MICROBIAL COMMUNITY EVOLUTION IN ORGANIC FRACTION OF MUNICIPAL SOLID WASTE BY ANAEROBIC DIGESTION

Backgrounds The organic matter originated from the household waste treatment facilities has potential agronomic properties as fertilizer and soil amendment. On the other hands, digestate products could contain pathogens or otherwise harmful microorganisms such as aerobic and anaerobic spore-forming bacteria. Objectives This work aimed to investigate in different process plants the bacterial population of organic fraction of municipal solid waste (OFMSW) at the beginning and at the end of the digestion process using both conventional culture approach and metagenomics by Next Generation Sequencing (NGS). To deeply characterize the population of spore-forming bacteria in digestates, aerobic/anaerobic spore-forming bacteria were isolated. Methods Six biowaste samples of OFMSW and the corresponding digestates were analyzed for total viable count, E. coli, coliforms, enterococci, aerobic/anaerobic spore forming bacteria, yeasts and moulds. Spore-forming bacteria were isolated and identified by 16S rRNA sequencing. For metagenomics analysis, the bacterial DNA was extracted using a commercial kit and 16S rRNA gene amplicons on V3-V4 region analyzed by Miseq (Illumina). Conclusions Output digestates showed a good hygienic quality and lower counts of bacteria than OFMSW samples. Most abundant spore-forming bacteria belonged to Bacillus aerophilus, B. amyloliquefaciens, B. cereus, B. licheniformis, B. safensis, B. subtilis and Clostridium sporogenes species. The bacterial community of OFMSWs was dominated by Firmicutes, Proteobacteria and Bacteriodetes, while the output digestates revealed higher presence of Synergistetes, Thermotogae and Euryarcheota. The study provides new insights into microbiota evolution of OFMSW digestate and potential spores that can contaminate soils and crops when digestate is used as fertilizer