Sodium hydroxide or tetramethylammonium hydroxide modified corncob combined with biodegradable polymers to prepare slow-release carbon source for wastewater denitrification

•NaOH and TMAOH pretreatment improved the biodegradability of corncob.•The released carbon source components were easily decomposed and utilized.•The release process of SPC-al and SPC-il followed the first order release equation.•PHBV/modified corncob composite was used as the carbon source for denitrification.