Removal of Phosphate and Nitrate from Impacted Waters via Slag-Driven Precipitation and Microbial Transformation

Excess nutrients in water such as nitrogen and phosphorus result in microbial growth and overfertilization of aquatic plants, increasing the rate of eutrophication in water bodies. This work investigated the application of an in situ nutrient removal technology utilizing the recycled materials basic oxygen furnace (BOF) slag and wood mulch. Thin layer column experiments and batch denitrification tests were conducted to determine the optimum combination of materials and conditions that allowed for phosphate removal by mineral precipitation using BOF slag as an alkaline substrate to stimulate phosphate removal by calcium phosphate precipitation and through binding with iron on the slag, and microbial denitrification using mulch as an organic substrate under the high-pH conditions necessary for calcium phosphate precipitation. The results of batch tests using cedar mulch and BOF slag leachates showed that denitrification was possible at initial pH values as high as 11. Thin-layer column experiments using BOF slag showed that unsaturated flow conditions and a high percentage of slag fines produced phosphate removal between 90% and 100%, whereas saturated flow conditions produced phosphate removal only between 20% and 60%.