Treatment Of Methyldopa Wastewater By Fenton-A/O System

According to the review of the various treatment methods of pharmaceutical wastewater and Fenton reagent, Fenton-A/O (anoxic and aerobic biodegradation) system appeared to be applicable for the treatment of Methyldopa wastewater. The processes of Fenton treatment, Fenton treatment-PAM flocculation or Fenton treatment-PAM flocculation-A/O for the composite wastewater and the industrial wastewater in which the Methyldopa was the main pollutant, were investigated respectively. The processes applicability for pollutant removal were conducted and the primary parameters were optimized in the experiment. Further more, the mechanism of Fenton to remove the methyldopa or COD_Cr was discussed and the kinetics model was proposed to describe the phenomena presented in the experiment. Finally, the processes of Fenton treatment, PAM flocculation and A/O methods were applied totreat the wastewater, and a plant was designed.Parameters, such as temperature, H₂O₂ concentration and Fe²⁺:H₂O₂ ratio, were investigated in terms of COD_Cr removal efficiency in the Fenton treatment of Methyldopa wastewater, in which a central composite design was carried out. With the COD_Cr predicated equation, the optimum conditions predicted by the model fitted very reasonably with the experimental data for the relative error below 2%.The mechanism of Methyldopa degradation by Fenton reagent was significantly different according to the Fe²⁺/H₂O₂ ratio. With high ratio of Fe²⁺:H₂O₂ (≥2) , the Fenton reaction was coagulation enhanced by H₂O₂; with medium ratio of Fe²⁺:H₂O₂ (=1 ) , the Fenton reaction could be characterized into two specific systems, oxidation and coagulation; with low ratio of Fe²⁺:H₂O₂ (≤0.2) , the Fenton reaction was oxidation, including H₂O₂ oxidation catalyzed by Fe²⁺ and degradation by a hydrated ferryl-complex Fe_aq⁴⁺. A kinetics model was adopted to describe the reaction and the rate equation could provide the evidence for the main reaction pathway, which was fitted very well with the experiment data for the relative error below 10%. The equation of reaction kinetics as follows:...