JP2013078712A - Device and method for treating organic wastewater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent biofouling of a reverse osmosis membrane at low cost in a water treatment device whereby biologically-treated water containing ammoniacal nitrogen is treated using a reverse osmosis membrane unit.SOLUTION: A chlorinated chemical agent such as sodium hypochlorite is added to biologically-treated water containing ammoniacal nitrogen to react the ammoniacal nitrogen with the chlorinated chemical agent for 3 min or more in a water storage tank. Chloramine is generated so that an effective chlorine concentration becomes 2 ppm or more in the biologically-treated water, and the biologically-treated water containing chloramine is supplied to the reverse osmosis membrane unit.

Description

  The present invention relates to a water treatment apparatus and a water treatment method in which organic wastewater such as sewage or industrial wastewater is biologically treated and then subjected to membrane treatment using a reverse osmosis membrane (RO membrane) device. The present invention relates to a water treatment apparatus and a water treatment method that can prevent fouling (biological degradation) at low cost.

  A wastewater containing organic matter such as sewage or industrial wastewater (organic wastewater) is generally treated by decomposing the contained organic matter by biological treatment such as an activated sludge method. In the conventional activated sludge method, the treated water after biological treatment is generally settled at the final sedimentation site as a solid-liquid separation means, but in recent years, a membrane separation device has been used as the solid-liquid separation means. The method of doing is also widespread.

  The RO membrane device can desalinate the water to be treated, and can obtain high-quality treated water. For this reason, when RO membrane apparatus is used as a membrane separation apparatus, the treated water can be utilized as drinking water, industrial water, or agricultural water.

  When pretreatment water after biological treatment is processed by the RO membrane device, fouling that clogs the RO membrane due to organic components or inorganic components contained in the treated water becomes a problem. In particular, when microorganisms using organic components or inorganic components contained in treated water after biological treatment as nutrients grow, structures called biofilms are formed on the RO membrane surface by the microorganisms or secretions thereof. The Since this biofilm is firmly attached to the surface of the RO membrane and has resistance to chemical substances, complete removal is difficult.

  When biofouling in which a biofilm is formed on the RO membrane of the RO membrane device occurs, the membrane differential pressure increases, the load on the water pump increases, and the RO membrane permeation rate decreases. For this reason, chemical cleaning of the RO membrane is required.

  However, a high concentration of sodium hypochlorite has a problem that the material of the RO membrane, in particular, the polyamide polymer RO membrane used as a high performance RO membrane is likely to be deteriorated by sodium hypochlorite. .

  As a disinfectant that can be sterilized at all times, a technique of adding an organically bound chlorine compound such as chloramine to water to be treated has been proposed. For example, Patent Document 1 uses any effect before the pretreatment water that has undergone the pretreatment is stored in the water storage tank in order to prevent biofouling during operation of the RO membrane device using the effect of inhibiting microbial growth by chloramine. A water treatment method and a water treatment method for adding chloramine to the flow path are disclosed.

  Patent Document 2 measures the concentration of ammonia nitrogen in the permeated water of a membrane separation device, adjusts the dilution rate of the sodium hypochlorite aqueous solution using the concentration as an index, and performs reverse washing of the membrane of the membrane separation device. A method and cleaning apparatus are disclosed.

JP 2008-29963 A JP 2007-275870 A

  In the invention disclosed in Patent Document 1, chloramine is added from the outside as a bactericidal component, but a biofouling inhibitor mainly composed of chloramine marketed by a pharmaceutical manufacturer is a relatively expensive drug. Chloramine also has the property of being easily decomposed by light. Furthermore, the invention disclosed in Patent Document 2 is an invention related to backwashing, and biofouling cannot be prevented during operation of the RO membrane device.

  An object of the present invention is to provide a water treatment apparatus and a water treatment method capable of preventing biofouling of an RO membrane at a low cost during operation of the RO membrane device.

  Ammonia nitrogen remains in the pretreated water after the organic wastewater is pretreated. If the present inventors add a chlorinated compound to the pretreated water, it becomes possible to generate chloramine in the water treatment apparatus, and continuously prevent biofouling of the reverse osmosis membrane at a low cost. I found that it was possible. In addition, when the ammonia concentration in the pretreatment water is high, the present inventors add chlorinated chemicals to the water to be treated to produce chloramine, and when the ammonia concentration in the pretreatment water is low, Furthermore, it has been found that if an ammonia-based drug is also added, biofouling of the reverse osmosis membrane can be prevented while suppressing the amount of the drug to be used to the minimum necessary, and the present invention has been completed.

Specifically, the organic wastewater treatment apparatus of the present invention comprises:
A pretreatment device for treating organic wastewater;
A water storage tank for storing the pretreated water treated by the pretreatment device;
A chlorine supply device for supplying an inorganic chlorine-based chemical to the water tank;
An ammonia supply device for supplying an ammonia-based chemical to the water tank;
A reverse osmosis membrane device for membrane separation of pretreated water supplied from the water tank,
Producing chloramines at a predetermined concentration by supplying an inorganic chlorine-based chemical and / or an ammonia-based chemical to the pretreated water in the water tank;
Biofouling of the reverse osmosis membrane is prevented by supplying pretreatment water containing the chloramines to the reverse osmosis membrane device.

In addition, the organic wastewater treatment method of the present invention includes:
A pretreatment process for pretreating organic wastewater;
A water storage process for storing pretreated pretreated water in a water tank;
A chlorine supply step of supplying an inorganic chlorine-based chemical to the water tank;
An ammonia supply step for supplying an ammonia-based chemical to the water tank;
The chlorine supply step and / or the ammonia supply step is performed for 3 minutes or longer, and a chloramine generation step for generating chloramines at a predetermined concentration in the stored pretreated water,
A biofouling prevention step for preventing biofouling of the reverse osmosis membrane by supplying the pretreatment water containing the chloramines to the reverse osmosis membrane device and performing membrane separation;
It is characterized by having.

  Compared to chloramine, inorganic chlorinated drugs such as sodium hypochlorite or ammonium salts such as ammonium sulfate are less expensive. In the present invention, chloramine is not added from the outside to the pretreated water, but by reacting ammoniacal nitrogen contained in the pretreated water with an inorganic chlorine-based chemical added to the pretreated water, Since chloramine is produced in the pretreated water, degradation of chloramine is not a problem, and the cost of the drug is low.

  Even if inorganic chlorine-based chemicals are added to pretreated water containing ammonia nitrogen, chloramine is not generated immediately, so inorganic chlorine-based chemicals are added to the pretreated water immediately before being supplied to the reverse osmosis membrane device. However, it is difficult to effectively prevent biofouling of reverse osmosis membranes. However, in the present invention, since pretreatment water is stored in a water tank and an inorganic chlorine-based chemical and / or ammonia-based chemical is supplied for 3 minutes or longer, chloramines are generated in the pretreated water at an effective concentration. It is possible. By supplying the pretreated water containing the chloramines to the reverse osmosis membrane device, biofouling of the reverse osmosis membrane can be effectively prevented.

  In the present invention, the chloramine concentration in the pretreatment water supplied to the reverse osmosis membrane device is 2 ppm or more, more preferably 5 ppm or more as an effective chlorine concentration, thereby suppressing the growth of microorganisms and biofau of the reverse osmosis membrane. The ring can be effectively prevented.

The organic wastewater treatment apparatus of the present invention comprises:
A flow meter for measuring a flow rate of pretreatment water supplied to the water tank;
An ammoniacal nitrogen concentration measuring device for measuring the ammoniacal nitrogen concentration of the pretreated water;
It is preferable to further include a control device that controls the supply amount of the inorganic chlorine-based chemical and / or the ammonia-based chemical to the water storage tank based on the measurement results of the flow meter and the ammonia nitrogen concentration measuring device.

Similarly, the organic wastewater treatment method of the present invention comprises:
A measurement step of measuring a flow rate of pretreatment water supplied to the water storage tank and an ammonia concentration of the pretreatment water supplied to the water storage tank;
A supply amount control step of controlling the supply amount of the inorganic chlorine-based chemical and / or the ammonia-based chemical to the water storage tank based on the flow rate of pretreatment water and the ammoniacal nitrogen concentration measured in the measurement step. It is preferable.

  When the ammoniacal nitrogen concentration in the pretreated water is high, the chloramine concentration in the pretreated water can be maintained at a certain concentration or higher by adding a theoretical amount of an inorganic chlorine-based chemical. However, when the concentration of ammoniacal nitrogen in the pretreatment water is low, the concentration of chloramine in the pretreatment water in the water storage tank cannot be maintained above a certain level even if the amount of inorganic chlorine-based chemical added is increased. Therefore, the flow rate of pretreatment water supplied to the water tank and the ammonia nitrogen concentration are measured, and when the ammonia nitrogen concentration is low, an ammonia-based chemical is added to the water tank according to the pretreatment water flow rate, It is preferable that the chloramine concentration in the pretreatment water in the water storage tank is a certain concentration or more.

The organic wastewater treatment apparatus of the present invention comprises:
It is preferable to further include a return path for returning the concentrated water of the reverse osmosis membrane device to the pretreatment device.

Similarly, the organic wastewater treatment method of the present invention comprises:
It is preferable to further include a recovery step of returning the concentrated water of the reverse osmosis membrane device to the pretreatment device that performs the pretreatment step.

  The pretreatment water containing chloramine supplied to the reverse osmosis membrane device is divided into permeated water and concentrated water. The permeated water is used as drinking water, industrial water or agricultural water, but the concentrated water is returned to the pretreatment device.

In the processing apparatus and processing method of the present invention,
The inorganic chlorinated drug is preferably sodium hypochlorite, and the ammonia-based drug is preferably ammonium sulfate.

  This is because these drugs are cheaper than chloramine and are easily available.

  According to the treatment apparatus and the treatment method of the present invention, since chloramine is generated using ammonia contained in the pretreatment water supplied to the reverse osmosis membrane apparatus, for preventing biofouling of the reverse osmosis membrane apparatus. The cost can be kept low.

The schematic block diagram explaining an example of the water treatment apparatus of this invention is shown.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following description.

  FIG. 1 is a schematic configuration diagram illustrating an example of the water treatment apparatus of the present invention. Sewage (organic wastewater) such as domestic wastewater is supplied to the biological treatment device 2 (pretreatment device) via the path 1 and pretreated. A specific example of the biological treatment apparatus 2 is an activated sludge tank or a sand filtration tank. By the biological treatment apparatus 2, organic substances contained in the sewage are aerobically decomposed by microorganisms. When the biological treatment apparatus 2 is an activated sludge tank, excess sludge is appropriately discharged from the path 16 to the outside.

  The pretreated water pretreated by the biological treatment apparatus 2 is supplied to the water storage tank 7 via the path 3 and stored therein. In the path 3, a flow meter 4 and an ammonia nitrogen concentration meter 5 (ammonia nitrogen concentration measuring device) are provided, and the flow meter 4 and the ammonia nitrogen concentration meter 5 are electrically connected to the control device 6. ing. The control device 6 is electrically connected to the pump P1 of the inorganic chlorine-based chemical tank 8, and controls on / off or output of the pump P1 and the pump P2.

  The inorganic chlorine-based chemical tank 8 stores an inorganic chlorine-based chemical such as a sodium hypochlorite aqueous solution. The inorganic chlorine-based chemical in the inorganic chlorine-based chemical tank 8 is injected from the passage 10 into the water storage tank 7 by the pump P1. The chlorine supply device 17 includes an inorganic chlorine-based chemical tank 8 in which the inorganic chlorine-based chemical is stored, and a pump P1 that supplies this inorganic chlorine-based chemical to the water storage tank 7. The ammonia-based drug tank 9 stores an ammonia-based drug such as an ammonium sulfate aqueous solution. The ammonia-based drug in the ammonia-based drug tank 9 is injected from the path 11 into the water tank 7 by the pump P2. The ammonia supply device 18 includes an ammonia-based chemical tank 9 in which the ammonia-based chemical is stored, and a pump P <b> 2 that supplies the ammonia-based chemical to the water storage tank 7.

  If ammoniacal nitrogen is contained in the pretreatment water in the water tank 7, chloramine is generated by the reaction shown in the following chemical formula when an aqueous sodium hypochlorite solution is added to the water tank 7 as an inorganic chlorine-based chemical. . Since this reaction is not completed instantaneously, in the present invention, an inorganic chlorinated chemical is injected into the water tank 7, and after 3 minutes or more has passed, the pretreated water in the water tank 7 is passed through the route 12 to the RO membrane. It supplies to the apparatus 13 (reverse osmosis membrane apparatus). At this time, it is preferable to stir the pretreatment water in the water tank 7. A pump P <b> 3 is provided in the path 12, and the pretreated water in the path 12 is boosted to a water pressure suitable for the operating conditions of the RO membrane device 13 and supplied to the RO membrane device 13.

  In the above chemical formula, theoretically, 1 mol of chloramines is produced from 1 mol of ammonia and 1 mol of sodium hypochlorite. However, in practice, the number of moles of ammonia is preferably at least twice the number of moles of sodium hypochlorite so that sodium hypochlorite does not remain in the pretreated water.

  In order to effectively prevent biofouling of the RO membrane of the RO membrane device 13, the chloramine concentration in the pretreated water supplied via the route 12 is set to 2 ppm or more, more preferably 5 ppm or more as the effective chlorine concentration. . If the ammonia concentration in the pretreatment water flowing through the path 3 is 2 ppm or more, the effective chlorine concentration in the pretreatment water in the water tank 7 is 2 ppm based on the measured values of the flow meter 4 and the ammonia nitrogen concentration meter 5. Thus, the control device 7 controls the amount of the inorganic chlorine-based chemical supplied from the path 10 to the water tank 7 by adjusting the output of the pump P1.

  The permeated water of the RO membrane device 13 is supplied from the path 14 to the outside and used as drinking water, industrial water, or agricultural water. Depending on the quality of the permeated water, further advanced treatment can be performed.

  On the other hand, the concentrated water of the RO membrane device 13 is returned to the biological treatment device 2 via the return path 15.

  Since the concentrated water to be returned contains inorganic salts, if the operation of the water treatment device is continued, the concentration of inorganic salts in the biological treatment device 2 increases, but excess sludge is discharged from the path 16 to the outside. In this case, inorganic salts can be discharged together.

  Here, if the concentration of ammoniacal nitrogen in the biologically treated water flowing through the path 3 is less than 2 ppm, the pretreated water in the water tank is supplied even if the chlorine based chemical is supplied from the inorganic chlorine based chemical tank 8 to the water tank 7. Chloramine cannot be made to have a chlorine concentration of 2 ppm or more. In such a case, based on the measured values of the flow meter 4 and the ammonia nitrogen concentration meter 5, the path 11 is connected to the water tank 7 so that the ammonia nitrogen concentration in the pretreated water in the water tank 7 is 2 ppm or more. The amount of the ammonia-based chemical supplied is controlled by the control device 7 by turning on / off the pump P2 or adjusting the output.

  At the same time, the control device 7 turns on / off the pump P1 to control the amount of inorganic chlorine-based chemicals supplied from the passage 10 to the water tank 7 so that the effective chlorine concentration in the pretreatment water in the water tank 7 is 2 ppm or more. Alternatively, control is performed by adjusting the output.

  In addition, in FIG. 1, the case where the supply amount of the inorganic chlorine type | system | group chemical | medical agent and / or ammonia type chemical | medical agent to the water tank 7 was controlled by controlling on / off of the pump P1 and the pump P2 or an output was demonstrated. However, the supply amount of the inorganic chlorine-based chemical and / or the ammonia-based chemical to the water tank 7 may be controlled by providing valves in the paths 10 and 11 and controlling the opening and closing of the valves.

(Concrete example)
When the effective chlorine concentration in the biologically treated water supplied to the RO membrane device is 2 ppm, the molar concentration of chloramines in the pretreated water is 2 / 35.5 × 10 ⁻³ = 5.63 × 10 ⁻⁵ mol / L. In this case, the amount of chloramine per 1 m ^{3 of} biologically treated water is 5.63 × 10 ^-2 mol.

When sodium hypochlorite is used as an inorganic chlorine-based chemical and ammonium sulfate is used as an ammonia-based chemical, sodium hypochlorite used per 1 m ^{3 of} pretreatment water supplied to the RO membrane device is 5.63 × 10 ^-2 × (23 + 35.5 + 16) = 4.20 g, and ammonium sulfate is 5.63 × 10 ⁻² × ((14 + 1 × 4) × 2 + 32 + 16 × 4) = 7.44 g. The amount used in the RO treatment facility with a daily treatment water volume of 10,000 tons is 42.0 kg of sodium hypochlorite and 74.4 kg of ammonium sulfate. If the market price is 12% sodium hypochlorite 28 yen / kg and ammonium sulfate 30 yen / g, the drug cost per day is calculated as (42.0 / 0.12 × 28) + (74.4 × 30) = 12024 yen . If the ammonia concentration in the pretreated water is 1.5 ppm or more, it is not necessary to add ammonium sulfate.

On the other hand, in the present invention, since ammonia (ammonium salt) contained in the pretreatment water is used, if the ammonia concentration in the biological treatment water supplied to the RO membrane device is 3 mg / L, the molar concentration of ammonia is 3 /1000/14=2.14×10 ⁻⁴ mol / L, which is more than 5.63 × 10 ⁻² mol / L, which is the required concentration of chloramines to achieve an effective chlorine concentration of 2 ppm, so the addition of ammonium sulfate is unnecessary It becomes. Therefore, in this case, the chemical cost in the treatment facility with a daily treatment water amount of 10,000 t is calculated as only sodium hypochlorite cost 42.0 / 0.12 × 28 = 9800 yen.

Moreover, the chloramine formulation marketed as a biofouling prevention agent is added by the density | concentration of 10-20 ppm according to the quality of the pretreatment water supplied to RO membrane apparatus. In the case of adding an intermediate value of 15 ppm, the chloramine preparation used per 1 m ^{3 of} pretreated water is 15/1000 × 1000 = 15 g. The amount of water used in an RO treatment facility with a daily treatment water volume of 10,000 tons is 150 kg, and if the market price is 300 yen / kg, the drug cost per day is 150 x 300 = 45000 yen.

  Thus, in the present invention, compared to the case where the chloramine preparation is added from the outside, the drug cost is 1/4 or less when the effective chlorine concentration in the pretreatment water supplied to the RO membrane device is the same 2 ppm. Can be reduced.

  The treatment apparatus and treatment method for organic wastewater of the present invention are useful in the field of treatment of wastewater containing organic matter.

1, 3, 10, 11, 12, 14: Path 2: Biological treatment device (pretreatment device)
4: Flow meter 5: Ammonia nitrogen concentration meter (ammonia nitrogen concentration measuring device)
6: Control device 7: Water tank 8: Inorganic chlorine-based chemical tank 9: Ammonia-based chemical tank 13: RO membrane device (reverse osmosis membrane device)
15: Return path 17: Chlorine supply device 18: Ammonia supply device P1, P2, P3: Pump

Claims (8)

An organic wastewater treatment device,
A pretreatment device for treating organic wastewater;
A water storage tank for storing the pretreated water treated by the pretreatment device;
A chlorine supply device for supplying an inorganic chlorine-based chemical to the water tank;
An ammonia supply device for supplying an ammonia-based chemical to the water tank;
A reverse osmosis membrane device for membrane separation of pretreated water supplied from the water tank,
Producing chloramines at a predetermined concentration by supplying an inorganic chlorine-based chemical and / or an ammonia-based chemical to the pretreated water in the water tank;
An organic wastewater treatment apparatus that prevents biofouling of a reverse osmosis membrane by supplying pretreatment water containing the chloramines to the reverse osmosis membrane device. A flow meter for measuring a flow rate of pretreatment water supplied to the water tank;
An ammoniacal nitrogen concentration measuring device for measuring the ammoniacal nitrogen concentration of the pretreated water;
The apparatus according to claim 1, further comprising: a control device that controls a supply amount of the inorganic chlorine-based chemical and / or the ammonia-based chemical to the water storage tank based on a measurement result of the flow meter and the ammonia nitrogen concentration measuring device. The organic wastewater treatment apparatus as described.   The organic wastewater treatment device according to claim 1, further comprising a return path for returning the concentrated water of the reverse osmosis membrane device to the pretreatment device.   The organic wastewater treatment apparatus according to any one of claims 1 to 3, wherein the inorganic chlorine-based chemical is sodium hypochlorite and the ammonia-based chemical is ammonium sulfate. A method for treating organic wastewater,
A pretreatment process for pretreating organic wastewater;
A water storage process for storing pretreated pretreated water in a water tank;
A chlorine supply step of supplying an inorganic chlorine-based chemical to the water tank;
An ammonia supply step for supplying an ammonia-based chemical to the water tank;
The chlorine supply step and / or the ammonia supply step is performed for 3 minutes or longer, and a chloramine generation step for generating chloramines at a predetermined concentration in the stored pretreated water,
A biofouling prevention step for preventing biofouling of the reverse osmosis membrane by supplying the pretreatment water containing the chloramines to the reverse osmosis membrane device and performing membrane separation;
A method for treating organic wastewater, comprising: A measurement step of measuring a flow rate of pretreatment water supplied to the water storage tank and an ammonia concentration of the pretreatment water supplied to the water storage tank;
A supply amount control step of controlling the supply amount of the inorganic chlorine-based chemical and / or the ammonia-based chemical to the water tank based on the flow rate of pretreatment water and the ammoniacal nitrogen concentration measured by the measurement step;
The processing method of the organic waste water of Claim 5 further provided.   The method for treating organic wastewater according to claim 5 or 6, further comprising a recovery step of returning the concentrated water of the reverse osmosis membrane device to a pretreatment device that performs the pretreatment step.   The method for treating organic wastewater according to any one of claims 5 to 7, wherein the inorganic chlorine-based chemical is sodium hypochlorite and the ammonia-based chemical is ammonium sulfate.

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