Applied Research Of Immobilized Phenol-degrading Strains

Phenol is a major pollutant of the industrial wastewater in the aeras of petroleum,paper manufacturing,agriculture,and medicine,and it can become a serious threat to the ecological environment and human health.The wastewater can be discharged only after phenol has been degraded to meet the standards.Generally,there are three common ways on reducing phenol,these ways are physical method,chemical method and biological method.However,biological method is the most cost-effective of them and there is no secondary pollution after treatment.In this research,Cupriavidus oxalaticus T2 and Acinetobacter.sp PR1 were immobilized in Ca-alginate beads to improve cells'ability to reduce phenol.At the same time,a novel freeze-drying technique was developed to improve the reusability of Ca-alginate beads.Which provides a potential application for large-scale reduction of phenol.External cultures were immobilized in the carrier of pure Ca-alginate in which silica was added to strengthen the mechanical stability of the immobilized beads.Calcium alginate hydrogel is a kind of natural polymer and has no toxic effect on cells,which makes immobilized cells good performance in phenol degradation rate.however,carriers made of Ca-alginate are biodegradable and have weak mechanical strength,which often lead to the poor performance of immobilized beads over time.In order to realize the long-term recycling of immobilized beads,a simple freeze-drying technique has been developed,by this way Ca-alginate beads can be reused all the time if they were freeze dried before swelling to crack.This research studied the effects novel freeze drying technique has on the reusability and the survival rate of Ca-alginate beads,it also tested how the degradation efficiency of Ca-alginate beads changes after different storage of time,which provided new ideas to improve the degradation efficiency and reusability of immobilized beads.The results were listed as follows:?1?Alginate was used as supporting material in which silica was added to immobilize Cupriavidus oxalaticus T2,then the resesrch optimized parameters in embedding process,the best single factor conditions were finally determined:SA concentration was 3%,Ca Cl₂concentration was 0.5%,addition ratio of cells solution(OD₆₀₀=1.5)was 50%,and Si O₂concentration was 1.5%.?2?The results of phenol reduction by free cells of T2 and immobilized T2 showed that the degradation rate of free cells was higher than that of immobilized cells at concentrations from 500 mg/L to 1 500 mg/L.When phenol concentration was increased to 2 000 mg/L or 2500 mg/L,the degradation rate of immobilized cells was higher than free cells.freeze drying technique was used to store the Ca-alginate beads,and after three months,about 70.83%cells survived after Ca Cl₂ freeze drying.?3?A strain of Acinetobacter sp.PR1 was isolated to degrade phenol under acidic conditions.Then environmental factors like phenol concentration and p H were studied to see how them affect PR1's degradation rate.The research also investigated the effects of freeze drying technique and acidic conditions on the reusability of the Ca-alginate beads.The results showed that Ca-alginate beads can be reused for more than 21 cycles of repeated Ca Cl₂ freeze drying and they can experience 16 cycles at p H 3 because acidic conditions can significantly reduce the swelling rate of the Ca-alginate beads.The survival rate of the Ca-alginate beads after freeze drying was 60%.?4?Reactor experiment:Ca-alginate beads immobilized Acinetobacter sp.PR1 were hardened first by immersing in a solution containing 0.6%?w/v?polyethyleneimine before freeze drying.Those dried beads were continuously used in the reactor for one month and finally successfully recovered.The freeze-drying frequency decreased from three cycles?about40 h?to 30 days,which significantly reduced operating costs and provided a bright prospect to apply microbial immobilization technology to industrialization.