Construction Of Microbial Flora With High Efficient DEHP Degradation And Study On Its Degradation Characteristics

Di-(2-ethylhexyl) phthalate (DEHP) which is widely distributed in the environment is one of the refractory organic pollutants. The structural formula of DEHP has a benzene ring and two adjacent long side chains, so DEHP has low water solubility and high chemical stability, making it difficult to be photo dissociated and biodegraded in the natural environment. DEHP is hard to be degraded by conventional water treatment processes. Consequently, it will flow into the natural water. This thesis is part of National Nature and Science Foundation Project《The Study of Bacterial Strains Screening and Degradation Characteristics in PAEs Wastewater Biological Treatment》(Project No.50778036). This thesis analysis the degradation pathway and the growth conditions of the active bacterial strains, building a group of high biodegradable and the most efficient microbial flora in the light of the effectiveness as biological indicator, achieving the purpose of thoroughly degraded DEHP in a secure, energy-efficient, short-time way.In the experiment, four pairs of DEHP degradation strains were isolated out from the soil and activated sludge by gradient-type domestication law, and their optimal growth and degradation conditions were also studied. The study found out that optimum growth temperature, pH, and the initial concentration of DEHP for bacterial strains WTZ-1, WTZ-R1, WTZ-R2, WTZ-2 were 30℃,pH=8-10,950mg/L;30℃,pH=7-8,470mg/L;25℃,pH=7-8,1450mg/L;25-30℃,pH=8-10,750mg/L, and the best degradation temperature, pH, the initial concentration of DEHP, and the adding amount of bacteria were 30℃,pH=8-10,470mg/L,3%;30℃,pH=7-8,1000mg/L,3%;25℃,pH=7,950mg/L,3%;25℃,pH=8,750mg/L,3%.In selecting the best environmental biodegradation conditions, the strains were tested in different ways and different proportions in the degradation experiment to find out the strains combination (WTZ) which had the most efficient degradation as the microbial flora degradation of DEHP. When the environment conditions were 30℃,pH=7.5,120r/min,adding amount of bacteria (3%), WTZ could degrade over 98.04% DEHP solution of a concentration of 950mg/L in three days, that is higher than other single bacterial strains(WTZ-1:93%;WTZ-R1:85.3%;WTZ-R2:87%;WTZ-2:53%).The degradation kinetics of the microbial flora (WTZ) was studied, and the microbial flora (WTZ) conforms to the exponential model of degradation kinetics, the degradation of DEHP could over 98% in four days as well. When the initial concentrations of DEHP were 470mg/L,950mg/L,1450mg/L,1950mg/L, kinetic equations and half lives were lnc=-0.037t+337.481, t_1/2=18.7;lnc=-0.048t+971.923,t_1/2=14.43;lnc=-0.052t+2215.053,t_1/2=13.3;lnc=-0.025t+2631.190,t_1/2=27.72.The results showed that the DEHP degradation of this microbial flora conforms to the exponential model of degradation kinetics, and the DEHP degradation is over 98% in four days. There are three composite bacterial strains in the microbial flora (WTZ). They (WTZ-1,WTZ-R1,WTZ-R2) were tested by 16SrDNA sequence analysis. The results: The bacterial strain WTZ-1 is Bacillus sp.; WTZ-R1 and WTZ-R2 are Rhodococcus sp..