Novel strategy to stimulate the food wastes anaerobic fermentation performance by eggshell wastes conditioning and the underlying mechanisms

•Eggshell conditioning enhanced the VFAs production from FW anaerobic fermentation.•FW solubilization, hydrolysis and acidification were synchronously enhanced.•Eggshell conditioning greatly improved the environmental conditions (i.e pH, ORP).•The key enzymes involved in carbohydrates and energy metabolisms were improved.•The functional genes distributed in fatty acid biosynthesis pathway were enhanced.