Past Downflow Hanging Sponge (DHS) designs have displayed limited denitrification. Poor denitrification occurs due to C-limitation and excess DO in lower sponges. A raw wastewater bypass was introduced to provide additional C and reduce DO. COD and TN removal rates of >84% and ∼74% were achieved with a 30%xA0;v/v bypass. DHS reactors with bypass are suitable for decentralised treatment applications.