Electrocoagulation of wastewater using aluminum, iron, and magnesium electrodes

A multidirectional pairwise coupling approach with spectral features unmixing to quantify total phosphorus, total nitrogen, and chlorophyll-a in urban rivers

Comprehensive and effective water quality monitoring is vital to water environment management and prevention of water quality from degradation. Unmanned aerial vehicle (UAV) remote sensing techniques have gradually matured and prevailed in monitoring water quality of urban rivers, posing great opportunity for more effective and flexible quantitative estimation of water quality parameter (WQP) than satellite remote sensing techniques. However, current UAV remote sensing methods often entail large quantities of cost-prohibitive in-situ collected training samples with corresponding chemical analysis in different monitoring watersheds, laying time and fiscal pressure on local environmental protection department. They suffer relatively low calculation accuracy and stability and their applicability in various watersheds is constrained. This study developed a unified two-stage method, multidirectional pairwise coupling (MDPC) with information sharing and delivery of different modeling stages to efficiently predict concentrations of WQPs including total phosphorus (TP), total nitrogen (TN), and chlorophyll-a (Chl-a) from hyperspectral data. MDPC incorporates exterior and interior feature interaction and gravity model variant to improve prediction accuracy and stability with consideration of mutual effect in the proximity. The structure design and workflow of MDPC ensure high robustness and application prospect due to achievement of good performance with less training samples, improving applicability and feasibility. The experiments show that MDPC has achieved good performance on retrieval of WQPs concentrations including TP, TN, and Chl-a, the results mean absolute percent error (MAPE) and coefficient of determination (R2) ranging from 6.34 % to 11.94 % and from 0.74 to 0.93. This study provides a systematic and scientific reference to formulate a feasible and efficient water environment management scheme.

Reduction of organic matter containing benzimidazole and toxicity in real livestock wastewater through advanced oxidation processes

Livestock wastewater (LWW) has a complex characteristic of high organic matter content, metals, nutrients, and pharmaceutical compounds. Advanced oxidation processes (AOP) are a potential option for treating this wastewater. This study evaluated real LWW and the performance of UV/H2O2 and UV/peroxymonosulfate (UV/PMS) for its treatment. The experiments were conducted in a UV photoreactor (16 mW/m2, λ = 254 nm). The oxidant agents (Ox) tested were H2O2 and PMS, each at low, medium, and high TOC/Ox molar ratios. A pretreatment based on chemical precipitation was implemented. Annually, the LWW showed total organic carbon (TOC) values of 859 ± 13.37 mg/L, 168.85 ± 1.62 mg/L of total Kjeldahl nitrogen (TKN), and toxicity of 96% v/v. In the dry season, albendazole (ABZ) (95.3 ± 35.16 mg/L), Cu (4.3 ± 0.23 mg/L), Fe (3.8 ± 0.38 mg/L), and suspended solids (SS) (1015 ± 586.9 mg/L) were identified, so pretreatment was implemented. The UV/PMS process with the lowest molar ratio [TOC/Ox 1:0.75] removed significantly lower TOC concentrations (p < 0.05), but toxicity decreased entirely. The study of mineralization and toxicity provided insight into the changes in LWW during treatment with AOP. Furthermore, it contributed to establishing the technical basis for implementing efficient treatment processes.

Electrocoagulation in treatment of municipal wastewater- life cycle impact assessment

The purpose of this study is investigation of electrocoagulation (EC) as a treatment of municipal wastewater, integrating life cycle impact assessment (LCIA) for assessing its environmental performance of investigated treatment. The study evaluated the effectiveness of EC in removing physico-chemical and microbial parameters using aluminum (Al) and iron (Fe) electrodes in monopolar and bipolar modes. Bipolar arrangement of Al(-)/Al/Al/Al(+) electrodes achieved the highest removals: 70% COD, 72% BOD5 followed by complete elimination of total phosphorous, turbidity and microbial parameters. This treatment was subject to investigation of the influence of reaction time (t = 10-60 min) on removals at higher current density (CD = 3.33 mA/cm2). In order to reduce energy consumption, the same reaction time range was used with a reduced CD = 2.33 mA/cm2. Following removal efficiencies obtained: 47-72% COD (higher CD) and 53-78% (lower CD); 69-75% BOD5 (higher CD) and 55-74% CD (lower CD); 12-21% NH4- (higher CD) and 7-22% NH4- (lower CD). Total P, NO3- and NO2- compounds showed the same removals regardless the CD. Decrease in current density did not influence removals of total suspended matter, turbidity, salinity as well as microbial parameters. The bipolar arrangement of Al(-)/Al/Al/Al(+) electrodes, assuming a lower CD = 2.33 mA/cm2 and t = 30 min, was assessed with the Recipe 2016Midpoint (H) and USEtox v.2 LCIA methods to explore the environmental justification of using EC for wastewater treatment. The LCIA results revealed that the EC process significantly reduces water eutrophication and toxicity for freshwater and marine ecosystems, but has higher impacts in global warming, fossil fuel consumption, human toxicity, acidification, and terrestrial ecotoxicity due to high energy consumption. This can be mainly explained by the assumption in the study that the EC precipitate is dispersed to agricultural soil without any pre-treatment and material recovery, along with relatively high energy consumption during the process.

Scientometric analysis of electrocatalysis in wastewater treatment: today and tomorrow

Electrocatalytic methods are valuable tools for addressing water pollution and scarcity, offering effective pollutant removal and resource recovery. To investigate the current status and future trends of electrocatalysis in wastewater treatment, a detailed analysis of 9417 papers and 4061 patents was conducted using scientometric methods. China emerged as the leading contributor to publications, and collaborations between China and the USA have emerged as the most frequent partnerships. Primary article co-citation clusters focused on oxygen evolution reaction and electrochemical oxidation, transitioning towards advanced oxidation processes ("persulfate activation"), and electrocatalytic reduction processes ("nitrate reduction"). Bifunctional catalysts, theoretical calculations, electrocatalytic combination technologies, and emerging contaminants were identified as current research hotspots. Patent analysis revealed seven types of electrochemical technologies, which were compared using SWOT analysis, highlighting electrochemical oxidation as prominent. The technological evolution presented the pathway of electro-Fenton to combined electrocatalytic technologies with biochemical processes, and finally to coupling with electrocoagulation. Standardized evaluation systems, waste resource utilization, and energy conservation were important directions of innovation in electrocatalytic technologies. Overall, this study provided a reference for researchers to understand the framework of electrocatalysis in wastewater treatment and also shed light on potential avenues for further innovation in the field.

Electrocoagulation flotation as a municipal wastewater (pre-)treatment technology: Effect of weather conditions and current density

Electrocoagulation (EC) is a promising compact alternative technology, despite its viability in municipal wastewater treatment (MWWT) is currently challenged by its energy-intensive and batch-mode operation. This study introduces an innovative continuous electrocoagulation flotation (ECF) design for MWWT. ECF shows promising pollutant removal efficiencies, with identical results using both iron (Fe) and aluminum (Al) anodes. At a current density (CD) of 120 A/m2, it achieved significant removals: 90% tCOD, 98% TP, 94% TSS, 60% BOD5, and 40% TN. Designed ECF is proposed as a pre-treatment step due to limited TN removal. The study investigated optimal ECF performance under varying weather conditions using CD ranges of 40, 80, and 120 A/m2. Both Fe and Al ECF outperformed in treating rainy weather (RW) and dry weather (DW) municipal wastewater (MWW). However, Al anode's super-faradaic behavior resulted in higher residual concentrations in effluent, (i.e., an average of 6.53-33.7 mg/L), and operational costs compared to Fe ECF. Optimized Fe ECF setting needs to be changed depending in the weather variation. Fe ECF achieved high removal rates for tCOD (94%) and TP (95%) in RW MWW at a low CD of 40 A/m2. Comparative to this, the optimum CD for treated DW MWW was between 40 and 80 A/m2, removing tCOD (71-73%) and TP (85-95%). Specifically, at these conditions, the operational expenses were respectively 0.47 ± 0.03 €/m3 (RW MWW), and 0.37 ± 0.02 €/m3 to 0.81 ± 0.04 €/m3 (DW MWW). Moreover, ECF enables resource recovery and a circular economy through anaerobic sludge digestion, with Fe ECF generating more biogas than Al.

Electrochemical-based processes for produced water and oily wastewater treatment: A review

The greatest volume of by-products produced in oil and gas recovery operations is referred to as produced water and increasing environmental concerns and strict legislations on discharging it into the environment cause to more attention for focusing on degradation methods for treatment of produced water especially electrochemical technologies. This article provides an overview of electrochemical technologies for treating oily wastewater and produced water, including: electro-coagulation, electro-Fenton, electrochemical oxidation and electrochemical membrane reactor as a single stage and combination of these technologies as multi-stage treatment process. Many researchers have carried out experiments to examine the impact of various factors such as material (i.e, electrode material) and operational conditions (i.e., potential, current density, pH, electrode distance, and other factors) for organic elimination to obtain the high efficiency. Results of each method are reviewed and discussed according to these studies, comprehensively. Furthermore, several challenges need to be overcome and perspectives for future study are proposed for each method.

Sequential treatment of landfill leachate by electrocoagulation/aeration, PMS/ZVI/UV and electro-Fenton: Performance, biodegradability and toxicity studies

This study presents a systematic study on sequential treatment of highly resistant landfill leachate by electrocoagulation (EC)/aeration, sulfate radical advanced oxidation process (SR-AOP) and electro-Fenton (EF). In case of SR-AOP, peroxymonosulfate (PMS) catalyzed by zero valent iron (ZVI) and ultraviolet irradiation (UV) system was developed. Treatment process was optimized in respect to COD removal. Analysis of results revealed that sequential application of EC/aeration, PMS/ZVI/UV, and EF processes provide an extraordinary performance and meet the environmental regulations. The source of iron for EF process was provided from previous process reducing the cost of sequential process. Separately, EC/aeration (inlet COD = 4040 mg/L), PMS/ZVI/UV (inlet COD = 1560 mg/L), and EF (inlet COD = 471 mg/L) removed 61, 69 and 82% of COD respectively. Overall, sequential processes of EC/aeration, PMS/ZVI/UV and EF could remove the COD, TOC and ammonia of the landfill leachate around 98%, 93% and 94%, respectively. The comparison of different sequences of following processes indicated that current configuration (EC/aeration-PMS/ZVI/UV-EF) could meet the discharge standards. Furthermore, humification degree was significantly improved after oxidative processes. Biodegradability study was also performed by means of BOD/COD, average oxidation state (AOS), and Zahn-Wellens test, and the best results associated with these indices were obtained 0.56, 2.37, and over 98%, respectively. Phytotoxicity of leachate was remarkably reduced and the final effluent can be considered as a non-phytotoxic wastewater.

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.

Optimization of phosphorus recovery using electrochemical struvite precipitation and comparison with iron electrocoagulation system

A batch monopolar reactor was developed for total phosphorus (TP) recovery using electrochemical struvite precipitation. This study involves the optimization of factors using response surface methodology to maximize the TP recovery. The optimal parameters for this study were found to be a pH of 8.40, a retention time of 35 min, a current density of 300 A/m² , and an interelectrode distance of 0.5 cm, resulting in 97.3% of TP recovery and energy consumption of 2.35 kWh/m³ . A kinetic study for TP removal revealed that at optimum operating conditions, TP removal follows second-order kinetics (removal rate constant(K) = 0.0117 mg/(m² ·min)). The system performance was compared to the performance of an iron electrocoagulation system. The composition of the precipitate obtained during the optimal runs were analyzed using X-ray diffraction and EDS analysis. X-ray diffraction analysis of the magnesium precipitate revealed the presence of struvite as the only crystalline compound. PRACTITIONER POINTS: Electrochemical struvite precipitation has the potential to recover total phosphorus from anaerobic bioreactor effluent. Optimum conditions for phosphorus recovery was found at a pH of 8.4, retention time of 35 min, current density of 300 A/m2, and interelectrode distance of 0.5 cm. The quadratic model predicted complete (100 %) TP recovery under optimized conditions, whereas 97.3 % recovery was observed under experimental conditions. TP removal under optimum conditions followed second-order rate equation (removal rate constant(K) = 0.0117 mg/(m² ·min)). XRD analysis of the precipitate revealed struvite as the only crystalline compound.

Study on influencing parameters and long-term operation of electrocoagulation phosphorus removal from small rural domestic sewage

Excessive discharge of phosphorus can produce eutrophication in aquatic environments, damaging public health, the living environment, and the economy. The conventional mechanical-biological phosphorus removal methods are not suitable for small rural domestic sewage due to the features of small scale, scattered distribution, intermittent emission, and large fluctuation. This work evaluated electrocoagulation (EC) with industrial steel as electrodes on small rural domestic sewage. Results showed that the best performance was achieved at a current density of 1 mA/cm², electrode distance of 2 cm, electrode number of 2, pH of 7, and Hydraulic Retention Time of 30 min, respectively. Under optimum conditions, the EC process removed 93.91% phosphorus while consuming around 0.25 kWh/m³ of electricity. In addition, the electrode passivation of EC was further investigated; the long-term research found that the phosphorus removal efficiency only decreased by 4.34% after 10 days of continuous flow operation, and the operational energy consumption was 0.07 kWh/m³ at a Cl^- concentration of 500 mg/L.

Adsorption of Cr(VI) by NaOH-modified microporous activated carbons derived from the wastes of Amaranthus retroflexus, Magnolia soulangeana, and Tanacetum Vulgar L.: mechanism, isotherms, and kinetic studies

The study was designed to synthesize microporous activated carbons from the wastes of three medicinal herbs by NaOH as an activator followed by pyrolysis. The prepared microporous activated carbons R. Weed (Amaranthus retroflexus Redroot pigweed modified with NaOH), S. Bod Magnolia soulangeana Soul-Bod treated with NaOH) and S. TY (Tanacetum Vulgar L. (Tansy) treated with NaOH) were deployed for dangerous Cr(VI) ion remediation from the aquatic system. The synthesized modified biosorbents were described by FT-IR, SEM, EDAX, and BET. Furthermore, it was found that biosorbent made from R. Weed seems to have a surface area of 588.155 m²/g and micropore volume of 0.331Cm³/g whereas biosorbent made from S. Bod and S. TY does have a surface area of 489.613 and 445.615 m²/g respectively. The effects of several variables such as pH, temperature, and contact time were explored. The kinetic studies were accomplished and it was noticed that equilibrium was confirmed at 6 min for R. Weed while at 8 and 10 min for S. Bod and S. TY respectively. The pertinence of different adsorption isotherms like Langmuir, Freundlich, and Temkin was explored. The optimum adsorption capacity for each adsorbent material in respect of monolayer coverage (Q_max) was calculated. The Q_max of Redroot pigweed (R. Weed), Soul-Bod (S. Bod), and Tansy (S. TY) biosorbents were 326.62, 181.69, and 108.14 mg/g respectively. The adsorption kinetics was described using pseudo-first-order and pseudo-second-order equations. Furthermore, it was found that each adsorbent material followed the pseudo-second-order kinetics which affirmed the chemosorption nature of adsorption. The thermodynamic variables that include ΔG, ΔH, and ΔS were determined for each adsorbent material. Moreover, the manufactured R. Weed biosorbent seems to have high recyclability. It will remediate Cr(VI) ions with a maximum remediation efficiency of up to 81% during six cycles of regeneration.

Can electrocoagulation technology be integrated with wastewater treatment systems to improve treatment efficiency?

Considerable amounts of domestic and industrial wastewater that should be treated before reuse are discharged into the environment annually. Electrocoagulation is an electrochemical technology in which electrical current is conducted through electrodes, it is mainly used to remove several types of wastewater pollutants, such as dyes, toxic materials, oil content, chemical oxygen demand, and salinity, individually or in combination with other processes. Electrocoagulation technology used in hybrid systems along with other technologies for wastewater treatment are reviewed in this work, and the articles reviewed herein were published from 2018 to 2021. Electrocoagulation is widely employed in integrated systems with other electrochemical technologies or conventional methods for effective removal of different pollutants with less cost and sometimes over shorter durations of operation. It has also been observed that the hybrid effects besides increasing the removal efficiency can overcome the disadvantages of using electrocoagulation alone, such as less sludge formation, high cost of operation and increased life of the used electrodes, and stable flux of water with longer periods of operation. More than 20 types of other technologies have been combined efficiently with electrocoagulation.

Treatment technologies for sustainable management of wastewater from iron and steel industry - a review

The iron and steel industries are a vital driving force for propelling the nation's economic growth. In 2019, to boost the economy and to achieve the target of five trillion economies by 2024, government of India entails investments in several steel-related sectors. However, since their inception, steel and iron industries have been coupled with extensive environmental pollution and vast water utilization. Discharged effluent from the different units of plant loaded with toxic, hazardous, and unused components which have various harmful environmental and health impacts and need treatment. In the present review, the pollutants treatment efficiency of various treatment techniques, effluent volume product quality, and various measures for sound management of wastewater are reviewed. As most conventional wastewater treatment methods are not sufficient for complete reclamation and remediation of effluent, the potential of more advanced treatment such as membrane separation and membrane bioreactors is relatively untouched. In the end, this paper concluded that the integrated system combining chemical treatment with membrane separation can ensure a worthy rate of pollutant removal. Reuse and effective management of wastewater with process intensification guarantee commercial viability and eco-friendliness.

Performance of an electrocoagulation-flotation system in the treatment of domestic wastewater for urban reuse

Domestic wastewater is an important alternative source of water in the face of a growing discrepancy between water availability and demand. The use of techniques that enable the urban reuse of treated sewage is essential to make cities more sustainable and resilient to water scarcity. The main goal of this study was to evaluate the performance of an electrocoagulation-flotation system in the treatment of domestic wastewater for urban reuse. The study was performed using raw domestic wastewater samples. The electrocoagulation-flotation system was a cylindrical reactor with aluminum electrodes. The treatment conditions involved agitation at 262.5 rpm, electrical current of 1.65 A, electrolysis time of 25 min, an initial pH of 6, and inter-electrode distance of 1 cm. Overall, the electrocoagulation-flotation system was highly efficient for removal of apparent color (97.9%), chemical oxygen demand (82.9%), turbidity (95.8%), and orthophosphate phosphorous (> 98.2%). The electrocoagulation-flotation system had a consumption of electrical energy ranging from 9.5 to 13.3 kWh m^-3, electrode mass from 294.7 to 557.0 g m^-3, and hydrochloric acid from 4.3 to 6.6 L m^-3. Sludge production in the system ranged from 1,125.7 to 1,835.7 g m^-3. Treated wastewater had a satisfactory quality for several urban reuse activities. The electrocoagulation-flotation system showed potential to be used for domestic wastewater treatment for urban reuse purposes.

Tertiary treatment of a mixture of composting and landfill leachates using electrochemical processes

The study investigated the treatment efficiency of coupled electrocoagulation (EC) and electrooxidation (EO) processes for landfill leachate treatment in batch and continuous mode. The EC process (iron anode and graphite cathode) at 18.2 mA/cm² for 2.5 min resulted in COD, turbidity, total phosphorus, total coliforms and fecal coliforms removal of 58.1, 72.9, 98.5, 97.9, and 97.2% respectively. Under the same operating conditions, the coupled EC/EO (Ti-Pt anode, bipolar iron electrode, and graphite cathode) processes showed that the COD, turbidity, total phosphorus, total coliforms, and fecal coliforms removal of 56.5%, 78.3%, 96.3%, 97.2% and fecal coliforms 72.7%, respectively. The energy costs associated with the EC and EC/EO were 0.11 and 0.25 $/m³, respectively. Compared to the batch configuration, the continuous configuration of EC resulted in similar processing performance. However, the EC/EO process resulted in the production of chlorates, perchlorates, and trihalomethanes as by-products. Moreover, the continuous process slightly increases the pH and ammonia concentration of the leachate and also resulted in the metallic sludge production with an average dryness of 4.2%. The toxicity tests determined that the treated effluent was not toxic to Rainbow trout and Daphnia.

Degradation of Azo Dyes with Different Functional Groups in Simulated Wastewater by Electrocoagulation

Increasing attention has been paid to the widespread contamination of azo dyes in water bodies globally. These chemicals can present high toxicity, possibly causing severe irritation of the respiratory tract and even carcinogenic effects. The present study focuses on the periodically reverse electrocoagulation (PREC) treatment of two typical azo dyes with different functional groups, involving methyl orange (MO) and alizarin yellow (AY), using Fe-Fe electrodes. Based upon the comparative analysis of three main parameters, including current intensity, pH, and electrolyte, the optimal color removal rates for MO and AY could be achieved at a rate of up to 98.7% and 98.6%, respectively, when the current intensity is set to 0.6 A, the pH is set at 6.0, and the electrolyte is selected as NaCl. An accurate predicted method of response surface methodology (RSM) was established to optimize the PREC process involving the three parameters above. The reaction time was the main influence for both azo dyes, while the condition of PREC treatment for AY simulated wastewater was time-saving and energy conserving. According to the further UV–Vis spectrophotometry analysis throughout the procedure of the PREC process, the removal efficiency for AY was better than that of MO, potentially because hydroxyl groups might donate electrons to iron flocs or electrolyze out hydroxyl free radicals. The present study revealed that the functional groups might pose a vital influence on the removal efficiencies of the PREC treatment for those two azo dyes.

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

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

Phosphate removal from aqueous solution by electrochemical coupling siderite packed column

The use of iron species to remove PO₄^3- is widely used, and the fresh Fe³⁺ produced in situ demonstrate better effect on the removal of PO₄^3- in many researches. Therefore, in order to develop a simpler and more efficient method for PO₄^3- removal, we designed an easy operation by electrochemically dissolving siderite to produce fresh Fe³⁺ in situ for PO₄^3- removal from wastewater. Results showed that current intensity at 20 mA, initial pH at 6, initial PO₄^3- concentration at 1 mM and influent flow rate at 2.5 mL min^-1 were the best parameters for removing PO₄^3-, ensuring that the PO₄^3- concentration of effluent can be kept below 1 mg L^-1 through the electrochemical system. Different from other studies, a large amount of Fe²⁺ can be dissolved from natural minerals without adding H⁺ to the system and Fe³⁺ species are generated in situ from the oxidation of the Fe²⁺ without using a specific oxidizer. This electrochemical treatment method with siderite as a packed column can be used as a new method of high efficiency, simple operation and low-cost for treating eutrophic water bodies.

Coupling of electrocoagulation and powder activated carbon for the treatment of sustainable wastewater

The present research work is based on an electrochemical technique in combination with powdered activated carbon (PAC) for the removal of micropollutants by adsorption as an advanced stage purification step from effluents of pilot plant wastewater treatment plants (WWTP). The effluents of sedimentation tank comprised of wastewater plus PAC (WWPAC). The pilot plant mainly consists of two parts: the first one consists of electrocoagulation (EC) reactor, and the second consists of electrophoretic deposition (EPD) discs and electroflotation (EF) setup. The electrocoagulation (EC) reactor consisted of the electrode material (Al and Fe). Both types of electrodes have been tested with the outflow of sedimentation tank. The outflow from the sedimentation tank has been entered into the EC reactor for the determination of EC reactor efficacy for the successful accomplishment of EC process at the designed pilot plant for WW treatment. The effect of different operational parameters, PAC dosage (20 mg), electrode nature (Fe and Al) and current density (0.34-2.02 A/m²), has been studied to find out the optimum conditions. Sludge volume index (SVI) of the sludge, thermogravimetric (TG), differential thermal analyses (DTA) and particle size distribution (PSD) of the flocs generated after the EC process has also been studied. The turbidity, pH and conductivity of effluents before and after EC treatment have also been carried out. The research work performed detailed analysis of the wastewater effluents at pilot plant scale and gave promising results for future work in advance wastewater treatment direction.

A critical review of state-of-the-art electrocoagulation technique applied to COD-rich industrial wastewaters

Electrocoagulation (EC) is one of the emerging technologies in groundwater and wastewater treatment as it combines the benefits of coagulation, sedimentation, flotation, and electrochemical oxidation processes. Extensive research efforts implementing EC technology have been executed over the last decade to treat chemical oxygen demand (COD)-rich industrial wastewaters with the aim to protect freshwater streams (e.g., rivers, lakes) from pollution. A comprehensive review of the available recent literature utilizing EC to treat wastewater with high COD levels is presented. In addition, recommendations are provided for future studies to improve the EC technology and broaden its range of application. This review paper introduces some technologies which are often adopted for industrial wastewater treatment. Then, the EC process is compared with those techniques as a treatment for COD-rich wastewater. The EC process is considered as the most privileged technology by different research groups owing to its ability to deal with abundant volumes of wastewater. After, the application of EC as a single and combined treatment for COD-rich wastewaters is thoroughly reviewed. Finally, this review attempts to highlight the potentials and limitations of EC. Related to the EC process in batch operation mode, the best operational conditions are found at 10 V and 60 min of voltage and reaction time, respectively. These last values guarantee high COD removal efficiencies of > 90%. This review also concludes that considerably large operation costs of the EC process appears to be the serious drawback and renders it as an unfeasible approach for handling of COD rich wastewaters. In the end, this review has attempted to highlights the potential and limitation of EC and suggests that vast notably research in the field of continuous flow EC system is essential to introduce this technology as a convincing wastewater technology.

Treatment of slaughterhouse wastewater by electrocoagulation and electroflotation as a combined process: process optimization through response surface methodology

The contamination of water with organic compounds has become an increasing concern in today's world. The cost-effective and sustainable treatment of industrial wastewaters is a major challenge. Advanced treatment techniques such as electrocoagulation-electroflotation offer economic and reliable solutions for the treatment of industrial wastewater. In this study, the electrocoagulation-electroflotation method was investigated for the simultaneous removal of chemical oxygen demand, total phosphorus, total Kjeldahl nitrogen, and color via response surface methodology. Factors such as electrode combination (Fe and Al), current density (10-20 mA/cm²), pH (3.0-9.0), and electrode distance (1-3 cm) were investigated in the treatment of wastewater to obtain maximum treatment efficiency. It was determined that chemical oxygen demand, total Kjeldahl nitrogen, total phosphorus, and color removal reached up to 94.0%, 77.5%, 97.0%, and 99.0%, respectively. Treatment costs were found as $0.71 with the Al-Fe electrode combination.

Suitability of electro-chemical reactor with copper electrode for sugar industry wastewater treatment: optimization of parameters, mechanism, kinetics and sludge analysis

The waste water generated from sugar industry contains a high degree of organic pollutant. Treating the sugar industry wastewater is thus crucial important for the environmental concern. The treated water can be reprocessed in different unit operation due to lack of fresh water. The purpose of this research work is to treat the sugarcane processing industry wastewater by electrochemical technology. The experiment was carried out with the copper electrode in batch mode. The input process parameters were optimized by using response surface methodology. At optimum condition at pH 6.79, current 4.97, electrode distance 1.41 and treatment ∼30 min, maximum 87.07% of chemical oxygen demand and 99.18% color removals was attained. A fairly high predicted value of regression coefficient for chemical oxygen demand (Pre-R 2) 0.81 and color (Pre-R 2) 0.851 and adjacent value for chemical oxygen demand (Adj-R 2) 0.46 and color (Adj-R 2) 0.589 was obtained between the experimental values and the calculate values by using a second-order regression model. The physicochemical characterizations of scum reveal less percentage of inorganic and it cane used as a micronutrient.

Electrocoagulation pre-treatment to simultaneously remove dissolved and colloidal substances and Ca2+ in old corrugated container wastewater

An effective electrocoagulation pre-treatment (ECP) method was proposed to simultaneously solve the problems of the micro stickies deposition and high Ca²⁺ content in old corrugated container (OCC) papermaking wastewater during the recycling process. The optimal ECP condition was investigated. The results indicated that the effect of an Al electrode on wastewater treatment was superior to that of a Fe or Mg electrode. The optimal treatment conditions of the current density, electrode distance and reaction time were 115 A m^-2, 5 cm and 60 min, respectively. After the ECP, the chemical oxygen demand (COD) and Ca²⁺ removal rates were 75.33% and 64.53%, respectively, and the turbidity and dissolved and colloidal substance (DCS) content decreased by 97.1% and 43.68%, respectively. The particle size of flocs in the liquid increased from 1.675 μm to 31.97 μm, and the floc content was 0.78 g L^-1 after ECP. The anode material and energy consumption were 0.1846 kg m^-3 and 4.56 kWh m^-3, respectively, and the cost of treatment was estimated to be 1.11 $ m^-3. The results demonstrate that ECP can effectively remove the micro stickies, COD, and Ca²⁺ in the OCC wastewater, which is conducive to reducing the cost of wastewater treatment and conform to the requirements of sustainable development.

Industrial wastewater treatment using magnesium electrocoagulation in batch and continuous mode

In the present study, the electrocoagulation (EC) performance of a Mg-Mg system was applied for the industrial wastewater treatment, from an industrial park that covers different activities such as: food, automotive, pharmaceutical, chemistry and cosmetics, after primary clarification. The effects of major operating parameters such as pH, reaction time, and current density were investigated for chemical oxygen demand (COD), color, and turbidity removal efficiency. The batch system was found convenient, achieving 63.52% COD, 96% color, and 99.32% turbidity removal at optimized operating conditions of pH 7.12, reaction time of 75 min, and current density of 201.5 A/m². On the other hand, for continuous EC, the process removed approximately 46.58%, 95.96%, and 87.19% of the COD, color, and turbidity respectively, at 90 min of retention time, current density 440 A/m², and a rate of 20 mL/min. Additionally, concerning nutrient removal (N and P), the EC system with Mg electrodes was highly efficient; batch treatment removed 97% of total phosphorus and 67% of ammoniacal nitrogen, whereas the continuous treatment removed 98.5% of total phosphorus and 83% of ammoniacal nitrogen. The sludge characterization before and after EC treatment was made by SEM, EDS, Fluorescence spectroscopy, IR spectroscopy. Minerals such as chlorite, crossite, richterite, pyroaurite, langbeinite as weel as aliphatic and polysubstituted aromatics compounds, sulfates and phosphates inorganic ions, and organic phosphorus were reduced. The energy cost in the batch EC is US$0.05/m³. A numerical CFD model was used to estimate the velocity fields and guarantee the presence of turbulent kinetic energy within a continuous flow reactor.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.

The role of synergistic effects between ozone and coagulants (SOC) in the electro-hybrid ozonation-coagulation process

In order to improve the dissolved organic matter removal efficiency, an electro-hybrid ozonation-coagulation (E-HOC) system was developed in this study, in which the electro-coagulation (EC) and ozonation occurred simultaneously in one integrated unit. Higher removal efficiency was observed for the E-HOC process compared with those of EC, ozonation and pre-ozonation-EC process for the treatment of wastewater treatment plant (WWTP) effluent and ibuprofen (IBP). 58.6% dissolved organic carbon (DOC) removal efficiency was achieved in the E-HOC process for the treatment of WWTP effluent at optimal operational condition (current density 15 mA/cm², initial pH 5 and ozone dosage 1.5 mg O₃/mg DOC). Based on the reactive oxygen species (ROS) detection and reactions on the electrodes, the synergistic effects between ozone and coagulants (SOC) were found to be involved in the E-HOC process. According to pseudo-first-order rate constant analyses, the contribution of five possible organic removal pathways was quantified. It was revealed that the peroxone and SOC effects exhibited almost equal contribution to IBP removal at initial pH 5 under different current densities, both of which played the dominant role in the E-HOC process. However, the contribution of the SOC effects decreased significantly when the initial pH increased to 7 and 9. As an important pathway for organic removal in the E-HOC process at initial pH 5, the mechanism of the SOC effects was analysed at initial pH 5. It was revealed the SOC effects can further improve hydroxyl radicals (•OH) generation, and the surface hydroxyl groups of the hydrolysed Al species generated from anode electrolysis were determined to be the active sites to generate ROS in the SOC effects.

Utilisation of polarity inversion for phosphorus recovery in electrochemical precipitation with anaerobic digestion effluent

Phosphorus is a non-replaceable and limited resource, whose future drought is a matter of concern. Its recovery from wastewater has gained attention as a method of making the recovered phosphorus available for beneficial use. This study applied electrolysis with a platinum-coated titanium electrode to an actual anaerobic digestion effluent and investigated the phosphorus removal and precipitation characteristics with various current values. The separation of the phosphorus precipitate from the sludge residue and the usefulness of the polarity inversion to recover the phosphorus precipitate were evaluated. The availability of the recovered precipitate as a fertiliser was also demonstrated. The anaerobic digestion effluent after the centrifugal dehydration process with a coagulant was collected from a wastewater treatment plant. Phosphorus was precipitated as a form of calcium phosphate, including hydroxyapatite, which was confirmed by X-ray diffraction. The generated gases from the electrodes during the electrolysis floated and condensed the sludge residue, leading to successful separation of the phosphorus precipitate from the sludge residue. The polarity inversion successfully detached the phosphorus precipitate from the electrode, and at least 3 min polarity inversion was enough to detach the whole phosphorus precipitate. The submerging phosphorus precipitate contained abundant phosphorus (12.6%), in which citric-acid-soluble phosphorus accounted for 94.4%, and the utilisation of the precipitate as a slow-release phosphorus fertiliser was suggested.

Hazardous waste treatment technologies

This is a review of the literature published in 2018 on topics related to hazardous waste management in water, soils, sediments, and air. The review covers treatment technologies applying physical, chemical, and biological principles for contaminated water, soils, sediments, and air. PRACTITIONER POINTS: The management of waters, wastewaters, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) was reviewed according to the technology applied, namely, physical, chemical and biological methods. Physical methods for the management of hazardous wastes including adsorption, coagulation (conventional and electrochemical), sand filtration, electrosorption (or CDI), electrodialysis, electrokinetics, membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, persulfate-based, Fenton and Fenton-like, and potassium permanganate processes for the management of hazardous were reviewed. Biological methods such as aerobic, anaerobic, bioreactor, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed.

Functionalized Poly(arylene ether nitrile) Porous Membrane with High Pb(II) Adsorption Performance

Porous materials with high specific surface area possess a broad application prospect in the treatment of wastewater. In this work, sulfonated poly(arylene ether nitrile) (SPEN) functionalized with a carboxylic acid group was successfully synthesized, which was subsequently transformed into SPEN porous membranes with cetyltrimethyl ammonium bromide (CTAB) as pore-forming agents to study the adsorption performance for lead ions in aqueous solution. Then, experiments were conducted to investigate the effect of pH, contact time and initial solution concentration on the adsorption performance of porous membranes, and the adsorption capacities of porous membranes with different content (0, 5 and 15 wt %) of CTAB were 183.60, 161.73 and 127.43 mg/g, respectively, which manifested that the adsorption capacity decreased with the increase of CTAB. The adsorption capacities of porous membranes increased with the increase of the initial concentration of lead ions, and the maximum reached was 246.96 mg/g. The simulation of adsorption kinetics revealed that the adsorption was accorded with the pseudo-second-order kinetic model and Langmuir equation, indicating that the adsorption process followed Langmuir monolayer adsorption. Thermogravimetric analysis demonstrated that the porous membranes had excellent thermodynamic properties both before and after adsorption. In addition, the change of adsorption peak in the Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) spectrum indicated that the absorption performance of porous membranes for lead ions benefited from the chelation between lead ions and the carboxylic acid group on SPEN. Moreover, the porous membranes maintained excellent adsorption properties after circulating five times under the conditions of acidic or alkaline, and the cycle regeneration effect was outstanding.