Abstract: This article mainly discusses the treatment of heavy metal wastewater treatment technology engineering, genetic engineering technology in the treatment of heavy metal wastewater by microorganisms and the transformation of the technological process.

Key words: heavy metal wastewater; microorganism; engineering reconstruction

Non-ferrous metal industry produces waste water in mining, mineral processing and smelting production process. According to its origin, it can be divided into mining waste water, mineral processing waste water, smelting waste water and processing wastewater. Non-ferrous waste water is more complicated and often contains various heavy metals such as CuCrbPzn and CdAs , And has the characteristics of large fluctuations in water quality and quantity. Containing heavy metal wastewater has high toxicity, if it is not effectively treated, its entry into the environment will endanger human health, soil pollution, there are some environmental risks, with a wide range of pollution, the degree of harm to a large extent.

Traditional heavy metal wastewater treatment technologies include chemical precipitation, carbon absorption, ion exchange, evaporation and membrane treatment, etc., but generally have the difficulty of dealing with low concentrations of wastewater, easy to cause secondary pollution and other shortcomings. Compared with the traditional treatment technology, biological treatment technology has the advantages of low cost, suitable for treating low concentration wastewater, no secondary pollution and the like.

First, the microbial treatment method

The use of bacteria, fungi biochemical metabolism, the separation of heavy metals and water or reduce its toxicity, so as to achieve the purpose of wastewater treatment. Especially suitable for heavy metal content is not high, high organic content of sewage treatment.

(A) adsorption method

The cell wall rich in polysaccharides and glycoproteins with hydroxyl, thiol, carboxyl, amino and other functional groups, it has good metal ion adsorption properties. Therefore, bacterial cells as adsorbent, can be the ideal treatment effect. Puranik and other fungi through Pb2 +, Zn2 + adsorption experiments, the results of the test results of the equivalent ion exchange, ion exchange is the main mechanism of microbial adsorption of heavy metals.

Microbial adsorption method according to cell activity can be divided into living cell adsorption and dead cell adsorption method, the living cell adsorption process includes extracellular adsorption and intracellular transfer; dead cell adsorption only extracellular adsorption process, where the adsorption method mainly refers to dead cells Extracellular adsorption. Dead cell adsorption method is not limited by the growth of ions and nutrients and other conditions, without the need for metabolic products, etc., the fermentation industry algae, seaweed, microbial residues and so on are promising biological adsorbents. Dead cell adsorption according to different biological species can be divided into fungal adsorption, algae adsorption, bacterial adsorption, plant symbiont adsorption. Ozdemir et al. Extracted the dead cell of Oobactrumanthropi from activated sludge and studied the wastewater treatment of chromium (VI), cadmium (II) and copper (II) with good treatment effect .

Recovery of precious metals in wastewater, the traditional adsorption method used in microorganisms and water separation is not easy, as its bottleneck. MTB cells contain ferromagnetic particles (ie, magnetosomes) arranged in a chain, so that the cells have permanent magnetic dipole moment and magnetic orientation. Under the action of an applied magnetic field, the MTB can move in a directional direction and is easy to be Separated from solution by magnetic separator. Therefore, the study of MTB as adsorption carrier has gradually become a hot issue. Song Huiping et al. Studied the adsorption characteristics of MTB to Au3 +, Cu2 + and Ni2 + in the cell system and ternary system. The results showed that MTB had a high adsorption selectivity to Au3 + in the ternary system and the adsorption rate was very high. Time to achieve complete adsorption. The adsorption selectivity of MTB to Au3 + and its own magnetocaloric properties provide a completely new and efficient method for gold recovery from gold-bearing effluent.

(B) Metabolic Act

Micro-organisms can precipitate or reduce the toxicity of heavy metal ions through the reduction reaction. For heavy metal SO42- -containing wastewater, anaerobic microorganisms mainly including sulfate-reducing bacteria (SRB) are often used to reduce high-valent heavy metal ions in anaerobic conditions and combine with the S2-compound produced by sulfate-reducing bacteria to form metal Sulfide precipitation, so as to achieve the purpose of separating heavy metal ions.

With the continuous deepening of research, more and more bacteria that can be used for heavy metal treatment have been discovered. For example, silicate bacteria in addition to the obvious ability to deal with COD and BOD, the copper, chromium and other elements also have obvious treatment effect. The mechanism of heavy metal wastewater treatment by silicate bacteria was studied. Three hypotheses were made on the mechanism of action: biosorption on the surface of microbial cells; flocculation of extracellular polymers; reduction of complexation of organic acids and amino acids with heavy metal ions Its toxicity.

Sadettin et al. Studied the bioconcentration of synthetic reactive dyes and Cr6 + by Phorium sp. The results showed that the initial tolerated concentrations of Cr6 + were 5.8 mg / L ~ 19.9mg / L, when the dye concentration is 12.5mg / L, the bioconcentration of Cr6 + is the largest. Cr6 + removal process can be divided into three stages: valence bond to the surface of microbial cells, transferred to the cells, Cr6 + intracellular reduction of Cr3 + and thus reduce the toxicity. Which intracellular reduction to reduce the toxicity of the main mechanism. The use of this bacterium can remove both heavy metal ions and reactive dyes that are resistant to the traditional biological treatment methods. The results show that the method is effective and has good application prospects in chemical wastewater treatment such as printing and dyeing.

(C) flocculation method

Biological flocculation method is the use of microorganisms or microorganisms produced by the flocculation of metabolites flocculation and precipitation of a decontamination method. Biological flocculant, also known as the third generation of flocculant, is a charged biological macromolecules, mainly protein, mucopolysaccharide, cellulose and ribose.

Currently accepted flocculation mechanism is ionic bond, hydrogen bonding theory.

Journal article classification query, do in the library of the library Silicate bacteria treatment of heavy metal wastewater one of the possible mechanisms is the biological flocculation. At present, there are many applications of silicate bacterial flocculation [10-11], and some have achieved remarkable results. Using genetic engineering technology, the expression of the metal-binding protein in the bacterial cells is separated, and then fixed on the surface of some inert carriers to obtain the high-enrichment capacity flocculant. Masaaki Terashima and his colleagues used E. coli to express the pmal-MT fusion protein (pmal-MT) and immobilized purified pmal-MT on Chitopeara resin using a transgenic technique to study its effect on Ca2 + And Ga2 +, the immobilized fusion protein-based resin has strong stability and its adsorptive capacity is more than ten times higher than that of pure resin.

  Second, genetic engineering technology in the treatment of heavy metal wastewater in the application of microorganisms  

The use of genetic engineering technology to build strains with high efficiency degradation is the current research focus, both domestic and foreign scholars have conducted a large number of studies, mainly committed to the use of genetic engineering technology, expression of specific metal binding protein or metal binding peptide on the surface of microorganisms and then increase the rich Or capacity to express a specific metal transport system at the cell membrane of a microorganism, express a metal-binding protein or a metal-binding peptide in a cell, thereby obtaining an efficient strain with high enrichment capacity and high selectivity. The capacity of the constructed strains was significantly increased, and the construction of highly selective recombinant bacteria made it possible to re-source heavy metals in wastewater.

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