Enrichment Of DEHP And DOP Degrading Bacteria And Its Degradation Characteristics

Di-?2-ethylhexyl?phthalate?DEHP?is one of the most widely used phthalic acid esters?PAEs?,which mainly used as plasticizer.Di-n-octyl phthalate?DOP?,a liner isomer of DEHP,is widely used in rubber hoses and decoration materials.As DEHP and DOP are not chemically bound to the products,they can be easily released to the environment.Therefore,they are widely distributed in the atmosphere,soil,rivers,seawater,wetlands,products and organisms,especially in seawater and saline wastewater.DEHP and DOP can be degraded through biodegradation and non-biodegradation,but biodegradation is the main way due to its high efficiency and no secondary pollution.At present,many microbial strains with the capacity to degrading DEHP and DOP have been isolated from different envirments.+However,just few reports about halotolerant strains or bacterial consortium in degrading DEHP and DOP have been reported.Besides,a large number of studies have reveled that bacterial consortium has a strong adaption to the adverse environment and higher degradation capacity owing to its species diversity.In this paper,bacterial consortium LF and a bacterial strain Lff was enciched from the sediment of Communist Canal in Xinxiang,Henan province.The optimal degradation conditions and degradation pathways of DEHP and DOP have been investigated in liquids condition,the bioaugmentation remediation of DEHP or DOP contaminated soil by LF and Lff were conducted.The main results are as follows:?1?The halotolerent bacterial consortium LF,with the capacity to degrading DEHP and DOP efficiently,has been enrichment from river sediment.Community analysis revealed that LF contained seven families and seven genera of bacteria.The predominant species was Gordonia sp.?54.93%?,Rhodococcus.sp.?9.92%?and Achromobacter sp.?8.47%?.The bacterial strain Lff,can degrade DEHP and DOP efficiently was isolated and purified from LF by plate steak and was identified as Gordonia sp.by 16S rDNA?accession number:MG385862?.?2?The optimal degradation conditions of LF for DEHP and DOP are both 30°C,pH 6.0.Under this condition,DEHP and DOP?1000 mg/l?can be degraded by 93.84%and 95.50%within 48 hours and96.89%and 99.11%within 72 hours.The optimum degradation conditions of Lff for DEHP and DOP are35°C,pH 7.0 and 35°C,pH 8.0,and DEHP and DOP?1000 mg/l?can be degraded about 90.50%and91.75%within 48 hours and 93.75%and 95.75%within 72 hours under this condition.Both LF and Lff exhibited great salt tolerance capacity in degrading DOP,and the degradation rate of DOP can maintain at81%-97%and 90%-93%respectively with NaCl contant within the range of 0-5%.Besides,the degradation rate of DEHP by LF and Lff reached to 85%-94%and 83%-90%respectively with the NaCl contant at0-4%and 0-5%,respectively.When the culture time was 24 h,the degradation rates of DEHP and DOP increased obviously with the increase of inoculum size,but the inoculum size on DEHP and DOP degradation rates was not obvious when the culture time extended to 48 h.?3?Kinetics analysis showed that the degradation of DEHP and DOP at different initial concentrations by LF and Lff were best fitted by the first-order kinetic equation.When the incubation time extended to 72 h,the degradation rate of DEHP and DOP exceeded 90%.DEHP?2000 mg/l?degradation rate by LF and Lff reached to 92.80%and 91.43%and DOP?2000 mg/l?degradation rate by LF and Lff reached to 96.74%and 93.13%,respectively.The half-life of DEHP is slightly longer and fluctuates between 3.35519 and 4.10288 days,while the half-life of DOP is between 0.239622 and 0.981443 days.Based on the intermediates detected by GC-MS,the biodegradation pathways of DEHP and DOP were proposed as follows:LF and Lff successively removed the two side chains of DEHP and DOP by?-oxidation and ester hydrolysis,and finally they were oxidized to CO₂ and H₂O.Substrates utilization testing indicates that LF and Lff also can degrade dimethyl phthalate?DMP?,diethyl phthalate?DEP?,dibutyl phthalate?DBP?and phthalic acid?PA?.?4?Soil remediation experiments showed that LF and Lff can remediate DEHP and DOP contaminated soil effectively.Both LF and Lff can degrade more than 80%of DEHP and DOP in soil within 35 days,and influence of the soil sterilizationon the degradation of DEHP and DOP can be neglected.Community analysis showed that the community structure of the soil changed slightly after the addition of DEHP and DOP.The change of the top ten dominant bacteria in DOP-contaminated soils was larger than DEHP-contaminated soils.Shannon index declined after the addation of DEHP and DOP no matter the inoculation of LF and Lff or not,but it recovered after a period of adaptation except for the non-inoculated DOP-contaminated soil.At the same time,UniFrac analysis showed that Lff had little effect on microbial community structure in the soil,and the UniFrac value was all less than 0.3.In general,the exotic strain Lff has little effect on the species abundance and community structure of the soil and it can be applied to the remediation of soil contaminated by DEHP and DOP.