Characteristics of solids produced from coal mine drainage and their suitability for phosphorus control in dairy manure management

One strategy to limiting eutrophication in waterways is to reduce the concentration of water-extractable P (WEP) in land-applied manure. In this study, we investigated the feasibility of using mine drainage residuals (MDR), waste solids produced in large quantities from coal mine drainage treatment, to reduce WEP in dairy manure. Twenty MDRs from treatment systems in Pennsylvania were collected and analyzed to determine concentrations of pollutants that may limit land application. Laboratory dose-response tests were conducted using the selected MDRs to determine the effectiveness and kinetics of WEP reduction, and three field-scale MDR application tests were conducted to demonstrate the process of using MDR to decrease manure WEP. The MDR–manure mixtures investigated in this study do not exceed biosolid land application concentration limits set by the USEPA. Amendment rates of 5–10 g MDR L⁻¹ of manure provided significant reductions in WEP. Iron-rich MDR, produced from passive and oxidant treatment of mine drainage, required 1–4 d to reduce WEP to an equilibrium concentration, while Ca-rich materials, produced from lime treatment, required 4–7 d. Three field studies at operating dairy farms confirmed the reduction in WEP when manure was amended with MDR. Unit costs calculated for a 1,900-m³ manure tank treated with 4.4 g L⁻¹ MDR were US$2.16 per 1,000 L of manure and $30 kg⁻¹ WEP removed. These findings indicate that the WEP of dairy manure is not a fixed chemical parameter and can be modified with amendments such as MDR.