Recycling Post-Consumer NPK from Wastewater Treatment Plants Back to Agriculture.

Every year, over 2 million tons of nitrogen, worth $2 billion, is flushed into the sewers for wastewater treatment plants to deal with. As much as half is treated to volatilize nitrogen as dinitrogen, nitrous oxide and ammonia gases; the remainder is either discharged into surface waters as ammonium-N or nitrate-N in effluent water or land-applied as biosolids. The bulk of phosphorus at sewage treatment facilities is within biosolids. When land-applied, these biosolids present a hazard to nearby waters, as buildup of labile phosphorus results in the eutrophication of surface water, a global problem that has worsened in recent decades. In addition, potassium is another nutrient commonly discharged into the environment at wastewater facilities.

As part of the International Year of the Soil, crop and soil scientists have called to improve recovery of nutrients from waste treatment facilities back to agriculture. At the same time, the Water Environment Federation has sought to shift their business from ‘wastewater treatment’ to ‘resource recovery’. Currently, most phosphorus treatment schemes are focused on meeting regulatory standards and preventing struvite precipitation (a phosphorus-containing mineral that is notorious for clogging pipes in treatment facilities), not phosphorus recovery. Wastewater facilities are currently not recovering nitrogen and potassium from wastewater. As the human population continues to grow, the demand for sustainable fertilizers will continue to increase in order to support greater agricultural productivity. Thus, recovering NPK from wastewater is one method to ensure this need is met.