Sulfadiazine degradation using hybrid AOP of heterogeneous Fenton/persulfate system coupled with hydrodynamic cavitation

Sulfadiazine (SDZ) is a prominent antibiotic pollutant that appears in wastewater discharges from domestic, agricultural and pharmaceutical sectors. In this paper, we have reported studies in SDZ degradation using a novel hybrid AOP that coupled hydrodynamic cavitation with heterogeneous Fenton and persulfate. Two solid Fenton catalysts (alpha-Fe2O3 and Fe3O4) in the form of nanoparticles were synthesized. The composition of reaction mixture was optimized using statistical techniques. Effect of four operating parameters, viz. (1) SDZ initial concentration, (2) inlet pressure of cavitating flow, (3) pH and (4) type of heterogeneous Fenton catalyst (at optimum loading), on SDZ degradation was studied. A kinetic model for SDZ degradation was proposed based on homogeneous Fenton/persulfate system, and experimental degradation profiles were analyzed vis-a-vis simulated profiles. The highest degradation of SDZ (81%) was obtained for SDZ initial concn.= 20 ppm, pH = 4, inlet pressure = 10 atm, Na2S2O8 = 348.5 mg/L, H2O2= 0.95 mL/L and alpha-Fe2O3 catalyst (181.8 mg/L). Kinetic model analysis showed best match between experimental and simulated profiles for [Fe2+]/[H2O2] initial ratio = 4. This indicated efficient catalytic activity of alpha-Fe2O3 nanoparticles - close to that of homogeneous catalyst. This is a consequence of high rate of mass transfer at surface of alpha-Fe2O3 particles due to intense turbulence and shear generated in cavitating flow in hydrodynamic cavitation reactor.