Assessment of diversity and composition of bacterial community in sludge treatment reed bed systems

Due to their low emission of odours and lack of the need to apply additional chemical agents, sludge treatment reed beds (STRBs) constitute an economically feasible and eco-friendly approach to sewage sludge management. Correctly designed and operated STRBs ensure effective reduction of the dry matter content coupled with the mineralisation of organic compounds. Successful operation of STRBs relies on complex interactions between the plants and microorganisms responsible for the decomposition of organic matter and nutrient cycling. While the biocenoses of wetland systems dedicated to wastewater treatment have been intensively investigated, in the case of sludge treatment applications, there is a deficit of available microbial data. The aim of this study was to explore the diversity and spatial distribution of the bacteria in three distinct STRBs which differ in maturation and feeding patterns. Analyses of the dry mass and organic matter content showed the general trend of the sludge stabilisation processes advancing through the bed depth, with the best performance in the Matured Continuous Feed (MCF) bed being noted. Samples from the MCF bed showed the statistically greatest biodiversity in relation to the other beds. Moreover, increased biodiversity of microorganisms was observed on the surface of the STRBs and the bottom zone of the MCF equipped with a passive aeration system, which proves the application of such solutions in order to enhance the performance of the process. The results of 16S rRNA gene sequencing revealed that Bacteroidetes, Proteobacteria and Firmicutes contributed approximately 80% of all identified sequences read. Network analysis revealed dominant role of Bacteroidetes in the formation of interspecies co-existence patterns. Nitrospira was the most abundant organism responsible for nitrogen metabolism in the STRBs.