Biodegradation of a mixture of 2,4-dichlorophenoxyacetic acid and multiple chlorophenols by aerobic granules cultivated through plasmid pJP4 mediated bioaugmentation

2,4-Dichlorophenoxyacetic acid (2,4-D) degrading aerobic granular sludge, obtained through plasmid pJP4 mediated bioaugmentation, was used for the degradation of a mixture of 2,4-D, 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) in a sequencing batch reactor. The removal rate of 2,4-D always stabilized at above 99%, indicating that the granules were still active in the presence of chlorophenols. The 2,4-D fed granules demonstrated a faster adaptation and higher degradation ability to 4-CP and 2,4-DCP than to 2,4,6-TCP. Nearly complete removals of 2,4-D and chlorophenols were achieved at the initial concentrations of approximately 400 mg/L of 2,4-D, 45 mg/L of 4-CP, 25 mg/L of 2,4-DCP, and 20 mg/L of 2,4,6-TCP and a hydraulic retention time (HRT) of 6 h. Each chlorophenol could be biodegraded and mineralized by the granules as the sole carbon source and the biodegradation followed Haldane inhibition model. The granules maintained a good settling ability and a dominant granular morphology as evidenced by the low sludge volume index (SVI) value (20–70 mL/g) and large granule size (400–610 μm) during the long-term operation (420 days). The finally obtained granules showed a different microbial community compared to the granule seeds, and were mainly composed of Novosphingobium sp., Aquincola tertiaricarbonis, Xanthomonas sp. and Pseudorhodoferax caeni.

► First study to apply 2,4-D degrading granules to degrade 2,4-D and chlorophenols. ► The seed granules were obtained through plasmid pJP4 mediated bioaugmentation. ► The granules could show fast adaptation and strong degradation to chlorophenols. ► Good settling ability and dominant granule morphology during 420-day operation. ► The dynamic changes of microbial community and dominant species were investigated.