Liquid treatment method and apparatus
A method for controlling a liquid treatment apparatus of the present disclosure includes: (i) providing the liquid treatment apparatus; (ii) treating a polluted liquid in a photocatalytic reaction tank by a photocatalytic reaction to produce a treated liquid; (iii) introducing a liquid mixture into a separation tank from the photocatalytic reaction tank through a feed passage by a circulation pump; (iv) introducing a filtrate to an outside of the separation tank through an extraction passage while filtering the liquid mixture introduced into the separation tank by a filtration membrane, and feeding the liquid mixture to the photocatalytic reaction tank through an overflow passage; and (v) making a flow rate of the liquid mixture measured by a liquid mixture flow meter higher than a flow rate of the filtrate measured by a filtrate flow meter by controlling the circulation pump by a controller.
1. A liquid treatment method using a liquid treatment apparatus, the method comprising:
(Ia) providing the liquid treatment apparatus comprising:
a first tank having an internal space for storing liquid mixture containing photocatalyst particles;
a light source for emitting ultraviolet light with which the photocatalyst particles are irradiated;
a second tank comprising a filtration membrane therein and having an internal space divided into a first chamber and a second chamber with the filtration membrane, a part of the filtration membrane being exposed to the second chamber;
a communication channel liquid-communicably coupling the internal space of the first tank and the second chamber of the second tank;
a circulation pump;
a discharge channel that establishes communication between the first chamber of the second tank and an outside of the liquid treatment apparatus; and
an overflow passage that is separately provided from and located above the communication channel, and liquid-communicably couples the internal space of the first tank and the second chamber of the second tank;
(Ib) supplying a polluted liquid to the first tank to prepare the liquid mixture containing the photocatalyst particles and the polluted liquid in the first tank;
(Ic) irradiating the photocatalyst particles contained in the liquid mixture stored in the internal space of the first tank with light emitted from the light source to convert the liquid mixture into a treated liquid in the first tank;
(Id) transferring the treated liquid into the second chamber of the second tank from the internal space of the first tank through the communication channel with the circulation pump; and
(Ie) filtering the treated liquid with the filtration membrane in the second tank to discharge a filtrate provided in the first chamber of the second tank from the first chamber of the second tank through the discharge channel;
wherein the overflow passage and the filtration membrane are configured such that an uppermost portion of the exposed part of the filtration membrane is located at a level equal to or lower than a maximum liquid level of the second tank at which the treated liquid in the second chamber starts to flow into the first chamber via the overflow passage, and
in the steps (Id) and (Ie), the following requirements (I)-(IV) are satisfied:
Requirement (I): a liquid level of the liquid mixture contained in the first tank is as high as or lower than a liquid level of the treated liquid contained in the second chamber of the second tank;
Requirement (II): a flow rate of the treated liquid through the communication channel is larger than a flow rate of the filtrate through the discharge channel;
Requirement (III): a part of the treated liquid contained in the second chamber of the second tank is returned back to the first tank through the overflow passage; and
Requirement (IV): the exposed part of the filtration membrane is immersed in the treated liquid contained in the second chamber of the second tank.
2. The method according to claim 1 , wherein
the liquid treatment apparatus further comprises a filtering pump for decompressing the first chamber of the second tank, a supply passage connected to the first tank, and a supply pump disposed in the supply passage;
the polluted liquid flows through the supply passage to the first tank; and
operation of the filtering pump starts during the operation of the circulation pump and the supply pump, at setup of the liquid treatment apparatus.
3. The method according to claim 1 , wherein
the liquid treatment apparatus further comprises a filtering pump for decompressing the first chamber of the second tank, and
the method further comprises:
lowering the flow rate of the filtrate with the filtering pump or stopping operation of the filtering pump, if the liquid level of the liquid mixture contained in the first tank is lower than a predetermined level.
4. The method according to claim 1 , wherein
the liquid treatment apparatus further comprises a supply passage connected to the first tank and a supply pump disposed in the supply passage;
the polluted liquid flows through the supply passage to the first tank; and
the method further comprises:
increasing a flow rate of the polluted liquid flowing through the supply passage, if the liquid level of the liquid mixture contained in the first tank is higher than a predetermined level.
5. The method according to claim 1 , wherein
the liquid level of the liquid mixture contained in the first tank is measured on the basis of intensity of light emitted from the light source.
6. The method according to claim 1 , wherein
the liquid treatment apparatus further comprises a filtering pump for decompressing the first chamber of the second tank, a supply passage connected to the first tank, and a supply pump disposed in the supply passage;
the polluted liquid flows through the supply passage to the first tank; and
operation of the filtering pump stops during the operation of the circulation pump and the supply pump, for stopping the liquid treatment apparatus.
7. The method according to claim 6 , wherein
the liquid treatment apparatus further comprises a backflow prevention mechanism that is disposed in the communication channel and prevents backflow of the treated liquid.
8. The method according to claim 1 , wherein
the first tank comprises a first subtank and a second subtank;
the liquid treatment apparatus comprises a second light source for emitting ultraviolet light with which the photocatalyst particles contained in the second subtank are irradiated;
the communication channel establishes communication between an internal space of the second subtank of the first tank and the second chamber of the second tank;
the overflow passage establishes communication between an internal space of the first subtank of the first tank and the second chamber of the second tank; and
the first tank comprises a channel which establishes communication between the internal space of the first subtank and the internal space of the second subtank.
9. The method according to claim 1 , wherein
the liquid treatment apparatus further comprises:
a third tank comprising a filtration membrane therein and having an internal space divided into a first chamber and a second chamber with the filtration membrane; and
a channel that establishes communication between the second chamber of the second tank and the second chamber of the third tank; and
the discharge channel further establishes communication between the first chamber of the third tank and an outside of the liquid treatment apparatus.
10. The method according to claim 1 , wherein
the polluted liquid is water containing a contaminant that is chemically changeable by photocatalytic reaction.
11. The method according to claim 1 , wherein a level of an uppermost portion of a bottom of the overflow passage is equal to or higher than a level of the uppermost portion of the exposed part of the filtration membrane.
12. The method according to claim 1 , wherein the overflow passage has a upward-convex shape.
13. The method according to claim 1 , wherein the overflow passage is disposed at a side face of the first tank and a side face of the second tank.
14. The method according to claim 1 , wherein in Requirement (I), a space is formed in the second chamber above the liquid level of the treated liquid contained in the second chamber.