Study on efficiency and mechanism of phosphorus removal from supernatant of anaerobically digested sludge—based on anion exchange and modified hydrotalcite adsorption methods

This study selected supernatant of anaerobically digested ferric phosphate sludge as the research object and investigated the phosphorus (P) removal effectiveness and mechanisms of three types of materials, including strong base anion exchanger (DOWEX66), weak base anion exchanger (IRA402-Cl) and modified hydrotalcite. The experimental results demonstrated that (1) The DOWEX66 showed higher P removal efficiency (33.3%) than IRA402-Cl (14.2%) at the same solid to liquid ratio (3 g/L) because DOWEX66 resin has tertiary amine functional groups with strong binding force to \rmH_2\rmPO_4^- ; (2) The breakthrough profiles of phosphate uptake by raw DOWEX 66 resin in column test indicated that the breakthrough point of phosphate adsorption was located at around 5 bed volumes, which suggested that anion exchange resin has limited P elimination ability and buffer solution system is beneficial to ion exchange between resin and phosphate; (3) The 300 ℃ calcined hydrotalcite showed efficient P removal ability in the iron and phosphorus concentrated solutions and reached the highest removal ratio of 89.0% ratio at solid to liquid ratio of 2 g/L. The 300 ℃ calcined hydrotalcite also showed good performance in separating iron and phosphorus elements, indicating that modified hydrotalcite can be applied as potential material to remove and to recycle phosphorus from sludge anaerobic digestion supernatant.