Fenton and Photo-Fenton Oxidation of Selected Pharmaceutical Compounds in Water

Abstract

In the present study, the degradation of three selected pharmaceuticals viz. paracetamol (PCM), amoxicillin (AMX) and diclofenac (DCF) is carried out using Fenton and UVC assisted photo-Fenton oxidation processes in batch mode at ambient temperature (27 ± 3o C). In addition to Fe2+, iron extracted from laterite soil (Fe (LS)) is also studied as an alternate catalyst in Fenton reagent. The experimental conditions like pH, [H2O2]0, [Fe2+]0, [Fe (LS)]0, are optimized by Fenton process for the initial concentration of 0.066 mM for PCM, 0.027 mM for AMX and 0.031 mM for DCF. For the optimization of the initial experimental conditions, drug degradation and chemical oxygen demand (COD) removal are measured as the objective parameters. The optimum pH for the degradation of PCM and AMX is 3.0 but for DCF and mixture of the drugs it is 3.5. The H2O2 is varied in the range 0 to 2.94 mM, Fe2+ is varied from 0 to 0.036 mM and Fe (LS) is varied from 0.004 to 0.036 mM for their optimization in Fenton oxidation. The optimum molar ratio of [H2O2]0 : [Fe2+]0 is observed to be 98.55 : 1 for PCM, 98.55 : 1 for AMX and 57.49 : 1 for DCF. However, the [H2O2]0 : [Fe (LS)]0 molar ratios are observed as 65.70 : 1 for PCM, 76.65 : 1 for AMX and 76.65 : 1 for DCF. Then, the Fenton and photo-Fenton oxidations are carried out at the optimal conditions for the initial drug concentration in the range of 0.066 – 0.331 mM for PCM, 0.027 – 0.137 mM for AMX and 0.031 – 0.157 mM for DCF. The degradation of PCM and AMX is 100 % but the degradation of the DCF is only 79.29 % with Fe2+ and 74.29 % with Fe (LS) in Fenton oxidation for 240 min of reaction time. However, in 120 minutes UV irradiation time, the photo – Fenton oxidation has demonstrated 100 % degradation of PCM and AMX for both the catalysts but DCF degradation is 98.57 % (with Fe2+) and 85.71 % (with Fe (LS)). It is also observed that the degradation and mineralization is more with Fe2+ than Fe (LS) for both PCM and DCF; but it is more with Fe (LS) than Fe2+ for AMX. In Fenton oxidation of mixture of drugs using Fe2+, the percent drug degradation is 68.55 (PCM), 70.77 (AMX), 62.56 (DCF) and percent COD removal is 64.80 in 240 min. Similarly, when Fe (LS) is used in Fenton oxidation, the percent drug degradation is 57.22 (PCM), 76.71 (AMX), 55.75 (DCF) and percent COD removal is 60.00 in 240 min. However, in photo-Fenton oxidation of mixture of drugs using Fe2+, the percent drug degradation is 70.01 (PCM), 75.70 (AMX), 64.79 (DCF) and percent COD removal is 74.40 in 120 min. On the other hand, using Fe (LS), the percent drug degradation is 59.98 (PCM), 77.87 (AMX), 59.29 (DCF) and percent COD removal is 58.40 in 120 min. The value of the pseudo secondorder rate constants for DCF > PCM > AMX when they are treated individually. The complete degradation of model drugs is observed with Fe2+ as well as Fe (LS) as catalysts in both the AOPs. Therefore, Fe (LS) may be effectively used as an alternate catalyst in Fenton’s reagent to degrade the selected drugs in water. The operating cost for the treatment of drugs in mixture is less by about 49 % with Fe2+ and 40 % with Fe (LS) in Fenton process and about 59 % with Fe2+ and 57 % with Fe (LS) in photo-Fenton process when compared to the costs for the treatment of the drugs individually. Furthermore, Fenton and photo-Fenton oxidation using Fe (LS) as catalyst appears to be a very promising technology for the oxidation of PCM, AMX and DCF in aqueous solutions.