Convective transport of dissolved gases determines the fate of the greenhouse gases produced in reactive drainage filters

Nitrogen Removal in Woodchip‐based Biofilters of Variable Designs Treating Agricultural Drainage Discharges

“…Retention of organic N accounted for 4 to 7% of the annual net TN removal. Greenhouse gas emissions in the CWs (Bruun et al, 2017) demonstrated that the amount of N 2 O‐N dissolved in the outflow ranged from 28 to 101 g N 2 O‐N m −2 yr −1 , supporting the finding that the major removal pathway of NO 3 was denitrification, with N 2 O production accounting for 2 to 5.5% of the N removal by the denitrification process.…”

“…The volume (m 3 ) of the distribution layer ( V 1 ) and the woodchips–seashell filter media ( V 2 ) was obtained from the measured depth and cross‐sectional area of each layer in the filter beds. The water‐filled porosity (m 3 m −3 ) for the distribution layer (θ 1 ) and the woodchips–seashell filter media (θ 1 ) was obtained for each material from the dry bulk density ρ b (kg m −3 ), the density of water (ρ w ), and the gravimetrical water content w dm (kg kg −1 ) measured from laboratory columns by Bruun et al (2017) according to the method described by Kjaergaard et al (2012). Dry bulk density (ρ b ) in the columns was determined from sample volume and sample dry weight after oven drying at 105°C (Table 1): …”

“…Statistical analyses and all other calculations were performed using th‐e SAS Software Package (SAS Institute, 2011). Calculation of N mass balances only included the solute N species NH 4 –N, NO 2 –N, NO 3 –N, organic N, and TN, whereas a mass balance for nitrous oxide (N 2 O) was published by Bruun et al (2017). Multiple linear statistical models were developed for each CW using the SAS STAT GLM and the SAS STAT MODEL procedures.…”

“…Although the effect of temperature on bioreactor performance is compelling (Christianson et al, 2012b; Addy et al, 2016; Hoover et al, 2016), there is a need for improving our understanding of the combined effects of temperature and HRT variations on the seasonal and annual variations in N reduction efficiency so that we can design and operate these systems better. In addition, HLR and hydraulic design (i.e., flow direction) may influence the solute transport and hydraulic efficiency of woodchip‐based biofilters (Bruun et al, 2016b; Pugliese et al, 2017), as well as the extent of greenhouse gas emissions (Bruun et al, 2017).…”

Performance of a field-scale biological permeable reactive barrier for in-situ remediation of nitrate-contaminated groundwater

“…CH4 emission fluxes were also comparable to those measured in wetlands (4-49 mg/(m 2 ꞏh)) (Whalen, 2005;Audet et al, 2013), constructed wetlands (1-47 mg/(m 2 ꞏh)) (Søvik et al, 2006) and undisturbed natural soil (1-20 mg/(m 2 ꞏh)) (Yang et al, 2013), and much lower than those measured in landfills (96 g/(m 2 ꞏh)) (Bruun et al, 2017 and references therein). Finally, N2O flux values measured for the PRB fell in the lower end of values reported in literature in riparian soils (0.02-31 mg/(m 2 ꞏh)) (Audet et al, 2013;Audet et al, 2014;Hinshaw and Dahlgren, 2016;Jurado et al, 2017 and references therein), European agricultural and forested ecosystems (0.4-137 mg/(m 2 ꞏh)) (Machfert et al, 2002) and constructed wetlands (<0.01-58 mg/(m 2 ꞏh)) (Søvik et al, 2006;Bruun et al, 2017). These values of N2O have been reported to not represent a significant contribution to the atmosphere compared to the direct emissions from agricultural fields (Hinshaw and Dahlgren, 2016;Jurado et al, 2017).…”