title: Biodegradation of agricultural herbicides in sequencing batch reactors under aerobic or anaerobic conditions.
abstract: This study investigated the biodegradability of the herbicides isoproturon and 2,4-dichlorophenoxyacetic acid (2,4-D) in sequencing batch reactors (SBRs). Two laboratory-scale (2L liquid volume) SBRs were employed: one reactor performing under aerobic and the other under anaerobic conditions. The aerobic SBR was operated at an ambient temperature (22+/-2 degrees C), while the anaerobic SBR was run in the lower mesophilic range (30+/-2 degrees C). Each bioreactor was seeded with a 3:1 mixture (by weight) of fresh sludge and biomass that had been previously exposed to both herbicides. The effect of herbicide concentration on either treatment process was explored at a hydraulic retention time (HRT) of 48 h, using glucose as a supplemental carbon substrate. Although no isoproturon degradation was observed in either system during the study, complete 2,4-D removal occurred after an acclimation period of approximately 30 d (aerobic SBR) and 70 d (anaerobic SBR). The aerobic reactor achieved complete 2,4-D utilization at feed concentrations up to 500 mg/L. A further increase to 700 mg/L, however, proved to be inhibitory since 2,4-D biodegradation was negligible. On the other hand, the anaerobic SBR was able to degrade 120 mg/L of 2,4-D, which corresponds to 40% of the maximum feed concentration applied. Moreover, glucose was consumed first throughout the experiment in a sequential utilization pattern relating to 2,4-D, with biodegradation of both substrates following closely first-order kinetics.
authors.affiliation: Department of Civil and Environmental Engineering, University of Auckland, Private Bag 92019, Auckland, New Zealand.
authors.forename: E
authors.initials: E
authors.lastname: Celis
authors.forename: P
authors.initials: P
authors.lastname: Elefsiniotis
authors.forename: N
authors.initials: N
authors.lastname: Singhal
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000737:chemistry / Q000378:metabolism*; D000332:Aerobiosis; D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D019149:Bioreactors; D005947:Glucose / Q000378:metabolism; D006540:Herbicides / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism; D010671:Phenylurea Compounds / Q000737:chemistry / Q000378:metabolism*
chemical_list: D006540:Herbicides; D010671:Phenylurea Compounds; D015084:2,4-Dichlorophenoxyacetic Acid; C028904:isoproturon; D005947:Glucose; D010100:Oxygen