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UBC Theses and Dissertations

A UBC fluidized bed reactor investigation of K-struvite Larson, Sean


The University of British Columbia (UBC) has been researching the removal and recovery of phosphorus and nitrogen from waste water by producing NH₄-struvite (MgNH₄PO₄:6H₂O) pellets in their patented Fluidized Bed Reactor (FBR), since the early 2000’s. This work has successfully produced a marketable, slow-release, fertilizer pellet applicable for stream or land application. Potassium is another common fertilizer nutrient, and is present in some waste water streams. However, at this time, little research has been done in incorporating it into the pellets produced by the UBC FBR. Producing a pellet with both NH4-struvite and K-struvite (MgKPO₄:6H₂O) may hold the potential to produce a full-complement NPK fertilizer. The research objectives of this project included furthering the understanding of some basic chemistry properties that might interfere with the formation of K-struvite in practical applications, producing a K-struvite pellet in the UBC FBR, and producing a full-complement struvite pellet in the UBC FBR. Research specifically included bench scale experiments investigating the interference of nitrogen feed products on K-struvite formation; UBC FBR experiments to produce K-struvite pellets; and UBC FBR experiments to produce pellets containing both K-struvite and NH4-struvite. The research results indicate that ammonia must be below 5.6 mM to stop significant interference with K-struvite production, with the K-struvite feed concentrations used. Nitrification feed products, nitrate and nitrite, were not shown to interfere with K-struvite production in this research. Building on past UBC research, K-struvite was formed in the UBC FBR. The attempt to pelletize pure K-struvite grown around seed material was successful in the reactor; however it was not successfully harvested, as it was unable to hold its structure when harvesting forces were applied. In further experiments, NH₄-struvite was used to coat the K-struvite pellet in the reactor; which allowed the pellet to both, hold structure when harvested, and contain both types of struvite, making it a full-complement NPK fertilizer. The range of phosphorus removal in this research varied from 0% to 100%, depending on initial feed and operating conditions. The main variables were pH, presence of ammonia, and hydraulic residence time. Typical K-struvite operation had a phosphorus removal of 60% to 80%.

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