Highly efficient and robust treatment of low C/N actual domestic sewage via integrated fermentation, partial-nitrification, partial-denitrification and anammox (IFPNDA)

•High NRE of 87.5 ± 2.1% was obtained from actual domestic sewage via IFPNDA.•Effluent TN reached 6.1 ± 0.7 mg/L without external organics and complex operations.•Robust N-removal highly depended on the linkage between double nitrite-suppliers.•VFAs concentration in domestic sewage was enhanced by fermentation.•IFPNDA with potential of energy-neutrality respond the novel concept WWTPs.