Browsing by Subject "Hydraulic Residence Time"

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    Metagenomic Survey Of Denitrifying Woodchip Bioreactors: Carbon And Nitrogen Cycling Under Varying Temperature And Flow Regimes
    (2020-02) Pauleon, Aaron
    The denitrifying woodchip bioreactor (WCBR) is a promising edge of field technology used as a biofilter of nitrate pollutants. These reactors have diminishing performance under low temperature and high flow conditions. In this study the taxonomic, nitrogen metabolism, and glycoside hydrolase profiles of meso-scale biochar-amended denitrifying woodchip bioreactors (WCBRs) are assessed and compared through shotgun metagenomic sequencing with reads aligned to protein coding sequences. Four treatment conditions: 14.5oC+12Hr hydraulic residence time (HRT), 14.5oC+4Hr, 6oC+12Hr, and 6oC+4Hr were analyzed in triplicate for the effects of temperature and flow rate (HRT) on the removal of nitrate from synthetic agricultural runoff water. The experimental design offered greater flow and temperature controls than field scale reactors while offering greater size and realism than most lab-scale reactors. Temperature and flow conditions had significant impacts in every category of analysis. The warm (14.5oC) and slow (12Hr HRT) WCBRs removed the greatest percentage of nitrate (75% of 30mg/L influent), were the most microbially abundant, and the most diverse. These reactors also had greatest average metagenomic potential for plant matter degrading enzymes. The taxonomic and functional analyses indicate bacterial dominance among extracted DNA, although ascomycete fungi were present across all treatments (0.7%-5.2%). By estimates, most bacteria across WCBRs were atypical denitrifiers (>50%) while a minority were typical denitrifiers (<12%). Large portions (78%) of the core nitrogen metabolism were attributed to the creation or assimilation of ammonia with nitrogen fixation appearing unexpectedly enriched (26%). Comparisons to bacteria-dominant midwestern corn soil reveal relatively high fungi representation, low archaea representation, and lower microbial diversity in the WCBR samples. The overall metagenomic commitments to nitrogen cycling and glycoside hydrolases were higher in the WCBRs befitting a concentrated nitrate and polysaccharide environment. The findings of this study highlight the otherwise unreported taxonomic and metabolic patterns of WCBRs, revealing topics for future study and potential avenues for further engineering to inform and enhance the use of denitrifying woodchip bioreactors moving forward.