This　work　demonstrates　the　feasibility　of　simultaneous　nitrogen　removal　and　external　waste　activated　sludge　(WAS)　reutilization/reduction　by　using　the　synergy　of　sludge　fermentation,　denitrification　and　anammox　processes　in　up-flow　reactors　(SFDA).　Pre-treated　domestic　wastewater　and　synthetic　wastewater　(containing　nitrite　similar　to　20　mg/L,　ammonium　similar　to　10　mg/L　in　both)　were　fed　to　1#　and　2#　SFDA,　respectively.　Long-term　operation　of　1#　SFDA　was　investigated　with　achieving　the　peak　ammonium　removal　rate　of　0.021　and　nitrite　removal　rate　of　0.081　kg　N/(m(3)d)　as　nitrogen　loading　rate　elevated　from　0.075　to　0.106　kg　N/(m(3)d).　Negative　effect　of　dissolved　oxygen　on　anammox　or　fermentation　in　the　2#　SFDA　was　demonstrated　negligible　due　to　rapid　depletion　by　microorganisms.　Furthermore,　a　＂net＂　sludge　reduction　of　38.8%　was　obtained　due　to　sludge　decay　and　organics　consumption　by　denitrification.　The　SFDA　process　was　expected　to　potentially　be　used　for　nitrogen　removal　and　WAS　reutilization/reduction　in　full-scale　application.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.