Two　biological　nitrogen　removal　processes　are　compared　in　the　aspect　of　nitrogen　removal,　process　operation　and　energy　saving.　Results　show　that　when　the　returned　sludge　ratio　is　50%　of　the　inflow　rate,　the　step-feeding　process　achieves　over　80%　total　nitrogen　(TN)　removal　efficiency,　but　the　TN　removal　efficiency　of　the　A/O　process　is　only　40%.　Moreover,　filamentous　sludge　bulking　can　be　well　restrained　in　the　step-feeding　process.　Given　the　conditions　of　a　returned　sludge　ratio　of　100%　and　a　nitrifying　liquor　recycle　ratio　of　200%,　the　TN　removal　efficiency　is　78.32%　in　the　A/O　process,　but　the　sludge　volume　index　(SVI)　value　increases　to　143　mL/g.　In　the　step-feeding　process,　the　SVI　is　only　94.4　mL/g　when　the　TN　removal　efficiency　reaches　81.1%.　The　step-feeding　process　has　distinct　advantages　over　the　A/O　process　in　the　aspects　of　practicability,　nitrogen　removal　and　operating　stability.