Method and apparatus for reusing wastewater

1. A method for reusing wastewater, the method comprising:

producing a mixed wastewater by mixing multiple types of wastewater (S 20 );

performing a first purification by passing the mixed wastewater through a flocculation-sedimentation unit (S 40 );

performing a second purification by passing an effluent of the flocculation-sedimentation unit through a membrane bioreactor (MBR) (S 60 );

performing a third purification by passing an effluent of the MBR through a reverse-osmosis membrane unit (S 80 ); and

reusing an effluent of the reverse-osmosis membrane unit as a cooling water or industrial water (S 100 ),

wherein the mixed wastewater refers to wastewater containing a mixture of hydrofluoric acid wastewater, other acidic wastewater, and alkaline wastewater produced from the semiconductor manufacturing process, or display manufacturing process, a total phosphorus (T-P) concentration in the mixed wastewater is 10 mg/L or less,

wherein the step (S 40 ) comprises:

producing a first treated water by passing the mixed wastewater through a first flocculation reactor (S 40 - 2 );

producing a third treated water by passing either the first treated water or a second treated water through a third flocculation reactor, wherein the second treated water is obtained by passing the first treated water through a second flocculation reactor (S 40 - 4 );

producing a fourth treated water by passing the third treated water through a fourth flocculation reactor (S 40 - 6 ); and

producing a fifth treated water and a sludge by passing the fourth treated water through a sedimentation tank (S 40 - 8 ),

wherein a first chemical and a second chemical are introduced into the first flocculation reactor, a third chemical is introduced into the third flocculation reactor, and a fourth chemical is introduced into the fourth flocculation reactor,

wherein the first chemical comprises slaked lime, the second chemical comprises a hydrogen peroxide scavenger, the third chemical comprises a pH control agent, and the fourth chemical comprises an anionic polymer flocculant,

wherein a pH of the first flocculation reactor is 10.0 to 11.5, and a pH of the third flocculation reactor is 6.5 to 7.5, wherein the effluent of the MBR is adjusted to a pH of 5.8 to 6.5 and then supplied to the reverse-osmosis membrane unit,

wherein the step (S 60 ) comprises:

producing a sixth treated water by passing the fifth treated water through an anoxic tank (S 60 - 2 );

producing a seventh treated water by passing the sixth treated water through an aerobic tank (S 60 - 4 );

producing an eighth treated water by passing the seventh treated water through a separation membrane tank (S 60 - 6 );

wherein the step (S 60 ) further comprises step (S 60 - 8 ) of passing an unfiltered water remaining in the separation membrane tank through a deaeration tank, and step (S 60 - 10 ) of passing an effluent of the deaeration tank through the anoxic tank.

2. The method of claim 1 ,

wherein no chemical is introduced into the second flocculation reactor.

3. The method of claim 1 ,

wherein a portion of the sludge produced in the step (S 40 - 8 ) is returned to the first flocculation reactor, and the remainder of the sludge is discharged to outside the sedimentation tank.

4. The method of claim 1 ,

wherein the aerobic tank has a fifth chemical or no chemical introduced thereinto, and the anoxic tank and the separation membrane tank have no chemical introduced thereinto.

5. The method of claim 4 ,

wherein the fifth chemical comprises sodium hydroxide.

6. The method of claim 1 ,

further comprising, between the step (S 60 ) and the step (S 80 ), step (S 70 ) of introducing at least one from among the third chemical, a sixth chemical, and a seventh chemical into the effluent of the MBR prior to being introduced into the reverse-osmosis membrane unit.

7. The method of claim 6 ,

wherein the sixth chemical comprises a disinfectant, and the seventh chemical comprises an anti-scaling agent.

8. The method of claim 1 ,

further comprising, between the step (S 80 ) and the step (S 100 ), step (S 90 ) of cleaning a reverse-osmosis membrane by adding an eighth chemical to the reverse-osmosis membrane unit, wherein the eighth chemical comprises a clean-in-place (CIP) cleaning agent.

9. An apparatus for reusing wastewater, comprising: a first flocculation reactor configured to produce a first treated water by flocculating a mixed wastewater;

a third flocculation reactor configured to produce a third treated water by further flocculating the first treated water;

a fourth flocculation reactor configured to produce a fourth treated water by further flocculating the third treated water;

a sedimentation tank configured to produce fifth treated water and sludge by settling the fourth treated water;

an anoxic tank configured to produce a sixth treated water by performing a denitrification reaction on the fifth treated water;

an aerobic tank configured to produce a seventh treated water by removing organic matter from the sixth treated water and performing a nitrification reaction on the sixth treated water;

a separation membrane tank configured to produce an eighth treated water by removing particulate matter from the seventh treated water; and

a reverse-osmosis membrane unit configured to produce a concentrated water and a produced water by removing organic matter and inorganic ion components from the eighth treated water,

wherein the mixed wastewater refers to wastewater containing a mixture of hydrofluoric acid wastewater, other acidic wastewater, and alkaline wastewater produced from the semiconductor manufacturing process, or display manufacturing process, a total phosphorus (T-P) concentration in the mixed wastewater is 10 mg/L or less,

wherein a first chemical and a second chemical are introduced into the first flocculation reactor, a third chemical is introduced into the third flocculation reactor, and a fourth chemical is introduced into the fourth flocculation reactor,

wherein the first chemical comprises slaked lime, the second chemical comprises a hydrogen peroxide scavenger, the third chemical comprises a pH control agent, and the fourth chemical comprises an anionic polymer flocculant,

wherein a pH of the first flocculation reactor is 10.0 to 11.5, and a pH of the third flocculation reactor is 6.5 to 7.5, wherein an effluent of the separation membrane tank is adjusted to a pH of 5.8 to 6.5 and supplied to the reverse-osmosis membrane unit,

further comprising a deaeration tank configured to remove dissolved oxygen from an unfiltered water remaining in the separation membrane tank and introduce the unfiltered water into the anoxic tank, and a second return line configured to return the unfiltered water remaining in the separation membrane tank to the deaeration tank.

10. The apparatus of claim 9 ,

further comprising a mixer mounted in the third flocculation reactor, wherein the mixer is configured to introduce carbon dioxide into the third flocculation reactor therethrough.

11. The apparatus of claim 9 ,

further comprising a first return line configured to return a portion of the sludge produced in the sedimentation tank to the first flocculation reactor.

12. The apparatus of claim 9 ,

wherein the separation membrane tank comprises a microfiltration membrane (MF) or an ultrafiltration membrane (UF).

13. The apparatus of claim 9 ,

wherein the reverse-osmosis membrane unit comprises a brackish water reverse-osmosis membrane or a seawater reverse-osmosis membrane.