Biodegradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in sequencing batch reactors

A bench-scale study using sequencing batch reactors (SBRs) was conducted to investigate the effects of hydraulic retention time (HRT), the presence or absence of supplemental substrate and variation in feed concentration on the biodegradation potential of 2,4-dichlorophenoxyacetic acid (2,4-D), one of the most commonly used phenoxy acid herbicides. A long acclimation period (about 4 months) was observed before 2,4-D biodegradation was established. At steady-state operation, all reactors achieved practically complete removal (>99%) of 2,4-D and the corresponding supplemental substrate (where applicable), regardless of the HRT applied, ranging from 12 to 48 h. A sequential utilization pattern of supplemental substrate and 2,4-D was observed throughout the study. The 2,4-D specific removal rates were affected by the type of supplemental substrate used (phenol or dextrose), being significantly lower (30 to 50%) in the case of dextrose. Overall, the changes in the feed concentration of supplemental substrate or 2,4-D did not produce a significant effect on the biodegradation behavior of 2,4-D.