Research Progress on Control of Water EnvironmentContaminated by Heavy MetalsXu Haisheng1 Zhao Yuanfeng2(1. Institute of life science and technology, Dalian Fisheries University, Dalian116023;2. Key Laboratory of Mariculture and Biotechnology, Ministry of Agriculture,Dalian 116023, China)Abstract: Some treatment methods for heavy metal wastewater are summarized in this paper, which are mainly based on the physical, chemical, Physical chemistry treatment, Biological treatment. The technology applications of bioengineering for wastewater reuse treatment are also summarized. It indicates that the comprehensive utilization and innocuous treatment of heavy metal wastewater become the main trend for the heavy metal contamination.Key Words: heavy metal contamination; treatment methods; comprehensive utilization; innocuousPrefaceTrace metals such as cadmium (C d), chromium (Cr), copper (Cu), lead (P b) and zinc (Zn) are classified as priority pollutants.Human living environment had polluted by industrial sewage, cultivate wastewater and electroplate heavy metal of wastewater, and becoming more and more serious [1].Heavy metal pollution has persistence and accumulation, can transfer along food chain and enrichment, endangering human body and other organism in any way. Take place caused by Hg pollution " minamata disease " and " itai itai disease " incident caused by C d pollution in Japan, A growing concern among heavy metal pollution control from domestic and international environmentalist extremely [2-4].1 Wastewater of heavy metal treatment methodsThe treatment method of heavy metal, up till now, have already developed a lot of heavy metal pollution control technology in the wastewater, generally adopt: (1) Physical treatment; (2) Chemical treatment; (3) Physical chemistry treatment; (4) Biological treatment.1.1 Physical treatmentPhysics method is used physics function to separate the suspending polluter from wastewater, change chemical property of material in the course of dealing with, such as electroplate degreasing, evaporation of wastewater is recycled, etc.. Physics method is regard as other treatment a link of method, seldom use alone in electroplate craft, Physics method including adsorption method, floatation, etc..1.1.1 Adsorption methodThe adsorption method is used for removing the micro- pollutant in the wastewater, to achieve the purpose of depth purifies. Mainly utilize solid absorbent physical absorption and chemistry to absorb performance, get rid of the course of many kinds of pollutant in wastewater. Polyethylene silica gel-polyethylene amine composite has important practical value in the absorbent material of the artificial synthesis. It has offered the prospect for the fact that economyretrieves the heavy metal in the wastewater.1.1.2 FloatationFloatation is take small bubble as carrier, seize impurity wadding one of ink, make it practical density smaller than water, then particle is carried by bubble float to the surface of water, formed dross and purged away, and solid-liquid separated and water purified.1.2 Chemical treatment,Chemical treatment is operate simple, steady and reliable suitable to apply in extensive range, can bear large water yield and high density load, can used in all kinds of and electroplate wastewater treatment. Shortcoming is electroplate mud to be apt to produce secondary pollution, treatment effect is often influenced greatly by operator when automatic degree being low.1.2.1 Chemistry oxidationChemistry oxidation is applied to cyanide waste mainly. Under alkaline condition, dissociate cyanide ion and combine with metal oxidize be transformed into nitrogen and carbon dioxide by oxidation. The commonly used oxidant is sodium hypochlorite, liquid chlorine and bleaching powder, can use air or the ozone as the oxidant.1.2.2 Chemical reductionChemical reduction process used in containing chromium wastewater treatment mainly,six price chromium be reduced to toxicity low 3 price chromium with reducer usually, then utilize neutralization precipitate remove three price chromium ion in the waste water. The commonly used reducer is green vitriol, sulfur dioxide, sulfite, etc. Now green vitriol-lime law is often adopted to deal with chromium wastewater electroplating factory.1.2.3 Chemistry precipitationChemistry precipitate law is point to add some chemical reagent to waste water, chemical reaction has taken place with pollutant of wastewater, form the precipitate difficult to dissolve, then solid-liquid separation, thus remove the pollutant in the waste water.Chemical precipitation is most commonly employed for most of the metals. Chemistry precipitate law can divide into Hydroxide precipitate law, chromate precipitate law, ferrite precipitate law, neutralization precipitate law and sulfide precipitate law, etc., according to use difference of precipitating agent.A lot of metal caustics are difficult to dissolve in water, the solubility of such heavy metal caustics as the copper, cadmium, chromium, lead, etc. is accumulated generally very lightly, so can adopt Hydroxide precipitate law and remove the heavy metal ion in the wastewater.The chromate precipitate law deal with limited to six price chromium only, precipitating agent to throw include chlorine barium, sulfide barium and carbonic acid barium, etc., called the barium salt law traditionally.Ferrite precipitate law treating containing chromium wastewater for 3 pieces of course, namely reduction reaction, co-precipitation and producing the ferrite. The ferrite law not only applied to containing chromium wastewater treatment, but also used for containing mercury and many kinds of metal ion and electroplating [5].Regulate pH value in order to get rid of method, heavy metal of pollutant call neutralization precipitate law. Divided into acid neutralization and alkaline neutralization according to the difference which deals with wastewater pH value, generally adopt the principle of controlling waste with abolished. So control pH value is the key containing lead and zinc ions wastewater in neutralization precipitate law.S ulfide precipitate law deal with heavy metal waste water is it get rid of rate to be high tohave, can precipitate mud metal in the dreg, precipitate article location high and easy recycle, and sediment small, low meeting pH value range advantaging such as being wide moisture content step by step, used widely.1.3 Physical-chemistry treatmentThe physical chemistry method is make wastewater purified through the comprehensive function of physics and chemistry. The operations most commonly used in wastewater treatment include: Dissolved air flotation; Ion exchange; Extraction; Activated carbon adsorption; Electrolysis.1.3.1 Dissolved air flotationDissolved air flotation is one treatment method what make air dissolve among water and reach saturated condition under certain pressure, then wastewater pressure strength reduce suddenly, dissolve air emit from water in the form of small bubble at this moment, finally to float. Apply to electroplate carrying chromium wastewater mainly. The flocculating constituent rise to the surface by buoyant function of countless small bubbles, water quality becomes clear.1.3.2 Ion - exchange treatmentIon exchange law to utilize exchange ion of ion exchange resin exchange with some ion of electroplate wastewater and remove it, make the wastewater purify. At present, adopt ion exchange law to electroplate wastewater containing chromium, nickel and alloy comparatively general in domestic. Usually combine with other technological process now.1.3.3 Extraction treatmentExtract law is a method to utilize not dissolve in water but can dissolve a certain solvent in water, put the material into wastewater, make the solute fully dissolve in the solvent, separate for removing or retrieve a certain material from the wastewater. Research on draw copper and zinc from containing cyanogen wastewater have more reports.1.3.4 Activated carbon adsorptionThe adsorption method is used for getting rid of the micro-pollutant of the wastewater mainly, achieve the purpose of depth purifies. The activated charcoal adsorption is a kind of effective and economy method to deal with the electroplate wastewater. Apply to include the chromium wastewater mainly.1.3.5 Electrolysis methodElectrolysis method is to make harmful substance of wastewater oxidize and reduce reacting through electrolytic course separately on positive and negative poles mainly, transform into a harmless material; or utilizing product of electrodes oxidize and reduction reacted with harmful substance in wastewater, produce the precipitate that does not dissolve in water, then separate and remove. Adopting electrolysis to deal with the dense waste liquid in some occasions, there are certain economic benefits. Utilizing the principle of electrolysis, the power flotation law used to remove the metal ion from wastewater.1.4 Biological treatmentThe biological treatment is mainly utilizing life of microorganism activity processes, is used for dealing with industrial sewage containing C d, P b, Ni and Zn. The method has such advantages as low expenses to deal with, little impact to environmental, high efficiency, etc.There is a very strong affinity between microorganism and heavy metal, so microorganism can collect a lot of heavy metal. The living beings used to remove, absorption and accumulation the heavy metal.In recent years, researches on utilize microorganism to absorb the heavy metal from the rare solution carried on, achieved lots of fruits [6-10], microorganism absorb the heavy metal in the wastewater is superior to the traditional administration method in investment, operating, operating managing, metal recovery, water retrieval and utilization etc. At present, to develop and utilize microorganism cell make as biological absorbent technology of wastewater treatment towards direction of nonpoisonous, harmless, has not secondary pollution stride forward one step. Utilize gene engineering to construct microorganism with absorb ability or peculiar performance absorb metal, will be a new developing direction in future.2.New technologyTo deal with containing kinds of heavy metal ion and other impurity wastewater, to reach final harmless treatment of the wastewater, such new crafts of harmless treatment studying as Sun Jie, etc. (2002) [13] were utilized the inducing crystallization principle, regard sodium carbonate as precipitating agent, heavy metal ion formed difficult to dissolve salt and crystallization deposit in surface of flowing silicon sand, thus achieve the goal of getting rid of heavy metal, final harmless treatment.Someone adopts the technology of mixing the pharmaceutical to melt regularly too, to the complexity and changeable of the heavy metal composition in the wastewater, adopt reasonable this method can improve mechanical intensity of absorbent, can improve the absorbing rate. Sun Jiashou, etc. (2002) [14] putting FS01 reagent into stone layers, strengthen their absorb ability, can be used for dealing with various kinds of and containing cyanogen and electroplating wastewater.In order to develop a method of efficient, cheap and dealing with heavy metal wastewater simply and conveniently, Zhang Xiaoyan, etc. (2002)[15] develop one water-soluble chelate resin (DTCR). Punish include EDTA complexing zinc wastewater and zinc waste liquid with DTCR, the result of treatment was remarkable, treated water was colourless and limpid, can recycle.Li Zengxin (2004)[16] has developed a new craft prepared copper sulphate and chromium vitriol from abolished catalyst on the basis of craft of old. Craft is simple, low costs, only produce low toxicity heavy 6-price chromium, and can retrieve two kinds of ion of copper chromium at the same time.It was reported [17], closed circulation craft was adopted to leaded electroplate and pickle wastewater, not only can retrieve some heavy metal in the wastewater; but also improve utilization ratio of resource, wastes again to retrieve. Someone adopted " evaporation - purify - recycle " new craft to deal with containing chromium and cyanogen electroplate wastewater, realize unity of harmless and reclamation, achieve the purpose of cleaning produce.3. Brief summaryIn sum, because of complexity and can't degradability for compositions of heavy metals, can only give temporary relief, can't get a permanent cure, will cause certain pollution to environment again. And stabilizing technology causes unpredictable influence that the dangerous composition will enter the environment again. Lots of new crafts have been developed now. Fully utilize the advantages of different treatment methods, comprehensive consideration investment and efficiency and impact on environment, etc., combine various kinds of methods, utilize purifying function in coordination of the microorganism and plant in nature, strengthened the effect of detoxifying of the biological course with physics or chemical method, it will be a effective way to purify heavy metal pollutes. So, comprehensive treatment has great research potentiality and opened up broad application prospect.References[1] Tu Jinbao (1989) Electroplate Wastewater and Control Manual [M]. Beijing: The publishinghouse of the mechanical industry.[2] Zhang Chun`ai. 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