Nutrient Recovery: Why It is Not an Option Anymore

Nitrogen (N) and phosphorus (P) are essential for life. Farmer s, gardeners and homeowners spend billions of dollars a year buying N and P for growing plants. Wastewater treatment agencies, on the other hand, spend billions of dollars a year taking what N and P they feasibly can out of wastewater before discharging treated effluent to the environment. There is something very disconnected about this arrangement.Processes for biologically removing N and P from the liquid stream in wastewater treatment plants are well established. Biological N removal in particular can be energy intensive. In wastewater treatment plants that use anaerobic digestion, the recycle flows from the solids treatment train can amount to one third or more of the N and P loads to the liquid treatment train. Because of the low flows and high concentrations of N and P in recycle streams from anaerobic digestion, the potential for nutrient recovery is high.The anthropogenic fixation of N from the atmosphere, nearly exclusively from the carbon-intense Haber-Bosch process, surpassed nature’s fixation of N several years ago. The massive release of bioavailable N to the environment has been referred to as “global fertilization.” While much P also is released into the environment, the global issue related to P is that the world is running out of high-phosphate deposits that are readily mined to feed the global appetite for P. The future is clear: Wastewater treatment plants must recover nutrients rather than remove them.The author argues that wastewater treatment plant operators must play a key role in identifying the path forward to sustainability for the water resources utility of the future. In order to do so, the wastewater treatment profession must refresh/retool/revamp how operators are educated, trained, and certified. It is fast approaching the point where the survival of the species depends on it.