Biochar increases nitrate removal capacity of woodchip biofilters during high-intensity rainfall. (15th November 2019)

• Record Type: Journal Article
• Authors: Berger, Alexander W.; Valenca, Renan; Miao, Yu; Ravi, Sujith; Mahendra, Shaily; Mohanty, Sanjay K.
• Is Part Of: Water research. Volume 165(2019)
• Publication Date: 2019-11-15
• Subjects: Denitrification -- Climate change impact -- Low impact development -- Eutrophication -- Extreme rainfall -- Bioinfiltration systems; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2019.115008
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Stormwater biofilters have been increasingly used to mitigate the impact of climate change on the export of contaminants including nitrate to water bodies. Yet, their performance is rarely tested under high-intensity rainfall events, which are predicted to occur more frequently under climate change scenarios. We examined the potential of biochar to improve the resilience of woodchip biofilters under simulated high-intensity rainfall events and linked denitrification to biochar-mediated changes in hydrological (physical), chemical, and biological properties of woodchip biofilters. Results showed that nitrate removal capacity of woodchip biofilters decreased with increases in rainfall intensity or duration and decreases in antecedent drying time. However, adding biochar to woodchips significantly decreased the exhaustion rate of woodchips, only when the hydraulic residence time (HRT) was less than 5 h. At longer HRT (>5 h), the benefits of biochar became less apparent. We attributed the improved denitrification during high nitrate loading to biochar's ability to decrease dissolved oxygen in pore water and increase water holding capacity and retention of dissolved organic carbon and nitrate—all of which could increase nitrate utilization. Biochar increased the net microbial biomass but did not affect the relative abundance of denitrifying genes, which indicates that a shift in microbial biomass could not fully explain the observed increase in nitrate removal in biochar-augmented woodchip biofilters. Overall, the results showed that biochar could increase the resiliency of woodchip biofilters for denitrification in high-intensity rainfall events, a worst-case scenario, thereby mitigating the water quality degradation during climate change. Graphical abstract: Image 1 Highlights: Nitrate removal capacity of biochar-augmented woodchip biofilters was tested. Biochar can increase biofilter resilience for nitrate removal. Benefits of biochar were more apparent when infiltration rate was high. Biochar helped denitrification by altering pore water retention and chemistry. Biochar increased biomass without changing the abundance of denitrifying bacteria.