Study On Immobilized Microbial Pellets Using Carbon-based Materials And Degradation Of Plasticizers In Water

Phthalate esters（PAES）are currently the most commonly used plastic additive,which are continuously released into the environment during the daily use of plastic products or the degradation process of waste plastics,resulting in environmental estrogen pollution issues.Microbial remediation is a low-cost,green,and universally applicable ecological remediation technology,but it is easily affected by the external environment in practical applications.The use of immobilized technology to load microorganisms on porous materials is an effective way to improve the adaptability of degradable bacteria in a practical environment.In this paper,di（2-ethylhexyl）phthalate（DEHP）,which was the most widely used pollutant in PAEs,was selected as a representative pollutant to enrich and isolate DEHP highly efficient degrading bacterial consortium（K1）from farmland soil covered with plastic mulch for over 30 years.In order to further enrich the microbial degradation system of DEHP,a strain capable of using DEHP as the sole carbon source and energy source for growth was isolated and purified from the bacterial consortium,Rhodococcus sp.KLW-1.The degradation ability,degradation mechanism,and substrate broad-spectrum of the bacterial population and single bacteria were analyzed.On this basis,waste biochar and sodium alginate were used as immobilized carriers to prepare immobilized microbe pellets to enhance the ability of microorganisms to treat simulated PAEs wastewater.The main contents and conclusions of the study were as follows:（1）The changes in microbial community structure in the original soil samples and consortium K1 were analyzed using high throughput sequencing technology.The results showed that the relative abundance of unclassified Comamandaceae,Achromobacter,and Pseudomonas in the bacterial consortium increased rapidly after enrichment and acclimation with DEHP as the sole carbon source.These bacteria may play a key role in the degradation process of DEHP by the consortium.PICRUSt analysis showed that the relative abundance of functional genes such as membrane transport,xenobiotics biodegradation and metabolism,and amino acid metabolism in bacterial consortium after enrichment and cultivation was significantly higher than that in original soil samples.Response surface methodology（RSM）was used to optimize the degradation conditions of DEHP.The results showed that under the optimal conditions（31.4℃,p H 7.3,concentration 420 mg/L）,the degradation efficiency of K1 for DEHP could reach 98.84%.After incubation for 72 h,the degradation efficiency of K1for different initial concentrations of DEHP（100-3000 mg/L）reached over 83%,and the degradation process conformed to the first order kinetic equation.Using gas chromatography mass spectrometry（GC/MS）,it was determined that the metabolites of DEHP were phthalic acid（PA）and 2-ethylhexanol（2-EH）,which suggested that bacterial consortium K1 might degrade DEHP through the de-esterification pathway.（2）Through further isolation and screening of K1 consortium,a strain with the strongest ability to degrade DEHP and grow as a sole carbon source and energy source was obtained.Through 16S r DNA sequence analysis,it was identified as Rhodococcus sp.RSM was used to optimize its degradation conditions.The results showed that under the optimal conditions（31.2℃,p H 7.2,concentration 60 mg/L）,KLW-1 could degrade more than 98.86%of DEHP.The degradation efficiency of strain KLW-1 for different initial concentrations of DEHP（50mg/L-300 mg/L）was above 98%,and the degradation process conformed to the first order kinetic equation.GC/MS analysis showed that strain KLW-1 had a DEHP metabolic pathway similar to that of K1 consortium.（3）Immobilized microbial pellets K1-BCP and KLW1-BCP were prepared by using sodium alginate embedding method to immobilize the obtained consortium and single bacteria on waste biochar,respectively.The response surface methodology was used to optimize the preparation conditions.The results showed that the KLW1-BCP prepared under the optimal conditions 3%sodium alginate（SA）,2%biochar（BC）,and 4%（Ca Cl₂）had good mass transfer performance and mechanical strength,and the degradation efficiency of DEHP was over 90.48%.Compared with bacterial consortium K1,immobilization significantly improved the adaptability and tolerance of strain KLW-1 to adverse environments.Under adverse environmental conditions of p H 5 and 9,immobilization increased the degradation efficiency of KLW-1 to DEHP by 16.42%and 11.48%,respectively.Under high stress conditions with a DEHP concentration of 500 mg/L,immobilized pellets were more stable and resistant to shock loading than free bacteria.After four cycles of utilization,the immobilized pellets maintain stable degradation efficiency for different PAEs.The above research indicates that immobilized pellets had certain practical promotion potential in practical environmental remediation.