This paper presents experimental results on the removal of Imidacloprid from waste water using homogeneous and heterogeneous photo-Fenton processes. Experiments were conducted in a 2 L photo reactor, initial concentrations in the range 10 - 40 mg L-1 Fe(II) and 100 - 450 mg L-1 H2O2; 30 - 150 min processing times.
Initial H2O2 concentration determined the extent of the oxidation process, whereas iron concentration played a key role in the process kinetics. Homogeneous photo-Fenton showed a fast initial reaction leading to 50% Imidacloprid degradation after less than 1 min treatment, followed by a slower process until full removal was achieved. Rapid Fe(II) oxidation to Fe(III) seems responsible for the initial Imidacloprid removal. TOC and COD removal up to 77% and 88%, respectively, were measured. Heterogeneous photo Fenton, using co-acrylic acid polyacrylamide resin as a solid support, presented similar trends than homogeneous applications, although the overall process proceeded at a slower rate.
Untreated Imidacloprid samples showed significant acute toxicity to Daphnia magna and genotoxic effects on Bacillus subtilis. Acute toxicity and genotoxicity remained detectable even after complete pesticide removal, showing that toxic by-products were present.