Underground degradation of lignite coal spoil material by a mixed microbial community under acid mine drainage conditions

In a field study, biogeochemical processes in a large lignite coal spoil area with moderate AMD generation were investigated. Underneath this area, large amounts of groundwater are impacted by degradation and transformation processes of coal remainders in the former open pit mining area. An investigation was performed to find out the sources for the ground and surface water contaminations of larger areas. Samples were taken from different places and different depths of the coal spoil area and were investigated for different metabolic groups of microorganisms. As a result, fungi are able to degrade humic matter in coal spoil heaps in a first step to oligomers. Other microorganisms do a further degradation of first intermediates in a commensalic community. Streptomycetes do a cleavage of lignocelluloses, strepto- and other actinomycetes also degrade cellobiose and xylose related parts of the humic coal spoil matter. The different members of the microbial community exist in different "floors" of the spoil area: fungi and most Actinomycetes prefer the oxic zone, whereas degraders of aromatic and heterocyclic compounds can also exist in the capillary and ground water zones; here more frequently Arthrobacter, Pseudomonas, Rhodococcus and Mycobacterium strains were detected. Ferric iron formed in biooxidation of pyrite seems to play an important role as a catalyst for oxic as well as anaerobic degradation of complex organic matter in the underground. A complex linkage between microbial Fe-, S-, C- and N-cycles was figured out on this site that induces a high and long-term impact on ground water contamination in this area.