Underwater water treatment unit and method for cleaning said unit

1. A method for cleaning a filtration membrane of an underwater unit including an umbilical connection for supplying the underwater unit with power;

an underwater water treatment system which includes the filtration membrane, a water intake which is suitable to bring a flow of water drawn from the environment of the system into the underwater unit, a pipe connecting said water intake and said filtration membrane, a discharge pipe for treated water and a supply pump which is suitable for carrying out water filtration;

a hydraulic cleaning circuit for cleaning said filtration membrane, said hydraulic cleaning circuit forming a loop between an inlet and an outlet of said filtration membrane, and having a discharge pipe;

two water storage tanks, each water tank being connected to the hydraulic cleaning circuit;

one cleaning product tank storing a cleaning product selected from among an acid and a base, the cleaning product tank being connected to the hydraulic cleaning circuit;

one cleaning pump which is suitable for setting a liquid in the hydraulic cleaning circuit into motion;

said filtration membrane being provided with a filtration membrane heating element, and one of the water storage tanks being provided with a heating element, said method including the sequential steps of:

a) cutting of the water intake into said filtration membrane;

b) injecting water contained in one of the water storage tanks into the hydraulic cleaning circuit, and making said water circulate in the loop using the cleaning pump;

c) heating the filtration membrane up to a temperature of between 15° C. and 40° C. inclusive using the filtration membrane heating element, the heating of the filtration membrane causing the water circulating in the loop to heat to a temperature of between 15° C. and 40° C.;

d) injecting the cleaning product contained in the cleaning product tank into the water circulating in the loop, while operating the heating element used to heat the filtration membrane in such a manner that the temperature of the water circulating in the loop remains stable and maintaining a circulation of a flow containing the cleaning product through the filtration membrane to clean the filtration membrane;

e) discharging the contents of the hydraulic cleaning circuit via the discharge pipe of the loop;

f) injecting water contained in the water storage tank provided with the heating element into the hydraulic cleaning circuit again, and making said water circulate in the loop; and

g) discharging the contents of the hydraulic cleaning circuit via the discharge pipe of the loop,

wherein the water injected into the hydraulic cleaning circuit during step f) is heated to a temperature of between 15° C. and 40° C. inclusive due to the heating element of the water storage tank.

2. The method for cleaning as claimed in claim 1 , wherein the cleaning product injected into the hydraulic cleaning circuit during step d) is an acid.

3. The method for cleaning as claimed in claim 1 , wherein said method includes, between step f) and step g), the steps:

d′) injecting a second cleaning product that is different from the cleaning product injected during step d) into the hydraulic cleaning circuit, said second cleaning product being contained in one storage tank;

e′) discharging the contents of the hydraulic cleaning circuit via the discharge pipe of the hydraulic cleaning circuit; and

f′) injecting water contained in one of the two water storage tanks into the hydraulic cleaning circuit again, and making said water circulate in the loop.

4. The method for cleaning as claimed in claim 3 , wherein the cleaning product injected into the hydraulic cleaning circuit during step d) is a base and the temperature obtained during step c) is between 30° C. and 40° C. and the cleaning product injected into the hydraulic cleaning circuit during step d′) is an acid.

5. The method for cleaning as claimed in claim 1 , wherein said method subsequently includes the steps:

h) resuming a water treatment in the water treatment system of the unit; and

i) replacing the water which has been used during steps b) and f), by injecting water obtained leaving the treatment system into the water storage tanks.

6. The method for cleaning as claimed in claim 1 , wherein the underwater water treatment unit is placed underwater, at a minimum depth of 500 meters.

7. The method for cleaning as claimed in claim 1 , wherein the contents of the hydraulic cleaning circuit are discharged into the water storage tanks which have been drained following step b).

8. The method for cleaning as claimed in claim 5 , wherein the water injected into the hydraulic cleaning circuit during step f′ is heated to a temperature of between 15° and 40° C. inclusive thanks to the at least one heating element of the at least two water storage tanks.

9. The method for cleaning as claimed in claim 2 , wherein the temperature obtained during step c) is between 25° C. and 35° C.

10. The method for cleaning as claimed in claim 1 , wherein the cleaning product injected into the hydraulic cleaning circuit during step d) is a base and the temperature obtained during step c) is between 30° C. and 40° C.

11. A method for cleaning a filtration membrane of an underwater unit including a battery supplying the underwater unit with power;

an underwater water treatment system which includes the filtration membrane, a water intake which is suitable to bring a flow of water drawn from the environment of the system into the underwater unit, a pipe connecting said water intake and said filtration membrane, a discharge pipe for treated water and a supply pump which is suitable for carrying out water filtration;

a hydraulic cleaning circuit for cleaning said filtration membrane, said hydraulic cleaning circuit forming a loop between an inlet and an outlet of said filtration membrane, and having a discharge pipe;

two water storage tanks, each water tank being connected to the hydraulic cleaning circuit;

one cleaning product tank storing a cleaning product selected from among an acid and a base, the cleaning product tank being connected to the hydraulic cleaning circuit;

one cleaning pump which is suitable for setting a liquid in the hydraulic cleaning circuit into motion;

said filtration membrane being provided with a filtration membrane heating element, and one of the water storage tanks being provided with a tank heating element, said method including the sequential steps of:

a) cutting of the water intake into said filtration membrane;

b) injecting water contained in one of the water storage tanks into the hydraulic cleaning circuit, and making said water circulate in the loop using the cleaning pump;

c) heating the filtration membrane up to a temperature of between 15° C. and 40° C. inclusive using the filtration membrane heating element, the heating of the filtration membrane causing the water circulating in the loop to heat to a temperature of between 15° C. and 40° C.;

d) injecting the cleaning product contained in the cleaning product tank into the water circulating in the loop, while operating the heating element used to heat the filtration membrane in such a manner that the temperature of the water circulating in the loop remains stable and maintaining a circulation of a flow containing the cleaning product through the filtration membrane to clean the filtration membrane;

e) discharging the contents of the hydraulic cleaning circuit via the discharge pipe of the loop;

f) injecting water contained in the water storage tank provided with the tank heating element into the hydraulic cleaning circuit again, and making said water circulate in the loop; and

g) discharging the contents of the hydraulic cleaning circuit via of the discharge pipe the loop again,

wherein the water injected into the hydraulic cleaning circuit during step f) is heated to a temperature of between 15° C. and 40° C. inclusive due to the tank heating element of the water storage tank.