Efficient phosphorus recovery by enhanced hydroxyapatite formation in a high loading anammox expanded bed reactor at 15 °C

Abstract

Abstract Wastewater such as digestate from waste biomass anaerobic digestion contains a high concentration of nutrients such as nitrogen and phosphorus. A novel process for simultaneous nitrogen removal and phosphorus recovery was recently developed based on the combination of the anammox process and hydroxyapatite (HAP) crystallization. This study firstly investigated the feasibility of operating this process under low temperature using an anammox-HAP type expanded bed reactor. By gradually increasing nitrogen loading and phosphorus loading rate, a nitrogen removal rate of 8.45\xa0±\xa00.49\xa0gN/L/d with a simultaneous phosphorus recovery rate of 0.63\xa0±\xa00.06\xa0gP/L/d was obtained at 15\xa0°C. The efficiency for both nitrogen removal and phosphorus recovery was higher than 80%. The addition of Ca2+ was confirmed to be an effective strategy to enhance the efficiency of phosphorus recovery by affecting the supersaturation condition of the solution. However, a high phosphorus load may result in excessively high mineral concentrations in the sludge and affect anammox performance. The granular sludge formed under low temperature conditions in this study has a typical double-layer structure of HAP-core and anammox biofilm. This study firstly demonstrated the feasibility of the anammox-HAP process even under low temperatures and give new options for future digestate treatment.