Microbial degradation of phthalic acid and its esters by aerobic granules in sequencing batch reactor [thesis]

Ping Zeng
Phthalates, including phthalic acid (PA) and phthalic acid esters (PAEs), have wide application in industry and have become ubiquitous pollutants in the environment. However, the conventional activated sludge process cannot effectively treat recalcitrant phthalate wastewater. Bioaugmentation is one of the strategies for enhancement of the recalcitrant compounds degradation. A key ingredient for a successful bioaugmentation strategy is bioseeds selection. Phthalic acid-degrading aerobic granules
more » ... (PA-degrading aerobic granules) were found to be potential bioseeds for PA and PAEs degradation based on the study of the formation and characteristics of PA-degrading aerobic granules. First, they can be formed and matured in three weeks at an OLR of 3.0 kg COD m -3 d -1 . Second, they provided high concentration of biomass which was certified to be useful for the degradation of PA and PAEs. They also can sustain as the high PA concentration as 4000 mg l -1 . And their compact structures could provide protection for the functional cells in aerobic granules. For the first time, the PA-degrading aerobic granules were considered as bioseeds for enhancement of PA and PAEs' degradation. The rapid and easy formation of PA-degrading aerobic granules makes it feasible for further application. The bioaugmentation strategy using PA-degrading aerobic granules as bioseeds has been successfully applied in phthalate degradation. The performances were investigated under different operation conditions, from the low organic loading rate (OLR) of 1.5 kg COD m -3 d -1 to the high OLR of12.4 kg COD m -3 d -1 , and from the biodegradable di-methyl phthalate (DMP) wastewater to the recalcitrant di-butyl phthalate (DBP) wastewater. The highest PA degradation OLR achieved by a PA-degrading aerobic granular system was 12.4 kg COD m -3 d -1 , with the total organic carbon (TOC) removal efficiency higher than 97.2%. When degrading DMP, the system innoculated with PA-degrading aerobic granules can reach steady state in 15 days at an OLR of 3.0 kg COD m -3 d -1 . The highest OLR of 6.0 kg COD m -3 d -1 can be achieved by PA-degrading aerobic granules with a DMP removal efficiency of 100%. For the recalcitrant compound DBP, the system innoculated I ATTENTION: The Singapore Abstract with PA-degrading aerobic granules could treat DBP at OLR of 1.5 kg COD m -3 d -1 , with a DBP removal efficiency of 100%. Such OLR has not been achieved by the conventional treatment processes in the DBP degradation. Thus, the PA-degrading aerobic granules exhibited good performance as bioseeds for bioaugmentation compared with the DMP acclimated activated sludge. The system innoculated with PA-degrading aerobic granules also exhibited a good performance in phthalates degradation compared with the conventional PAEs treatment processes. This application provides a better choice for the industrial phthalates wastewater treatment. To probe deeper into the underlying reasons behind the successful application of PA-degrading aerobic granules as bioseeds, the variations of degradation rates and enzyme activities were traced in the DMP degradation process. The PA-degrading aerobic granules were found to originally possess constitutive enzymes catalyzing DMP and mono methyl phthalate (MMP) hydrolysis. They also have dioxygenase with high enzyme activity since they are cultivated with PA. During the DMP degradation process, the activity of esterase (DMP) increased from 1.01×10 -3 to 0.112 U mg -1 protein. The activity of esterase (MMP) increased from 0.062 to 0.342 U mg -1 protein. A high activity of dioxygenase was maintained in the range from 0.097 to 0.133 U mg -1 protein. As a result, the reaction rates of DMP degradation changed from k 1 > k 3 > k 2 to be k 3 > k 2 > k 1 , which makes the phthalate degradation proceed smoothly. Thus, it is quite important to keep the enzyme activity and the order of the reaction rates in k 3 > k 2 > k 1 in phthalates industrial wastewater treatment. 16 rDNA denaturing gradient gel electrophoresis (DGGE) and culture isolation methods were combined to assess the change of microbial community structure and the functionally important species in PA-degrading aerobic granules cultivated at an OLR of 3.0 kg COD m -3 d -1 . Although the microbial community structure of PA-degrading aerobic granules has changed during the DMP degradation process, some dominant species kept constant during the entire process. Further studied indicated that strain PA-02, a dominant species in PA-degrading aerobic granules, II ATTENTION: The Singapore Abstract III possessed the ability to degrade both PA and PAEs. In the initial stage of DMP degradation, they were the critical DMP degraders, which contributed to the steady operation of the reactor. Kinetic studies revealed that PA-02 was robust under high concentrations of DMP and PA. Even when the PA concentration was increased to 1000.0 mg l -1 , the specific PA degradation rate was about 0.25 g-PA g -1 biomass h -1 . The corresponding value for DMP was 0.067 g-DMP g -1 biomass h -1 at 1000 mg l -1 . Thus the improvement of this functional bacteria ratio by seeding with PA-aerobic granules will enhance the degradation efficiency in the future application of this bioaugmentation strategy. The storage experiment results showed that the 8 weeks storage had no significant influence on the structure of PA-degrading aerobic granules. However, more than 94% bioactivity of PA-degrading aerobic granules in terms of SOUR was lost after storage. In recovery experiments using storage aerobic granules as inocula, the TOC removal efficiency, PA degradation ability and bioactivity were completely resumed within a week. Thus, the storage aerobic granules also can be used as bioseeds to quickly start up an aerobic granular reactor. Besides fresh aerobic granules, the stored aerobic granules can be applied in industrial wastewater treatment as a source of bioseeds. This study provided the information of phthalates wastewater treatment by the system inoculated with PA-degrading aerobic granules. Such information would be essential for the design of compact, high-rate aerobic granular systems for the treatment of industrial phthalates wastewater. This study probably for the first time shows that the PA-degrading aerobic granules could be used as a bioseeds for efficient phthalates removal from industrial wastewater.
doi:10.32657/10356/12164 fatcat:xuxc4uuw3javxatpgnygg3u2vy