Study On Bacterial Function Of High-Efficiency Paracetamol-Degrading Aerobic Granule

Frequent occurrence of pharmaceutical compounds in aquatic environments has raised a concern about their potential effects including aquatic toxicity, genotoxicity and endocrine disruption on environment. Controlling the emission of this compound has become a focus in the pollution control field. Recently, the treatment of aqueous paracetamol solutions by electrochemical method and ozone oxidation treatment has been reported. Compared to other conventional methods, biodegradation technology has several advantages such as high-efficiency, low-energy consumption, ambient reaction coditions, and low secondary pollution, which is considered to be a promising method to remove such compounds.Aerobic granular sludge that can degraded paracetamol, was successfully developed in a sequencing batch reactor (SBR). The mature granular sludge consisted of a wide variety of bacteria, mainly including coccoid-like and rod-shaped bacterium. The Michaelis-Menten equation could be fitted to the experimental data of paracetamol degradation by 0.31 g-paracetamol/(g-VSS·h). The PCR-DGGE fingerprints indicated that the dominant organisms responsible for paracetamol degradation closely related to Ensifer, Pseudomonas, Cupriavidus, Lysobacter, Sinorhizobium and Ochrobactrum.Several bacteiral strains capable of degrading paracetamol were isolated from a high-efficiency paracetamol-degrading aerobic granules. Based on morphological characteristics, physiological and biochemical characteristics, 16S rRNA sequences and the Biolog identification, these three isolates were assigned to be Cupriavidus, Lysobacter and Pseudomonas. The optimal conditions for the growth of the strains were all at 25~35℃and pH 7~8. F1, F2, fg-2 were able to degrade paracetamol up to 400mg/L, 2500mg/L and 2000mg/L respectively. Carbon balance illustrated that the carbon recovery rate of more than 90% was obtained below the tolerance concentrations. The main metabolic intermediates identified by GC-MS and LC-MS were hydropquinone and p-aminophenol. The identification of metabolites suggested a possible main route for paracetamol biodegradation, in which acetyl group was replaced by hydrogen atom to form p-aminophenol as the first degradation product. p-aminophenol was further converted to the ring fission substrate p-phenol, which finally entered TCA cycles. For all the extracts from strain F1,F2,fg-2 on paracetamol, the activities of hydroquinone 1,2-dioxygenase and catechol 1,2-dioxygenase were significantly high, which suggested the two enzymes might play important roles in degrading paracetamol.The analysis indicated that F1 possessed the strongest autoaggregation ability with the autoaggregation indices of about 70.6%. Four coaggregation pairs (F1+F3, F1+fg-2, F2+fg-2, F3+fg-2) had coaggregation indices greater than 40%, indicating the good aggregation interactions might exert an important role in the granulation of aerobic activated sludge. The comparison and analysis on degradation, mineralization rate, specific growth rate, specific degradation rate and SOUR by strains, microbial consortium and aerobic granules indicated the biodegradation performance of microbial consortium and aerobic granules were much better than any pure bacterial strain. It was proposed that the synergistic effect exerted by different strains in the microbial consortia possibly strengthened biodegradation of paracetamol.