Performance and Microbial Community Structure of Bioaugmentation in a Sequencing Batch Reactor Treating Bis(2-ethylhexyl) Phthalate Wastewater at Low Temperature

Abstract

The feasibility of enhanced degradation of bis(2-ethylhexyl) phthalate (DEHP) by activated sludge inoculated with DEHP-degrading strains at a low temperature (1°C) and microbial community dynamics was investigated in a sequencing batch reactor. Bioaugmentation shortened the start-up period and significantly improved the DEHP degradation efficiency. At an influent DEHP concentration of .1 mg L−1 and an operating temperature of 14°C, DEHP removal rates of 74.3 and 34.2% were recorded on Day 21 in the bioaugmented and noninoculated control reactors, respectively. Successive increases in the DEHP concentration to .4 mg L−1 and the operational temperature to 1°C resulted in poor bioreactor performance. Only 57.4 and 16.3% of DEHP in the test and control reactors was removed on Day 78, respectively. The addition of glucose significantly improved the performance of the two bioreactors (p<.5), and 79.8 and 36.4% DEHP removal was achieved in the test and control reactors on Day 1. Real-time quantitative polymerase chain reaction (q-PCR) analysis showed that the 3,4-phthalate dioxygenase gene (phtA) and DEHP removal were positively correlated (r=.95, p<.5) during Phase I (the start-up period) and Phase II (with increased DEHP concentration and decreased temperature). Illumina sequencing analysis revealed that there was an obvious shift in the bacterial community during the bioaugmentation process. The relative abundance of Thauera, Nitrospira, and Nitrosomonas gradually decreased with decreasing temperatures and increasing DEHP concentrations. In contrast, Rhodococcus, Arcobacter, and Acinetobacter species continuously increased, concomitantly with increased DEHP removal. Overall, Rhodococcus, Arcobacter, Acinetobacter, Alcaligenes, and Bordetella contributed to a significant increase in DEHP degradation and were probably the key genera responsible for DEHP wastewater treatment at low temperatures.