The walnut shell filter is a filtration device suitable for treating oil-containing wastewater. The filter utilizes walnut shells, which have strong adsorption capacity, high compressive strength, stable chemical properties, high hardness, and good hydrophilicity. The walnut shells are specially processed to enhance their performance. One of the key features of this filter is its easy regeneration of filter media through backwashing with the influent water, eliminating the need for gas sources or chemical agents.