Liquid treatment method and apparatus

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.