Recovery and Removal of Phosphorus via Struvite (MgNH4PO4. 6H2O) Crystallization in Fluidized Bed Reactor from Domestic Wastewater

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Addis Ababa University


Phosphorus is a vital nutrient for food production which is produced from limited, non-renewable resource called phosphate fossil. At the present rate of utilization, the world’s reserve of phosphate fossil will be exhausted soon. However, wastewater contain huge amount of phosphorus which can be recycled to reduce depletion of phosphate fossil. Beside this fact, phosphorus should be removed from wastewater before discharging it into water bodies, to avoid eutrophication. One of the promising methods of phosphorus recovery in to useful end product is struvite crystallization. The present study focuses on recovery of phosphorus via struvite crystallization from domestic wastewater in fluidized bed reactor. Response surface experimental design was implemented to optimize process parameters such as pH (8 – 12), ammonium to phosphate molar ratio (1 - 4), magnesium to phosphate molar ratio (0.5 – 2.5) and reaction time (1hr. – 5 hr.) using model solution. The optimized value for pH, ammonium to phosphate molar ratio, magnesium to phosphate molar ratio and reaction time were found to be 10, 2.9, 1 and 4 hr. respectively. Under this optimized value 81% and 74% phosphorus removal efficiency was achieved from model solution and domestic wastewater respectively. Similarly, 1.29 and 2.9 gram of struvite yield was obtained from 10 litter of model solution and domestic wastewater respectively. Although higher amount of struvite yield (2.9 gram) was obtained from domestic wastewater, struvite crystal purity was lower (68.7%). Elemental composition of crystals precipitated under optimized condition indicate that octahedral struvite crystals was the dominant compound which was further identified by scanning electron microscope, Fourier transform infrared spectroscopy and X-ray diffraction. This study also investigated the potential of Basaka Lake water as locally available magnesium source for struvite crystallization. Seventy nine percent (79%) and sixty eight percent (68%) phosphate removal efficiency were achieved from model solution and domestic wastewater respectively by employing Basaka Lake water as a source of magnesium. Overall, struvite crystallization from domestic wastewater is a sustainable eco-friendly approach for removal of phosphorus via struvite which can be used as fertilizer in agricultural sector.



Fluidized Bed Reactor, Crystallization, Struvite, Response Surface, Phosphorus Recovery