Quality of groundwater in eastern Croatia. The problem of arsenic pollution

Groundwater in the area of eastern Croatia contains high concentrations of iron, manganese, ammonia, organic substances and arsenic. The appearance of inorganic arsenic in groundwater is mainly caused by arsenic from natural geological sources. Since the groundwater is the main source of drinking water for the population in this area, almost 200,000 people are daily drinking water with arsenic concentration ranging from 10 to 610 μg/L. The Croatian legislation recently revised the maximum concentration limit (MCL) for arsenic in drinking water to 10 μg/L. The population in the two towns (Osijek and Vinkovci) of this region is supplied with groundwater processed by coagulation-filtration method, but in the other towns and villages water treatment implies only rapid sand filtration. Both methods for water treatment have resulted with higher arsenic concentration than MCL, so the main goal of this study was determination of population exposure to arsenic via drinking water and possible improvement of drinking water quality. Population exposure to arsenic via drinking water is determined with hair analysis, since the hair arsenic concentration is one of three most commonly employed biomarkers used to identify or quantify overall arsenic exposure. During this study the preliminary analyses of hair arsenic concentrations in several towns and villages in eastern Croatia were provided. The positive correlation between heightened arsenic concentration in drinking water and hair arsenic concentration was determined. In order to improve drinking water quality e.g. arsenic removal from contaminated drinking water, different modified adsorbents were used and compared (zeolite–clinoptilolite, manganese greensand and cationic exchange resin). Adsorbents were chemically modified and saturated with Fe(III) ions, while the arsenic solutions were prepared by processed groundwater.     

化学法脱硫铁矿烧渣砷的研究

硫铁矿烧渣是以硫铁矿为原料生产硫酸过程中排出的一种固体废弃物,主要成分是Fe2O3、SiO2,可用作炼铁原料,但砷质量分数过高将严重影响烧渣的应用.作者用化学法对硫铁矿烧渣进行脱砷处理,可使烧渣中的ω(砷)降至0.045%以下,ω(铁)达到62.23%.脱砷的最佳工艺条件为:ω(脱砷剂)=21.63%,温度为50℃,ω(矿浆)=23.08%,反应时间为90 min,搅拌速度为500 r/min.     

pH值对地下水除铁除锰影响机理的研究

以洞庭湖区地下水为水源,通过调节试验原水的pH值,考察不同pH值条件下铁锰去除效果的变化,试验结果表明：随着pH值的升高,铁的去除从最初没有效果（pH值小于6.5）到接触氧化除铁（pH值在6.5～7.5）,再过渡到空气氧化除铁法（pH值大于7.5）;锰的去除在pH值大于5.0时为生物除锰法,在pH值小于5.0时生物除锰丧失了除锰能力.     

Effect of operating conditions on iron corrosion rates in zero-valent iron systems for arsenic removal

Owing to newly established water quality standards, the use of the zero-valent iron (ZVI) method for arsenic removal is gaining attention. The spontaneous chemical oxidation of ZVI by dissolved oxygen, a complex process involving a variety of metastable ferrous–ferric intermediate species, was studied in short-term batch experiments using two different commercially available ZVI materials. Differences in corrosion rates may be attributed to the different specific reactivity of these materials. The effects of pH, ZVI loading, initial conductivity and dissolved oxygen concentration on both Fe(II) and Fe(III) kinetic profiles were investigated. ZVI corrosion rates in the presence of As(III) and As(V) were also studied. Depending on the pH, the concentrations of Fe(II) and Fe(III) are significantly influenced by the presence of As(III) and As(V). Our results may be important from a technological point of view, since it is well known that iron corrosion rates govern the generation of sites for arsenic removal.     

Effect of operating conditions in removal of arsenic from water by nanofiltration membrane

The removal of arsenic from synthetic waters and surface water by nanofiltration (NF) membrane was investigated. In synthetic solutions, arsenic rejection experiments included variation of arsenic retentate concentration, transmembrane pressure, crossflow velocity and temperature. Arsenic rejection increased with arsenic retentate concentration. Arsenic was removed 93-99% from synthetic feed waters containing between 100 and 382 μg/L as V, resulting in permeate arsenic concentrations of about 5 μg/L. Under studied conditions, arsenic rejection was independent of transmembrane pressure, crossflow velocity and temperature. In surface water, the mean rejection of As V was 95% while the rejection of sulfate was 97%. The co-occurrence of dissolved inorganics does not significantly influence arsenic rejection. The mean concentration of As in collected permeated was 8 μg/L. The mean rejection of TDS, total hardness and conductivity were 75, 88 and 75% respectively.     

地下水纤维滤料除铁中试研究

进行了纤维滤料地下水除铁中试研究，试验结果表明纤维滤料具有成熟期短（14d）、除铁效率高的特点。在滤速为20m／s时能将原水中Fe从11．6mg／L去除至0．3mg／L以下。三价铁是影响出水水质的重要因素．应减少曝气后停留时间及控制曝气量以减少滤前三价铁的含量。分析了纤维滤料除铁的机理及特点．确定了纤维滤料过滤器合适的反冲洗强度及步骤。     

自然有机物对地下水混凝除铁的影响试验研究

通过模拟试验,考察了自然有机物的浓度、分子质量以及溶液的pH、温度对地下水混凝除铁的影响,并研究了预氧化在混凝除铁中的作用.结果表明,有机物的浓度越高、分子质量越大,有机铁的去除率越高.当Fe2 与分子质量＞10 ku的有机物络合时,用混凝除铁能取得良好的效果;当Fe2 与分子质量＜4 ku的有机物络合时,采用预氧化混凝工艺能达到较好的除铁效果.在pH6.0～7.5的范围内,降低pH有利于混凝除铁.温度升高对混凝除铁有利.     

Arsenic removal by coagulation and filtration: comparison of groundwaters from the United States and Bangladesh

Arsenic contamination of drinking water is a concern in many parts of the world. In the United States, the Environmental Protection Agency recently reduced the maximum contaminant level of arsenic in drinking water from 50 to 10 μ/L (ppb). In Bangladesh the arsenic concentration in drinking water can be as high as hundreds of parts per billion while the maximum contaminant level is 50 ppb. Consequently, there is a great need for new cost-effective methods to remove arsenic from drinking water. Here arsenic removal by coagulation and filtration was investigated using groundwater from a city in southern Colorado in the United States and from Sonargaon in Bangladesh. The results of the bench-scale experiments conducted indicate that coagulation with ferric ions followed by filtration is effective in reducing arsenic concentration in the water tested. However, the actual efficiency of removal is highly dependent on the raw water quality. Further, addition of a polyelectrolyte coagulant aid may lead to improved permeate fluxes during tangential flow microfiltration but has little effect on the residual arsenic concentration.     

高锰酸盐药剂预氧化去除受污染地下水中铁、锰

通过单因子试验考察了进水pH、预氧化时间及原水本底成分对高锰酸钾、高锰酸盐复合药剂(PPC)预氧化去除受污染地下水中铁、锰效果的影响.试验结果表明,在使用KMnO4及PPC预氧化时,进水无需调节pH便能取得较好的铁、锰去除效果;综合技术经济因素考虑,PPC及KMnO4的预氧化时间应定为10 min;原水本底成分极大地影...     

地下水除铁除锰水厂反冲洗废水混凝试验研究

通过试验,研究了地下水除铁除锰水厂反冲洗废水混凝处理的效果、影响因素以及混凝机理。结果表明,CPF和PAM的混凝效果最好,氯化铁次之,PAC较差,硫酸铝最差;含铁量为100mgL左右的冲洗废水自然沉淀效果较差,而投加少量混凝剂后,这种冲洗废水可在较短的时间内获得很好的沉淀效果;在混凝后的最初的10．30min内,废水上清液的含铁量急剧下降,此后随着沉淀时间的增加,上清液含铁量缓慢降低;当pH值为7．5左右时,硫酸铝、氯化铁和PAC的混凝机理可能以电性中和作用与吸附架桥作用为主,PAM可能主要是吸附架桥作用,而CPF的混凝机理除了吸附架桥作用以外,还可能存在一定的电性中和作用。     

Nitrate removal from groundwater by a novel three-dimensional electrode biofilm reactor

The contamination of nitrate in groundwater has become an ever-increasing environmental problem. To improve denitrification rate effectively, a novel three-dimensional (3D) bio-electrochemical reactor was developed, which introduced activated carbon (AC) into the cathode chamber as the third bipolar electrode. The influence parameters such as temperature, pH, current and initial nitrate loading were investigated systematically. The role of the third electrode was explored and a possible denitrification mechanism was suggested. The presence of AC not only provided much more sites for biofilm formation and hydrogen gas yield, but also produced carbon dioxide to afford a favorable anoxic environment. Thus, the 3D reactor showed good denitrification performance in wider conditions. The denitrification rate could reach 0.222 mg NO₃ N/cm²/d while the current efficiency could reach as high as 227%, indicating promising for nitrate removal from groundwater.     

水相氧化法脱除黄磷中砷的研究

采用水相氧化法，使用硝酸溶液和氧化增强剂进行工业黄磷脱砷试验。对硝酸质量分数、氧化增强剂中铁与黄磷中砷的质量比、硝酸溶液与黄磷的体积比、反应时间与反应温度等因素对黄磷中砷的脱除率的影响进行了单因素实验，并通过正交实验，得到了水相氧化法脱除黄磷中砷的最优工艺条件，即硝酸质量分数25％，反应温度65℃，铁与砷的质量比60，硝酸与黄磷体积比5：1，反应时间4h。实验结果表明，在最优条件下，可使黄磷中砷的质量分数由310mg／kg降至15mg／kg。水相氧化法工艺流程和设备简单，操作安全，易于实现工业放大。     

饮用水除砷吸附剂的研究进展

砷在水体中主要以As(Ⅲ)和As(Ⅴ)的无机酸形式存在,对人体的危害很大,吸附法是国内外研究最广泛的饮用水除砷技术之一.详细说明了饮用水除砷的吸附剂类型,指出:复合材料效率高、费用低,目前应用最为广泛;纳米材料与砷结合后性质稳定,除砷效率最高,是今后的主要发展方向;生物吸附材料以其高吸附率、低成本成为研究的热点.     

负载铁离子活性炭除砷的研究进展

砷污染是一个严重的世界问题,在其诸多的去除方法中,负载铁离子活性炭兼顾了活性炭和混凝沉淀的优势,可高效去除砷离子.作者对负载铁离子活性炭的制备方法、影响砷去除率的主要因素和吸附模型的研究现状进行了详细评述,其中负载铁离子活性炭的孔径结构、表面性质,负载铁离子的形貌、分布、种类和质量等决定着其吸附容量;通过调节搅拌时间、...     

An overview of arsenic removal by pressure-drivenmembrane processes

Management of hazardous wastes, such as arsenic, is one of major public concern. Arsenic is a naturally occurring metalloid, which is widely distributed in nature. Recently, arsenic in drinking water attracted attention because some of the drinking water resources contain considerable concentrations of arsenic which cause acute; and chronic symptoms in many countries, especially in Bangladesh, China, Mongolia, and Taiwan. In 2001, the USEPA promulgated a rule lowering the arsenic MCL from 5 μgL⁻¹ to 10 μgL⁻¹. This paper offers an overview of geochemistry, distribution, sources, regulations, acute and chronic symptoms, and applications of membrane technologies in the water treatment research that have already been realized or that are suggested on the basis of bench or lab scale research. These membrane technologies include RO, NF, UF, and MF. Most of theses applications have proven to be reliable in removing arsenic from water. The possible influence of some source water parameters, membrane material, membrane types, membrane processes on arsenic removal efficiency by membrane technologies are also explored. This review paper also offers data relating to regulations of arsenic standard, acute and chronic symptoms that are caused by the exposure of arsenic to explain why water treatments need to use the membrane technology to meet the MCL standard.     

Synthesis of the cotton cellulose based Fe(III)-loaded adsorbent for arsenic(V) removal from drinking water

A novel macroporous bead adsorbent, Fe(III)-loaded ligand exchange cotton cellulose adsorbent [Fe(III)LECCA], is synthesized for selective adsorption of arsenate anions [As(V)] from drinking water in batch and column systems. As(V) adsorption on Fe(III)LECCA was independent of pH, especially in drinking water pH range. Film diffusive control mechanism will benefit As(V) exchange with Fe(III)LECCA whether in batch or in column experiments. When treating the tap water at 26.0 BV/h, the column still preserves 83% of the original saturation adsorption capacity of the As(V) aqueous solution. These results have indicated that Fe(III)LECCA has the potential to act as an adsorbent for the removal of As(V) from drinking water considering its availability, nontoxicity and cost-effectiveness.     

Electrochemical removal of arsenic from technical grade phosphoric acid

The electrolytic de-arsenication of technical grade phosphoric acid 85 wt % by cathodic deposition in order to produce chemically pure phosphoric acid was examined. Polarization curves using Cu, Pb, 316L stainless steel and graphite as cathodic rotating discs were determined. The best results were achieved for copper where the arsenic deposition takes place in a range of potentials without hydrogen evolution. Long term experiments in a laboratory batch reactor with a rotating cylinder cathode of copper showed that the electrodeposited arsenic was a non-conductor, poorly adherent and can be detached from the electrode by means of an ultrasonic cleaner. Experimental results with a pilot plant reactor with a three-dimensional cathode of copper nets showed a high degree of scatter. However, typical values of the figures of merit are: fractional conversion per pass 24%, specific energy consumption 250 kWh kg⁻¹ As for a volumetric flow rate of 1.5 dm³ min⁻¹ at 60 A and 3.4 V of cell voltage.     

饮用水除砷技术研究新进展

重点介绍了近年来各种除砷新技术的研究进展,内容包括:强化混凝、吸附、离子交换、膜法、预氧化除砷技术。评价了各除砷技术的优缺点与适用范围,并认为饮用水除砷技术的发展将呈现出以下特点:As(Ⅲ)和As(V)同步去除技术的开发;易于取得或制备、生物化学稳定性高、吸附容量大、选择性高、再生能力强的新型除砷吸附剂的开发;多种除砷技术联合,多重去除机理协同的除砷流程的开发;低能耗、低成本除砷技术的开发;生物除砷技术的开发。     

地下水固锰除铁工程设计

地下水固锰除铁工艺中在跌水曝气后过氧化问题一直是该工艺的关键内容,将跌水曝气池、滤池、反冲洗水池合建形成一体化固锰除铁单元,可以根据水量控制曝气强度,防止过曝气,稳定过滤水头,而且可以节约占地,减少滤池面积,并方便运行管理。     

Arsenic removal from drinking water by a “loose” nanofiltration membrane

The removal of arsenic from water by a “loose” nanofiltration (NF) membrane was investigated. Prior to the arsenic removal studies, the loose NF membrane was characterized for molecular weight cut-off and pore size by saccharide retention measurements, and electrokinetic charge by streaming potential measurements. In addition, separation of both single salt and mixed salt electrolyte solutions was studied to investigate the ion transport properties of the membrane. Arsenic rejection experiments included variation of pH, arsenic feed concentration, and presence of background electrolyte. In general, arsenic rejection increased with increasing pH and arsenic feed concentration, and was enhanced in the presence of 0.01 M NaCl. Arsenic was removed 60–90% from synthetic feed waters containing 10, 32, 100, and 316 μg/L As(V), resulting in permeate arsenic concentrations of 4, 6, 10, and 25μg/L, respectively. The behavior of the membrane is consistent with the extended Nernst-Planck equation model predictions for an uncharged membrane where size exclusion controls ion retention. However, separation of Arsenic species was a due to a combination of size exclusion, preferential passage of more mobile ions, and charge exclusion.