Biodegradation of 2,4-dicholophenoxyacetic acid using an acidogenic anaerobic sequencing batch reactor

A bench-scale study was carried out to investigate the potential to biologically treat 2,4-dicholophenoxyacetic acid (2,4-D) contaminated wastewater in an anaerobic sequencing batch reactor (ASBR), operated in the acid-phase digestion mode. The effects of 2,4-D feed concentration (20 to 200 mg L–1) and temperature (ambient and 33 °C) on biodegradation were investigated at a hydraulic retention time of 48 h and a solids retention time of 10 d, using glucose as a supplemental substrate. Following a long acclimation period of about 100 d, complete 2,4-D degradation was observed at feed concentrations of 20 and 100 mg L–1. However, at a 2,4-D concentration of 200 mg L–1, only 65% removal was achieved. Overall, operation at an ambient temperature resulted in a slightly better performance than that at 33 °C. An adaptation period of approximately a week was required any time the 2,4-D concentration was increased, indicating a sensitive behavior towards shock loadings. On the other hand, glucose was completely and readily degraded throughout the study. A sequential utilization pattern of glucose and 2,4-D was also observed, with degradation of both substrates following first-order kinetics. Moreover, volatile fatty acids (VFAs) were the main products of acidogenesis, accounting for 65% of the effluent soluble chemical oxygen demand (COD), with acetic acid being by far the most predominant VFA detected. Key words: anaerobic sequencing batch reactor, acidogenesis, kinetics, 2,4-D, glucose, volatile fatty acids.