Fig. 14. Shirasu-porous-glass (SPG) membrane used to produce bulk nanobubbles. The process starts by pumping a solution consists of water and sodium dodecyl sulphate (SDS) from the water phase storage tank into the membrane module. Then, the compressed air is purged into the membrane through the membrane holes to form bulk nanobubbles inside the membrane. Then, the produced bulk nanobubbles are collected in the storage tank. A flowmeter, a pressure gauge, and a laser diffraction particle size analyzer are used to measure the flow of the water-SDS solution, air pressure, and size of the generated nanobubbles, respectively.¹³⁰.