A comparative study of electrocoagulation and electro-Fenton for food industry wastewater treatment: Multiple response optimization and cost analysis

ABSTRACT

In this study, response surface methodology was applied for food wastewater by electrocoagulation (EC) and electro-Fenton (EF) processes. The optimum conditions for the chemical oxygen demand (COD) removal were found to be 21.36 min, pH 10 and 86 mA/cm² in EC, whereas 27.11 min, pH 2.38, 86 mA/cm² and H₂O₂/COD:2 in EF process. COD removal efficiencies were determined to be 29.4% for EC and 59.1% for EF processes and higher than 99% total suspended solids removal efficiencies were achieved. It can be concluded that high COD removal was obtained (4998 mg/L COD removal by EC and 10,047 mg/L COD removal by EF).     

聚铁混凝法深度处理老龄垃圾渗滤液的工程应用运行分析

将聚铁混凝工艺成功应用于老龄垃圾渗滤液的深度处理,对渗滤液生化处理出水的COD去除率可达65%以上,总结了近400 d的运行情况,分析了反应pH、进水pH和进水COD对COD去除率的影响。结果表明,进水pH（≤8.5）和进水COD（≤850 mg/L）对COD去除率的影响不大,聚铁混凝的最适反应pH范围较宽,在3.3~5.6之间,但反应pH大于6.0时COD去除率会急剧降低。     

铁碳微电解处理印染废水的效能及生物毒性变化

为了提高铁碳微电解工艺处理实际印染废水的效率,采用响应面法进行工艺条件优化。以COD去除率为响应值,初始pH、铁投加量、铁碳质量比及反应时间为实验因素,构建响应面模型,分析模型的显著性。结果表明：当初始pH为3.53、铁投加量为83.92g/L、铁碳质量比为0.82及反应时间为78.48min时,COD去除率的预测值为75.25%,与实测值相差0.23%（＜2%）,可以利用该模型预测COD去除率的变化。同时采用大肠杆菌对铁碳微电解工艺进出水的生物毒性进行检测,与进水组相比,出水组中乳酸脱氢酶（LDH）释放量由对照组的2.13倍下降至对照组的1.64倍,同时活性氧物质（ROS）产生水平由对照组的19.26倍下降至对照组的4.81倍,细胞死亡率由98.1%下降至61.5%,对数期由5h延长至9h,且BOD₅/COD从0.151升至0.416,因此铁碳微电解工艺具有降低印染废水生物毒性的作用。     

Pre-Treatment of Pistachio Processing Industry Wastewaters (PPIW) by Electrocoagulation using Al Plate Electrode

The objective of the present study is to assess the efficiency of electro-coagulation treatment of pistachio processing industry wastewaters (PPIW) using an aluminum plate electrode. The effect of some of the parameters was examined on the removal of chemical oxygen demand (COD), total organic carbon (TOC), and total phenols (TP) removal efficiency. The treatment was carried out in a batch system. The influences of current density (from 1 to 6 mA cm^?2), initial pH of wastewater (from 2 to 8), constant pH of wastewater (from 3 to 7), stirring speed (from 100 to 500 rpm), and supporting electrolyte concentration (from 10 to 50 mg L^?1 NaCl) on removal efficiency were investigated to determine the best experimental conditions. The evaluation of the physico-chemical parameters during the treatment by electrocoagulation showed that the best removal efficiency was obtained under the conditions of 180 min electrolysis time, wastewater with constant pH of 6, and 6 – mA cm^?2 current density. Under such experimental conditions, COD, TOC, and TP removal efficiency were found to be 60.1%, 50.2%, and 77.3%, respectively, while energy consumption was 39.6 kW-h m^?3. The results of the study show that the electrocoagulation can be applied to PPIW pre-treatment.     

Influence of Experimental Parameters in the Treatment of Distillery Effluent by Electrochemical Oxidation

The electrochemical oxidation of distillery effluent was studied in a batch reactor in the presence of supporting electrolyte NaCl using Mixed Metal Oxide (MMO) electrode. The effect of operating parameters such as current density, initial pH, and initial electrolyte concentration on the percentage of Chemical Oxygen Demand (COD) removal, power consumption, and current efficiency were studied. The maximum percentage removal of COD was observed to be 84% at a current density of 3 A/dm²at an electrolyte concentration of 10 g/l with an effluent COD concentration of 1000 ppm and at an initial pH of 6. The operating parameters for the treatment of distillery effluent by electrochemical process were optimized using response surface methodology by CCD. The quadratic regression models with estimated coefficients were developed for the percentage removal of COD and power consumption. It was observed that the model predictions matched with experimental values with an R² value of 0.9504 and 0.9083 for COD removal and power consumption respectively. The extent of color removal and oxidation of organic compounds were analyzed using UV spectrophotometer and HPLC.     

Bilge Water Treatment in an Upflow Electrochemical Reactor using Pt Anode

Bilge water treatment was studied in an upflow electrochemical reactor (UECR) in order to design a compact onboard wastewater treatment system. The influence of retention time on the removal efficiencies of chemical oxygen demand (COD) and turbidity were analyzed, and optimized using response surface methodology (RSM) for maximizing the removal efficiencies. The best operating performance was obtained at 390 min retention time and 480 min reaction time for cost effective analysis with the composition of 100% bilge water (COD_o = 3080 mg/L) and 50/50% seawater/fresh water, 12.8 mA/cm² current density, and 32°C reaction temperature. Under response surface optimized conditions, the responses were estimated as; 90% COD removal, 97% turbidity removal, outlet pH value of 8.1, mass transfer coefficient of 0.494 × 10^?5 m/s, and mean energy consumption of 44.8 kWh/kg COD removed.     

钠型累托石处理印染废水

文章的正交实验研究表明:(1)用改性累托石处理印染废水中的浊度及COD,在废水pH为5,改性累托石用量为110 mg/L,搅拌时间为20 min,搅拌速率为50 r/min时,最优化条件下,经验证实验,COD去除率可达50%。浊度去除率可达96,71%。(2)影响浊度去除率的因素主次顺序是:改性累托石用量pH搅拌速率搅拌时间。影响COD去除率的因素主次顺序是:改性累托石用量pH搅拌时间搅拌速率。     

深度氧化技术处理焦化废水的研究

首先用改性焦炭、硫酸铝、PAM对焦化废水进行预处理,结果表明改性焦炭预处理焦化废水效果最佳,COD去除率为29.7%。然后利用Fenton试剂对焦化废水深度处理,单因素实验和正交试验结果表明,当pH=4,H2O2投加量为15mmol.L-1,[Fe2＋]/[H2O2]=1∶10,反应时间30min时,处理效果最佳,COD去除率可达92%。各因素对COD去除率影响的强弱顺序为：pH〉H2O2投加量〉Fe2＋/H2O2的摩尔比。     

内循环式铁碳微电解/H2O2耦合工艺处理多晶硅有机废水

针对铁碳微电解反应中填料易板结及处理效率低等问题,通过增加内循环装置改进反应器结构,同时将铁碳微电解与H₂O₂进行工艺耦合,用于处理多晶硅有机废水,考察了Fe-C投加量、初始pH值、H₂O₂投加量、反应时间等工艺条件对COD去除率的影响,并通过响应面法优化了工艺条件。结果表明,各工艺条件对多晶硅有机废水COD去除效果的影响大小为：铁碳投加量>反应时间>H₂O₂投加量>初始pH值,其最适宜工艺条件为：铁碳投加量250 g·L^-1,初始pH值2.8,H₂O₂投加量112 mL·L^-1,反应时间83 min,该反应条件下COD的去除率为71.26%。铁碳/H₂O₂降解多晶硅有机废水COD的动力学回归方程为Y=0.5273X-0.6347,降解COD的速率常数为0.527 3 min^-1。     

Comparative study of electrocoagulation and electrochemical Fenton treatment of aqueous solution of benzoic acid (BA): Optimization of process and sludge analysis

Benzoic acid containing synthetic solution was pretreated by acid precipitation at various pH (1-3) and temperature (15-60 °C). Pre-treated solution was further treated by electrocoagulation (EC) and electrochemical Fenton (EF) processes using iron anode and graphite cathode. Optimization of independent operating parameters, namely, initial pH: (3-11), current density (A/m²): (15.24-76.21), electrolyte concentration (mol/L): (0.03-0.07) and electrolysis time (min): (15-95) for EC process and pH: (1-5), current density (A/m²): (15.24-76.21), H₂O₂ concentration (mg/L): (100-500) and electrolysis time (min): (15-95) for EF process, was performed using central composite design (CCD) in response surface methodology (RSM). Maximum removal efficiencies of BA- 76.83%, 88.50%; chemical oxygen demand (COD) - 69.23%, 82.21% and energy consumption (kWh/kg COD removed) - 30.86, 21.15 were achieved by EC and EF processes, respectively, at optimum operating conditions. It was found that EF process is more efficient than EC process based on removal of BA and COD with lower energy consumption. The sludge obtained after EC and EF treatments was analyzed by XRD, FTIR, DTA/TGA and SEM/EDX techniques.     

Electrochemical pretreatment of heavy oil refinery wastewater using a three-dimensional electrode reactor

The pretreatment of heavy oil refinery wastewater (HORW) was experimentally investigated using a three-dimensional electrode reactor (TDER) with granular activated carbon (GAC) and porous ceramsite particle (PCP) as the combination particle electrode and DSA^® type anodes as the anode. The results showed that higher chemical oxygen demand (COD) removal was obtained in TDER comparing with the two-dimensional electrode reactor (without particle electrodes packed), and combination particle electrode was favorable to improve the COD removal efficiency and reduce the energy consumption. The treated HORW under the optimal experimental condition (GAC percentage = 75%, current density = 30 mA/cm², pH not adjusted and treatment time = 100 min) presented that the removal efficiencies of COD, total organic carbon and toxicity units were 45.5%, 43.3% and 67.2%, respectively, and the ratio of 5-day biochemical oxygen demand to COD was increased from 0.10 to 0.29, which is beneficial for further biological treatment. Furthermore, the application of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to characterize polar compounds in HORW and their oxidation products was well demonstrated to reveal the composition variation.     

Degradation of azo dye C.I. Acid Red 18 using an eco-friendly and continuous electrochemical process

Continuous anodic oxidation of azo dye C.I. Acid Red 18 by using PbO₂ electrode in aqueous solution was studied. To reach the best conditions of the process, the influence of various operating parameters such as pH, current density, hydraulic retention time (HRT) and dye concentration on the removal rate of chemical oxygen demand (COD) and color, as indexes showing the amount of efficiency, was investigated. The findings showed that, respectively, 99.9% and 80.0% of the dye and COD were removed (at optimized conditions). Mineralization current efficiency results indicated that at the beginning of the reaction mineralization occurred quickly at a low current density, whereas at high amounts the rate of mineralization the efficiency decreased. At the optimum conditions, the majority of COD was removed only with 38.2 kWh/kg COD of energy consumption in 120 min. By controlling HO?/dye concentration ratio via the parameters adjustment, particularly HRT and current density, this system can treat Acid Red 18 well even at high concentrations. Furthermore, the voltammetry study illustrated that electroactive intermediates created during the process were mineralized at current density of 8.6mA/cm².     

微电解+Fenton处理DDNP废水的实验研究

采用微电解+Fenton法处理DDNP废水,考虑微电解系统的活性炭的投加量,Fe/C,pH,反应时间等因素在不同条件下原水的COD去除情况及色度变化。实验结果表明,最佳pH为4,Fe的投加量为30 g/L,最佳Fe/C为3/2,最佳反应时间60 min。COD的去除最高可达到58.8%。Fenton系统H2O2的投加量为4 mg/L,微电解+Fenton系统的COD去除率为87.53%。     

CNTs/PMS高级氧化体系去除水中的环丙沙星

针对当前抗生素废水处理的难题,以环丙沙星（CIP）为研究对象,采用碳纳米管（CNTs）活化过硫酸氢盐（PMS）对其进行降解。考察了PMS浓度、CIP浓度、CNTs投加量、初始pH等因素对CIP降解效果的影响。研究结果表明,在pH为2.73～11.38范围内,PMS的浓度为1.5mmol/L、CNTs投加量为15mg/L时,初始浓度为5mg/L的CIP降解效果达到最佳,CNTs在反应过程中集吸附和催化于一体,且作为催化剂可实现多次循环利用。借助电子顺磁共振捕获技术和自由基猝灭反应对降解过程中的活性物质进行分析与鉴定,实验结果表明,在整个反应体系中起主导作用的活性基团是硫酸根自由基（SO₄ ^?-）。通过中间产物分析,发现氧化反应主要发生在哌嗪基团、喹诺酮核心的C－F键及环丙烷环上。这些结果可应用于抗生素废水的工业处理。     

UV/TiO_2/Fenton光催化氧化皂素废水的特性研究

皂素废水属于高难度难降解工业废水。采用UV/TiO2与Fenton氧化法相结合的工艺对皂素废水处理进行了研究,考察了pH值、H2O2用量、温度、反应时间等因素对处理效果的影响。实验表明,常温下pH值为5.0、H2O2用量为20 mL/L、反应时间取45 min时,TiO2光催化作用下对皂素废水中COD去除率可达94%以上,满足国家排放标准的要求。     

Combination of Chemical Coagulation and Photo-Fenton Oxidation Process for the Treatment of Beet Sugar Industry Wastewater: Optimization of Process Conditions by Response Surface Methodology

The beet sugar industry generates large volumes of wastewater with high levels of chemical oxygen demand (COD) and color content, which are discharged into the nearby environment without adequate treatment. The aim of this study was to investigate the treatment possibility of this wastewater by using the photo-Fenton oxidation combined with a coagulation process. Central composite design and response surface methodology were used to evaluate the relationships between color and COD reduction and the photo-Fenton oxidation parameters (i.e. Fenton’s reagent dosage, pH, and reaction time).

The combined treatment results showed 59% of COD and 83.9% of color removal were obtained at optimum conditions (pH: 6.2; Fe²⁺ dosage: 20 ppm; H₂O₂ dosage: 1500 ppm; and reaction time of 15 min). Finally, the results of gel permeation chromatography showed that low molecular weight fraction of the wastewater impurities is more degraded than high molecular weight fraction during oxidation/coagulation process. Therefore, the results obtained from this study showed that an appropriate combined method for the treatment of beet sugar industry wastewater can be designed and implemented.     

Electrochemical removal of the insecticide imidacloprid from water on a boron-doped diamond and Ta/PbO<Subscript>2</Subscript> anodes using anodic oxidation process

The removal of pesticides from water is a major environmental concern. This study investigates the electrochemical removal of the insecticide imidacloprid (IMD) from aqueous solutions on a boron-doped diamond (BDD) and Ta/PbO₂ anodes under galvanostatic electrolysis. The influence of operating parameters, such as applied current density (50–100 mA cm^?2), initial chemical oxygen demand COD (0) (281–953 mg L^?1), temperature (25–65 °C) and pH (3.0–10.0) on COD and instantaneous current efficiency (ICE), was studied using the BDD electrode. The degradation efficiency of IMD increased by increasing current density and temperature, but noticeably decreased by the increase of initial pH value and initial concentration of IMD. The COD decay follows a pseudo-first-order kinetic, and the process was under mass transport control. COD removal reaches 90% when using an apparent current density of 100 mA cm^?2, initial COD of 953 mg L^?1, pH of 3.0 and at 25 °C after 4.5 h electrolysis time. Compared with Ta/PbO₂, BDD anode has shown better performance and rapidity in the COD removal using the same electrolysis device.     

Treatment of olive mill wastewater by the combination of ultrafiltration and bipolar electrochemical reactor processes

The main purpose of this study was to investigate the removal of the chemical oxygen demand (COD) from olive mill wastewater (OMW) by the combination of ultrafiltration with electrocoagulation process. Ultrafiltration process equipped with CERAVER membrane was used as pre-treatment for electrochemical process. The obtained permeate from the ultrafiltration process allowed COD removal efficiency of about 96% from OMW. Obtained permeate with an average COD of about 1.1 g dm⁻³ was treated by electrochemical reactor equipped with a reactor with bipolar iron plate electrodes. The effect of the experimental parameters such as current density, pH, surface electrode/reactor volume ratio and NaCl concentration on COD removal was assessed. The results showed that the optimum COD removal rate was obtained at a current density of 93.3 A m⁻² and pH ranging from 4.5 to 6.5. At the optimum operational parameters for the experiments, electrocoagulation process could reduce COD from 1.1 g dm⁻³ to 78 mg dm⁻³, allowing direct discharge of the treated OMW as that meets the Algerian wastewater discharge standards (<125 mg dm⁻³).     

Degradation of azo dye from aqueous solutions using nano-SnO2/Ti electrode prepared by electrophoretic deposition method: Experimental Design

In this work, degradation of C.I. Acid Red 33 (AR33) in aqueous solutions was investigated. The combined electrolysis–ozone (ECO) process optimized based on SnO₂ nanoparticles electrode (nano-SnO₂/Ti) as anode using response surface methodology (RSM) involving a five-level central composite design (CCD). The nano-SnO₂/Ti electrode was prepared using electrophoretic deposition (EPD) method. The electrode was characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV). The initial pH, current density, reaction time and electrolyte concentration were selected as independent variables in central composite design while color removal efficiency was considered as the response function. Based on analysis of variance (ANOVA), the coefficient of determination value (R² = 0.981) was high. In optimum conditions, maximum color removal efficiency (93.2%) was obtained after 16 min; and the removal of chemical oxygen demand (COD) was reduced to 57.1% after 60 min.     

PHOTOCATALYSIS BY IRON-RICH MONTMORILLONITE FOR THE TREATMENT OF DYEING WASTEWATER

This study investigates the photocatalytic degradation of dyeing wastewater by iron-rich montmorillonite (MMt) under a 25 W low-pressure mercury lamp (λ = 254 nm, I = 48.4 μW/cm²). Exposing MMt to UV irradiation worked to catalyze the photobleaching of wastewater used in the dyeing process. COD removal efficiencies of 65.0% and 74.0% were achieved in 1 g/L MMt suspensions at a pH of 3 in the absence and presence of 30 min of UV irradiation, respectively. A decolorization efficiency of 71.4% was reached with 1 g/L MMt suspensions at a pH of 3 after 30 min of UV irradiation, while only 4.9% decolorization was attained in darkness. These results indicate that iron-rich MMt is a good photocatalyst for decolorization and COD removal in wastewater from dyeing processes. A low pH value is beneficial to the decolorization of dyeing wastewater. A preliminary photocatalytic mechanism is proposed: the iron in the MMt is responsible for the decolorization of the wastewater because it produces a highly oxidative species of hydroxyl radicals (^?OH).