# Evaluation of Nitrogen and Phosphorus Removal
## 1 Introduction  
The discharge of nitrogen (N) and phosphorus (P) from agricultural production areas due to storm-driven runoff can degrade water quality and lead to eutrophication, cause fish kills, and decrease the esthetic value of water bodies [1]. One specific harmful production area wastewater originates from silage storage bunkers on confinement dairy farms. To store feed for livestock throughout the year, plant material, typically chopped corn or hay, is packed in horizontal concrete floored and walled bunkers and covered with polyethylene taps. This process, known as ensiling, promotes anaerobic fermentation of soluble carbohydrates by producing organic acids, which preserve proteins in the feed and inhibit bacterial growth that can cause spoilage [2]. Silage leachate is a byproduct from the ensiling process, which is extremely high in nutrient content, consisting of average concentrations of over 3500 mg L\({}^{-1}\) for total N (TN), 800 mg L\({}^{-1}\) for total P (TP), 5-day biochemical oxygen demand (BOD) of over 60,000 mg L\({}^{-1}\), and a pH between 3.5 and 5 [3]. Controlling the moisture content of ensiled forageby optimizing timing for harvesting plant material is recommended to limit concentrated leachate production [4], but appropriate harvest timing is often difficult to achieve in the Northeastern United States, due to unfavorable drying conditions and a limited harvest period. During storm events, exposed silage particles and leachate on impervious storage bunker surfaces mix with precipitation and are transported as runoff [4]. While dilution with rainwater yields lower nutrient concentrations in silage bunker runoff more than the concentrated leachate, nutrients are still a major concern if released into surface waters [3; 4; 5; 6]. Runoff concentrations from silage bunkers generally depend on storm size and intensity, concentration of undiluted silage leachate, and seasonality [4]. Best management practices to reduce leachate losses and subsequent environmental degradation are recommended or required on many dairy farms [3]. Management options include intercepting silage leachate so that it can be disposed of properly (e.g., stored, aerated, and diluted to be applied as fertilizer to hay lands or other feed crops during the growing season) [7]. There are minimal data available describing silage leachate composition changes after storage, and more research is needed in this area [3]. For storm-driven silage runoff, vegetative treatment areas (VTAs) are often recommended. VTAs are vegetated systems located downslope of a pollution source designed to treat runoff and provide a buffer zone to the surrounding environment [8]. In a New York study of three VTAs receiving silage bunker runoff, [PERSON] [6] found significant ammonium-N (NH4\({}^{+}\)-N) mass removal at all sites and one VTA had 40% soluble reactive P (SRP) mass removal. Incoming nitrate-N (NO3\({}^{-}\)-N) concentrations were low, and some sites experienced a net export, presumably due to nitrification processes within the VTA. Whereas VTAs are generally an economically viable and low maintenance option for farms, several concerns still exist. These issues include surface runoff remaining untreated [9], vegetative burning due to high acidity in the runoff [10], neglected operation and maintenance demands [6], and subsurface leaching that can lead to groundwater contamination [9]. Accordingly, there is a need to explore alternative remediation practices for silage bunker leachate and storm-driven runoff. In this research study two technologies for managing silage bunker runoff were evaluated. First, a moving-bed biofilm bioreactor (MBBR) is considered, which is a tank-based wastewater treatment technology that incorporates engineered carriers to provide surface area for biofilm growth and which are suspended through aeration [11]. The goal of this technology is to increase the removal of organic matter and nutrients.