Technical and economic analysis of electrocoagulation for the treatment of poultry slaughterhouse wastewater

Optimizing electrocoagulation for poultry slaughterhouse wastewater treatment: a fuzzy axiomatic design approach

White meat consumption is increasing day by day, and accordingly, there is an increase in the amount of wastewater resulting from the processes. Today, the reuse of wastewater has become a goal within the scope of the Green Deal. For this reason, wastewater treatment with high pollution and volume has gained importance. In this study, the fuzzy axiomatic design (FAD) method, one of the multi-criteria decision-making methods, has been used. With this method, coagulation, electrocoagulation (EC), dissolved air flotation (DAF), and anaerobic treatment alternatives preferred in poultry slaughterhouse wastewater (PSW) treatment were compared with each other and their information contents were calculated. The information content from the smallest to the largest is EC, DAF, coagulation, and anaerobic treatment, respectively. This treatment method was chosen because the smallest information content is in electrocoagulation. EC was applied to bloody PSW containing 1% blood by volume. The effectiveness of Fe and Al electrodes for PSW treatment in the batch EC reactor has been compared. The effective surface areas of 2 anodes and 2 cathodes connected bipolarly in the processes are 288 cm2. The electrolyte, pH, time, and current density effects on energy consumption were also investigated. The optimum conditions for Al and Fe electrodes were found to be 0.5 g·L-1 NaCl concentration, pH 5, 0.639 mA·cm-2 current density, and 5 min time. Under optimum conditions for the Fe electrode, COD, TOC, TN, and oil-grease removal efficiencies were determined as 76.3%, 71.8%, 70%, and 74%, respectively. Moreover, the highest COD, TOC, TN, and oil-grease removal efficiencies were achieved with an Al electrode (82.2%, 82.3%, 82.7%, and 78.9%, respectively). The experimental data were fit to a variety of isotherms and kinetic models to determine the characteristics of the EC. The results indicated that the pseudo-second-order equation provided the best fit for COD removal. Under optimum conditions, the operating cost was calculated as $3.39 and $3.09 for Al and Fe electrodes, respectively. In this study, the fuzzy axiomatic design method was used for the first time to select the most appropriate treatment method for PSW. In addition, blood, a major problem for the poultry slaughterhouse industry, was mixed with PSW at a ratio of 1% (v/v) and treated with EC for the first time with high removal efficiency. By treating PSW, which has a high pollution load, with electrocoagulation, the pollution load of the water to be given to secondary treatment has been greatly reduced.

Integration of electrochemical processes in a treatment system for landfill leachates based on a membrane bioreactor

The use of electrocoagulation (EC) and anodic oxidation (AO) processes was studied for improving a treatment system for landfill leachates based on a membrane bioreactor (MBR) and a nanofiltration step. The main limitation of the current full-scale system is related to the partial removal of organic compounds that leads to operation of the nanofiltration unit with a highly concentrated feed solution. Application of the EC before the MBR participated in partial removal of the organic load (40 %) with limited energy consumption (2.8 kWh m-3) but with additional production of iron hydroxide sludge. Only AO allowed for non-selective removal of organic compounds. As a standalone process, AO would require a sharp increase of the energy consumption (116 kWh for 81 % removal of total organic carbon). But using lower electric charge and combining AO with EC and MBR processes would allow for achieving high overall removal yields with limited energy consumption. For example, the overall removal yield of total organic carbon was 65 % by application of AO after EC, with an energy consumption of 21 kWh m-3. Results also showed that such treatment strategy might allow for a significant increase of the biodegradability of the effluent before treatment by the MBR. The MBR might then be dedicated to the removal of the residual organic load as well as to the removal of the nitrogen load. The data obtained in this study also showed that the lower electric charge required for integrating AO in a coupled process would allow for strongly decreasing the formation of undesired by-products such as ClO3- and ClO4-.

Treatment of effluents from Food Services Establishment (FSEs) by physico-chemical processes: a case study for Trinidad & Tobago

BACKGROUND

Effluents from Food Services Establishments (FSEs) contain primarily Fats, Oil and Grease (FOG) which severely impact on sewers and the environment when released in high concentrations. In Trinidad & Tobago, it is estimated that approximately 231,304 kg/day of unaccounted for FOG bearing wastewaters from FSEs, are released into the environment with no viable treatment in the country. This research explored the optimization of physico-chemical processes for the treatment of FOGs for subsequent release into sewers.

RESULTS

Bench-scale studies analysed the characteristics of FSE's effluents from three popular sources, conducted the treatment of these effluents using Jar Tests, and subsequently confirm results via a pilot plant study. Characterization showed the mean concentration of the parameters examined to be; FOG (511 mg/l ± 116 mg/l), Suspended Solids (446 mg/l ± 146 mg/l), Chemical Oxygen Demand (2229 mg/l ± 963 mg/l) and pH (6 ± 0.3). Jar Tests were conducted using Poly-aluminium Chloride (PACl) as coagulant, anionic and cationic polyelectrolytes as flocculant aids with suitable pH adjustments of samples to determine the isoelectric point for the coagulant. Effluent results showed FOG removal levels of 99.9% and final effluent concentration of 0.17 mg/l. This was attained using PACl concentration of 250 mg/l, a 0.1% low cationic polyelectrolyte (CP 1154) at 4 mg/l with the pH of sample adjusted to 8. The pilot plant achieved a 97.4% removal of FOG (residual of 16.8 mg/l) using the same coagulant dosing, and pH value, but increasing the strength of the flocculant aid to 0.1% medium cationic (CP1156) at 5 mg/l.

CONCLUSION

Experimentation showed high concentrations of emulsified FOG can be efficiently removed to levels below the permissible requirements (20 mg/l) for entry into sewer systems in Trinidad and Tobago using coagulation, flocculation and sedimentation techniques. Pilot scale study also revealed that a higher strength and/or dose of the cationic polyelectrolyte and increased times in primary and final tanks were required to attain the desired results as in the bench level study, where equipment limitations in the flocculation tank were faced. This is in alignment with theory where factors critical for agglomeration is equipment type and density charge. It is, concluded that the optimum combination of chemicals and the respective dosages attained at the bench level study should prove effective should the right equipment be made available.

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.

Electrocoagulation for nutrients removal in the slaughterhouse wastewater: comparison between iron and aluminum electrodes treatment

The poultry slaughterhouse wastewater has a high pollutant load, mainly organic matter, and nutrient content. The nitrogen and phosphorus discharge can cause eutrophication of the receiving water bodies. Electrocoagulation has been studied for several pollutants removal from different sources. The objective of this work was to evaluate the electrocoagulation process in the poultry slaughterhouse wastewater treatment using both iron and electrodes to remove total nitrogen and phosphorus. After the raw and polished wastewater characterisation, a 2³ Central Composite Rotatable Design was applied to evaluate the current density, initial pH, and electrocoagulation time influence on the nutrients removal and to find the optimum condition of nutrients removal. Once the optimum condition for nutrient removal was stablished, other physicochemical, microbiological, and ecotoxicological parameters, as well as the treatment cost, were investigated to determine which electrode material was the most efficient. For raw wastewater, applying the optimum treatment condition of 20 mA cm^-2 current density, initial pH 6.2, and time of 20 min, the nitrogen and phosphorus removal presented similar for both electrode materials. Besides being cheaper ($ 4.13 m^-3), iron electrode treatment presented better Chemical Oxygen Demand, oils and greases, solids, and ecotoxicity removal. For polished wastewater, the treatment with aluminum electrode was more efficient under the applied current density of 30 mA cm^-2, initial pH 8 and time of 10 min, obtaining the lowest cost $ 3.89 m^-3. In the iron electrode case, the final pH exceeds the limits established by local legislation requiring correction for release into water bodies.

Treatment technologies for bakers' yeast production wastewater

Researchers in recent years have utilized a broad spectrum of treatment technologies in treating bakers' yeast production wastewater. This paper aims to review the treatment technologies for the wastewater, compare the process technologies, discuss recent innovations, and propose future perspectives in the research area. The review observed that nanofiltration was the most effective membrane process for the treatment of the effluent (at >95% pollutant rejection). Other separation processes like adsorption and distillation had technical challenges of desorption, a poor fit for high pollutant load and cost limitations. Chemical treatment processes have varying levels of success but they are expensive and produce toxic sludge. Sludge production would be a hurdle when product recovery and reuse are targeted. It is difficult to make an outright choice of the best process for treating the effluent because each has its merits and demerits and an appropriate choice can be made when all factors are duly considered. The process intensification of the industrial-scale production of the bakers' yeast process will be a very direct approach, where the process optimisation, zero effluent discharge, and enhanced recovery of value-added product from the waste streams are important approaches that need to be taken into account.

The application of electrochemical processes in oily wastewater treatment: a review

Oily wastewater is becoming a concern worldwide due to its quantities and the presence of contaminants and its sustainable treatment should be cost-effective and meet all requirements so the contaminants are not transferred to the environment. The paper reviews the state-of-the-art in the oily wastewater treatment by electrochemical processes such as electrochemical advanced oxidation processes and electrocoagulation. Efficiency of oily wastewater treatment has been thoroughly investigated with its expression as a function of the main technological (process) parameters. Fe and Al electrodes, as well as their combination have proven to be very effective in oily wastewater treatment with slightly better performance of Al electrodes. Higher current densities and longer reaction times result with higher COD, TOC, turbidity, phenol and oil and grease removal efficiencies, but with resulting increase in wastewater temperature and energy consumption, so there is a strong need for the process optimization. There is a need for further research on the treatment efficiencies of different contaminants (heavy metals, total hydrocarbons, organic halogens, cyanides, etc.). A lack of research is presented on the treatment efficiency with electrodes of different materials as well as the analyses of the sludge production and its further treatment and use or disposal.

Poultry Slaughterhouse Wastewater Remediation Using a Bio-Delipidation Pre-Treatment Unit Coupled with an Expanded Granular Sludge Bed Reactor

The treatment of poultry slaughterhouse wastewater (PSW) with an Expanded Granular Sludge-Bed Bioreactor (EGSB) is hindered by the washout of activated sludge, and difficulties associated with the operation of the three-phase separator and the determination of the optimum up-flow velocity for sludge-bed fluidization. This results in a poor reactor functionality, and thus a poor performance due to pollutants such as fats, oil and grease (FOG) in the PSW being treated. Hydrolyzing the FOG content with a bio-delipidation, enzyme-based agent in a pre-treatment unit would significantly improve the effectiveness of the primary PSW treating system, i.e., the EGSB. In this study, PSW was pre-treated for 48 h with a biological mixture containing bioflocculants and bio-delipidation constituents. The pre-treated PSW was further treated in an EGSB. The PSW FOG, total chemical oxygen demand (tCOD) and total suspended solids (TSS) content were determined to assess the effectiveness of the pre-treatment process as well as to observe the remedial action of the combined pre-treatment-EGSB system. An increased treatment efficacy was noted for the combined PSW treatment system, whereby the tCOD, FOG and TSS removal averaged 76%, 88% and 87%, respectively. The process developed is intended for micro, small and medium poultry slaughterhouses.

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.

Physical and Biological Treatment Technologies of Slaughterhouse Wastewater: A Review

Physical and biological treatment technology are considered a highly feasible and economic way to treat slaughterhouse wastewater. To achieve the desired effluent quality for disposal or reuse, various technological options were reviewed. However, most practical operations are accompanied by several advantages and disadvantages. Nevertheless, due to the presence of biodegradable organic matter in slaughterhouse waste, anaerobic digestion technology is commonly applied for economic gain. In this paper, the common technologies used for slaughterhouse wastewater treatment and their suitability were reviewed. The advantages and disadvantages of the different processes were evaluated. Physical treatments (dissolved air floatation (DAF), coagulation–flocculation and sedimentation, electrocoagulation process and membrane technology) were found to be more effective but required a large space to operate and intensive capital investment. However, some biological treatments such as anaerobic, facultative lagoons, activated sludge process and trickling filters were also effective but required longer start-up periods. This review further explores the various strategies being used in the treatment of other wastewater for the production of valuable by-products through anaerobic digestion.

Evaluation of Electrochemical Methods for Poultry Slaughterhouse Wastewater Treatment

Understanding the efficiency of different wastewater treatment technologies tested under real conditions is essential for successful decision making by engineers and managers. In this study, real poultry slaughterhouse wastewater coming from defeathering, cooling, and evisceration processes was treated using a lab-scale electrochemical process by use of iron-iron (Fe-Fe), iron-graphite (Fe-Gr) and aluminum-graphite (Al-Gr) electrode combinations. A water quality index (WQI) was developed and used as a tool for evaluating and classifying the effectiveness of different electrode combinations. The Al-Gr electrode combination showed an impressive performance achieving an “excellent” status for all of the three studied sources of wastewater with a WQI ranging from 13 to 34. The Fe-Gr electrode combination showed an “excellent” status performance for the wastewater from the cooling process as classified by the WQI and “good water” class for the defeathering and evisceration processes. The lower performance, which was highly affected by the increase in turbidity, was observed for the Fe-Fe electrode combination with a “poor water” status for the wastewater coming from defeathering and cooling processes and “good water” status for evisceration process.

Cheese manufacturing wastewater treatment by combined physicochemical processes for reuse and fertilizer production

Making cheese manufacturing environmentally sustainable is a major concern in the integrated management of this industrial sector. This concern is mainly due to the environmental impact of the discharge of its wastewaters, carrying heavy loads of salinity, nutrients, organic matter, solids and oils and fats. These discharges must meet increasingly stringent quality requirements. Some physicochemical (e.g. coagulation-flocculation, precipitation, oxidation) and biological (e.g. aerobic and anaerobic bioreactors and wetlands) treatments have been studied to address this problem. However, these treatments involve costs that some producers cannot sustain, face difficulties with biological reactor operational stability and often fail to consistently produce effluents compatible with discharge standards. In this context, aiming at the design of a simple and economical treatment method, several precipitation processes were tested using a fixed dosage of CaCO₃ (75 g/L), combined with different dosages of FeCl₃, FeSO₄ or Ca(OH)₂. The goal of the treatment was to produce a supernatant that would be evaluated as to its suitability for discharge into natural water courses or municipal treatment systems, or for reuse applications. The generated sludge would be evaluated for possible agricultural valorization. Through the measurement of the relevant supernatant quality parameters and using statistical analysis, it was possible to choose the best dosages for each of the tested coagulants (1.0, 1.0 and 0.6 g/L for FeCl₃, FeSO₄ and Ca(OH)₂, respectively). Among these, the most efficient treatment was obtained with CaCO₃ 75 g/L + FeSO₄ 1.0 g/L. For this best-case scenario, the treatment led to removal yield values of 55.1% for chemical oxygen demand (COD), 92.0% for total phosphorus, 95.7% for turbidity, 59.1% for total phenols, 94.3% for nitrates, 71.0% for nitrites, 51.0% for total solids (TS) and 97.2% for oils and fats. The treatment did not produce an effluent supernatant with adequate quality for direct discharge into water courses, serving however as an efficient pretreatment for agricultural reuse. All the sludges generated in these treatments showed good potential for agricultural valorization due to their high nutrient content, along with pH and conductivity values within the acceptable ranges for soil application. Thus, this work contributes for a better integration of the cheese manufacturing industry in the overall aims of water and nutrient resources recovery in rural, agricultural areas.

Treatment of slaughterhouse wastewater by acid precipitation (H2SO4, HCl and HNO3) and oxidation (Ca(ClO)₂, H2O2 and CaO₂)

The treatment of slaughterhouse wastewater was investigated by both acid precipitations and by oxidation processes. Precipitation tests were developed using three acids (H₂SO₄, HCl and HNO₃) at different operating pH (1-6). A decrease of the precipitation pH led to an increase of the conductivity values of the supernatant. Precipitation processes allowed the removal of chemical oxygen demand (COD) (41-97%), turbidity (56-99%) and total phosphorus (27-56%). Total phenols were removed (15-96%) from pH ≥ 2, depending on the precipitation process. Generally, precipitation processes decreased the hydroxide and bicarbonates species. Additionally, three different oxidation processes were tested at different concentrations (1-15 g L^-1): Ca(ClO)₂, H₂O₂ and CaO₂. When Ca(ClO)₂ and CaO₂ were applied, an increase of the supernatant conductivity was achieved. COD removal ≥71% and turbidity elimination in the range of 85-100% were achieved by using oxidation processes. CaO₂ was very effective to remove total phosphorus (81-96%). The increase of the oxidant concentration in H₂O₂ and Ca(ClO)₂ oxidation processes led to a decrease in the removal of total phenols and bicarbonates species. Optical density of the microorganism cultures was efficiently eliminated (up to 100%) by oxidation processes. In addition, acid precipitation and oxidation allowed to remove total solids (TS), total volatile solids (TVS), total suspended solids (TSS), ammonia nitrogen, nitrates and biochemical oxygen demand (BOD₅). Acid precipitation and oxidation produced sludge rich in organic matter and nutrients (Ca, Mg, P, Cl, Na and K). Despite the high removal efficiencies, a post-treatment following the precipitation and oxidation processes can be required.

Sewage sludge disintegration by electrocoagulation

In this research, reduction of sludge production and improvement of sludge stabilization degree were aimed, and in this regard, the samples received from an urban wastewater treatment plant were subjected to electrocoagulation (EC) as a disintegration technique. A monopolar EC reactor was designed and iron electrode was used for sludge disintegration. The effect of reaction time, pH and varying current densities on disintegration degree (DD) was determined, and the optimum conditions were found as pH 7, 30 min (reaction time), and 150 A/m² (current density). DD was found as 84.23%, and soluble chemical oxygen demand was found as 675.2 mg/L under optimum conditions. In this research, the disintegration stage of sludge was defined with the best second-order kinetic model. The operating cost was estimated as 0.078 €/m³ for optimum conditions. Also, the EC-induced disintegration ability of sludge was determined using total suspended solids, total organic carbon, capillary suction time, particle size distribution, specific surface area and viscosity. The findings showed that EC technique can be an effective means for sludge disintegration.

Hydrogen production from municipal wastewaters via electrohydrolysis process

Nowadays, studies investigating alternative treatment processes for domestic wastewater have gained momentum. Rather than using conventional treatment plants which require energy and high amount of chemicals in order to treat the wastewaters, it is a viable option to use effective methods and to get clean energy in the form of hydrogen with alternative methods. Therefore, the aim of this study is to investigate the effect of electrohydrolysis process on domestic wastewater treatability at different DC voltages (4, 6, 8 and 10 V). Maximum hydrogen production was obtained from 8 V DC for 4 h reaction time. Under optimum conditions (8 V DC and 4 h operation time), 82% turbidity, 75% color, 86% TSS, 84% COD, 82% sCOD, 75% BOD, 38% oil and 40% total coliform removal efficiencies were achieved, respectively. It is a huge advantage to use this method which meets effluent discharge standards in such a short time without biological sludge production requiring additional operating cost. It has been shown that with the electrohydrolysis method, sustainable clean energy production and simultaneous pollution reduction can be achieved for domestic wastewater.

Efficiency analysis of the electrocoagulation and electroflotation treatment of poultry slaughterhouse wastewater using aluminum and graphite anodes

The application of electrocoagulation (EC) and electroflotation (EF) was investigated for the treatment of poultry slaughterhouse wastewater in a bench scale unit cell electrolyzer with different EC-to-EF ratios at current densities of 3, 9, and 15 mA cm^-2. The EC-to-EF ratio was controlled by current reversal using aluminum and graphite electrodes. The electrochemical treatment showed satisfactory removal efficiencies for Al coagulant loads greater than 51.8 mg L^-1. The 4/5 EC to EF ratio (69.1 mg L^-1 Al and 32.2 NmL L^-1 additional EF gas) and 3/5 (51.8 mg L^-1 Al/64 NmL L^-1 additional EF gas) presented the best results for the removal of COD (76-85%), color (93-99%), and turbidity (95-99%), with the additional benefit of reducing the electrode consumption and sludge disposal costs proportionally to the EC-to-EF ratio. The effects of the EC-to-EF ratio and the current density on efficiency of the electrochemical treatment for the removal of COD, apparent color, turbidity, TSS, TSD, and NH₃-N were discussed in the light of the physicochemical and electrochemical processes underlying the removal mechanism for each parameter. In particular, the blow-off mechanism seems to play an important role in the NH₃-N removal, whereas indirect electrooxidation mechanism accounts for a fraction of the soluble COD removal for the electrodes configuration used in the treatment.

Optimization of the pretreatment of wastewater from a slaughterhouse and packing plant through electrocoagulation in a batch reactor

The purpose of this study is to evaluate the removal of chemical oxygen demand (COD), turbidity and color of wastewater from a pig slaughterhouse and packing plant through the electrochemical technique and to optimize the ΔV (electric potential difference) and HRT (hydraulic retention time) variables in an electrocoagulation batch reactor using aluminum electrodes. The experimental design used was rotatable central composite design. For turbidity, the values for removal efficiency obtained varied from 92.85% to 99.28%; for color, they varied from 81.34% to 98.93% and for COD, they varied from 58.61% to 81.01%. The best optimized conditions of treatment were at 25 min for the HRT and 25 V for the ΔV, which correspond to electrical current of 1.08 A and a current density of 21.6 mA cm^-2. The aluminum residue varied from 15.254 to 54.291 mg L^-1 and the cost of the treatment was US$4.288 m^-3. The novelty of the work was the simultaneous optimization of three response variables using the desirability function applied to the treatment of wastewater from slaughterhouses.

Arsenic removal by electrocoagulation process: Recent trends and removal mechanism

Arsenic contamination in drinking water is a major issue in the present world. Arsenicosis is the disease caused by the regular consumption of arsenic contaminated water, even at a lesser contaminated level. The number of arsenicosis patients is increasing day-by-day. Decontamination of arsenic from the water medium is the only one way to regulate this and the arsenic removal can be fulfilled by water treatment methods based on separation techniques. Electrocoagulation (EC) process is a promising technology for the effective removal of arsenic from aqueous solution. The present review article analyzes the performance of the EC process for arsenic removal. Electrocoagulation using various sacrificial metal anodes such as aluminium, iron, magnesium, etc. is found to be very effective for arsenic decontamination. The performances of each anode are described in detail. A special focus has been made on the mechanism behind the arsenite and arsenate removal by EC process. Main trends in the disposal methods of sludge containing arsenic are also included. Comparison of arsenic decontamination efficiencies of chemical coagulation and EC is also reported.

Sono assisted electrocoagulation process for the removal of pollutant from pulp and paper industry effluent

In the present work, the efficiency of the sonication, electrocoagulation, and sono-electrocoagulation process for removal of pollutants from the industrial effluent of the pulp and paper industry was compared. The experimental results showed that the sono-electrocoagulation process yielded higher pollutant removal percentage compared to the sonication and electrocoagulation process alone. The effect of the operating parameters in the sono-electrocoagulation process such as electrolyte concentration (1-5 g/L), current density (1-5 A/dm²), effluent pH (3-11), COD concentration (1500-6000 mg/L), inter-electrode distance (1-3 cm), and electrode combination (Fe and Al) on the color removal, COD removal, and power consumption were studied. The maximum color and COD removal percentages of 100 and 95 %, respectively, were obtained at the current density of 4 A/dm², electrolyte concentration of 4 g/L, effluent pH of 7, COD concentration of 3000 mg/L, electrode combination of Fe/Fe, inter-electrode distance of 1 cm, and reaction time of 4 h, respectively. The color and COD removal percentages were analyzed by using an UV/Vis spectrophotometer and closed reflux method. The results showed that the sono-electrocoagulation process could be used as an efficient and environmental friendly technique for complete pollutant removal.

Emerging usage of electrocoagulation technology for oil removal from wastewater: A review

Electrocoagulation is a simple and efficient treatment method involving the electrodissolution of sacrificial anodes and formation of hydroxo-metal products as coagulants, while the simultaneous production of hydrogen at the cathode facilitates the pollutant removal by flotation. Oil is one of the most important hydrocarbon products in the modern world. It can cause environmental pollution during various stages of production, transportation, refining and use. Electrocoagulation treatment is particularly effective for destabilization of oil-in-water emulsions by neutralizing charges and bonding oil pollutants to generated flocs and hydrogen bubbles. The development of electrocoagulation technologies provided a promising alternative for oil removal from wastewater. This paper presents a review of emerging electrochemical technologies used for treating oil-containing wastewater. It includes a brief description of the oily wastewater origin and characteristics. The treatment processes developed so far for oily wastewater and the electrocoagulation mechanisms are also introduced. This paper summarizes the current applications of electrocoagulation for oil removal from wastewater. The factors that influence the electrocoagulation treatment efficiencies as well as the process optimization and modeling studies are discussed. The state-of-the-art and development trends of electrocoagulation process for oil removal are further introduced.

Electrocoagulation for the treatment of textile industry effluent--a review

Various techniques such as physical, chemical, biological, advanced oxidation and electrochemical are used for the treatment of industrial effluent. The commonly used conventional biological treatment processes are time consuming, need large operational area and are not effective for effluent containing toxic elements. Advanced oxidation techniques result in high treatment cost and are generally used to obtain high purity grade water. The chemical coagulation technique is slow and generates large amount of sludge. Electrocoagulation has recently attracted attention as a potential technique for treating industrial effluent due to its versatility and environmental compatibility. This technique uses direct current source between metal electrodes immersed in the effluent, which causes the dissolution of electrode plates into the effluent. The metal ions, at an appropriate pH, can form wide range of coagulated species and metal hydroxides that destabilize and aggregate particles or precipitate and adsorb the dissolved contaminants. Therefore, the objective of the present manuscript is to review the potential of electrocoagulation for the treatment of industrial effluents, mainly removal of dyes from textile effluent.

Modification of activated sludge properties caused by application of continuous and intermittent current

This study investigated the impact of direct current (DC) field on the activated sludge properties for potential improvement of the biological as well as membrane treatment processes. Three mixed-liquor suspended solids (MLSS) concentrations (5,000, 10,000 and 15,000 mg/l) were subjected to current densities (CD) ranging from 5 to 50 A/m² at five electrical exposure modes (time-ON/time-OFF). The results showed that CD between 15 and 35 A/m² increased the filterability of the sludge more than 200 times when compared with the untreated reference sludge. The average removals of protein, polysaccharides and organic colloids from the sludge supernatant at this range of CD were 43%, 73% and 91%, respectively, while the average reduction of the specific resistance to filtration (SRF) was 4.8 times higher. The changes of sludge properties depended on the current density, electrical exposure mode and the MLSS concentration. At CD of 25 A/m² and MLSS below 10,000 mg/l, shorter time-OFF was needed in each electrical cycle, while more time-OFF was needed at higher MLSS concentrations. It was concluded that proper application of the DC field could improve biomass in terms of its dewaterability and the removal of SMP, which are highly correlated to membrane fouling in the submerged membrane electro-bioreactor (SMEBR).

Integration of kinetic modeling and desirability function approach for multi-objective optimization of UASB reactor treating poultry manure wastewater

An integrated multi-objective optimization approach within the framework of nonlinear regression-based kinetic modeling and desirability function was proposed to optimize an up-flow anaerobic sludge blanket (UASB) reactor treating poultry manure wastewater (PMW). Chen-Hashimoto and modified Stover-Kincannon models were applied to the UASB reactor for determination of bio-kinetic coefficients. A new empirical formulation of volumetric organic loading rate was derived for the first time for PMW to estimate the dimensionless kinetic parameter (K) in the Chen-Hashimoto model. Maximum substrate utilization rate constant and saturation constant were predicted as 11.83 g COD/L/day and 13.02 g COD/L/day, respectively, for the modified Stover-Kincannon model. Based on four process-related variables, three objective functions including a detailed bio-economic model were derived and optimized by using a LOQO/AMPL algorithm, with a maximum overall desirability of 0.896. The proposed optimization scheme demonstrated a useful tool for the UASB reactor to optimize several responses simultaneously.

Slaughterhouse wastewater treatment by combined chemical coagulation and electrocoagulation process

Slaughterhouse wastewater contains various and high amounts of organic matter (e.g., proteins, blood, fat and lard). In order to produce an effluent suitable for stream discharge, chemical coagulation and electrocoagulation techniques have been particularly explored at the laboratory pilot scale for organic compounds removal from slaughterhouse effluent. The purpose of this work was to investigate the feasibility of treating cattle-slaughterhouse wastewater by combined chemical coagulation and electrocoagulation process to achieve the required standards. The influence of the operating variables such as coagulant dose, electrical potential and reaction time on the removal efficiencies of major pollutants was determined. The rate of removal of pollutants linearly increased with increasing doses of PACl and applied voltage. COD and BOD₅ removal of more than 99% was obtained by adding 100 mg/L PACl and applied voltage 40 V. The experiments demonstrated the effectiveness of chemical and electrochemical techniques for the treatment of slaughterhouse wastewaters. Consequently, combined processes are inferred to be superior to electrocoagulation alone for the removal of both organic and inorganic compounds from cattle-slaughterhouse wastewater.

Optimization of energy costs in the pretreatment of olive mill wastewaters by electrocoagulation

In this study, the electrocoagulation process was evaluated as a pretreatment process for olive mill wastewaters. Aluminium (Al) and iron (Fe) electrodes, several contact times and 0.5, 1 and 2 A currents were used to compare chemical oxygen demand (COD) removal efficiencies for each case. The optimum contact time and current were 45 minutes and 1 A, respectively, which resulted in a COD removal of 58.7% with an Al electrode. Experimental data from distinct operational conditions were used to fit a model for COD removal efficiencies. Energy consumption was also predicted. Under optimum operational conditions, the treatment cost was approximately Euro 0.13 kg(-1) CODremoved and Euro 4.41 m(-3). The results showed that the electrocoagulation process was a cost-effective method for the pretreatment of olive mill wastewaters.

The efficiency of electrocoagulation in treating wastewater from a dairy industry, part I: iron electrodes

Iron electrodes were used for electrocoagulation (EC) treatment of wastewater from a dairy plant. Electrolysis time, pH, current density and distance between electrodes were considered to assess the removal efficiency of chemical oxygen demand (COD), total solids (TS) and their fractions and turbidity. Samples were collected from the effluent of a dairy plant using a sampling methodology proportional to the flow. The treatments were applied according to design factorial of half fraction with two levels of treatments and three repetitions at the central point. The optimization of parameters for treating dairy industry effluent by electrocoagulation using iron electrodes showed that electric current application for 15 minutes, an initial sample pH close to neutral (pH 7.0) and a current density of 50 A (.)(m-2) resulted in a significant reduction in COD by 58 %; removal of turbidity, suspended solids and volatile suspended solids by 95 %; and a final treated effluent pH of approximately 9.5. Negative consequences of the type of electrode used were the emergence of an undesirable color and an increase in the proportion of dissolved solids in the treated effluent.

Treatment of textile wastewater by a hybrid electrocoagulation/nanofiltration process

Untreated effluents from textile industries are usually highly coloured and contain a considerable amount of contaminants and pollutants. Stringent environmental regulation for the control of textile effluents is enforced in several countries. Previous studies showed that many techniques have been used for the treatment of textile wastewater, such as adsorption, biological treatment, oxidation, coagulation and/or flocculation, among them coagulation is one of the most commonly used techniques. Electrocoagulation is a process consisting in creating metallic hydroxide flocks within the wastewater by the electrodissolution of soluble anodes, usually made of iron or aluminium. This method has been practiced for most of the 20th century with limited success. In recent years, however, it started to regain importance with the progress of the electrochemical processes and the increase in environmental restrictions in effluent wastewater. This paper examines the use of electrocoagulation treatment process followed by nanofiltration process of a textile effluent sample. The electrocoagulation process was studied under several conditions such as various current densities and effect of experimental tense. Efficiencies of COD and turbidity reductions and colour removal were studied for each experiment. The electrochemical treatment was indented primarily to remove colour and COD of wastewater while nanofiltration was used to further improve the removal efficiency of the colour, COD, conductivity, alkalinity and total dissolved solids (TDS). The experimental results, throughout the present study, have indicated that electrocoagulation treatment followed by nanofiltration processes were very effective and were capable of elevating quality of the treated textile wastewater effluent.

Removal of Fe(II) from tap water by electrocoagulation technique

Electrocoagulation (EC) is a promising electrochemical technique for water treatment. In this work electrocoagulation (with aluminum as electrodes) was studied for iron Fe(II) removal from aqueous medium. Different concentration of Fe(II) solution in tap water was considered for the experiment. During EC process, various amorphous aluminum hydroxides complexes with high sorption capacity were formed. The removal of Fe(II) was consisted of two principal steps; (a) oxidation of Fe(II) to Fe(III) and (b) subsequent removal of Fe(III) by the freshly formed aluminum hydroxides complexes by adsorption/surface complexation followed by precipitation. Experiments were carried out with different current densities ranging from 0.01 to 0.04 A/m2. It was observed that the removal of Fe(II) increases with current densities. Inter electrode distance was varied from 0.005 to 0.02 m and was found that least inter electrode distance is suitable in order to achieve higher Fe(II) removal. Other parameters such as conductivity, pH and salt concentration were kept constant as per tap water quality. Satisfactory iron removal of around 99.2% was obtained at the end of 35 min of operation from the initial concentration of 25 mg/L Fe(II). Iron concentration in the solution was determined using Atomic absorption spectrophotometer. By products obtained from the electrocoagulation bath were analyzed by SEM image and corresponding elemental analysis (EDAX). Cost estimation for the electrocoagulation was adopted and explained well. Up to 15 mg/L of initial Fe(II) concentration, the optimum total cost was 6.05 US$/m3. The EC process for removing Fe(II) from tap water is expected to be adaptable for household use.

Treatment of leachate by electrocoagulation using aluminum and iron electrodes

In this paper, treatment of leachate by electrocoagulation (EC) has been investigated in a batch process. The sample of leachate was supplied from Odayeri Landfill Site in Istanbul. Firstly, EC was compared with classical chemical coagulation (CC) process via COD removal. The first comparison results with 348 A/m2 current density showed that EC process has higher treatment performance than CC process. Secondly, effects of process variables such as electrode material, current density (from 348 to 631 A/m2), pH, treatment cost, and operating time for EC process are investigated on COD and NH4-N removal efficiencies. The appropriate electrode type search for EC provided that aluminum supplies more COD removal (56%) than iron electrode (35%) at the end of the 30 min operating time. Finally, EC experiments were also continued to determine the efficiency of ammonia removal, and the effects of current density, mixing, and aeration. All the findings of the study revealed that treatment of leachate by EC can be used as a step of a joint treatment.

Treatment of the baker's yeast wastewater by electrocoagulation

In the laboratory-scale experiments, treatment of baker's yeast production wastewater has been investigated by electrocoagulation (EC) using a batch reactor. Effects of the process variables such as pH, electrode material (Fe and Al), current density, and operating time are investigated in terms of removal efficiencies of chemical oxygen demand (COD), total organic carbon (TOC), turbidity, and operating cost, respectively. The maximum removal efficiencies of COD, TOC and turbidity under optimal operating conditions, i.e., pH 6.5 for Al electrode and pH 7 for Fe electrode, current density of 70 A/m2 and operating time of 50 min were 71, 53 and 90% for Al electrode and 69, 52 and 56% for Fe electrode, respectively. Al electrode gave 4.4 times higher removal efficiency of turbidity than Fe electrode due to interference from color of dissolved iron. The operating costs for Al and Fe electrodes in terms of $/m3 or $/kg COD were 1.54 and 0.82, 0.51 and 0.27, respectively.

Techno-economical evaluation of electrocoagulation for the textile wastewater using different electrode connections

The bench scale of an electrocoagulation (EC) unit requires a detailed study discerning the effects of continuous variables such as pH, current density and operating time, and type variables such as electrode material and connection mode. This paper presents the results of the treatment of a textile wastewater by EC process. Two electrode materials, aluminum and iron, were connected in three modes namely, monopolar-parallel (MP-P), monopolar-serial (MP-S), and bipolar-serial (BP-S). COD and turbidity removals were selected as performance criteria. For a high COD removal, acidic medium is preferable for both electrode materials. For a high turbidity removal, acidic medium is preferable for aluminum, and neutral medium for iron. High current density is favorable for both removals in the case of iron. In the aluminum case, the current density exhibits a pronounced effect on COD removal, depending strongly on the connection mode, but it has a negligible effect on the turbidity removal. MP-P with iron or MP-S with aluminum electrode are suitable configurations in regard with the overall process performance. Moreover, process economy is as important as removal efficiencies during the process evaluation task. Various direct and indirect cost items including electrical, sacrificial electrodes, labor, sludge handling, maintenance and depreciation costs have been considered in the calculation of the total cost. The results show that MP-P mode is the most cost-effective for both electrode types. Both electrodes show similar results in reducing COD and turbidity, but iron is preferred as a low cost material. Finally, a comparative study showed that EC was faster and more economic; consumed less material and produced less sludge, and pH of the medium was more stabilized than chemical coagulation (CC) for similar COD and turbidity removal levels. For CC, FeCl(3) was the preferable salt in view of its techno-economic performance. On the other hand, iron was the preferred electrode material in EC with MP-P system in experimental conditions such as, 30 Am(-2) of current density and 15 min of time, the treatment cost was $ 0.245 m(-3). Consequently, the operating cost of CC was 3.2 times as high as the operating cost of EC.