How to calculate the size of an oil separator in an oil depot? Are there any guidelines I can refer to?

I have posted this standard document in the resource sharing area; you can go and get it! Standards of the People’s Republic of China – Code for Design of Outdoor Drainage Systems GBJ14-87 (1997 edition). Announcement on Partial Revision to Engineering Construction Standards, No. 12. Table of Contents: Chapter 1 General Provisions; Chapter 2 Discharge Quantities: Section 1 Domestic Sewage and Industrial Waste Water Quantities; Section 2 Rainwater Volume; Section 3 Combined Flow Volume. Chapter 3 Drainage Pipes and Their Associated Structures: Section 1 General Provisions; Section 2 Hydraulic Calculations; Section 3 Pipes; Section 4 Inspection Wells; Section 5 Drop Wells; Section 6 Water-Sealing Wells; Section 7 Rainwater Inlets; Section 8 Outlets; Section 9 Drainage for Intersections; Section 10 Underground Pipes; Section 11 Canals; Section 12 Comprehensive Pipe Design. Chapter 4 Drainage Pump Stations: Section 1 General Provisions; Section 2 Collection Tanks; Section 3 Pump Rooms. Chapter 5 Site Selection and Overall Layout of Sewage Treatment Plants. Chapter 6 Sewage Treatment Structures: Section 1 General Provisions; Section 2 Gratings; Section 3 Grit Chambers; Section 4 Sedimentation Tanks: (I) General Provisions; (II) Conventional Sedimentation Tanks; (III) Sloped-Plate (Tube) Sedimentation Tanks; (IV) Double-Layer Sedimentation Tanks. Section 5 Biofilm Processes: (I) General Provisions; (II) Biological Filters; (III) Rotating Biological Contactors; (IV) Biological Contact Oxidation Tanks. Section 6 Activated Sludge Processes: (I) General Provisions; (II) Aeration Tanks. Section 7 Oxygen Supply Facilities: (I) General Provisions; (II) Blower Rooms. Section 8 Recirculated Sludge and Excess Sludge. Section 9 Stabilization Ponds. Section 10 Irrigated Fields. Section 11 Disinfection. Chapter 7 Sludge Treatment Structures: Section 1 General Provisions; Section 2 Sludge Thickeners and Wet Sludge Ponds; Section 3 Digestion Tanks; Section 4 Sludge Drying Sites. Section 5 Mechanical Sludge Dewatering: (I) General Provisions; (II) Vacuum Filters; (III) Pressure Filters. Chapter 8 Oily Wastewater and Phenolic Wastewater. Appendix 1 Method for Formulating Rainfall Intensity Formulas; Appendix 2 Minimum Clearances Between Drainage Pipes and Other Underground Pipelines (Structures); Appendix 3 Allowable Concentrations of Harmful Substances in the Water Feed to Biological Treatment Structures; Appendix 4 Conversion Relationships between Non-Standard and Standard Units of Measurement Used in This Code; Appendix 5 Explanation of Terms Used in This Code. Appendix: List of the Organizations Responsible for Compiling This Code, the Organizations That Participated in Its Development, and the Main Drafters