Biochar role in improving pathogens removal capacity of stormwater biofilters

Abstract

Stormwater treatment systems such as biofilters have been used to treat and reuse stormwater in water-stressed urban areas. However, the pathogen removal capacity of these systems is low and unreliable. Pathogens are difficult to remove because of many reasons: conventional biofilter amendments have low removal capacity, and previously removed pathogens can grow in biofilters or be remobilized during intermittent infiltration of stormwater. Variable climate affects removal and increases uncertainty to biofilter performance. Adding biochar to biofilter media can help overcome some of these challenges. Biochar removes pathogens because of hydrophobic interaction and straining, limits remobilization of previously attached bacteria during intermittent flow by increasing residual moisture content, and provides conditions for native microbial communities to strive and out-compete pathogens for nutrients. However, all biochars are not made equal. Thus, bacterial removal capacity varies with biochar properties: removal increases with surface area and fixed carbon content and decreases with volatile matter and ash content. Additionally, the removal efficiency also depends on biochar size and how they are applied such as the presence of compost and compaction conditions. Collectively, these results indicate that biochar with specific properties and application methods can effectively increase the pathogen removal capacity of biofilters in variable climate conditions.