1. Sludge treatment

Activated sludge pretreatment

​ Wastewater treatment on the basis of activated sludge is a core technology, but it generates an enormous amount of sludge called waste activated sludge (WAS). It is of necessity to reduce the volume prior to disposal. Anaerobic digestion (AD) is a biological way of achieving it; what is better, it concomitantly produces biogas. High biodegradability, enhancing methane production, can be achieved by sludge pre-treatment, and so far, many pretreatment methods including thermal, physical, and chemical treatments have been studied. Our group focuses on hydrodynamic cavitation (HC) which is a physical means best suited for sludge treatment; energy consumption is drastically reduced while having the benefit of easy scaling-up and efficient method. When a fluid passes through an orifice plate or a venturi tube, pressure drops below vapor pressure and as a result, bubbles are generated. When the fluid pressure is restored at a distance from the throat, cavities subsequently collapse. This phenomenon causes an increase in pressure (100-5,000 atm) and temperature (500-15,000 K), leading to form hydroxyl radicals because of hemolytic cleavage of the water molecules.