Abstract: At the time of loading a ship, ballast water is sent to a ceramic filter membrane having a mesh of 9 to 12 ?m by a filtration pump, and at the time of unloading, ballast seawater is sent to the membrane by the filtration pump to be filtrated under pressure. Thus, marine organisms larger in size than this mesh are removed. The permeated water containing marine organisms smaller in size than the mesh is sterilized with a chemical agent made of chlorine or ozone in a facility for sterilizing with chemical agent, and then discharged into the sea or poured into the ballast tank. With this, it is possible to purify a large amount of ballast water, in a short time, into a level at which the water quality standard according to the guideline can be cleared without requiring any large-sized facility or any high-concentration chemical agent.

Abstract: A method of wastewater reutilization by which reusable water can be stably obtained from a wastewater. Ozone is added to a wastewater, such as water resulting from sewage treatment, in such a small amount as to result in a residual ozone concentration as measured before membrane filtration of 0.01-1.0 mg/L. Ozone is thus brought into contact with fine solids contained in the wastewater to alter the surface properties of the fine solids so that the solids are easily to coagulate. Thereafter, a coagulant, e.g., PACl, is added from a coagulant addition device(3). The fine solids are coagulated in a coagulation tank(5) or a line mixer and the resultant water is subjected to membrane filtration with an ozone-resistant separation membrane(6) such as ceramic membrane. Thus, reusable water is obtained which has a residual ozone concentration, as measured after filtration through the membrane, less than 0.5 mg/L.