Study On Mechanism Of Carboxymethyl Cellulose Fortified CFP312 For Degradation Of Phenanthrene In Non-aqueous Phase Liquid

Polycyclic aromatic hydrocarbons(PAHs)are common organic pollutants in the environment.Because of its nonpolar structure,it is often tightly adsorbed in the soil gap or miscible with dense non-aqueous phase liquid(NAPL),which is difficult to be biologically extracted.As an important mechanism for PAHs removal,microbial degradation is limited by its low bioavailability.Therefore,the improvement of remediation methods to promote the rapid biodegradation of PAHs has attracted much attention.However,there are still many PAHs degrading microorganisms that are difficult to adapt to these strengthening methods.This study screened an efficient PAHs degrading bacterium and determined its characteristics and classification.By analyzing the phenanthrene degradation of degrading bacteria in aqueous solution system(as),water organic solvent two-phase distribution system(AOTS),micellar aqueous solution system(MAS),cloud point system(CPS)and mud water system(SAS),its application potential was judged.The strain was hydrophobically modified to determine the appropriate modifier.Taking it as a representative,the effect of the modifier on the strain and whether it can promote the degradation of phenanthrene in NAPL were analyzed.Finally,the interaction between modifier and degrading bacteria was explored from the aspects of zeta potential,surface tension,viscosity and microstructure.The specific contents and results are as follows:(1)A mesophilic strain CFP312(15–37 °C,optimum 30 °C)with phenanthrene as the sole carbon source and energy source was screened out.It has been identified as Moraxella sp.by colony and cell morphology observation,physiological and biochemical test and 16 s r DNA homology analysis.The study found that when the concentration of phenanthrene was 400 mg/L,the removal rate of phenanthrene at 48 h and 60 h reached 84 % and 90 %,respectively,and the degradation rates were 1.21 and 1.29 mg/(L·h).During the degradation of phenanthrene,3,4-dihydroxyphenanthrene was detected as an intermediate product.Therefore,it is inferred that the degrading bacteria complete its biodegradation process by double-oxygenating the 3 and 4positions of phenanthrene.In AOTS,MAS and CPS,the degrading bacteria showed excellent adaptability to various degradation systems.In addition,the degrading bacteria also showed the ability to efficiently treat phenanthrene-contaminated soil in SAS,indicating that it has great application potential in environmental remediation.(2)The hydrophobicity modification of bacterial CFP312 was carried out by surfactants,twelve alcohols,chitosan and Carboxymethyl cellulose(CMC).The results showed that Trition X-100,rhamnolipid,sophorolipid,Tween 80 and other surfactants and lauryl alcohol could not enhance the hydrophobicity of the strain,and had no effect on the emulsification and emulsion stability of n-tetradecane,but both chitosan and CMC could improve the hydrophobicity of CFP312.After the bacteria were modified with chitosan and CMC,their contact angles increased from 30° to 78.83° and 90.86°,respectively,and promoted the formation of stable Pickering emulsion by n-tetradecane.The oil and water interface of the emulsion was observed by microscope.The emulsion formed by CMC had obvious bacterial adhesion at the oil-water interface,while the chitosan had no bacterial adhesion.(3)CFP312 produced flocculation precipitation in MSM(Minimal salt medium,MSM)salt solution of chitosan,but no obvious flocculation precipitation in MSM salt solution of CMC.After the flocculation reaction of CFP312 with chitosan and CMC,n-tetradecane could not be emulsified.By strengthening the degradation experiment of phenanthrene in NAPL,it is shown that CMC has a very good promoting effect on the treatment of phenanthrene by CFP312.When the concentration of CMC is 10 g/L,the effect is the best,and the degradation rate of phenanthrene on the 2nd and 5th days reaches 93.37 %,99.06 %.In contrast,chitosan inhibited the degradation of phenanthrene by CFP312.(4)To explore the interaction of chitosan and CMC with CFP312.It was found that the zeta potential and surface tension of bacteria-chitosan and bacteria-CMC solutions decreased after adding equal amount of CFP312,but the solution viscosity changed differently.Chitosan has a greater effect on bacterial surface tension than CMC.With the increase of CMC concentration,the viscosity of bacterial CMC solution decreased rapidly from 92.3 ± 0.3 m Pa·s to 3.0 ± 0 m Pa·s;The viscosity of bacterial chitosan solution increased slightly with the increase of chitosan concentration.The SEM structures of bacterial CFP312,bacteria-chitosan and bacteria-CMC polymer showed that CFP312 was rod-shaped and independently distributed;bacteria-chitosan polymer formed a dense network structure;bacteria-CMC polymer showed a loose network structure,which may be the reason why CMC promotes the degradation of phenanthrene by CFP312.In this study,the hydrophobic modification of Moraxella CFP312 was carried out for the first time.By clarifying the interaction between chitosan,CMC and CFP312,it provides theoretical support for strengthening the biological treatment of phenanthrene in NAPL.