Characteristics of the adsorption of dissolved organic matter by charcoals carbonized at different temperatures

We investigated the adsorptive volume and rate, adsorption isotherm, and the pH dependence of charcoals obtained from carbonizing cedar (Cryptomeria japonica D. Don) wood chips at various temperatures; these charcoals were used to remove dissolved organic matter (DOM) that was eluted from rice-straw. In order to confirm the adsorption characteristics, three experiments were carried out in the laboratory. The adsorption characteristics were estimated by determining the total organic carbon (TOC) concentration, adsorption isotherm and the pH in solutions. Results showed that the trend of DOM adsorption effect by charcoals was categorized into two groups: group-1 (charcoals carbonized at less than 750 degrees C) and group-2 (charcoals carbonized at more than 850 degrees C). Group-2 adsorbed a greater amount of DOM and at a more rapid rate than group-1. The adsorption isotherm for group-2 followed the Freundlich model. In particular, the Freundlich constants, K and 1/N, for the charcoal carbonized at 1,050 degrees C indicated that this charcoal had higher adsorption volume and adsorption intensity for DOM than other charcoals. Furthermore, this charcoal adsorbed TOC irrespective of the initial pH value in sample water. This indicated that charcoals carbonized at 1,050 degrees C could change the pH value of the water contaminated with acid to neutral.