Microbial Nitrate-dependent Anaerobic Ferrous Oxidizing Process And Removal Of Heavy Metals By Its Product

In the environment,denitrification process is an important part of the hydrochemical cycle of carbon and nitrogen.Through this process,nitrogen in the soil and water can be returned to the atmosphere,which is significance for maintaining the balance of carbon and nitrogen in the environment.At the same time,this is the core process of common denitrification technology currently.Heavy metals can exert toxic effects on denitrifying bacteria during denitrification,inhibit cell growth,and reduce the activity of enzymes required for denitrification.Thus,it will affect denitrification efficiency.Nitrate-dependent anaerobic ferrous oxidizing?NAFO?refers to the metabolic process of the coupling of ferrous and nitrite by microbial groups with specific functions.During the reaction process,nitrite is mainly denitrified into nitrogen,ferrous is oxidized to iron oxide,and finally deposite with the formation of sediments NAFO can tolerate and remove heavy metals,because of the adsorption of iron oxide.The purpose of this study is to explore the effect of NAFO process on the tolerance and removal of heavy metals,and finally provide the theoretical basis for the study of NAFO process for wastewater denitrification and heavy metal removal.The results are as follows:?1?High concentrations of Cd inhibited the removal rate of denitrification process and NAFO process.But,NAFO with ferrous iron as the electron donor is more resistant to Cd and the denitrification rate was higher at the same Cd concentration than that of the common heterotrophic denitrification system.NAFO removes toxic effects by removing heavy metals.?2?Particle product of suspension culture of NAFO reaction is an amorphous Fe-cell complex and amphoteric electrolyte with pHpzc value 8.82±0.25.The main component of it is Fe???,specific surface area is 10.9m2/g with pore size at 2.5nm and 4.5nm,which is shown that is a typical mesoporous material.There are iron oxide hydroxyl and carboxylic acid,amide and other organic functional groups and the deposition of phosphate on the surface.?3?NAFO particles have high adsorption capacity for Pb,Cd,Zn and Ni at the appropriate pH,and the removal rates of Pb and Cd are higher than 95%at pH 4 to 7,the removal rate of Zn remained above 98%at pH 5 to 8,and the average removal rate of Ni reached 90%to 99%at pH 6.The adsorption model of heavy metals fit to pseudo second-order model and Freundlich isotherm model.The adsorption belongs to chemical adsorption process.NAFO solid particles is a potential adsorbent for heavy metal pollution wastewater.?4?The removal efficiency of NO₃-N and TP were more than 94%in the biofilm reactor with NAFO process,and the concentration was stable at 0⁰.5mg/L and 0¹mg/L.However,the effluent COD,SS and VSS were high.It can not solve the problem by reducing the concentration of influent organic matter but bring interference and impact.?5?The top,middle,bottom and effluent particles?SS?of the NAFO reactor are different crystalline Fe-cell complex minerals.The pHpzc were 6.85±0.00,6.77±0.00 and6.58±0.06 and 8.58±0.06,respectively.These four particles belong to the micron level of particles with pore size concentrated between 3⁴ nm,belonging to mesoporous materials.Specific surface area of the bottom reached 98.99m²/g,and the surface of the active groups were abundant.The optimum pH of four particles for Cd ions adsorption were 7,6,8,8respectively.The optimum pH of bottom particles and effluent SS for Ni ions were 6,7,and the average removal rate were Ni?>92%?>Cd?>81%?.The adsorption model of heavy metals fit to pseudo second-order model and Freundlich isotherm model.The adsorption belongs to chemical adsorption process,too.