Simultaneous removal of organic and inorganic pollutants in tannery wastewater using electrocoagulation technique

Tannery wastewater can cause severe environmental problems related to its high chemical oxygen demand, high biochemical oxygen demand, high total suspended solids, high oil and grease contents together with the elevated chromium concentration and objectionable color. The one-step electrocoagulation process was carried out to simultaneously remove chromium and various pollutants from tannery wastewater at ambient temperature in the laboratory scale. Low-cost commercial iron plates were employed in this study as anodes and cathode materials. Effects of various parameters were investigated including types of electrode configuration, initial pH of wastewater (7–9), current density (15.7–24.6 Am⁻²) and circulating flow rate of wastewater (0–3.67 lmin⁻¹). The optimum condition was found by applying the mono-polar electrode in a parallel connection at the current density of 22.4 Am⁻², flow rate of wastewater of 3.67 lmin⁻¹ and 20 min electrolysis time. The initial pH of wastewater ranging from 7–9 provided the similar removal efficiency. At optimum condition, more than 95% of chromium and pollutants except TKN and TDS were eliminated from the wastewater and the properties of the treated wastewater met the standard and permitted to discharge into the environment. The required energy consumption at optimum condition was less than 0.13 kWhm⁻³ wastewater. In addition, the COD reduction was fit very well with the first-order kinetics model.     

Investigation of shipyard wastewater treatment using electrocoagulation process with Al electrodes

In this study, shipyard oily wastewater treatment was investigated by electrocoagulation (EC) using aluminum electrodes in a batch reactor by evaluating different operation conditions. The maximum chemical oxygen demand (COD) removal efficiency of 88.83% was obtained at current density of 3 mA/cm². The removal efficiency was gradually improved with increasing current density and decreased with increasing COD concentration. However, initial pH value was not determinant factor for this process. Total energy and electrode cost were calculated as $0.88 per m³ treated wastewater. The result of this research shows that EC process seems to be an efficient method for the oily wastewater treatment.     

电絮凝法处理含油废水的研究

通过石墨-石墨、铝-石墨、铅-石墨、铁-石墨和铝-铁等5种电极组合分别处理含32#机油的废水。研究发现，铝-石墨为最佳电极组合，通过正交实验设计，选择固体悬浮物(SS)、化学需氧量(COD)和含油量的去除率较大的条件是：电解质(NaCl)为3g，电解电压为10V，电解时间为25min。     

Treatment of dairy wastewater by electrocoagulation process: Advantages of combined iron/aluminum electrodes

ABSTRACT

The objective was to assess the efficiency of electrode material in an electrocoagulation (EC) process for wastewater treatment by comparing the efficiency of aluminum (Al–Al), iron (Fe–Fe) and combined Fe–Al electrodes. The treatment of synthetic dairy wastewater, characterized by high levels of 5-day biological oxygen demand (BOD₅) and chemical oxygen demand (COD), was used to compare electrode materials. Experimental results showed that all electrodes materials achieved the same final removal yield in the range of current studied (55% COD, 60% total organic carbon, 90% total nitrogen, and nearly 100% turbidity) when equilibrium was achieved. But at fixed current density and initial concentration of dairy waste, the Al–Al assembly exhibited the fastest elimination, whereas the slowest removal rate was observed with the Fe–Fe electrodes, even though adsorption was always the main removal mechanism. Finally, an Fe–Al system using an Fe anode with an Al cathode emerged as a techno-economic trade-off because of the low price of iron: both metals contributed to the removal of dairy waste, and the treatment time to achieve equilibrium values was closer to the Al–Al assembly at fixed current density. Moreover, experimental results proved the additivity of the mechanisms reported for Al–Al and Fe–Fe systems with Fe–Al.     

Heavy metal ions removal from wastewater using electrocoagulation processes: A comprehensive review

A vast number of publications have investigated the application of electrocoagulation (EC) process in heavy metal ions removal from wastewaters. Most of these studies were simple lab-scale using synthetic wastewater with the absence of holistic and systematic approach to consider the process complexity. This comprehensive review considers the fundamental aspects of EC processes such as mechanisms, kinetic models, and isotherm models used by different researchers. Furthermore, the impact of the main design and process operational parameters on the removal efficiency is discussed and analyzed. Many concluding remarks and perspectives are stated to give insights for possible future investigations.     

Comparison of electrocoagulation and chemical coagulation with fiber filters for water treatment

A combined electrocoagulation(EC)-fiber filter system has been presented as a new technology for water treatment. The objective of this study was to evaluate the feasibility of applying an aluminum EC-fiber filter for water treatment. We compared the water treatment efficiency of the chemical coagulation (CC)-fiber filter and EC-fiber filter. A comparison of the EC and CC processes reveals that EC significantly outperformed CC when the water to be filtered using fiber filters was pretreated with aluminum. For particle size less than 6 μm, the removal efficiency was 66%, 43% for EC and CC, respectively, and the average removal efficiency of the total organic carbon (TOC) was 50%, 65% for CC and EC. Therefore, EC reduced the amount of aluminum utilized by 25%, and the effluent turbidity improved by approximately 0.11 NTU to 0.19 NTU. Also, the average log removal value (LRV) for heterotrophic plate count (HPC) was 2.5 and 1.9 for EC and CC. respectively. Therefore, the aluminum used for EC proved to be excellent for pretreating the water to be filtered by a fiber filter.     

Oilfield produced water treatment in internal-loop airlift reactor using electrocoagulation/flotation technique

Oilfield produced water is large quantities of salty water trapped in underground formations and subsisted under high temperatures and pressures that are brought to the surface along with oil during production. Produced water(PW) contains a lot of pollutants such as hydrocarbons and metals, this water must be treated before disposal. Therefore, different techniques are being used to treat produced water. Electrocoagulation is an efficient treatment technique involving the dissolution of anodes and formation of electro-coagulants, while the simultaneous generation of H_2 bubbles at the cathode leads to the pollutant removal by flotation. Electrocoagulation(EC)method is one of the most promising and widely used processes to treat oilfield produced water. In the present work, a conventional internal-loop(draught tube) airlift reactor was utilized as electrocoagulation/flotation cell for PW treatment by inserting two aluminum electrodes in the riser section of the airlift reactor. The EC airlift reactor was operated in a batch mode for the liquid phase. Different experimental parameters were studied on the oil and turbidity removal efficiencies such as current density, initial pH, electrocoagulation time, and air injection.The experimental results showed that mixing of the oil droplets in the PW was accomplished using only the liquid recirculation resulted by H_2 microbubbles generated by EC process which enhanced the oil removal. The experimental results further showed that the EC time required achieving ≥ 90% oil removal efficiency decreases from 46 to 15 min when operating current density increases from 6.8 to 45.5 mA·cm~(-2). This reactor type was found to be highly efficient and less energy consuming compared to conventional existing electrochemical cells which used mechanical agitation.     

Mass-producible low-cost flexible electronic fabrics for azo dye wastewater treatment by electrocoagulation

Electrocoagulation is progressively becoming an ecologically friendly water treatment method owing to its lack of secondary pollution,high active ingredient concentration,high treatment effectiveness,simple equipment,and simplicity of automated control implementation.Herein,electrocoagulation is offered as a method for treating wastewater containing azo dyes using a revolutionary flexible electronic fabric that can be mass-producible at a reasonable price.A computer-controlled machine embroiders...     

Treatment of potato chips manufacturing wastewater by electrocoagulation

Treatment of wastewater from potato chips manufacturing by electrocoagulation (EC) was investigated. Experiments were conducted to determine the optimum operating conditions such as electrode type, pH, current density and retention time. Aluminium and iron electrodes were used, and aluminium electrodes were found to be more suitable since it had a higher removal rate of COD, turbidity and suspended solids than the iron electrode. The removal efficiencies of COD and turbidity were high, being 60% and 98%, respectively, with retention time < 40 min. 0.05–1.75 kg (per kg COD removed) of dried sludge was removed. COD removal kinetics during EC process was described by a macro-kinetics model. Results from the kinetic studies showed that the kinetic data fit the second-order kinetic model well. The operating costs investigated in the present study were the energy cost of EC and the material cost due to the consumption of aluminium electrode. Operating costs were varied in the range of 0.48 to 5.42 $/m³ and 0.62 to 6.32 $/m³ wastewater treated at 20–300 A/m² and 5–40 min, respectively. The energy consumption was 4 kWh/m³ for wastewater treated less than 8 min under typical operating conditions.     

陶瓷膜在染料及漂染废水处理中的应用

考察了以陶瓷膜为过滤介质的旋叶压滤机对絮凝后的废水进行处理的过滤速率及其影响因素,进行了动态过滤与终端过滤的比较,以及陶瓷膜与有机膜在废水处理效果上的对比研究。     

Charged modified tight ceramic ultrafiltration membranes for treatment of cationic dye wastewater

Tight ceramic uitrafiltration membranes have been proven to exhibit good rejection performance for reactive dye wastewater at high temperatures because of their high thermal and chemical resistance.However,the application of ceramic membranes for the treatment of cationic dye wastewater is chal-lenging because of their surface charge.In this study,a ceramic membrane is modified by grafting aminosilane (KH-551) to enhance the positive charge of the membrane surface.The rejection perfor-mance of the charged modified ceramic membrane toward the methylene blue solution is significantly improved.The modification substance is bonded to the ceramic membrane surface via covalent bonding,which imparts good thermal stability.The modified ceramic membrane exhibits stable separation perfor-mance toward the methylene blue solution.Overall,this study provides valuable guidance for the adjust-ment of the ceramic membrane surface charge for treating industrial cationic dye wastewater.     

染料工业废水处理研究进展

综述了染料工业废水处理方法的研究进展,主要介绍了物理法、化学法、电化学法、生化法中各种方法的特点、原理及其近年来应用的新技术和研究进展。     

The effects of alternating current electrocoagulation on dye removal from aqueous solutions

The main goal of this study is to investigate the effects of alternating current (AC) on dye removal from aqueous solutions by electrocoagulation (EC). An EC system with parallel-connected aluminium electrodes was operated in batch mode. Two different aqueous dye solutions were used: one was obtained from Dianix Yellow CC (DY) and the other was obtained using Procion Yellow (PY). The experiments employing direct current (DC) were carried out using a DC power supply. The AC experiments were conducted using rectangular wave, which is produced with an adjustable time relay connected to the output of DC power supply. This current is called alternating pulse current (APC) in order to refer AC system in this study. Total organic carbon (TOC) and dye removal efficiencies were measured to assess treatment efficiency. Operating cost was calculated for both power supply systems and alternating pulse current was found superior to direct current for the treatment of reactive and disperse dyes used in this study.     

胶原多肽基表面活性剂对染料废水的泡沫分离性能

以结晶紫溶液模拟染料废水,研究了胶原多肽基表面活性剂(CBS)对染料废水的泡沫分离性能。通过单因素实验考察了pH、气速、表面活性剂质量浓度、泡沫相与液相高度比(H_F/H_L)、染料初始浓度、乙醇添加量等因素对废水中染料分离的影响。结果表明,CBS适用于碱性条件下染料废水的泡沫分离;随着气速的升高,染料的去除率增加,但富集比降低;随着CBS用量的增加,染料的去除率先增加而后降低,富集比随CBS用量的增加而降低;当泡沫相高度与液相高度比为3左右时,染料去除率较高;添加适量的乙醇对泡沫分离是有利的;在较佳的分离条件下,染料的去除率可达80%,富集比达到16。上述研究结果表明,胶原多肽基表面活性剂可用于染料废水的泡沫分离。     

3D printing of NiZn ferrite architectures with high magnetic performance for efficient magnetic separation

Magnetic materials with desired architectures and high performance have become increasingly important for applications. In this work, NiZn ferrites with mesh structures have been successfully fabricated from preliminary precursors by three-dimensional (3D) printing accompanied by the solid-state reaction. The influence of compositions on structural and magnetic properties of NiZn ferrites were systematically investigated. It was obvious that the saturation magnetization was significantly enhanced to 77 emu/g for NiZn ferrites with a zinc concentration of 0.4, which was a much higher value compared to Ni ferrites. This is attributed not only to the well-known cationic distribution, but also to the grain growth with extraordinarily high crystallinity. Consequently, NiZn ferrites with intricate mesh structures were utilized for magnetic separation, and the distributions of magnetic flux density were simulated. Overall, the fabrication of NiZn ferrites by 3D printing is attractive for scaled-up applications, and also paves the promising avenue for magnetic separation.     

高级氧化技术处理染料废水的研究进展

由于染料废水中含有高浓度难降解有机污染物,对其有效处理一直是个难题.综述了近几年国内外采用湿式氧化法、Fenton法、光化学与光催化氧化法、电化学法、臭氧氧化法、微波辅助氧化法和超声氧化法等高级氧化技术处理染料废水的进展情况,并指出了高级氧化技术在染料废水处理中的发展趋势.     

对氯甲苯的合成与分离工艺评述

介绍了国内外对氯甲苯的合成与分离工艺。     

Development of bubble column for foam separation

The foam separation of metal in model wastewater is performed by using two different bubble columns in a continuous operation mode. The equipment and operation conditions are changed, and the foam flow rate and metal concentration in foam flow are measured. The foam flow ratio (the ratio of foam flow rate to the inlet one) increases with increasing gas velocity, with decreasing liquid velocity, with decreasing foam layer height and with decreasing metal concentration in model wastewater. Metal enrichment (the ratio of metal concentration in foam flow to that in inlet flow) shows the reverse tendencies. When a draft tube is inserted in the bubbling layer, the foam flow rate decreases. The enrichment is strongly governed by the foam flow ratio. Since the foam flow ratio is adjusted by means of the equipment and operation conditions, the metal concentration in foam flow is controlled to be a desired value. This paper was presented at The 5th International Symposium on Separation Technology-Korea and Japan held at Seoul between August 19 and 21, 1999.     

A comparison between catalytic ozonation and activated carbon adsorption/ozone-regeneration processes for wastewater treatment

Two methods based on the use of granular activated carbon (GAC) and ozone to remove organic compounds from water have been investigated. Both methods have been applied to degrade an aqueous solution of gallic acid and a secondary effluent from a wastewater treatment plant (WWTP). One of the methods, namely catalytic ozonation, implies simultaneous ozonation and adsorption onto GAC. This process takes advantage of the oxidizing power of ozone and the adsorption capacity of GAC but also of the catalytic transformation of ozone into secondary oxidants on the GAC surface. The efficiency of catalytic ozonation was compared to those of single adsorption and single ozonation. It was found that the catalytic process highly improves the conversion of total organic carbon (TOC) and makes a more efficient use of ozone than the single ozonation process. To illustrate the reusability of the catalyst, the GAC was reused four times through a series of consecutive experiments. No loss of catalytic activity was observed when treating the WWTP effluent but some deactivation could be appreciated when treating the aqueous solution of gallic acid. This deactivation could be attributed to some porosity destruction and surface oxidation produced as a result of reactions of aqueous ozone on the GAC surface. The other method investigated is an adsorption-regeneration process (namely GAC/O₃-regeneration) that comprises two steps: dynamic adsorption onto GAC and further regeneration of the spent GAC with gaseous ozone. The adsorption stage of the GAC/O₃-regeneration experiments was carried out in a continuous flow adsorption column and breakthrough curves were obtained. It was observed that the GAC used in this work adsorbed gallic acid very efficiently but exhibited limited capacity to remove chemical oxygen demand (COD) from the WWTP effluent. The optimum ozone dose to regenerate the spent GAC after gallic acid adsorption was found to be about 0.4 g O₃/g GAC, with results showing around 90% regeneration efficiency. As a result of incomplete regeneration, the GAC adsorption capacity progressively decreased with the number of adsorption–regeneration cycles. The GAC/O₃-regeneration method was not successful at treating the WWTP effluent as low adsorption uptake was observed. Moreover, the GAC became damaged after regeneration because of excessive oxidation of its surface.     

Simultaneous treatment of dye wastewater and surfactant wastewater by foam separation: Experimental and mesoscopic simulation study

Foam separation for simultaneous removal of rhodamine B (RhB) and cetyl trimethyl ammonium bromide (CTAB)/sodium dodecyl benzene sulfonate (SDBS) from model wastewater was studied. The effect of the surfactant type, aeration rate, temperature, and initial pH on the removal efficiency and enrichment ratio of dye/surfactant were investigated. The results indicated that electrostatic attraction between the dye and surfactant have a great effect on the recovery of the dye and surfactant. The aeration rate has significant influence on the CTAB and RhB removal and enrichment, while the initial pH has a great effect on the RhB removal, but little effect on CTAB removal. Moreover, dissipative particle dynamics (DPD) was employed to simulate the interaction between the surfactant and the dye.