Modification Of Polyurethane Foam For Cell Immobilization To Remove Phenol

Carrier material is the basis for constructing an immobilized cell system,and the properties of material directly affect the efficiency of cell immobilization and its biodegradation.Therefore,the understanding of the relationship between material properties and cell immobilization,as well as biodegradation is very important for constructing a high efficient immobilized cell system.On the basis of previous researches,the effects of surface modification and bulk modification of polyurethane foam on the strain of Alcaligenes sp.DN25 immobilized were investigated,and the removal efficiency of phenol by different modified polyurethane foam immobilized cell systems were further investigated.The main researches included three aspects:(1)The polyurethane foam was synthesized by one-step with high porosity and stable pore structure,which could effectively immobilize Alcaligenes sp.DN25.The results showed that the dry weight of immobilized cells increased by12.3%and 20.9%respectively after addition of Fe²⁺and Fe³⁺ions in the immobilized culture system,indicating that iron ions promoted the growth of the strains on materials.The polyurethane foam(PUF)was modified by two methods,magnetic iron oxide surface coating and chemical oxidation-iron oxide surface modification.The results showed that the two modified immobilized cells can completely degrade 1160 mg/L phenol in 48 h,which was18 h shorter than the unmodified PUF immobilized cell system,and the degradation rate of phenol increased by 34.5%.In addition,the study found that during the first 12 h,the removal of phenol was mainly caused by carrier foam and the equilibrium adsorption rate was about 47.9%,indicating that the removal of phenol by immobilized cell system included the two parts of carrier adsorption and biodegradation.Furthermore,the impact of immobilized cells on the removal of phenol and reusability were investigated under the conditions of initial p H value of 6.0-9.0,salt concentration of 0%-4.0%.The results showed that the,of the modified PUF immobilization system can completely degraded 900 mg/L phenol in 48 h at p H value of 9.0 and 76 h at salt concentration of 4.0%respectively,and the phenol removal rate of immobilized cells can still maintain 100%after 7 cycles,which indicated that the immobilized system had good environmental tolerance and stability and laid a foundation for further development of practical application.(2)The polyurethane foam was modified by chitosan,graphene oxide and magnetic iron oxide,respectively.The results showed that the modified polyurethane foam prepared by adding CS,GO and Fe₃O₄to 2.00 g,0.20 g and1.00 g per 100%polyols was more suitable for the growth of the polyurethane foam.The time for the complete removal of 1160mg/L phenol from the corresponding immobilized cells was 54 h,60 h and 54 h,respectively,while the time for the unmodified PUF immobilized cells was 66 h.When 3 substances were added at the same time,the biomass of the GO-CS-Fe₃O₄-PUF composite foams was 20.1%higher than that of the unmodified PUF materials.(3)The effect of foam pore structure on immobilization and phenol removal was studied.When the average pore size of polyurethane foam was 150?m,the maximum biomass reached 0.0253±0.0010 g.Moreover,the degradation rate of 900 mg/L phenol did not change significantly at the initial p H value of6.0-9.0 and salt concentration of 0%-4.0%.As for the removal to 500 mg/L phenol,the immobilized cells were able to reuse 11 times,which showed the advantages of the immobilized cell system in environmental conditions and system stability.