Spatial and temporal changes in microbial community composition in a full-scale woodchip bioreactor for treating mine water

Abstract: Incomplete detonation of nitrogen-based explosives can lead to abundant levels of nitrate in mine groundwater. The possibility of reducing nitrogen levels from the wastewater through denitrification, anammox and DNRA has been investigated using a full-scale bioreactor. The bioreactor is situated subsurface and is filled with pine woodchips. Groundwater is pumped to the bioreactor and subsequently discharged to a drainage ditch. In this thesis the distribution of the microbial community was determined using quantification of functional genes representing a specific functional community. The 16S rRNA gene was used as proxy for the total bacterial community, nirS and nirK for nitrite reduction, nosZI and nosZII genes for nitrous oxide reduction, nrfA for DNRA, and hdh for anammox reaction. Denitrification appeared as the main nitrogen-reducing process in the bioreactor due to more abundant levels of functional genes. The abundance of nitrous oxide reductase was higher than nitrite oxide, indicating good nitrouse oxide reduction. Anammox could not be detected and DNRA was suggested in the end of the bioreactor due to a decrease in nitrate concentration. The distribution of abundances was not affected by the depth or the time which samples were collected. However, abundances collected at different lengths of the bioreactor showed significant differences for 16S rRNA and the functional genes nirS, nosZI and nrfA. This suggests changing environmental conditions along the bioreactor length. Creating an assay for quantification of sulphate reducing bacteria was also investigated. This was not achieved and the size and distribution of the sulphate reducing community remains to investigate. The bioreactor in the present study can reduce nitrogen from mining water but further analysis are needed in order to understand long-term temporal changes.