Removal of chemical oxygen demand from textile wastewater using a natural coagulant

A biomaterial was successfully synthesized from Plantago ovata by using an FeCl₃-induced crude extract (FCE). The potential of FCE to act as a natural coagulant was tested for the pretreatment of real textile wastewater. Tests were performed to evaluate the effects of FCE quantity, salt concentration, and wastewater pH on chemical oxygen demand (COD) reduction during a coagulation/flocculation process. Experimental results indicated that the wastewater could be effectively treated by using a coagulation/flocculation process, where the BOD₅/COD ratio of the effluent was improved to 0.48. A low coagulant dose, 1.5mg/L, achieved a high COD removal percentage, 89%, at operational conditions of neutral pH and room temperature. The experimental data revealed that the maximum COD removal occurred at water pH<8. Increasing the salt promoted the COD removal. The settling and filterability characteristics of the sludge were also studied. Scanning electron microscopy and energy dispersive spectroscopy studies were conducted to determine the sludge structure and composition, respectively. Overall, FCE as an eco-friendly biomaterial was revealed to be a very efficient coagulant and a promising option for the removal of COD from wastewaters.     

Treatments of stainless steel wastewater containing a high concentration of nitrate using reverse osmosis and nanomembranes

A nanomembrane (NTR 729HF) and three different types of reverse osmosis (RO) membranes (CPA2, LFC1, and ESPA1) were tested for the treatment of high concentration of nitrate wastewater from stainless steel industry. All the tested RO membranes showed higher rejection rates (90–99% at 1000–60 mg/L of NO₃⁻ -N) than the NF membrane. The rejection rate and flux of RO membranes were not highly affected by pH variation and Ca²⁺ as co-existing ion. However, the rejection rate of NF, which was 67% at 60 mg/L of feed concentration, was decreased as pH decreased and Ca²⁺ concentration increased indicating that charge repulsion is one of the major rejection mechanisms. As nitrate concentration increased from 20 to 1000 mg/L in feed water, the removal rate decreased from 67 to 20% in NF membrane. The flux of RO was relatively high and ESPA1 (a low-pressure RO type) showed more than two times higher flux compared to the NF. ESPA1 was successfully tested for a longterm experiment with real stainless steel wastewater for 30 days of experimental period. Current study implicates that RO membranes could be an alternative for the treatment of stainless steel wastewater.     

High temperature desulphurization by fine limestone during staged fluidized‐bed combustion

This paper reviews the SO₂ emission from a 0.3 m² stainless‐steel fluidized‐bed combustor. Fine coal was premixed with fine limestone and fed pneumatically under the bed. The SO₂ emission was found to depend largely on air staging ratio and bed temperature, which agrees with previous observations. The SO₂ emission observed in sorbent‐free tests (reported earlier by Khan and Cibbs, 1995) was found to be proportional to the sulphur content of the fuel when limestone was added, the sulphur capture at a fixed Ca/S molar ratio was dependent on oxygen stoichiometry and bed temperature. Finely sized limestone enhanced the effectivity of the sorbent at low bed temperature and air staging ratio. During staged combustion, the combustion efficiency depended largely on primary air to coal ratio. Around 90% combustion efficiency was observed at 1 m/s fluidizing velocity which was reduced when fluidizing velocity was increased to 1.5 and 2 m/s. This reduction is due to increased elutriation of finer coal particles from the combustor.     

Electrochemical peroxidation as a tool to remove arsenic and copper from smelter wastewater

Electrochemical peroxidation (ECP) is a method that recently has been applied in the treatment of heavy metal polluted wastewater. This method is based on the anodic dissolution of iron to ferrous ions that reacts with H₂O₂ to produce tiny particles of ferric oxides. These oxides adsorb metals efficiently from aqueous solutions. In the present study, the technique was tested experimentally on copper smelter wastewaters with high concentrations of copper and arsenic. A completely mixed airlift batch reactor was used, and the copper and arsenic removal was measured both for synthetic and real wastewater samples. The concentric iron electrodes acted as ferrous ion source when applying a constant direct current with current reversal every minute and the H₂O₂ was added dropwise. Initial pH was fixed at 3.5, 5.0 and 6.5, respectively. The best results with the synthetic wastewater showed >99% removal of copper and 80% removal of arsenic (at pH 6.5). When treating the real wastewater samples, both arsenic and copper could be removed more than 99% for all pH levels studied. It can be concluded that presence of other substances in the real wastewater favours the arsenic adsorption and/or precipitation. The copper and arsenic removal velocity was found to be dependent of pH—with the fastest removal at pH 3.5. The ECP could be regarded as a promising remediation method for treating highly contaminated wastewaters since arsenic (from 1000 mg L⁻¹) and copper (from 300 mg L⁻¹) was removed nearly completely from copper smelter wastewaters.     

A one-step electrochlorination/electroflotation process for the treatment of heavy metals wastewater in presence of EDTA

This study demonstrated the feasibility of simultaneous removal of heavy metals and EDTA in an electrolytic undivided cell equipped with Ti/RuO₂ as anode and stainless steel as cathode. In absence of EDTA, results show that nickel and copper removal by EF process is pH sensitive. In addition, nickel and copper may be substantially removed by EF. Removal efficiencies were 99.6% and 97%, respectively. In presence of EDTA, the metal removal by the EF process was inhibited. The inhibition rate was found to be dependent on EDTA/metal molar ratio. A one-step process, involving the combination of two techniques electrochlorination (EC) and electroflotation (EF), was set thanks to chloride addition. In situ generated active chlorine allowed the decomplexation of M-EDTA. Then, free metal ions were removed by precipitating and subsequent floating to the surface by rising electrogenerated bubbles. The obtained results revealed that, with 0.6 EDTA/metal molar ratio, removal efficiencies were 77% and 78% for nickel and EDTA, respectively, in the case of nickel–EDTA solutions. Removal efficiencies were 89% and 96% for copper and EDTA, respectively, in the case of copper–EDTA solutions. Furthermore, heavy metal removal efficiency by the combined process showed to be affected by chloride content and current intensity.     

Simultaneous removal of chromium and organic pollutants in tannery wastewater by electroprecipitation technique

The simultaneous removal of chromium and other organic pollutants from tannery wastewater was investigated in a batch electrochemical membrane reactor. This reactor, having a total capacity of 1 liter, was separated into two compartments (anodic and cathodic compartments) by using an anionic membrane. A stainless steel sheet with the square holes having total surface area of 0.0215 m² and a Ti/RuO₂ grid was used as the cathode and anode, respectively. The results indicated that the optimum condition for removal of chromium from tannery wastewater was found at the current density of 60.5 A/m² at initial pH of 4.5. At this condition, more than 98% of chromium was removed within 60 min. Some organic pollutants contained in wastewater such as oil and grease, color and the level of biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total kjeldahl nitrogen (TKN) were also markedly reduced.     

电-Fenton预处理兰炭废水

采用电-Fenton法预处理煤低温干馏兰炭废水,考察了阴极材料、反应时间、反应p H值、电流密度和极板间距对电-Fenton反应的影响。最后选择不锈钢板作为阳极,石墨板作为阴极,最佳试验条件为电反应p H值为4.0,反应时间为150 min,极板间距为3 cm,电流密度为5.0 m A/cm2。在此最佳条件下,CODCr去除率达到57.30%,该方法为治理兰炭废水提供了借鉴思路。     

Fenton氧化–曝气生物滤池处理电镀铜镍废水的研究

采用Fenton氧化–曝气生物滤池(BAF)组合工艺对电镀铜镍废水进行了处理。研究了初始pH、ρ(Fe2+)/ρ(H2O2)比值以及H2O2投加量对CODCr去除率的影响,并对该组合工艺进行了经济分析。试验结果表明,经该组合工艺处理后,废水中CODCr去除率达到86%,Cu2+、Ni2+浓度均符合相关排放标准。     

Removal of Arsenic from Wastewaters by Airlift Electrocoagulation: Part 3: Copper Smelter Wastewater Treatment

The arsenic content in wastewater is of major concern for copper smelters. A typical complex wastewater treatment is needed with a combination of chemical and physical processes. Electrocoagulation (EC) has shown its potential for arsenic removal due to the formation of ferric hydroxide-arsenate precipitates. This work evaluates the feasibility of EC as a treatment process at various stages during conventional copper smelter wastewater treatment – with a focus on arsenic. The reactor used is a batch airlift electrocoagulator. The results showed that raw copper smelter wastewater was difficult to treat for arsenic and heavy metals with EC, mainly due to the very low pH. On the other hand, after a preliminary Ca(OH)₂ treatment for sulphate and heavy metal removal, arsenic could be removed totally by EC. In addition, EC could also be applied as a final remediation control tool for arsenic since the national threshold value for wastewater discharge could rapidly be reached when the conventional method did not clean the wastewater sufficiently.     

Removal of Copper in Aqueous Solution by Apple Wastes

Abstract

Removal of copper from a solution was investigated to evaluate the cation-exchange capacities of apple residues from agricultural wastes. The effects of solution pH, ionic strength, co-ion, ligands, initial metal concentrations, and particle size of apple residues were studied. The optimal pH range for copper removal by apple residues was shown to be from pH 5.5 to 7.0, and the maximum percentage of copper removal was 91.2%. Increasing ionic strength, up to 0.1 N, has little effect on metal uptake. The presence of co-ions such as lead decreases the removal capacity of copper as expected. The presence of ligands, such as EDTA and ammonia, also reduces metal removal efficiency due to the formation of a metal-ligand complexation in solution. Equilibrium of copper sorption was established very rapidly initially and decreased markedly after 1 hour. Equilibrium isotherms of copper fit the Langmuir equation adequately. Column experiments showed that the dynamic capacity of chemically modified apple residues was four to five times higher than that of raw residues which contained acidic groups such as carboxylic and phenolic functional groups. The adsorbed copper ions were completely recovered with three bed volumes of 0.5 N HCl. Thus, modified apple residues could be applied successfully for metal removal from wastewater.     

Anode-support system for the direct electrorefining of cement copper Part III: Pretreatment and process conditions to refine industrial cement

This paper describes the final part of a study on the utilization of a special anode-support system for the electrorefining of industrial cement copper produced by small mines. This type of cement is obtained from the leaching solutions of copper oxide minerals by precipitation with iron scrap. The cement is highly contaminated with iron, different metallic and non-metallic compounds and chloride. Therefore it is necessary to purify the cement copper before the electrorefining process. A two-stage method of purification is proposed, washing with water (pH4) to eliminate chloride and soluble species and magnetic removal of the metallic iron. A circular cell provided with an annular AISI-316 stainless steel mesh supporting the mass of cement copper was utilized. A vertical rotary cylinder of AISI-316 stainless steel was used as the cathode. As operating conditions, a solution of CuSO4.5H2O: 150gdm-3 and H2SO4: 50gdm-3, jc: 5.0Adm-2, T: 40°C, u: 60rpm, were used. A cement copper of 85% purity was utilized. Under these recommended operating conditions it is possible to obtain copper sheets of good quality, meeting the ASTM B-11591 specification for commercial cathodes.     

电化学法对印染废水CODCr的处理效果研究

印染废水成分复杂,可生化降解性差。采用Fe-PbO2/不锈钢为阳极,不锈钢为阴极,活性炭为颗粒电极,电催化氧化处理上海某印染厂废水。当pH为3,电流密度为0.028 A/cm2,硫酸铝浓度为0.16 mol/L,极板距离为6 cm,电解时间为10 min时CODCr去除率达到71.1%,BOD5/CODCr由处理前的0.126上升为0.34,可生化降解性明显提高。Fe-PbO2/不锈钢阳极和不锈钢阳极在印染废水中的循环伏安曲线表明镀PbO2层的不锈钢电极具有较好的催化活性。     

磁絮凝去除工业废水中铜离子的试验研究

采用磁絮凝对工业废水中重金属铜离子进行试验研究,讨论了聚合硫酸铁(PFS)投加量、静沉时间、温度、pH值、磁粉投加量对处理效果的影响.试验结果表明PFS投加量为100mg/L,pH值为8.0,静沉时间为20min,磁粉投加量为400mg/L时对含铜废水有良好的处理效果,铜离子去除率超过了97%,出水铜离子的质量浓度低于...     

CO2对石灰石脱硫剂的活化作用

在间歇式鼓泡反应器的烟气脱硫实验装置中,研究了CO2气体活化处理对石灰石脱硫剂浆液烟气脱硫效率的影响. 依据脱硫过程中石灰石脱硫剂浆液pH值随脱硫反应时间的变化规律,初步分析了CO2对石灰石脱硫剂的活化作用及活化后石灰石脱硫剂的烟气脱硫过程机理. 结果表明,CO2气体的活化处理促进了石灰石在水溶液中的溶解,进而改善了石灰石脱硫剂浆液的烟气脱硫反应活性,使处理后的石灰石脱硫剂浆液的烟气脱硫效率和脱硫剂的利用率提高. 基于流化床反应器连续过程的实验结果,证实了CO2对石灰石脱硫剂的活化作用. 为提高石灰石在烟气脱硫中的反应活性提供了一种新的工艺,可用于烟气脱硫中对石灰石脱硫剂浆液的活化.     

Simultaneous treatment of semiconductor wastewater and distillery slops by mixing and precipitation/coagulation

Organic matter (chemical oxygen demand, COD) removal with decolorization in waste distillery slops and copper removal in a semiconductor industry wastewater were achieved in a single step mixing and precipitation/coagulation treatment system. The process utilized the complementary properties of the positively charged copper ions in semiconductor wastewater and net negative charge of melanoidin (organic chromophoric pollutant) in distillery slops to mutually neutralize each other. Copper ions served as coagulant for slops and melanoidin served as precipitant for copper. The volumetric ratio of the wastewater and pH were optimized to attain maximum removal of organic matter and copper. The optimum volumetric ratio for the evaluated semiconductor wastewater to distillery slops was found to be 2–3 with an equilibrium pH of around pH 6. At optimum conditions, average removals of COD and copper were 86% and 92%, respectively, in an actual and undiluted system. Decolorization efficiency using the diluted distillery slops was 89%. The process can be considered an effective pretreatment procedure for simultaneous gross removal of copper and color/COD, particularly in highly concentrated waste streams. Copyright © 2005 Society of Chemical Industry     

厌氧生物法处理皂素废水的试验研究

采用UASB厌氧反应器处理高浓度皂素废水,试验结果表明,当温度控制在35～40℃、pH在6.8～7.5之间、COD容积负荷保持在6.0kg/(m3.d)时,COD去除率可达到90%以上。     

上流式厌氧污泥床反应器处理凉果废水性能研究

采用上流式厌氧污泥床反应器(UASB)法处理凉果废水,考察废水厌氧处理过程中COD、浊度、脱色率、pH、电导率、悬浮物去除率的变化规律。结果表明:随着厌氧时间的增加,UASB反应器对废水的处理效果不断提高。在最适宜的厌氧时间条件下,废水的COD去除率达62.0%、浊度去除率达41.1%、吸光度及脱色率分别为0.498及48.4%、pH为5.4、悬浮物去除率达30.3%。故,UASB法可作为凉果废水的预处理方式,以降低后续废水的好氧处理难度。     

Remineralization of desalinated water by limestone dissolution filter

Remineralization by the limestone process is now widely used in the post-treatment sections of MSF desalination plants and RO plants.This paper discusses the optimization of the process design based on our experiments, process simulation and the data obtained from actual plant operation. The following aspects were considered.

• &#x02022;- evaluation of limestone dissolution kinetics.
• &#x02022;- design parameters of limestone filter bed, such as LHSV, particle size, CO₂ concentration, etc.
• &#x02022;- effect of backwashing
• &#x02022;- CO₂ availability from MSFE venting system.
• &#x02022;- residual CO₂ desorption before a alkali dosing, etc.

Through this study, the residual CO₂ desorption process by a simple air bubble column has been developed.With the application of this process, alkali consumption for pH adjustment is remarkably reduced and a high by-pass ratio of limestone filter (about 70%) can be realized. This process will contribute to reduce not only the variable cost, but the fixed cost of a remineralization plant.     

Selective removal of copper ions from multi‐component aqueous solutions using modified silica impregnated with LIX 84

A silica support impregnated with 2‐hydroxy‐5‐nonylacetophenone oxime (LIX 84) was prepared after surface modification by ‐aminopropyltriethoxysilane. Fixed‐bed tests were conducted to investigate the capabilities of the prepared adsorbent with respect to the selective removal of copper ions from multi‐metal solutions. Break‐through curves were obtained using the modified silica for a solution containing Cu²⁺, Cd²⁺, Ni²⁺, Co²⁺ and Zn²⁺, as well as an industrial electronics wastewater sample. The copper adsorption capacities for the multi‐metal solution and the wastewater were 0.175 and 0.198 mmolg⁻¹, respectively under the conditions used in this study. The copper recovery ratios for the modified silica treated with the multi‐metal solution and the wastewater were 86 and 91%, respectively after treating with 0.1 moldm⁻³ HNO₃. The results show that the modified silica, prepared here, has potential value for the selective removal of copper ions from multi‐component aqueous solutions containing multi‐metals using a fixed‐bed reactor. © 2000 Society of Chemical Industry     

Low cost adsorbents obtained from ash for copper removal

We investigated the utilization of ash and modified ash as a low-cost adsorbent to remove copper ions from aqueous solutions such as wastewater. Batch experiments were conducted to determine the factors affecting adsorption of copper. The influence of pH, adsorbent dose, initial Cu²⁺ concentration, type of adsorbent and contact time on the adsorption capacity of Cu²⁺ from aqueous solution by the batch adsorption technique using ash and modified ash as a low-cost adsorbent were investigated. The optimum pH required for maximum adsorption was found to be 5. The results from the sorption process showed that the maximum adsorption rate was obtained at 300 mg/L when a different dosage of fly ash was added into the solution, and it can be concluded that decreasing the initial concentration of copper ion is beneficial to the adsorption capacity of the adsorbent. With the increase of pH value, the removal rate increased. When the pH was 5, the removal rate reached the maximum of over 99%. When initial copper content was 300 mg/L and the pH value was 5, the adsorption capacity of the zeolite Z 4 sample reached 27.904 mg/g. The main removal mechanisms were assumed to be the adsorption at the surface of the fly ash together with the precipitation from the solution. The adsorption equilibrium was achieved at pH 5 between 1 and 4 hours in function of type of adsorbent. A dose of 1: 25 g/mL of adsorbent was sufficient for the optimum removal of copper ions. For all synthesized adsorbents the predominant mechanism can be described by pseudo-second order kinetics.