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UBC Theses and Dissertations

Ammonia recovery from municipal wastewater through a struvite formation-thermal decomposition cycle Wilson, Connor Walter


Bench-scale batch experiments were performed to assess the potential for ammonia removal and recovery from municipal post-digestion waste streams via struvite (MgNH4PO4•6H2O) crystallization using thermally decomposed struvite as a source of magnesium and orthophosphate. To simulate this process, newberyite (MgHPO4•3H2O), a synthesized surrogate for thermally decomposed struvite, was added to various ammonia solutions including synthetic struvite crystallizer effluent and synthetic dewatering centrate. The main objective of this study was to develop the concept of the proposed technology through evaluation of the effects of chemical and physical factors on the rates and mechanisms of ammonia removal, orthophosphate solubilization, and overall newberyite-to-struvite conversion efficiency. A model was developed using PHREEQC software to simulate each batch experiment and to predict the solid and liquid phase compositions that would result from these systems attaining chemical equilibrium. Experimental and model-predicted results were employed for the delineation of near optimal conditions for efficient transformation of newberyite into struvite. Ammonia removal efficiencies as high as 87% were achieved while maintaining orthophosphate residuals as low as 10 mg/L PO4-P. Measurements of liquid phase compositions at reaction times approaching equilibrium compared well with that predicted by the model. Results suggested an optimum within a region of 1 to 3 hour reaction times, pH between 7 and 8, temperature between 10° and 25° C, and at a newberyite dose that provides a suspension Mg:N:P molar ratio of 1:1:1. Although the results of the present study illustrate the potential of this technology, it is recommended that further research be performed employing the newberyite-containing material produced by the pilot-scale struvite thermal decomposition reactor located at the University of British Columbia.

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