Nutrient Recovery from Wastewater Treatment Plants.

Closing the loop for nutrients in wastewater treatment streams is evolving as a necessary, sustainable development objective, driven by the need to reduce the consumption of limited natural resources (e.g., phosphate rock), reduce greenhouse gas emissions and conserve energy.  For municipal wastewater, the value of phosphorus recovery in the form of struvite (i.e., magnesium ammonium phosphate) has numerous environmental and economic benefits: lower operational and maintenance costs from reduced struvite encrustation, a cost-effective method of reducing nutrient discharges into receiving waters, a reduction in sludge volumes for disposal, a new source of revenue from the recovered fertilizer, recovery of a valuable resource and 10:1 greenhouse gas credits.  Until recently, struvite has largely been viewed as more of a threat to municipal wastewater treatment plants than an opportunity.  UBC has developed a patented process for struvite recovery using an upflow struvite reactor that self-seeds the growth of crystals, eliminating the requirement for the use of bedding materials like sand and dolomite clay to serve as the particle nucleus.  A full scale project developed by Ostara Nutrient Recovery Technologies Inc. is now operating in Edmonton, Alberta, Canada, which treats the supernatant equivalent to 200,000 population equivalents, and recovers 180 tonnes per year of struvite at 97% purity, and provides 2,000 tonnes per year of greenhouse gas credits.  When this system is expanded to serve the entire 1,000,000 population of Edmonton, it will generate 1,200 tonnes per year of struvite and 12,400 tonnes of greenhouse gas credits.  A recent survey by Stantec has identified more than 1,000 municipalities in North America and Europe that would be prime candidates for the installation of struvite recovery reactors.  Capital costs are typically recovered in 3 to 5 years though savings on operation and maintenance, and sales of struvite.  Phosphorus recovery from wastewater treatment plants therefore represents a significant new source of recoverable nutrients, and should be adopted as a “best operating practice” for municipal wastewater treatment plants in order to conserve and recover this most valuable, and strategically vital resource. An example of ecological restoration using recovered struvite will also be presented.