Patent ID: 7776224

Claim:
An apparatus for treating ballast water, comprising: a first pump that takes on sea water; a filter apparatus having a filter that filtrates the sea water sent from the first pump and traps plankton with sizes corresponding to a sieve opening of the filter, the sieve opening being in the range of 10 to 200 μm; the filter apparatus also having a reverse washing device that washes away plankton trapped by the filter; a bactericide supply apparatus having a plurality of injection ports for supplying bactericide to the filtrate sea water; a bactericide supply amount-control device that controls an amount of bactericide to be supplied from the bactericide supply apparatus, a venturi tube apparatus that is located downstream of the filter apparatus and is constructed by arranging a plurality of venturi tubes in parallel, the plurality of injection ports being arranged in each of a radial direction and a circumferential direction within a cross-section of an inlet of the venturi tube apparatus; a ballast tank that holds the sea water fed from the venturi tube apparatus; a second pump that discharges the sea water from the ballast tank into the sea; and a bactericide-decomposer supply apparatus that supplies bactericide-decomposer to the sea water discharged from the ballast tank so as to decompose the bactericide remaining in the sea water; wherein the amount of the sea water sent from the first pump to the venturi tube apparatus is controlled such that a flow velocity at the inlet of the venturi tube apparatus is in the range of 2 to 3 m/sec, and a flow velocity at each throat part of the venturi tubes is in the range of 10 to 40 m/sec, the ratio of the sum of sectional areas of the throat parts of the venturi tubes to a sectional area at the inlet of the venturi tube apparatus being in the range of 7.5 to 20%, the venturi tube apparatus generates cavitation in the sea water at the throat parts of the venturi tubes, thus diffusing the bactericide in the sea water to sterilize bacteria, and also destroying plankton or damaging plankton so as to promote penetration of the bactericide into a body of plankton, the amount of bactericide to be supplied is controlled to be sufficient to sterilize bacteria and plankton in the filtrate sea water and also to prevent regrowth of bacteria and plankton in the sea water kept in the ballast tank, and the amount of bactericide-decomposer to be supplied is controlled based on a measurement of bactericide concentration in the sea water discharged from the ballast tank.