Applicability of electrochemical methods to carwash wastewaters for reuse. Part 2: Electrocoagulation and anodic oxidation integrated process

Efficient treatment of old landfill leachate by peroxodisulfate assisted electro-oxidation and electro-coagulation combined system

Efficient removal of chemical oxygen demand (COD) and ammonium-N (NH4+-N) is the key issue for treatment of old landfill leachate. In this study, a peroxodisulfate assisted electro-oxidation and electro-coagulation coupled system (POCS) adopting Ti/SnO2-Sb2O3/TiO2 and Fe dual-anode was constructed for synergistic removal of COD and NH4+-N in old landfill leachate. Laboratory experiment results showed that with current density of 20 mA cm-2, initial pH value of 8.0 and peroxodisulfate (PDS) concentration of 60 mM, the POCS system can reach removal efficiencies of 84.2% for COD and 39.8% for NH4+-N. The POCS effectively reduced the complexity of macromolecular organics and avoided the need to add acid or base to adjust pH value. The residual NH4+-N could be effectively recovered through struvite precipitation with a 93.8% purity of the precipitate.

Techno-environmental study on the consequences of carwash wastewater and its management methods

Carwash wastewater (CWW) is an important source of environmental pollution. The aim of this study was to investigate the characteristics of CWW and technical comparison of its treatment methods. For this purpose, a systematic search was conducted and after three stages of screening the found articles, finally 30 articles were selected for this review. The results showed that due to the differences in the type of washing, the geological condition, the type of car, and the climatic conditions, the CWWs have temporal and spatial variation in the concentration of pollutants. However, the most important pollutants of CWW include oil, suspended solids, detergents, and organic compounds. The most widely used methods in CWW treatment in the main stages included chemical coagulation and electrocoagulation, which reduce turbidity by more than 90% and COD by more than 50% in the best efficiency. Also, membrane technology was a common method in CWW treatment systems to achieve proper effluent quality. COD reduction by ultrafiltration, nanofiltration, microfiltration, and reverse osmosis was 95-77%, more than 90%, 81-73%, and 87%, respectively. The efficiency of membrane technologies in reducing turbidity was often more than 90% and in few cases more than 50%. Sludge production in the coagulation process, energy consumption in electrochemical processes, and the low water recovery rate in membrane processes are important challenges in CWW treatment that must be managed by modifying the process or using combined methods.

Hybrid of sodium polytungstate polyoxometalate supported by the green substrate for photocatalytic degradation of auramine-O dye

Nowadays, textile industries have severely polluted the ecosystem and water sources via disposal of highly thermo- and photo-stable dyes within the ecology that require practical strategies to remove them from nature. In studies, the photocatalytic disinfection technique has been shown to have widespread applications in indoor air, environmental health, detection, biological, biomedical, laboratory hospital, pharmaceutical food industry, plant safety, waste water, effluents disposal, and drinking water disinfection. Herein, the sodium polytungstate (SPT) polyoxometalate (POM) was synthesized through a multi-step production procedure and hence modified via employing a green protocol by using tartaric acid, glutamic acid, and kombucha solvent toward efficient and total complete removal of the highly toxic, stable, and carcinogenic auramine-O (AO) dye from aqueous media. In this regard, developed materials were well-characterized, and their photocatalysis performance for photodegradation of AO dye was examined. Achieved results showed that the optimum absorption conditions were achieved at pH of 5.0, 15 mg/L of AO concentration, 0.04 g of photocatalyst dosage, and 110 min irradiation time, where SPT and modified SPT via green protocol showed full desirability (desirability function (DF) index of 1) along with 71.75 and 100% removal percentage, respectively. Obtained results justified the superior photocatalytic role of the SPT POM and its derived nanocluster that can be used for the complete removal of highly stable dyes from aqueous media till reaching the drinking water standard.

Artificial neural network (ANN) and response surface methodology (RSM) algorithm-based improvement, kinetics and isotherm studies of electrocoagulation of oily wastewater

The work reported here focuses on the oil and grease removal from wastewater by the electrocoagulation process and using modeling and optimization for obtaining the results considering four major operating parameters, viz. current density, pH, electrode distance and reaction time. 31 experiments were designed by design of experiments (DOE) of response surface methodology (RSM) and the analysis of variance (ANOVA) studies confirmed the agreement of the experimental results. Artificial neural network (ANN) was also utilized to determine predicted response using neural networks for 4-10-1 arrangement. Both the responses predicted by RSM and ANN were in alignment with the experimental results. Maximum removal of 78% was attained under the working parameters of 80 A m^-2, 3.6 pH, electrode distance of 0.005 m and reaction time of 20 min.

A Review of On-Site Carwash Wastewater Treatment

In recent years, people’s environmental awareness has increased. The high density of the urban population has caused a considerable increase in the demand for car washing services, which has created large quantities of car wash wastewater. The main pollutants in car wash wastewater are detergents, dirt, oil, and grease. Untreated wastewater released into rainwater sewer systems or other water bodies may pollute the water and generate excessive bubble foams, which negatively affects urban appearance. Car washes are divided into mechanical car washes and manual or self-service car washes. In general, car washes have a small operation and scale, occupy limited land, and cannot afford wastewater treatment costs. Therefore, most car washes are not equipped with wastewater treatment facilities. Consequently, the discharge of wastewater from car washes negatively affects the water quality in the surrounding environment and results in wasteful use of water resources. This study reviewed 68 research papers on the quality, treatment techniques, treatment costs, and treatment effectiveness of car wash wastewater to provide a reference for car wash operators to contribute to the preservation of water resources. We found that there is a higher chance of recycling car wash wastewater when combing two different techniques for car wash wastewater treatment.

A Study of Car Wash Wastewater Treatment by Cyclo-Flow Filtration

With the increase in transportation demand and facilities in this era and the significant improvement in people’s living standards, the annual production and sales of vehicles are steadily increasing. With this, the issues of car wash wastewater treatment and water pollution are becoming more and more serious. Car wash wastewater mainly comprises fine sand, slick oil, suspended solids (SS), and surfactants, and can be quantified as chemical oxygen demand (COD) on a normative basis. This study examines the use of cyclo-flow filtration with high filtrate flux to treat car wash wastewater to solve issue of limited space in metropolitan areas and increase the willingness of the industry to invest in car wash equipment to recover water resources. The average removal rates of SS and COD are about 81% and 43%, respectively. Compared with current technology, the price of recycled water can compensate for operating costs, requiring minimal operating space owing to the single-unit cyclo-flow filtration system.

Waste tea residue adsorption coupled with electrocoagulation for improvement of copper and nickel ions removal from simulated wastewater

The present research involves removing copper and nickel ions from synthesized wastewater by using a simple, cheap, cost-effective, and sustainable activated green waste tea residue (AGWTR) adsorption coupled with electrocoagulation (ADS/EC) process in the presence of iron electrodes. By considering previous studies, their adsorbents used for treating their wastewaters firstly activate them by applying either chemicals or activating agents. However, our adsorbent was prepared without applying neither chemicals nor any activating agents. The operating parameters such as pH, hydraulic retention time, adsorbent dose, initial concentration, current density, and operating cost for both metals were optimized. In ADS/EC, the removal efficiency was obtained as 100% for copper and 99.99% for nickel ions. After the ADS/EC process, Fourier transform infrared (FT-IR) spectroscopy, Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS) analysis were used to characterize the adsorbent green waste tea residue. The adsorption isotherm and kinetic model results showed that the Langmuir and the pseudo-second-order were well-fitted to the experimental adsorption data better than the Freundlich and pseudo-first-order models for both Cu²⁺ and Ni²⁺ with their maximum adsorption capacity of 15.6 and 15.9 mg g⁻¹, respectively. The above results give an option to recycle the metal-based industrial effluents, tea industry-based wastes, enabling a waste-to-green technique for adsorbing and removing the heavy metals and other pollutants in water.

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.

Bioelectrochemical treatment of actual carwash wastewater associated with sustainable energy generation in three-dimensional microbial fuel cell

Carwash garages are worldwide cleaning facilities. Discharge of their untreated or improperly treated wastewaters highly contributes to the pollution of water resources. Sodium dodecyl sulfate (SDS), a widely used anionic surfactant in the carwash shampoos represents the major constituent of the carwash wastewater. In this study, a new configuration of three-dimensional MFC packed with irregular shaped graphite granules to support and join the plain anodes in the anodic section. The performance of the 3D-MFC was evaluated in two operational modes; continuous and batch. The evaluation was carried out mainly in terms of the removal efficiency of organic content, in particular SDS as well as oil and grease associated with bioenergy generation from actual carwash wastewater used to fuel the MFC. The results demonstrated that maximum removal efficiencies of COD, SDS, and oil and grease were 87%, 88%, and 90%, respectively. Also, the results demonstrated that during the continuous mode operation maximum current density and power output were 1786 mA/m³ and 482 mW/m³, respectively. At batch operation mode, the maximum current density and power output were 1793 mA/m³ and 478 mW/m³, respectively indicating that the performance of the 3D-MFC was comparable in both operation modes.

SARS-CoV-2: fate in water environments and sewage surveillance as an early warning system

The carwash is known as one of the most important urban services that brings about the production of huge volume of wastewater with high turbidity and high chemical oxygen demand (COD). Seasonal and carwash location features affect the quality of carwash wastewater. Various methods with special focus on chemical processes have been employed for carwash wastewater treatment and eliminating different pollutants from this wastewater of great concern for the environment. This review was conducted for identifying and comparing the efficiency of chemical processes for carwash wastewater treatment. To this aim, key words were identified and a search protocol was defined to search studies in three databases: Scopus, Web of Science, and PubMed. The results of this systematic review indicated that coagulation (66%) is the most common chemical processes for carwash wastewater treatment. Although chemical processes are able to reduce the turbidity and COD over 80%. Due to the characteristics of carwash wastewater, chemical processes are a necessary pretreatment for processes such as membrane technology. Rapid treatment and high efficiency are the advantages of wastewater treatment by chemical methods, but the energy consumption and sludge volume are two main factors in selection the chemical processes for carwash wastewater treatment.

Efficient technologies for carwash wastewater treatment: a systematic review

Carwash wastewater (CWW) is considered as an important source of either water pollution or water consumption. Therefore, its treatment is critical not only from the prevention of environmental contamination but also from the recycling of such high-volume water source. Unfortunately, the effective treatment of CWW is almost unknown, complex, and expensive. To overcome the former challenge, this study aimed to systematically review different technologies for CWW treatment. For this, a comprehensive literature survey was conducted and 48 research articles were found suitable to be included in the investigation. The included studies were of coagulation and adsorption (n = 5), membrane-based technologies (n = 15), and electrochemical (n = 11) and combined (n = 17) systems. This comprehensive review showed that the treatment methods of advanced filtration membrane techniques, electrical and chemical coagulation, and advanced oxidation processes can be effective in the removal of pollutants from carwash wastewater (CWW). The mining of different studies, however, showed that the combined methods are the most promising option in the remediation of such wastewater.

Study of the Effects of the Addition of Fly Ash from Carwash Sludge in Lime and Cement Pastes

Sludge from carwash wastewater treatment plants has been evaluated as substitute for lime paste, as well as its behavior in cement mortars. Dry sludge waste was used with (CSlud) and without (USlud) pretreatment and have been characterized. The pastes were prepared with weight replacement of 5, 10, 15, and 20% of sludge. The formation of calcium silicate hydrate was determined by TGA, both in lime and cement pastes. The compressive strength properties were evaluated in mortars. It was found the mixtures which present the best results were those of 5 and 10% for USlud, and 10 and 20% for CSlud.

Purification of real car wash wastewater with complex coagulation/flocculation methods using polyaluminum chloride, polyelectrolyte, clay mineral and cationic surfactant

In the present study, real car wash wastewater was purified by different coagulation/flocculation methods. As coagulant, polyaluminum chloride ('BOPAC'), conventional iron(III) chloride, iron(III) sulfate, and aluminum(III) chloride were used, while as flocculant non-ionic and anionic polyelectrolytes were investigated. The effects of added clay mineral (Na-bentonite) and cationic surfactant (hexadecyltrimethyl ammonium bromide - 'HTABr') were also investigated. The use of BOPAC was significantly more effective than conventional coagulants. Extra addition of clay mineral was also beneficial in relation to both the sediment volume and sedimentation speed, while polyelectrolyte addition enhanced further the sedimentation. Moreover, the simultaneous addition of HTABr significantly enhanced the color removal efficiency due to the successful in-situ generation of organophilic bentonite. In summary, the application of 100 mg L^-1 Na-bentonite with 20 mg L^-1 Al³⁺ (from BOPAC) and 0.5 mg L^-1 anionic polyelectrolyte resulted in the efficient reduction of the turbidity (4-6 NTU), the COD (158 mg L^-1) and the extractable oil content (4 mg L^-1) with efficiencies of 98%, 59%, and 85%, respectively. By applying organophilic bentonite in high concentration (500 mg L^-1) with identical concentrations of BOPAC and anionic polyelectrolyte, significant color removal (5 times lower absorbance at λ = 400 nm) and 27% lower sediment volume were achieved.

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.

Comparative study of electrochemical hybrid systems for the treatment of real wastewaters from agri-food activities

Agri-food wastewaters are characterized by high contents of hardly biodegradable organics and large amounts of inorganics especially nitrogen and phosphorus. The present work investigates the efficiency of two electrochemical treatment processes, namely electrochemical oxidation/reduction (EOR), electrocoagulation (EC) and their combination for the treatment of two types of effluents collected from poultry slaughterhouse (SHWW) and dairy (DWW) industries. The optimization of these treatment systems in terms of pollutant performance removal and energy cost were carried out. The EOR treatment was assessed on a bipolar cell with Boron-Doped Diamond (BDD) supported on silicon electrodes. While, the EC treatment was performed on a reactor containing mild steel electrodes with parallel configuration. The simultaneous removal efficiencies of the organic matter in term of the chemical oxygen demand (COD), nitrates, ammonium/ammonia and phosphates, as well as the electric energy consumption (EEC), were evaluated for the different electrochemical scenarios. Results indicated that the EOR treatment shows the highest removal efficiencies of COD, nitrates and ammonia from the two studied wastewaters. While, the phosphates were removed only by the EC process. On the other hand, the EC process shows a relatively low cost in term of EEC (0.01 kWh/g COD^-1), which is about 13 times lower than the one consumed during the EOR process. The combination of the two processes leads to the improvement of the removal rate of all coexistent pollutants when the EC technology was used as a pre-treatment step. While, this coupling mode has the highest EEC. However, when the EOR process was used before the EC one, the removal rates of COD and nitrates were globally similar to the EOR process alone with a relatively low EEC.

Electrochemical advanced oxidation processes (EAOPs) as alternative treatment techniques for carwash wastewater reclamation

Electrochemical advanced oxidation processes such as electrooxidation (EO), electrooxidation with hydrogen peroxide generation (EO-H₂O₂) and electro-Fenton process (EF) have been investigated as alternative treatment techniques for complete removal of anionic surfactants and organic matters from real carwash wastewater. The electrochemical processes were performed with acidified real carwash wastewater using boron doped anode and carbon felt cathode. In all cases, the chemical oxygen demand (COD) removal efficiency was always increased with rise in applied current and complete organic matter decay was achieved at applied current of 500 mA or above after 6 h of electrolysis. Faster and higher COD decay was observed with EF compared to either EO or EO-H₂O₂ treatment, at all currents and electrolysis time. Besides, complete degradation of anionic surfactants - the major organic content of the wastewater could be achieved at all applied currents studied irrespective of the process used, indicating the efficacy of processes for total remediation of real carwash wastewater. The short-chain carboxylic acids formed as the final organic byproducts were identified and quantified by ion-exclusion chromatography. More so, lower energy consumption and higher current efficiency were achieved with EF compared to EO-H₂O₂. Electrochemical treatment was found to be a powerful technology for the complete abatement of organic matter in carwash wastewater for possible reuse.

Tertiary treatment of landfill leachate by an integrated Electro-Oxidation/Electro-Coagulation/Electro-Reduction process: Performance and mechanism

This study presents an integrated Electro-Oxidation/Electro-Coagulation/Electro-Reduction (EO/EC/ER) process for tertiary landfill leachate treatment. The influence of variables including leachate characteristics and operation conditions on the performance of EO/EC/ER process was evaluated. The removal mechanisms were explored by comparing results of anode, cathode, and bipolar electrode substitution experiments. The performance of the process in a scaled-up reactor was investigated to assure the feasibility of the process. Results showed that simultaneous removal of carbonaceous and nitrogenous pollutants was achieved under optimal conditions. Ammonia removal was due to the free chlorine generation of EO while organic matter degradation was achieved by both EO and EC processes. Nitrate removal was attributed to both ER and EC processes, with the higher removal achieved by ER process. In a scaled-up reactor, the EO/EC/ER process was able to remove 50-60% organic matter and 100% ammonia at charge of 1.5 Ah/L with energy consumption of 15 kW h/m³. Considering energy cost, the process is more efficient to meet the requirement of organic removal efficiency less than 70%. These results show the feasibility and potential of the EO/EC/ER process as an alternative tertiary treatment to achieve the simultaneous removal of organic matter, ammonia, nitrate, and color of leachate.

Performance of ceramic ultrafiltration and reverse osmosis membranes in treating car wash wastewater for reuse

Reusing treated effluents in industries is a great option to conserve freshwater resources. For example, car wash centres all over Australia are estimated to use 17.5 billion litres of water and discharge it as wastewater and spend $75 million a year for both purchasing fresh water and for treating and/or discharging the wastewater. Therefore, it is important to develop simple but reliable systems that can help to treat and reuse car wash wastewater. Significant savings could also be associated with the implementation of such systems. This study evaluates the performance of granular and membrane filtration systems with coagulation/flocculation and sedimentation in treating car wash wastewater for the purpose of reuse. Overall, 99.9% of turbidity, 100% of suspended solids and 96% of COD were removed from the car wash wastewater after treating by coagulation, flocculation, sedimentation, sand filtration, ceramic ultrafiltration and reverse osmosis and the treated water meets the standards required for class A recycled water in Australia and standards imposed in Belgium and China. The treated water can be reused. However, optimisation is required to reduce the sludge produced by this system.

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

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

Electrochemical treatment of carwash wastewater using Fe and Al electrode: Techno-economic analysis and sludge characterization

The present study was conducted to investigate the electrochemical treatment of carwash wastewater using electrocoagulation (EC) process with Fe and Al electrodes. The effects of operating conditions such as initial pH (2-10), current density (0.1-5 mA/cm²) and operating time (5-50 min) on chemical oxygen demand (COD), oil-grease, chloride removal efficiencies as well as total operating costs were studied. The optimum conditions that achieve higher removal efficiencies were found as pH: 8, current density: 3 mA/cm², operating time: 30 min for Fe electrode and pH: 6, current density: 1 mA/cm², operating time: 30 min for Al electrode. The removal efficiencies for COD, oil-grease and chloride were obtained as 88%, 90% and 50% for Fe and 88%, 68% and 33% for Al electrodes under the optimum conditions. The total operating costs at the optimum conditions were calculated as 0.6 $/m³ and 0.3 $/m³ for Fe and Al electrodes, respectively. The sludge samples generated after EC process were characterized with Fourier transform infrared (FTIR) spectroscopy and zeta potential measurements for both electrodes. The analyses showed the presence of hydroxides and oxyhydroxides in the sludge samples and the surface of the sludge samples was negatively charged in the wide range of pH. As a conclusion, this study revealed that EC process using Fe electrode should be a feasible technology for higher COD and oil-grease removals from carwash wastewaters.

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: Simply a Phase Separation Technology? The Case of Bronopol Compared to Its Treatment by EAOPs

Electrocoagulation (EC) has long been considered a phase separation process, well suited for industrial wastewater treatment since it causes a quick, drastic decay of organic matter content. This research demonstrates that EC also behaves, at least for some molecules like the industrial preservative bronopol, as an effective transformation technology able to yield several breakdown products. This finding has relevant environmental implications, pointing to EC as a greener process than described in literature. A thorough optimization of EC was performed with solutions of bronopol in a simulated water matrix, yielding the complete disappearance of the parent molecule within 20 min at 200 mA (∼20 mA/cm(2)), using Fe as the anode and cathode. A 25% of total organic carbon (TOC) abatement was attained as maximum, with bronopol being converted into bromonitromethane, bromochloromethane, formaldehyde and formic acid. N atoms were accumulated as NO3(-), whereas Br(-) was stable once released. This suggests that mediated oxidation by active chlorine, as well as by hydroxyl radicals resulting from its reaction with iron ions, is the main transformation mechanism. Aiming to enhance the mineralization, a sequential combination of EC with electro-Fenton (EF) as post-treatment process was proposed. EF with boron-doped diamond (BDD) anode ensured the gradual TOC removal under the action of (•)OH and BDD((•)OH), also transforming Br(-) into BrO3(-).

Influence of bentonite in polymer membranes for effective treatment of car wash effluent to protect the ecosystem

In this study, modified polyethersulfone (PES) and cellulose acetate (CA) membranes were used in the treatment of car wash effluent using ultrafiltration. Hydrophilic sulfonated poly ether ether ketone (SPEEK) and bentonite as nanoclay were used as additives for the PES and CA membrane modification. Performances of modified membranes were compared with commercial PES membrane with 10kDa molecular weight cut off (MWCO). The influencing parameters like stirrer speed (250-750rpm) and transmembrane pressure (100-600kPa) (TMP) were varied and their effects were studied as a function of flux. In the treatment of car wash effluent, a higher permeate flux of 52.3L/m(2)h was obtained for modified CA membrane at TMP of 400kPa and stirrer speed of 750rpm. In comparison with modified PES membrane and commercial PES membrane, modified CA membranes showed better performance in terms of flux and flux recovery ratio. The highest COD removal (60%) was obtained for modified CA membrane and a lowest COD removal (47%) was observed for commercial PES membrane. The modified membranes were better at removing COD, turbidity and maintained more stable flux than commercial PES membrane, suggesting they will provide better economic performance in car wash effluent reclamation.

Treatment of real wastewater produced from Mobil car wash station using electrocoagulation technique

This paper deals with the electrocoagulation of real wastewater produced from a car wash station using a new cell design featuring a horizontal spiral anode placed above a horizontal disc cathode. The study dealt with the chemical oxygen demand (COD) reduction and turbidity removal using electrodes in a batch mode. Various operating parameters such as current density, initial pH, NaCl concentration, temperature, and electrode material were examined to optimize the performance of the process. Also, characterization of sludge formed during electrocoagulation was carried out. The results indicated that the COD reduction and turbidity removal increase with increasing the current density and NaCl concentration; pH from 7 to 8 was found to be optimum for treating the wastewater. Temperature was found to have an insignificant effect on the process. Aluminum was superior to iron as a sacrificial electrode material in treating car wash wastewater. Energy consumption based on COD reduction ranged from 2.32 to 15.1 kWh/kg COD removed depending on the operating conditions. Finally, the sludge produced during electrocoagulation using aluminum electrodes was characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analysis.

Performance of a wall cascade constructed wetland treating surfactant-polluted water

Carwashes are highly water-consuming processes that require wastewater treatment before discharge into a sewer system due to the complex composition of leachate. Anionic surfactants (AS) are the main constituents of this wastewater because of their cleaning and solubilization properties; they can be potentially dangerous for the environment if not adequately treated. Constructed wetlands (CWs) are low-cost systems increasingly used to treat different types of wastewater; however, there are few studies on their use for the treatment of carwash wastewater. In this study, an innovative constructed wetland arranged in a "cascade" to simulate a wall system (WCCW) was experimented in 2010 and 2011 to treat AS. Three plant species were tested at different AS inlet concentrations (10, 50, and 100 mg L(-1)) with two hydraulic retention times (HRTs; 3 and 6 days): ribbon grass (Typhoides arundinacea (L.) Moench (syn. Phalaris arundinacea L.) var. picta; Ta), water mint (Mentha aquatica L.; Ma), and divided sedge (Carex divisa Hudson; Cd). All plant species grew constantly over the experimental period, showing a capacity to tolerate even the highest AS concentration. Using the HRT of 6 days, raising the inlet concentration increased the AS outlet concentration, with similar values for the treatments (median values of 0.13-0.15, 0.47-0.78, and 1.19-1.46 mg L(-1) at inlet concentrations in the order 10, 50, and 100 mg L(-1)). The shorter HRT led to significant differences among treatments in the reduction of outlet concentration, the best result being given by the tanks vegetated with Ma (A = 97.7 % with outlet concentration 0.35 mg L(-1)). After treatments of the WCCW, the AS content was reduced almost completely, with removal in the ranges 0.07-10.2 g m(-2) day(-1) for tanks planted with Ta, 0.10-9.1 g m(-2) day(-1) for Ma tanks, and 0.11-9.5 g m(-2) day(-1) for Cd tanks depending on the inlet concentration.

Treatment of papermaking tobacco sheet wastewater by electrocoagulation combined with electrochemical oxidation

Attempts were made in this study to examine the efficiency of electrocoagulation (EC) using aluminum (Al) anode and stainless steel net cathode combined with electrochemical oxidation with a β-PbO₂anode or a mixed metal oxide (MMO) anode for treatment of papermaking tobacco sheet wastewater, which has the characteristics of high content of suspended solids (SS), intensive color, and low biodegradability. The wastewater was first subjected to the EC process under 40 mA/cm² of current density, 2.5 g/L of NaCl, and maintaining the original pH of wastewater. After 6 minutes of EC process, the effluent was further treated by electrochemical oxidation. The results revealed that the removal of SS during the EC process was very beneficial to mass transfer of organics during electrochemical oxidation. After the combined process, 83.9% and 82.8% of chemical oxygen demand (COD) removal could be achieved on the β-PbO₂and MMO anodes, respectively. The main components of the final effluent were biodegradable organic acids, such as acetic acid, propionic acid, butyric acid, valeric acid, and hexahyl carbonic acid; the 5-day biochemical oxygen demand/chemical oxygen demand (BOD₅/COD) ratio increased from 0.06 to 0.85 (Al + β-PbO₂) or 0.80 (Al + MMO). Therefore, this integrated process is a promising alternative for pretreatment of papermaking tobacco sheet wastewater prior to biological treatment.

Application of electrochemical technology for removing petroleum hydrocarbons from produced water using lead dioxide and boron-doped diamond electrodes

Although diverse methods exist for treating polluted water, the most promising and innovating technology is the electrochemical remediation process. This paper presents the anodic oxidation of real produced water (PW), generated by the petroleum exploration of the Petrobras plant-Tunisia. Experiments were conducted at different current densities (30, 50 and 100 mA cm(-2)) using the lead dioxide supported on tantalum (Ta/PbO2) and boron-doped diamond (BDD) anodes in an electrolytic batch cell. The electrolytic process was monitored by the chemical oxygen demand (COD) and the residual total petroleum hydrocarbon [TPH] in order to know the feasibility of electrochemical treatment. The characterization and quantification of petroleum wastewater components were performed by gas chromatography mass spectrometry. The COD removal was approximately 85% and 96% using PbO2 and BDD reached after 11 and 7h, respectively. Compared with PbO2, the BDD anode showed a better performance to remove petroleum hydrocarbons compounds from produced water. It provided a higher oxidation rate and it consumed lower energy. However, the energy consumption and process time make useless anodic oxidation for the complete elimination of pollutants from PW. Cytotoxicity has shown that electrochemical oxidation using BDD could be efficiently used to reduce more than 90% of hydrocarbons compounds. All results suggest that electrochemical oxidation could be an effective approach to treat highly concentrated organic pollutants present in the industrial petrochemical wastewater and significantly reduce the cost and time of treatment.

Sequential electrochemical treatment of dairy wastewater using aluminum and DSA-type anodes

Dairy wastewater is characterized by a high content of hardly biodegradable dissolved, colloidal, and suspended organic matter. This work firstly investigates the performance of two individual electrochemical treatments, namely electrocoagulation (EC) and electro-oxidation (EO), in order to finally assess the mineralization ability of a sequential EC/EO process. EC with an Al anode was employed as a primary pretreatment for the conditioning of 800 mL of wastewater. A complete reduction of turbidity, as well as 90 and 81% of chemical oxygen demand (COD) and total organic carbon (TOC) removal, respectively, were achieved after 120 min of EC at 9.09 mA cm(-2). For EO, two kinds of dimensionally stable anodes (DSA) electrodes (Ti/IrO₂-Ta₂O₅ and Ti/IrO₂-SnO₂-Sb₂O₅) were prepared by the Pechini method, obtaining homogeneous coatings with uniform composition and high roughness. The (·)OH formed at the DSA surface from H₂O oxidation were not detected by electron spin resonance. However, their indirect determination by means of H₂O₂ measurements revealed that Ti/IrO₂-SnO₂-Sb₂O₅ is able to produce partially physisorbed radicals. Since the characterization of the wastewater revealed the presence of indole derivatives, preliminary bulk electrolyses were done in ultrapure water containing 1 mM indole in sulfate and/or chloride media. The performance of EO with the Ti/IrO₂-Ta₂O₅ anode was evaluated from the TOC removal and the UV/Vis absorbance decay. The mineralization was very poor in 0.05 M Na₂SO₄, whereas it increased considerably at a greater Cl(-) content, meaning that the oxidation mediated by electrogenerated species such as Cl₂, HClO, and/or ClO(-) competes and even predominates over the (·)OH-mediated oxidation. The EO treatment of EC-pretreated dairy wastewater allowed obtaining a global 98 % TOC removal, decreasing from 1,062 to <30 mg L(-1).

Role of electrode materials for the anodic oxidation of a real landfill leachate--comparison between Ti-Ru-Sn ternary oxide, PbO(2) and boron-doped diamond anode

In this paper the electrocatalytic properties of Ti-Ru-Sn ternary oxide (TiRuSnO(2)), PbO(2) and boron-doped diamond (BDD) anodes have been compared for the electrochemical oxidation of a real landfill leachate from an old municipal solid waste landfill (average values of COD 780 mg dm(-3) and NH(4)(+)-N266 mg dm(-3)). The experiments have been performed using an undivided flow cell equipped with a stainless steel cathode, under constant current of 2 A and flow-rate of 420 dm(3) h(-1). The performance of the electrodes has been compared measuring the time evolution of aromatic compounds, COD, ammonium, colour removal, current efficiency and energy consumption. The experimental results indicated that after 8 h of electrolyses TiRuSnO(2) anode yields only 35% COD, 52% colour and 65% ammonium removal. Using PbO(2) ammonium and colour were completely removed but a residual COD (i.e. 115 mg dm(-3)) was present. On the contrary BDD enables complete COD, colour and ammonium removal due to the electrogeneration of hydroxyl radicals from water discharge and active chlorine from chloride ions oxidation. BDD also exhibits greater current efficiency along with a significantly lower energy cost than other electrodes. These results indicated that the electrochemical oxidation with BDD anode is an effective process for the treatment of landfill leachate.