The use of calcined paper mill sludge as a chemical precipitant in the simultaneous removal of ammonium and phosphate:paper mill waste recycling and reuse

Abstract The European Union’s (EU) circular economy strategy aims to increase recycling and re-use of products and waste materials. According to strategy, the use of industry waste material and side flows should be more effective. In this research, a chemical precipitation method to simultaneously remove phosphate and nitrogen using calcined paper mill sludge was tested. Paper mill sludge is a waste material formed in the paper-making process. It mainly contains calcium carbonate and cellulose fibers. Objective of this research was to test whether the industrial waste could be used as low cost precipitation chemical for ammonium and phosphate removal from wastewaters or the precipitate could be suitable for fertilizer use. The study results indicated that calcined paper mill sludge removed as much ammonium nitrogen and phosphate as commercial CaO. Furthermore, the results showed that calcined paper mill sludge removed efficiently phosphate from the liquid phase of anaerobic digestate, which leads to formation of hydroxyapatite, Ca₅(PO₄)₃(OH). In this study we have shown, that calcined paper mill sludge can be used to manufacture recycled, slow-release fertilizers. Other possible mechanisms for the removal of phosphate and ammonium were also considered