Potassium recovery from centrate: taking advantage of autotrophic nitrogen removal for multi-nutrient recovery

Abstract

Potassium is a key macronutrient, but little attention has been paid to its recovery from waste streams. This study investigates simultaneous recovery of phosphorus and potassium in the form of potassium struvite (MgKPO 4 ·6H 2 O) from centrate after nitrogen removal by partial nitritation–anammox (PNA). Lab-scale batch experiments to assess the influence of pH, Mg:P ratio and temperature on nutrient removal were conducted on effluent from two PNA reactors fed with centrate from municipal wastewater treatment plants. RESULTS: pH had a strong impact on potassium removal, which increased up to pH 11. At this pH, a product containing 11.4% P, 3.51% N and 4.34% K was obtained. X-ray diffraction confirmed the presence of potassium struvite together with ammonium struvite (MgNH 4 PO 4 .6H 2 O). PNA reduced the alkalinity by 90%, which surpasses the performance of conventional CO 2 stripping by aeration. CONCLUSION: Coupling PNA with struvite precipitation allows for the recovery of N, P and K in a multi-nutrient product and may drastically reduce the need for alkali dosing for pH control