■How many times a year is cleaning required? According to Article 10 of the Sewage Treatment Tank Law, the sewage treatment tank manager must conduct maintenance inspections and cleaning of the sewage treatment tank once a year. However, the ministerial ordinance stipulates that for aeration tanks, cleaning must be done at least once every six months. Cleaning can be entrusted to a sewage cleaning contractor authorized by the mayor. The cleaning records must be kept by the sewage treatment tank manager for three years. ■It doesn't necessarily mean complete removal! The technical standards for cleaning in the ministerial ordinance specify the amount to be removed based on the type of tank: 1. Sedimentation separation chamber, sludge storage tank, etc.: Remove all sludge and scum. 2. Disinfection tank, aeration tank without sludge transfer device, etc.: Remove an appropriate amount of sludge and scum. 3. Aeration tank (sewage treatment tank without sludge storage tank): Remove to maintain an appropriate concentration of suspended solids in the mixed liquid after filling with water. ■Post-removal tasks After removal, cleaning of the equipment may be performed as necessary, and tap water may be used for filling some tanks. During cleaning when usage is suspended, all contents must be removed. Additionally, it is stipulated that necessary measures must be taken to ensure that the removed sludge and other materials are properly treated.

■Where does the extracted sludge go? In the fiscal year 2023, out of 14.38 million kL of sewage treatment plant sludge, 13.01 million kL (90.5%) is processed at sewage treatment facilities. The next highest amount is sent to the sewer system, accounting for 1.19 million kL (8.3%). When combined with the sludge from portable toilets, a total of 19.22 million kL is processed, with 98.8% handled either at sewage treatment facilities or through sewer system input. The residue produced after processing at sewage treatment facilities, including that from portable toilets, amounts to 690,000 tons, of which 69.8% is incinerated at the facility or at waste incineration facilities. ■Things to confirm at factories and businesses 1. Type of equipment: Is it a sewage treatment plant for domestic wastewater or equipment for treating wastewater from production processes? 2. Contractor: Does the cleaning have the permit for sewage treatment cleaning, and do the transportation of sludge and other activities have the permit for general waste disposal? 3. Records: Are maintenance inspection and cleaning records kept for three years? ■Different classifications for each facility It is important to note that even within the same site, the classification of sludge and contractors may vary depending on the equipment. Our company offers inspections of wastewater treatment facilities at businesses and consultations regarding the chemicals used in wastewater treatment. Please feel free to contact us first.