DI water is used for cleanings in the pre-cleaning tank and the ultrasonic cleaning tank. Since the cleaning water is repeatedly filtered as many as six to ten times per hour, the water quality is always maintained clean even under continual operations. Wastewater treatment, therefore, is utterly unneeded. WORK is never exposed above the water surface. Just one pass ultrasonic cleaning can remove any stains! Industrial wastewater is never drained under the circulation treatment method.