Recovery of Phosphorus from Agricultural Effluents with Mine Drainage Ochres.

Excessive phosphorus (P) inputs to the environment have resulted in the formation of harmful algal blooms and anoxic dead zones, leading to the degradation of sensitive water bodies all across the world.  Meanwhile, depletion of high grade P deposits has raised the question of the sustainability of the P consumption cycle as it currently exists.  The development of new technology to recycle P is urgently needed to address these issues.  Currently available technology consists of treatment with metal salts which adsorb and precipitate P into a waste sludge.  This sludge can, at best, be utilized as a soil amendment, but is often landfilled, leading to the loss of the contained P.  In addition, treatment costs are high due to the cost of the metal salt reagent and of the resulting sludge disposal.  Promising results have been achieved using fixed bed sorption of P using low cost iron oxides, or ochres, obtained from the treatment of mine drainage.  Following the sorption step, the ochre can be regenerated and the P recovered through treatment at elevated pH with sodium hydroxide, after which the P can be precipitated into a potentially marketable fertilizer product.  The process has been demonstrated at the bench scale in the laboratory and at a larger scale in the field.  We are currently operating a 100,000 gallon per day treatment system processing aquaculture effluents to evaluate capital and operating costs.  Results from the initial six months of operation of this system show 73% recovery of P before regeneration, and illustrate the potential of this new technology for economic recovery and recycle of P from agricultural wastewaters.