Phosphorus speciation in municipal biosolids for efficient phosphorous recovery

Phosphorus, an essential element for crop production, is obtained from mines concentrated in a handful of countries. Researchers estimate that 20 to 30% of mined phosphorus is wasted with sewage outfalls. This creates an opportunity to recycle the phosphorus from biosolids produced at wastewater treatment plants. In order to efficiently recycle phosphorus, we need to understand how different wastewater treatment processes affect the phosphorus speciation in biosolids. This study presents the speciation data obtained from samples collected at five wastewater treatment plants in central Texas. Primary, secondary, thickened and dewatered biosolids were obtained from these treatment plants and analyzed for organic, poly- and orthophosphates in the liquid and solid phases. The results indicate that gravity thickeners can hydrolyze polyphosphates into recoverable orthophosphates but poor performance of the thickener may inhibit this process. Chemical removal of phosphorus from wastewater is effective at removing phosphorus from the water phase but the phosphorus may then be unrecoverable via struvite precipitation.