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.     

电絮凝-超滤组合技术处理含铜废水

采用电絮凝-超滤（electrocoagulation-ultrafiltration,EC-UF）组合技术对含铜废水中的铜离子进行了处理实验研究。讨论了电流密度、初始pH、初始铜浓度和初始电导率等因素对铜的去除效果和膜污染的影响,并分析了这些影响因素对EC-UF组合技术效率的作用机制。结果表明,在电流密度J=50 A·m-2、初始铜浓度C（Cu2+）≤40 mg·L-1、初始pH=4~8、初始电导率σ=2 mS·cm-1、电解时间20 min的条件下,废水中铜的去除率达到99.6%并有效的减缓了膜污染。本研究为EC-UF组合技术除铜的实践应用提供了科学依据。     

诱导结晶法去除地下水中氟离子简

针对现行高氟地下水处理工艺中存在的工艺复杂、运行管理困难等问题,提出采用诱导结晶法除氟。其技术核心是在高氟水中投加氟磷灰石作为晶种,并投加磷酸盐和钙盐使水中氟离子在晶种表面生成氟磷酸钙（Ca₁₀（PO₄） ₆F₂）结晶。通过单因素实验得出最佳工艺条件：投加8g/L氟磷灰石,并投加NaH₂PO₄和CaCl₂,使钙离子、磷酸根离子和氟离子的摩尔比为10：5：1,搅拌速度为100 r/min,反应时间1 h。反应中磷酸根离子和钙离子的利用率分别达到98%和25%以上。电子扫描显微镜（SEM）表征晶种在参与反应后,表面有结晶生成。研究表明,采用诱导结晶法可将水中氟离子浓度从5~10 mg/L降至1 mg/L以下,达到饮用水水质标准。     

诱导结晶法去除地下水中氟离子

针对现行高氟地下水处理工艺中存在的工艺复杂、运行管理困难等问题,提出采用诱导结晶法除氟。其技术核心是在高氟水中投加氟磷灰石作为晶种,并投加磷酸盐和钙盐使水中氟离子在晶种表面生成氟磷酸钙（Ca10（PO4） 6F2）结晶。通过单因素实验得出最佳工艺条件：投加8g/L氟磷灰石,并投加NaH2PO4和CaCl2,使钙离子、磷酸根离子和氟离子的摩尔比为10：5：1,搅拌速度为100 r/min,反应时间1 h。反应中磷酸根离子和钙离子的利用率分别达到98%和25%以上。电子扫描显微镜（SEM）表征晶种在参与反应后,表面有结晶生成。研究表明,采用诱导结晶法可将水中氟离子浓度从5~10 mg/L降至1 mg/L以下,达到饮用水水质标准。     

电絮凝对电厂循环冷却水中硬度的去除

以某电厂冷却塔循环冷却水为处理对象,利用电絮凝法,以铝板为牺牲阳极去除水中的Ca²⁺和Mg²⁺,分别考察了电絮凝过程中不同电流密度、电解时间、溶液初始pH、阳极极板数量对总硬度去除率的影响。结果表明：增加电流密度、延长电解时间有利于Ca²⁺和Mg²⁺的去除;当电流密度为10 mA·cm⁻²,电解时间为90 min时,Ca²⁺和Mg²⁺去除率分别达到93.5%和95.8%,总硬度去除率为94.6%;相对于酸性和中性条件,碱性条件更有利于Ca²⁺和Mg²⁺的去除,当初始pH为10时,Ca²⁺和Mg²⁺去除率分别达到85.4%和97.7%,总硬度去除率为93.5%;随极板数量的增加,Ca²⁺和总硬度去除率均有所提高;投加Na₂CO₃有利于Ca²⁺和总硬度的去除。上述结果可为进一步提高电絮凝过程中总硬度的去除率提供参考。     

电混凝去除水中锑污染物

采用电混凝技术对水中锑污染物进行处理,利用阳极电解铁板产生亚铁和三价铁离子,通过絮凝与共沉淀作用去除Sb（Ⅲ）和Sb（V）污染物,并详细探讨了电流密度、溶液初始pH、电解质离子及通入N2对锑去除效率的影响。结果发现,锑初始浓度为1 mg/L时,反应30 min后Sb（Ⅲ）浓度低于5.0 μg/L,Sb（V）浓度为28.1 μg/L,表明Sb（Ⅲ）去除效率明显优于Sb（V）。另外,研究发现,电流密度及初始pH对Sb（Ⅲ）的去除效率影响较小,增大电流密度会提高Sb（V）去除效率,溶液初始pH为4.5时Sb（V）去除效率最高;Mg2+与HCO3-有助于Sb（V）的去除,Ca2+、SiO32-和PO43-对Sb（V）的去除有一定的抑制作用;通入N2会提高Sb（V）的去除率。     

铝铁电极联用电絮凝法处理Cu-EDTA络合废水

采用电絮凝法处理Cu-EDTA模拟废水,研究电极组合方式、初始pH值和氯化钠浓度3个因素对化学需氧量(COD)和Cu去除效果的影响。实验研究发现,当电极组合方式为2个铝阳极和2个铁阴极,起始pH值为3,氯化钠浓度为0.5 g/L,换极周期为40 min,反应时间为80 min时,COD去除率达到78.7%,Cu离子去除率达到99.9%。通过实验研究确定EDTA的去除机制主要是:酸性条件下的次氯酸氧化作用,碱性条件下的氢氧化物絮凝沉淀作用及单核态铝/铁与多核态铝/铁电荷中和作用,Cu的去除机制主要是氢氧化物的絮凝沉淀作用和铁电极的电沉积作用。     

Removal of arsenic from groundwater by granular titanium dioxide adsorbent

A novel granular titanium dioxide (TiO2) was evaluated for the removal of arsenic from groundwater. Laboratory experiments were carried out to investigate the adsorption capacity of the adsorbent and the effect of anions on arsenic removal. Batch experimental results showed that more arsenate [As(V)] was adsorbed on TiO2 than arsenite [As(III)] in US groundwater at pH 7.0. The adsorption capacities for As(V) and As(III) were 41.4 and 32.4 mgg(-1) TiO2, respectively. However, the adsorbent had a similar adsorption capacity for As(V) and As(III) (approximately 40 mgg(-1)) when simulated Bangladesh groundwater was used. Silica (20 mgl(-1)) and phosphate (5.8 mgl(-1)) had no obvious effect on the removal of As(V) and As(III) by TiO2 at neutral pH. Point-of-entry (POE) filters containing 3 l of the granular adsorbent were tested for the removal of arsenic from groundwater in central New Jersey, USA. Groundwater was continuously passed through the filters at an empty bed contact time (EBCT) of 3 min. Approximately 45,000 bed volumes of groundwater containing an average of 39 microgl(-1) of As(V) was treated by the POE filter before the effluent arsenic concentration increased to 10 microgl(-1). The total treated water volumes per weight of adsorbent were about 60,000 l per 1 kg of adsorbent. The field filtration results demonstrated that the granular TiO2 adsorbent was very effective for the removal of arsenic in groundwater.     

Removal of arsenic from contaminated groundwater by solar-driven membrane distillation

Experimental investigations were carried out on removal of arsenic from contaminated groundwater by employing a new flat-sheet cross flow membrane module fitted with a hydrophobic polyvinylidenefluoride (PVDF) microfiltration membrane. The new design of the solar-driven membrane module in direct contact membrane distillation (DCMD) configuration successfully produced almost 100 per cent arsenic-free water from contaminated groundwater in a largely fouling-free operation while permitting high fluxes under reduced temperature polarization. For a feed flow rate of 0.120 m³/h, the 0.13 μm PVDF membrane yielded a high flux of 74 kg/(m² h) at a feed water temperature of 40 °C and, 95 kg/m² h at a feed water temperature of 60 °C. The encouraging results show that the design could be effectively exploited in the vast arsenic-affected rural areas of South-East Asian countries blessed with abundant sunlight particularly during the critical dry season.     

吹脱-电化学催化氧化组合工艺去除地下水中氨氮

以上海某钢铁工业区固废堆场氨氮污染的地下水为研究对象,研究了单独电化学氧化法、光/电协同氧化法、吹脱-电化学催化氧化组合法对氨氮的去除效果,提出能高效除氨氮且适合工程实际应用的吹脱-电催化氧化组合工艺。结果表明,相较单独电化学氧化,光/电协同氧化体系中的强氧化活性物质(HO·、HOCl、ClO⁻等)通过自由基链式反应和光解反应生成氧化性更弱的ClO·,反而削弱氨氮去除效果。而吹脱-电催化氧化组合工艺下氨氮、总氮的去除率分别为97.62%、90.23%,出水满足《地下水质量标准》(GB/T 14818-2017)IV类标准。电子顺磁共振(EPR)和活性氯生成实验证实HO·和活性氯(HOCl、ClO⁻、Cl₂)在氨氮转化过程中的重要作用。本实验为进一步研究和设计基于电化学法处理废水中的氨氮技术和组合工艺提供了理论依据。     

Removal of arsenic from groundwater by micellar-enhanced ultrafiltration (MEUF)

The removal characteristics of arsenate using micellar-enhanced ultrafiltration (MEUF) were investigated. Among four different cationic surfactants used, hexadecylpyridinium chloride (CPC) showed the highest removal efficiency of arsenic (96%), and the removal efficiency with hexadecyltrimethylammonium bromide (CTAB) was 94%. But the removal efficiency with benzalkonium chloride (BC) was the lowest (57%) due to higher critical micelle concentration (CMC) of BC than those of other surfactants. Over 80% of arsenic was removed with octadecylamine acetate (ODA). On the effect of solution pH on the arsenic removal, since the valance of arsenate decreases from trivalent to monovalent as pH decreases, the removal was reduced at lower pH. The presence of 0.45mM of nitrate and 0.01mM of phosphate reduced the removal efficiency by 5-8%. This decrease was because of the competition between the arsenate, nitrate and phosphate for the binding sites of the surfactant micelle. Similar decrease in the removal of arsenate was observed with CPC, CTAB and ODA in the presence of these anions. In cross-flow filtration, the removal efficiency of arsenic was similar to that in the dead-end system. However, the decline in flux was less than that in dead-end filtration. In order to lower the concentration of the surfactant in the effluent, the effluent was treated with powdered activated carbon (PAC) before discharging to the environment. Over 98% surfactant was removed with 1gl(-1) of PAC. In conclusions, the MEUF is considered as a feasible process using CPC or CTAB to remove the arsenate from groundwater compared with the other solid based adsorbent processes.     

PRB技术对地下水中重金属离子的处理研究

实验模拟地下环境,以受重金属离子Pb(Ⅱ)、As(Ⅲ)、Cd(Ⅱ)、Cr(Ⅵ)、Fe(Ⅱ)和总Mn污染的地下水为研究对象,利用还原铁粉、铸铁粉、铸铁粉与颗粒活性炭的混合物为可渗透反应墙(PRB)的主要介质,石英砂为辅助介质,设计了3种反应器.在有效孔隙率为60%～65%、水力停留时间为12.0～14.4 h的条件下,考察其对污染物的去除效果.结果表明:3种反应器对Pb(Ⅱ)、As(Ⅲ)、Cd(Ⅱ)、Cr(Ⅵ)均有较高的去除效果,去除率达98%以上;总Mn的去除率分别达98%、89%和66%;Fe(Ⅱ)的去除率分别达83%、56%和49%.考察了3种反应器内pH、Eh、DO的关系及对重金属离子去除效果的影响,分析了污染物的去除机理.综合考虑处理效果与成本,笔者认为以铸铁粉与石英砂的混合物为PRB的反应介质,应用PRB技术原位处理受上述重金属离子污染的地下水是可行的.     

基于电絮凝法处理矿区高浓度含氟地下水动力学分析

采用铝电极电絮凝体系对矿区高含氟地下水进行处理,研究了高氟浓度下电絮凝除氟过程,分别考察了电流密度、极板间距、进水氟质量浓度及pH对除氟效果和动力学常数的影响,并建立了电絮凝除氟动力学方程模型。结果表明：最佳除氟参数为电流密度为450 A·m⁻³,极间距为5 mm,pH为6.0~7.0;当进水氟质量浓度为12.1 mg·L⁻¹时,经60 min电絮凝除氟后可使进水氟质量浓度由12.1 mg·L⁻¹降为0.6 mg·L⁻¹以下,整个除氟过程遵循一级反应动力学模型且除氟动力学常数取决于电流密度、极板间距和进水氟质量浓度。絮体结构与成分分析表明,在pH=6.0~7.0条件下,电絮凝体系中主要形成的无定型羟基铝化合物使除氟效果达到最好,较高的进水氟质量浓度有助于提高铝离子利用效率。     

煅烧的水滑石同时去除水体中砷和氟

为探讨水滑石类材料对水体中氟、砷离子的同时去除效果,采用共沉淀法合成(Mg∶Al=2∶1)纳米类水滑石(LDHs),用傅立叶转换红外光谱、电子扫描透射电镜、X射线晶体衍射等手段对合成的材料进行了表征,并研究纳米材料在不同初始浓度、pH、吸附时间、阴离子干扰条件下其同时除砷氟性能。结果表明,煅烧后的水滑石(LDOs)对砷最大吸附量为51.02 mg/g,对氟最大吸附量为36.63 mg/g。吸附动力学实验表明,煅烧水滑石对砷的吸附在前6 h内基本完成,对氟的吸附在前10 h内基本完成。砷氟共存溶液保持pH=4~10及pH=6~8时,水滑石分别对砷、氟保持良好的吸附效率。对比不同阴离子对水滑石共除砷氟效率的影响,水滑石除砷速率受到阴离子影响力大小为:HPO2-4CO2-3NO-3Cl-SO2-4;水滑石除氟速率受到阴离子影响力大小为:CO2-3HPO2-4SO2-4Cl-NO-3。材料再生循环利用4次后,对砷和氟的吸附效率均能达到90%以上。实验结果表明,所合成的水滑石是一种优秀的能共除砷氟的吸附剂。     

铁电絮凝产羟自由基氧化降解地下水中磺胺

为了揭示铁电絮凝(EC)过程中尚未被认识的羟自由基氧化机制,以磺胺污染的地下水为对象进行电絮凝降解研究。通过淬灭自由基、厌氧电絮凝和加Fe(III)盐等对照实验,探究反应体系是否存在羟自由基氧化机制;并对不同电解质、溶液pH、初始磺胺浓度、电流强度条件下的电絮凝降解磺胺效率进行了测定。研究结果表明：铁电絮凝处理磺胺废水反应体系存在羟自由基氧化降解磺胺机制;地下水中,阴离子对铁电絮凝氧化效果的影响较小。对模拟江汉平原含0.2 mg·L-1 As(III)和0.1 mg·L-1磺胺的地下水进行铁电絮凝处理,在30 mA的电流条件下,As(III)在4 h内的去除率达到100%,而磺胺达到68.6%。     

复配介质去除地下水中腐殖酸

以模拟地下水为研究对象,进行了复配介质去除地下水中腐殖酸的实验研究。探讨了配比、粒径、固液比、pH和温度对腐殖酸去除效果的影响。腐殖酸的浓度通过紫外分光光度法测定。结果表明:在不加活性炭的条件下,H物质∶X物质∶Q物质=1∶8∶8时,其硬度较好;在初始pH=6.34、反应时间为4 h时,去除率可达到95%以上;当反应时间≤1 h时,去除率随粒径增大而减小,而当反应时间为2～6 h时,小粒径和中等粒径复配介质对腐殖酸去除率略高于大粒径;一定浓度范围内,腐殖酸的去除率与固液比呈正相关,但固液比增大时,并不能无限提高去除率,当固液比为1∶200～1∶50时,去除率呈现平台;pH对复配介质去除效果影响不大,而温度对腐殖酸的去除有显著影响,较低温度(16.8℃)下的去除率比较高温度(35.0℃)下的去除率高5%。该复配介质去除地下水中腐殖酸是有效可行的,可作为PRB(permeable reactive barrier,渗透反应格栅)的潜在反应介质。     

复合介质渗透反应格栅去除地下水中的氨氮

针对受低浓度氨氮污染的地下水,实验筛选组合了不同的反应介质,利用串联的多介质填充柱模拟渗透反应格栅,通过物理吸附及生物硝化-反硝化作用来实现氮的去除。结果表明,在进水氨氮浓度为10 mg/L、流速为0.5 m/d的条件下,模拟柱对氨氮的去除率达到98%以上,且不会出现亚硝酸盐及硝酸盐浓度的升高。水体经过释氧柱后溶解氧由2mg/L升高至10 mg/L以上,表明释氧材料可提供硝化细菌所需的好氧环境。好氧柱中填充易于生物挂膜的生物陶粒及对氨氮有较强吸附能力的沸石,二者联用通过生物硝化-物理吸附协同作用实现对氨氮的去除,其中生物作用实现的氨氮去除量占总去除量的50%左右。后续厌氧反应柱填充海绵铁除氧并利用松树皮颗粒作为碳源,创造反硝化菌生长条件,硝酸盐氮浓度可由10 mg/L降低至5 mg/L以下,实现对好氧反应阶段所产生的硝酸盐的去除,避免了地下水的二次污染。     

Removal of low concentrations of ammonium and humic acid from simulated groundwater by Vermiculite/Palygorskite mixture

Contaminants in water are classified into different types based on their physical and chemical properties. Thus, more than one type of sorbents may be needed for their removal. In this article, a combination of vermiculite with palygorskite was studied for their simultaneous removal of ammonium and humic acid from simulated groundwater. Batch results showed that the Langmuir model described ammonium adsorption well with an adsorption capacity of 22 mg/g while the humic acid adsorption data fitted to the linear adsorption better, suggesting different removal mechanisms of these two types of contaminants. Kinetic studies showed an instantaneous removal of ammonium and humic acid. A column packed with mixture of equal volumes of vermiculite and palygorskite could treat 100 pore volumes for ammonium removal at an initial concentration of 10 mg/L and 500 pore volumes for humic acid removal at an initial concentration of 20 mg/L before the effluent concentrations exceeded the standard.     

电混凝处理电镀综合废水

采用电混凝法处理酸性电镀综合废水,首先研究了不同电流密度对总氰化物、重金属和化学需氧量（COD）去除率的影响。实验结果表明,电混凝可有效去除酸性电镀综合废水中的氰化物与重金属。随着电流密度的增大,总氰化物与重金属的去除率逐渐提高。当电流密度为10mA／cm2时,废水中残留的总氰化物、Cu2＋、Ni2＋、Cr6＋和Zn2＋ 的浓度分别为23．0、25．0、4．5、0．2和0．2mg／L。为了进一步提高去除率,在电化学体系中添加H2O2,随着H2O2投量的增大,总氰化物、重金属、COD去除率不断提高。当H2O2投量为3mL／L时,处理过废水中残留总氰化物、Cu2＋、Ni2＋、Cr6＋、Zn2＋和COD的浓度分别为0．2、2．0、3．0、1．5、0．1和220mg／L。     

Recovery of hydrogen and removal of nitrate from water by electrocoagulation process

The present study provides an optimization of electrocoagulation process for the recovery of hydrogen and removal of nitrate from water. In doing so, the thermodynamic, adsorption isotherm, and kinetic studies were also carried out. Aluminum alloy of size 2 dm² was used as anode and as cathode. To optimize the maximum removal efficiency, different parameters like effect of initial concentration, effect of temperature, pH, and effect of current density were studied. The results show that a significant amount of hydrogen can be generated by this process during the removal of nitrate from water. The energy yield calculated from the hydrogen generated is 3.3778 kWh/m³. The results also showed that the maximum removal efficiency of 95.9 % was achieved at a current density of 0.25 A/dm², at a pH of 7.0. The adsorption process followed second-order kinetics model. The adsorption of NO ₃ ^? preferably fitting the Langmuir adsorption isotherm suggests monolayer coverage of adsorbed molecules. Thermodynamic studies showed that adsorption was exothermic and spontaneous in nature. The energy yield of generated hydrogen was ~54 % of the electrical energy demand of the electrocoagulation process. With the reduction of the net energy demand, electrocoagulation may become a useful technology to treat water associated with power production. The aluminum hydroxide generated in the cell removes the nitrate present in the water and reduced it to a permissible level making the water drinkable.