Zerovalent iron and/or biochar amendments to stormwater BMPs to enhance roadway runoff treatment efficiency.
The transportation sector is often identified as a major source of nutrients (nitrogen and phosphorus) to receiving waters. Stormwater runoff from highways and roadways carries many pollutants such as sediment, nutrients, bacteria, oil, metals, chemicals, road salt, pet droppings and litter. These pollutants, if runoff control measures are not implemented, may have detrimental impact to surrounding water resources. This situation is further compounded with global climate change, which has made severe storms and flooding more commonplace. Stormwater discharges from roadways are considered point sources of pollution and thus subject to regulation under the National Pollution Discharge Elimination System (NPDES) permitting program. In order to minimize environmental impacts and comply with stringent regulations, existing stormwater management systems must remove nutrients such as nitrogen and phosphorus from stormwater runoff. Green stormwater management systems require substantial land area and may not work effectively during winter months. We will evaluate the application of biochar and zero-valent iron to existing stormwater BMPs. The hypothesis is that incorporation of these materials into soil or media used in bioretention cells, sand filters or bioswales will significantly enhance removal of nitrogen and phosphorus from stormwater runoff. Objectives: The goal of this project is to evaluate the feasibility of incorporating two treatment systems into stormwater BMPs: biochar, which can be included as an amendment to sand filters, bioswales, and the unsaturated zone of bioretention cells, and zero-valent iron (ZVI), which would be incorporated as a continuously submerged anoxic zone at the bottom of bioretention cells. As part of this one-year project, we will produce data that will allow for an assessment of the potential of these two amendments for significantly reducing nutrient loads from stormwater BMPs. This work will include a preliminary analysis of the costs and associated benefits of these two technologies.
Nutrient loading to surface waters is one of the leading causes of water quality impairment, and in order to meet the water quality standards in the state's nutrient impaired waterways the Total Maximum Daily Loads (TMDL) regulations require the systematic reduction of all point source discharges of nitrogen and phosphorus into these waterways. Sand filters, bioswales, bioretention cells are some of the BMPs employed for reducing pollutants in stormwater. These BMPs employ a filter medium, e.g., sand or soil, where pollutants are removed by filtration or biological and chemical processes. Typically, water flow through these media is unsaturated resulting in oxic conditions. While nutrients can be removed in sand filters, bioswales, and bioretention cells, removal rates are often low, particularly for nitrate. An innovative feature of the proposed technology involves use of biochar to remove nitrogen and phosphorus in the unsaturated portions of sand filters, bioswales, and bioretention systems, and ZVI iron to enhance the removal of nitrate in bioretention systems. Each of these amendments are known to remove nitrogen and phosphorus compounds. Integration of biochar and ZVI require small land area and will enhance the treatment efficiency of stormwater filtering systems.This technology emphasizing reuse of waste materials and has great potential to establish a new market sector.
Soni M Pradhanang
University of Rhode Island
June 12, 2015
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