Study On Degradation Characteristics And Growth Kinetics Of Cold-tolerant And Alkali-resistant Nitrobenzene-degrading Bacteria

Nitrobenzene is a common and widely used chemical raw material for the synthesis of rubber,explosives,herbicides,insecticides,dyes and medicines,but it is highly toxic to humans.The demand for nitrobenzene in China's chemical industry is increasing,and its emissions are also increasing,causing serious persistent pollution to the natural environment.At present,the treatment methods of nitrobenzene mainly include physical method,chemical method and biological method.Among them,the biological method has the advantages of low cost,green environmental protection,thorough treatment,and good ecological recovery,which makes it an ideal method for treating nitrobenzene wastewater.However,considering that the environmental conditions of the polluted site are extremely complex,it is difficult for the degrading bacteria to survive and play a role,and the characteristics of low temperature in northern my country also increase the difficulty of the application of biological methods.Therefore,the premise of applying biological method is to obtain a cold-resistant and widely adaptable high-efficiency nitrobenzene-degrading strain after screening and domestication.In this study,a cold-resistant and efficient nitrobenzene-degrading bacteria NB-1was screened from the groundwater of the Jihua nitrobenzene leakage site.Morphological characterization and 16sr RNA alignment analysis were performed on strain NB-1.The strain NB-1 was identified as Pseudomonas frederiksbergensis.The growth and degradation characteristics of strain NB-1 were investigated.The results showed that the bacteria were not only resistant to low temperature(4?),but also had alkali tolerance(p H 11),salt tolerance(2.5%),high-concentration nitrobenzene tolerance(1200 mg/L),and broad substrate growth.The results showed that the bacteria not only had cold tolerance(4?),but also had alkali tolerance(p H 11),salt tolerance(2.5%),high concentration of nitrobenzene tolerance(1200 mg/L)and wide substrate growth spectrum.The optimum degradation environment was as follows:temperature between 15 and 25?,p H=7.0,salinity between 0.3%and 0.5%,and shaking speed at 120 rpm.Strain NB-1 degrades nitrobenzene with an initial concentration of 100 mg/L at 25?,p H=7.0,salinity of 0.3%,inoculum size of 1%,and rotation speed of 120 rpm.The degradation rate of nitrobenzene reached 99.99%in 14 h,the removal rate of TOC reached 91.97%after 16 h,and almost completely mineralized after 24 h.The growth kinetics of strain NB-1 was studied under optimal conditions,and the Haldane-Andrews model had the best fit.The coefficients of the model are:?_m=4.9197 h^-1,K_s=10.51 L/(mg·h),K_i=802.9 mg/L.Based on the Haldane-Andrews model,the response surface methodology(RSM)was used to construct models with the true maximum specific growth rate(?_m'),specific affinity(a _A)and inhibition coefficient(K_i)as the response values.Each model was considered statistically reliable.The EMR values of the coefficients and the response surface plots show that there are great differences between the models,and the effects of different factors and their interactions on different response values are quite different.It can be known from the simulation of?-S relationship under different conditions:When the initial nitrobenzene concentration is less than 20.33 mg/L,a _Aplays a decisive role in the growth of strain NB-1.At this time,the optimal environment for strain NB-1 is:temperature=24.67?,p H=7.30,salinity=0.53%;When the initial nitrobenzene concentration is greater than 20.33 mg/L,?_m'plays a decisive role in the growth of strain NB-1.At this time,the optimum environment for strain NB-1 is:temperature=25.00?,p H=7.59,salinity=0.25%.Using?_m',a _A,and K_ias indicators to determine the optimal environmental conditions when strain NB-1 was treated with different concentrations of nitrobenzene.This provides more targeted guidance for optimizing processing.The study on the screening,degradation characteristics and growth kinetics of nitrobenzene degrading bacteria provided theoretical basis and technical support for the application of strain NB-1 in practical engineering.