Summary:

One of the most frequently applied methods of mixed municipal solid waste biological treatment in mechanical-biological treatment installations (MBT) is their disposal in aerobic biostabilization process. The process comprises an intensive phase and maturation phase. The intensive phase relies on waste heating in result of organic matter breakdown conducted by microorganisms settling the wastes. Microorganisms living in wastes have optimal conditions for development, i.e. a considerable space volume, optimal material fragmentation and organic matter availability. The aim of the aerobic biostabilization process is stabilizing and hygienization of wastes, so that they become a valuable raw material for other recovery processes (e.g. RDF production) or their disposal is safe for the environment and do not pose any epidemiological hazard for people employed in waste treatment plants.
Analyses presented in the paper aimed to determine the number and species composition of vegetative and endospore bacteria, mold fungi, actinomycetes and pathogenic microorganisms, i.e. Staphylococcus spp., E. coli, Salmonella spp., Shigella spp., E. faecalis, C. perfringens, settling municipal wastes prior to and after aerobic stabilization process. The aerobic stabilization process (intensive phase) was conducted in a laboratory BKB 100 bioreactor using the wastes, characterized by low share of biodegradable wastes (<40 %), obtained from MBT installation during the period from December 2015 to February 2016. The temperature, loss on ignition, waste density, ash content, moisture and pH were monitored during the analyses. The research was conducted on the undersize and oversize fraction separated from mixed municipal wastes on MBT installation.
The maximal temperature reached in the bioreactor, between c.a. 40 and 55oC, persisting for many hours is insufficient for efficient elimination of the determined microorganism groups. Paradoxically, the conditions created in the bioreactor proved convenient for the microorganisms, therefore an increase in their number was observed. Only in one case, when the share of biodegradable wastes exceed the value of 45 % it was observed, that the aerobic stabilization process of these wastes was going correctly and caused among others a decrease in loss on ignition.