Microwave-assisted carbofuran degradation in the presence of GAC, ZVI and H2O2: Influence of reaction temperature and pH

Abstract

Carbofuran degradation in microwave (MW)-assisted granular activated carbon (GAC)/zero-valent iron (ZVI)/hydrogen peroxide (H2O2) system(s) was investigated under different reaction temperatures, i.e. 30 degrees C, 50 degrees C and 80 degrees C, and at varying pHs, i.e. 2, 4, 6, 8 and 10. Batch experiments were conducted using a modified-MW reactor (750W power and 2450 MHz frequency) at 100 mg L-1 carbofuran concentration. The lower MW-reaction temperatures, i.e. 30 degrees C and 50 degrees C, have produced poor carbofuran degradation efficiencies whereas complete carbofuran degradation (100%) was observed at 80 degrees C and pH 6 in all the systems, i.e. MW with GAC, ZVI and H2O2. Under the similar conditions, insignificant carbofuran removal/degradation (2-24%) was observed in the presence of GAC/ZVI/H2O2 without MW. On the other hand, the carbofuran degradation rate was accelerated under the alkaline pHs, i.e. pH 8 and 10 (at 80 degrees C), and 100% carbofuran degradation was observed within 10 min in all the MW-assisted systems. However, the complete carbofuran degradation was accomplished rapidly (5 min) in the MW-assisted GAC and ZVI systems under pH 10 and 80 degrees C. Carbofuran removal in the MW-assisted systems was modeled using the first-order reaction kinetics and a maximum removal rate constant of 4.17 min(-1) was obtained in the MW-assisted ZVI system. A maximum of 86% carbofuran mineralization was achieved in the MW-assisted GAC system via hydrolysis and the removal of carbamate group. The comparison of energy consumption in MW-assisted systems with other processes reveals that the MW-assisted process is highly efficient and cost-effective for carbofuran degradation and mineralization. (C) 2010 Elsevier B.V. All rights reserved.