A preliminary study for assessing the reduction of viability of Ascaris spp. eggs (%) by photo-Fenton reaction was performed in this work. Laboratory oxidation trials were carried out with synthetic egg suspensions (initial viability = 60%) in an UV photo-reactor according to an orthogonal central composite design of experiments. The evaluated factors were pH, H2O2 dose, reaction time, and weight ratio Fe3+/H2O2. A mathematical model predicting the residual viability of eggs was developed and found adequate, as a function of these factors. The statistical analysis showed that only pH, H2O2 dose and weight ratio Fe3+/H2O2 had significant effects on the egg viability. The minimal residual viability of eggs, calculated from the mathematical model, was 13.80% at experimental oxidation conditions of pH= 2.3, 48.4 mg H2O2 /L, reaction time= 45.6 min and weight ratio Fe3+/H2O2= 0.07. The inactivation value was better than the results reported in tests of intact single-celled eggs upon exposure to UV light alone and in experiments using chemicals such as strong acids and hydroxyl radicals (OH) at basic pH medium. Thus, the higher efficiency of photo-Fenton reaction can be attributed to the combined effect of acid pH, UV radiation and OH produced by the Fenton's reaction over the inner egg membrane.

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