Microbial Activity in Sanitary Landfills–A Possible Source of the Humic Substances in Groundwater?

Humic substances account for the main part of the dissolved organic carbon in groundwater. Since groundwater aquifers located near to sanitary landfills usually contain higher concentrations of dissolved organic carbon, we made experiments in the laboratory to determine whether humic substances can be formed from simple non-humified organic substances by a complex micro-flora of municipal refuse. In liquid cultures incubated for two months humic substances were produced, especially when casein or starch was added. The highest amounts of humic acid-like substances were yielded from cultures inoculated with the indigenous microflora from a rotted (aerobic) landfill. Minor yields were obtained when the inoculum originated from a compacted (anaerobic) landfill or from a five years old landfill containing refuse and sewage sludge. Spectral characteristics indicated some similarities but also differences in the UV and visible regions between the newly formed humic acids and a humic acid from groundwater.