Biodegradation of two commercial herbicides (Gramoxone and Matancha) by the bacteria Pseudomonas putida

Abstract

The purpose of this project was to evaluate the biodegradation of two commercial herbicides (Gramoxone and Matancha) by the bacteria Pseudomonas putida. Gramoxone's active ingredient is Paraquat (1,1'-dimethyl-4,4'-bipyridylium) and Matancha's is 2,4-D (2,4-dichlorophenoxiacetic acid). To carry out the biodegradation experiments, a factorial design 2³ was executed, where the independent variables were: herbicide concentration, nutrient concentration and the use or no use of activated charcoal (AC) in the same experiment with bacteria. Duplicate experiments were performed for a period of three days using 500 ml bioreactors. The best results obtained when no AC was used were: 47,29% degradation for Gramoxone (by UV/VIS) and 68.72% for Matancha (by HPLC). The treatments carried out with the use of AC for either of the two herbicides gave more than 95% degradation at 72 h. In fact, under these conditions most of the experiments showed at least a 90% removal at 24 h. It is clear that the dual combination of adsorption by AC and biological activity by the bacteria was very effective, in particular when at least 10% nutrients were added. The statistical study of the results showed that AC is a highly significant variable, and that there are significant interactions between the three variables used in the experimental design. The application of these experiments to wastewater (COD = 584.11) confirmed that it is possible to remove more than 90% of either of these herbicides in a 24 h period.