Green hydrogen derived from municipal wastewater via bioconversion by attached microalgae onto various sizes of polyurethane foam cubes

•Immobilization of microalgae onto polyurethane foam could increase hydrogen yield.•Attached microalgae could ferment nutrients in municipal wastewater into hydrogen.•Attached microalgal hydrogen production was impacted by polyurethane foam size.•COD played essential role than ammoniacal nitrogen to produce microalgal hydrogen.•Statistical model was derived to predict attached microalgal hydrogen production.