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.