BioHaven™ Wild Floating Islands: Floating Habitat

Products and Technologies // 173

Newspaper Nitrate Treatment

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Bioretention is a method for improving the quality of stormwater runoff before it reaches waterways and bodies. Stormwater, having collected surface pollutants from impervious surfaces such as parking lots and roads, is directed into a vegetated bioretention facility. The contaminated stormwater flows through a vegetated layer of engineered soil before it infiltrates or collects in a slotted under-drain, and finally discharges into a nearby stream or water body. The soil and mulch substrate filters and absorbs sediment and heavy metals. The vegetation acts as a filter for sediments and also maintains an active microbial population that can break down chemicals and uptake some excess nutrients.

Some pollutants are more difficult to filter with bioretention. Nitrate, one of the primary nutrient pollutants that contribute to the degradation of water bodies, will travel unabated through a soil matrix. Allen P. Davis’s research at the University of Maryland investigates new technological modifications to bioretention to capture and treat nitrate runoff. His work explores microbial denitrification, one of the few natural pathways for treating nitrates. Denitrification organisms convert the nitrate in the water into a harmless nitrogen gas. However, effective denitrification requires an anaerobic (without oxygen) condition with access to a source of carbon.

Interestingly, shredded newspaper, a synthetic waste material, has proven itself as an effective source of carbon for denitrification. In laboratory research Allen Davis found that it performed best in comparison to a number of other organic materials, including straw and sawdust. In order to test its capacity in the field, Davis and his team modified a standard bioretention system. Shredded newspaper is mixed with coarse sand to create a new layer under the soil media. This layer is kept continuously saturated with water by keeping the underdrain elbowed upward, thus maintaining an anaerobic condition. The field test uses a ratio of 17g (0.6oz) of newspaper per 1kg (2.2lbs) of sand. Future measurements and monitoring will determine the effectiveness of this modification in improving the nitrate levels of the adjacent parking lot stormwater discharges.

Research: Allen P. Davis, PhD, Civil and Env. Eng. Director, Maryland Water Resources, University of Maryland

174 Digestive Bioretention MediuM //

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