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 chemical mechanical polishing wastewater by electrocoagulation: system performances and sludge settling characteristics

Treatment of copper chemical mechanical polishing (CMP) wastewater from a semiconductor plant by electrocoagulation is investigated. The CMP wastewater was characterized by high suspended solids (SS) content, high turbidity (NTU), chemical oxygen demand (COD) concentration up to 500 mgl(-1) and copper concentration up to 100 mgl(-1). In the present study, electrocoagulation was employed to treat the CMP wastewater with an attempt to simultaneously lower its turbidity, copper and COD concentrations. The test results indicated that electrocoagulation with Al/Fe electrode pair was very efficient and able to achieve 99% copper ion and 96.5% turbidity removal in less than 30 min. The COD removal obtained in the treatment was better than 85%, with an effluent COD below 100 mgl(-1). The effluent wastewater was very clear and its quality exceeded the direct discharge standard. In addition, sludge settling velocities after electrocoagulation were measured and the data were employed to verify the empirical sludge settling velocity models. Finally, the sludge settling characteristic data were also utilized to establish the relation between the solids flux (G) and the initial solids concentration.     

Electrolytic treatment of an industrial wastewater from a hosiery plant.

Textile plant wastewater being treated in a facultative pond system had too high of a solids concentration to be reused in the dying and rinsing processes. Electrocoagulation was evaluated to further treat the pond effluent to remove turbidity, which was caused by dyes and microorganisms. A range of amperages were tested for removal of turbidity and chemical oxygen demand (COD). Electrocoagulation lowered the turbidity from 1400 NTU to below 50 NTU; and COD was lowered from 550 mg/L to approximately 250 mg/L, which was acceptable for reuse. In addition, a laboratory-scale sedimentation study was conducted on the electrocoagulated pond effluent, which indicated that a settling time of 35 minutes would provide for 80% removal of suspended solids, which was acceptable for reuse of the water in plant processes.     

Coagulation and precipitation as post-treatment of anaerobically treated primary municipal wastewater.

The main objective of this study was to investigate the feasibility of coagulation as a post-treatment method of anaerobically treated primary municipal wastewater. Both mesophilic and ambient (20 degrees C) temperature conditions were investigated in a laboratory-scale upflow anaerobic sludge bed (UASB) reactor. In addition, optimization of the coagulant, both in terms of type and dose, was performed. Finally, phosphorus removal by means of aluminum and iron coagulation and phosphorus and ammonia nitrogen removal by means of struvite precipitation were studied. Anaerobic treatment of primary effluent at low hydraulic retention times (less than 15 hours) resulted in mean chemical oxygen demand (COD) removals ranging from 50 to 70%, while, based on the filtered treated effluent, the mean removals increased to 65 to 80%. Alum coagulation of the UASB effluent gave suspended solids removals ranging from approximately 35 to 65%. Turbidity removal reached up to 80%. Remaining COD values after coagulation and settling were below 100 mg/L, while remaining total organic carbon (TOC) levels were below 50 mg/L. Filterable COD levels were generally below 60 mg/L, while filterable TOC levels were below 40 mg/L. All coagulants tested, including prepolymerized aluminum and iron coagulants, demonstrated similar efficiency compared with alum for the removal of suspended solids, COD, and TOC. Regarding struvite precipitation, optimal conditions for phosphorus and nitrogen removal were pH 10 and molar ratio of magnesium: ammonia-nitrogen: phosphate-phosphorus close to the stoichiometric ratio (1:1:1). During struvite precipitation, removal of suspended solids reached 40%, while turbidity removal reached values up to 80%. The removal of COD was approximately 30 to 35%; yet, when removal of organic matter was based on the treated filterable COD, the removal increased to approximately 65%. In addition, nitrogen was removed by approximately 70%, while phosphorus removal ranged between approximately 30 and 45% on the basis of the initial phosphorus concentration. Finally, size fractionation of the organic matter (COD) showed that the various treatment methods were capable of removing different fractions of the organic matter.     

电絮凝处理煤层气产出水

采用电絮凝法处理煤层气产出水,通过铁和铝2种电极材料的处理效果的比较,选择铝电极进行实验,研究了电极间距、原水pH值以及电流密度等因素对电絮凝处理效果的影响。实验结果表明,电絮凝法对煤层气产出水的化学需氧量(COD)和固体悬浮物(SS)具有良好的去除效果,原水pH接近中性时处理效果较好,电絮凝处理过程中不需添加可溶性盐和改变pH值。实验中确定的电絮凝处理条件为:电极间距1 cm,电流密度30 A/m2,反应10 min后,出水的COD、SS分别为9.6 mg/L和8.5 mg/L,去除率分别达到75.1%和88.8%,出水pH为7.8,电能消耗为1.75 kWh/m3。     

超声强化电絮凝处理洗车废水的试验研究

针对洗车行业对水资源的浪费及污染现状,采用超声强化电絮凝处理洗车废水.考察了电流密度、初始pH、极板间距、处理时间等因素对洗车废水处理效果的影响,并讨论了超声强化电絮凝机制.结果表明,超声强化电絮凝处理洗车废水的最佳条件是电流密度1,500 mA/cm2、初始pH无需调节、极板间距为1.5cm、处理20 min,COD与浊度去除率分别为68.77％、96.89％,出水达到《城市污水再生利用城市杂用水水质》(GB/T 18920-2002)要求.可见,超声能改变电絮凝反应动力学过程,强化电絮凝去除污染物效果.     

电絮凝处理油田生化出水

为了减轻对后续处理中超滤膜的污染,采用电絮凝法处理油田生化出水,降低油田生化出水中的有机物含量。研究了电流强度、曝气时间和pH值对水中总有机碳（TOC）和浊度除去效果的影响以及pH值随曝气时间的变化趋势,通过红外光谱对絮凝处理前后水中总溶解固体进行了分析,优化了电絮凝的工艺条件。研究表明,当水流速度控制在50mL/s,电流强度为2 A,500 mL絮凝出水的曝气时间为30 min时,整套絮凝工艺对TOC的去除率为48%,浊度去除率为42.9%,COD去除率为44%。     

Transformation characteristics of refractory pollutants in plugboard wastewater by an optimal electrocoagulation and electro-Fenton process

The treatment of the plugboard wastewater was performed by an optimal electrocoagulation and electro-Fenton. The organic components with suspended fractions accounting for 30% COD were preferably removed via electrocoagulation at initial 5 min. In contrast, the removal efficiency was increased to 76% with the addition of H(2)O(2). The electrogenerated Fe(2+) reacts with H(2)O(2) and leads to the generation of (·)OH, which is responsible for the higher COD removal. However, overdosage H(2)O(2) will consume (·)OH generated in the electro-Fenton process and lead to the low COD removal. The COD removal efficiency decreased with the increased pH. The concentration of Fe(2+) ions was dependent on the solution pH, H(2)O(2) dosage and current density. The changes of organic characteristics in coagulation and oxidation process were differenced and evaluated using gel permeation chromatography, fluorescence excitation-emission scans and Fourier transform infrared spectroscopy. The fraction of the wastewater with aromatic structure and large molecular weight was decomposed into aliphatic structure and small molecular weight fraction in the electro-Fenton process.     

Effectiveness of electrocoagulation process in removing organic compounds from slaughterhouse wastewater using monopolar and bipolar electrolytic cells

Slaughterhouse wastewaters contain varied and high amounts of organic matter (e.g., proteins, blood, fat). In order to produce an effluent suitable for stream discharge, electrochemical techniques have been particularly explored at the laboratory pilot scale for organic compounds removal from poultry slaughterhouse (PS) effluent. Electrocoagulation (EC) process was tested using either mild steel or aluminium electrodes arranged in bipolar (BP) or monopolar configuration system. Results showed that the best performance was obtained using mild steel BP electrode system operated at a current intensity of 0.3A, through 60 or 90 min of treatment. Under these conditions, removals of 86+/-1% and 99+/-1% were measured for BOD and oil and grease, respectively, whereas soluble COD and total COD were removed by 50+/-4% and 82+/-2%, respectively. EC is also efficient for decolorization (red-color) and clarification of the PS effluent. Removals of 89+/-4% and 90+/-4% have been measured for total suspended solids and turbidity, respectively. Electrochemical coagulation operated under the optimal conditions involves a total cost of 0.71 USD $ per cubic meter of treated PS effluent. This cost includes energy and electrode consumptions, chemicals, and sludge disposal.     

电催化氧化技术处理制革综合废水

选择DSA电极中的钛基掺硼金钢石膜电极(Ti/BDD),用于制革综合废水的电催化氧化处理研究,考察了在不同的电流密度、电压、电解质、pH值和电解时间等因素对COD去除率和电流效率的影响。结果表明,控制电流密度为30mA/cm2,电压为8.0 V,电解质(NaCl)浓度为2.0 g/L,pH为4.0,电催化氧化处理2 h后,废水的COD和NH4+-N的去除率分别达到了83.6%和90.3%,BOD/COD为0.45,比能耗为35.34 kWh/kg COD,电流效率为37%。     

Microbiological and performance evaluation of sequencing batch reactor for textile wastewater treatment

This study focused on laboratory-scaled and real-scaled treatment plant performances and microbiological investigations for the optimum treatment of textile industry wastewater performed with sequencing batch reactor (SBR). As a result of experimental studies of laboratory-scaled SBR treatment unit, optimum treatment efficiency was taken from 0.5 h filling to 1.5 h. reaction to 1.5 h. settlement to 0.5 h. discharge-idle periods. Average chemical oxygen demand (COD) removal efficiency of SBR of laboratory-scaled textile industry was 75%, whereas average turbidity and color removal (coloration number [RES, m(-1)] 586 nm) efficiencies were 90% and 75%, respectively. Optimum reaction and settlement periods were used in a real-scaled plant, and plant efficiency was examined for parameters such as COD, phenol, pH, mixed liquor suspended solids (MLSS) and sludge volume index (SVI). In this study, optimum reaction and settlement periods for treatment of textile industry wastewater were determined within a SBR in a laboratory-scaled plant. These reaction and settlement periods were verified with the measurement of COD, color, and turbidity parameters. Floc structure and protozoa-metazoa species of activated sludge in a SBR were also determined. Optimum reaction and settlement times were used in a real-scaled plant, and plant efficiency was examined for COD, Phenol, pH, MLSS, and SVI parameters. The corresponding values were found as appropriate, acceptable, and meaningful because of variance value of statistical analysis. Protozoa and metazoan in the activated sludge in the laboratory-scaled plant were investigated. Peranema sp., Epistylis sp., Didinium sp., Chilodonella sp., Opercularia sp., Vorticella sp. as protozoa species and Habrotrocha sp., Philodina sp. as metazoa species were determined.     

Treatability studies on wastewater from textile dyeing factories in Bursa, Turkey

The textile industry is one of the most rapidly developing industries in Turkey. It generates a large amount of wastewater, with corresponding concerns about pollution. The main sources of pollution in wastewater are the dyeing and finishing processes. The dyestuffs and polyvinyl alcohol (PVA) are the main refractory organics of concern in terms of meeting more stringent effluent standards of chemical oxygen demand (COD) and colour. In this study, wastewaters from textile dyeing factories in Bursa were characterised, and physical, chemical and biological treatability studies were carried out. In the physical and chemical studies, 60.80% COD, 80% suspended solids (SS) and 10.92% turbidity removal efficiencies were obtained. In the biological studies, 90% COD and 40% SS removal were obtained. The initial soluble inert COD of wastewater was determined by using comparison methods. The initial inert COD of wastewater and the microbial product concentration were determined as 37 mg/l and 13 mg/l, respectively.     

Pilot-scale studies on the treatment of tannery effluents by electroflotation

A pilot-scale electroflotation system with a treatment capacity of 0.8 m³ per hour has been designed and built. The system is equipped with a conditioning tank, a rectifier, flow meters, an energy meter and pumps. Iron, aluminium and titanium coated with oxides of tantalum, ruthenium and iridium were used as electrodes. The system was installed within the premises of the Common Effluent Treatment Plant (CETP), which receives effluents from nearly 200 tanneries. The effectiveness of electroflotation for the separation of suspended solids, sulphur species, chromium and other chemicals contributing to COD and BOD were studied. The separation of suspended solids and chromium by electroflotation was nearly complete (>95%) and their concentration in the processed samples can be maintained well below the discharge limits. The removal of COD was observed to be 15–20% greater than with conventional chemical coagulation. Furthermore, the entire spectrum of pathogenic bacteria was eliminated to the extent of 99.97% by subjecting the effluent to electroflotation.     

Coagulant recovery from water treatment plant sludge and reuse in post-treatment of UASB reactor effluent treating municipal wastewater

In the present study, feasibility of recovering the coagulant from water treatment plant sludge with sulphuric acid and reusing it in post-treatment of upflow anaerobic sludge blanket (UASB) reactor effluent treating municipal wastewater were studied. The optimum conditions for coagulant recovery from water treatment plant sludge were investigated using response surface methodology (RSM). Sludge obtained from plants that use polyaluminium chloride (PACl) and alum coagulant was utilised for the study. Effect of three variables, pH, solid content and mixing time was studied using a Box–Behnken statistical experimental design. RSM model was developed based on the experimental aluminium recovery, and the response plots were developed. Results of the study showed significant effects of all the three variables and their interactions in the recovery process. The optimum aluminium recovery of 73.26 and 62.73 % from PACl sludge and alum sludge, respectively, was obtained at pH of 2.0, solid content of 0.5 % and mixing time of 30 min. The recovered coagulant solution had elevated concentrations of certain metals and chemical oxygen demand (COD) which raised concern about its reuse potential in water treatment. Hence, the coagulant recovered from PACl sludge was reused as coagulant for post-treatment of UASB reactor effluent treating municipal wastewater. The recovered coagulant gave 71 % COD, 80 % turbidity, 89 % phosphate, 77 % suspended solids and 99.5 % total coliform removal at 25 mg Al/L. Fresh PACl also gave similar performance but at higher dose of 40 mg Al/L. The results suggest that coagulant can be recovered from water treatment plant sludge and can be used to treat UASB reactor effluent treating municipal wastewater which can reduce the consumption of fresh coagulant in wastewater treatment.     

Electrocoagulation-integrated hybrid membrane processes for the treatment of tannery wastewater

Three different combinations of treatment techniques, i.e. electrocoagulation combined with microfiltration (EMR), membrane bioreactor (MBR) and electrocoagulation integrated with membrane bioreactor (hybrid MBR, (HMBR)), were analysed and compared for the treatment of tannery wastewater operated for 7 days under the constant trans-membrane pressure of 5 kPa. HMBR was found to be most suitable in performance as well as fouling reduction, with 94 % of chemical oxygen demand (COD) removal, 100 % chromium removal and 8 % improvement in percentage reduction in permeate flux compared to MBR with only 90 % COD removal and 67 % chromium removal. The effect of mixed liquor suspended solids on fouling was also investigated and was found to be insignificant. EMR was capable of elevating the flux but was not as efficient as HMBR and MBR in COD removal. Fouling reduction by HMBR was further confirmed by SEM-EDX and particle size analysis.     

Removal of arsenic from water by electrocoagulation

In the present study electrocoagulation (EC) has been evaluated as a treatment technology for arsenite [As(III)] and arsenate [As(V)] removal from water. Laboratory scale experiments were conducted with three electrode materials namely, iron, aluminum and titanium to assess their efficiency. Arsenic removal obtained was highest with iron electrodes. EC was able to bring down aqueous phase arsenic concentration to less than 10 microgl(-1) with iron electrodes. Current density was varied from 0.65 to 1.53 mAcm(-2) and it was observed that higher current density achieved rapid arsenic removal. Experimental results at different current densities indicated that arsenic removal was normalized with respect to total charge passed and therefore charge density has been used to compare the results. Effect of pH on arsenic removal was not significant in the pH range 6-8. Comparative evaluation of As(III) and As(V) removal by chemical coagulation (with ferric chloride) and electrocoagulation has been done. The comparison revealed that EC has better removal efficiency for As(III), whereas As(V) removal by both processes was nearly same. The removal mechanism of As(III) by EC seems to be oxidation of As(III) to As(V) and subsequent removal by adsorption/complexation with metal hydroxides generated in the process.     

Municipal wastewater treatment using novel constructed soil filter system

The study gives a new approach for contaminant removal from municipal wastewater using constructed soil filter (CSF) and presents performance of two CSF units located in Mumbai, India. In this system, natural weathered rock is formulated which combines sedimentation, infiltration and biochemical processes to remove suspended solids and oxidisable organics and inorganics of the wastewater. Results show elevated dissolved oxygen (DO) levels, removal of COD (136-205 to 38-40 mg l(-1)) and BOD (80-125 to less than 12 mg l(-1)) suspended solids from 135-203 to 13-18 mg l(-1) and turbidity from 84-124 to 8-11 NTU, bacterial removal of 2.4-3.1 log order for Total coliform and Fecal coliform from site I which is almost 8 years old facility, and site II which is 3 years old. Estimated hydraulic retention time of 0.5-1.0 h, hydraulic loading of 0.036-0.047 m(3)m(-2)h(-1), no pretreatment, high DO levels in the effluent, no bio-sludge production, no mechanical aeration, low energy requirement (0.04 kW h m(-3)) and green aesthetic ambience are its unique features.     

Biodegradation and toxicity of wastewater from industry producing mineral fibres for thermal insulation

The water chemistry, toxicity, and biodegradation of wastewater from an industry producing mineral fibres for thermal insulation were studied. Values for COD, BOD5, suspended solids, and phenol exceeded permissible values for the wastewater discharged into a nearby river and acute toxicity was also detected. Consequently, the effluent should be treated in a municipal wastewater treatment plant so its ready biodegradability was investigated. We found that the wastewater was readily biodegradable, therefore we assume it can be treated in the wastewater treatment plant as the ratio of the wastewater flow rate and the minimal total inflow into the sewage treatment plant would be one to at least 30.     

Phosphorus removal from municipal wastewater by hydrous ferric oxide reactive filtration and coupled chemically enhanced secondary treatment: part I--performance.

This work examines the performance of a hydrous ferric oxide (HFO) reactive filtration (RF) process with coupled chemically enhanced secondary treatment (RECYCLE) for phosphorus removal from municipal wastewater (HFO-RF-RECYCLE). A 3-month, 0.95-ML/d (0.25-mgd) demonstration of HFO-RF-RECYCLE was performed at a municipal wastewater treatment plant equipped with oxidation ditches and secondary clarifiers. Influent to the plant averaged 6.0 mg/L phosphorus, with a tertiary effluent average of 0.011 mg/L phosphorus. Iron doses to the plant were low, at 5 mg/L. Inline recycling of HFO solution rejects to the plant influent resulted in a maximum 90.3%, dose-dependent reduction of phosphorus in the secondary effluent at 4.5 ML/d (1.2 mgd). Other results included reduction of total suspended solids and turbidity. A mass balance analysis was performed. We conclude that HFO-RF-RECYCLE may allow very low levels of phosphorus discharge from municipal wastewater treatment plants with a ferric-iron-based tertiary filtration process and residual recycling.     

三维电极法处理钻井废水影响因素分析

采取电化学法处理某钻井废水,考察了三维电极系统处理钻井废水时,废水浓度、电流密度、处理时间、电解质浓度和pH值对废水COD降解率的影响,实验结果表明,三维电极法处理钻井废水效果显著;增大电流密度、提高电解质浓度和延长处理时间能使COD去除率提高;最佳pH值为9。正交实验得到最优水平组合为A2B3C2D3E4,在此条件下COD去除率为86.56%。