Nutrient recovery from deammonification effluent in a pilot study using two-step reject water treatment technology

Abstract The aim of this study was to assess the possibility of phosphorus and nitrogen recovery from the liquid fraction of digestates (reject water) pilot study using a two-step technology, where the precipitation of biogenic compounds in the form of magnesium ammonium phosphate (struvite) will be preceded by a deammonification process. The tests confirmed the possibility of nutrient recovery from deammonification effluent. A removal efficiency from 85.0 to 92.0% of PO43− ions and from 13.0 to 21.0% of NH4+ ions in the form of magnesium salt was achieved, at a pH in the range of 8.7–9.0. However, when the pH value was from 9.1 to 9.3, phosphate ions were precipitated not only as magnesium salts, but also as calcium salts. The maximum struvite crystal sizes ranged from 0.72 to 1.65 mm, and was determined by the concentration of the suspended solids in the reject water, whose presence was a factor limiting the crystallization of struvite.