Low-cost defluoridation of water using broken bricks
活性氧化铝饮用水除氟的研究进展
活性氧化铝饮用水除氟的研究进展摘要：活性氧化铝能够作为一种优良的饮用水除氟剂，很多学者在此方面进行了大量的研究。
文章简述了国内外在饮用水领域进行除氟的研究意义和概况，从活性氧化铝的制备方法、实验研究、除氟机理、应用开发等方面，综述了活性氧化铝除氟的研究进展，为活性氧化铝除氟材料的进一步研究和应用提供了依据。
关键词：活性氧化铝；除氟；饮用水氟是人体不可缺少的微量元素，氟元素可以通过饮用水、食物和呼吸等各种途径进入人体，其中最主要的途径是饮用水。
但是，当饮用水中氟的浓度过高（大于1.5 mg/L）时，反而会损害人体的健康。
我国氟含量超标的地下水分布广泛，同时，化工、电子、电镀、金属表面清洗、冶金及农药等行业含氟废水的产生、排放，也严重污染着人类赖以生存的水资源。
近年来，我国因饮用水中氟含量超标而造成的氟中毒的现象已较为严重，约有7 700万人长期饮用水中氟含量超标，氟斑牙患者达4 000余万，氟骨症患者达260余万，饮用水的除氟成为我国急需解决的问题。
因此，开发简单、便捷的除氟方法，研究新型、高效的除氟材料，保障水质安全，具有重要的社会意义。
目前，饮用水除氟的方法有很多，如：吸附法、化学沉淀法、混凝沉降法、电化学法、反渗透法和离子交换法等，其中吸附法对氟的吸附效果显著，是除氟的主要方法。
饮用水除氟使用的吸附剂主要有：活性氧化铝（γ-Al2O3）、活性氧化镁、沸石、聚合铝盐、活性炭、分子筛等。
吸附剂使用的球状活性氧化铝比表面积大（大于260 m2/g）、孔容积大（大于0.40 ml/g），存在大量晶格缺陷，因此具有较强的吸附性能，且其机械强度高、物化稳定性好、耐高温及抗腐蚀性能好，能够作为一种优良的饮水除氟剂。
国内对活性氧化铝除氟技术的研究和应用一致较为重视，但由于对其除氟机理的研究还不充分，实际应用中还存在一些技术问题，阻碍了该除氟方法的进一步推广和普及。
目前，与活性氧化铝除氟性能相关的研究主要有制备方法、除氟实验、除氟机理、除氟技术应用等四个方面。
节约用水的原因和措施英语作文
节约用水的原因和措施英语作文Water conservation is a critical issue that affects individuals, communities, and the global environment. The reasons for the need to conserve water and the measures that can be taken to do so are multifaceted and important to understand.One of the primary reasons for the need to conserve water is the scarcity of freshwater resources. While water covers the majority of the Earth's surface, only a small percentage of that water is suitable for human consumption and use. The vast majority of the world's water is saltwater, which is not suitable for drinking, agriculture, or industrial purposes without extensive and costly treatment. Additionally, many regions of the world are experiencing severe droughts and water shortages due to climate change, population growth, and other factors, further exacerbating the scarcity of freshwater resources.Another reason for the need to conserve water is the impact that water usage has on the environment. The extraction and use of water can have a significant impact on ecosystems, habitats, and wildlife. For example, the diversion of water from rivers and lakes can disrupt the natural flow of water and negatively impact the organisms thatdepend on those water sources. Additionally, the treatment and distribution of water can consume large amounts of energy, which in turn can contribute to greenhouse gas emissions and climate change.Furthermore, the increasing demand for water due to population growth and economic development has put a strain on water resources around the world. As more people require access to clean water for drinking, sanitation, agriculture, and industry, the demand for water continues to rise. This increased demand can lead to the overexploitation of water resources, which can have long-term consequences for the availability and quality of water.To address these issues, there are a number of measures that can be taken to conserve water. One of the most important measures is to improve water efficiency in various sectors, such as agriculture, industry, and residential use. This can be achieved through the use of water-efficient technologies, such as low-flow toilets, showerheads, and irrigation systems, as well as through the adoption of water-saving practices, such as turning off taps when not in use and taking shorter showers.Another important measure is to improve water infrastructure, such as by repairing leaks in water pipes and upgrading water treatment facilities. This can help to reduce water waste and improve the overall efficiency of water distribution and treatment.In addition to these technical measures, there is also a need to raise awareness and promote behavioral changes among individuals and communities. This can be achieved through education and outreach programs that teach people about the importance of water conservation and provide them with practical tips and strategies for reducing their water usage.Overall, the need to conserve water is a critical issue that requires a multifaceted approach involving technological, infrastructural, and behavioral changes. By taking these measures, we can help to ensure that water resources are used more efficiently and sustainably, and that they are available for generations to come.。
二氧化钛去除水中氟离子的研究进展
二氧化钛去除水中氟离子的研究进展龚向红1，付娆2，冯江涛2*(1.义乌市水处理有限责任公司，浙江 义乌 322000； 2. 西安交通大学能源与动力工程学院环境工程系，陕西 西安 710049)摘要：中国是典型的大面积高氟地区，因此，对饮用水中氟离子去除的研究尤为重要。
二氧化钛作为一种新型除氟剂的理想材料，具备良好的应用前景。
文章简述了二氧化钛材料的液相合成技术，指出了当前二氧化钛材料合成的发展方向。
并进一步综述了二氧化钛作为吸附剂吸附去除水中氟离子的研究现状，深入探讨了影响吸附过程的因素以及相应的吸附机理。
最后，提出了二氧化钛吸附去除氟离子过程中亟待研究和解决的问题。
关键词：二氧化钛；吸附；氟离子中图分类号： TQ0 文献标志码：A 文章编号：1008-4800(2021)11-0058-02DOI:10.19900/ki.ISSN1008-4800.2021.11.029Research Progress of Fluoride Removal from Water by Titanium DioxideGONG Xiang-hong 1, FU Rao 2, FENG Jiang-tao 2* (1.Yiwu Water Treatment Co., Ltd., Yiwu 322000, China ;2.Department of Environmental Engineering, Xi'an Jiaotong University, Xi'an 710049, China )Abstract: China is a typical large area with high fluoride, so it is very important to study the removal of fluoride from drinking water. As an ideal material of new defluoridation agent, titanium dioxide has a good application prospect. In this paper, the liquid phase synthesis technology of titanium dioxide materials is briefly described, and the development trend of titanium dioxide materials synthesis is pointed out. In addition, the research status of fluoride removal by titanium dioxide as adsorbent was reviewed, and the factors affecting the adsorption process and the adsorption mechanism were discussed. Finally, the problems that need to be studied and solved in the process of fluoride removal by titanium dioxide adsorption are put forward.Keywords: titanium dioxide; adsorption; fluoride ion0引言氟能维持人体正常的生理活动，是人体必需的微量元素之一。
羟基磷灰石相关复合材料的研究进展
第46卷第3期2021年6月广州化学Guangzhou ChemistryV ol. 46 No. 3Jun. 2021文章编号：1009-220X(2021)03-0022-08 DOI:10.16560/ki.gzhx.20210313羟基磷灰石相关复合材料的研究进展范云辉，王世革，黄明贤*（上海理工大学理学院，上海200093）摘要：羟基磷灰石（HAp）作为骨骼中的无机矿物成分，是天然的生物陶瓷材料。
由于特殊的结构组成，其具有良好的生物相容性和生物活性。
然而，纯的HAp纳米颗粒容易团聚且机械强度低，因此往往需要进一步改性和功能化用于合成HAp相关的复合材料。
本综述对元素或官能团掺杂、聚合物/HAp交联、HAp固定在载体材料表面等方式制备的HAp复合材料，及其在环境中分离纯化应用的研究进展进行讨论与分析。
最后对HAp相关复合材料的发展前景做出了总结与展望。
关键词：羟基磷灰石；复合材料；分离纯化中图分类号：O651 文献标识码：A对羟基磷灰石（HAp）材料的研究已经进行了半个多世纪，其作为动物骨骼的无机组分，是重要的生物材料。
近年来，随着纳米科学的不断发展，合成的纳米HAp的应用范围越来越广。
有关HAp的综述报道，主要是涉及不同的制备方法（包括固态法[1-2]、传统的化学沉淀法[3-4]、溶胶凝胶法[5-6]、水热法[7-8]、模板法[9-10]等）的总结[11]，HAp纳米材料作为骨和牙齿替代物的应用，以及药物输送和癌症治疗方面的研究[12-15]。
可以发现，关于HAp复合材料及其在分离纯化中应用的报道较少。
因此，本文对HAp相关复合材料的结构设计和在环境中作为分离纯化材料的最新进展进行了简单的归纳总结。
1 概述HAp作为脊椎动物牙齿和骨骼中的主要无机成分，在生物陶瓷领域引起了广泛关注。
HAp属于磷酸钙，是磷灰石中的一种。
磷灰石的一般结构式可以表示为M10(ZO4)6X2，这里M，ZO4和X可以分别被替换成下列离子[16-17]：M=K，Mg，Mn，Pb，Co，Zn，Au，Ba，Cd，Al，Fe，La，Ce，Si，Ti等；ZO4=CO3，SiO4，HPO4，SeO2等；X=F，Cl等。
219385450_钙盐-混凝法处理高氟废水的实验研究
DOI ：10.19965/ki.iwt.2022-0724第 43 卷第 6 期2023年 6 月Vol.43 No.6Jun.，2023工业水处理Industrial Water Treatment 钙盐-混凝法处理高氟废水的实验研究崔兵1，金怡2，杨泽坤1（1.中煤科工集团杭州研究院有限公司，浙江杭州 311201；2.杭州电子科技大学材料与环境工程学院，浙江杭州 310018）[ 摘要 ] 含氟废水会对环境造成巨大危害，但传统钙盐法难以实现含氟废水达标排放。
为解决某光伏企业的高氟废水处理问题，本研究对实际生产废水进行研究，确立了一级钙盐联合二级混凝的工艺路线，并对高氟废水进行单因素实验和正交试验，以钙盐种类及投加量、反应pH 、混凝剂种类为变量，以出水残氟质量浓度为考察指标，为工程应用确定了一种合适的除氟工况。
结果表明，影响除氟效果的因素依次为钙氟物质的量比>二级混凝反应pH>复合除氟剂（DAMW-03）用量>一级钙盐反应pH 。
最优除氟工况为：一级钙盐反应以CaCl 2为钙源，钙源投加量为理论钙氟物质的量比（0.5）的1.25倍以上，并使用Ca （OH ）2调节pH=8；二级混凝反应可添加50 mg/L PAC 或复合除氟剂（DAMW-03），控制pH 在5~7，最终可实现中性出水且出水ρ（F -）可稳定小于5 mg/L 。
一级钙盐法联合二级混凝法可使高氟废水稳定达标排放，具有处理效率高、试剂易得、处理成本较低等优点。
［关键词］ 含氟废水；钙盐沉淀；混凝沉淀；正交试验［中图分类号］ X703.1 ［文献标识码］A ［文章编号］ 1005-829X （2023）06-0150-06Research on the treatment of high fluoride wastewater bycalcium salt -coagulation methodCUI Bing 1，JIN Yi 2，YANG Zekun 1（1.Hangzhou Research Institute of China Coal Technology & Engineering Group ，Hangzhou 311201，China ；2.College of Materials & Environmental Engineering ，Hangzhou Dianzi University ，Hangzhou 310018，China ）Abstract ：Fluorine -containing wastewater does great harm to the environment ，but the traditional calcium salt method is difficult to achieve the standard discharge of fluorinated wastewater. In order to solve the problem of highfluorine wastewater treatment in a photovoltaic enterprise ，the experiments were conducted on the wastewater which came from enterprise production. The process route of the first -order calcium salt combined with the secondary co⁃agulation was established. The single factor experiment and orthogonal experiment were carried out on the high fluo⁃rine wastewater. Taking the types and dosage of calcium salt ，pH and types of coagulant as variables ，and the re⁃sidual fluorine concentration as the investigation index ，a suitable defluorination condition was determined for the engineering application. The experimental results showed that the factors affecting the fluoride removal efficiencywere in the order of ratio of calcium to fluoride>secondary coagulation reaction pH>composite defluorination agent （DAMW -03） dosage>first -order calcium salt reaction pH. The optimal defluorination conditions were as follows ：the first -order calcium salt reaction could use CaCl 2 as the calcium source ，the amount of CaCl 2 added was more than 1.25 times of theoretical ratio of calcium to fluorine （0.5），and Ca （OH ）2 was used to adjust pH=8，50 mg/L PAC or composite defluorination agent （DAMW -03） could be added to the secondary coagulation reaction ，and controlledpH between 5-7. Finally ，neutral effluent could be achieved ，and ρ（F -） of the effluent could be stably less than 5 mg/L. The first -order calcium salt method combined with the second -stage coagulation method could make the high -fluorine wastewater stably meet the discharge standard. It had the advantages of high treatment efficiency ，easy availability of reagents and low treatment cost.Key words ：fluorinated wastewater ；calcium salt sedimentation ；coagulation sedimentation ；orthogonal experiment开放科学（资源服务）标识码（OSID ）：工业水处理 2023-06，43（6）崔兵，等：钙盐-混凝法处理高氟废水的实验研究在“双碳”目标影响下，多晶硅生产现处于蓬勃发展阶段〔1〕。
Fluoride in drinking water and its removal
Journal of Hazardous Materials B137(2006)456–463Fluoride in drinking water and its removalMeenakshi∗,R.C.MaheshwariCentre for Rural Development and Technology,Indian Institute of Technology,Delhi,Hauz Khas,New Delhi,IndiaReceived2March2005;received in revised form15February2006;accepted16February2006Available online28February2006AbstractExcessivefluoride concentrations have been reported in groundwaters of more than20developed and developing countries including India where19states are facing acutefluorosis problems.Various technologies are being used to removefluoride from water but still the problem has not been rooted out.In this paper,a broad overview of the available technologies forfluoride removal and advantages and limitations of each one have been presented based on literature survey and the experiments conducted in the laboratory with several processes.It has been concluded that the selection of treatment process should be site specific as per local needs and prevailing conditions as each technology has some limitations and no one process can serve the purpose in diverse conditions.©2006Published by Elsevier B.V.Keywords:Fluoride;Fluorosis;Ground water;Soil water;Drinking water;Treatment1.IntroductionWater is an essential natural resource for sustaining life and environment that we have always thought to be available in abundance and free gift of nature.However,chemical compo-sition of surface or subsurface is one of the prime factors on which the suitability of water for domestic,industrial or agri-cultural purpose depends.Freshwater occurs as surface water and groundwater.Though groundwater contributes only0.6% of the total water resources on earth,it is the major and the pre-ferred source of drinking water in rural as well as urban areas, particularly in the developing countries like India because treat-ment of the same,including disinfection is often not required. It caters to80%of the total drinking water requirement and 50%of the agricultural requirement in rural India.But in the era of economical growth,groundwater is getting polluted due to urbanization and industrialization.Over the past few decades,the ever-growing population, urbanization,industrialization and unskilled utilization of water resources have led to degradation of water quality and reduction in per capita availability in various developing countries.Due to various ecological factors either natural or anthropogenic, the groundwater is getting polluted because of deep percolation ∗Corresponding author.E-mail address:mpahwa2000@(Meenakshi).from intensively cultivatedfields,disposal of hazardous wastes, liquid and solid wastes from industries,sewage disposal,sur-face impoundments etc.[1–4].During its complexflow history, groundwater passes through various geological formations lead-ing to consequent contamination in shallow aquifers.Presence of various hazardous contaminants likefluoride, arsenic,nitrate,sulfate,pesticides,other heavy metals etc.in underground water has been reported from different parts of India[5–9].In many cases,the water sources have been ren-dered unsafe not only for human consumption but also for other activities such as irrigation and industrial needs.Therefore,now there is a need to focus greater attention on the future impact of water resources planning and development taking into con-sideration all the related issues.In India,fluoride is the major inorganic pollutant of natural origin found in groundwater.In this paper detailed review on sources,ill effects and techniques available forfluoride removal is done.2.Occurrence and sourcesFluoride in minute quantity is an essential component for normal mineralization of bones and formation of dental enamel [10].However,its excessive intake may result in slow,progres-sive crippling scourge known asfluorosis.There are more than 20developed and developing nations that are endemic forflu-orosis.These are Argentina,U.S.A.,Morocco,Algeria,Libya,0304-3894/$–see front matter©2006Published by Elsevier B.V. doi:10.1016/j.jhazmat.2006.02.024Meenakshi,R.C.Maheshwari/Journal of Hazardous Materials B137(2006)456–463457 Table1Districts known to be endemic forfluoride in various states of India[18]States Districts Range offluorideconcentration(mg/L) Assam Karbianglong,Nagaon0.2–18.1Andhra Pradesh All districts except Adilabad,Nizamabad,West Godhavari,Visakhapattnam,Vijzianagaram,Srikakulam0.11–20.0Bihar Palamu,Daltonganj,Gridh,Gaya,Rohtas,Gopalganj,Paschim,Champaran0.6–8.0Delhi Kanjhwala,Najafgarh,Alipur0.4–10.0Gujarat All districts except Dang 1.58–31.0Haryana Rewari,Faridabad,Karnal,Sonipat,Jind,Gurgaon,Mohindergarh,Rohtak,Kurukshetra,Kaithal,Bhiwani,Sirsa,Hisar0.17–24.7Jammu and Kashmir Doda0.05–4.21 Karnataka Dharwad,Gadag,Bellary,Belgam,Raichur,Bijapur,Gulbarga,Chitradurga,Tumkur,Chikmagalur,Manya,Banglore,Mysore0.2–18.0Kerala Palghat,Allepy,Vamanapuram,Alappuzha0.2–2.5 Maharashtra Chandrapur,Bhandara,Nagpur,Jalgaon,Bulduna,Amravati,Akola,Yavatmal,Nanded,Sholapur0.11–10.2Madhya Pradesh Shivpuri,Jabua,Mandla,Dindori,Chhindwara,Dhar,Vidhisha,Seoni,Sehore,Raisen and Bhopal0.08–4.2Orrissa Phulbani,Koraput,Dhenkanal0.6–5.7Punjab Mansa,Faridcot,Bhatinda,Muktsar,Moga,Sangrur,Ferozpur,Ludhiana,Amritsar,Patila,Ropar,Jallandhar,Fatehgarh sahib0.44–6.0 Rajasthan All the32districts0.2–37.0 Tamilnadu Salem,Periyar,Dharampuri,Coimbatore,Tiruchirapalli,Vellore,Madurai,Virudunagar 1.5–5.0Uttar Pradesh Unnao,Agra,Meerut,Mathura,Aligarh,Raibareli,Allahabad0.12–8.9West Bengal Birbhum,Bhardaman,Bankura 1.5–13.0Egypt,Jordan,Turkey,Iran,Iraq,Kenya,Tanzania,S.Africa, China,Australia,New Zealand,Japan,Thailand,Canada,Saudi Arabia,Persian Gulf,Sri Lanka,Syria,India,etc.[11].In India, it wasfirst detected in Nellore district of Andhra Pradesh in1937 [12].Since then considerable work has been done in different parts of India to explore thefluoride laden water sources and their impacts on human as well on animals[13–17].At present, it has been estimated thatfluorosis is prevalent in17states of India(Table1).The safe limit offluoride in drinking water is1.0mg/L[19]. The endemicfluorosis in India is largely of hydrogeochemical origin.It has been observed that low calcium and high bicar-bonate alkalinity favor highfluoride content in groundwater [20,21].Water with highfluoride content is generally soft,has high pH and contains large amount of silica.In groundwater, the natural concentration offluoride depends on the geolog-ical,chemical and physical characteristics of the aquifer,the porosity and acidity of the soil and rocks,temperature,the action of other chemicals and the depth of wells.Due to large number of variables,thefluoride concentrations in groundwa-ter range from well under1.0mg/L to more than35.0mg/L [22].As the amount of water consumed and consequently the amount offluoride ingested is influenced primarily by air tem-perature,USPHS[23]has set a range of concentrations for maximum allowablefluoride in drinking water for communi-ties based on the climatic conditions as shown in Table2.Fluorine is highly reactive and is found naturally as CaF2. It is an essential constituent in minerals like topaz,fluorite,fluorapatite,cryolite,phosphorite,theorapatite,etc.[24].The fluoride is found in the atmosphere,soil and water.It enters the soil through weathering of rocks,precipitation or waste run off. Surface waters generally do not contain more than0.3mg/L of fluoride unless they are polluted from external sources.Though drinking water is the major contributor(75–90%of daily intake), other sources offluoride poisoning are food,industrial exposure, drugs,cosmetics,etc.[25].Thefluoride content of some major food products is given in Table3.3.Health impacts offluorideFluorine being a highly electronegative element has extraor-dinary tendency to get attracted by positively charged ions like calcium.Hence the effect offluoride on mineralized tissues likeTable2USPHS recommendations for maximum allowablefluoride in drinking waterAnnual average of maximum daily air temperature(◦C)Recommendedfluoride concentration(mg/L)Maximum allowablefluorideconcentration(mg/L) Lower Optimum Upper10–120.9 1.2 1.7 2.4 12.1–14.60.8 1.1 1.5 2.2 14.7–17.70.8 1.0 1.3 2.0 17.8–21.40.70.9 1.2 1.8 21.5–26.20.70.8 1.0 1.6 26.3–32.50.60.70.8 1.4458Meenakshi,R.C.Maheshwari/Journal of Hazardous Materials B137(2006)456–463Table3Fluoride concentration in agricultural crops and other edible items[26]Food item Fluoride concentration(mg/kg) CerealsWheat 4.6Rice 5.9MaizePulses and legumes 5.6Green gram dal 2.5Red gram dal 3.7Soyabean 4.0VegetablesCabbage 3.3Tomato 3.4Cucumber 4.1Ladyfinger 4.0Spinach 2.0Lettuce 5.7Mint 4.8Potato 2.8Carrot 4.1FruitsMango 3.7Apple 5.7Guava 5.1Nuts and oil seedsAlmond 4.0Coconut 4.4Mustard seeds 5.7Groundnut 5.1BeveragesTea60–112Aerated drinks0.77–1.44Spices and condimentsCorriander 2.3Garlic 5.0Turmeric 3.3Food from animal sourcesMutton 3.0–3.5Beef 4.0–5.0Pork 3.0–4.5Fishes 1.0–6.5OthersRock salts200.0–250.0Areca but(supari) 3.8–12.0Beetle leaf(pan)7.8–12.0Tobacco 3.2–38bone and teeth leading to developmental alternations is of clini-cal significance as they have highest amount of calcium and thus attract the maximum amount offluoride that gets deposited as calcium–fluorapatite crystals.Tooth enamel is composed prin-cipally of crystalline hydroxylapatite.Under normal conditions, whenfluoride is present in water supply,most of the ingested fluoride ions get incorporated into the apatite crystal lattice of calciferous tissue enamel during its formation.The hydroxyl ion gets substituted byfluoride ion sincefluorapatite is more stable than hydroxylapatite.Thus,a large amount offluoride gets bound in these tissues and only a small amount is excreted Table4Effects offluoride in water on human healthFluoride concentration(mg/L)Effects<1.0Safe limit1.0–3.0Dentalfluorosis(discoloration,mottling andpitting of teeth)3.0–4.0Stiffened and brittle bones and joints4.0–6.0and above Deformities in knee and hip bones andfinallyparalysis making the person unable to walk orstand in straight posture,cripplingfluorosisthrough sweat,urine and stool.The intensity offluorosis is not merely dependent on thefluoride content in water,but also on the fluoride from other sources,physical activity and dietary habits.The various forms offluorosis arising due to excessive intake offluoride are briefly discussed below(Table4)[27,28].3.1.DentalfluorosisDue to excessivefluoride intake,enamel loses its lustre.In its mild form,dentalfluorosis is characterized by white,opaque areas on the tooth surface and in severe form,it is manifestated as yellowish brown to black stains and severe pitting of the teeth. This discoloration may be in the form of spots or horizontal streaks[29].Normally,the degree of dentalfluorosis depends on the amount offluoride exposure up to the age of8–10,as fluoride stains only the developing teeth while they are being formed in the jawbones and are still under the gums.The effect of dentalfluorosis may not be apparent if the teeth are already fully grown prior to thefluoride over exposure.Therefore,the fact that an adult shows no signs of dentalfluorosis does not necessarily mean that his or herfluoride intake is within the safety limit.3.2.SkeletalfluorosisSkeletalfluorosis affects children as well as adults.It does not easily manifest until the disease attains an advanced stage.Fluo-ride mainly gets deposited in the joints of neck,knee,pelvic and shoulder bones and makes it difficult to move or walk.The symp-toms of skeletalfluorosis are similar to spondylitis or arthritis. Early symptoms include sporadic pain,back stiffness,burning like sensation,pricking and tingling in the limbs,muscle weak-ness,chronic fatigue,abnormal calcium deposits in bones and ligaments.The advanced stage is osteoporosis in long bones and bony outgrowths may occur.Vertebrae may fuse together and eventually the victim may be crippled.It may even lead to a rare bone cancer,osteosarcoma andfinally spine,major joints, muscles and nervous system get damaged.3.3.Other problemsThis aspect offluorosis is often overlooked because of the notion prevailing thatfluoride only affects bones and teeth[30]. Besides skeletal and dentalfluorosis,excessive consumption of fluoride may lead to musclefibre degeneration,low haemoglobinMeenakshi,R.C.Maheshwari/Journal of Hazardous Materials B137(2006)456–463459levels,deformities in RBCs,excessive thirst,headache,skin rashes,nervousness,neurological manifestations(it affects brain tissue similar to the pathological changes found in humans with Alzheimer’s disease),depression,gastrointestinal problems,uri-nary tract malfunctioning,nausea,abdominal pain,tingling sensation infingers and toes,reduced immunity,repeated abor-tions or still births,male sterility,etc.It is also responsible for alterations in the functional mechanisms of liver,kidney, digestive system,respiratory system,excretory system,central nervous system and reproductive system,destruction of about 60enzymes.The effects offluoride in drinking water on animals are analogous to those on human beings.The continuous use of water having highfluoride concentration also adversely affects the crop growth.3.4.Solutions to the problemA community with excessivefluoride in its water supply may meet the local MCL in one or more of several ways.Fluoride poisoning can be prevented or minimized by:ing alternate water sources.2.By improving the nutritional status of population at risk.3.By removing excessfluoride(defluoridation).3.4.1.Alternate water sourcesAlternate water sources include surface water,rainwater and low-fluoride groundwater.Since surface water is often heavily contaminated with biological and chemical pollutants,it cannot be used for drinking purposes without treatment and disinfec-tion making it too expensive and complex for application in poor communities.Rainwater is usually a much cleaner water source and may provide a low-cost simple solution.The prob-lem however is its uneven distribution limited storage capacity in communities or households.The fact thatfluoride is unevenly distributed in groundwater and its concentration keeps on chang-ing with time both vertically and horizontally,implies that every well has to be tested individually and regular monitoring has to be done,which is not always possible in rural areas.Thus the option of using alternate water sources has its own limitations.3.4.2.Better nutritionClinical data indicate that adequate calcium intake is directly associated with a reduced risk of dentalfluorosis[31].Vitamin C also safeguards against the risk[32].Though,measures to improve the nutritional status of an affected population might be an effective supplement to the technical solutions of the problem, practically it sounds non-feasible.3.4.3.Defluoridation of waterDefluoridation of drinking water is the only practicable option to overcome the problem of excessivefluoride in drink-ing water,where alternate source is not available.During the years following the discovery offluoride as the cause offluo-rosis,extensive research has been done on various methods for removal offluoride from water and wastewater.These meth-ods are based on the principle of adsorption[33],ion-exchange [34],precipitation–coagulation[35,36],membrane separation process[37,38],electrolytic defluoridation[39],electrodialysis [40–42],etc.3.4.3.1.Adsorption.Several adsorbent materials have been tried in the past tofind out an efficient and economical deflu-oridating agent.Activated alumina,activated carbon,activated alumina coated silica gel,calcite,activated saw dust,activated coconut shell carbon and activatedfly ash,groundnut shell, coffee husk,rice husk,magnesia,serpentine,tricalcium phos-phate,bone charcoal,activated soil sorbent,carbion,defluoron-1,defluoron-2,etc.,are different adsorbent materials reported in the literature[43–51].The most commonly used adsorbents are activated alumina and activated carbon.Thefluoride remov-ing efficiency of activated alumina gets affected by hardness and surface loading(the ratio of totalfluoride concentration to activated alumina dosage).Chloride does not affect the defluori-dation capacity of activated alumina.The process is pH specific, so pH of the solution should be between5.0and6.0because at pH>7,silicate and hydroxide become stronger competitor of thefluoride ions for exchange sites on activated alumina and at pH less than5,activated alumina gets dissolved in acidic environment leading to loss of adsorbing media[52].The process is highly selective but it has low adsorption capacity, poor physical integrity,requires acidification and pretreatment and its effectiveness forfluoride removal reduces after each regeneration.Mckee and Johnston1934,investigated the use of powdered activated carbon forfluoride removal and achieved good results [53].The process is pH dependent with good results only at pH 3.0or less.Therefore,the use of this material is expensive due to need of pH adjustment.Activated alumina technique for defluoridation is being prop-agated in several villages by the voluntary organizations funded by UNICEF or other agencies to provide safe drinking water. Sarita Sansthan,Udaypur,Rajasthan is disseminating the tech-nique with the practical assistance of UNICEF by providing a bucket(approximately20L capacity)fitted with a microfilter at the bottom containing5kg of activated alumina.3.4.3.1.1.Advantages.•The process can removefluoride up to90%.•Treatment is cost-effective.3.4.3.1.2.Limitations.•The process is highly dependent on pH and works best only in a narrow pH range(5–6).•High concentration of total dissolved salts(TDS)can result in fouling of the alumina bed.•Presence of sulfate,phosphate or carbonate results in ionic competition.•The process has low adsorption capacity,poor integrity and needs pretreatment.•The regeneration is required after every4–5months and effec-tiveness of adsorbent forfluoride removal reduces after each regeneration.460Meenakshi,R.C.Maheshwari/Journal of Hazardous Materials B137(2006)456–463•Disposal offluoride laden sludge and concentrated regenerant is also a problem.3.4.3.2.Ion-exchange.Fluoride can be removed from water supplies with a strongly basic anion-exchange resin containing quarternary ammonium functional groups.The removal takes place according to the following reaction:Matrix-NR3+Cl−+F−→Matrix-NR3+F−+Cl−Thefluoride ions replace the chloride ions of the resin.This process continues until all the sites on the resin are occupied. The resin is then backwashed with water that is supersaturated with dissolved sodium chloride salt.New chloride ions then replace thefluoride ions leading to recharge of the resin and starting the process again.The driving force for the replacement of chloride ions from the resin is the stronger electronegativity of thefluoride ions.3.4.3.2.1.Advantages.•Removesfluoride up to90–95%.•Retains the taste and colour of water intact.3.4.3.2.2.Limitations.•Efficiency is reduced in presence of other ions like sulfate, carbonate,phosphate and alkalinity.•Regeneration of resin is a problem because it leads tofluoride rich waste,which has to be treated separately beforefinal disposal.•The technique is expensive because of the cost of resin,pre-treatment required to maintain the pH,regeneration and waste disposal.•Treated water has a very low pH and high levels of chloride.3.4.3.3.Coagulation–precipitation.Lime and alum are the most commonly used coagulants.Addition of lime leads to pre-cipitation offluoride as insoluble calciumfluoride and raises the pH value of water upto11–12.Ca(OH)2+2F−→CaF2+2OH−As lime leaves a residue of8.0mg F−/L,it is used only in conjunction with alum treatment to ensure the properfluoride removal[54–56].As afirst step,precipitation occurs by lime dosing which is followed by a second step in which alum is added to cause coag-ulation.When alum is added to water,essentially two reactions occur.In thefirst reaction,alum reacts with some of the alka-linity to produce insoluble aluminium hydroxide[Al(OH)3].In the second reaction,alum reacts withfluoride ions present in the water.The bestfluoride removal is accomplished at pH range of 5.5–7.5[57].3.4.3.3.1.Advantages.•The Nalgonda technique of defluoridation is based on com-bined use of alum and lime in a two-step process and has been claimed as the most effective technique forfluoride removal [58,59].•Under Rajiv Gandhi Drinking Water Mission,severalfill and draw(F&D)type and handpump attached(HPA)plants based on Nalgonda technique have come up in rural areas for which design and technology has been developed by NEERI,Nag-pur.3.4.3.3.2.Limitations.After having10years experience with these plants,the following serious drawbacks have been experienced:•The process removes only a smaller portion offluoride (18–33%)in the form of precipitates and converts a greater portion of ionicfluoride(67–82%)into soluble aluminium fluoride complex ion,and therefore this technology is erro-neous.Also,as the soluble aluminiumfluoride complex is itself toxic,adoption of Nalgonda technique for defluorida-tion of water is not desirable[60].•Due to use of aluminium sulfate as coagulant,the sulfate ion concentration increases tremendously and in few cases,it crosses the maximum permissible limit of400mg/L,which causes cathartic effect in human beings.•The residual aluminium in excess of0.2mg/L in treated water causes dangerous dementia disease as well as pathophysiolog-ical,neurobehavioural,structural and biochemical changes. It also affects musculoskeletal,respiratory,cardiovascular, endocrine and reproductive systems[61].•Due to organoleptic reasons,users do not like the taste of treated water.•Regular analysis of feed and treated water is required to calcu-late the correct dose of chemicals to be added,because water matrix keeps on changing with time and season as evident from our earlier studies conducted in laboratory.•Maintenance cost of plant is very high.On an average as experienced in the recent years,a plant of10,000L per day capacity requires Rs.3000every month on maintenance.•The process is not automatic.It requires a regular attendant for addition of chemicals and looking after treatment process.•Large space is required for drying of sludge.•Silicates have adverse effect on defluoridation by Nalgonda technique.Temperature also affects the defluoridation capac-ity.3.4.3.4.Membrane process.Although various conventional techniques of water purification described earlier are being used at present to solve the problem of groundwater pollution, none of them is user-friendly and cost-effective technique due to some or the other limitation and has either no or very long pay back period.In the recent years,RO membrane process has emerged as a preferred alternative to provide safe drinking water without posing the problems associated with other conventional methods.RO is a physical process in which the contaminants are removed by applying pressure on the feed water to direct it through a semipermeable membrane.The process is the reverse of natural osmosis as a result of the applied pressure to the concentrated side of the membrane,which overcomes the natural osmotic pressure.RO membrane rejects ions based on size and electrical charge.The factors influencing theMeenakshi,R.C.Maheshwari/Journal of Hazardous Materials B137(2006)456–463461 Table5Comparative analysis of various techniques forfluoride removalSample no.Initialfluoride concentration(mg/L)Fluoride concentration after treatment(mg/L)Activated alumina Activated saw dust Nalgonda Reverse osmosis 1 4.2 1.13(73.10) 1.42(66.19) 1.32(68.57)0.32(92.38) 27.8 1.96(74.87) 2.32(70.26) 2.24(71.29)0.63(91.93) 38.6 2.23(74.07) 2.56(70.23) 2.47(71.30)0.78(90.93) 49.3 2.11(77.31) 2.42(73.98) 2.31(71.16)0.88(90.54) 58.2 2.17(73.54) 2.43(70.37) 2.34(71.46)0.77(90.61)6 6.8 1.81(73.38) 2.16(68.24) 1.95(71.32)0.56(91.76) Values in parentheses show the percentfluoride removal.membrane selection are cost,recovery,rejection,raw water characteristics and pretreatment.Efficiency of the process is governed by different factors such as raw water characteristics, pressure,temperature and regular monitoring and maintenance, etc.There are two types of membranes that can removefluoride from water:NF and RO.NF is a relatively low pressure process that removes primarily the larger dissolved solids as compared to RO.Conversely,RO operates at higher pressures with greater rejection of all dissolved solids.Fluoride removal efficiencies upto98%by membrane processes have been documented by many researchers.In the past,the use of membrane technology for water treat-ment,particularly for drinking water production had been con-sidered uneconomical in comparison with conventional means, but in the recent years the increased demand and contamina-tion of water,rise in water quality standards and the prob-lems associated with other methods have led to reconsideration of membrane technology for water purification.The progres-sive technical improvements in design and materials of the membranes have made the water treatment process econom-ically competitive and highly reliable.Also,the capital and operational costs of RO plant go on decreasing with increas-ing plant capacity[62].Thus with improved management,this new technology for drinking water production might be the best option.Furthermore,membrane processes present sev-eral advantages as compared with other treatment methods [63].3.4.3.4.1.Advantages.•The process is highly effective forfluoride removal.Mem-branes also provide an effective barrier to suspended solids, all inorganic pollutants,organic micropollutants,pesticides and microorganisms,etc.•The process permits the treatment and disinfection of water in one step.•It ensures constant water quality.•No chemicals are required and very little maintenance is needed.•Life of membrane is sufficiently long,so problem of regener-ation or replacement is encountered less frequently.•It works under wide pH range.•No interference by other ions is observed.•The process works in a simple,reliable automated operat-ing regime with minimal manpower using compact modular model.3.4.3.4.2.Limitations.•It removes all the ions present in water,though some minerals are essential for proper growth,remineralization is required after treatment.•The process is expensive in comparison to other options.•The water becomes acidic and needs pH correction.•Lot of water gets wasted as brine.•Disposal of brine is a problem.•The performance of all the above processes has been tested in the laboratory.A comparative analysis of thefluoride removal by various processes is presented in Table5.4.ConclusionThe literature survey and the laboratory experiments have indicated that each of the discussed techniques can removefluo-ride under specified conditions.Thefluoride removal efficiency varies according to many site-specific chemical,geographical and economic conditions,so actual applications may vary from the generalizations made.Any particular process,which is suit-able at a particular region may not meet the requirements at some other place.Therefore,any technology should be tested using the actual water to be treated before implementation in the field.References[1]A.Kass,Y.Yechieli Gavrieli,A.Vengosh,A.Starinsky,The impact offreshwater and wastewater irrigation on the chemistry of shallow ground-water:a case study from the Israeli Coastal aquifer,J.Hydrol.300(1–4) (2005)314–331.[2]C.Amina,L.K.Lhadi,A.Younsi,J.Murdy,Environmental impact ofan urban landfill on a coastal aquifer,J.Afr.Earth Sci.39(3–5)(2004) 509–516.[3]O.Oren,Y.Yechieli,J.K.Bohlke,A.Dody,Contamination of groundwaterunder cultivatedfields in an arid environment,Central Arava Valley,Israel, J.Hydrol.290(3/4)(2004)312–328.[4]F.Anwar,Assessment and analysis of industrial liquid waste and sludgedisposal at unlined landfill sites in arid climate,Waste Manage.23(9) (2003)817–824.。
水怎样节约英语作文
水怎样节约英语作文Title: Strategies for Water Conservation。
Water conservation is a critical issue that affects every individual, community, and ecosystem. Given its significance, it is essential to explore effective strategies to conserve water resources. In this essay, we will delve into various methods and practices that can be implemented to conserve water.To begin with, raising awareness about the importance of water conservation is paramount. Educating individuals about the finite nature of water resources and the consequences of wasteful usage can lead to behavioral changes. Schools, communities, and government agencies can organize workshops, seminars, and campaigns to disseminate information about water conservation practices.Moreover, adopting water-saving technologies and practices can significantly reduce water consumption.Installing low-flow faucets, showerheads, and toilets can minimize water wastage without compromising functionality. Additionally, implementing drip irrigation systems in agriculture and landscaping can deliver water directly to plant roots, reducing evaporation and runoff.Furthermore, practicing responsible water management in industries is crucial for conservation efforts. Industries can invest in water recycling and reuse systems to minimize freshwater consumption. Implementing efficient cooling systems and processes can also reduce water usage in manufacturing and production activities.In addition to technological solutions, policy interventions play a vital role in promoting water conservation. Governments can enact and enforce regulations that mandate water-saving practices in various sectors. Implementing water pricing mechanisms that reflect the true cost of water usage can incentivize conservation efforts among consumers and industries alike.Individuals can also contribute to water conservationthrough simple lifestyle changes. Turning off taps while brushing teeth, fixing leaks promptly, and watering plants during cooler parts of the day can collectively make a significant difference in water conservation efforts.Furthermore, promoting sustainable agricultural practices can help conserve water in farming activities. Crop rotation, soil moisture monitoring, and mulching techniques can enhance water retention in soil, reducing the need for irrigation. Encouraging the cultivation of drought-resistant crops can also mitigate water demand in water-stressed regions.Additionally, protecting and restoring natural ecosystems such as wetlands, forests, and watersheds is crucial for maintaining water balance. These ecosystems play a vital role in regulating water flow, filtering pollutants, and replenishing groundwater resources. Conservation efforts should focus on preserving these ecosystems and preventing further degradation.In conclusion, water conservation is a multifacetedissue that requires collective action at individual, community, and governmental levels. By raising awareness, adopting efficient technologies, implementing policies, and making lifestyle changes, we can mitigate water scarcity and ensure sustainable water management for future generations. It is imperative that we prioritize water conservation as a fundamental aspect of environmental stewardship and responsible citizenship.。
水资源短缺(雅思范文)
4.What are the causes of water scarcity?What are your solution？Not always does good news come alone.While NASA has reportedly found the evidence that liquid water did once exit on Mars,the water issue on another planet,the earth , should not be neglected.It is widely noted that the water resource on our home planet is becoming increasingly scarce in recent years, and, diverse contributing factors can be identified behind it.In the following,I shall explore the possible reasons for it and present my personal suggestions to water shortage. The most obvious reason is the growing trend of overpopulation in major cities around the world. With their population skyrocket ing to an unprecedented level of over 1- million in some giant cities such Tokyo, Shanghai, and Mexico City, the urban infrastructure is often hard-pressed to cope with the problem of providing clean water to city dweller s.Moreover, in an attempt to provide adequate food supplies to their huge populations, many developing countries are undergo ing a large-scale agricultural expansion that requires significantly more water resources for irrigation and livestock farming than before. Also, water as an essential component of their production is increasingly demanded by various industries, such as fabric, chemistry and manufacturing.Other reasons that result in a global dearth of water supplies includerampant deforestation, encroach ing desertification and contamination of rivers, lakes and underground water.Faced with this daunting challenge, the first priority is for governments to adjust their economic policies, promote sustainable development and stop damaging the natural environment. Besides, Third World countries need to launch nationwide campaigns to advocate the benefits of birth control and educate citizens on the use of contraceptive devices.Also, the public’s ecological awareness should be raised to a higher level where people of all ages can understand the utmost importance of preserving natural resources and switch accordingly to more environmentally friendly ways of life.In addition, every family can be encouraged to reuse water within the household. For example, in most Asian societies where rice is the staple food, the water used after cleaning rice contains various nutrients for plant growth and is an excellent detergent to flush the toilet. Furthermore, the intriguing idea of converting the inexhaustible sea water to fresh water supplies will be the ultimate solution.unprecedented [ʌn’presidəntid] adj.前所未有的, 无前例的The air crash caused an unprecedented number of deaths.这次空难的死亡人数是空前的。
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Environmental fluoride has received much attention on account of the fact that an optimum concentration was found to reduce the incidence of dental caries. Low levels of fluoride are required for humans as it has beneficial effects on tooth and bone structures. However ingestion of excessive fluorides, mainly through drinking water causes dental and skeletal fluorosis (WHO 1970). The chronic toxicity by excessive fluoride intake has long been observed as skeletal abnormalities. The most common manifestation of the toxicity of fluoride in drinking water is dental fluorosis. Long-term ingestion of excessive fluoride has a chronic effect on the kidneys as well. The optimum level suggested by WHO is 0.7 mg/ L from infancy to 16 years. Fluorosis is related to the geology and climatic conditions of the place and the levels of fluoride. There is a distinctly geographical pattern in the incidence of fluorosis in Sri Lanka. The fluoride rich and fluoride poor areas have been demarcated and are closely linked with climate and geology. Geochemical surveys on the fluoride content of groundwater in Sri Lanka reveals that in the dry zone areas in Polannaruwa and Anuradhapura in the North-central province, Uda-Walawe and Wellawaya in the Southern Province and in Maho have high fluoride content (Dissanayake (1979)). High fluorides are in the plains especially in the dry zone, while the low fluoride areas are in the central high lands and in the western plains where the rainfall is high. With the rainfall fluoride is leached from rocks and soils and carried away in solution whereas in the dry zone evaporation causes upward capillary action of fluoride ions. The fluoride content of water obtained from lakes, artisan wells and rivers is mostly below 0.5 mg/L. Several defluoridation methods have been known to remove the excess of fluoride in drinking water to avoid endemic
Prevention of fluorosis
Dental fluorosis is irreversible and therefore treatment is sophisticated and expensive. Thus the prevention of fluorosis is best and is the only form of treatment in Sri Lanka. Excessive fluoride content of water can be reduced to a desired limit by precipitation and adsorption. The adsorption method involves the contact of the fluoride containing water with a suitable adsorbent. Various substances such as activated carbon, activated alumina, activated bauxite, zeolite, hydroxyapatite etc.., have been used for fluoride removal from water (Choi et al (1979)). The ion-exchange, adsorption and precipitation are the usual means of defluoridation. However, most of the available materials for defluoridation are expensive and technically non-feasible in rural communities in Sri-Lanka. Hence the need to find locally available defluoridation media for safe and easy use at both household and small community level is desirable. National Water supply and Drainage Board has distributed low cost defluoridators among people in the affected areas. Easily available, Laterite or freshly burnt bricks broken into pieces has been used as filter media. Upward flow technique has been used to get more retention time. The performance of the sampled defluoridators has been monitored at regular intervals to see how well they are functioning. It was observed that at certain sites the desired effluent qualities
WIJESUNDARA
30th WEDC International Conference, Vientiane, Lao PDR, 2004 PEOPLE-CENTRED APPROACHES TO WATER AND ENVIRONMENTAL SANITATION
Low-cost defluoridation of water using broken bricks
T. Wijesundara, Sri Lanka
A low cost domestic defluoridator has been developed by the National Water Supply & Drainage Board of Sri Lanka to remove excess fluoride in drinking water to avoid endemic Fluorosis. Broken pieces of freshly burnt bricks are used as filter media in these units. A kinetic model for fluoride uptake in the filter with broken bricks as defluoridating agent is considered and the model parameters are estimated using experimental data. Data concerning the uptake of fluoride on broken brick pieces are obtained from water in batch in the defluoridator. The reaction rate parameter, k, and the capacity parameter fm are estimated and the model fits the collected data satisfactorily. fm is estimated to 0.10 mg/g and k which is a function of initial concentration varies between 0.001 and 0.0005 L/ (mg.ho.5) for low and high initial concentration. Broken bricks could be used as filter media for concentration of fluoride in raw wate