Regeneration of 4-Nitrophenol-adsorbed activated carbon by fenton's reagent

Abstract

Activated carbon has been widely used to eliminate organic hazardous contaminants from wastewater by adsorption. The used activated carbon might be disposed without further regeneration or ex situ regenerated by thermal desorption for further reuse purpose. This study presents another altemative for in sifu regenerating activated carbon by using Fenton's reagent (Fe2+ and H2O2). Two major objectives of this study were investgated. The first one was to study the adsorption and desorption of 4-nitrophenol by GAC with different source material such as bituminous coal, palm shell, and coconut shell. Their particle size and properties were quite similar to one another (8-16 mesh size and 970 mg/g iodine number). The second was to study the efficiency of regenerating 4-NP-adsorbed GAC by Fenton's reagent with the optimal ratio of 4-NP: H2O2: Fe2+ under various initial pH conditions. The resulth showed that the adsorption of 4-NP by three different types of GAC in aqueous solutio was best described by the Freundlich isotherm equation (XM = KCe1/n). Bituminous coal had the highest adsorption capacity of 90.25 mg/g at 5mg/l equilibrium concentration, and the constants of K and 1/n derived from Freundlich isotherm equation were 45.70 and 0.42, respectively. The desorption rate of bituminous coal was also the desorption rate increased with increasing high pH and temperature. In addition, the percentages of 4-NP removed from GAC were 36%, 44%, and 57% at time of 120 min under the initial pH conditions of 3, 5, 7 respectively. Such a result implies that the higher the initial pH of Fenton's reagent, the higher the higher the regenerated capacity of 4-NP-contaminated GAC. Since the H2-O2 was applied at a relatively high dosage, Fenton-like reaction pathway (Fe3+ and H2O2) is believed to carry on the formation of Fe2+ for further Fenton's oxication of 4-NP. This was evidenced by a nearly complete consumption of H2O2 within the initial reaction period of 10 min. Another interesting finding was that the pH dropped down to around 2-3 even at a neutral pH of 7 after the first 10 min reaction. Furthermore, the results showed that the adsorption capacity of the Fenton-regenerated GAC was 57.8mg/g and the Freundlich isotherm constants of K and 1/n were 28-32 and 0.44, respectively. Comparing to the adsorption capacity of fresh GAC, which is 90.3 mg/g, the adsorption capacity of Bituminous-based GAC after Fenton's regeneration was reduced by 36 %.