Study On Removal Of Nonylphenol In Water By Microorganism Immobilized On Biochar

The microorganism immobilization technology based on biochar is a promising wastewater treatment,it can not only utilize the strong adsorption capacity of biochar to absorb organic contaminants in water but also use microorganisms immobilized on its surface to degrade and thoroughly remove the contaminants.Further research was needed on the type of biochar and the percentage of adsorption and biodegradation in the removal process.Therefore,nonylphenol(NP),an environmental estrogen,was selected as the target contaminant in this paper.Through studying the physicochemical properties,adsorption capacity of different biochar and biodegradation ability of bacteria immobilized on biochar,the suitable carrier for microorganism immobilization was screened out.And the orthogonal experiment was used to optimize the preparation conditions of immobilized bacteria.On this basis,the reuseability of bacteria immobilized on bamboo charcoal and applewood charcoal were compared,the importance of adsorption and biodegradation were analyzed,and the effects of immobilization on microbial community structure were also investigated with quantitative PCR and 16S rRNA.The main results were as follows:(1)Seven kinds of biochar were collected and prepared including bomboo charcoal(BC),oak charcoal(OC),pine charcoal(PC),straw charcoal(SC),coconut shell charcoal(CSC),walnut shell charcoal(WSC),applewood charcoal(AWC).On the one hand,adsorption experiments showed that the NP adsorption capacity of BC,PC and WSC were stronger(K_f>20000(mg/kg)/(mg/L)~n),while that of AWC and OC were poorer(K_f>1000(mg/kg)/(mg/L)~n).The adsorption properties of biochar had positive correlation with their specific surface area,Zeta,pore volume and micropore volume and negative correlation with O/C,(O+N)/C,acidic functional groups.On the other hand,biodegradation experiments showed that the biodegradation efficiency of NP by bacteria immobilized on bamboo charcoal,pine charcoal,walnut shell charcoal was significantly higher than that of free bacteria,which may be related to the zeta and specific surface area of biochar.Combining these two aspects,as well as the difficulty of the source and mechanical properties of biochar,bamboo charcoal was the material more suitable for microorganism immobilization.(2)The optimum conditions for the preparation of immobilized microorganism were determined by orthogonal experiments and the results were as follows:30?,pH=7,35-mesh.The biodegradation of NP by immobilized was affected by pH,temperature,salinity,and NP initial concentration.Compared with free bacteria,the immobilized bacteria had better acid and alkali resistance,high temperature resistance,salt tolerance and substrate tolerance.(3)The results of recycling experiments showed that after eight rounds of reuse,the cumulative removal rate and degradation rate of NP in water by bacteria immobilized bamboo charcoal were 93.95%and 41.86%,respectively,significantly higher than that of bacteria immobilized on apple charcoal(69.60%and 22.78%)and free bacteria(64.79%and 19.49%)(P<0.01).The bacteria immobilized on biochar combined the adsorption of biochar and the degradation of bacteria.In the first round,the removal rate of NP was 100%and the degradation rate of NP was 45.00%.While in the eighth round,the removal rate of NP was 75.01%and the degradation rate of NP was 43.39%.The improvement of the degradation/removal rate ratio indicated that the long-term NP removal effect should be more dependent on biodegradation.In addition,the amount of residual NP in bacteria immobilized on bamboo charcoal still accounted for about 50%,which reminding us that the carrier recycling could not be ignored.(4)The effect of immobilization on the microorganisms was reflected on the change of microbial biomass and microbial community structure.Microbial biomass was depended on the biochar carriers,while microbial community structure was more affected by degradation time.Pseudomonas,Achromobacter,Ochrobactrum and Stenotrophomonas were the dominant bacteria for NP degradation.The addition of biochar(especially bamboo charcoal)could promote the growth of microorganism and slow down the change of the dominant microflora in the process of degradation.Thus,bacteria immobilized on bamboo charcoal had better NP degradation rate than the free bacteria.In summary,bamboo charcoal was a suitable carrier material for microorganism immobilization among the biochar.Bacteria immobilized on bamboo charcoal had good long-term removal rate and degradation rate.In addition,although bacteria immobilized on biochar had dual functions of adsorption and biodegradation,the long-term removal of NP was more dependent on biodegradation.This paper will provide theoretical foundation and technical support for the application of microorganisms immobilized on biochar.