Innovative Bio retention Strategies: Enhancing Dissolved Nitrogen Removal with Biochar-Amended High-Permeability Media for Urban Storm water Treatment

Nutrient pollution from stormwater leads inland and coastal water bodies to become eutrophic, which results in sea grass receding and harmful algal blooms (HAB) flourishing. These human-induced effects destabilize the ecosystems, and some HABs threaten human health directly. A possible solution to this problem is bioretention, defined as the storage and controlled discharge of storm water runoff in an ecologically constructed setting. But since it is largely reliant on particle settling as a nutrient removal process, it struggles with pollutants such as dissolved nitrogen. This is particularly inconvenient in India, where nitrogen is the limiting nutrient for HAB growth owing to the geological significance of phosphorus. Several conventional bio retention systems are limited by their low hydraulic loading rates (HLRs) and extensive footprint requirements, rendering them impractical for densely urbanized areas. To address these constraints, we performed a series of bench-scale, column, and pilot-scale experiments using a novel mixed media of high-permeability gravel amended with biochar. These tests were designed to characterize the hydraulic and physical properties of the amended media, assess its runoff treatment performance under a high HLR representative of extreme precipitation events, and quantify its mass removal efficiency for dissolved nitrogen species at a low HLR corresponding to median storm conditions. Collectively, these investigations aim to identify a more space-efficient solution capable of handling both extreme and typical storm water loads. To determine the air-to-water ratio in the soil and assess whether aerobic nitrification or anaerobic denitrification is promoted, HPG was amended with biochar at different volumetric ratios and tested for porosity and moisture retention at the bench scale. Porosity and moisture‐retention capacity increased in direct proportion to the percentage of biochar in the media. Saturated hydraulic conductivity was determined through column tests, and found to be slightly reduced.