Recovery and Reuse of Phosphorus in Agricultural Waste Streams by Mine Drainage Treatment Residuals.

Excess phosphorus (P) releases to the environment have resulted in significant impairment of aquatic ecosystems such as the Chesapeake Bay, the Gulf of Mexico, and other water bodies world-wide.  Meanwhile, depletion of high-grade P-bearing deposits continues and the possibility of future shortages of fertilizer P has been suggested.  Some strategies for recycling of P have emerged, such as the production of struvite in municipal sewage treatment plants, but these strategies are not applicable to many other types of waste streams.  It is well-known that Fe and Al oxyhydroxides have a strong affinity for phosphates in water, but application of reagent grade commodities such as ferric sulfate and aluminum sulfate to wastewater treatment is expensive and uneconomic in many cases.  The precipitated Fe/Al oxyhydroxide residuals formed by the treatment of acid mine drainage are a low-cost source of the same materials used to remove P from water and present an attractive alternative to reagent-based commodity chemicals for the removal of P from agricultural waste streams.  The sorbed P can be stripped from these materials using sodium hydroxide solution and precipitated by adding Ca salts to form hydroxyapatite precipitates that can be recycled into fertilizer.  The mine drainage residuals can also be regenerated and reused for a number of additional treatment cycles.   The results of several years of research on P sorption capacity, sorption kinetics, and fixed bed treatment of waste streams will be presented to demonstrate the feasibility of using mine drainage residuals to recover and recycle P.  Application of this novel technology will simultaneously help to decrease mine drainage treatment costs, prevent degradation of aquatic ecosystems, and recycle valuable nutrients.