Correction to “Tensor Products of Modules and the Rigidity of Tor”,

Nutrient Cycling in Marine EcosystemsNutrient cycling is a fundamental process in marine ecosystems,playing a crucial role in maintaining the health and productivity of oceanic environments.The cycling of essential nutrients such as nitrogen, phosphorus,and carbon supports the growth of marine organisms, drives primary production,and sustains the complex food webs that characterize marine ecosystems.This essay explores the mechanisms, significance,and challenges of nutrient cycling in marine environments.Mechanisms of Nutrient CyclingBiological ProcessesPhotosynthesis and RespirationPhotosynthesis and respiration are key biological processes that drive nutrient cycling in marine ecosystems.Phytoplankton,the primary producers in the ocean,use sunlight to convert carbon dioxide(CO2) and inorganic nutrients into organic matter through photosynthesis.This process not only produces oxygen but also forms the base of the marine food web.When phytoplankton and other marine organisms respire, they release CO2and other nutrients back into the water,making them available for reuse.DecompositionDecomposition is another critical biological process in nutrient cycling. When marine organisms die,their bodies are broken down by bacteria and other decomposers.This decomposition process releases nutrients such as nitrogen and phosphorus back into the water column,where they can be taken up by primary producers.The recycling of nutrients through decomposition ensures the continuous availability of essential elements for marine life.Physical ProcessesUpwellingUpwelling is a physical process that brings nutrient-rich deep water to the surface.This occurs when wind-driven currents push surface water away from the coast,allowing deeper water to rise and replace it. Upwelling zones are among the most productive areas in the ocean, supporting high levels of primary production and rich biodiversity.The influx of nutrients from upwelling fuels the growth of phytoplankton, which in turn supports higher trophic levels.Ocean CurrentsOcean currents play a significant role in the distribution and cycling of nutrients.These currents transport nutrients across vast distances, connecting different regions of the ocean.For example,the thermohaline circulation,also known as the global conveyor belt,moves nutrient-rich water from the deep ocean to the surface and from the poles to the equator.This circulation helps maintain nutrient balance and supports marine productivity on a global scale.Chemical ProcessesNitrogen FixationNitrogen fixation is a chemical process that converts atmospheric nitrogen(N2)into a form that can be used by marine organisms,such as ammonium(NH4+).This process is carried out by specialized bacteria and cyanobacteria,known as diazotrophs.Nitrogen fixation is essential for replenishing the nitrogen supply in marine ecosystems,as nitrogen is a critical nutrient for the growth of phytoplankton and other organisms.DenitrificationDenitrification is the process by which nitrate(NO3-)is converted back into nitrogen gas(N2),which is then released into the atmosphere.This process is carried out by anaerobic bacteria in low-oxygen environments, such as sediments and oxygen minimum zones.Denitrification helps regulate the nitrogen cycle by removing excess nitrogen from the ocean, preventing nutrient over-enrichment and maintaining ecological balance.Significance of Nutrient CyclingSupporting Primary ProductionNutrient cycling is essential for supporting primary production in marine ecosystems.The availability of nutrients such as nitrogen,phosphorus, and iron determines the growth and productivity of phytoplankton. These primary producers form the base of the marine food web, providing energy and nutrients for higher trophic levels,including zooplankton,fish,and marine mammals.Healthy nutrient cycling ensures a continuous supply of essential elements,sustaining the productivity and biodiversity of marine ecosystems.Maintaining Ecosystem BalanceNutrient cycling helps maintain the balance and stability of marine ecosystems.The recycling of nutrients through biological,physical,and chemical processes ensures that essential elements are available in the right amounts and forms for marine organisms.This balance prevents nutrient deficiencies and excesses,which can lead to ecological disruptions such as algal blooms,hypoxia,and loss of biodiversity. Effective nutrient cycling supports the resilience and health of marine ecosystems.Carbon SequestrationNutrient cycling plays a role in carbon sequestration,a process that removes CO2from the atmosphere and stores it in the ocean. Phytoplankton photosynthesis captures CO2,and a portion of the organic carbon produced is transported to the deep ocean through the biological pump.This sequestration of carbon in the deep ocean helps mitigate the impact of greenhouse gas emissions and contributes to climate regulation.Nutrient cycling is thus interconnected with the global carbon cycle and climate system.Challenges in Nutrient CyclingHuman ImpactsHuman activities have significantly altered nutrient cycling in marine ecosystems.Agricultural runoff,wastewater discharge,and industrial pollution introduce excessive nutrients,particularly nitrogen andphosphorus,into coastal waters.This nutrient over-enrichment,known as eutrophication,can lead to harmful algal blooms,hypoxia(low oxygen levels),and the degradation of marine habitats.Managing nutrient inputs and reducing pollution are critical for protecting nutrient cycling processes.Climate ChangeClimate change poses a major challenge to nutrient cycling in marine ecosystems.Rising sea temperatures,ocean acidification,and changes in ocean circulation patterns can disrupt the distribution and availability of nutrients.For example,warming waters can reduce the efficiency of upwelling,limiting the supply of nutrients to surface waters.Ocean acidification can affect the ability of certain organisms,such as shell-forming plankton,to utilize nutrients effectively.Understanding and mitigating the impacts of climate change on nutrient cycling is essential for sustaining marine ecosystems.OverfishingOverfishing can disrupt nutrient cycling by altering the structure and function of marine food webs.The removal of key species,such as top predators and herbivores,can have cascading effects on nutrient dynamics.For example,the decline of large predatory fish can lead to an increase in smaller fish and invertebrates,which may alter nutrient recycling rates and patterns.Sustainable fishing practices are necessary to maintain the integrity of nutrient cycling processes.ConclusionNutrient cycling is a vital process that sustains the health and productivity of marine ecosystems.Through biological,physical,and chemical mechanisms,essential nutrients are recycled and made available to marine organisms,supporting primary production, ecosystem balance,and carbon sequestration.However,human impacts, climate change,and overfishing pose significant challenges to nutrient cycling.Addressing these challenges requires effective management and conservation strategies to protect nutrient cycling processes and ensure the resilience and sustainability of marine ecosystems.By understandingand valuing the importance of nutrient cycling,we can work towards a healthier and more productive ocean.。

化学化工英语试题及答案一、选择题（每题2分，共20分）1. Which of the following is a chemical element?A. WaterB. OxygenC. HydrogenD. Carbon答案：B, C, D2. The chemical formula for table salt is:A. NaOHB. NaClC. HClD. NaHCO3答案：B3. What is the process called when a substance changes from a solid to a liquid?A. SublimationB. VaporizationC. MeltingD. Condensation答案：C4. In the periodic table, which group contains alkali metals?A. Group 1B. Group 2C. Group 17D. Group 18答案：A5. What is the name of the process where a substance decomposes into two or more substances due to heat?A. CombustionB. OxidationC. ReductionD. Decomposition答案：D6. Which of the following is a physical property of a substance?A. ColorB. TasteC. SolubilityD. Reactivity答案：A7. What is the term for a compound that releases hydrogen ions (H+) when dissolved in water?A. BaseB. AcidC. SaltD. Neutral答案：B8. The law of conservation of mass states that in a chemical reaction:A. Mass is lostB. Mass is gainedC. Mass remains constantD. Mass can be converted into energy答案：C9. Which of the following is a type of chemical bond?A. Ionic bondB. Covalent bondC. Hydrogen bondD. All of the above答案：D10. What is the name of the process where a substance absorbs energy and changes from a liquid to a gas?A. MeltingB. VaporizationC. SublimationD. Condensation答案：B二、填空题（每题2分，共20分）1. The symbol for the element iron is ________.答案：Fe2. The pH scale ranges from ________ to ________.答案：0 to 143. A compound that produces a basic solution when dissolvedin water is called a ________.答案：base4. The smallest particle of an element that retains its chemical properties is called a ________.答案：atom5. The process of separating a mixture into its individual components is known as ________.答案：separation6. The study of the composition, structure, and properties of matter is called ________.答案：chemistry7. The process of a substance changing from a gas to a liquid is called ________.答案：condensation8. A(n) ________ reaction is a type of chemical reactionwhere two or more substances combine to form a single product. 答案：synthesis9. The volume of a gas at constant temperature and pressureis directly proportional to the number of ________.答案：moles10. The process of converting a solid directly into a gas without passing through the liquid phase is known as ________. 答案：sublimation三、简答题（每题10分，共30分）1. Explain what is meant by the term "stoichiometry" in chemistry.答案：Stoichiometry is the calculation of the relative quantities of reactants and products in a chemical reaction.It is based on the law of conservation of mass and involvesthe use of balanced chemical equations and the molar massesof substances to determine the amounts of reactants needed to produce a certain amount of product or the amounts ofproducts formed from a given amount of reactant.2. Describe the difference between a physical change and a chemical change.答案：A physical change is a change in the state or form of a substance without altering its chemical composition. Examples include melting, freezing, and boiling. A chemical change, on the other hand, involves a change in the chemical composition of a substance, resulting in the formation of new substances. Examples include combustion and rusting.3. What are the three main types of chemical bonds, and givean example of each.答案：The three main types of chemical bonds are ionic bonds, covalent bonds, and metallic bonds. An ionic bond is formed when electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions. An example is the bond between sodium (Na) and chloride (Cl) in table salt (NaCl). A covalent bond is formed when two atoms share electrons, as seen in water (H2O) where hydrogen atoms share electrons with oxygen. Metallic bonds occur in metals, where a "sea" of delocalized electrons is shared among positively charged metal ions, as in sodium metal。

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.。

任晓莉，杨璐，乔鹏，等. 复合酶法提取槐花多糖的工艺优化及其抗氧化活性[J]. 食品工业科技，2024，45（7）：8−14. doi:10.13386/j.issn1002-0306.2023070216REN Xiaoli, YANG Lu, QIAO Peng, et al. Optimization of Extraction Process of Polysaccharide from Sophora japonica by Compound Enzyme Method and Its Antioxidant Activity[J]. Science and Technology of Food Industry, 2024, 45(7): 8−14. (in Chinese with English abstract). doi: 10.13386/j.issn1002-0306.2023070216· 特邀主编专栏—食品中天然产物提取分离、结构表征和生物活性（客座主编：杨栩、彭鑫） ·复合酶法提取槐花多糖的工艺优化及其抗氧化活性任晓莉*，杨　璐，乔　鹏，缪奕锴，杨懿昂，代秋红，张贤德（太原工业学院环境与安全工程系，山西太原 030008）摘　要：目的：采用复合酶法提取槐花多糖，对提取工艺进行优化，并评价其体外抗氧化活性。

方法：通过单因素实验考察复合酶添加量、pH 、复合酶比例和酶解时间对得率的影响，在单因素实验基础上，采用响应面法确定槐花多糖的最佳提取参数，并以V C 为对照，通过测定槐花多糖对DPPH·和ABTS +·的清除率及总还原力，考察所提取的槐花多糖的抗氧化活性。

结果：复合酶法提取槐花多糖的最佳提取参数为：复合酶添加量23.8 mg/g ，pH4.8，果胶酶与纤维素酶比例0.912:1，该工艺下槐花多糖得率为10.71%，所提取的槐花多糖对DPPH·和ABTS +·均表现出较好的清除能力，当槐花多糖溶液浓度为2.8 mg/mL 时，对DPPH·和ABTS +·的清除率分别达到同浓度下V C 的94.19%和99.79%，总还原力达到V C 的75.99%。

生物酶与季铵盐的复合物英文回答：Enzymes are proteins that act as catalysts inbiological reactions. They are highly specific and can speed up chemical reactions by lowering the activation energy required for the reaction to occur. Enzymes can bind to specific molecules called substrates and convert them into products.Quaternary ammonium salts, also known as quats, are organic compounds that contain a positively charged nitrogen atom and four organic groups attached to it. They are widely used as disinfectants, surfactants, and fabric softeners due to their antimicrobial and surface-active properties.The formation of a complex between enzymes and quaternary ammonium salts can have various effects. In some cases, the complex formation can enhance the activity ofthe enzyme, while in others, it can inhibit or even denature the enzyme.One example of a complex between an enzyme and a quaternary ammonium salt is the interaction between cholinesterase and the pesticide paraoxon. Cholinesteraseis an enzyme that breaks down acetylcholine, a neurotransmitter involved in nerve signal transmission. Paraoxon is an organophosphate pesticide that irreversibly inhibits cholinesterase by forming a covalent bond with the enzyme's active site. This complex formation leads to the accumulation of acetylcholine, causing overstimulation of nerve cells and ultimately leading to paralysis or death.Another example is the complex between the enzyme trypsin and the quaternary ammonium salt benzalkonium chloride. Trypsin is a protease enzyme that cleaves peptide bonds in proteins. Benzalkonium chloride, commonly used as a disinfectant, can inhibit trypsin activity by binding to the enzyme's active site and preventing substrate binding. This complex formation can be useful in controlling trypsin activity in certain applications, such as in the productionof protein-based drugs.中文回答：酶是一种在生物反应中起催化剂作用的蛋白质。

苏柳，贺伟华，张干，等. 两种常用适配体的纳米金比色法快速检测牛奶中黄曲霉毒素M 1的评价研究[J]. 食品工业科技，2024，45（8）：284−292. doi: 10.13386/j.issn1002-0306.2023050332SU Liu, HE Weihua, ZHANG Gan, et al. Evaluation of Gold Nanoparticles Colorimetric Sensing Based on Two Commonly Aptamer for Rapid Detecting Aflatoxin M 1 in Milk[J]. Science and Technology of Food Industry, 2024, 45(8): 284−292. (in Chinese with English abstract). doi: 10.13386/j.issn1002-0306.2023050332· 分析检测 ·两种常用适配体的纳米金比色法快速检测牛奶中黄曲霉毒素M 1的评价研究苏　柳1，贺伟华1, +，张　干1，陈爱亮2，章钢刚1，赖晓翠1，邓省亮1,*（1.江西省科学院微生物研究所，江西南昌 330096；2.中国农业科学院农业质量标准与检测技术研究所，北京 100081）摘　要：目的：建立基于不同序列长度适配体的纳米金（Gold nanoparticles ，AuNPs ）比色传感法快速定量检测牛奶中的黄曲霉毒素M 1（Aflatoxin M 1，AFM 1），并评价目前文献报道中常用的21（A21）和72个碱基（A72）长度的AFM 1适配体在实际样品中的检测性能。

方法：采用柠檬酸钠还原法制备AuNPs 溶液，加入AFM 1适配体及AFM 1标准品后，适配体与AFM 1特异性结合形成特殊三维结构，随着NaCl 溶液加入，AuNPs 溶液的稳定性被破坏而发生聚集，导致溶液颜色变化，通过测定AuNPs 溶液的吸光值和吸收光谱定量检测AFM 1。