Treatment of dyehouse waste‐water by supercritical water oxidation: a case study

BACKGROUND: Supercritical water oxidation (SCWO) of dyehouse waste‐water containing several organic pollutants has been studied. The removal of these organic components with unknown proportions is considered in terms of total organic carbon concentration (TOC), with an initial value of 856.9 mg L^?1. Oxidation reactions were performed using diluted hydrogen peroxide. The reaction conditions ranged between temperatures of 400–600 °C and residence times of 8–16 s under 25 MPa of pressure. RESULTS: TOC removal efficiencies using SCWO and hydrothermal decomposition were between 92.0 and 100% and 6.6 and 93.8%, respectively. An overall reaction rate, which consists of hydrothermal decomposition and the oxidation reaction, was determined for the hydrothermal decomposition of the waste‐water with an activation energy of 104.12 ( ± 2.6) kJ mol^?1 and a pre‐exponential factor of 1.59( ± 0.5) × 10⁵ s^?1. The oxidation reaction rate orders for the TOC and the oxidant were 1.169 ( ± 0.3) and 0.075 ( ± 0.04) with activation energies of 18.194 ( ± 1.09) kJ mol^?1, and pre‐exponential factor of 5.181 ( ± 1.3) L^0.244 mmol^?0.244 s^?1 at the 95% confidence level. CONCLUSION: Results demonstrate that the SCWO process decreased TOC content by up to 100% in residence times between 8 and 16 s under various reaction conditions. The treatment efficiency increased remarkably with increasing temperature and the presence of excess oxygen in the reaction medium. Color of the waste‐water was removed completely at temperatures of 450 °C and above. Copyright © 2010 Society of Chemical Industry     

Treatment of an industrial chemical waste‐water using a granular activated carbon adsorption‐microwave regeneration process

BACKGROUND: Industrial waste‐water is posing an ever‐greater environmental hazard. Recently, a process for purification combining activated carbon adsorption and microwave regeneration has drawn much attention. In this study, the effectiveness of this process for the treatment of industrial waste‐water from a chemical plant was tested. RESULTS: The effects of various factors including solution pH, granular activated carbon (GAC) dosage and contact time on the adsorption efficiency of organic compounds were studied. The regeneration of the exhausted GAC under microwave radiation was investigated, and the optimal conditions were: microwave power 400 W, radiation time 3 min for 10 g GAC. Under the optimal conditions the regenerated GAC recovered 97.6% of its original adsorption capacity. Repetitive uses of the GAC showed that it maintained a stable performance in the first few repetitions, but a decrease was observed after further repetitions. A GAC weight loss of about 10% at the sixth repetition was observed and a decrease in the surface area and increase in the surface basicity were observed for the regenerated GAC. Economic evaluation of the microwave regeneration process suggested that the total cost was about 24.3% of the GAC price at a pilot scale. CONCLUSIONS: A satisfactory regeneration of the chemical waste‐water exhausted GAC could be achieved under microwave radiation. The GAC adsorption‐microwave regeneration process was applicable for the treatment of this chemical waste‐water. Copyright © 2012 Society of Chemical Industry     

Removal of manganese from water by electrocoagulation: Adsorption,kinetics and thermodynamic studies

The present study provides an electrocoagulation process for the removal of manganese (Mn) from water using magnesium as anode and galvanised iron as cathode. The various operating parameters like effect of initial pH, current density, electrode configuration, inter‐electrode distance, coexisting ions and temperature on the removal efficiency of Mn were studied. The results showed that the maximum removal efficiency of 97.2% at a pH of 7.0 was achieved at a current density 0.05 A/dm² with an energy consumption of 1.151 kWhr/m³. Thermodynamic parameters, including the Gibbs free energy, enthalpy and entropy, indicated that the Mn adsorption of water on magnesium hydroxides was feasible, spontaneous and endothermic. The experimental data were fitted with several adsorption isotherm models to describe the electrocoagulation process. The adsorption of Mn preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. In addition, the adsorption kinetic studies showed that the electrocoagulation process was best described using the second‐order kinetic model at the various current densities. © 2012 Canadian Society for Chemical Engineering     

Cobalt removal from waste‐water by means of supported liquid membranes

BACKGROUND: Supported liquid membranes (SLM) are an alternative technique to remove and recover metals from diluted process solutions and waste‐water. In the present work, the removal of Co(II) from a synthetic CoSO₄ solution containing initial amounts of cobalt(II) in the range 100–200 ppm (0.1–0.2 g dm^?3) has been studied on a pilot scale. By performing batch equilibrium experiments, the optimal settings, i.e. the composition of the organic phase, the pH of the feed, the type and concentration of the stripping agent were determined. RESULTS: It is shown that the equilibrium characteristics of a synergistic extractant mixture containing di‐2‐ethyl‐hexylphosphoric acid (D2EHPA) and 5‐dodecylsalicylaldoxime (LIX 860‐I) are superior to D2EHPA. Both hydrochloric acid and sulfuric acid have been evaluated as stripping solutions in liquid–liquid extraction tests and as the receiving phase in a SLM configuration. Although equilibrium tests showed no difference in stripping characteristics between both chemicals, it was observed that in a SLM configuration the stability of the system when hydrochloric acid is used is poor. With a commercially available SLM module (Liqui‐Cel Extra‐Flow 4 × 28) having a surface area of 19 m², a steady Co(II) flux of 0.140 gm^?2h^?1 has been obtained at influent concentrations of cobalt between 100 and 200 ppm with 3 mol dm^?3 sulfuric acid as stripping phase. CONCLUSIONS: The results obtained show that a supported liquid membrane containing a synergistic mixture of LIX 860‐I and D2EHPA gives the possibility of recovering cobalt from dilute solutions. Copyright © 2008 Society of Chemical Industry     

水处理电絮凝技术的研究进展与挑战

电絮凝是一种用于处理不同类型饮用水和废水有效的电化学方法,近年来由于其高效地处理大量难处理污染物的能力而受到了广泛的关注。它成功地处理了有机和无机污染物且同时却很少产生副产物。在过去的十年里大量的研究致力于利用电絮凝处理饮用水和废水,从受污染的地下水到受高度污染的炼油厂废水都是其处理范围。本文首先介绍了电絮凝的基本原理及优缺点并回顾了近年来有关电絮凝用于水处理的文献,重点关注当前在饮用水和废水中的具体应用方面取得的成功以及未来应用的潜力。随后分析了影响电絮凝效率的几个因素,最后指出最近的电絮凝大多集中在去除特定污染物的研究上,而没有关注开发模型或工业应用,并且如果能降低电絮凝的成本,此方法将会有一个巨大的突破。     

太阳能电絮凝技术在水处理中的研究进展

太阳能电絮凝技术（SPEC）是一种水处理新技术,其结合了太阳能光伏发电可再生、可持续的特点和电絮凝处理废水无需添加化学药剂、产泥量少、设备易操作、占地小的优势,为太阳能丰富的地区带来了更加高效、环保和节能的水处理方法。本文阐明了电絮凝的原理,并分析了阳极材料、电极连接方式、电流密度、初始pH、电导率和极板间距对废水中污染物去除效率的影响。随后,重点综述了国内外学者对SPEC技术处理染料废水、含磷废水、含油废水、偏远地区分散式废水和SPEC与其他技术耦合处理废水的研究进展。最后,点明了SPEC技术当前存在的不足及挑战,并对未来的研究方向提出了展望。     

Electrochemical degradation of pulp and paper industry waste‐water

BACKGROUND: Conventional biological waste‐water treatment techniques are insufficient to degrade large quantities of dissolved lignin discharged by small‐scale paper mills. The current investigation is aimed at comparing the overall performance of basic electrochemical reactor configurations such as batch, batch recirculation, recycle and single pass systems, in removing the organic part of waste‐water from a small‐scale, agro‐based paper industry. The effect of current density, supporting electrolyte concentration, duration of electrolysis, specific electrode surface and fluid flow rate on the removal of pollutants and energy consumption are critically evaluated. The improvement in biodegradability of the effluent during treatment is also noticed. RESULTS: The batch recirculation mode of operation was found to be superior in comparison with a batch system using the same specific electrode surface for both COD removal (73.3 vs. 64%) and capacity utilization (rate constant 1.112 × 10^?3 vs. 1.049 × 10^?3 cm s^?1). The pollutant removal performance of the batch recirculation system improved considerably with increase in the circulation flow rate. At the best operating point in the recycle system, 59% of COD was removed, corresponding to a current efficiency of 68.9% and specific energy consumption of 18.46 kWh kg^?1. The biodegradability index of the waste‐water was improved from 0.18 ± 0.01 to 0.36 ± 0.01. CONCLUSION: A recycle reactor was the best configuration, because of its flexibility of operation. Circulation flow rate and withdrawal flow rate enable the control of transfer coefficients and treatment duration respectively. Electrochemical treatment not only removes the bulk of the organic matter, but also makes the remaining pollutants more easily biodegradable. Copyright © 2009 Society of Chemical Industry     

Simultaneous removal of COD and NH3‐N in secondary effluent of high‐salinity industrial waste‐water by electrochemical oxidation

BACKGROUND: Electrochemical oxidation has been applied successfully in industrial waste‐water treatment. The simultaneous removal of COD_Cr and NH₃‐N, as well as the corresponding mechanisms and reaction zone, were examined in this study. The reaction kinetics and the significant factors that affect removal performance were also studied. RESULTS: The COD_Cr removal efficiency without chlorides in waste‐water was only 11.8% after 120 min of treatment, which was much lower than the efficiency with chlorides, and agitation did not improve the performance. When the current density was increased from 2.5 to 10 mA cm^?2, the removal efficiency was improved. The removal efficiencies of COD_Cr and NH₃‐N were less at initial pH = 11 than at pH = 3 and 8.7 (without adjustment). The COD_Cr and NH₃‐N removal efficiencies were decreased by about 30% and 50%, respectively, when the electrode distance was increased from 4 to 12 cm. Instantaneous current efficiency decreased with increase in current density. CONCLUSIONS: The degradation of pollutants occurred mainly at the boundary layer between the electrode and the bulk solution. The indirect oxidation by active chlorine generated from the chlorides was proven to be the primary mechanism of electrochemical oxidation treatment. The removal of COD_Cr in this study followed a pseudo‐first‐order kinetic model. Copyright © 2011 Society of Chemical Industry     

Contributions of electrochemical oxidation to waste‐water treatment: fundamentals and review of applications

OVERVIEW: This paper provides an overview of some fundamental aspects of electrochemical oxidation and gives updated information on the application of this technology to waste‐water treatment. In recent years, electrochemical oxidation has gained increasing interest due to its outstanding technical characteristics for eliminating a wide variety of pollutants normally present in waste‐waters such as refractory organic matter, nitrogen species and microorganisms. IMPACT: The strict disposal limits and health quality standards set by legislation may be met by applying electrochemical oxidation. However, treatment costs have to be cut down before full‐scale application of this technology. Deployment of electrochemical oxidation in combination with other technologies and the use of renewable sources to power this process are two steps in this direction. APPLICATIONS: Effluents from landfill and a wide diversity of industrial effluents including the agro‐industry, chemical, textile, tannery and food industry, have been effectively treated by this technology. Its high efficiency together with its disinfection capabilities makes electro‐oxidation a suitable technology for water reuse programs. Copyright © 2009 Society of Chemical Industry     

电絮凝技术在水处理中的应用

电絮凝作为一种环境友好型技术,具有占地面积小、去除污染物种类广、去除效率高、工艺操作简便等优势被广泛应用到各种难降解污染废水的处理中。从探讨电絮凝技术的基本原理、影响因素出发,分析了当下利用电絮凝进行废水处理的热点及重点研究。最后采用文献计量学方法分析了电絮凝技术的研究热点及发展趋势。     

Pilot‐scale treatment of waste‐water from carbon production by a combined physical–chemical process

BACKGROUND: Due to its strong colour, high concentrations of fluorides and chemical oxygen demand (COD_Cr) and large amount of suspended solids (SS), the waste‐water from carbon production (WCP) seriously affects the stability of the circulating system of Guizhou Branch, Aluminium Corporation of China. In this paper, the performance of a pilot‐scale (24 m³ d^?1) combined treatment plant, consisting of chemical precipitation, coagulation, and Fenton oxidation, for the treatment of WCP was investigated. RESULTS: Lime precipitation and hydrated ferrous sulphate (HFS) coagulation, with polyacrylamide (PAM) as a coagulation aid, proved to be effective in the removal of colour (>70%), suspended solids (SS) (>90%) and fluoride (>80%) from the WCP. Subsequent Fenton oxidation combined with coagulation as a final treatment efficiently removed SS, F^?, COD_Cr, dissolved organic carbon (DOC) and colour. The average total removal efficiencies of these parameters in the pilot‐scale combined technology were as follows: SS = 98.8%, F^? = 95.7%, COD_Cr = 94.8%, DOC = 91.8% and colour = 98.3%, giving an average effluent quality: colour 24 (multiple), COD_Cr 168 mg L^?1, DOC 80 mg L^?1, F^? 38 mg L^?1 and SS 44 mg L^?1, consistent with the reusable water limits for the process. CONCLUSIONS: The current experimental results and the economic evaluation suggest that the combined process could be advantageous and feasible for the treatment of WCP. Copyright © 2009 Society of Chemical Industry     

Effects of alternating and direct current in electrocoagulation process on the removal of fluoride from water

BACKGROUND: When direct current (DC) is used in electrocoagulation processes, an impermeable oxide layer may form on the cathode and corrosion of the anode may occur due to oxidation. This prevents effective current transfer between the anode and cathode, so the efficiency of the electrocoagulation process declines. These disadvantages of DC have been reduced by adopting alternating current (AC). The main objective of this study is to investigate the effects of AC and DC on the removal of fluoride from water using an aluminum alloy as anode and cathode. RESULTS: Results showed that removal efficiencies of 93 and 91.5% with energy consumption of 1.883 and 2.541 kWh kL^?1 was achieved at a current density of 1.0 A dm^?2 and pH 7.0 using an aluminum alloy as electrodes using AC and DC, respectively. For both AC and DC, the adsorption of fluoride fitted the Langmuir adsorption isotherm. The adsorption process follows second‐order kinetics and temperature studies showed that adsorption was exothermic and spontaneous in nature. CONCLUSIONS: The aluminum hydroxide generated in the cell removed the fluoride present in the water and reduced it to a permissible level thus making it drinkable. It is concluded that an alternating current prevents passivation of the aluminum anode during electrocoagulation and avoids the additional energy wasted due to the resistance of the aluminum oxide film formed on the anode surface. Copyright © 2010 Society of Chemical Industry     

复极式电凝聚-电气浮方法处理洗衣废水

采用复极式电凝聚．电气浮方法处理洗衣废水。研究了pH、水力停留时间（HRT）和电流强度对处理过程的影响。结果表明,在较宽的pH范围（pH=4～9）、较短的水力停留时间（HRT=5～10min）下,悬浮物、阴离子表面活性剂（MBAS）、COD和磷酸盐均可得到有效去除。     

Utilization of organically stabilized proteinous solid waste for the treatment of coloured waste‐water

BACKGROUND: Solid waste emanating from tanneries contains a high percentage of protein with raw trimmings from hides constituting a significant percentage of the solid waste. In this study, organically stabilized trimmings (OST) have been used as an adsorbent material for removal of colour from waste‐water. RESULTS: Various parameters such as adsorbent dosage, dye concentration and pH have been optimized. The effect of neutral salts on the dye adsorption capacity of OST has also been studied. The adsorption of dye by OST follows the Freundlich isotherm. More than 99% removal of colour has been achieved. Commercial trials prove the potential use of organically stabilized trimmings for the treatment of colored wastewater. CONCLUSIONS: Dye loaded OSTs have been employed in the manufacture of a tanning salt, which can be used in the leather industry. Thus, a holistic solution to the challenging solid waste disposal problem has been developed. Copyright © 2009 Society of Chemical Industry     

Optimization of the process parameters for the removal of boron from drinking water by electrocoagulation—a clean technology

BACKGROUND: There are a number of articles related to removal of boron by electrocoagulation using aluminium electrodes, but there are fewer articles describing the use of magnesium as the anode material. The main disadvantage of aluminium electrodes is the residual aluminium present in the treated water due to cathodic dissolution, which can create health problems. In the case of magnesium electrodes, there is no such disadvantage. This paper presents the results of studies on the removal of boron using magnesium and stainless steel as anode and cathode, respectively. RESULTS: Results show that a maximum removal efficiency of 86.32% was achieved at a current density of 0.2 A dm^?2 and pH of 7 using magnesium as the anode and stainless steel as the cathode. The adsorption of boron fitted the Langmuir adsorption isotherm, suggesting monolayer coverage of adsorbed molecules. The adsorption process follows second‐order kinetics. Temperature studies showed that adsorption was endothermic and spontaneous in nature. CONCLUSIONS: The magnesium hydroxide generated in the cell remove the boron present in the water and reduced to a permissible level and making it drinkable. The process scale up results was consistent with the results obtained from the laboratory scale, showing the robustness of the process. Copyright © 2010 Society of Chemical Industry     

电絮凝水处理技术阳极优化的研究

简介了电絮凝法处理废水的基本原理,重点探讨了目前电絮凝水处理技术中存在的阳极钝化问题,以及影响阳极钝化的主要因素,并提出了解决阳极钝化的方法和建议.在实际处理工艺中,可以从采用新型电极、磁场效应以及改进电源技术等方面着手,对工作阳极做进一步优化,降低电能消耗和材料消耗,以促进电絮凝水处理技术的推广应用.     

Effects of alternating current (AC) and direct current (DC) in electrocoagulation process for the removal of iron from water

In practice, direct current (DC) is used in an electrocoagulation processes. In this case, an impermeable oxide layer may form on the cathode as well as corrosion formation on the anode due to oxidation. This prevents the effective current transfer between the anode and cathode, so the efficiency of electrocoagulation processes declines. These disadvantages of DC have been diminished by adopting alternating current (AC) in electrocoagulation processes. The main objective of this study is to investigate the effects of AC and DC on the removal of iron from water using zinc as anode and cathode. The results showed that the optimum removal efficiency of 99.6% and 99.1% with the energy consumption of 0.625 and 0.991 kWh kL^?1 was achieved at a current density of 0.06 A dm^?2, at pH of 7.0 using AC and DC, respectively. For both AC and DC, the adsorption of iron was preferably fitting Langmuir adsorption isotherm, the adsorption process follows second order kinetics and the temperature studies showed that adsorption was exothermic and spontaneous in nature. © 2011 Canadian Society for Chemical Engineering     

电絮凝法处理含锰废水试验研究

采用周期换向电絮凝法处理含锰废水,考察了初始pH值、电流密度、初始浓度等因素对处理效果的影响.结果表明,当初始pH值为9.0,总锰初始质量浓度为40 mg/L,处理时间为5 min,电流密度为23.81 A/m2,电极换向周期为15 min时,总锰的去除率超过98％.电絮凝出水经曝气、絮凝和过滤处理后满足GB18918-2002《城镇污水处理厂污染物排放标准》的要求.