. We demonstrated a continuous EC-ICP operation that removed >95% of suspended solids and reduced the salinity from brackish range (20 mM NaCl) to a potable level (<8.6 mM NaCl). We also demonstrated that our system is flexible in terms of the type and concentration of contaminants it can handle. Combining two different electrochemical processes into a single system, we can reduce unnecessary voltage drop by having a shared anode, and achieve both seamless integration and energy efficient operation. Our system will find applications as a small-scale water treatment system, if properly scaled up in the future.

Assessment of the efficacy of membrane filtration processes to remove human enteric viruses and the suitability of bacteriophages and a plant virus as surrogates for those viruses

Here, we evaluated the efficacy of direct microfiltration (MF) and ultrafiltration (UF) to remove three representative human enteric viruses (i.e., adenovirus [AdV] type 40, coxsackievirus [CV] B5, and hepatitis A virus [HAV] IB), and one surrogate of human caliciviruses (i.e., murine norovirus [MNV] type 1). Eight different MF membranes and three different UF membranes were used. We also examined the ability of coagulation pretreatment with high-basicity polyaluminum chloride (PACl) to enhance virus removal by MF. The removal ratios of two bacteriophages (MS2 and φX174) and a plant virus (pepper mild mottle virus; PMMoV) were compared with the removal ratios of the human enteric viruses to assess the suitability of these viruses to be used as surrogates for human enteric viruses. The virus removal ratios obtained with direct MF with membranes with nominal pore sizes of 0.1-0.22 μm differed, depending on the membrane used; adsorptive interactions, particularly hydrophobic interactions between virus particles and the membrane surface, were dominant factors for virus removal. In contrast, direct UF with membranes with nominal molecular weight cutoffs of 1-100 kDa effectively removed viruses through size exclusion, and >4-log₁₀ removal was achieved when a membrane with a nominal molecular weight cutoff of 1 kDa was used. At pH 7 and 8, in-line coagulation-MF with nonsulfated high-basicity PACls containing Al₃₀ species had generally a better virus removal (i.e., >4-log₁₀ virus removal) than the other aluminum-based coagulants, except for φX174. For all of the filtration processes, the removal ratios of AdV, CV, HAV, and MNV were comparable and strongly correlated with each other. The removal ratios of MS2 and PMMoV were comparable or smaller than those of the three human enteric viruses and MNV, and were strongly correlated with those of the three human enteric viruses and MNV. The removal ratios obtained with coagulation-MF for φX174 were markedly smaller than those obtained for the three human enteric viruses and MNV. However, because MS2 was inactivated after contact with PACl during coagulation pretreatment, unlike AdV, CV, MNV, and PMMoV, the removal ratios of infectious MS2 were probably an overestimation of the ability of coagulation-MF to remove infectious AdV, CV, and caliciviruses. Thus, PMMoV appears to be a suitable surrogate for human enteric viruses, whereas MS2 and φX174 do not, for the assessment of the efficacy of membrane filtration processes to remove viruses.

The roles of bacteriophages in membrane-based water and wastewater treatment processes: A review

Membrane filtration processes have been widely applied in water and wastewater treatment for many decades. Concerns related to membrane treatment effectiveness, membrane lifespan, and membrane fouling control have been paid great attention. To achieve sustainable membrane operation with regards to low energy and maintenance cost, monitoring membrane performance and applying suitable membrane control strategies are required. As the most abundant species in water and wastewater, bacteriophages have shown great potential to be employed in membrane processes as (1) indicators to assess membrane performance considering their similar properties to human pathogenic waterborne viruses; (2) surrogate particles to monitor membrane integrity due to their nano-sized nature; and (3) biological agents to alleviate membrane fouling because of their antimicrobial properties. This study aims to provide a comprehensive review on the roles of bacteriophages in membrane-based water and wastewater treatment processes, with focuses on their uses for membrane performance examination, membrane integrity monitoring, and membrane biofouling control. The advantages, limitations, and influencing factors for bacteriophage-based applications are reported. Finally, the challenges and prospects of bacteriophage-based applications in membrane processes for water treatment are highlighted.

Electrolytic removal of alizarin red S by Fe/Al composite hydrogel electrode for electrocoagulation toward a new wastewater treatment

This paper studies Fe/Al composite hydrogel electrode electrocoagulation (EC) and adsorption of alizarin red S (ARS). ARS removal efficiency and degradation mechanism when applying Fe/Al composite hydrogel electrode were investigated. The optimum experimental factors and degradation of ARS were discussed. ARS degradation was optimal operation at initial pH 3 with O₂.The experimental results showed that the COD removal efficiency was better, reaching to about 90 % when applying the novel electrode system. The discoloration rate also reached the best effect of 99 % in the superior technical conditions. The optimum electrolysis time is about 30 min. Results revealed that the efficiency in the EC process with Fe/Al composite hydrogel electrodes were much better than that in conventional electrode system. In addition, Fe/Al composite hydrogel electrodes are environment-friendly material, which reuse waste and reduce cost. Hydrogel has certain iron exchange capacity to eliminate the residual metal irons. It is found that the application of ultrasonic helps to accelerate the electrocoagulation of ARS. This study not only realizes the ultrasonic, flotation, coagulation, and adsorption of the combination but also gains economy and environment. Consequently, the unique performance of Fe/Al composite hydrogel electrodes opens promising perspectives for fast, high, and economical treatment of wastewater containing dyes or/and organic contaminants.

Aluminum electrocoagulation as pretreatment during microfiltration of surface water containing NOM: A review of fouling, NOM, DBP, and virus control

Electrocoagulation (EC) is the intentional corrosion of sacrificial anodes (typically aluminum or iron) by passing electricity to release metal-ion coagulant species and destabilize a wide range of suspended, dissolved, and macromolecular contaminants. It can be integrated ahead of microfiltration (MF) to effectively control turbidity, microorganisms, and disinfection by-products (DBPs) and simultaneously maintain a high MF specific flux. This manuscript summarizes the current knowledge on MF pretreatment by aluminum EC particularly focusing on mechanisms of (i) electrocoagulant dosing, (ii) (bio)colloid destabilization, (iii) fouling reductions, and (iv) enhanced removal of viruses, natural organic matter (NOM), and DBP precursors. Electrolysis efficiently removes hydrophobic NOM, viruses, and siliceous foulants. Aluminum effectively electrocoagulates viruses by physically encapsulating them in flocs, neutralizing their surface charge and reducing electrostatic repulsion, and increasing hydrophobic interactions between any sorbed NOM and free viruses. New results included herein demonstrate that EC achieves DBP control by removing NOM, reducing chlorine-reactivity of remaining NOM, and inducing a slight shift toward more brominated trihalomethanes and haloacetic acids. EC reduces MF fouling by forming large flocs that tend to deposit on the membrane surface, i.e. decrease pore penetration and forming more permeable cakes and by reducing foulant mass in case of significant floc-flotation.

Microstickies agglomeration by electric field

Microstickies deposits on both paper machine and paper products when it agglomerates under step change in ionic strength, pH, temperature and chemical additives. These stickies increase the down time of the paper mill and decrease the quality of paper. The key property of microstickies is its smaller size, which leads to low removal efficiency and difficulties in measurement. Thus the increase of microstickies size help improve both removal efficiency and reduce measurement difficulty. In this paper, a new agglomeration technology based on electric field was investigated. The electric treatment could also increase the size of stickies particles by around 100 times. The synergetic effect between electric field treatment and detacky chemicals/dispersants, including polyvinyl alcohol, poly(diallylmethylammonium chloride) and lignosulfonate, was also studied.

Numerical modeling of an electrically enhanced membrane bioreactor (MBER) treating medium-strength wastewater

In this paper, a numerical model of an electrically enhanced membrane bioreactor (MBER) was developed. MBER is a reactor that combines biological decomposition, membrane filtration and electrocoagulation of wastewater pollutants in a hybrid unit. To assess its design, the final contents and removal efficiencies of organics, nutrients, and metals were carried out using varying influent compositions. In a 60-day test of a laboratory-scale MBER, experimental results were used to calibrate and validate the model. The modeling results were in agreement with the experimental data and showed that the MBER can remove 99% of total phosphorus (TP), 99.9% of chemical oxygen demand (COD), 91% of total nitrogen (TN), 79% of nickel (Ni), 89% of iron (Fe), and 80% of chromium (Cr), using a current density of 15 A/m(2) intermittently supplied in a cycle of 5 min ON and 15 min OFF.

The Impact of Capsid Proteins on Virus Removal and Inactivation During Water Treatment Processes

This study examined the effect of the amino acid composition of protein capsids on virus inactivation using ultraviolet (UV) irradiation and titanium dioxide photocatalysis, and physical removal via enhanced coagulation using ferric chloride. Although genomic damage is likely more extensive than protein damage for viruses treated using UV, proteins are still substantially degraded. All amino acids demonstrated significant correlations with UV susceptibility. The hydroxyl radicals produced during photocatalysis are considered nonspecific, but they likely cause greater overall damage to virus capsid proteins relative to the genome. Oxidizing chemicals, including hydroxyl radicals, preferentially degrade amino acids over nucleotides, and the amino acid tyrosine appears to strongly influence virus inactivation. Capsid composition did not correlate strongly to virus removal during physicochemical treatment, nor did virus size. Isoelectric point may play a role in virus removal, but additional factors are likely to contribute.

Escherichia coli Attenuation by Fe Electrocoagulation in Synthetic Bengal Groundwater: Effect of pH and Natural Organic Matter

Technologies addressing both arsenic and microbial contamination of Bengal groundwater are needed. Fe electrocoagulation (Fe-EC), a simple process relying on the dissolution of an Fe(0) anode to produce Fe(III) precipitates, has been shown to efficiently remove arsenic from groundwater at low cost. We investigated Escherichia coli (E. coli) attenuation by Fe-EC in synthetic Bengal groundwater as a function of Fe dosage rate, total Fe dosed, pH, and presence of natural organic matter (NOM). A 2.5 mM Fe dosage simultaneously achieved over 4-log E. coli attenuation and arsenic removal from 450 to below 10 μg/L. E. coli reduction was significantly enhanced at pH 6.6 compared to pH 7.5, which we linked to the decreased rate of Fe(II) oxidation at lower pH. 3 mg/L-C of NOM (Suwanee River fulvic acid) did not significantly affect E. coli attenuation. Live-dead staining and comparisons of Fe-EC with chemical coagulation controls showed that the primary mechanism of E. coli attenuation is physical removal with Fe(III) precipitates, with inactivation likely contributing as well at lower pH. Transmission electron microscopy showed that EC precipitates adhere to and bridge individual E. coli cells, resulting in large bacteria-Fe aggregates that can be removed by gravitational settling. Our results point to the promising ability of Fe-EC to treat arsenic and bacterial contamination simultaneously at low cost.

Relative insignificance of virus inactivation during aluminum electrocoagulation of saline waters

Combined removal and inactivation of the MS2 bacteriophage from model saline (0-100 mM NaCl) waters by electrochemical treatment using a sacrificial aluminum anode was evaluated. Both chemical and electrodissolution contributed to coagulant dosing since measured aluminum concentrations were statistically higher than purely electrochemical predictions using Faraday's law. Electrocoagulation generated only small amounts of free chlorine in situ but effectively destabilized viruses and incorporated them into Al(OH)3(s) flocs during electrolysis. Low chlorine concentrations combined with virus shielding and aggregation within flocs resulted in very slow disinfection rates necessitating extended flocculation/contact times to achieve significant log-inactivation. Therefore, the dominant virus control mechanism during aluminum electrocoagulation of saline waters is "physical" removal by uptake onto flocs rather than "chemical" inactivation by chlorine. Attenuated total reflectance-Fourier transform infrared spectroscopy provided evidence for oxidative transformations of capsid proteins including formation of oxyacids, aldehydes, and ketones. Electrocoagulation significantly altered protein secondary structures decreasing peak areas associated with turns, bends, α-helices, β-structures, and random coils for inactivated viruses compared with the MS2 stock. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) measurements showed rapid initial RNA damage following a similar trend as plaque assay measurements of infectious viruses. However, ssRNA cleavage measured by qRT-PCR underestimated inactivation over longer durations. Although aluminum electrocoagulation of saline waters disorders virus capsids and damages RNA, inactivation occurs at a sufficiently low rate so as to only play a secondary role to floc-encapsulation during residence times typical of electrochemical treatment.

Mechanisms of physically irreversible fouling during surface water microfiltration and mitigation by aluminum electroflotation pretreatment

A modified poly(vinylidene fluoride) membrane was used to directly microfilter untreated Lake Houston water, which was then regenerated by surface washing and hydraulic backwashing, a process that was cycled five times. The source water was also electrochemically precoagulated using aluminum and microfiltered, and the membrane was physically regenerated for five cycles. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize foulants on membrane surfaces and rigorously deduce their contributions to physically irreversible fouling after cycles 1 and 5. Hydrophobic molecules primarily appeared to initiate fouling during microfiltration of untreated raw water because O-H/N-H bands were attenuated while C-H bands remained relatively unchanged in FTIR-spectra of membrane surfaces after only one cycle. However, O-H/N-H and symmetric and asymmetric C(═ O)O(-) stretching bands significantly intensified with continued filtration/regeneration of untreated water, showing the importance of hydrophilic molecules and the role of complexation, respectively, to longer term irreversible fouling. Distinct C-H bands were detected in floated flocs after electrolysis, suggesting the sorption and subsequent removal of a substantial portion of the hydrophobic moieties present in Lake Houston water during pretreatment. Consequently, hydrophilic compounds appeared to contribute more to irreversible fouling in pretreated waters throughout the course of filtration as evidenced by significantly more intense O-H bands (compared with C-H bands) on the membrane surface after cycles 1 and 5. Therefore, electroflotation pretreatment reduced accumulation of hydrophobic foulants but simultaneously increased complexation of hydrophilic foulant molecules along with any carried-over aluminum hydroxide precipitates evidenced by increasing Al and O concentrations via XPS and intense C(═ O)O(-) stretching bands in IR spectra.

Mechanisms of MS2 bacteriophage removal by fouled ultrafiltration membrane subjected to different cleaning methods

An ultrafiltration unit with a polyvinylidene fluoride (PVDF) membrane of 40 nm nominal pore size was used to study bacteriophage MS2 removal under different membrane conditions: pristine membrane, membrane fouled by soluble microbial product (SMP) extracted from membrane bioreactor (MBR) feedwater, backwashed membrane, and chemically cleaned membrane. The order of MS2 removal by these membranes was as follows: fouled membrane > backwashed membrane > chemically cleaned membrane ≈ pristine membrane. A linear correlation between membrane relative permeability and MS2 removal was found. Mass balance analysis showed a high percentage of MS2 in the concentrate for the fouled membrane as compared with the pristine membrane. Quartz crystal microbalance (QCM) results showed faster kinetics of MS2 adhesion to the pristine membrane than to the SMP-fouled membrane. In agreement with QCM results, an attractive force between MS2 and the pristine membrane was detected using an atomic force microscope (AFM), whereas a repulsive force was detected for the interaction between MS2 and the fouled membrane. The presence of SMP on the membrane surface led to higher rejection of MS2 due to both pore blocking and repulsion between MS2 and the SMP layer. Chemical cleaning removed most of the SMP foulant and as a result led to a lower MS2 removal.