Microbial utilization and transformation of humic acid-like substances extracted from a mixture of municipal refuse and sewage sludge disposed of in a landfill

“Capsule”: Humic acid-like structures do not play a role in long-term stabilization of landfill refuse. The purpose of the research was to establish whether humic acid-like substances (HA) related to municipal refuse disposed of in a landfill can resist microbial degradation and if they contribute, in that way, to long-term stabilization of landfill refuse. Using a mixture of 0.1 M Na 4P 2O 7 + 0.1 M NaOH, we extracted HA from municipal refuse mixed with sewage sludge and disposed of for up to 12 months, in a 40-m 3 model landfill. In laboratory experiments under aerobic conditions, up to 50% of HA was utilized as a supplementary source of nutrients by an assemblage of soil microorganisms in only 21 days. The microbial utilization was enhanced to over 80%, and up to 98%, respectively, if HA served as the sole source of carbon or nitrogen. Remaining HA which could be re-isolated from microbial cultures were lower in carbon (