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1 Bioflocculation
Bioflocculation is a method of decontamination using a microbial or microbially produced metabolite for flocculation and sedimentation. Microbial flocculants are metabolites that have a flocculating activity and are produced by microorganisms and secreted outside the cell. It is generally composed of macromolecules such as polysaccharides, proteins, DNA, cellulose, glycoproteins, and polyamino acids. The molecules contain various functional groups that enable colloidal suspensions in water to aggregate and precipitate. The application of microbial flocculation method to treat wastewater is safe, convenient, non-toxic, does not produce secondary pollution, has good flocculation effect, and has a fast growth and is easy to realize industrialization. It has broad application prospects.
2 Biosorption method
The biosorption method utilizes the chemical structure and component characteristics of the organism itself to adsorb metal ions dissolved in water, and then removes the metal ions in the aqueous solution through solid-liquid two-phase separation. With the use of extracellular polymers to separate metal ions, some bacteria release proteins during the growth process that remove soluble heavy metal ions from the solution into precipitates. Biosorbents have been widely used since they have the characteristics of wide source, low price, strong adsorption capacity, and easy separation and recovery of heavy metals.
3 Biochemical method
Biochemical method refers to the removal of wastewater containing heavy metals by microorganisms, which converts soluble ions into insoluble compounds. Sulfate bioreduction is a typical biochemical method. This method is based on the sulphate reduction of sulphate-reducing bacteria under anaerobic conditions. The sulphate is reduced to H2S, and the heavy metal ions in the waste water react with the generated H2S to produce a metal sulfide precipitate with low solubility. Removal, while the reduction of H2SO4 can convert SO42- to S2- and increase the pH of the wastewater, because many heavy metal ion hydroxides have a very small ion product and precipitate.
According to the mechanism of biological removal of heavy metal ions can be divided into biological flocculation, bio-adsorption, biochemical and phytoremediation.