Research progress on hazards and treatment technology of mine wastewater

2.5 Biological Method

Biological method can purify sewage through the interaction between biological organisms or their metabolites and metal ions, which has the advantages of low cost and environmental friendliness, and has become a research hotspot in various countries. Biological methods include biological adsorption method, sulfate reducing bacteria method and so on. Biosorption is the use of microorganisms (living, dead or their derivatives) to separate heavy metal ions from water systems. The mechanism of microbial separation of heavy metal ions from solution is divided into two situations: one is extracellular enrichment and extracellular precipitation, and the other is adsorption or complexation on the cell surface. The adsorption or complexation of the cell surface has no requirement on whether the microorganism is active, while the large concentration of intracellular and extracellular often requires the microorganism to be active. Sulfate Reducing Bacterial (SRB) is used to reduce S042- to H2S and further oxidize H2S to elemental S by biological oxidation. The method consists of three steps: First, SRB reduces S042- to sulfide, which can not only remove S042- in wastewater, but also increase the pH value of wastewater and reduce the harm of wastewater to the environment; Secondly, S2-1 produced in the reduction process reacts with heavy metal ions in the wastewater to generate heavy metal sulfide precipitation, which effectively removes heavy metal ions in the wastewater. Finally, H2S(S2-) is oxidized to elemental sulfur by biological oxidation. Biological treatment of mine wastewater has the advantages of low cost, easy management, strong applicability, no secondary pollution, recyclable metal resources, etc. Therefore, biological treatment has great potential in mine wastewater treatment. For example, Esteves et al. used modified sargasso as adsorbent to treat zinc-containing wastewater with a mass concentration of 98 mg/L, and the removal rate of zinc could reach 99.7%. From 1994 to 1998, funded by the US Environmental Protection Administration, SRB was used to treat and control the acid mine wastewater of Lily-Offenboi Mine. The semi-industrial test results showed that the removal rates of Zn, A1, Mn, Cd and Cu were 99%, 99%, 96%, 98% and 96%. Using maple sawdust and sawdust as organic carbon sources in the reactor, Carmen M. Neculita and Gerald J. Zury conducted an experimental study on the treatment of acid mine wastewater by SRB. The results showed that the concentration of SO42- in the wastewater could be reduced from 5500 mg /L to less than l m/L, Fe, M, Cd, Fe, Fe, Fe, Fe, CD, Fe, Fe, Fe, Fe, CD, and so on. The removal rates of Zn and Mn were above 91.8%. James M. Coastro et al. used the mixture of potato skins and manure from beef cattle factory As electron donor to conduct the biological treatment experiment of mine wastewater, which greatly improved the water quality of wastewater. The concentrations of S042-, Fe and AS decreased from 1200, 100 and 5 mg/L to near zero respectively, and the pH value increased to neutral.  The removal rates of Fe and Cu were both greater than 90%, and the concentration of S042-was also significantly reduced.

Three knots

At present, there are 5 methods to treat mine wastewater: acid-base neutralization method, coagulation sedimentation method, chemical oxidation method, constructed wetland method and biological method. Acid-base neutralization method and coagulation sedimentation method have the advantages of simple process, convenient operation and low operating cost, but there are also serious scaling, large amount of sediment, easy to cause secondary pollution and other disadvantages. The most significant feature of chemical oxidation method is that it is simple to operate and can effectively treat various forms of pollutants, but the treatment cost is high, so it is difficult to promote and apply in production practice. Constructed wetland method has the advantages of low investment, simple operation, strong impact resistance and low operating cost, but it covers a large area, is easily affected by the external environment, and has some limitations on some difficult to treat wastewater. As a new practical technology, the microbial method has the advantages of low cost, easy management, strong applicability, no secondary pollution, can recover the shortage of raw material elemental sulfur and some heavy metal ions such as copper, zinc, etc., and is increasingly used in wastewater treatment. However, how to maintain the activity of microorganisms at room temperature and how to eliminate the inhibition of heavy metal ions on microorganisms? And the mechanism of microbial action in wastewater treatment, etc., need to be further studied.