Biogeochemical cycles and microbial community dynamics in replicate woodchip bioreactors

Abstract

<p>Woodchip bioreactors have been extensively studied to understand factors that influence denitrification in order to achieve nutrient reduction goals from nonpoint sources of pollution. Further study will allow us to better understand the usable lifetime of these systems and the microbial community that drives denitrification, as well as the impact of hydraulic retention time (HRT) on these factors. We performed a battery of physical and chemical tests on woodchips excavated from replicate woodchip bioreactors following two years of continuous operation. Though we did not observe preferential woodchip consumption based on particle size, we observed spatial patterns of woodchip degradation that may be related to nitrate load. We also extracted DNA from woodchips sampled during two years for 16S rRNA amplicon sequencing and qPCR measurement of various denitrification genes. We observed patterns in the microbial community that may be related to the differences in substrate composition between HRTs. We did not observe statistical differences in qPCR results between HRTs, which may imply that detection of denitrifying genes may not be the most practical method of predicting system performance at the field or pilot scale. Replacing a portion of the bioreactor fill material may be an attractive way to minimize woodchip bioreactor management costs.</p>