Study On Degradation Characteristics Of Marine Oil Spill By Embedding Immobilized Crude Oil Degrading Bacteria

With the continuous development of the world economy,crude oil,as an important strategic reserve material,has been widely used on a global scale.Almost 90%of the world's crude oil is transported through the ocean.In the course of transportation,oil spills may occur due to damage,collision,overturning,etc.,and in the event of an oil spill,it will cause a certain impact on the entire ecosystem.In order to find more effective and environmental-friendly oil spill repair technology,bioremediation came into being.In this research,the effects of free bacteria and embedded immobilized bacteria on crude oil were analyzed,which provided technical and theoretical support for the later marine oil spill bioremediation.In this paper,four crude oil-degrading bacteria screened from oil-contaminated areas were mixed to obtain high-efficiency crude oil mixed degrading bacteria.Then the degradation analysis and kinetics simulation of crude oil by free bacteria and embedded immobilized bacteria were carried out.Finally,response surface analysis method was used to simulate various factors under different conditions?nitrogen-phosphorus ratio,bacterial liquid addition amount,modified material addition amount,pH?.The effect of degradation of crude oil is obtained,and the optimal preparation conditions and degradation conditions of the pellet are prepared.The main research situation is as follows:?1?In order to study the effects of nutrient stimulation on microbial metabolism,the degradation of free bacteria before and after adding N and P nutrients was analyzed.The degradation rate increased from 65.78%to 72.47%,indicating that adding a certain proportion of nutrient salts can improve the degradation rate.Gas chromatography?GC?was used to study the degradation characteristics of free bacteria.The results showed that the selected mixed high-efficiency degrading bacteria had good degradation ability to C11-C32short-chain alkanes.By fitting different degradation kinetic models,it is found that the first-order degradation kinetics equation can better describe the degradation process of free bacteria,and the crude oil has a shorter half-life and a faster degradation rate after adding N and P nutrients.?2?Sodium alginate was used as an embedding agent,jute was modified as an adsorbent,and CaCl₂ was used as a crosslinking agent to immobilize the free bacteria.The effects of different embedding agent concentration,adsorbent addition amount,crosslinker concentration and crosslinking time on immobilized pellets were analyzed.It was found that when the concentration of sodium alginate was 4%,the amount of modified jute added was6g/L,the concentration of CaCl₂ is 3%and the crosslinking time is 12h,the physical indexes of the pellets reach the ideal state.To further illustrate the activity of bacteria after being embedded into alginate beads,comparative analysis of the effect of each bead on the removal of oil entrapped in different states was researched.It was found that the addition of a certain amount of adsorbent had an adsorption effect on crude oil,and the degradation effect of the added microspheres was good,indicating that the sodium alginate pellets would not deactivate the degrading bacteria.?3?The effects of N,P nutrient addition,bacterial solution addition,modified jute addition and pH on the degradation were investigated by response surface analysis.Using the predictive model to predict the optimal value,it is found that when N:P=14.07:1,the amount of bacterial liquid added is 13.56mL,the added amount of modified jute is 6g/L,and the degradation environment pH is 7.13,immobilized pellet can reach the best degradation rate was 88.21%.According to the actual situation,the prediction results were verified,degradation rate was 85.52%,and the error was only about 2.7%.?4?By comparing the degradation curves of free bacteria and immobilized bacteria,it was found that the degradation process of immobilized bacteria is a process of slowly releasing microorganisms,so the stable degradation period is about ten days,while the free bacteria is seven days.For the degradation of normal paraffins,it also has a better degradation effect on short-chain alkanes of C11-C32,which is similar to that of free bacteria,but for the degradation of some alkanes,the effect of immobilized bacteria is better.Through the kinetic model analysis,it is found that the secondary degradation kinetics model can be better used to describe the degradation process of the embedded immobilized bacteria.It is indicated that the degradation process of crude oil by immobilized bacteria is affected by various conditions,and the degradation process of free bacteria is affected by a single factor.