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UBC Theses and Dissertations

Optimization of phosphorus recovery from anaerobic digester supernatant through a struvite crystallization fluidized bed reactor Ghosh, Shayok


Phosphorus is an essential element for all living organisms, but its supply is limited. On the other hand, phosphorus recovery from domestic wastewater can satisfy 15-20 % of current phosphate rock demand. Moreover, struvite scaling is a concern for wastewater engineers as it clogs various equipment. Recovering phosphorus as struvite pellets from wastewater can yield sustainable solution for both problems. Although several technologies have already been available to recover phosphorus from wastewater with reasonable P- recovery efficiency, these technologies possess a number of shortcomings such as higher capital and operating cost, production of fines instead of pellets etc. This study aimed at optimization of phosphorus recovery from wastewater by developing a sustainable and efficient technology. To accomplish this purpose, a new crystallization fluidized bed reactor (FBR) was developed and impact of different physio-chemicals (supersaturation ratio) and hydrodynamic (up-flow velocity, nozzle velocity and configurations) parameters on its performance were analyzed to determine optimum operating conditions. This reactor achieved over 90% of P removal from synthetic supernatant with up to 18% of P recovery. Lower P-recovery was resulted due to lack of proper harvesting mechanism. Results showed that P-removal efficiency was increased with increase in initial supersaturation ratio up to a value of 6.5. But increase in supersaturation ratio yielded lower P-recovery with higher fines production. A value in the range of 5.5-6.0 was suggested by this study for optimum output. Low up-flow velocity was found to be associated with higher P-removal and recovery efficiency, where high up-flow velocity was found to be associated with the production of more large sized pellets and fines. But, higher nozzle velocity was found to be responsible for accomplishing higher P-removal and recovery efficiency. Two nozzles on opposite side yielded higher P-recovery efficiency with more large sized pellets and lower fine production. Based on these results, this study concluded that 40 cm/min up-flow velocity with 18.04 cm/min nozzle velocity and two nozzles on opposite side might be optimum operating conditions. Analysis on the performance of up-scaled reactor showed that optimum conditions for pilot scale and up-scaled reactor might be different due to different hydrodynamic conditions.

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