Degradation of sulfamethoxazole by a new modified Fenton-like process using Cu(II)-nitrilotriacetic acid complex as catalyst at neutral pH in aqueous medium

Abstract

Fenton process is among the most effective advanced oxidation process in wastewater treatment, but the necessity to work at acidic pH, in order to avoid metal precipitation, limits its large-scale application. In this work, a new Fenton-like process using copper(II)-nitrilotriacetic acid (CuII -NTA) complex as catalyst, was used for the activation of hydrogen peroxide (H2O2) to degrade sulfamethoxazole (SMX) in aqueous medium under neutral pH conditions. The results showed that the CuII -NTA/H2O2 process was not efficient in the degradation of SMX. The reason being that the generation of HO radicals is still limited by the extremely slow CuII -NTA/CuI -NTA redox cycle. Therefore, the combination of hydroxylamine (HA) accelerate the CuI recovery to induce the continuous production of HO radicals by the decomposition of H2O2. It was evident that the steady-state CuI concentration in CuII-NTA/HA/H2O2 process was much elevated than the CuII -NTA/H2O2 process due to the quick regeneration of CuI -NTA complex by HA. Kinetic profiles were evaluated under a wide range of experimental conditions in order to assess the effects of the initial concentrations, working pH, Cu(II):NTA molar ratio and reaction temperature. The results showed that the degradation rates were enhanced with the increase of H2O2 and CuII -NTA concentration during SMX oxidation. SMX was fully (83.64 %) degraded for an initial SMX concentration of 0.01 mM and an optimal Cu(II):NTA molar ratio of 1:1. Solution pH influenced SMX degradation and the highest degradation rate constant was achieved at pH 7.2. The radical scavenging experiments indicates that hydroxyl radical (HO) has major role for SMX degradation. The presence of metal ions such as MgII, CaII and MnII had no impacts or little inhibitory effect on the CuII -NTA complex catalyzed Fenton-like reaction, however, a complete degradation of SMX was achieved in the presence of FeIII ions. Also, the effects of various inorganic anions such as Cl−, SO42−, NO3− and HCO3− on the oxidation efficiency of SMX were studied. The efficiency of mineralization of aqueous solution of SMX was evaluated by measuring total organic carbon (TOC). These results demonstrate that CuII -NTA catalyzed Fenton-like oxidation may be an efficient approach for remediation of wastewater containing antibiotics.