Study On The Screening Of Fungal Stain For High-efficient Degradation Of Odor Compounds And Its Degradation Characteristics

2-methylisoborneol(2-MIB)is one of the typical odor compounds in the source of drinking water,which has brought great challenge to the safety and quality of drinking water.At present,physical and chemical methods have been applied in the drinking water treatment plants to remove odor compounds in the source of drinking water,such as activated carbon adsorption and ozone oxidation.Recently,microbial degradation of odor compounds has become a research hotspot due to its great potential in the treatment of drinking water or wastewater.However,it is essential to find the microorganisms with good capability in the degradation of ordor compounds.For this purpose,2-MIB was used as the model system in this study.An fungal strains with high degradation efficiency of 2-MIB was screened and isolated from samples collected in the sources of drinking water(Tai Lake).The 2-MIB degradation condition was also optimized for this strain.After that,possible degradation pathways of 2-methylisoborneol by this strainwas explored.Based on thses results,the degradation condition and efficitiency of 2-MIB by immobilized fungal mycelium in bamboo charcoal-sodium alginate particles was further investigated.In addition,the immobilized fungal cells were applied in the continuous degradation of 2-MIB in fixed bed reactor.The main conclusions of this study are as follows:(1)Using the water and mud of Tai Lake as the microbial sources,12 strains of2-MIB degrading filamentous fungi were obtained after enrichment culture,dilution-plating and single colony selection.After 5-day culture in the degradation medium with 20?g/L of 2-MIB,all 12 fungal strains exhibited the degradation ability for 2-MIB and the degradation efficiency was higher than 50%.Among the tested strains,the strain TH-W-02(2F)possessed the degradation efficiency of more than99%.After the strain identification,Fusarium oxysporum JSU TH-W-02(2F)was selected as the fungal strain with high-efficient degradation of 2-MIB and used in further study.(2)The 2-MIB degradation condition of F.oxysporum JSU TH-W-02(2F)wasIIIoptimized by one-factor experiment using degradation efficiency and initial degradation rate as indexes.The optimal conditionfor 2-MIB degradation were as follows:p H 6.5,26 ~oC,loading volume 150 m L/250 m L,inoculation amount 10%(v/v),rotation speed 150 r/min.At the initial 2-MIB concentration of 200?g/L,the degradation efficiency reached more than 95%after 3-day culture under the optimized condition.According to the identification and analysis of intracellular and extracelluar intermediate metabolites during the 2-MIB degradation by F.oxysporum JSU TH-W-02(2F)under the optimal condition,the possible metabolic pathways of2-methylisoborneol were obtained.The degradation of 2-methylisoborneol by F.oxysporum JSU TH-W-02(2F)involved the pathway with initial ring cleavage and the pathway without initial ring cleavage.The final degradation product of 2-MIB was glycerol.Based on the analysis of intracellular and extracelluar metablic pathway,the following mechanism can be deduced:2-MIB may firstly be degraded into long-chain compounds or complex cyclic compounds by extracellular degradation;and then part of these compounds was transferred into the cell,degraded into short-chain compounds and secreted into the broth;finally,these compounds were transformed into glycerol.It indicated that the 2-MIB degradation by F.oxysporum JSU TH-W-02(2F)was contributed to the synergistic effect of intracellular metabolism and extracelluar metabolism.(3)The bamboo charcoal-sodium alginate particles were fabricated and used for the immobilization of F.oxysporum JSU TH-W-02(2F)mycelium.The 2-MIB degradation condition of immobilized mycelium in flask was optimized by one-factor experiment using degradation efficiency as index and the optimal condition was obtained as follows:inoculation amount 30 g/L,loading volum150 m L/250 m L,rotation speed 120 r/min.The immobilized mycelium provided good degradation abilityunder the optimized condition,where the degradation efficiency of no less than98%was achieved at the 2-MIB concentration of 200?g/L within 2 days and the contribution of adsorption to 2-MIB removal was 17.8%.The immobilized mycelium exhibited excellent reusability and storage stability.The degradation efficiency of immobilized mycelium kept more than 92%after 20 cycles and no activity loss occurred after the storage of 30 days.Furtherly,the bamboo charcoal-sodium alginate particles with immobilized mycelium were loaded into fixed bed reactor for the continuous treatment of 2-MIB.After optimization,the best treatment condition in fixed bed was established as follows:loading rate 55%(v/v),residence time 3.5 h.The teatment results of different initial 2-MIB concentration showed that the system possessed good adaptability to the operationburden.In the ideal system using mineral salt medium,fixed bed reactor reached the steady stage after the star-up stage of 5days,where the degradation efficiency was higher than 97%.However,in the lake water system,the star-up stage prolonged to 7 days and the degradation efficiency remained more than 95%at the steady stage.The characterization results by scanning electron microscopy and laser confocal microscopy showed that the mycelium immobilized in bamboo charcoal-sodium alginate could grow in both tested systems and it could degrade 2-MIB to meet the demand of growth and metabolism,resulting the removal of 2-MIB.These results indicated that the fixed bed reactor with the immobilized mycelium in bamboo charcoal-sodium alginate particles exhibited good potential in future application.