CHARACTERIZATION OF THE DISSOLVED ORGANIC CARBON IN LANDFILL LEACHATE-POLLUTED GROUNDWATER

Abstract

Samples of dissolved organic carbon (DOC) were obtained from landfill leachate-polluted groundwater at Vejen Landfill, Denmark. The humic acids, fulvic acids and the hydrophilic fraction were isolated and purified. Based on DOC measurements, the fulvic acid fraction predominated, accounting for about 60% of the total amount of DOC with an apparent molecular weight of about 1800 Da. The hydrophilic fraction constituted about 30% of the total amount of DOC with an apparent molecular weight of about 2100 Da, and the humic acid fraction made up about 10% of the total amount of DOC with an apparent molecular weight of about 2600 Da. The elemental compositions of the humic acids, fulvic acids and the hydrophilic fraction were in the ranges typical for humic substances from other origins. The O/C ratios for humic acids, fulvic acids and the hydrophilic fraction were similar in the leachate-polluted groundwater. For humic acids the O/C ratios were slightly higher than reported in the literature, indicating a high content of carboxylic groups, phenolic groups or carbohydrates. Acid-base titration indicated that, in the fulvic acids and the hydrophilic fraction, carboxylic acids were the dominating functional group, representing about 6 meq g −1. The weakly acidic groups in fulvic acids and the hydrophilic fraction represented about 1 and 3 meq g −1, respectively. The total acidity in fulvic acids and the hydrophilic fraction accounted for 48–57% of the O/C ratio. In the humic acids, carboxylic groups made up about 3 meq g −1 and the weakly acidic groups made up about 1.5 meq g −1. The total acidity accounted for 29–32% of the O/C ratio. The characterization of DOC in leachate-polluted groundwater in terms of humic acids, fulvic acids and hydrophilic fraction showed that the hydrophilic fraction resembles, in many ways, humic and fulvic acids; thus, a distinction between the fractions may be related to the methods only and be of little practical value. The three fractions constituting the DOC content in a sample should all be considered when evaluating processes such as metal complexation and transport of metals and hydrophobic, organic contaminants. © 1998 Elsevier Science Ltd. All rights reserved