Study On Treatment Of Sulfur-containing Wastewater By N₂/H₂ Gas-lift Internal Circulation SRB Reactor

In the production process of non-ferrous mining and smelting,a large amount of acid mine drainage is generated in the mining area and waste rock field due to oxidized leaching of sulfide minerals,and industrial furnace kiln flue gas wet desulfurization produces a large amount of sulfur-containing flue gas eluent,etc.It has the common characteristics of low p H,high sulfate and high heavy metals.Traditional treatment mostly uses lime-alkali neutralization,it can produce a large amount of solid waste such as calcium sulfate,which not only has risks of occupying lots of land and polluting groundwater,but also waste resources of valuable metals and sulfur.Sulfate-reducing bacteria（SRB）can reduce sulfite and sulfate to form sulfur ions,which has been widely concerned in the treatment of sulfate-containing wastewater.At present,most researches use organic materials（excess sludge,agricultural waste,high-concentration organic wastewater,etc.）as the electron donor of SRB,resulting in high residual organic matter in biochemical effluent,and it is difficult to achieve the effective recovery of valuable metals and sulfur.In addition,SRB biochemical activity is susceptible to acid and heavy metal toxicity inhibition.The above problems limit the promotion and application of SRB biotechnology.In this study,N₂/H₂ gas stripping internal circulation SRB reactor was used to treat sulfur-containing wastewater,and hydrogen was used as the SRB electron donor to reduce sulfate to S^2-,HS^-,H₂S.It could avoid direct contact between SRB and heavy metals/strong acids by means of N₂/H₂ blowing off H₂S and biochemical effluent S^2-reflow,and achieve resource recycling of heavy metals and sulfur in wastewater sulfidation precipitation of heavy metals and the comproportionation of SO₃^2-and S^2-.And the gas was used as the electron donor,the residual organic pollutants in effluent was lower,and the effluent can be directly discharged to meet the standard.In the process of applying this technology to the treatment of acid mine drainage and flue gas desulfurization wastewater,a series of studies were carried out on the domestication of specific bacteria,metabolic process behavior,optimal conditions,resource recovery conditions of valuable metals and sulfur.The main research results are as follow:（1）The sulfide in the H₂-lift internal circulation bioreactor was mainly∑S^2-,and the low concentration of SO₃^2-and S₂O₃^2-was difficult to detect.Sulfur balance analysis showed that the total S content decreased with the increase of reaction time,and the undetected sulfur components may be S₂O₆^2-,S₂O₈^2-,etc.The N₂/H₂ gas-lift internal circulation SRB-reactor has the following advantages in the treatment of acid mine drainage:the effluent TOC≤3 mg·L^-1,and the effluent quality could reach the first-class standard of Integrated Wastewater Discharge Standard;the removal rates of Zn,Cu,Fe,and Mn were higher than 94.3%,95.2,90.7,and 78.3%,respectively,and the Cu²⁺and Zn²⁺effluent concentrations were 0.52,1.99 mg·L^-1;Zn and Cu could be preferentially and completely removed,and the purity of the acquired valuable metal sulfide was 98.23%.Sulfate reduction kinetic analysis showed that medium concentration SO₄^2-and neutral p H were beneficial to the SRB metabolism.（2）The microorganisms in the N₂/H₂ gas-lift internal circulation SRB-reactor were mainly Desulfovibrio.In addition,its also include Pseudomonas,Clostridium and Methanogens.There was a certain cooperative and competitive relationship among Desulfovibrio,Pseudomonas and Clostridium,resulting in lower total organic carbon content.The metabolic activity of Methanogens was lower than that of Desulfovibrio under H₂ culture conditions.The analysis of the mechanism of biological carbon fixation for feeding Desulfovibrio with inorganic nutrients showed that organic carbon can still be detected in bioreactors without carbon sources.（3）The optimal p H for the treatment of SO₂ flue gas in the H₂-lift internal circulation bioreactor was controlled between 6.2-7.0.The flue gas desulfurization and sulfur recovery（H₂-SRB）_（aq）-SO_2（aq）process was proposed based on the advantages of N₂/H₂ gas-lift internal circulation SRB-reactor,and its reaction process mechanism and optimization conditions:the sulfur turbidity reached the maximum at p H=（3.34±0.11）and ORP=（-110±20）m V,and the sulfur yield was higher than 40%;the increase in p H was not benefited to the formation of sulfur,which disappeared gradually under nearly neutral conditions;biological sulfur contained microbial metabolites and biomacromolecular,which not only made the average particle size of biosulfur larger than chemical sulfur,but also hindered the growth of sulfur crystals;compared with biosulfur containing a large amount of biomacromolecules,the physicochemical properties of biosulfur in（H₂-SRB）_（aq）-SO_2（aq）was closed to chemical sulfur;the stability of biosulfur was far lower than chemical sulfur,but chemical sulfur and biosulfur had the aggregation of unstable equivalence at p H 5.1.