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

BACKGROUND 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 (MgKPO4 center dot 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 (MgNH4PO4 center dot 6H(2)O). PNA reduced the alkalinity by 90%, which surpasses the performance of conventional CO2 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. (c) 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.