Isolation And Degradation Of Dominant Bacteria Of Plasticizing Agent In Refinery Wastewater

Dibutyl phthalate (DBP), di-n-octyl adipate (DOA) are two typical plasticizing agent andwidely used in the industry of PVC material. Both of them are environmental hormone-likesubstances. They have carcinogenic, teratogenic, mutagenic effect to animals and humans byinterfering with the normal level of hormone in the body. In particular, they have a relativelylarge impact on reproductive system. The GC-MS analysis of the biotreated effluent showedthat these two substances accounted for a large proportion in the substances which hardly bedegraded of the biotreated effluent. So, it has a great significance to search for an effectivemethod of removing such pollutants on human survival and environmental protection.In this study, dibutyl phthalate (DBP) and di-n-octyl adipate(DOA) were used as thetarget substrates to isolate two dominant strains which could degrade the correspondingsubstrates from the activated sludge of petrochemical wastewater treatment. And they werenamed DBP-WUST and DOA6respectively. The two strains were identified according to themorphological observation, physiological and biochemical characteristics and sequenceanalysis of16S rDNA. The effects of temperature, pH, inoculum size, shaking speed andother factors on degradation by the two strains were studied. The degradation kinetics andbroad spectrum of substrates by the two strains were also researched. What’s more, themetabolic pathway of DBP degradation and treatment effect of actual refinery wastewater byremoving COD were demonstrated by strain DBP-WUST. The research conclusions are asfollows:(1) Separately got a DBP or DOA degrading bacterium, named DBP-WUST and DOA6.The two strains were identified as Elizabethkingia sp. and Bacillus sp. It is the first reportabout Elizabethkingia sp. whit the activity of degrading DBP.(2) The optimum initial pH, temperature, shaking speed, inoculation amount and saltconcentration for DBP-WUST utilizing DBP was pH=7.0, temperature35°C, shaking speed150r/min, inoculation amount7%and salt concentration0.5%(m/v), respectively. ForDOA6, the optimum conditions was initial pH=8.0, temperature30°C, shaking speed150r/min and inoculation amount2%. At the corresponding optimum conditions, the strainDBP-WUST could degrade400mg/L DBP completely within60h or the strain DOA6coulddegrade200mg/L DOA completely after80h.(3)The results of broad spectrum of substrates showed that strain DBP-WUST couldeffectively use DOA, have a certain degree of degrading on pyridine, ethylbenzene andnaphthalene, but couldn’t use quinoline, xylene or nitrobenzene; while strain DOA6was ableto use paraxylene, DBP, ethylbenzene and naphthalene, but not quinoline, pyridine or nitrobenzene. The biodegradation of DBP was in accordance with the first-order reactionkinetics while the biodegradation of DOA was fit to the zero-order reaction kinetics by the twocorresponding strains.(4)The degradation pathway of DBP by strain DBP-WUST was proposed as followed:DBPâ†'MBPâ†'PA. Firstly, one ester bond of DBP breaks down by hydrolyzation and formsmonobutyl phthalate (DMP). Secondly, the other ester bond breaks down and forms phthalicacid(PA). At last, DBP has passed several ring-opening reactions for complete mineralizationto H2O and CO2. Strains DBP-WUST can quickly adapt to the refinery wastewaterenvironment to reduce the COD of the wastewater effectively. It means that the strain not onlyhas the ability to degrade DBP in the refinery wastewater, but can degrade other organics in it.