Integrated “adsorption-catalysis-adsorption” green strategy for efficient adsorption for the removal of methylene blue and catalytic preparation of hydrocarbon-rich, low N/O bio-oil

•This study promoted the cycling of carbon and nitrogen in wastewater systems.•The “adsorption-catalysis-adsorption” strategy improved the recovery of waste.•Improved quality of bio-oil obtained with regenerated catalyst.•The maximum adsorption capacity of regenerated bio-char was 554.38 mg·g−1.