Study On Mn(?) Removal Mechanism Of Nitrifying Acinetobacter Sp.AL-6 And The Preliminary Application Of Environmental Treatment Of Manganese Pollution

China is the world's largest producer of electrolytic manganese metal,and its output accounts for 98.5%of the world's electrolytic manganese output.Electrolytic manganese slag is a solid waste produced by acid leaching and neutralization of manganese ore during the preparation process of electrolytic manganese,and is a key pollutant in the electrolytic manganese industry.In recent decades,the storage of electrolytic manganese slag in my country has exceeded 160 million tons,and approximately 10 million tons of electrolytic manganese slag have been produced every year.Rainwater scouring and percolation caused a large amount of soluble Mn(?)and NH₄⁺-N in the electrolytic manganese slag to enter the groundwater and soil environment with the leachate,causing serious environmental pollution.Because the oxidation-reduction potential(ORP),dissolved oxygen(DO)concentration and p H required for Mn(?)oxidation and nitrification were different,it was challenging to simultaneously remove Mn(?)and NH₄⁺-N with a single treatment system.Microbial method has great potential in dealing with environmental pollution problems and has attracted much attention.Compared with traditional physical and chemical methods,it has great advantages in economy,sustainability and removal efficiency.This article focused on exploring a bacteria that could remove Mn(?)while nitrifying,and was used to deal with the combined pollution of Mn(?)and NH₄⁺-N to the environment.By studying the ability of strain to simultaneously remove Mn(?)and NH₄⁺-N and their reaction metabolism mechanism,the strain could play an effective role in environmental restoration,and provided theoretical support for improving the treatment efficiency of Mn(?)and NH₄⁺-N.This study explored the Mn(?)removal performance of strain AL-6 under different concentrations of Mn(?)and NH₄⁺-N,and analyzed the interaction process between Mn(?)removal and nitrification behavior.The process of cell manganese metabolism and the location distribution of oxidative active factors were studied.Scanning electron microscope(SEM),energy dispersive spectrometer(EDS),X-ray diffraction(XRD)and Fourier transform infrared spectroscopy(FTIR)were used to explore the mechanism of strain AL-6 removing Mn(?).At the same time,the strain AL-6 was applied to the simulated Mn(?)polluted environment including soil environment and groundwater environment,and the potential of the strain AL-6 for environmental remediation was initially explored.The experimental results found that:(1)In the early stage,the research group isolated and screened a strain with heterotrophic nitrification-aerobic denitrification function from the activated sludge of sewage treatment plant,and was identified as Acinetobacter baumannii AL-6(Gen Bank accession number:KY930369).The strain AL-6 was inoculated into a nitrification medium containing 100 mg/L of Mn(?)and NH₄⁺-N at a ratio of 1%(v/v),and cultured at 30°C and 120 rpm for 144 h.Strain AL-6 entered the stable period of growth at 96 h,and its OD₆₀₀value reaches the maximum of about 0.962.After 144 h,the removal rates of Mn(?)and NH₄⁺-N were 98.86%and 61.80%,respectively.(2)The removal efficiency of strain AL-6 to different Mn(?)concentrations(25,50,100,200,300 mg/L)was 17.4%,96.8%,98.9%,99.0%,98.7%,respectively.The removal ratio of 100 mg/L NH₄⁺-N under different Mn(?)concentrations was 60.7%(control group),50.5%,62.6%,61.8%,64.2%,67.2%.It was found that with the increase of Mn(?)concentration within a certain range,the growth of the strain was stimulated and the removal efficiency of Mn(?)was promoted.At the same time,the presence of a certain concentration of Mn(?)could promote the removal of NH₄⁺-N and accumulate certain intermediate products.(3)The remaining concentrations of Mn(?)after 144 h in the experiment under different NH₄⁺-N concentrations(30,50,100,150,200 mg/L)were 1.26,1.60,1.93,24.30,94.16 mg/L,respectively.The increase in the concentration of NH₄⁺-N obviously inhibited the removal of Mn(?)by the strain,and the reason might be the result of the competitive inhibition of the electron acceptor.(4)The mechanism of intracellular and extracellular manganese metabolism and the location of the distribution of oxidative active factors had been studied.It was found that extracellular effects played a leading role in the process of manganese biosorption and oxidation,especially the extracellular oxidation process.The results of SEM-EDS,FTIR,and XRD showed that the bacterial cells cultured in the manganese-containing medium had a large number of flake substances attached to the surface,the main components of which were Mn O₂and Mn₂O₃.It showed that strain AL-6 mainly removed soluble manganese in water by converting Mn(?)into high-valence manganese oxide.In addition,the appearance of Mn-O functional groups and the increase of Mn and O element levels further confirmed the biological oxidation information.The changes of-OH,N-H and-CH₂groups and the emergence of new functional groups(such as C-H and C-O)provided more possibilities for the adsorption and bonding of Mn²⁺.(5)A preliminary study was conducted on the remediation potential of strain AL-6in a simulated soil manganese pollution environment,and it was found that strain AL-6could effectively fix the heavy metal manganese in the soil environment and effectively prevent the migration of manganese ions in the soil.Cell adsorption,functional group complexation and heavy metal redox reactions played a major role in the immobilization of soil heavy metal manganese.Moreover,it was found that the strain AL-6 could adapt to the complex water environment polluted by Mn(?)and NH₄⁺-N in the simulated manganese polluted groundwater environment.It could effectively remove manganese in groundwater and had potential application potential.