Media amendments facilitate nitrogen removal in biofilters treating real combined sewer overflows

Biofiltration treatment systems facilitate interactions between plants, soil media, and microbes to treat nitrogen-rich waters like stormwater and greywater. Novel nitrogen removal processes, such as anammox-assisted Simultaneous Nitrification, Anammox, and Denitrification (SNAD), can be effective in directly converting ammonia to nitrogen, but these have not been adequately researched within the biofilters. This research aims to study the role of biofilter media amendments that would influence the treatment of high-strength real combined sewer overflows (CSOs). For this study, conventional sand biofilters are amended with zeolite, scoria, engineered media, biochar and coconut coir, and a long-term (40-week) evaluation under varying operational conditions was conducted. It is found that bioretention systems with media exhibiting higher specific surface area, porosity, and cation exchange capacity had enhanced nitrogen removal. Media properties such as high porous surface area and ammonia buffering capacity further influenced the presence of nitrogen-transforming microbial communities. The study will be significant in providing engineered solutions and suggesting design modifications to treat uncontrolled CSOs.