Insights into a novel nitrogen removal process based on simultaneous anammox and denitrification (SAD) following nitritation with in-situ NOB elimination

•Optimal contribution rate of anammox achieved at a COD/NH+ 4-N ratio of 2.5•Anammox with low Gibbs free energy occurred prior to the denitrification•Zeolite sequence batch reactor (ZSBR) provides fast nitritation effluent•ZSBR can meet the nitrite influent requirement of up-flow blanket filter (UBF)•Low-carbon and economical nitrogen removal are achieved in ZSBR-UBF