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Pilot-scale demonstration of nitrogen recovery in the form of ammonium phosphate (AP) from anaerobic digestate
Dong, D., Choi, O. K., Lee, K., & Lee, J. W. (2020). Pilot-scale demonstration of nitrogen recovery in the form of ammonium phosphate (AP) from anaerobic digestate. Bioresource Technology, 297, 122392. Article 122392. https://doi.org/10.1016/j.biortech.2019.122392
Nitrogen in anaerobic digestate was recovered as ammonium phosphates (APs), a valuable fertilizer, in a pilotscale system consisting of ammonia stripper, absorber and crystallizer. The dissolved ammonium concentration in the anaerobic digestate was stripped and then absorbed into the phosphoric acid (42.5 wt%) with 95% absorbing efficiency. As the NH3 stripping continued, both the N/P ratio and pH, key operating parameters in the absorber are optimized N/P = 0.6 and pH = 1.7. The residual AP solution after crystallization was reused to enhance the crystallization efficiency up to 88%. The overall recovery efficiency of APs was estimated at 72% of the input nitrogen mass. Analyses of SEM and XRD revealed that the recovered AP crystals were mainly composed of mono-ammonium phosphate (MAP). This pilot-scale study demonstrated that nitrogen load in anaerobic digestates could be effectively recovered as a valuable fertilizer source of AP crystals.
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