Natural organic matter (NOM) removal by electrochemical methods — A review

Degradation of humic acid by UV/PMS: process comparison, influencing factors, and degradation mechanism

In natural water bodies, humic acid (HA), generated during the chlorination disinfection process at water treatment plants, can produce halogenated disinfection by-products, increasing the risk to drinking water safety and posing a threat to human health. Effectively removing HA from natural waters is a critical focus of environmental research. This study established a synergistic ultraviolet/peroxymonosulfate (UV/PMS) system to remove HA from water. It compared the efficacy of various UV/advanced oxidation processes (AOPs) on HA degradation, and assessed the influence of different water sources, initial pH, oxidant concentration, and anions (HCO3 -, Cl-, NO3 -) on HA degradation. The degradation mechanism of HA by the UV/PMS process was also investigated. Results showed that under the conditions of 3 mmol L-1 PMS concentration, 10 mg L-1 HA concentration, initial solution pH of 7, and a reaction time of 240 minutes, the mineralization rate of HA by UV/PMS reached 94.15%. The pseudo-first-order kinetic constant (k obs) was 0.01034 and the single-electric energy (EE/O) was 0.0157 kW h m-3, indicating superior HA removal efficiency compared to other systems. Common anions (HCO3 -, Cl-, NO3 -) in water were found to inhibit the degradation of HA, and acidic conditions were more conducive to HA removal, with the optimal pH being 3. Free radical quenching experiments showed that both sulfate radical (SO4 -˙) and hydroxyl radical (˙OH) radicals were involved in HA degradation, with SO4 -˙ being the primary oxidant and ˙OH as the auxiliary species. Analyses using 3D-excitation-emission matrix (EEM), parallel factor analysis (PARAFAC), specific fluorescence index, and absorbance demonstrated that UV/PMS technology could effectively degrade HA in water. This study provides theoretical references for further research on the removal of HA and other organic substances using UV/PMS technology.

Environment-friendly and efficient electrochemical degradation of sulfamethoxazole using reduced TiO2 nanotube arrays-based Ti membrane coated with Sb-SnO2

This study focused on the preparation, characterization, and sulfamethoxazole (SMX) removal performance of the SnO₂-coated reactive electrochemical membrane (REM). This REM was fabricated by loading SnO₂ on the reduced TiO₂ nanotube arrays (RTNA)-based Ti membrane (TM). Regarding the dopant for SnO₂, Sb was more effective in boosting the electrocatalytic activity than Bi, and the energy consumption for Sb-SnO₂-coated REM (TM/RTNA/ATO) was lower than Bi-SnO₂-coated REM (TM/RTNA/BTO). As for the internal layer, RTNA provided TM/RTNA/ATO with more electroactive surface areas and prolonged the service lifetime. Compared with batch mode, the SMX removal efficiency in flow-through mode was increased up to 8.4-fold. The SMX degradation performances were also affected by fluid velocity, current density, initial SMX concentration, and electrolyte concentration. The synergistic effects of ^•OH oxidation and direct electron transfer were responsible for the effective removal of SMX. TM/RTNA/ATO was proved to be stable and durable by multi-cycle and accelerated lifetime tests. Its extensive applicability was verified with high removal efficiencies of SMX in the surface water and wastewater effluent. These results demonstrate the promise of TM/RTNA/ATO for water treatment applications.

Comparison of the formation of aldehydes and carboxylic acids in ozonated and electrochemically treated surface water

This study compared effects of conventional ozonation and electrochemical oxidation (EO) on the formation of aldehydes and aliphatic carboxylic acids produced via the oxidation of natural organic matter (NOM) present in a low-mineralized surface water with a relatively low NOM concentration. Conventional ozonation and EO were effective in degrading the aromatic moiety of NOM characterized by the absorbance at 254 nm. Yields of aliphatic carboxylic acids in the ozone treated water were dominated by formate, acetate and oxalate, while no acetate was observed in the case of EO treatment. The speciation of aldehydes was similar in the case of ozonation and EO treatment, but the aldehydes yields were notably higher for ozonation. The presence of the elevated carbonate concentration moderated the changes in disinfection by-products (DBPs) concentration in the EO treated water due to the interception of ∙OH by HCO₃^-, while it did not affect ozonation treatment. This study allows gaining more insights into the nature of processes characteristic and optimization of disinfections based on ozonation and EO methods.

Experimental investigation of the performance of anaerobic membrane bioreactor with electrolytic regeneration (AMBER) for challenges and options in wastewater treatment

Significant changes in wastewater services are necessary for achieving the sustainable development goals (SDGs), by utilizing resource recovery, recycle, and reuse in urban wastewater-treatment plants. Based on recent experiences, to improve the filtration behavior of a membrane bioreactor, a hybrid system including an upgraded anaerobic baffled reactor coupled with an electrolysis process and a nanocomposite-membrane was developed. The system, called an anaerobic membrane bioreactor with electrolytic regeneration (AMBER), is a bio-electrochemical process that is expected to be simultaneously efficient in both biogas augmentation and fouling mitigation. The goals were to enhance the stability and efficiency of the anaerobic membrane bioreactor. The integration of the electrolytic process with the ABR (EABR) using a pair of iron electrodes enhanced the removal of contaminants in the ABR while successfully maintained pH in the optimum range for anaerobic digestion (6.8 to 7.2). Then, the performance of AMBER in pollutant removal, including organic load, suspended solids, and microbial load, were investigated over 240 days. The results showed that configuration considerably enhanced permeate flux, as it reduced the deposition of extracellular polymeric substances (EPS) on the surface of the nanocomposite membrane, leading to a reduction in membrane fouling. EPS was extracted and quantified to compare the effect of biogas backwash on the function of the membrane reactor. After 7 d of operation with a daily biogas backwash, the flux reduction was approximately 13 % for the conventional combination of the anaerobic baffled reactor and the membrane bioreactor (AMBR), while it was limited to 4 % in AMBER. After cleaning by the biogas, EPS formation decreased 63 % in AMBER when compared to the AMBR. The results revealed that AMBER can be considered an environmentally competitive bioenergy technology for wastewater treatment with the purpose of water recovery and reuse, employing optimized operational conditions, application of antifouling membranes, and electrically-based strategies.

Electrochemical Methods for Water Purification, Ion Separations, and Energy Conversion

Agricultural development, extensive industrialization, and rapid growth of the global population have inadvertently been accompanied by environmental pollution. Water pollution is exacerbated by the decreasing ability of traditional treatment methods to comply with tightening environmental standards. This review provides a comprehensive description of the principles and applications of electrochemical methods for water purification, ion separations, and energy conversion. Electrochemical methods have attractive features such as compact size, chemical selectivity, broad applicability, and reduced generation of secondary waste. Perhaps the greatest advantage of electrochemical methods, however, is that they remove contaminants directly from the water, while other technologies extract the water from the contaminants, which enables efficient removal of trace pollutants. The review begins with an overview of conventional electrochemical methods, which drive chemical or physical transformations via Faradaic reactions at electrodes, and proceeds to a detailed examination of the two primary mechanisms by which contaminants are separated in nondestructive electrochemical processes, namely electrokinetics and electrosorption. In these sections, special attention is given to emerging methods, such as shock electrodialysis and Faradaic electrosorption. Given the importance of generating clean, renewable energy, which may sometimes be combined with water purification, the review also discusses inverse methods of electrochemical energy conversion based on reverse electrosorption, electrowetting, and electrokinetic phenomena. The review concludes with a discussion of technology comparisons, remaining challenges, and potential innovations for the field such as process intensification and technoeconomic optimization.

Miniaturized Method for Chemical Oxygen Demand Determination Using the PhotoMetrix PRO Application

The analysis of chemical oxygen demand (COD) plays an important role in measuring water pollution, but it normally has a high ecological price. Advances in image acquisition and processing techniques enable the use of mobile devices for analytical purposes. Here, the PhotoMetrix PRO application was used for image acquisition and multivariate analysis. Statistical analysis showed no significant difference in the results compared to the standard method, with no adverse effect of the volume reduction. The cost of analysis and waste generation were reduced by one third, while the analysis time was reduced by one fifth. The miniaturized method was successfully employed in the analysis of several matrices and for the evaluation of advanced oxidation processes. The AGREE score was improved by 25% due to miniaturization. For these reasons, the miniaturized PhotoMetrix PRO method is a suitable option for COD analysis, being less hazardous to the environment due to reductions in the chemicals used and in waste generation.

Assessing the performance of coral reef-like floc towards the removal of low molecular weight organic contaminant

The removal of low molecular weight (MW) organics by coagulation is always a challenge in water treatment. In this study, we proposed a novel coagulation strategy: continuous dosing coagulation (CDC). The metallic coagulant and alkali were continuously dosed into water that was pre-acidized, rather than adding all the coagulant and alkali at once as in conventional coagulation (CC). The CDC process promoted the removal of different low MW organics, performing 15% better than the CC process. The best performance occurred at initial pH 6 and the coagulant dosing rate was 2 mg/(L·min). Under optimal conditions, the continuously dosed coagulant formed medium polymer Al in the early stages, which bound low MW organics to form complexes. Then, the subsequently dosed coagulant could adhere to the primary complexes and form coral reef-like surfaces with higher zeta potential and specific surface area. Each freshly formed surface bound contaminants and covered the previous surface. As a result, more dissolved low MW organic contaminants were included in the interior of flocs. However, in the CC process, all the coagulant was dosed at once, resulting in the rapid formation of aluminum hydroxide clusters, which had cotton-like surfaces with fewer binding sites. To achieve similar organic removal in treating secondary effluent, the CDC dosage was half of the CC dosage, indicating the potential economic benefits. The CDC process is a promising technology and the application in various water treatments should be further investigated.

Reduced cathodic scale and enhanced electrochemical precipitation of Ca2+ and Mg2+ by a novel fenced cathode structure: Formation of strong alkaline microenvironment and favorable crystallization

Electrochemical precipitation is a promising technique for hardness abatement without the addition of external ions. However, the scale layer on cathode deteriorated the removal efficiency and limited the practical application. Herein, a fenced cathode structure was designed to prevent cathodic precipitation. The cathode was fenced by a crystallization-inducing material for separating the OH- production and crystallization processes. Precipitation on the cathode was confirmed to shift to the crystallization-inducing material, and the clean fenced cathode provided efficient long-term OH- production. At a current density of 40 A/m2, the Ca2+ or Mg2+ removal efficiency increased by 12.8% or 46.1%, respectively, compared to those of a traditional cathode. Thermodynamic equilibrium in synthetic water and mine water, mass transfer and the location of precipitation were analyzed to elucidate the electrochemical precipitation process. The enhanced mechanism was ascribed to the crystallization-inducing material, which remarkably promoted the crystallization process, and hindered OH- migration, thereby increased the pH of alkaline microenvironment. Notably, a recovery design was proposed to recover pure calcite and brucite from alkalinity-free wastewater. The design reveals a promising strategy for enhancing the crystallization process and reducing cathodic scale, also initiating a new research direction toward hardness removal.

Methods for stability assessment of electrically conductive membranes

The surface properties of electrically conductive membranes (ECMs) govern their advanced abilities. During operation, these properties may differ considerably from their initially measured properties. Depending on their operating conditions, ECMs may undergo various degrees of passivation. ECM passivation can detrimentally impact their real time performance, causing large deviations from expected behaviour based on their initially measured properties. Quantifying these changes will enable consistent performance comparisons across the active and electrically conductive membrane research field. As such, consistent methods must be established to quantify ECM membrane properties. In this work, we proposed three standardized methods to assess the electrochemical, chemical, and physical stability of such membrane coatings: 1) electrochemical oxidation, 2) surface scratch testing, and 3) pressurized leaching. ECMs were synthesized by the most common approach - coating support ultrafiltration (UF) and/or microfiltration (MF) polyethersulfone (PES) membranes with carbon nanotubes (CNT) cross-linked with polyvinyl alcohol (PVA) and two types of cross-linkers (either succinic acid (SA) or glutaraldehyde (GA)). We then evaluated these ECMs based on the three standardized methods: 1) We evaluated electrochemical stability as a function of electro-oxidation induced by applying anodic potentials. 2) We measured the scratch resistance to quantify the surface mechanical stability. 3) We measured physical stability by quantifying the leaching of PVA during separation of a model foulant (polyethylene oxide (PEO)). Our methods can be extended to all types of electrically conductive membranes including MF, UF, nanofiltration (NF), and reverse osmosis (RO) ECMs. We propose that these fundamental measurements are critical to assessing the viability of ECMs for industrial MF, UF, NF, and RO applications.•Anodic-oxidation was used to check the electrochemical stability of ECMs•Depth of penetration resulted from scratch test is an indicator of the electrically conductive membrane coating's mechanical stability•The leaching of the main components forming the nanolayer was quantified to assess the membranes' physical stability.

Importance of Combined Electrochemical Process Sequence and Electrode Arrangements: A Lab-scale Trial of Real Reverse Osmosis Landfill Leachate Concentrate

Reverse osmosis (RO) is a widely applied technique for wastewater effluent reuse and landfill leachate treatment. The latter generates a refractory RO leachate concentrate (ROLC), for which cost-effective treatment is required. This study focuses on a two-step electrochemical method consisting of aluminum-based electrocoagulation (EC), and simultaneous electrooxidation-electrocoagulation with a titanium-based lead dioxide (Ti/ß-PbO₂) anode and aluminum cathode (EO_EC) assembly. The sequence and electrode arrangements of the combined electrochemical process were investigated to determine the organic transformation, Ti/ß-PbO₂ anode viability, and energy consumption. Series-based EC-EO_EC decreased the total chemical oxygen demand (COD) from 8750 mg L^-1 to 380 mg L^-1, a 96% removal efficiency, in 3.5 hours at 141 A m^-2. Under a low energy consumption of 28.7 kWh kg_COD^-1, the ROLC biodegradability (BOD₅/COD) significantly increased from 0.015 to 0.530, which was ascribed to aromatic removal (e.g., -C=C) and an increase in -COOH functional groups. Furthermore, the rapid removal of natural organic matter and increase in pH elevation from EC suppressed the dissolution of Pb from the Ti/ß-PbO₂ anode during the subsequent EO_EC, thereby leaving 0.061 mg L^-1 in the ROLC after treatment. The treatment cost was 3.86 USD kg_COD^-1, which was approximately 34% lower than that of previously reported electrochemical processes for ROLC treatment. These findings obtained with a real RO concentrate provide a foundation for scaling up this new electrochemical treatment approach.

Enhanced decomposition of long-chain perfluorocarboxylic acids (C9-C10) by electrochemical activation of peroxymonosulfate in aqueous solution

The decomposition of long-chain perfluorocarboxylic acids (PFCAs), including perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA), were investigated by electrochemical activation of peroxymonosulfate (PMS) on porous Ti/SnO₂-Sb membrane anode. The results indicated that PMS activation could efficiently promote PFNA/PFDA decomposition, with pseudo-first-order rate constants about 3.12/2.06 times as compared with that of direct electro-oxidations. The energy consumptions of PFNA and PFDA decomposition were 36.31 and 37.46 kWh·m^-3·order^-1, respectively. The quantitative detection results of •OH with electron paramagnetic resonance (EPR) demonstrated that PMS activation promoted •OH formation. The inhibited performance in radical scavengers indicated both •OH and SO₄^•- might be mainly involved in PFNA decomposition, while SO₄^•- might be mainly involved in PFDA decomposition during PMS activation process. The mineralization mechanism for long-chain PFCAs decomposition which was mainly by repeating CF₂-unzipping cycle via radical reaction based on the intermediates verification and mass balance of C and F, was proposed. These results suggested that electrochemical activation of PMS on porous Ti/SnO₂-Sb membrane anode exhibited high efficiency in mineralizing PFNA and PFDA under mild conditions. This work might provide an efficient way for persistent organic pollutants, including, but not limited to long-chain PFCAs elimination from wastewater.

Effects of fulvic acids on the electrochemical reactions and mass transfer properties of organic cation toluidine blue: Results of measurements by the method of rotating ring-disc electrode

This study examined effects of aquatic and soil natural organic matter (NOM) exemplified by standard Suwannee River fulvic acid (SRFA) and Pahokee Peat fulvic acid (PPFA), respectively, on the electrochemical (EC) reactivity and mass transfer properties of the cationic organic probe toluidine blue (TB) that forms complexes with NOM. EC measurements that were carried out using the method of rotating ring-disc electrode (RRDE) showed that for disc potentials below -0.4 V vs. the standard Ag/AgCl reference electrode, TB molecules undergo EC reduction accompanied by the formation of EC-active products that undergo oxidation at the ring electrode. EC reactions of TB in the range of potentials -0.2 to -0.4 V were determined to involve free TB⁺ cations and TB species adsorbed on the electrode surface. The EC reduction of TB species at the disc potentials < -0.4 V was controlled by the mass transfer of the free TB⁺ cations and TB/NOM complexes to the electrode surface. Formation of TB/NOM complexes caused the mass transfer-controlled TB currents to undergo a consistent decrease. The observed changes were correlated with the extent of TB/NOM complexation and decreases of the diffusion coefficients of TB/NOM complexes that have higher molecular weights (MW) than the free cations. Properties of the intermediates formed upon the reduction of TB⁺ cations were also affected by NOM. These results demonstrate that RRDE measurements of EC reactions of TB or possibly other EC active probes allow probing the complexation of EC-active organic species with NOM and mass transfer properties of NOM complexes and ultimately NOM itself.

Removal of natural organic matter from aqueous solutions using electrocoagulation pulsed current: optimization using response surface methodology

The use of the pulsed current can be an alternative to decrease the electrode polarization, as well as achieving lower energy consumption. This study investigated the electrocoagulation through pulsed current for the removal of natural organic matter from water. The experiments were carried out using Box-Behnken factorial design with the response surface methodology for the design of experiments, modeling and interpreting of the results. The electrocoagulation cell consisted of an acrylic reactor with 4 L capacity with four electrodes of aluminum, in parallel connection mode. The experimental independent variables studied were: current density (5.5 to 44.5 A m^-2), electrodes spacing (2 to 7.6 mm), stirring rate (200 to 1,000 rpm), frequency (500 to 5,000 Hz), humic acid concentration (5 to 20 mg L^-1) and NaCl (100 to 300 mg L^-1) as supporting electrolyte, evaluating the residual apparent color (RAC) and electric energy consumption (EEC). The pH of the solution increased during the experiments, reaching basic values. The response surface regression procedure was employed to fit the second-order polynomial, and the model fitted well to the obtained values, reaching R² 0.9995 (RAC) and R² 0.9989 (EEC). The lowest RAC was 11.8 Hazen units (96.2% color removal), where the EEC was 0.393 kWh m^-3.

Enhanced perfluorooctanoic acid degradation by electrochemical activation of peroxymonosulfate in aqueous solution

Perfluorooctanoic acid (PFOA) was efficiently decomposed at Ti/SnO₂-Sb anode via peroxymonosulfate (PMS) activation. PFOA degradation followed both pseudo-zero-order (0-30 min) and pseudo-first-order (30-120 min) kinetics. The pseudo-first-order kinetics constant could increase to 0.0484 min^-1 (3.84 times higher than that without PMS) during 30-120 min electrolysis. The inhibited performance in radical scavengers implied both sulfate radical (SO₄^•-) and hydroxyl radical (•OH) contributed to PFOA degradation. The •OH quantitative detection experiments demonstrated that SO₄^•- formed from PMS activation could promote •OH generation (from 0.12 mM to 0.24 mM). Electron spin resonance (ESR) tests further proved that SO₄^•- and •OH were generated during PFOA degradation. According to linear sweep voltammetry (LSV) analyses, the oxygen evolution potential (OEP) value of Ti/SnO₂-Sb electrode increased from 1.59 V to 1.72 V (vs SCE) via PMS addition, indicating the inhibited oxygen evolution which was beneficial for the reactive species formation (i.e. •OH, SO₄^•-). On the basis of intermediates verification and mass balance of carbon and fluorine, PFOA was proposed to be oxidized into short-chain perfluorocarboxylic acids mainly by •OH and SO₄^•-.

Sugar beet industry process wastewater treatment using electrochemical methods and optimization of parameters using response surface methodology

Sugar production is a water intensive process that produces a large amount of wastewaters with high concentration of chemical oxygen demand (COD), mostly consists of organic carbon compounds. Conventional treatment methods are limited to provide the necessary treatment of effluent COD to meet the regulatory limits prior to discharge. The treatment performance of electrooxidation (EO) and electrochemical peroxidation (ECP) for organic removal were investigated in a laboratory scale study. The experimental conditions were optimized for both EO and ECP using Box-Behnken Design (BBD) and the models provided highly significant quadratic models for both treatment methods. The effects of pH, H₂O₂ dosage, current density, and operation time were investigated using BBD. The results showed that EO could remove 75% of organics at optimum conditions of pH 5.3; current density of 48.5 mA cm^-2; and operation time of 393 min. The predicted values were in reasonable agreement with measured values. ECP could remove total and soluble COD and total and dissolved organic carbon by 65, 64, 66, and 63%, respectively at optimum conditions of H₂O₂ dosage of 21 mL L^-1; current density of 48 mA cm^-2; and operation time of 361 min. The methods were compared based on removal efficiency and energy consumption during operation.

Recent advances in thin film composites membranes for brackish groundwater treatment with critical focus on Saskatchewan water sources

Drinking water scarcity is an ever-increasing global concern. This issue appears as a greater threat to the countries with no access to sea water resources or rivers, since their potential water resources are only limited to ground waters only. There are serious concerns with the treatment of ground water resources, including landfill leachates, agricultural contaminations (pesticides, herbicides, and fertilizers), and rural contaminations. Membrane separation has been proved to be the governing technology in water and wastewater treatment plants, as these methods are responsible for more than half of the market share of the world's desalination capacity. This study intends to offer a holistic view of the groundwater contamination with specific focus on Saskatchewan province in Canada, and the recent efforts in the groundwater treatment using thin film composite membrane technology. This study begins with an introduction of the general aspects of ground water and membrane separation, polluting agents, and their sources. It is followed by a discussion of Saskatchewan's groundwater status and various issues. Furthermore, the recent research that became available since 2010 is reviewed in details and the results are summarized with respect to purification efficiency. Different affecting parameters in a groundwater-thin film composite system are synthesized and an in-depth overview is presented.

Treatment of canola-oil refinery effluent using electrochemical methods: A comparison between combined electrocoagulation + electrooxidation and electrochemical peroxidation methods

A comparative study of combined electrocoagulation (EC) + electrooxidation (EO) and electrochemical peroxidation (ECP) treatment processes were carried out to treat canola oil refinery (COR) wastewaters. The effect of applied current density and operation time in the removal of organic pollutants were investigated and discussed. Total chemical oxygen demand (TCOD), soluble chemical oxygen demand (sCOD), total organic carbon (TOC), dissolved organic carbon (DOC) and total suspended solids (TSS) were measured. Using only EC process was found to be significantly successful in removing suspended and colloidal pollutants and could remove more than 90% TCOD and 80% of TOC at current densities between 0.91 and 13.66 mA cm^-2. From the statistical model, the optimized conditions for TCOD at a current density of 7.61 mA cm^-2 and TOC at 7.99 mA cm^-2 under 40 min operation, validated to remove 93.45% and 94.5% respectively. However, the maximum removal of dissolved organic pollutants was relatively low in EC process and reported to be 75% for sCOD and 74% for DOC. Therefore, EC + EO process were run to increase the removal of sCOD and DOC to 99 and 95%, respectively. On the other hand, treatment using ECP process achieved a removal of sCOD and DOC between 77 and 86%. TSS were removed completely in both EC + EO and ECP processes. A statistical model was applied to compare the performance of two methods and found that the combined EC + EO process provided lightly better treatment compared to ECP method.

An overview of the uses of high performance size exclusion chromatography (HPSEC) in the characterization of natural organic matter (NOM) in potable water, and ion-exchange applications

Natural organic matter (NOM) constitutes the terrestrial and aquatic sources of organic plant like material found in water bodies. As of recently, an ever-increasing amount of effort is being put towards developing better ways of unraveling the heterogeneous nature of NOM. This is important as NOM is responsible for a wide variety of both direct and indirect effects: ranging from aesthetic concerns related to taste and odor, to issues related to disinfection by-product formation and metal mobility. A better understanding of NOM can also provide a better appreciation for treatment design; lending a further understanding of potable water treatment impacts on specific fractions and constituents of NOM. The use of high performance size-exclusion chromatography has shown a growing promise in its various applications for NOM characterization, through the ability to partition ultraviolet absorbing moieties into ill-defined groups of humic acids, hydrolysates of humics, and low molecular weight acids. HPSEC also has the ability of simultaneously measuring absorbance in the UV-visible range (200-350 nm); further providing a spectroscopic fingerprint that is simply unavailable using surrogate measurements of NOM, such as total organic carbon (TOC), ultraviolet absorbance at 254 nm (UV₂₅₄), excitation-emission matrices (EEM), and specific ultraviolet absorbance at 254 nm (SUVA₂₅₄). This review mainly focuses on the use of HPSEC in the characterization of NOM in a potable water setting, with an additional focus on strong-base ion-exchangers specifically targeted for NOM constituents.

Advanced oxidation processes for the removal of natural organic matter from drinking water sources: A comprehensive review

Natural organic matter (NOM), a key component in aquatic environments, is a complex matrix of organic substances characterized by its fluctuating amounts in water and variable molecular and chemical properties, leading to various interaction schemes with the biogeosphere and hydrologic cycle. These factors, along with the increasing amounts of NOM in surface and ground waters, make the effort of removing naturally-occurring organics from drinking water supplies, and also from municipal wastewater effluents, a challenging task requiring the development of highly efficient and versatile water treatment technologies. Advanced oxidation processes (AOPs) received an increasing amount of attention from researchers around the world, especially during the last decade. The related processes were frequently reported to be among the most suitable water treatment technologies to remove NOM from drinking water supplies and mitigate the formation of disinfection by products (DBPs). Thus, the present work overviews recent research and development studies conducted on the application of AOPs to degrade NOM including UV and/or ozone-based applications, different Fenton processes and various heterogeneous catalytic and photocatalytic oxidative processes. Other non-conventional AOPs such as ultrasonication, ionizing radiation and plasma technologies were also reported. Furthermore, since AOPs are unlikely to achieve complete oxidation of NOM, integration schemes with other water treatment technologies were presented including membrane filtration, adsorption and others processes.

Abatement of humic acid from aqueous solution using a carbonaceous conjugated microporous polymer derived from waste polystyrene

Humic acid (HA) is a major constituent of natural organic matter (NOM) found in water systems. Although NOM generally does not have any known harmful effects to humans, it imparts repulsive organoleptic properties to water, reacts with disinfectants to produce toxic products, and interferes with the efficiency of water treatment processes. The removal of NOM and related compounds from water is therefore important to render water potable and suitable for other applications. In this work, a hitherto unreported carbonaceous conjugated microporous polymer (CCMP) prepared through the organic-polymeric-precursor-controlled carbonization of hypercrosslinked post-consumer waste polystyrene (WPS) was evaluated for its capacity to remove HA from synthetic wastewater. This advanced material retained the morphology of the precursor material, while its porosity and chemical integrity were significantly improved. The approach is an environmentally friendly way of handling WPS while at the same time remediating NOM-contaminated water. Overall, with a maximum adsorption capacity of 340 mg/g in batch experiments, and a maximum initial removal rate of 95.7% in column experiments, the results showed that CCMP can be used for the remediation of HA-contaminated water at high pH.

Removal of natural organic matter in drinking water treatment by coagulation: A comprehensive review

Natural organic matter (NOM) is a complex matrix of organic substances produced in (or channeled to) aquatic ecosystems via various biological, geological and hydrological cycles. Such variability is posing a serious challenge to most water treatment technologies, especially the ones designed to treat drinking water supplies. Lately, in addition to the fluctuating composition of NOM, a substantial increase of its concentration in fresh waters, and also municipal wastewater effluents, has been reported worldwide, which justifies the urgent need to develop highly efficient and versatile water treatment processes. Coagulation is among the most applied processes for water and wastewater treatment. The application of coagulation to remove NOM from drinking water supplies has received a great deal of attention from researchers around the world because it was efficient and helped avoiding the formation of disinfection by products (DBPs). Nonetheless, with the increased fluctuation of NOM in water (concentration and composition), the efficiency of conventional coagulation was substantially reduced, hence the need to develop enhanced coagulation processes by optimizing the operating conditions (mainly the amount coagulants and pH), developing more efficient inorganic or organic coagulants, as well as coupling coagulation with other water treatment technologies. In the present review, recent research studies dealing with the application of coagulation for NOM removal from drinking water supplies are presented and compared. In addition, integration schemes combining coagulation and other water treatment processes are presented, including membrane filtration, oxidation, adsorption and others processes.

Mineralization of pyrrole, a recalcitrant heterocyclic compound, by electrochemical method: Multi-response optimization and degradation mechanism

In this study, the electrochemical (EC) oxidation of a recalcitrant heterocyclic compound namely pyrrole has been reported using platinum coated titanium (Pt/Ti) electrodes. Response surface methodology (RSM) comprising of full factorial central composite design (CCD) with four factors and five levels has been used to examine the effects of different operating parameters such as current density (j), aqueous solution pH, conductivity (k) and treatment time (t) in an EC batch reactor. Pyrrole mineralization in aqueous solution was examined with multiple responses such as chemical oxygen demand (COD) (response, Y₁) and specific energy consumption (SEC) in kWh/kg of COD removed (response, Y₂). During multiple response optimization, the desirability function approach was employed to concurrently maximize Y₁ and minimize Y₂. At the optimum condition, 82.9% COD removal and 7.7 kWh/kg of COD removed were observed. Degradation mechanism of pyrrole in wastewater was elucidated at the optimum condition of treatment by using UV-visible spectroscopy, Fourier transformed infra-red spectroscopy (FTIR), cyclic voltammetry (CV), ion chromatography (IC), higher performance liquid chromatography (HPLC) and gas chromatography-mass spectroscopy (GC-MS). The degradation pathway of pyrrole was proposed on the basis of the various analysis.

Production of demineralized water for use in thermal power stations by advanced treatment of secondary wastewater effluent

The operation and efficiency of a modern, high-tech industrial full-scale water treatment plant was investigated in the present study. The treated water was used for the supply of the boilers, producing steam to feed the steam turbine of the power station. The inlet water was the effluent of municipal wastewater treatment plant of the city of Bari (Italy). The treatment stages comprised (1) coagulation, using ferric chloride, (2) lime softening, (3) powdered activated carbon, all dosed in a sedimentation tank. The treated water was thereafter subjected to dual-media filtration, followed by ultra-filtration (UF). The outlet of UF was subsequently treated by reverse osmosis (RO) and finally by ion exchange (IX). The inlet water had total organic carbon (TOC) concentration 10-12 mg/L, turbidity 10-15 NTU and conductivity 3500-4500 μS/cm. The final demineralized water had TOC less than 0.2 mg/L, turbidity less than 0.1 NTU and conductivity 0.055-0.070 μS/cm. Organic matter fractionation showed that most of the final DOC concentration consisted of low molecular weight neutral compounds, while other compounds such as humic acids or building blocks were completely removed. It is notable that this plant was operating under "Zero Liquid Discharge" conditions, implementing treatment of any generated liquid waste.

The role of graphene oxide and graphene oxide-based nanomaterials in the removal of pharmaceuticals from aqueous media: a review

In this review paper, the ill effects of pharmaceuticals (PhAs) on the environment and their adsorption on graphene oxide (GO) and graphene oxide-based (GO-based) nanomaterials have been summarised and discussed. The adsorption of prominent PhAs discussed herein includes beta-blockers (atenolol and propranolol), antibiotics (tetracycline, ciprofloxacin and sulfamethoxazole), pharmaceutically active compounds (carbamazepine) and analgesics such as diclofenac. The adsorption of PhAs strictly depends upon the experimental conditions such as pH, adsorbent and adsorbate concentrations, temperature, ionic strength, etc. To understand the adsorption mechanism and feasibility of the adsorption process, the adsorption isotherms, thermodynamics and kinetic studies were also considered. Except for some cases, GO and its derivatives show excellent adsorption capacities for PhAs, which is crucial for their applications in the environmental pollution cleanup.

Removal of natural organic matter (NOM) and its constituents from water by adsorption - A review

Natural organic matter (NOM) is produced through metabolic reactions in water supply in drinking water sources and has been reported to cause several problems including objectionable taste and color of water, formation of disinfection by-products (DBPs) and reducing the amount of dissolved oxygen in water. The removal of NOM and its constituents from water is a challenging issue worldwide. Many technologies have been examined for this purpose. The properties and amount of NOM, however, can significantly affect the process efficiency. In the present work, an overview of the recent research studies dealing with adsorption method for the removal of NOM and related compounds from water is presented. A wide variety of conventional and non-conventional adsorbents have been reviewed for their potential in NOM removal from water. As revealed from the literature reviewed, modified adsorbents, composite materials and few nanomaterials have shown promising results for NOM removal from water. The main findings obtained for the removal of NOM using different adsorbents have been discussed in this review.

Treatment of wastewater from the dairy industry using electroflocculation and solid whey recovery

The aim of this study was to investigate the efficiency of electroflocculation for the treatment of wastewater from the dairy industry and the recovery of solid whey. An electrochemical apparatus containing two aluminum or iron electrodes, a power source, an electroflocculation cell and magnetic stirring was employed. The following experimental conditions were monitored: electroflocculation time, initial pH of wastewater and applied potential intensity. Chemical oxygen demand, turbidity and final pH were the response variables. The chemical oxygen demand and turbidity decreased by employing aluminum or iron electrodes, applied potential intensity of 5 V, distance between two electrodes of 2 cm, 60 min electroflocculation time and initial wastewater pH of 5.0. The removal rates of organic matter based on the measure of chemical oxygen demand and turbidity when employing aluminum electrodes were 97.0 ± 0.02% and 99.6 ± 3.00 × 10(-4)%, respectively, with a final pH of 6.72. The removal rates of organic matter when employing iron electrodes were 97.4 ± 0.01% and 99.1 ± 1.00 × 10(-4)%, respectively, with a final pH of 7.38. In conclusion, electroflocculation is an excellent alternative for the dairy wastewater treatment in comparison to conventional treatment methods. The water used in food production and equipment washing is recovered with this method, resulting in a liquid that can be properly disposed. It is also possible to recover solid whey after electroflotation, which can then be used in the production of food supplements for humans and animals. Therefore, the dairy wastewater treatment process employing electroflocculation leads to sustainable food production.