Kinetics of atrazine biodegradation by suspended and immobilized mixed microbial cells cultivated in continuous systems

Background: Using a suspended or immobilized microbial community obtained through chemostat selection from agricultural soils formerly treated with triazinic herbicides, the atrazine biodegradation kinetics in continuous aerobic reaction systems was studied. Results: When microbial cells were continuously cultivated on atrazine as the sole nitrogen and carbon source, atrazine removal efficiencies η_ATZ near to 100% were reached, although accumulation of metabolic byproducts was detected. The fluidized-bed biofilm reactor allowed atrazine removal rates R_V,ATZ higher than that permitted by suspended cell cultures with similar removal efficiencies. In this system, the highest volumetric removal rate was obtained (R_V,ATZ = 12.2mg L^-1 h^-1), with herbicide removal efficiencies η_ATZ near 100% and reduced accumulation of byproducts. Conclusions: With the operational conditions probed in continuous suspended-cell culture, increasing the C:N ratio in the inflowing medium resulted in higher cell growth yields but not in better atrazine removal rates. Kinetic results showed that for similar working conditions higher R_V,ATZ values and reduced amounts of degradation byproducts of recalcitrant organic compounds could be expected with multi-stage biofilm reactors.