Simultaneous degradation of pharmaceuticals in fixed and fluidized bed reactors using iron-modified diatomite as heterogeneous Fenton catalyst

Abstract

The aim of this study was to evaluate the use of pelletized iron-modified diatomite as heterogeneous Fenton catalyst for the removal of carbamazepine, clindamycin, gemfibrozil, ketoprofen, florfenicol, and sulfamethazine, and to compare its performance in fixed and fluidized bed reactor configurations. The prepared catalyst pellets were characterized by XRD, SEM, ED-XRF, BET, and compression strength analysis. Applying a Taguchi L9 design of experiments, the oxidation of a mixture of six common pharmaceuticals was studied under different operating conditions (initial pH, particle size, space time, and H2O2 initial concentration) for both reactor configurations. Under the best operating conditions, overall pharmaceutical degradations by the Fenton reaction were 32.6 % and 31.8 % in the fluidized and fixed bed reactors, respectively. Among the analyzed pharmaceuticals, clindamycin was the one presenting the highest removal (88.8 % fixed, 89.7 % fluidized), followed by gemfibrozil (70.4 % fixed, 100 % fluidized), ketoprofen (36.2 % fixed, 35.1 % fluidized), carbamazepine (19.0 % fixed, 21.1 % fluidized), sulfamethazine (18.1 % fixed, 21.1 % fluidized), and florfenicol (4.6 % fixed, 7.0 % fluidized). The initial pH was the most sensitive variable, presenting the best performance at pH 3. After 10 h of operation, the catalyst suffered a 27.9 % decrease in its activity when operated in the fixed bed reactor, whereas in the fluidized bed reactor its deactivation was 52.1 %. The catalyst was also evaluated in a real wastewater matrix, showing basically the same activity as in synthetic wastewater; TOC overall removal was 31 % for the fixed bed and 36 % for the fluidized bed reactor. Finally, the electrical energy per order (EEO) consumed in both reactors was calculated to compare their energy efficiency; the fixed bed configuration presented the lowest value (1.01 Wh/m3/order), suggesting that this is a more energy-efficient configuration for commercial wastewater treatment applications.