Heavy Metal Wastewater Treatment
Technology and Its Prospects Abstract: This paper reviews the treatment of heavy metal waste water chemical, physical chemical and biological methods, and gave details of one of the biological method. Concluded in recent years, heavy metal wastewater treatment Technology trends.
Keywords:: Biosorption of heavy metal wastewater ultrafiltration
With the rapid Economic development, a large number of wastewater
discharge of heavy metals in soil and water increased the accumulation of heavy metal pollution is also becoming increasingly serious. Easy as heavy metals and bioaccumulation through the food chain, constitute a biological and a serious threat to human health. How to efficiently deal with heavy metal pollution has become a common human concern. The heavy metal pollution in the sewage in the zone is also more serious, according to the detection of Changsha Environmental Monitoring Station, we found that nickel in waste water zone (Ni) there is excessive intermittent phenomenon, in the time monitoring of sludge also found that the sludge in the total cadmium, total nickel, total copper over agricultural sludge when the limits of pollution control standards here, so the treatment of heavy metals carried out, as well as prospects for the Development
Heavy metal pollution in domestic and foreign scholars have done a lot of governance issues in the study [1,2]. Has Development and Application of the
wastewater treatment methods include chemical, physical chemical and biological methods, including chemical precipitation, electrolysis, ion exchange, membrane separation, activated carbon and silica gel adsorption, bio-flocculation, bio-absorption, plants and other methods remediation. Use of chemical, physical-chemical methods will be one's remaining years of pollution, could easily lead to secondary pollution, and for large basin, low concentrations of harmful heavy metal contamination difficult to handle. The biological method is effective, low Investment and operation of low-cost, easy to manage and
operate, and no secondary pollution, etc., have become an increasing concern. Here are several ways to explore this:
A chemical method
Chemical methods include chemical precipitation and electrolytic method, mainly applied to wastewater containing high concentration of heavy metal ions treatment.
The principle of chemical precipitation method is through a chemical
reaction so that the state of waste water was dissolved heavy metals into the water insoluble heavy metal compounds, by filtration and separation to remove sediment from the aqueous solution, including the neutralization precipitation, sulfide precipitation, ferrite co-precipitation method . Because of the precipitation agent and environmental conditions, precipitation is often the concentration of water is mainly the need for further processing, the resulting sediment treatment and disposal must be good, otherwise it will cause secondary pollution.
Electrolysis is the use of electrochemical properties of metals, metal ions in electrolysis time from a relatively high concentration of solution separated, and then use it. Electrolysis method is mainly used for electroplating wastewater treatment, the shortcomings of this approach is the concentration of heavy metal ions in water does not drop very low. Therefore, the electrolysis inappropriate to deal with lower concentrations of waste water containing heavy metal ions.
Two physical-chemical methods
Ion exchange and membrane separation Technology for waste water
containing low concentrations of heavy metal ions treatment.
Ion-exchange method is carried out in the ion-exchange devices, this method using ion-exchange agent to complete. Required in the switch in the exchange with different types of agents, including heavy metals, when the liquid through the exchange agent, exchange agent with the water on the ion exchange of heavy metal ions to achieve the purpose of removing heavy metal ions in water. This approach by the exchange agent varieties, yield and cost. In recent years, domestic and foreign scholars on the ion exchange agent Research and Development carried out extensive Research work [4,5]. With the
ion-exchange agents continue to emerge, in the electroplating wastewater advanced treatment, the recovery of high-priced metal salts, etc., ion-exchange method are increasingly showing its advantages.
Membrane separation Technology is the use of a special kind of
semi-permeable membrane under pressure in the outside world, does not change the chemical form of the solution, based on the solvent and solute separation or enrichment methods, including electrodialysis, and membrane electrolysis. Electrodialysis is a direct current electric field effects, using anion and cation exchange membrane on the solution of anion and cation selective permeability to heavy metal ions in aqueous solution and water separation of a physical and chemical processes. Diaphragm electrolysis is a membrane separating the anode and cathode electrolysis device and method of electrolysis, electrodialysis and electrolysis effect is to combine the methods. The above method have experienced in the operation of electrode polarization, fouling and corrosion problems.
Bio-flocculation method is the use of micro-organisms or microbial
metabolites produced by conducting flocculation precipitation of a decontamination method . Microbial flocculant is formed by the microorganisms themselves, a highly efficient flocculation of natural polymer materials, and its main ingredient is sugar, protein, mucopolysaccharide, cellulose, and nucleic acid. Since the majority of micro-organisms have a certain linear structure, and some have higher surface charge, or a strong hydrophilic particles through a variety of roles with the combined play a very good flocculation. Currently developed with a flocculation of the micro-organisms are bacteria, fungi, actinomycetes, yeast and algae, etc. A total of 17. Flocculation of heavy metals in which there are 12. Chen et al  the use of microorganisms extracted from a variety of chitosan as flocculant recovery of simulated industrial wastewater Pb2, Cr3, Cu2, in the ion concentration of 100mg / L in 200mL water by adding 10mg chitosan treatment solution of Cr3, Cu2 concentration of less than 0.1mg / L, Pb2 concentrations of less than 1 mg / L, obtained satisfactory results. Microbial flocculation waste water treatment safe and convenient non-toxic, does not produce secondary pollution, the flocculation effect is good, and the growth of microorganisms quickly, is easy to implement industrialization and so on. In addition, the micro-organisms through genetic engineering, domestication, or construct strains with special functions. Therefore, microbial flocculation method has broad prospects for development.
3.2 Biological assay
Biosorption through a series of bio-chemical effect is to make for heavy metal ions are adsorbed microbial cells broad understanding of these roles, including complexation, chelate, ion exchange, adsorption and so on. These micro-organisms isolated from the solution of the mechanism of metal ions in the extracellular concentration, precipitation; cell surface adsorption or complexation; intracellular enrichment. Which cell surface adsorption or complexation of the life and death of micro-organisms are present, while the intracellular and extracellular accumulation of a large number of micro-organisms are often required with the activity. Many studies have shown that microbes living and dead micro-organisms for heavy metal ions have a greater absorption capacity, as a biological adsorbent from the biological source of the low concentration of aqueous solution containing heavy metal ions adsorption of heavy metals, and there is easy access to micro-organisms of practical value . For example: the yeast fermentation process is a good biosorbent biological source, a large number of algae from the ocean is also a cheap biological sources [8,9]. Zhao et al  use of marine red tide organism Prorocentrum (Prorocentrum micans) and formaldehyde in vivo to kill the algae on the Cu2, Pb2, Ni2, Zn2, Ag1, Cd2 adsorption capacity of research, experiments show that metal ions mixed fluid absorption by Prorocentrum after 30min, the ion concentration decreased significantly and to achieve a balance Prorocentrum of live and dead bodies of these six kinds of metal ions have similar adsorption capacity.
The use of carrier by physical or chemical method to micro-organisms by the pre-fixed adsorbent, the adsorbent mechanical strength and chemical stability, enhanced life-cycle extension, can improve the depth and efficiency of wastewater treatment to reduce the adsorption - desorption cycle losses. In recent years, many scholars at home and abroad to carry out the immobilized cell treatment of toxic waste water containing heavy metals Research work
[10,11]. Adsorbent with a source of bio-wide, low price and strong adsorption capacity, easy separation and recovery of heavy metals and other characteristics, and the use of the death of microbes as biological sources have easily immobilized and can be made according to specific biological needs and the repeated use of adsorbent. Therefore, the bio-assay has good prospects for industrial applications. At this stage the majority of China's sewage treatment plant using activated sludge treatment method, so you can consider the area in need of removal of heavy metals, through the domestication of activated sludge (in this process should be taken to avoid excessive heavy metal poisoning, so that the activated sludge ), and bio-inoculation vaccine strains corresponding to achieve low concentration of heavy metals found in sewage disposal.
3.3 Plant remediation technology
Plants on the mechanism of absorption and accumulation of heavy metals, mainly two aspects: First, the use of well-developed root system of plants to absorb heavy metal waste water filtering effects, to the enrichment and accumulation of heavy metals. Second, the principle of the use of micro-organisms and heavy metals and microbial activity of the pro-and role of the heavy metals into less toxic product. Has accumulated through the harvesting or removal and accumulation of heavy metals in plants, branches, reducing the concentration of heavy metals in soil or water to achieve pollution control, rehabilitation of the environment.
Remediation technology in plants can use a lot of plants, there are algae, plants, herbs, woody plants and so on. Its main characteristic is highly resistant to heavy metal toxicity and accumulation capacity of different types of plants to heavy metals have different absorption and accumulation capacity, and its resistance to toxicity varies.
Hao Yun-Tao et al  Isolation and Screening of Resistance to heavy metals obtained a height oval Chlorella (Chlorella ellipsoidea), and the effects of different concentrations of heavy metals copper, zinc, nickel, cadmium in the algae growth and its impact on the role of absorption and accumulation of heavy metal ions. The results showed that the algae on the Zn2 and Cd2 has a high tolerance. Tolerance of the four kinds of heavy metals followed by zinc