Removal of humic substances by nano zero-valent iron supported on activated carbon and implementation of response surface methodology

Abstract

In this study, the activated carbon was used as a coating material to enhance the nano zero-valent iron (nZVI) and handle it as an adsorbent to remove humic acids (HA). Response surface methodology was applied to reveal the process variables on HA removal. The selected independent variables were adsorbent concentration, time, initial HA concentration and pH. According to the results, the four selected variables were found to be all effective in removal and time was the most effective parameter. While AC/nZVI concentration and time variables have positive effects on the removal, initial HA concentration and pH variables have negative effects. When the process is optimized, it is found that 30 min of contact time is required even for the lowest selected initial concentration (5 mg/L) to be removed completely. For the total removal of highest selected HA concentration, 100 mg/L AC/nZVI can be adequate with 78 min of contact time and at pH 3. The results obtained by isotherm and kinetic modelling showed that the removal of HA can be occurred via adsorption and also oxidation by nZVI. Maximum adsorption capacity was determined as 3.78 mg/g. Langmuir isotherm is found to be suitable for HA removal by AC/nZVI.