Treatment of mixed industrial wastewater by electrocoagulation and indirect electrochemical oxidation

A review of electrooxidation systems treatment of poly-fluoroalkyl substances (PFAS): electrooxidation degradation mechanisms and electrode materials

The prevalence of polyfluoroalkyls and perfluoroalkyls (PFAS) represents a significant challenge, and various treatment techniques have been employed with considerable success to eliminate PFAS from water, with the ultimate goal of ensuring safe disposal of wastewater. This paper first describes the most promising electrochemical oxidation (EO) technology and then analyses its basic principles. In addition, this paper reviews and discusses the current state of research and development in the field of electrode materials and electrochemical reactors. Furthermore, the influence of electrode materials and electrolyte types on the deterioration process is also investigated. The importance of electrode materials in ethylene oxide has been widely recognised, and therefore, the focus of current research is mainly on the development of innovative electrode materials, the design of superior electrode structures, and the improvement of efficient electrode preparation methods. In order to improve the degradation efficiency of PFOS in electrochemical systems, it is essential to study the oxidation mechanism of PFOS in the presence of ethylene oxide. Furthermore, the factors influencing the efficacy of PFAS treatment, including current density, energy consumption, initial concentration, and other parameters, are clearly delineated. In conclusion, this study offers a comprehensive overview of the potential for integrating EO technology with other water treatment technologies. The continuous development of electrode materials and the integration of other water treatment processes present a promising future for the widespread application of ethylene oxide technology.

Insights into current bio-processes and future perspectives of carbon-neutral treatment of industrial organic wastewater: A critical review

With the rise of the concept of carbon neutrality, the current wastewater treatment process of industrial organic wastewater is moving towards the goal of energy conservation and carbon emission reduction. The advantages of anaerobic digestion (AD) processes in industrial organic wastewater treatment for bio-energy recovery, which is in line with the concept of carbon neutrality. This study summarized the significance and advantages of the state-of-the-art AD processes were reviewed in detail. The application of expanded granular sludge bed (EGSB) reactors and anaerobic membrane bioreactor (AnMBR) were particularly introduced for the effective treatment of industrial organic wastewater treatment due to its remarkable prospect of engineering application for the high-strength wastewater. This study also looks forward to the optimization of the AD processes through the enhancement strategies of micro-aeration pretreatment, acidic-alkaline pretreatment, co-digestion, and biochar addition to improve the stability of the AD system and energy recovery from of industrial organic wastewater. The integration of anaerobic ammonia oxidation (Anammox) with the AD processes for the post-treatment of nitrogenous pollutants for the industrial organic wastewater is also introduced as a feasible carbon-neutral process. The combination of AnMBR and Anammox is highly recommended as a promising carbon-neutral process for the removal of both organic and inorganic pollutants from the industrial organic wastewater for future perspective. It is also suggested that the AD processes combined with biological hydrogen production, microalgae culture, bioelectrochemical technology and other bio-processes are suitable for the low-carbon treatment of industrial organic wastewater with the concept of carbon neutrality in future.

Combination of electrocoagulation with solar photo Fenton process for treatment of landfill leachate

The aim of the present work was to provide a viable and active way to remove COD and colour from landfill leachate treated by adopting combined process of electrocoagulation and solar photo Fenton process. Coagulating agents such as metal hydroxides are created by the electrolysis process through self-sacrificial electrodes. Aluminium and iron dissolves at the anode and hydrogen gas are generated at the cathode when aluminium and iron electrodes are utilised. The contaminants interact with the coagulating agent to generate enormous organic flocs. The leachate was obtained from a landfill in Madurai and then it was characterised in terms of its major predominant pollutants. In this study, the electrocoagulation process was used in conjunction with the solar photo Fenton process to treat the leachate under ideal conditions of pH = 7, NaCl = 2 g/L, voltage = 4 V, Al & Fe electrodes and inter electrode distance = 3 cm with a COD and colour removal effectiveness of 75% and 76%, respectively. Furthermore, the effluent from the electrocoagulation process was treated using a solar photo Fenton process at pH = 3, H2O2 = 10 g/L and Fe2+ = 1 g/L with COD and colour reduction effectiveness of 90% and 91%, respectively. In this combination of treatment systems, leachate biodegradability increased from 0.35 to 0.73, favouring the biological oxidation process in conventional treatment plants. This research demonstrates that employing this paired electrocoagulation-solar photo Fenton to treat landfill leachate can achieve consistent treatment effects with high removal efficiencies, and that it is an acceptable treatment technique for landfill leachate.

Sustainable application of electrocatalytic and photo-electrocatalytic oxidation systems for water and wastewater treatment: a review

Wastewater treatment and reuse have risen as a solution to the water crisis plaguing the world. Global warming-induced climate change, population explosion and fast depletion of groundwater resources are going to exacerbate the present global water problems for the forthcoming future. In this scenario, advanced electrochemical oxidation process (EAOP) utilising electrocatalytic (EC) and photoelectrocatalytic (PEC) technologies have caught hold of the interest of the scientific community. The interest stems from the global water management plans to scale down centralised water and wastewater treatment systems to decentralised and semicentralised treatment systems for better usage efficiency and less resource wastage. In an age of rising water pollution caused by contaminants of emerging concern (CECs), EC and PEC systems were found to be capable of optimal mineralisation of these pollutants rendering them environmentally benign. The present review treads into the conventional electrochemical treatment systems to identify their drawbacks and analyses the scope of the EC and PEC to mitigate them. Probable electrode materials, potential catalysts and optimal operational conditions for such applications were also examined. The review also discusses the possible retrospective application of EC and PEC as point-of-use and point-of-entry treatment systems during the transition from conventional centralised systems to decentralised and semi-centralised water and wastewater treatment systems.

Electrochemical-based approaches for the treatment of pharmaceuticals and personal care products in wastewater

In recent times, emerging contaminants (ECs) like pharmaceuticals and personal care products (PPCPs) in water and wastewater have become a major concern in the environment. Electrochemical treatment technologies proved to be more efficient to degrade or remove PPCPs present in the wastewater. Electrochemical treatment technologies have been the subject of intense research for the past few years. Attention has been given to electro-oxidation and electro-coagulation by industries and researchers, indicating their potential to remediate PPCPs and mineralization of organic and inorganic contaminants present in wastewater. However, difficulties arise in the successful operation of scaled-up systems. Hence, researchers have identified the need to integrate electrochemical technology with other treatment technologies, particularly advanced oxidation processes (AOPs). Integration of technologies addresses the limitation of indiviual technologies. The major drawbacks like formation of undesired or toxic intermediates, s, energy expenses, and process efficacy influenced by the type of wastewater etc., can be reduced in the combined processes. The review discusses the integration of electrochemical technology with various AOPs, like photo-Fenton, ozonation, UV/H2O2, O3/UV/H2O2, etc., as an efficient way to generate powerful radicals and augment the degradation of organic and inorganic pollutants. The processes are targeted for PPCPs such as ibuprofen, paracetamol, polyparaben and carbamezapine. The discussion concerns itself with the various advantages/disadvantages, reaction mechanisms, factors involved, and cost estimation of the individual and integrated technologies. The synergistic effect of the integrated technology is discussed in detail and remarks concerning the prospects subject to the investigation are also stated.

Sanitary landfill leachate treatment by aerated electrochemical Fenton process

The aerated electrochemical Fenton procedure was investigated as a viable treatment approach for electrolytic degradation and decolourization of sanitary landfill leachate. The optimization effects of initial pH, applied voltage, H₂O₂ concentration and combination of iron electrodes on detoxification were demonstrated by COD and colour removal from stabilized leachate, respectively. The study illustrates that, under the optimum experimental parameters voltage of 4.5 V, electrolysis time of 90 min, H₂O₂ dosage of 5 g/L, pH 3, 99% of chemical oxygen demand (COD) and 100% colour are removed from stabilized leachate, and the biodegradability ratio of the five-day biochemical oxygen demand (BOD₅) to COD increases from 0.1 to 0.72. In addition, the pure catalytic metallic iron anode and cathode electrode used in the electrochemical Fenton process was first electro-oxidized to Fe²⁺ for use during the Fenton reaction, then with Fe³⁺ that was reverted back to Fe²⁺ under the applied electrochemical-magnetic field, resulting in the iron dissolution and regeneration circuit (Fe²⁺/Fe³⁺/Fe²⁺). Additionally, Fe²⁺/Fe³⁺ served as bridges for agglomerates to coalesce into big, closely packed particles for better filterability and sedimentation action. As a preparatory step for the biochemical treatment, this technology has been effectively used to treat stabilized landfill leachate containing toxic refractory recalcitrant organics on a large scale. Additionally, by estimating the scientific experiment with a regression model approach for the outcomes, RSM software was employed in order to standardize the ECF treatment process, significantly reducing the number of test cases and trials.

Electrochemical treatment of aquaculture wastewater effluent and optimization of the parameters using response surface methodology

The electrocoagulation (EC) and electrooxidation (EO) processes are employed widely as treatment processes for industrial, agricultural, and domestic wastewater. In the present study, EC, EO, and a combination of EC + EO were evaluated as methods of removing pollutants from shrimp aquaculture wastewater. Process parameters for electrochemical processes, including current density, pH, and operation time were studied, and response surface methodology was employed to determine the optimum condition for the treatment. The effectiveness of the combined EC + EO process was assessed by measuring the reduction of targeted pollutants, including dissolved inorganic nitrogen species, total dissolved nitrogen (TDN), phosphate, and soluble chemical oxygen demand (sCOD). Using EC + EO process, more than 87% reduction was achieved for inorganic nitrogen, TDN, and phosphate, while 76.2% reduction was achieved for sCOD. These results demonstrated that the combined EC + EO process provided better treatment performance in removing the pollutants from shrimp wastewater. The kinetic results suggested that the effects of pH, current density, and operation time were significant on the degradation process when using iron and aluminum electrodes. Comparatively, iron electrodes were effective at reducing the half-life (t_1/2) of each of the pollutants in the samples. The application of the optimized process parameters on shrimp wastewater could be used for large-scale treatment in aquaculture.

Application of Electrochemical Oxidation for Water and Wastewater Treatment: An Overview

In recent years, the discharge of various emerging pollutants, chemicals, and dyes in water and wastewater has represented one of the prominent human problems. Since water pollution is directly related to human health, highly resistant and emerging compounds in aquatic environments will pose many potential risks to the health of all living beings. Therefore, water pollution is a very acute problem that has constantly increased in recent years with the expansion of various industries. Consequently, choosing efficient and innovative wastewater treatment methods to remove contaminants is crucial. Among advanced oxidation processes, electrochemical oxidation (EO) is the most common and effective method for removing persistent pollutants from municipal and industrial wastewater. However, despite the great progress in using EO to treat real wastewater, there are still many gaps. This is due to the lack of comprehensive information on the operating parameters which affect the process and its operating costs. In this paper, among various scientific articles, the impact of operational parameters on the EO performances, a comparison between different electrochemical reactor configurations, and a report on general mechanisms of electrochemical oxidation of organic pollutants have been reported. Moreover, an evaluation of cost analysis and energy consumption requirements have also been discussed. Finally, the combination process between EO and photocatalysis (PC), called photoelectrocatalysis (PEC), has been discussed and reviewed briefly. This article shows that there is a direct relationship between important operating parameters with the amount of costs and the final removal efficiency of emerging pollutants. Optimal operating conditions can be achieved by paying special attention to reactor design, which can lead to higher efficiency and more efficient treatment. The rapid development of EO for removing emerging pollutants from impacted water and its combination with other green methods can result in more efficient approaches to face the pressing water pollution challenge. PEC proved to be a promising pollutants degradation technology, in which renewable energy sources can be adopted as a primer to perform an environmentally friendly water treatment.

Recent advances and applicable flexibility potential of electrochemical processes for wastewater treatment

This study examined >140 relevant publications from the last few years (2018-2021). In this study, classification was reviewed depending on the operation's progress. Electrocoagulation (EC), electrooxidation (EO), electroflotation (EF), electrodialysis (ED), and electro-Fenton (EFN) processes have received considerable attention. The type of action (individual or hybrid) for each electrochemical procedure was evaluated, and statistical analysis was performed to compare them as a new manner of reviewing cited papers providing a massive amount of information efficiently to the readers. Individual or hybrid operation progress of the electrochemical techniques is critical issues. Their design, operation, and maintenance costs vary depending on the in-situ conditions, as evidenced by surveyed articles and statistical analyses. This work also examines the variables affecting the elimination efficacy, such as the applied current, reaction time, pH, type of electrolyte, initial pollutant concentration, and energy consumption. In addition, owing to its efficacy in removing toxins, the hybrid activity showed a good percentage among the studies reviewed. The promise of each wastewater treatment technology depends on the type of contamination. In some cases, EO requires additives to oxidise the pollutants. EF and EFN eliminated lightweight organic pollutants. ED has been used to treat saline water. Compared to other methods, EC has been extensively employed to remove a wide variety of contaminants.

Combined electrocoagulation and electrooxidation treatment system for real effluents from the fishing industry

Fishing industries are characterized by high water consumption and a considerable content of organic matter and salt in their wastewater. In this work, a combined electrochemical process was studied at laboratory scale for the treatment of real wastewater from the processing of mackerel from an industrial facility located in the province of Buenos Aires that discharges to the sewer, which the plant is currently using and does not produce an effluent in discharge conditions. Taking advantage of the high conductivity of these effluents, in the electrocoagulation stage with aluminum anodes, it was possible to remove the coarsest fraction of suspended matter, achieving a Chemical Oxygen Demand (COD) removal of about 60%, at pH 7.5, showing a higher efficiency over the conventional treatment. Despite this superiority, the necessary removal was still not achieved; therefore, the wastewater treated by electrocoagulation was then subjected to electrooxidation, using a graphite anode and a titanium cathode, and with a first-order oxidation kinetics, achieving a final COD value lower than the discharge limit, after 7.5 min of processing at pH 6, obtaining an efficient treatment for removal of high concentrations dissolved organic matter and colloidal/suspended particles in this kind of effluent. All treatments were performed in batches. The removal of pollutants in the wastewater was verified by means of spectroscopic and voltammetric techniques; at the same time, these techniques, together with SEM-EDX analysis, proved the superiority of electrocoagulation over chemical coagulation. This study laid the groundwork for the design of modifications to the plant to achieve discharge parameters in accordance with current legislation.

Electrochemical-based approaches for the treatment of forever chemicals: Removal of perfluoroalkyl and polyfluoroalkyl substances (PFAS) from wastewater

Electrochemical based approaches for the treatment of recalcitrant water borne pollutants are known to exhibit superior function in terms of efficiency and rate of treatment. Considering the stability of Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are designated as forever chemicals, which generating from various industrial activities. PFAS are contaminating the environment in small concentrations, yet exhibit severe environmental and health impacts. Electro-oxidation (EO) is a recent development that treats PFAS, in which different reactive species generates at anode due to oxidative reaction and reductive reactions at the cathode. Compared to water and wastewater treatment methods those being implemented, electrochemical approaches demonstrate superior function against PFAS. EO completely mineralizes (almost 100 %) non-biodegradable organic matter and eliminate some of the inorganic species, which proven as a robust and versatile technology. Electrode materials, electrolyte concentration pH and the current density applying for electrochemical processes determine the treatment efficiency. EO along with electrocoagulation (EC) treats PFAS along with other pollutants from variety of industries showed highest degradation of 7.69 mmol/g of PFAS. Integrated approach with other processes was found to exhibit improved efficiency in treating PFAS using several electrodes boron-doped diamond (BDD), zinc, titanium and lead based with efficiency the range of 64 to 97 %.

Advanced oxidation process: a sustainable technology for treating refractory organic compounds present in industrial wastewater

The world faces tremendous challenges and environmental crises due to the rising strength of wastewater. The conventional technologies fail to achieve the quality water that can be reused after treatment means "zero effluent" discharge of the industrial effluent. Therefore, now the key challenge is to develop improved technologies which will have no contribution to secondary pollution and at the same time more efficient for the socio-economic growth of the environment. Sustainable technologies are needed for wastewater treatment, reducing footprint by recycling, reusing, and recovering resources. Advanced oxidation process (AOP) is one of the sustainable emerging technologies for treating refractory organic contaminants present in different industrial wastewaters like textile, paper and pulp, pharmaceuticals, petrochemicals, and refineries. This critical review emerges details of advanced oxidation processes (AOPs), mentioning all possible permutations and combinations of components like ozone, UV, the catalyst used in the process. Non-conventional AOP systems, microwave, ultrasound, and plasma pulse assisted are the future of the oxidation process. This review aims to enlighten the role of AOPs for the mineralization of refractory organic contaminants (ROC) to readily biodegradable organics that cannot be either possible by conventional treatment. The integrated AOPs can improve the biodegradability of recalcitrant organic compounds and reduce the toxicity of wastewater, making them suitable for further biological treatment.

Pre-treatment of real pharmaceutical wastewater by heterogeneous Fenton and persulfate oxidation processes

This study compares the pre-oxidation of pharmaceutical wastewater by hydroxyl radical based advanced oxidation (HR-AOP) and a sulfate radical based advanced oxidation process (SR-AOP). The heterogeneous Fenton process is chosen as a model HR-AOP and persulfate (PS) activation as a model SR-AOP. The pre-treatment efficacy of both processes in terms of TOC, and COD removals using Fe₃O₄-rGO catalyst were considered. Under the investigated experimental conditions, both processes yielded fluctuating COD values with time. The heterogeneous Fenton process discovered to be the most efficient to remove 68.7% TOC in 180 min of treatment, when Fe₃O₄-rGO: H₂O₂ = 300 mg L^-1:150 mM H₂O₂ was used at pH 3. Notably, the heterogeneous Fenton system was not considerably inhibited at the natural pH of pharmaceutical wastewater (6.75), as the process successfully removed 64.6% TOC. On the other hand, in persulfate activation studies, Fe₃O₄-rGO: PS = 400 mg L^-1: 5 mM was the ideal condition for removing 59.5% TOC in 180 min at pH 3. Whereas the natural pH condition significantly inhibited the TOC removal, as only 20.8% TOC removal was feasible. The wastewater characterisation before and after Fenton treatment reveals that Fenton oxidation leads to an increase in inorganics (chlorides: 160 ± 15 mg L^-1, nitrates: 63.14 ± 3.08 mg L^-1, sulfates: 266.31 ± 31.39 mg L^-1) necessitating an additional treatment step to reduce COD and inorganics further.

Evaluation of scrap metallic waste electrode materials for the application in electrocoagulation treatment of wastewater

The constant need for sacrificial electrodes is one of the limitations of applying the EC in wastewater treatment. Accordingly, this study proposes a sustainable alternative in reusing scrap metallic wastes as electrode materials. Four different types of metallic wastes (beverage cans, used aluminum (Al) foil, scrap iron, and scrap mild steel) are proposed as sacrificial electrodes for grey water (GW) treatment using the EC technique. At electrical current densities (CD) ranging between 5 and 20 mA/cm², the treatment performance was evaluated for a reaction time of 10 min in terms of the removal efficiency of some key parameters such as color, turbidity, chemical oxygen demand (COD), and electrical conductivity, energy and material consumption, and metal contamination of GW from electrodes. The results demonstrated that using metallic wastes as sacrificial electrodes can achieve a considerable reduction in color, turbidity, COD, and electric conductivity of about 97.2%, 99%, 88%, and 89%, respectively. However, their reuse as electrodes revealed some important concerns. Al foil undergoes quick and substantial perforation and loss of surface area during electrolysis. The scrap iron and scrap mild steel were found to cause metal contamination by increasing Fe ions in the treated GW. Generally, metal scrap wastes can serve effectively as alternative sustainable electrodes. However, further research is recommended regarding the operating costs, which are considered crucial aspects of the EC process in terms of energy consumption and the most efficient method of fabricating the metallic wastes into a form suitable for reuse in the EC technique.

A Case Study of Swine Wastewater Treatment via Electrochemical Oxidation by Ti4O7 Anode

With the rapid development of breeding industry, the efficient treatment of dramatically increasing swine wastewater is gradually becoming urgent. In particular, the development of application technologies suitable for the relatively small piggeries is critical due to the time cost and space requirements of conventional biological methods. In this study, Electrochemical oxidation (EO) was selected to systematically explore the treatment performance of three different swine wastewaters by Ti₄O₇ anode. It was observed that the colors changed from dark brown to light yellow after 60 min treatment at 50 mA/cm², and the removal rates of turbidity and suspended solids ranged from 89.36% to 93.65% and 81.31% to 92.55%, respectively. The chemical oxygen demand (COD), ammonia nitrogen (NH₃-N) and total phosphorus (TP) of all the three swine wastewaters were simultaneously removed to a very low concentration in 120 min, especially for sample III, 61 ± 9 mg/L of COD, 6.6 ± 0.4 mg/L of NH₃-N and 5.7 ± 1.1 mg/L of TP, which met the Discharge Standard of Pollutants for Livestock and Poultry Breeding (GB 18596-2001). Moreover, 70.93%-85.37% mineralization rates were also achieved in 120 min, confirming that EO treatment by Ti₄O₇ could efficiently remove the organic matters in wastewater. Excitation-emission matrix (EEM) and UV-vis spectrum characterization results further proved that aromatic compounds and macromolecules in wastewater were rapidly removed, which played important roles in the mineralization processes. The findings here provided an efficient and environment-friendly technology for swine wastewater treatment.

Clay-Alginate Beads Loaded with Ionic Liquids: Potential Adsorbents for the Efficient Extraction of Oil from Produced Water

Produced water (PW) generated from the petroleum industry, during the extraction of oil and gas, has harmful impacts on human health and aquatic life, due to its complex nature. Therefore, it is necessary to treat it before discharging it into the environment in order to avoid serious environmental concerns. In this research, oil adsorption from PW was investigated using clay-alginate beads loaded with ionic liquids (ILs), as the adsorbent material. The effects of several process parameters, such as the initial concentration of oil, contact time, pH, and temperature on the removal efficiency of the beads, were analyzed and optimized. Different characterization methods, such as the Fourier transform infrared spectrophotometer (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and thermal gravimetric analysis (TGA), were used to investigate the surface morphology, the chemical bond structure and functional group, and the thermal stability of the ILs-based beads. The results revealed that the clay-alginate-ILs beads indicated a removal efficiency of 71.8% at the optimum conditions (600 ppm initial oil concentration, 70 min contact time, 10 pH, and at room temperature) with an adsorption capacity of 431 mg/g. The FTIR analysis confirmed the successful chemical bond interaction of the oil with the beads. The SEM analysis verified that the beads have a porous and rough surface, which is appropriate for the adsorption of oil onto the bead’s surface. The TGA analysis provides the thermal degradation profile for the clay-alginate-ILs. The beads used in the adsorption process were regenerated and used for up to four cycles.

Electrocoagulation and electrooxidation technologies for pesticide removal from water or wastewater: A review

Pesticides are known to be threats to the environment and human health. Excessive use of pesticides in agricultural practice can contaminate water bodies, leading to cancer, asthma, neurological disorders, reproductive defects, and hormonal disruption. Electrochemical methods such as electrocoagulation and electrooxidation can be used for pesticide removal due to their numerous advantages such as high efficiency, less sludge production, and low operational cost. During electrocoagulation, dissolution of anode metals results in metal hydroxide complexes, which precipitate with the contaminant present in the reactor. Simultaneously, electro-flotation occurs at the cathode and results in the evolution of hydrogen gas bubbles, leading to flotation of floc to the top surface of the reactor. This review focuses on the removal mechanisms, kinetics, modeling, effects of influencing factors, and sludge characterization of pesticide removal using electrocoagulation and electrooxidation. Major influencing factors include cell configuration, electrode material, current density, pH, supporting electrolyte concentration. In general, aluminum and iron are the most common electrodes used for pesticide removal using electrocoagulation, while boron-doped diamond was used to a far greater extent as the electrode in electrooxidation studies. Greater than 99% removal efficiency was observed in both processes. Overall, this review summarizes the use of electrochemical methods for pesticide removal and offers valuable information to researchers in this area of study.

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.

Performance of a Three-Dimensional Electrochemical Reactor (3DER) on Bisphenol A Degradation

This study constructed a three-dimensional electrochemical reactor (3DER) using meshed stainless steel sheets and titanic magnetite particles (TMP) to investigate bisphenol A (BPA) degradation through the synergistic action of electrical current and TMP. We examined some TMP characteristics, such as particle size, specific surface areas, X-ray diffraction, surface imaging, elemental constituents, and electrical resistivity. It was found that TMP was a micron-level material with excellent electrical conductivity, and it could be regarded as a magnetite-based material comprising Fe(II) and Fe(III). The single-factor experiment determined the optimal conditions for BPA removal in 3DER, specifically by introducing 200 ml of BPA-simulated wastewater (10 mg L⁻¹) into 3DER. At the initial pH of 9.00, current and electrodes gap of 300 mA and 15 mm, respectively, and adding 1 ml of 0.5 M potassium peroxymonosulfate and 1 g TMP, > 98% of BPA was removed after 55 min of electrochemical reaction. In addition, liquid chromatography–mass spectrometry identified the intermediates formed during the BPA treatment, showing two possible pathways for BPA degradation. The final degradation intermediates were chain organics with simple molecular structures. This research provided an understanding of the potential application of 3DER for BPA removal in water.

A predictive toolset for the identification of degradation pattern and toxic hazard estimation of multimeric hazardous compounds persists in water bodies

An array of industrial processing units generates many multimeric hazardous compounds, such as complex technical lignin and its toxic derivatives, thereby persist in expelled water bodies. The inclusion of some group of motifs in the complex technical lignin structure helps it resist degrade biologically, most often even recalcitrant. Relatively small concentrations of lignin are harmful to aquatic organisms and can trigger environmental hazards. Sadly, the entire biotransformation pathway and insightful information about these toxic derivatives are incomplete and missing in the literature. This is mainly because the current conventional treatments often fail to identify all transformed compounds and their environmental fate. Thus, a robust toolset is much needed to cover this literature gap. Inadequate performance of conventional remediation processes and biological degradation patterns can be maximally optimized with the aid of predictive toolset methods that could offer better degradability and complete transformed compound information. A predictive toolset-assisted biodegradation pattern determination is a multifaceted and reliable analytical technique that can help to overcome existing shortcomings by providing an entire transformation pathway. Considering the above critiques, this work reports on the degradation pattern, and toxicological endpoints of five hazardous compounds, i.e., 2-chlorosyringaldehyde, 5-chlorovanillin, catechol, guaiacyl 4-O-5 guaiacyl, and syringyl β-O-4 syringyl β-O-4 sinapyl alcohol, that persists in water matrices. The predictive transformation pattern was revealed notably less complex end-products of catechol as; succinate, and 2-Oxo-4-pentenoate. The gastrointestinal (GI) absorption rate was found high for all tested compounds, excluding trimer compound, i.e., syringyl β-O-4 syringyl β-O-4 sinapyl alcohol. The toxicity and persistence profile tested via Toxtree showed that the Cramer Rules, Verhaar Scheme, and Structural Alerts for Reactivity, (START) biodegradation ability as positive, and all five target compounds were found as class-II persistent compounds. Furthermore, the Ecological Structure-Activity Relationships (ECOSAR)assisted testing specifies that all tested derivatives have multiple aquatic toxic levels. In summary, the current findings endorse the hazardous compounds and undertake prescreening of the deprivation policy to protect the environment.

Electrocoagulation pretreatment of pulp and paper wastewater for low pressure reverse osmosis membrane fouling control

Low pressure reverse osmosis (LPRO) has been increasingly used in advanced treatment of pulp and paper wastewater (PPWW) for the purpose of water reuse. However, membrane fouling is a major problem encountered by full-scale RO systems due to the organic and inorganic contents of the feedwater. Electrocoagulation (EC) as an effective treatment for foulants removal can be applied in pre-filtration. Therefore, the LPRO membrane fouling mechanism and the membrane fouling control performance by EC treatment were investigated in this study. EC pretreatment could reduce the membrane fouling and improve the membrane flux by 31%, by effectively removing and/or decomposing the organic pollutants in PPWW. Fluorescent spectrometry analyses of the feedwater and the permeate revealed that humic acid-like and fulvic acid-like organics in PPWW were the major foulants for the LPRO membranes. Fourier transformation infrared spectrometry results confirmed that the organic foulants contained benzoic rings and carboxylic groups, which were typical for organic substances. EC effectively removed organic pollutants containing functional groups such as carboxylic acid COH out-of-plane bending, olefin (trans), and NH₃⁺ symmetrical angle-changing. Moreover, the extended Derjaguin-Landau-Verwey-Overbeek model suggested that the membrane filtered 30-min EC-treated PPWW had the strong repulsion force to foulants due to the higher cohesion energy (12.1 mJ/m²) and the lower critical load, which theoretically explained the reason of EC pretreatment on membrane fouling control.

Mixed industrial wastewater treatment by the combination of heterogeneous electro-Fenton and electrocoagulation processes

Mixed industrial wastewater treatment efficiency of combined electro-Fenton (EF) and electrocoagulation (EC) processes was investigated in the present study. Alkali modified laterite soil was used as a heterogeneous EF catalyst and found superior performance than the raw laterite soil. Initially, the effect of catalyst dosage, initial pH, and applied voltage on the performance of EF process was carried out. A total of 54.57% COD removal was observed after 60 min of the EF treatment. Further treatment was carried out with EC process at different voltages. A total of 85.27% COD removal after 2 h treatment was observed by combining two electrochemical processes. Performance of EF followed by EC (EF + EC) process was compared with EC followed by EF (EC + EF) process. Even though efficiency is the same, EF + EC is a better strategy than EC + EF as it nullifies the neutralization requirement after EF process in addition to high mineralization efficiency, enhanced biodegradability, and lesser sludge generation.

A critical review in electrocoagulation technology applied for oil removal in industrial wastewater

EC process, which stands for Electrocoagulation, is considered a widespread wastewater remediation method that is investigated widely for an extensive variety of wastewater resources, based on its flexibility, easy setup, eco-friendly nature, and low footprint. The critical operative factors in the EC process and the crucial relation between EC and the typical chemical coagulation approach had been thoroughly evaluated because they are the main variables that govern the process of contaminant elimination. As a result, the EC process requires further investigations for scale-up simulations in the manufacturing scopes and optimization of operational parameters. Furthermore, the current paper studies the novel integrated separation methods with the combined EC process and also their limitations for improved wastewater remediation process for cleaner wastes, recycling processes, and water recovery. In this paper, the EC enhancement processes toward oil removal from wastewater have been reviewed which includes a concise representation of the source and features of oily wastewater. Additionally, the advanced remediation methods for oil-contained wastewater and the electrocoagulation process are presented. This review summarized the present utilization of electrocoagulation to eliminate oil from wastewater. Besides the process optimization and modeling investigations, the parameters that significantly affect the electrocoagulation remediation effectiveness are evaluated. Finally, the cutting-edge and sophisticated methods of electrocoagulation process for oil removal are presented.

Iron/titanium oxide-biochar (Fe2TiO5/BC): A versatile adsorbent/photocatalyst for aqueous Cr(VI), Pb2+, F- and methylene blue

This is the first report of the metal Fe-Ti oxide/biochar (Fe₂TiO₅/BC) composite for simultaneous removal of aqueous Pb²⁺, Cr⁶⁺, F^- and methylene blue (MB). Primary Fe₂TiO₅ nano particles and aggregates were dispersed on a high surface area Douglas fir BC (∼700 m²/g) by a simple chemical co-precipitation method using FeCl₃ and TiO(acac)₂ salts treated by base and heated to 80 °C. This was followed by calcination at 500 °C. This method previously was used without BC to make the neat mixed oxide Fe₂TiO₅, exhibiting a lower energy band gap than TiO₂. Adsorption of Cr(VI), Pb(II), fluoride, and MB on Fe₂TiO₅/BC was studied as a function of pH, equilibrium time, initial adsorbate concentration, and temperature. Adsorption isotherm studies were conducted at 5, 25, and 45 ℃ and kinetics for all four adsorbates followed the pseudo second order model. Maximum Langmuir adsorption capacities for Pb²⁺, Cr⁶⁺, F^- and MB at their initial pH values were 141 (pH 2), 200 (pH 5), 36 (pH 6) and 229 (pH 6) mg/g at 45 ℃ and 114, 180, 26 and 210 mg/g at 25 ℃, respectively. MB was removed from the water on Fe₂TiO₅/BC by synergistic adsorption and photocatalytic degradation at pH 3 and 6 under UV (365 nm) light irradiation. Cr⁶⁺, Pb²⁺, F^-, and MB each exhibited excellent removal capacities in the presence of eight different competitive ions in simulated water samples. The removal mechanisms on Fe₂TiO₅/BC and various competitive ion interactions were proposed. Some iron ion leaching at pH 3 catalyzed Photo-Fenton destruction of MB. Fe₂TiO₅, BC, and Fe₂TiO₅/BC bandgaps were studied to help understand photocatalysis of MB and to advance supported metal oxide photodegradation using smaller energy band gaps than the larger bandgap of TiO₂ for water treatment. A long range goal is to photocatalytically destroy some sorbates with adsorbents to avoid the need for regeneration steps.

Establishment of electrochemical treatment method to dye wastewater and its application to real samples

It is of great significance to study the treatment of organic dye pollution. In this work, a method of electrochemical treatment for reactive blue 19 dye (RB19) wastewater system was established, and it was applied to the actual dye wastewater treatment. The effects of applied voltage, electrolyte concentration, electrode spacing, and initial concentration on the removal effect of RB19 have been studied in detail. The results show that the removal rate of RB19 can reach 82.6% and the chemical oxygen demand (CODcr) removal rate is 54.3% under optimal conditions. The removal of RB19 in the system is mainly the oxidation of hydroxyl free radicals. The possible degradation pathway is inferred by ion chromatography: hydroxyl free radicals attack the chromophoric group of RB19 to make it fall off, and then decompose it into ring-opening. The product is finally oxidized to CO2 and water. The kinetic fitting is in accordance with the zero-order reaction kinetics. At the same time, using the established electrochemical system to treat the actual dye wastewater has also achieved good results. After 3 hours of treatment, the CODcr removal rate of the raw water is 44.8%, and the CODcr removal of the effluent can reach 89.5%. The degradation process conforms to the zero-order reaction kinetics. The result is consistent with the electrochemical treatment of RB19.

N-Doped Biochar as a New Metal-Free Activator of Peroxymonosulfate for Singlet Oxygen-Dominated Catalytic Degradation of Acid Orange 7

In this paper, using rice straw as a raw material and urea as a nitrogen precursor, a composite catalyst (a nitrogen-doped rice straw biochar at the pyrolysis temperature of 800 °C, recorded as NRSBC800) was synthesized by one-step pyrolysis. NRSBC800 was then characterized using XPS, BET, TEM and other technologies, and its catalytic performance as an activator for permonosulfate (PMS) to degrade acid orange 7 (AO7) was studied. The results show that the introduction of N-doping significantly improved the catalytic performance of NRSBC800. The NRSBC800/PMS oxidation system could fully degrade AO7 within 30 min, with the reaction rate constant (2.1 × 10 ^-1 min^-1) being 38 times that of RSBC800 (5.5 × 10^-3 min^-1). Moreover, NRSBC800 not only had better catalytic performance than traditional metal oxides (Co₃O₄ and Fe₃O₄) and carbon nanomaterial (CNT) but also received less impact from environmental water factors (such as anions and humic acids) during the catalytic degradation process. In addition, a quenching test and electron paramagnetic resonance (EPR) research both indicated that AO7 degradation relied mainly on non-free radical oxidation (primarily singlet oxygen (¹O₂)). A recycling experiment further demonstrated NRSBC800's high stability after recycling three times.

Critical review of advanced oxidation processes in organic wastewater treatment

With the development of industrial society, organic wastewater produced by industrial manufacturing has caused many environmental problems. The vast majority of organic pollutants in water bodies are persistent in the environment, posing a threat to human and animal health. Therefore, efficient treatment methods for highly concentrated organic wastewater are urgently needed. Advanced oxidation processes (AOPs) are widely noticed in the area of treating organic wastewater. Compared with other chemical methods, AOPs have the characteristics of high oxidation efficiency and no secondary pollution. In this paper, the mechanisms, advantages, and limitations of AOPs are comprehensively reviewed. Besides, the basic principles of combining different AOPs to enhance the treatment efficiency are described. Furthermore, the applications of AOPs in various wastewater treatments, such as oily wastewater, dyeing wastewater, pharmaceutical wastewater, and landfill leachate, are also presented. Finally, we conclude that the main direction in the future of AOPs are the modification of catalysts and the optimization of operating parameters, with the challenges focusing on industrial applications.

Tetracyclines in the environment: An overview on the occurrence, fate, toxicity, detection, removal methods, and sludge management

Tetracyclines (TCs) are a group of broad-spectrum antibiotics having vast human, veterinary, and aquaculture applications. The continuous release of TCs residues into the environment and the inadequate removal through the conventional treatment systems result in its prevalent occurrence in soil, surface water, groundwater, and even in drinking water. As aqueous TCs contamination is the tip of the iceberg, and TCs possess good sorption capacity towards soil, sediments, sludge, and manure, it is insufficient to rely on the sorptive removal in the conventional water treatment plants. The severity of the TCs contamination is evident from the emergence of TCs resistance in a wide variety of microorganisms. This paper reviews the recent research on the TCs occurrence in the environmental matrices, fate in natural systems, toxic effects, and the removal methods. The high performance liquid chromatography (HPLC) determination of TCs in environmental samples and the associated technology developments are analyzed. The benefits and limitations of biochemical and physicochemical removal processes are also discussed. This work draws attention to the inevitability of proper TC sludge management. This paper also gives insight into the limitations of TCs related research and the future scope of research in environmental contamination by TCs residues.

Various wastewaters treatment by sono-electrocoagulation process: A comprehensive review of operational parameters and future outlook

Electrochemical processes are a promising alternative to traditional water treatment systems because they have advantages than conventional techniques such as chemical storage, small treatment systems, no alkalinity depletion, remote adjustment, and cost-effectiveness. The most crucial electrochemical method is Electrocoagulation (EC). Through creating cationic species, the EC causes the neutralization of pollutant surface charges and destabilizes suspended, emulsified or dissolved contaminants led to attracting particles of opposite charge and form flocculants. The main drawback of the EC process is a passive film forming on the electrode surface over time. Ultrasonic (US) waves breaking down sediments formed at the electrode surface and generate high amounts of radical species to remove pollutants by creating high-pressure points inside the solution during the cavitation phenomenon. Although EC systems are considered as an exemplary renaissance in water and wastewater treatment, various parameters related to these types of systems in pollutant degradation have not been fully addressed. To present a comprehensive vision of the current state of the art, and progress the treatment efficiency and agitate new studies in these fields, this review aimed to provide an overview of electrocoagulation's application in pollutant degradation, besides the advantages, associated disadvantages and further strategies for improving the performance of this technique. Moreover, this review discussed various parameters affecting the EC/US process, including nanoparticles addition, electrolyte concentration, current intensity, electrode distance, temperature, oxidant addition, pH, pollutant concentration, reaction time, and electrode combination, chloride addition, and ultrasonic frequency. Also, the efficiency of the EC/US process for disinfection, as well as treatment of car-washing, textile, pulp, and paper industry, oily, brewery wastewater, surfactant, humic acid, and heavy metals, are addressed.

An overview on combined electrocoagulation-degradation processes for the effective treatment of water and wastewater

Electrocoagulation (EC) process is found as effective water and wastewater treatment method, as it can able to remove a variety of pollutants, treat various industrial wastewater, and able to handle fluctuations in pollutant quality and quantity. The performance of EC process can be improved significantly in combination with degradation processes. Different combinations of EC process with Fenton, electro-Fenton, photo-Fenton, photocatalysis, sonochemical treatment, ozonation, indirect electrochemical oxidation, anodic oxidation and sulfate radical based advanced oxidation process are found very effective for the treatment of water and wastewater. Enhanced performance of EC process in combination with degradation process was reported in most of the articles.

Treatment of dairy industry wastewater by combined aerated electrocoagulation and phytoremediation process

As dairy industries has been emerged as one of the most rapidly developing industry in both small as well as large scale, the volume of effluent generated is also very high. In the present study, aerated electrocoagulation combined with phytoremediation treatment was conducted in dairy industry wastewater. Electrocoagulation was performed with aluminium and iron electrodes and effect of various operating parameters such as electrode combination, pH, and voltage were tested. Electrocoagulation was found effective at neutral pH and its efficiency increased with increase in applied voltage. The maximum COD removal efficiency of 86.4% was obtained in case of Al-Fe electrode combination with aeration at 120 min reaction time, initial pH 7, voltage 5 V. Significant growth of Canna indica was observed in electrocoagulation treated wastewater compared to raw dairy wastewater. COD removal of 97% was achieved when combined electrocoagulation and phytoremediation process was used. Thus, it proves to be a proficient method for the treatment of dairy industry wastewater. In addition to the above, bacterial toxicity tests were performed to investigate the toxic nature of wastewater and the results showed that both treated and untreated wastewater favoured bacterial growth.