Four years of development and field-testing of IHE arsenic removal family filter in rural Bangladesh

UNESCO-IHE has been developing an arsenic removal family filter with a capacity of 100 L/day based on arsenic adsorption onto iron oxide coated sand, a by-product of iron removal plants. The longer term and field conditions performance of the third generation of eleven family filters prototypes were tested in rural Bangladesh for 30 months. All filters achieved initially highly effective arsenic removal irrespective of arsenic concentration and groundwater composition. Arsenic level in filtrate reached 10 mug/l after 50 days of operation at one testing site and after 18 months of continuous operation at other 3 testing sites. Arsenic level at other 7 sites remained below the WHO guideline value till the end of study. Positive correlation was found between arsenic removal capacity of the filter and iron concentration in groundwater. In addition to arsenic, iron present in groundwater at all testing sites was also removed highly effectively. Manganese removal with IHE family filter was effective only when treating groundwater with low ammonia. A simple polishing sand filter, after IHE family filter, resulted in consistent and effective removal of manganese. IHE family filters were easy to operate and were well accepted by the local population.     

改进AHP法灰色关联和模糊综合评价在地下水质评价中的适用性

以改进层次分析法(AHP)权重值研究为目的,通过对数据的标准规范化处理自行构造判断矩阵,采用MATLAB计算研究区地下水质的权重值,将所得权重值运用于灰色关联和模糊综合评价两种方法,以白城地区为例对地下水中铁、砷、氟等9项指标进行评价。结果表明:铁、钠、氯化物、硝酸盐(N)、硫酸盐、溶解性总固体、总硬度、砷、氟的权重分别为0.137、0.105、0.130、0.113、0.106、0.070、0.057、0.209、0.073。两种方法评价结果具有较高的空间一致性,白城地区水质总体较差,Ⅰ～Ⅴ类水占比分别为12%、13%、9%、14%、52%,西北部洮儿河扇形地区水质远优于东南部平原区。通过两种方法的适用性验证,表明改进的AHP法是符合实际的。     

过度开采对地下水水化学特征的影响研究

为探究过度开采对地下水水化学特征的影响,通过对比分析研究区1997年和2010年的地下水水位与水质资料,研究了过度开采条件下地下水水位与水化学特征的动态规律及两者之间的联系。研究结果表明:1997年和2010年研究区地下水水位与水化学特征的空间变化规律具有很高的一致性,表现为地下水水位降幅较大的区域对应的镁离子、硫酸盐含量增幅也相对较大,地下水水化学特征受地下水水位变化的影响较大。空间叠加分析结果表明:镁离子、硫酸盐与地下水水位变化较大的区域空间重合率分别为72.2%,53.1%。过度开采通过改变地下水补径排条件及饱和带、非饱和带的水环境变化对地下水水化学特征产生影响,因此对于地下水不可盲目、过度开采。     

Influence of groundwater composition on subsurface iron and arsenic removal

Subsurface arsenic and iron removal (SAR/SIR) is a novel technology to remove arsenic, iron and other groundwater components by using the subsoil. This research project investigated the influence of the groundwater composition on subsurface treatment. In anoxic sand column experiments, with synthetic groundwater and virgin sand, it was found that several dissolved substances in groundwater compete for adsorption sites with arsenic and iron. The presence of 0.01 mmol L(-1) phosphate, 0.2 mmol L(-1) silicate, and 1 mmol L(-1) nitrate greatly reduced the efficiency of SAR, illustrating the vulnerability of this technology in diverse geochemical settings. SIR was not as sensitive to other inorganic groundwater compounds, though iron retardation was limited by 1.2 mmol L(-1) calcium and 0.06 mmol L(-1) manganese.     

Validity of the Latest Research Findings on Causes of Groundwater Arsenic Contamination in Bangladesh

Abstract

The groundwater arsenic contamination problem in Bangladesh is the worst in the world. Two hypotheses are prevailing as the cause (mobilization) of groundwater arsenic contamination in Bangladesh. One is called “pyrite oxidation” and the other is “oxy-hydroxide reduction.” According to the first hypothesis, groundwater arsenic contamination is human-made, which has a relationship with excessive groundwater withdrawal. On the other hand, according to the second one, the contamination is natural. The British Geological Survey (BGS) conducted an investigation to identify the cause of groundwater arsenic contamination in Bangladesh. Based on their findings, they rejected the pyrite oxidation hypothesis and accepted the oxy-hydroxide reduction hypothesis. However, several experts are opposing their research findings. Therefore, a case study is undertaken to examine the validity of the BGS findings. Although we obtained results which are similar to the BGS, the errors in the estimates of percent of wells contaminated, the key parameter of these analyse show that the present as well as BGS results are not dependable to make any conclusion about the cause of contamination. Moreover, the validity test shows that space-dependent relationships among different hydro-geological parameters for the heterogeneous aquifer system are not valid to represent time-dependent phenomena. Therefore, the conclusion made by the BGS is not valid. Still, there is a possibility that the pyrite oxidation hypothesis could be accepted. For a final conclusion we must observe these relationships in a time domain by generating reliable time-dependent field data.     

荷兰地下水中的砷对饮用水供给的影响

介绍了荷兰饮用水的供给状况,地下水中砷的分布,饮用水中的砷,以及8个典型水文系统中砷的形成过程、水化学特征,分析了荷兰地下水中砷的活动过程,主要包括:吸附和阴离子交换、黄铁矿的氧化反应和氧(氢氧)化铁的还原性溶解以及砷酸盐被还原成亚砷酸盐,并针对不同的情况提出了相应的治理措施。     

Risk-Based Evaluation for Meeting Future Water Demand of the Brahmaputra Floodplain Within Bangladesh

A risk-based evaluation is performed for meeting future water demands in the Brahmaputra Floodplain Area within Bangladesh (BFA). This evaluation is carried out using three risk-based performance indicators: reliability, resiliency and vulnerability. The vulnerability indicator has been redefined incorporating the aspect of a supply failure. The analysis includes the impacts of climate change on both water demands and resources, and the generation of synthetic flows of the Brahmaputra River using time series models. The simulated values of the indicators reveal that the expected demand of the BFA up to the year 2050 can be supplied with the proposed Brahmaputra Barrage inside Bangladesh under the ‘no change’ in climatic condition, provided that the groundwater remains usable. However, if groundwater becomes unusable due to widespread arsenic contamination and/or a climate change occurs, it would not be possible to meet the future water demand of the region with high reliability, moderate resiliency and low vulnerability.     

库计水源地地下水水化学特征分析

以库计水源地地下水为研究对象,在分析研究区水文地质条件的基础上,系统研究了研究区地下水的水化学时空变化特征：从外围分水岭向内以及由内部分水岭向周边,地下水水化学类型总体上沿地下水流向,呈HCO₃型→HCO₃•Cl型→HCO₃•SO₄•Cl型→SO₄•Cl型逐步过渡变化规律;在垂向上,中、浅层地下水水力联系较为密切,分带规律不明显,深部地下水水质略差;在时间上,由于白垩系含水层厚度巨大,垂向水力联系密切,且水位埋藏普遍较深,季节性变化对地下水水质影响有限,地下水水质相对稳定。     

Geostatistically based management of arsenic contaminated ground water in shallow wells of Bangladesh

This paper investigates the effectiveness of geostatistical approaches, specifically ordinary kriging, for regional management of arsenic contaminated shallow ground water in Bangladesh. The arsenic database for reference comprised the nation-wide survey (of 3534 drinking wells) completed in 1999 by the British Geological Survey (BGS) in collaboration with the Department of Public Health Engineering (DPHE) of Bangladesh. A Monte Carlo (MC) framework was devised for selection of randomly-sampled networks of wells from this reference database. Each randomly sampled network was assumed an equi-probable exploratory field campaign designed commensurably with the requirements of rapidity and cost-effectiveness in a rural setting. In general, the kriging method was found to underestimate the arsenic concentration at non-sampled locations. This underestimation exceeded the safe limits at the Holocene region of Southcentral Bangladesh. The probability of successful prediction of safe wells for this region was found to be 72% (WHO safe limit – 10 ppb) and 78% (Bangladesh safe limit – 50 ppb). For the Pleistocene Northwestern region of Bangladesh, the safe well prediction probability was in the ranges of 90%–97%. The relatively more contaminated Holocene region in Southcentral Bangladesh, on other hand, was found more amenable to accurate geostatistical prediction of unsafe wells. Findings from this study exemplify that, while mainstream geostatistical approaches (e.g., ordinary kriging) may not provide the most accurate prediction of mean arsenic concentration at non-sampled locations, they can delineate an approximate strategy for management of arsenic contaminated shallow ground water if applied carefully. The kriging methodology is applied to a test case in Bangladesh; the approach, however, is general and is expected to have application in rural settings for other developing countries where arsenic contamination of ground water is also widespread (e.g., parts of India, Vietnam, Taiwan and Mexico).     

海河平原区地下水中砷的时空分布特征

地下水是海河平原区的主要供水水源,于2014年3-11月采集了研究区内269个采样井的水样,检测了其中砷浓度。监测数据表明所有采样井的砷浓度均达到了Ⅲ类水水质要求。采用统计分析方法分析了海河平原区地下水中砷的时空变异特征。结果表明:砷的离散程度和变异系数均较高,在空间上呈现东高西低的趋势,砷浓度高的地区集中在天津、河北的环渤海地区以及河北省中部地区;在时间分布方面,夏季和秋季空间变异性较强,春季空间变异性中等,冬季空间变异性最弱;为预防砷中毒造成的危害,选择地下水开采井位时要避开富砷沉积物,井的上部妥善封闭。     

河套盆地晚更新世以来黄河改道对高砷地下水分布的控制机制

针对河套盆地开展了历时多年的水文地质环境地质调查,利用采集的298组浅层地下水样品以及收集并甄选的382个水文地质钻孔记录分析发现:河套盆地内95%的高砷地下水(As质量浓度10μg/L)集中在黄河决口、改道形成的古河道影响带及黄河决口扇裙带。其中,盆地南部首次发现了较为集中的高砷地下水,其分布范围与黄河北岸的晚更新世以来黄河决口、改道形成的4个大型决口扇,在空间上有着良好的对应关系。黄河古河道带及决口扇裙带表现为较强的还原环境及蒸发浓缩作用以及较弱的地表水补给强度。受pH值、含铁氧化物的还原性溶解等因素影响,决口扇裙带浅层地下水中砷的含量略低于平原中部黄河古河道带。结果表明:黄河古河道带及决口扇裙带特定的沉积环境控制着地下水的水文地球化学过程,进而对高砷地下水的分布具有决定性的作用。     

Occurrence of Arsenic-contaminatedGroundwater in Alluvial Aquifers from Delta Plains,Eastern India: Options for Safe Drinking Water Supply

Arsenic contamination in groundwater used for drinking purposes has been envisaged as a problem of global concern. Exploitation of groundwater contaminated with arsenic within the delta plains in West Bengal has caused adverse health effects among the population within a span of 8-10 years. The sources of arsenic in natural water are a function of the local geology, hydrology and geochemical characteristics of the aquifers. The retention and mobility of different arsenic species are sensitive to varying redox conditions. The delta plains in West Bengal are characterized by a series of meander belts formed by the fluvial processes comprising different cycles of complete or truncated fining upward sequences (sand-silt-clay). The arseniferous groundwater belts are mainly located in the upper delta plain and in abandoned meander channels. Mineralogical investigations have established that arsenic in the silty clay as well as in the sandy layers occurs as coatings on mineral grains. Clayey sediments intercalated with sandy aquifers at depths between 20 and 80 m are reported as a major source of arsenic in groundwater.Integrated knowledge on geological, hydrologicaland geochemical characteristics of the multi-level aquifer system of the upper delta plain is therefore necessary in predicting the origin, occurrence and mobility of arsenic in groundwater in West Bengal. This would also provide a basis for developing suitable low-cost techniques for safe drinking water supply in the region.     

Assessing Groundwater Geospatial Variation Using Microgravity Investigation in the Arid Riyadh Metropolitan Area,Saudi Arabia: a Case Study

A combination of relative microgravity measurements at ground surface, and depth to water and water table measurements from adjacent wells were used to estimate geospatial variation of groundwater. A highly accurate portable Grav-Map gravimeter was used for gravimetric measurements at locations nearby a 42 well water table monitoring program. To efficiently correlate the two data sets, wells were clustered into five groups by geological unit and water saturation. Microgravity data was processed, interpreted, and correlated with both the depths to groundwater and the water table levels. Regression analyses revealed a strong negative correlation for microgravity and depth to groundwater in all five clusters; correlation coefficients varied between 0.70 and 0.97, and measured 0.78 over the entire study area. Microgravity values increased as groundwater depth decreased, likely because rising groundwater fills voids and fractures within soil and rocks, increasing rock density and therefore relative gravity. To validate the correlation, we superimposed a map of depths to water on the first derivative of microgravity measurements. The shallowest groundwater depths were positively related to the zero first derivatives, having intersection areas within a 75 % significance interval. Negative first derivatives covered the rest of the study area, with relative gravity decreasing with increasing groundwater depth. This technique can precisely and efficiently determine changes in subsurface geology and geospatial changes in depths to the groundwater table. Distances between microgravity stations should be small, to better detect small changes in gravity values, reflecting density contrasts underground.     

贵州省都柳江砷污染事件的应急供水技术与实施要点

2007年12月底发生的贵州都柳江砷污染事件,造成下游三都县县城水厂被迫停水。清华大学张晓健教授及其课题组于2008年1月2日前往现场协助当地开展应急供水工作。应急处理采用了预氯化铁盐混凝法除砷净水工艺,先采用预氯化把水中可能存在的三价砷(亚砷酸)氧化成五价砷(砷酸氢根),再采用铁盐混凝剂混凝,用氢氧化铁絮体络合吸附砷酸根或是形成难溶的砷酸铁沉淀物,从而通过混凝沉淀过滤的净水过程进行除砷处理。经现场试验、设备改造、生产性运行调试和水质监测,应急除砷处理取得成功,出水达到《生活饮用水卫生标准》的水质要求,三都县县城水厂从1月6日15:00恢复正常供水,成为应对突发性砷污染的城市应急供水国内首次成功案例。     

焦作地区地下水水化学特征分析及水质评价

2017年对焦作地区42个地下水样品进行了采集和测试,综合运用数理统计、Piper三线图和相关性分析等方法分析了该区地下水水化学特征,并运用单因子评价和基于主成分分析的模糊综合评价法对研究区地下水水质进行了评价。研究结果表明:地下水中Ca²⁺、Mg²⁺、SO^2-₄和HCO₃^-占主要优势,浅层地下水水化学类型按地下水径流方向由HCO₃-Ca型逐渐演变为HCO₃·SO₄-Ca·Mg型和HCO₃·SO₄·Cl-Ca ·Mg型,深层地下水水化学类型主要为HCO₃·SO₄-Ca·Mg型,局部为HCO₃·SO₄-Ca·Mg型;水体离子组分变化主要受碳酸盐、硫酸盐和岩盐等风化溶滤作用影响;单因子评价结果显示TH、Mg²⁺、TDS、SO^2-₄等组分的超标是影响地下水质量的主要因素;模糊综合评价结果显示研究区浅层及深层地下水质满足Ⅲ类水及以上标准的采样点,分别占总采样点的61%和75%。研究成果可为该地区水质评价和水资源合理开发利用提供依据。     

Development and Application of a Watertable Model for the Assessment of Waterlogging in Irrigated Semi-arid Regions

Direct measurement of groundwater recharge is nearly impossible. So there are various direct and indirect methods and sophisticated models have been used for its estimation. However, the use of multiple approaches has been recommended to estimate the groundwater recharge since each individual approach is associated with some limitations. In many cases, different approaches complement each other and help refine the conceptual model of recharge processes. In this study, a simple watertable model, which is a combination of the groundwater budget and watertable fluctuation, was developed. The model is unique, simple, cost effective, and easy to apply. The model requires input parameters that are readily available or obtainable and which can be accurately measured. The model was applied to estimate the seasonal long?Cterm (30?years, e.g., from 1981 to 2011) groundwater recharge of a canal command located in Jhajjar district of Haryana State (India), where watertable is rising. The results were analysed to provide an overview of the process dynamics that led to watertable rise in the command area. The calculated watertable depths reasonably matched with the observed ones for all the seasons which were confirmed by the high R?Csquared value of 0.963. The mean error and root mean squared error were low at ?C0.0068 and 0.2548?m, respectively, while the model efficiency was 0.83. Different water management alternatives were studied to examine the effect of variation in model parameters on its output. Among the alternatives studied, increased tubewell draft had a higher impact on the overall water balance followed by reduced rice area and canal lining, respectively.     

滹沱河流域平原区地下水流场异常变化与原因

应用数理统计相关分析方法,对过去50年滹沱河流域平原区地下水流场演变特征及其与降水量和开采量之间关系的研究表明,常年性地下水位降落漏斗是地下水流场发生异变的标志性特征.在气候不断旱化背景下,地下水开采量和开采强度的不断增大导致该平原区地下水系统从1971年以前的补给-开采的自然均衡状态,经过1971-1979年期间补给-开采基本均衡状态,至1980年之后演变为严重超采状态.同天然状态下地下水流场相比,漏斗区地下水流方向与区域流场明显不一致,某些地段甚至逆向流动.关联分析结果表明,开采量是滹沱河流域平原区地下水流场异变的主导因素,降水量变化是重要影响因素.降水量增减通过影响地下水开采量大小和补给量多少的变化,对地下水流场产生不同的影响.减少开采量或降水量连年显著增大,区内地下水流场异变才能够产生根本性转变.因此,适时调控开采量.使其与气候变化规律相一致,有利于遏制该区地下水流场异变态势.     

Groundwater Use for Irrigation and its Productivity: Status and Opportunities for Crop Intensification for Food Security in Bangladesh

Bangladesh has a large and growing population that will demand more food and place greater pressure on resources. Dry season irrigated Boro rice production is important for national food security. Dry season irrigation mainly uses groundwater, but the extent of its use is not well known. We assessed groundwater use and water productivity of Boro in the northwest region of Bangladesh using remote sensing based energy balance modelling, crop classification and secondary statistics. The energy balance modelling shows a large spatial variation in the actual evapotranspiration (ET_a) from about 325 to 470 mm, with an overall spatial average of 365 mm during dry season. The estimated values of ET_a correspond well with independent values from field and regional scale soil and water balance modelling results. From spatial estimates of ET_a and effective rainfall, we computed regional net groundwater use for Boro production in 2009 as 2.4 km³. Groundwater is being used unsustainably in some areas, and a spatial time series (1990 to 2010) of pre- and post-monsoon groundwater depth changes in the northwest region of Bangladesh suggests that, with the current level of groundwater use, falling groundwater levels may pose a long term threat to the sustainability of irrigated agriculture in much of the region. Boro water productivity varies from 0.95 to 1.35 kg/m³, allowing the identification of high performing “bright” and low performing “hot” spots and the development of strategies to reduce crop yield/productivity gaps and ensure future food security.     

Groundwater Drought in the Northwestern Districts of Bangladesh

Prolonged absence of groundwater within the operating range of shallow tube-wells during dry season is a common problem in the northwestern districts of Bangladesh in the recent years. In this paper, groundwater scarcity and drought in three northwestern districts of Bangladesh have been investigated. The Cumulative Deficit approach from a threshold groundwater level has been used for the computation of severity of groundwater droughts. Monthly groundwater fluctuation data collected from 85 sites is used for the study. The study shows that groundwater scarcity in 42% area is an every year phenomenon in the region. Analysis of groundwater hydrographs and rainfall time-series reveals that ever increasing groundwater extraction for irrigation in the dry season and recurrent droughts are the causes of groundwater level drop in the region.     

不同灌水方式下作物与地下水的相互影响效应

为了节约灌溉水资源,利用实验室内相关装置模拟浅层地下水条件,对沪油15号油菜施以不同灌水方式,研究了不同灌水方式下作物与浅层地下水之间的相互影响效应。结果表明:在表层6 cm深度土壤,不同灌水方式下土壤含水量动态变化的差异非常明显,这些差异与地下水条件无关;在稍深一些的20 cm土层深度处,在无地下水处理的交替灌溉条件下,很难看出不同灌水沟下土壤含水量的波动变化。这说明在有浅层地下水的情况下,对作物进行交替灌溉能够促使作物更有效地利用浅层地下水。