Analytical determination of the microbial utilization and transformation of humic acids extracted from municipal refuse

Humic substances are usually the refractory part of natural organic matter, and in a landfill they can retain inorganic and organic micropollutants. This study has investigated analytically whether humic acids (HA) extracted by use of alkali from either fresh municipal refuse or from refuse disposed of in a landfill for up to 12 months can resist microbial degradation under aerobic conditions. When added as a supplementary nutrient source, up to 63.6% of HA was utilized and this percentage was enhanced to a mean value of 88.5% when different HA preparations were used as the sole source of carbon. In cultures of a soil microbial community containing the same preparations as sole sources of nitrogen, HA was usually completely utilized. The remaining HA re-isolated from some microbial cultures were highly depleted in carbon and, simultaneously, the nitrogen content was enhanced. The FTIR spectra were indicative of strong participation of aliphatic structural units in the refuse-related HA preparations. Because of the microbial activity, different carbonaceous substances were primarily removed from the HA structure, and an increase in nitrogenous molecular groups became apparent. The structural transformations brought about by soil microorganisms "in vitro" corresponded to those occurring naturally in HA obtained from refuse aged for 12 months in a landfill.