Effects of Ca2+ on biological nitrogen removal in reverse osmosis concentrate and adsorption treatment

[Display omitted] •Ca ions present in the ROC caused the negative effect on the biological treatment of nitrogen.•Aerobic granular sludge removed (adsorbed) Ca ions effectively.•XPS and TEM analysis confirmed the Ca ions adsorbed on surface very clearly. This study aims to investigate the effects of calcium ions present in the reverse osmosis (RO) concentrate on the removal of nitrate nitrogen and the absorption process of calcium ions using various carriers. The results of the analysis show that the denitrification of nitrate nitrogen delayed upon the injection of calcium ions at concentrations 500mg/L. The adsorption of calcium ion was investigated by the development of adsorption isotherm equation, and aerobic granular sludge was found to be excellent.