■Detergents Mix and Don't Separate?! The oil in wastewater can be categorized into free oil that separates if left alone, solid fats that can be filtered out, and emulsified oil that is finely mixed with detergents. Emulsified oil is difficult to separate even when left undisturbed, requiring a separate treatment to break the emulsion. Therefore, detergents should not be added to the separation tank. ■Oil Treatment Agents Do Not Decompose Oil treatment agents, which are primarily composed of surfactants similar to those in detergents, only disperse the oil into fine particles without breaking it down, as confirmed by product testing. Like emulsified oil, they become difficult to separate in the separation tank. ■What Are the Standards for Wastewater? According to national general wastewater standards, the permissible limit for normal hexane extractable substances is set at 5 mg/L for mineral oils and 30 mg/L for animal and vegetable oils and fats (applicable to factories and businesses with an average daily wastewater volume of over 50 cubic meters). Normal hexane extractable substances refer to the amount of substances extracted using normal hexane as a solvent and are used as a guideline for the oil content in wastewater. When discharging into public sewer systems, the standards of the Sewer Law and local ordinances apply, with some municipalities requiring mineral oil to be below 5 mg/L.

■ Oil spills on rainy days?! In actual incidents, there have been cases where rainwater could not be processed due to sediment accumulating in the separation tank at a fueling station, causing diesel to flow into the drainage ditch. Additionally, because of a lack of cleaning, kerosene and heavy oil overflowed due to rain, with some flowing into rivers. ■ Countermeasures indicated by accident examples In another case, due to neglecting inspections and cleaning, kerosene overflowed from the tank into the adjacent retention pond. As a countermeasure, thorough regular inspections and daily checks, as well as the timely removal of accumulated oil, have been suggested. ■ What to do for daily management? 1. Inspection: Open the lid and check for oil accumulation, sediment buildup, and connected drainage ditches. 2. Record: Conduct inspections and cleaning regularly, and document the results in a log or similar. 3. Disposal: Store pumped oil and sludge in waste oil tanks and outsource their disposal as industrial waste. 4. Do not introduce: Do not place exchanged waste oil or coolant into the tank. 5. Cleaning: Regularly remove accumulated oil and sediment while the amounts are still small. Our company offers consultations for the inspection and maintenance of wastewater treatment facilities. Please feel free to contact us.