Vol. 12, No.1, pp.15-21 (2018)
Nonthermal Plasma Combined with Packed Bed to Purify Methanol Wastewater
M. Chen1, J. Liu1, N. Sheng2, X. Wang1, and Z. Wang1
1School of Chemical Engineering, Anhui University of Science and Technology, China
2School of Earth and Environment, Anhui University of Science and Technology, China
Abstract
A synergistic method, which was non-thermal plasma (NTP) combined with packed bed adsorption effect, has been adopted to purify high concentration methanol wastewater in this research. The results showed that purification effect of the combination process is better than the single process. In the initial reaction stage of the combination process, the rapid decrease of COD dominated by adsorption process of packed bed. With the prolongation of the reaction time, the continuous decline of COD depended on oxidation process of NTP. The methanol, both in liquid phase and adsorbed in the packed bed, oxidized by active groups which are generated by NTP. This phenomenon could prolong the service life of packed bed, increase specific surface area and enhance the adaptability to the variation of water quality. The maximum degradation rate of COD could reach more than 90% in this experiment. According to the data, the reaction kinetics analysis showed that adsorption process of packed bed followed the pseudo-second order adsorption kinetic equation. In the initial stage of NTP oxidation process, COD degradation process followed the first order kinetic model. However, with the prolongation of the discharge time and the decrease of methanol concentration, the reaction order increased. In the synergistic system, the adsorption process of packed bed would be influenced by oxidation process of NTP, and vice versa. The concentration ratio of contaminant and hydroxyl radical (·OH) in liquid phase would change constantly. The early stage of synergistic degradation process followed the first order kinetic model. However, with the decline of the concentration ratio, the degradation process followed the second order reaction kinetic model or multi-order reaction kinetic model.
Keywords - Non-thermal plasma, packed bed, high concentrate methanol wastewater, synergistic effect, reaction kinetics