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Simultaneous management of nitrogen and phosphorus in dewatered sludge liquor by combining ANAMMOX process with struvite crystallization Hassan, Parssa


A process combination of anaerobic ammonium oxidation (ANAMMOX), followed by struvite crystallization, was examined for simultaneous removal of nutrients (nitrogen and phosphorus) from dewatered sludge liquor or centrate. Phosphorus recovery as struvite can recover more than 90% P from centrate; however, the effluent after struvite crystallization still contains high concentrations of ammonium nitrogen (NH₄-N). ANAMMOX is a cost effective alternative process for NH₄-N removal and this process can remove 85% - 90% of NH₄-N from centrate, but leaves high concentration of phosphorus phosphate (PO₄-P) in the treated effluent. Combining ANAMMOX and struvite recovery can offer a sustainable solution for managing phosphorus and nitrogen at wastewater treatment plants. The ANAMMOX process, followed by a struvite crystallization process, was selected as the combination sequence for this first study. Synthetic feed was prepared with different molar ratios of Mg: NH₄-N: PO₄-P to mimic centrate, partially nitrified centrate and centrate treated by ANAMMOX process (ANAMMOX effluent). To determine the molar ratio of Mg: NH₄-N: PO₄-P, centrate was obtained from Lulu Island Wastewater Treatment Plant and partial nitrification, followed by ANNAMOX process, was conducted on this batch of centrate. Jar tests were conducted to determine the struvite formation potential from synthetic ANAMMOX effluent, as it has a very low N: P ratio. Pure struvite formed successfully in the jar tests with P-removal efficiency up to 88%. The process combination was upgraded to bench-scale, fluidized bed reactors for further investigation on the nutrient recovery efficiencies and associated chemical costs. The process combination successfully reduced NH₄-N concentration to 70 mg/L from an initial value of 800 mg/L. The concentration of PO₄-P was reduced to 15 mg/L in the final treated effluent, from a starting value of 119 mg/L. Overall, the combination resulted in phosphorus-phosphate (PO₄-P) removal rate as high as 87% and ammonium-nitrogen (NH₄-N) as high as 92%. The mean particle size for struvite from ANAMMOX effluent ranged between 90 - 160 μm, and was larger than struvite particle formed from centrate. However, chemical costs associated with caustic and magnesium consumption, were found to be higher for the process combination, compared to just struvite formation using centrate.

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