Selective demineralization of water by nanofiltration application to the defluorination of brackish water

Nanofiltration is generally used to separate monovalent ions from divalent ions, but it is also possible to separate ions of the same valency by careful application of the transfer mechanisms involved. Analysis of the retention of halide salts reveals that small ions like fluoride are the best retained, and that this is even more marked under reduced pressure when selectivity is greatest. The selectivity desalination of fluorinated brackish water is hence feasible and drinking water can be produced directly at much lower cost than using reverse osmosis by optimizing the pressure for the type of water treated.     

Photo-reductive defluorination of perfluorooctanoic acid in water

Globally distributed and highly stable, perfluorooctanoic acid (PFOA) has prompted much concern regarding its accumulation in the natural environment and its threats to ecosystems. Therefore, it is desirable to develop an effective treatment against PFOA pollution. In this study, a photo-reduction method is developed and evaluated for the decomposition of perfluorooctanoic acid (PFOA) in aqueous phase with potassium iodide (KI) as a mediator. The experiment was conducted under 254 nm irradiation at room temperature and pH 9 under anaerobic conditions. Ultraviolet photolysis of iodide solutions led to the generation of hydrated electrons (e_aq⁻, E_aq/e°= −2.9 V), which contributed to the defluorination of PFOA. Defluorination was confirmed by fluoride release of 98%, indicating almost complete defluorination of PFOA. Kinetic analysis indicated that the PFOA decomposition fit the first-order model with a rate constant of 7.3 × 10⁻³ min⁻¹. Besides fluoride ions, additional intermediates identified and quantified include formic acid, acetic acid, and six short-chain perfluorocarboxylic acids (C1-C6). Furthermore, small amounts of CF₃H and C₂F₆ were also detected as reaction products by using GC/MS. With observation of the degradation products and verification via an isotopic labeling method, two major defluorination pathways of PFOA are proposed: direct cleavage of C-F bonds attacked by hydrated electrons as the nucleophile; and stepwise removal of CF₂ by UV irradiation and hydrolysis. This method was applied to the decomposition of PFOA in wastewater issued from a fluorochemical plant and proved to be effective.     

Effects of water chemistry on arsenic removal from drinking water by electrocoagulation

Exposure to arsenic through drinking water poses a threat to human health. Electrocoagulation is a water treatment technology that involves electrolytic oxidation of anode materials and in-situ generation of coagulant. The electrochemical generation of coagulant is an alternative to using chemical coagulants, and the process can also oxidize As(III) to As(V). Batch electrocoagulation experiments were performed in the laboratory using iron electrodes. The experiments quantified the effects of pH, initial arsenic concentration and oxidation state, and concentrations of dissolved phosphate, silica and sulfate on the rate and extent of arsenic removal. The iron generated during electrocoagulation precipitated as lepidocrocite (γ-FeOOH), except when dissolved silica was present, and arsenic was removed by adsorption to the lepidocrocite. Arsenic removal was slower at higher pH. When solutions initially contained As(III), a portion of the As(III) was oxidized to As(V) during electrocoagulation. As(V) removal was faster than As(III) removal. The presence of 1 and 4 mg/L phosphate inhibited arsenic removal, while the presence of 5 and 20 mg/L silica or 10 and 50 mg/L sulfate had no significant effect on arsenic removal. For most conditions examined in this study, over 99.9% arsenic removal efficiency was achieved. Electrocoagulation was also highly effective at removing arsenic from drinking water in field trials conducted in a village in Eastern India. By using operation times long enough to produce sufficient iron oxide for removal of both phosphate and arsenate, the performance of the systems in field trials was not inhibited by high phosphate concentrations.     

A new design of the electrocoagulation apparatus for removal of micromycetes from water

A new design of the electrocoagulation apparatus consisting of an inert anode and cathode made of stainless steel was developed. The formation of a coagulant takes place due to the corrosion of ferrous plates located in the anode plane. The following optimum parameters for the operation of the apparatus were defined: current density??21 mA/cm², current strength??60 mA, area of ferrous plates??3 cm². The application of this apparatus makes possible to convert efficiently Fe²⁺ to Fe³⁺ allowing the user to reduce the consumption of coagulant and remove to the maximum extent contaminants including micromycetes from water.     

Treatment of dairy effluents by electrocoagulation using aluminium electrodes

This work sets out to examine the efficiency of an electrolytic treatment: electrocoagulation, applied to dairy effluents. The experiments were carried out using a soluble aluminium anode on artificial wastewater derived from solutions of milk powder. The flocks generated during this treatment were separated by filtration. The analysis of the filtrates showed that the chemical oxygen demand (COD) was reduced by up to 61% while the removal of phosphorus, nitrogen contents, and turbidity were 89, 81 and 100%, respectively. An analogous treatment applied to phosphate and lactose solutions revealed that lactose was not eliminated, a fact that could account for the rather poor lowering of the COD. Compared to the chemical coagulation treatment with aluminium sulphate, the efficiency of the electrocoagulation technique was almost identical. However the wastewaters treated by electrocoagulation differed by the fact that they exhibited a lower conductivity and a neutral pH value (by contrast to the acid nature of the solution treated by the chemical coagulation). This result (low conductivity, neutral pH) tends to show that it may be possible to recycle the treated water for some industrial uses. Moreover, the electrocoagulation process uses fewer reagents: the mass of the aluminium anode dissolved during the treatment is lower compared to the quantity of the aluminium salt used in chemical coagulation. These two observations clearly show that the electrocoagulation technique is more performing.     

Comparative study of arsenic removal by iron using electrocoagulation and chemical coagulation

This research studied As(III) and As(V) removal during electrocoagulation (EC) in comparison with FeCl₃ chemical coagulation (CC). The study also attempted to verify chlorine production and the reported oxidation of As(III) during EC. Results showed that As(V) removal during batch EC was erratic at pH 6.5 and the removal was higher-than-expected based on the generation of ferrous iron (Fe²⁺) during EC. As(V) removal by batch EC was equal to or better than CC at pH 7.5 and 8.5, however soluble Fe²⁺ was observed in the 0.2-μm membrane filtrate at pH 7.5 (10-45%), and is a cause for concern. Continuous steady-state operation of the EC unit confirmed the deleterious presence of soluble Fe²⁺ in the treated water. The higher-than-expected As(V) removals during batch mode were presumed due to As(V) adsorption onto the iron rod oxyhydroxides surfaces prior to the attainment of steady-state operation. As(V) removal increased with decreasing pH during both CC and EC, however EC at pH 6.5 was anomalous because of erratic Fe²⁺ oxidation. The best adsorption capacity was observed with CC at pH 6.5, while lower but similar adsorption capacities were observed at pH 7.5 and 8.5 with CC and EC. A comparison of As(III) adsorption showed better removals during EC compared with CC possibly due to a temporary pH increase during EC. In contrast to literature reports, As(III) oxidation was not observed during EC, and As(III) adsorption onto iron hydroxides during EC was only 5-30% that of As(V) adsorption. Also in contrast to literature, significant Cl₂ was not generated during EC, in fact, the rods actually produced a significant chlorine demand due to reduced iron oxides on the rod. Although Cl₂ generation and As(III) oxidation are possible using a graphite anode, a combination of graphite and iron rods in the same EC unit did not produce As(III) oxidation. However, a two-stage process (graphite anode followed by iron anode in separate chambers) was effective in As(III) oxidation and removal. The competing ions, silica and phosphate interfered with As(V) adsorption during both CC and EC. However, the degree of interference depends on the concentration and presence of other competing ions. In particular, the presence of silica lowered the effect of phosphate with increasing pH due to silica’s own significant effect at high pHs.     

邕江水源水质特征与变化趋势

通过对南宁市两个水源点2007-2009年监测数据的统计分析,得出邕江水源的自然水质特征和污染指标表现情况.结果表明,邕江原水的自然水质特征主要表现为浊度受季候水期影响较大,水的酸碱度为中性略偏弱碱,硬度适中;粪大肠菌群指标对邕江水源水质状况影响最大,近年来邕江水源的水质总体上保持稳定,未出现劣变的趋势.     

砖瓦行业脱硫、脱氟设备选型应注意的问题

随着我国对粘土实心砖限时禁用政策的实施,各地利用煤矸石、页岩等工业废渣替代粘土生产烧结空心砖的建设项目越来越多.然而这些废渣在焙烧过程中释放出的SO2、HF等有害气体,严重影响人体健康、动植物的生长,破坏生态环境,给国民经济造成了巨大的损失.据有关资料介绍,砖瓦行业应对因排放SO2而引起的酸雨污染负有40%的责任.我国对这些有害气体的排放有明确的控制指标,国家标准GB9078-1996<工业窑炉大气污染物排放标准>中,对二类区内砖瓦行业窑炉排放烟气中要求SO2浓度＜850mg/m3,氟化物浓度＜6mg/m3,随着国家对环保的重视,排放标准在未来几年将更为严格.     

Comparison of polyaluminum silicate chloride and electrocoagulation process,in natural organic matter removal from surface water in Ghochan,Iran

Removal of natural organic matter (NOM) is one of the most important objectives of water treatment plants but reducing these pollutants either present in water as dissolved or suspended form is not as efficient as is required in conventional treatment plants. The purpose of this study was comparison performance of composite polyaluminum silicate chloride (PASiC) and electrocoagulation (EC) process by aluminum electrodes in NOM removal from raw surface water. In this study, the effects of turbidity, total organic compounds (carbons) (TOC), adsorption at a wavelength of 254 nm (UV254), chemical oxygen demand (COD), alkalinity, residual aluminum in finished water by application of EC process and PASiC were investigated. The results demonstrate that PASiC coagulant at optimum concentration of 1–5 ml/L was capable of removing TOC, COD, U.V., and turbidity from raw water by 93.77, 93.5, 63 and 95 %, respectively. In contrast, EC process, removed TOC, COD, UV and turbidity from raw water by 89, 99.75, 37 and 50%, respectively. The pilot-scale results demonstrated the significant advantage of PASiC compared to EC process in removal of NOM and turbidity form raw water. Residual aluminum in finished water was below the recommended WHO guidelines 0.2 mg/L for both processes. Finally it can be concluded that PASiC and EC process are reliable, efficient and cost-effective methods for removal of NOM from surface water.     

Features of biosorption filtration of aromatic compounds in water treatment

The paper has studied features of biosorption filtration of phenol, o-nitrophenol, and o-aminobenzoic acid through activated carbon. The study has shown antibate relationship between the value of the variation of free energy of Gibbs adsorption and the removal rate from the water of aromatic compounds by a layer of activated carbon in the mode of biostabilization.     

涡流电凝聚—接触过滤工艺处理低浊度原水

将电凝聚与混合反应、接触过滤等工艺通过优化组合,形成涡流电凝聚—接触过滤一体化净水试验装置,对其用于处理低浊度原水进行了试验研究,讨论了电解时间（t）、电流密度（I）、穿孔板的开孔率、pH值以及温度等因素对该组合工艺的影响,试验结果表明各因素均满足生活饮用水的浊度标准。     

Alternative design for electrocoagulation treatment of cromium-containing electroplating wastewater

An alternative design of electrocoagulator for the chromium-containing wastewater treatment has been proposed. The processes of electrocoagulation treatment of such water were investigated. Effective design and operating parameters have been determined that allow the specified wastewater to be purified in accordance with normative requirements.     

净水供水一体化设备处理高藻低浊水库水研究

采用净水供水一体化设备对珠海市唐家水厂水库原水进行净化处理。结果表明,一体化净水供水设备对浊度、藻类、有机物和细菌均有较好的处理效果,运行期间浊度和CODMn的平均去除率分别为97％和46％,藻类去除率大于99％,细菌的截留率达到100％,出水水质满足《生活饮用水卫生标准》（GB5749--2006）限值要求。     

Optimization of electrocoagulation technology of purifying wastewaters of ions of heavy metals

The article proposes results on optimization of electrocoagulation technology of purifying of ions of heavy metals. A phase composition of electrogenerated aluminum hydroxide in a neutral medium was established. Found conditions for floatation of the mass of coagulated pollutants and their successful removal off water surface. Optimized are parameters of coagulation with aluminum anodes presented in an upgraded edition of SNiPa 2.04.03-85, namely: current anodic density, specific aluminum consumption, etc.     

姬家峁水源地廊道取水数值模拟及水资源评价

在简要介绍研究区水文地质条件的基础上，初步选定了三种开采方案，并用数学模型的有限元法评价了地下水资源的允许开采量，同时提出和论证了最佳开采方案，这对于研究区地下水的合理开发具有重要的指导意义。     

Comparison of electrocoagulation and chemical coagulation pretreatment for enhanced virus removal using microfiltration membranes

This research studied virus removal by iron electrocoagulation (EC) followed by microfiltration (MF) in water treatment using the MS2 bacteriophage as a tracer virus. In the absence of EC, MF alone achieved less than a 0.5-log removal of MS2 virus, but, as the iron-coagulant dosage increased, the log virus removal increased dramatically. More than 4-log virus removal, as required by the Surface Water Treatment Rule, was achieved with 6-9 mg/L Fe³⁺. The experimental data indicated that at lower iron dosages and pH (<∼8 mg Fe/L and pH 6.3 and 7.3) negatively charged MS2 viruses first adsorbed onto the positively charged iron hydroxide floc particles before being removed by MF. At higher iron dosages and pH (>∼9 mg Fe/L and pH 8.3), virus removal was attributed predominantly to enmeshment and subsequent removal by MF. Additionally, the experimental data showed no obvious influence of ionic strength in the natural water range of 10⁻⁷-10⁻² M on MS2 virus removal by EC-MF. Finally, EC pretreatment significantly outperformed chemical coagulation pretreatment for virus removal. The proposed mechanism for this improved performance by EC is that locally higher iron and virus concentrations and locally lower pH near the anode improved MS2 enmeshment by iron flocs as well as adsorption of MS2 viruses onto the iron floc particles.     

沈阳:计划用水依法管水

以创建全国节水型城市为契机,沈阳市城市节水管理力度也在不断加强,目前,沈阳市工业用水单位已基本纳入计划用水管理范围,对日供水量5立方米以上的大生活用水单位也逐步实行了计划管理。在工业用水方面,积极采用循环用水、一水多用、串联使用和污水处理回用等节水技术措施,使全市工业用水重复利用率达到80％,间接冷却水循环利用率达到95．5％,城市污水处理率达到81％．工业废水排放达标率达到100％。     

化学沉淀法去除水中镉的特性研究

考察了氢氧化物沉淀法和硫化物沉淀法对镉的去除效果。结果表明,两种方法均能将0.025mg/L的镉降低到《生活饮用水卫生标准》限值(0.005mg/L)以内,除镉效果稳定。氢氧化物沉淀法中,三氯化铁作为混凝剂对镉的去除效果明显优于聚合氯化铝,能有效去除0.250mg/L的镉,且处理后铁残余浓度未超标;硫化钠沉淀法除镉效果好,但硫化钠投加量增加到0.20mg/L时,上清液硫化物会超标。     

Advanced oxidation processes coupled with electrocoagulation for the exhaustive abatement of Cr-EDTA

Using Cr-EDTA as a model system, a two-step method has been investigated for the abatement of persistent chromium complexes in water. The treatment consists of an oxidative decomposition of the organic ligands by means of ozonization or electrochemical oxidation at a boron doped diamond (BDD) electrode, followed by removal of the metal via electrochemical coagulation. In the designed synthetic waste, EDTA has been used both as a chelating agent and as a mimic of the organic content of a typical wastewater provided by a purification leather plant. A crucial point evaluated is the influence of the oxidative pretreatment on the chemical modification of the synthetic waste and hence on the electrocoagulation efficacy.Because of the great stability of Cr complexes, such as Cr-EDTA, the classical coagulation methods, based on ligand exchange between Cr(III) and Fe(II) or Fe(III), are ineffective toward Cr abatement in the presence of organic substances. On the contrary, when advanced oxidation processes (AOPs), such as ozonization or electrooxidation at a BDD anode are applied in series with electrocoagulation (EC), complete abatement of the recalcitrant Cr fraction can be achieved. ECs have been carried out by using Fe sacrificial anodes, with alternating polarization and complete Cr abatement (over 99%) has been obtained with modest charge consumption. It has been found that Cr(III) is first oxidized to Cr(VI) in the AOP preceding EC. Then, during EC, Cr(VI) is mainly reduced back to Cr(III) by electrogenerated Fe(II). Thus, Cr is mainly eliminated as Cr(III). However, a small fraction of Cr(VI) goes with the precipitate as confirmed by XPS analysis of the sludge.     

气囊堵水在供水管道上的应用

通过试验,分析论证了气囊在供水管道上应用的可能性,并提出了具体的建议,指出带导流孔的气囊在供水管道中凭借其在堵水作业中发挥出的独特技术优势和经济优势,具有大面积推广的实用价值。