The Mechanism For Enhanced In Removing Nitrogen By Recombinant Genetic Engineering Bacteria And Advanced Nitrogen Removal In Green Rust System

The nitrogenous wastewater discharge and nitrogen pollution have become increasing environmental dangers because of the development of industry and agriculture. It is necessary to find some new methods to solve the nitrogen pollution problems. In this paper, nitrite and hydrazine were eliminateed by nirS recombinant genetic engineering bacteria and HZO recombinant genetic engineering bacteria, respectively. Green rust was carried out to reduce nitrite. In biological denitrification system, the influence factors and bacterial performances were investigated. The mechanism of the reactions was also studied. Meanwhile, the relationship between Eh and reduction products and influence factors and reaction equations had been discussed in GRI-CO₃^2-/NO^2- system. The main results and conclusions of this paper were as following:（1） Under the condition of NO^2--N concentration 20 mg/L and bacterial dosage 30 m L, 80% NO^2--N was degraded within 600 min by nirS recombinant genetic engineering bacteria. With the increase of bacterial dosage（from 0 m L to 50 m L） and NO^2--N concentration（from 10 mg/L to 65 mg/L）, the removal efficiency of NO^2--N increased first, and then decreased. The effects of gene mutation, expression vector and host bacteria on NO^2--N removal were negligible.（2） In nirS recombinant genetic engineering bacteria /NO^2- system, the bacteria could reach stationary phase in a short time. Although the NO^2--N concentration was increased, the bacteria still kept in stationary phase. The nitrogen removal efficiency remained at 70% with the nirS recombinant genetic engineering bacteria generation increase. Due to the effect of gene mutation, the bacteria denitrification performance could stably passed to seventh generation. The trace Fe（II） which was an essential element for bacterial growth addition could promote nirS recombinant genetic engineering bacteria denitrification process.（3） The use of 20 m L bacterial dosage created a 78% removal efficiency of the added N₂H₄-N（85 mg/L） within 1600 min. In HZO recombinant genetic engineering bacteria denitrification process, the bacteria remained at 70% removal efficiency when spread to sixth generation and showed a good generation performance.（4） The recombinant protein of HZO recombinant genetic engineering bacteria was successful expressed at 20?C, overnight or 37?C, 5 h by expression experiments, and had a certain activity. The purity and concentration of recombinant protein were measured by SDS-PAGE and SK3071 non-interference protein assay kit and reached 90% and 0.58 mg/m L, respectively.（5） GRI-CO₃^2- was synthesized by coprecipitation method. The solid-phase samples before and after reduction experiments were characterized by XRD, FTIR and XPS. The process of NO^2- reduction by GRI-CO₃^2- was studied. Results indicated that 97.1% NO^2- was degraded, and the TN removal efficiency was 90%; over 71.34% N₂O and 14.06% N2 were achieved by the oxidation of GRI-CO₃^2- to Fe3O4; 4.68% NH4+ and 2.97% NO3- were also formed in the denitrification process. The addition of oxidation product Fe₃O₄ improved the GRI-CO₃^2- reduction ability of which was beneficial to the recycle and reuse of Fe₃O₄.（6） By the calculation and adjustment of Eh, the formation order of the reduction products in GRI-CO₃^2-/NO^2- system was as following: N₂ O, N₂ and NH⁴⁺. The generation of different reduction products was depended on Eh of the reaction system. Compared with initial nitrite concentration, pH played a decisive role in Eh of GRI-CO₃^2-/NO^2- system. Additionally, The NO^2- degradation was found to be first order kinetics based on dynamic simulation.