Biodegradation of the herbicide Diuron in a packed bed channel and a double biobarrier with distribution of oxygenated liquid by airlift devices: influence of oxygen limitation.

From agricultural soils, where the herbicide Diuron has been frequently applied, a microbial community capable of degrading Diuron and 3,4-dichloroaniline was obtained. The volumetric rates and degradation efficiencies of Diuron and 3,4-DCA were evaluated in two distinct biofilm reactors, which differ in their operating conditions. One is a horizontal fixed bed reactor; plug-flow operated (PF-PBC) with severe limitation of oxygen. In this reactor, the air was supplied to an equalizer reservoir at the start of the PF-PBC reactor. The other is a compartmentalized aerobic biobarrier with internal recirculation of liquid aerated through airlift devices (ALB), continuously or intermittently operated. Both reactors were inoculated with a microbial community capable of degrading Diuron, isolated from a sugarcane field. In the oxygen-limited PF-PBC reactor, 3,4-DCA accumulation was detected, mainly in the middle zone of the packed channel. On the contrary, in the fully aerobic ALB reactor, minimal accumulation of catabolic byproducts was detected, and high Diuron removal efficiencies and removal rates were obtained when it was continuously operated in steady-state conditions. Additionally, the influence of oxygen limitation on the kinetic behavior of the PF-PBC reactor was determined, and a method to estimate the local removal rates of Diuron RV,CD along the plug-flow channel is described. It was observed that the local values of the instantaneous removal rate of Diuron dCD/dt are high in the aerobic region of the PF-PBC reactor; but, suddenly decay in the reactor zones limited by dissolved oxygen.