JP6877255B2 - Wastewater treatment system and wastewater treatment method - Google Patents

Description

The present invention relates to a wastewater treatment system and a wastewater treatment method for reducing the volume of excess sludge generated by biological treatment of organic wastewater by using ozone.

As a method for treating organic wastewater, treatment using microorganisms such as the standard activated sludge method is widely used. In the treatment using microorganisms, the microorganisms proliferate with the treatment to generate excess sludge containing activated sludge and other suspended matter. Excess sludge is sludge that is unnecessary for water treatment, so it is incinerated as industrial waste and disposed of in landfill. Disposal of such surplus sludge requires a large amount of energy and cost, including securing of new land, and therefore, reduction of the amount of surplus sludge generated is required.

As one of the methods for reducing the amount of excess sludge generated, sludge volume reduction treatment using ozone is known. This is a process of solubilizing excess sludge containing microorganisms and the like by decomposing it with ozone to reduce the volume of excess sludge. The effect of reducing the volume of excess sludge, that is, the effect of reducing the volume of sludge, varies depending on the amount of excess sludge treated and the amount of ozone used. If the amount of excess sludge treated or the amount of ozone used is insufficient, the expected sludge volume reduction effect cannot be obtained. On the contrary, if the amount thereof is too large, the microorganisms are decomposed more than necessary and the microbial activity contributing to the wastewater treatment is lowered, so that the water quality of the treated water may be deteriorated.

Therefore, in the wastewater treatment system, a method of controlling the amount of excess sludge to be treated or the amount of ozone used to be an appropriate value is being studied. For example, in Patent Document 1, the retained sludge amount in the system is calculated from the sludge concentration and the mixed liquid amount of the mixed liquid in the biological treatment tank, and the sludge concentration and the separated sludge amount of the separated sludge in the solid-liquid separation tank, and the retained sludge is obtained. The amount of modified sludge is increased or decreased based on the difference between the amount and the target retained sludge amount, and the set amount of sludge drawn from the mixed solution or separated sludge is increased or decreased.

Further, in Patent Document 2, the efficiency of biological treatment is improved and ozone treatment is performed by controlling the amount of returned sludge so that a predetermined concentration of MLSS (Mixed Liquid Suspended Solids) is always maintained in the biological treatment tank. The load on the is reduced. Further, in Patent Document 3, it is determined whether or not advanced treatment is necessary based on the water quality data of wastewater or effluent, and if necessary, the operating conditions of the ozone generator are determined based on the water quality and the amount of water. ing.

Japanese Unexamined Patent Publication No. 2007-253011 Japanese Unexamined Patent Publication No. 9-99292 Japanese Unexamined Patent Publication No. 7-251186

As described above, various control methods have been studied so that the amount of excess sludge treated and the amount of ozone used are appropriate values, but the amount of excess sludge generated is the amount of organic wastewater flowing into the biological treatment tank. Since it fluctuates with changes in water quantity, water quality, temperature, etc., the optimum sludge volume reduction effect can be obtained while satisfying preset water quality standards for discharged water (for example, discharged water quality standards set in each country). It was difficult to control the amount of ozone used.

In Patent Document 1, the amount of retained sludge in the system is monitored and an appropriate amount of drawn sludge is set, but the amount of ozone injected into the drawn sludge is not controlled. Further, in Patent Document 2, the treatment amount is determined so as to maintain the MLSS in the biological treatment tank at a predetermined concentration, but the ozone usage amount is not controlled, and 10% to 20% per sludge SS weight. Is only stated to be suitable.

Therefore, the methods described in Patent Documents 1 and 2 cannot cope with fluctuations in the amount of ozone required for decomposition of activated sludge when the water quality such as COD (Chemical oxygen demand) in the biological treatment tank changes. , It is difficult to meet the effluent quality standards. Further, even if the effluent quality standard can be satisfied, there is a possibility that ozone is excessively supplied, which causes a problem of high cost.

Further, in Patent Document 3, the operating conditions of the ozone generator are determined based on the water quality data of wastewater or discharged water, but this method cannot determine the amount of ozone used according to the amount of excess sludge that fluctuates. It is difficult and it is difficult to obtain the optimum sludge volume reduction effect. Further, in these Patent Documents 1-3, no measures are taken to improve the ozone treatment efficiency, and there is a problem that the amount of ozone used increases and the running cost increases.

The present invention has been made to solve the above-mentioned problems, and even if the amount of excess sludge generated fluctuates, the sludge that stably satisfies the preset water quality standard of the discharged water and is the optimum sludge. It is an object of the present invention to obtain a wastewater treatment system and a wastewater treatment method capable of controlling the amount of ozone used so as to obtain a volume reduction effect.

The wastewater treatment system according to the present invention includes a biological treatment tank that biologically treats organic wastewater under aerobic conditions to generate sludge-containing treated water containing active sludge, and a sludge-containing treatment that is generated in the biological treatment tank. A solid-liquid separation unit that separates water into concentrated sludge and treated water, sludge-containing treated water generated in a biological treatment tank, or concentrated sludge separated in the solid-liquid separation unit is extracted at a predetermined sludge withdrawal flow rate for ozone treatment. The ozone reaction section that returns the treated sludge-containing treated water or concentrated sludge to the biological treatment tank, the ozone generator that generates ozone and supplies it to the ozone reaction section, and the sludge-containing treated water in the biological treatment tank. A sludge concentration measuring means for measuring the sludge concentration of the mixed liquid containing the mixture, a water quality measuring means for measuring the water quality data excluding the sludge concentration of each of the mixed liquid, the treated water, and the discharged water obtained by disinfecting the treated water, and the sludge of the mixed liquid. The sludge withdrawal flow rate is determined based on the concentration, the amount of ozone used in the ozone treatment is determined based on the product of the sludge concentration of the mixed solution and the sludge withdrawal flow rate, and the mixed solution and treated water measured by the water quality measuring means, respectively. It is provided with a calculation and control device for adjusting the sludge withdrawal flow rate and the amount of ozone used based on the water quality data of any one or more of the discharged water.

Further, the wastewater treatment method according to the present invention includes a biological treatment step of biologically treating organic wastewater under aerobic conditions to generate sludge-containing treated water containing active sludge, and a sludge produced in the biological treatment step. The sludge concentration of each of the solid-liquid separation step of separating the contained treated water into concentrated sludge and treated water, the mixed solution containing sludge-containing treated water generated in the biological treatment step, the treated water, and the discharged water obtained by disinfecting the treated water. A modification to perform ozone treatment by extracting sludge-containing treated water generated in the biological treatment process or concentrated sludge separated in the solid-liquid separation process at a predetermined sludge withdrawal flow rate in the water quality data acquisition process for acquiring water quality data excluding and a quality process, in the reforming step, based on the sludge concentration in the mixed-solution determines the sludge withdrawal rate, to determine the ozone consumption in the ozone processing based on the product of sludge concentration and sludge withdrawal rate of the mixture together, mixture, process water, and adjusts the sludge withdrawal rate and ozone usage based on any one or more of the water quality data of the flowing water release及beauty.

According to the wastewater treatment system according to the present invention, the amount of ozone used in the ozone treatment is determined based on the product of the sludge concentration of the mixed liquid in the biological treatment tank and the sludge extraction flow rate, and further, the mixed liquid, the treated water, and the discharged water are determined. By adjusting the sludge withdrawal flow rate and the amount of ozone used based on any one or more of the water quality data, the amount of organic wastewater flowing into the biological treatment tank, the amount of excess sludge generated due to fluctuations in water quality and temperature. It is possible to control the amount of ozone used so that the preset water quality standard of discharged water can be stably satisfied and the optimum sludge volume reduction effect can be obtained even if there is a fluctuation in the amount of sludge.

Further, according to the wastewater treatment method according to the present invention, the amount of ozone used in the ozone treatment is determined based on the product of the sludge concentration of the mixed liquid in the biological treatment step and the sludge extraction flow rate, and the mixed liquid, the treated water, and the discharge are further determined. Since the sludge withdrawal flow rate and the amount of ozone used are adjusted based on the water quality data of any one or more of the water, the surplus due to the fluctuation of the amount, water quality, and temperature of the organic waste water flowing into the biological treatment process. Even if the amount of sludge generated fluctuates, it is possible to control the amount of ozone used so that the preset water quality standard of discharged water can be stably satisfied and the optimum sludge volume reduction effect can be obtained.

It is a schematic diagram which shows the structure of the wastewater treatment system which concerns on Embodiment 1 of this invention. It is a figure which shows the method of determining the sludge withdrawal flow rate and ozone use amount in the wastewater treatment system which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the structure of the wastewater treatment system which concerns on Embodiment 2 of this invention. It is a figure which shows the relationship between the ozone concentration and the convergence value of the ozone injection amount. It is a schematic diagram which shows the structure of the wastewater treatment system which concerns on Embodiment 3 of this invention.

Embodiment 1.
Hereinafter, the wastewater treatment system and the wastewater treatment method according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view showing a configuration of a wastewater treatment system according to the first embodiment. The wastewater treatment system according to the first embodiment includes a biological treatment tank 1, an air diffuser 2, a solid-liquid separation tank 7, a disinfection pond 8, an ozone reaction tank 9, an ozone generator 12, and the like. In FIG. 1, W1 is wastewater to be treated, W2 is sludge-containing treated water, W3 is treated water, and W4 is discharged water.

Further, the wastewater treatment method according to the first embodiment mainly includes a biological treatment step, a solid-liquid separation step, and a reforming step. In the biological treatment step, the organic wastewater W1 is biologically treated under aerobic conditions to produce sludge-containing treated water W2 containing activated sludge. In the solid-liquid separation step, the sludge-containing treated water W2 produced in the biological treatment step is separated into concentrated sludge and treated water W3. Further, in the reforming step, the sludge-containing treated water W2 (or the concentrated sludge separated in the solid-liquid separation step) generated in the biological treatment step is drawn out at a predetermined sludge withdrawal flow rate to perform ozone treatment.

In carrying out these steps, the sludge withdrawal flow rate is determined based on the sludge concentration of the mixed liquid containing the sludge-containing treated water W2 in the biological treatment step, and in the ozone treatment based on the product of the sludge concentration of the mixed liquid and the sludge withdrawal flow rate. Determine the amount of ozone used. Further, the sludge extraction flow rate and the amount of ozone used are adjusted based on the water quality data of any one or more of the mixed liquid, the treated water W3, and the discharged water W4.

The treatment and operation in each part constituting the wastewater treatment system according to the first embodiment will be described. The biological treatment tank (aeration tank) 1 biologically treats the wastewater W1 under aerobic conditions to generate sludge-containing treated water W2 containing activated sludge mainly composed of aggregates of aerobic microorganisms. That is, a mixed liquid of wastewater W1 and sludge-containing treated water W2 exists in the biological treatment tank 1, and the ratio of sludge-containing treated water W2 in the mixed liquid increases as the biological treatment progresses.

The air diffuser 2 supplies the air sent from the air supply device 3 into the biological treatment tank 1, and sets the biological treatment tank 1 as an aerobic condition. As the air supply device 3, a blower, a compressor, or the like is used depending on the required amount of air supply. Further, a sludge concentration measuring device 4 which is a sludge concentration measuring means is installed in the biological treatment tank 1 to measure the sludge concentration of the mixed solution in the biological treatment tank 1. Further, a water quality measuring device 5a, which is a water quality measuring means, is installed in the biological treatment tank 1 to measure the water quality of the mixed liquid in the biological treatment tank 1.

The sludge-containing treated water W2 generated in the biological treatment tank 1 is transferred to the solid-liquid separation tank 7 which is a solid-liquid separation portion via the pipe 6a. As the solid-liquid separation tank 7, a terminal sedimentation tank, a membrane separation tank, or the like is used, and the sludge-containing treated water W2 produced in the biological treatment tank 1 is separated into concentrated sludge and treated water W3. A part of the separated concentrated sludge is returned to the biological treatment tank 1 via the pipe 6b for returning the concentrated sludge. A pump (not shown) for returning concentrated sludge is connected to the pipe 6b.

The treated water W3 separated from the concentrated sludge in the solid-liquid separation tank 7 is transferred to the disinfection pond 8 via the pipe 6c. A water quality measuring device 5b for measuring the water quality of the treated water W3 is installed in the pipe 6c. The treated water W3 is disinfected in the disinfection pond 8 and then discharged as discharged water W4 to a river or the like via a pipe 6d. The discharged water W4 must meet the water quality standards of the discharged water (in the case of Japan, the discharged water quality standards specified by the Sewerage Act, etc.), and the water quality of the discharged water W4 is measured in the pipe 6d. A water quality measuring instrument 5c is installed.

Further, in order to reduce the volume of excess sludge in the biological treatment tank 1, the sludge-containing treated water W2 in the biological treatment tank 1 is drawn out through the sludge extraction pipe 6e. A sludge flow meter 10a and a sludge extraction pump 11a for measuring the sludge extraction flow rate are installed in the pipe 6e. The sludge-containing treated water W2 extracted is subjected to ozone treatment in the ozone reaction section, and excess sludge containing microorganisms and the like is decomposed. The ozone reaction unit includes an ozone reaction tank 9, a pipe 6 g for circulating sludge-containing treated water drawn from the biological treatment tank 1, and an ejector 17 for injecting ozone into the sludge-containing treated water.

The "sludge treatment ratio", which is the quotient obtained by dividing the amount of ozone-treated sludge per day by the amount of excess sludge generated per day, is determined by the sludge extraction flow rate measured by the sludge flow meter 10a. The sludge extraction pump 11a extracts the sludge-containing treated water W2 at a sludge extraction flow rate determined so as to have a set sludge treatment ratio, and transfers it to the ozone reaction tank 9. The size of the sludge extraction pump 11a is determined by the sludge extraction flow rate calculated from the amount of excess sludge generated, the sludge treatment ratio, the number of sludge treatments per day, the installation position of the sludge extraction pump 11a, and the pressure loss of the pipe 6e. Etc. are determined.

A sludge return pipe 6f is connected to the lower part of the ozone reaction tank 9, and the sludge-containing treated water after ozone treatment is returned to the biological treatment tank 1. A pump or the like may be used to return the sludge-containing treated water, but when the ozone reaction tank 9 is arranged above the biological treatment tank 1, it can be returned by free fall. The method of setting the sludge treatment ratio and the sludge extraction flow rate will be described in detail later with reference to the flowchart of FIG.

The ozone generator 12 applies a high AC voltage between the opposing electrodes via a dielectric to continuously generate a discharge, and oxygen is passed through the discharge space to generate ozone gas. A general ozone concentration meter (not shown) is used for measuring the concentration of ozone generated by the ozone generator 12. The ozone concentration meter may be installed in the ozone injection pipe 14a or may be incorporated in the ozone generator 12. The ozone flow rate is measured by an ozone gas flow meter 16 installed in the pipe 14a.

A power supply device, a raw material supply device, and a cooling device (all not shown) are connected to the ozone generator 12. The raw material of ozone supplied to the ozone generator 12 is not particularly limited, but in addition to liquid oxygen, oxygen generated by PSA (Pressure Swing Adsorption) or PVSA (Pressure Vacuum Swing Adsorption) can be used. .. Further, in order to maintain the ozone generation efficiency, an additional gas supply unit may be provided to which 0.05% to 0.5% of nitrogen, air, or the like is added depending on the oxygen flow rate to be supplied.

The cooling device for cooling the ozone generator 12 includes a refrigerant circulation pump that circulates the cooling medium and a cooler that cools the cooling medium that has absorbed the heat generated by the ozone generator 12. As the cooler, a heat exchanger, a chiller, a refrigerator or the like can be used. As the cooling medium, in addition to tap water, ion-exchanged water, antifreeze, scale remover, water mixed with a corrosion inhibitor, or the like can be used.

The ozone generated by the ozone generator 12 is introduced into the gas suction port of the ejector 17 via the ozone injection pipe 14a. The ejector 17 is installed in a sludge circulation pipe 6 g attached to the side surface of the ozone reaction tank 9, and ozone is injected into the sludge-containing treated water that is pulled out from the ozone reaction tank 9 and circulates in the pipe 6 g to make contact with the sludge-containing treated water. Let me. In addition to the ejector 17, a sludge flow meter 10b and a sludge circulation pump 11b are installed in the pipe 6g.

The sludge-containing treated water into which ozone is injected by the ejector 17 flows into the ozone reaction tank 9 from the lower part of the ozone reaction tank 9 to which the pipe 6 g is connected, and is used to draw the sludge-containing treated water from the biological treatment tank 1. Along with this, it moves upward and returns to the pipe 6g. By circulating the sludge-containing treated water in this way, a stirring effect can be obtained, and the reaction effect between sludge and ozone in the ejector 17 can be enhanced. The waste ozone accumulated in the ozone reaction tank 9 is transferred to the waste ozone decomposition device 18 via the ozone discharge pipe 14b. The waste ozone decomposition device 18 decomposes the waste ozone into oxygen and then releases it to the atmosphere.

The data storage device 19 stores data used for calculation and calculation by the control device 21, and in the first embodiment, at least a sludge concentration measuring device 4, a water quality measuring device 5a, 5b, 5c, and a sludge flow meter It stores data including the measured values of 10a, 10b, and the ozone gas flow meter 16. The data storage device 19 is signal-connected to the sludge concentration measuring device 4, the water quality measuring device 5a, 5b, 5c, the sludge flow meter 10a, 10b, and the ozone gas flow meter 16, respectively, and collects data including the measured values online. doing.

The experimental data input device 20 stores various experimental data including the sludge concentration, water quality, and the correlation data between the temperature and the amount of ozone used or the sludge volume reduction effect of the mixture. The experimental data input to the experimental data input device 20 assumes various situations, that is, sludge concentration, water quality, temperature, etc., for the wastewater W1, the mixed solution, the treated water W3, and the discharged water W4, and is actual or equivalent. It was obtained by conducting an ozone treatment experiment or a verification test on the generated sludge.

Specifically, correlation data between sludge concentration (MLSS or organic content concentration) of sludge-containing treated water and ozone usage or sludge volume reduction effect, COD of sludge-containing treated water, BOD (Biochemical oxygen demand), TOC (Total) Correlation data between water quality data such as Organic Carbon) and ozone usage or sludge volume reduction effect, ozone usage data for discharged water quality data or difference data between discharged water and discharged water quality standard, sludge-containing treated water or concentration Data on the concentration and amount of ozone injected with respect to the initial data such as sludge sludge concentration and COD, and organic substances with respect to the value of the gas-liquid flow rate ratio (ozone flow rate / sludge circulation flow rate, hereinafter referred to as G / L) of the ejector 17. Data such as fluctuations in index data (COD, absorbance, etc.) indicating biodegradability are input to the experimental data input device 20.

The calculation and control device 21 is signal-connected to the data storage device 19, the experimental data input device 20, the sludge extraction pump 11a, the sludge circulation pump 11b, and the ozone generator 12, respectively. The calculation and control device 21 acquires data necessary for the calculation from the data storage device 19 and the experimental data input device 20 and executes the calculation, and satisfies the discharge water quality standard and obtains the optimum sludge volume reduction effect. And determine the amount of ozone used. Further, the calculation and control device 21 controls the sludge extraction pump 11a, the sludge circulation pump 11b, and the ozone generator 12 so as to obtain the determined sludge extraction flow rate and ozone usage amount.

Next, a method of determining the sludge withdrawal flow rate and the ozone usage amount by the calculation and control device 21 will be described with reference to the flowchart of FIG. First, in step S1, the sludge concentration of the mixed solution in the biological treatment tank 1 measured by the sludge concentration measuring device 4 is acquired from the data storage device 19. Since the sludge in the biological treatment tank 1 has a high sedimentation property, the sludge concentration measurement by the sludge concentration measuring device 4 is performed by sufficiently using the mixed solution in the biological treatment tank 1 at the timing immediately before the sludge-containing treated water W2 is drawn out. It is done after stirring in. That is, the sludge concentration of the mixed solution measured by the sludge concentration measuring device 4 is substantially equal to the sludge concentration of the sludge-containing treated water W2.

Subsequently, in step S2, the sludge withdrawal flow rate is determined based on the sludge treatment ratio set in advance and the sludge concentration obtained in step S1. The sludge treatment ratio is set to an appropriate value according to the microbial load and the amount of excess sludge generated in the biological treatment tank 1, and is input to the experimental data input device 20.

If the sludge treatment ratio is less than 2.0, the amount of decomposition of microorganisms in the activated sludge by ozone treatment is not sufficient, and the amount of excess sludge may not be sufficiently reduced. Further, if it exceeds 4.0, the microorganisms in the activated sludge may be excessively decomposed by the ozone treatment, the microbial activity may decrease, and the water quality of the treated water W3 may deteriorate. Therefore, the value of the appropriate sludge treatment ratio is set to 2.0 or more and 4.0 or less, preferably 3.0 or less.

Subsequently, in step S3, the amount of ozone used in the ozone treatment is determined from the product of the sludge concentration of the mixed solution acquired in step S1 and the sludge withdrawal flow rate determined in step S2. Here, the amount of ozone used is determined from the product of the sludge concentration and the sludge withdrawal flow rate with reference to the data of the amount of ozone injected per fixed amount of sludge with respect to the preset sludge treatment ratio. The data of the ozone injection amount required for a certain amount of sludge is stored in the experimental data input device 20.

Next, in step S4, the water quality data of the mixed solution, the treated water W3, and the discharged water W4 measured by the water quality measuring instruments 5a, 5b, and 5c, respectively, are acquired from the data storage device 19. Subsequently, in step S5, from the correlation data between the sludge concentration and the ozone usage amount or the sludge volume reduction effect stored in the experimental data input device 20, and the correlation data between the water quality data and the ozone usage amount or the sludge volume reduction effect. , The sludge concentration acquired in step S1 and the correlation data related to the water quality data acquired in step S4 are referred to.

Specifically, the related correlation data for any one or more of the mixed liquid, the treated water W3, and the discharged water W4 acquired in step S4 is referred to, and the sludge withdrawal flow rate and ozone are based on the water quality data. Adjust the usage. For example, when the COD value of the water quality data of the mixed solution acquired in step S4 is higher than usual, the correlation data between the COD stored in the experimental data input device 20 and the ozone usage amount or the sludge volume reduction effect is extracted and referred to. To do.

Subsequently, in step S6, based on the referenced correlation data, the sludge concentration acquired in step S1 and the water quality data acquired in step S4 are subjected to appropriate sludge treatment ratios and ozone injection amount convergence values (normal values). ) Is calculated. The convergence value of the ozone injection amount is a value obtained by dividing the product of the ozone concentration and the ozone flow rate by the product of the sludge concentration of the sludge-containing treated water and the sludge extraction flow rate, and is represented by the following formula (1). ..

X = (C (O ₃ ) / F (O ₃ )) / (C (SS) / F (SS)) (1)
Here, X is the convergence value of the ozone injection amount (mgO ₃ / gSS), C (O ₃ ) is the ozone concentration (mgO ₃ / L), F (O ₃ ) is the ozone flow rate (L / min), and C (SS). ) Is the sludge concentration (gSS / L) of the sludge-containing treated water, and F (SS) is the sludge extraction flow rate (L / min).

The convergence value of the ozone injection amount sufficiently decomposes the sludge in the sludge-containing treated water, sufficiently decomposes the excess sludge in the biological treatment tank 1, and suppresses the increase of unreacted ozone due to the excessive ozone injection. From the viewpoint of the _{above, 20 mgO 3} / gSS or more and 50 mgO ₃ / gSS or less are preferable. In addition, the ozone concentration takes into consideration the ozone concentration that can be generated by the current ozone generator 12, improves the biodegradability of sludge in the sludge-containing treated water, and promotes the reduction of the volume of excess sludge in the biological treatment tank 1. From the viewpoint of causing the problem, 100 mg / L or more and 400 mg / L or less are preferable.

The amount of excess sludge generated per day for determining the sludge treatment ratio varies with changes in the amount of wastewater W1 flowing into the biological treatment tank 1, water quality, organic matter load, temperature, and the like. Therefore, in order to obtain the optimum sludge volume reduction effect, the sludge concentration (MLSS, organic content concentration), COD, BOD, TOC, DO (Dissolved Oxygen), pH, and phosphorus concentration of the mixed solution in the biological treatment tank 1 are obtained. It is necessary to determine an appropriate sludge treatment ratio and convergence value of ozone injection amount based on water quality data such as nitrogen concentration, water amount, and temperature.

For example, the appropriate sludge treatment ratio and the convergence value of the ozone injection amount differ between the case of sewage treatment and the case of wastewater treatment of private factory wastewater. In the case of private factory wastewater with a higher coexisting COD value than public sewage treatment plants, or in the case of wastewater containing substances that easily consume ozone, ozone reacted first with substances that consume ozone more easily than sludge. It was later found by experiments that it reacts with sludge, and the convergence value of the appropriate ozone injection amount is larger than that of the public sewage treatment plant. Therefore, it is necessary to determine the amount of ozone to be added based on the water quality data (COD, etc.) of the mixture with respect to the amount of ozone used determined based on the product of the sludge concentration of the mixture and the sludge extraction flow rate.

Further, when the treated water W3 is discharged into a river or the like as discharged water W4 through the disinfection pond 8, it must satisfy the discharged water quality standard. Since there is a time lag of several days between the water quality of the mixed solution in the biological treatment tank 1 and the water quality of the final discharged water W4, it is possible that the fluctuation of the water quality is transmitted, so that the water quality data of the discharged water W4 meets the discharged water quality standard. Therefore, it is necessary to determine an appropriate sludge treatment ratio and convergence value of ozone injection amount.

Subsequently, in step S7, the sludge withdrawal flow rate and the ozone usage amount are adjusted so as to satisfy the appropriate sludge treatment ratio and the convergence value of the ozone injection amount obtained in step S6. Once the convergence value of the appropriate ozone injection amount, the sludge concentration, and the sludge withdrawal flow rate are determined, the appropriate ozone usage amount (ozone concentration and ozone flow rate) can be calculated by the above formula (1).

Specifically, the optimum parameters (sludge extraction flow rate, ozone usage amount, time and number of ozone treatments per day, etc.) that satisfy the convergence value of the sludge treatment ratio and the ozone injection amount obtained in step S6 are automatically set. The sludge extraction pump 11a, the sludge circulation pump 11b, and the ozone generator 12 are controlled based on these parameters.

In step S7, an example of adjusting the sludge withdrawal flow rate and the ozone amount based on the water quality data of the discharged water W4 will be described. The calculation and control device 21 refers to the difference data of any item (for example, COD value) of the water quality data of the discharged water W4 from the discharged water quality standard with reference to the correlation data between the COD value of the discharged water and the sludge volume reduction effect. , Determine the set value of sludge withdrawal flow rate that does not exceed the discharged water quality standard. The output of the sludge extraction pump 11a is controlled so as not to exceed this set value, and the flow rate measured by the sludge flow meter 10a is maintained at a value smaller than the set value. The output of the sludge extraction pump 11a can be controlled by using, for example, an inverter.

Further, the calculation and control device 21 refers to the difference data of the COD value of the discharged water W4 from the discharged water quality standard with reference to the correlation data between the COD value of the discharged water and the amount of ozone used, and uses ozone that does not exceed the discharged water quality standard. Determine the amount setting. The ozone concentration and ozone flow rate of the ozone generator 12 are controlled so as not to exceed this set value, and the amount of ozone used in the ozone treatment is maintained at a value smaller than the set value.

Further, in step S7, an example of adjusting the sludge extraction flow rate and the ozone amount based on the water quality data of the mixed liquid in the biological treatment tank 1 will be described. The experimental data input device 20 stores the water quality data of the mixed solution in the biological treatment tank 1 and the correlation data of the amount of ozone added. The calculation and control device 21 determines the amount of ozone added suitable for the water quality data of the mixed solution with reference to this correlation data, and adjusts the ozone concentration and the ozone flow rate.

Further, in step S7, the sludge withdrawal flow rate and the amount of ozone used may be adjusted according to the time and number of times the ozone treatment is carried out in a day. The number and time of treatment per day are appropriately determined for the amount of sludge to be treated per day, which is determined based on the sludge treatment ratio. It is known that the time interval for ozone treatment affects the water quality of sludge, and if the number of treatments is large and the interval is too short, the water quality tends to deteriorate. Therefore, the time and interval for performing the ozone treatment may be determined based on the difference between the discharged water quality standard and the water quality data of the discharged water W4.

As a method of determining the time and interval for drawing out the sludge-containing treated water W2 from the biological treatment tank 1, the value of the soluble organic matter concentration of the mixed solution stored in the data storage device 19 is input to the experimental data input device 20 for dissolution. It can be determined by referring to the correlation data between the concentration of organic matter and the time and number of times the ozone treatment is performed in a day. Further, the ozone injection amount can be adjusted by changing the time and interval at which the sludge circulation pump 11b draws out the sludge-containing treated water W2.

Further, as a method of adjusting the ozone usage amount in step S7, there is a method of adjusting the ozone flow rate and G / L in the ejector 17. The G / L in the ejector 17 is not particularly limited as long as it can sufficiently decompose sludge in the sludge-containing treated water, but it is not particularly limited, but ozone and sludge are efficiently reacted and unreacted due to excessive ozone injection. It is set to suppress the increase in ozone.

As a result of conducting an experiment (260 nm absorbance measurement) on the relationship between the G / L value in the ejector 17 and the convergence value of the ozone injection amount, the smaller the G / L value in the ejector 17, the better the ozone treatment efficiency, and the ozone injection amount. It was confirmed that the convergence value of was small. From this experimental result, the calculation and control device 21 circulates sludge-containing treated water in 6 g of the pipe so that the G / L value in the ejector 17 becomes the minimum value based on the determined sludge withdrawal flow rate and ozone usage amount. It is desirable to control the flow rate of ozone and the concentration and flow rate of ozone injected into the ejector 17. Specifically, G / L is set to 0.01 or more and 0.3 or less, and more preferably 0.2 or less.

The wastewater treatment system according to the first embodiment is not limited to the configuration shown in FIG. 1, and can be modified in various ways. For example, in FIG. 1, the solid-liquid separation tank 7 is arranged separately from the biological treatment tank 1, but it can be separated into concentrated sludge and treated water W3 by a solid-liquid separation membrane arranged in the biological treatment tank 1. ..

Further, in FIG. 1, the sludge-containing treated water W2 generated in the biological treatment tank 1 is extracted and transferred to the ozone reaction tank 9, but the concentrated sludge separated in the solid-liquid separation tank 7 is extracted and the ozone reaction tank 9 is extracted. May be transferred to. In that case, the sludge withdrawal flow rate from the solid-liquid separation tank 7 is determined based on the sludge concentration of the concentrated sludge in the solid-liquid separation tank 7 and the sludge treatment ratio set in advance. The sludge concentration of the concentrated sludge in the solid-liquid separation tank 7 can be obtained from the sludge concentration of the sludge-containing treated water W2 transferred from the biological treatment tank 1 to the solid-liquid separation tank 7 and the concentration ratio of the solid-liquid separation tank 7. it can.

Further, in FIG. 1, the ozone reaction section includes the ozone reaction tank 9, but the ozone reaction tank 9 may not be provided. Further, although the ejector 17 is used as the ozone injection method, a method such as an air diffuser type or a mechanical stirring type may be adopted. Further, the data storage device 19 collects data including the measured values of the sludge concentration measuring device 4 and each water quality measuring device 5a, 5b, 5c, etc. online, and the operator collects a part or all of the data. May be entered by.

As described above, according to the wastewater treatment system and the wastewater treatment method according to the first embodiment, the amount of ozone used in the ozone treatment is determined based on the product of the sludge concentration of the mixed liquid in the biological treatment tank 1 and the sludge extraction flow rate. The wastewater W1 flowing into the biological treatment tank 1 is determined, and the sludge extraction flow rate and the amount of ozone used are adjusted based on the water quality data of any one or more of the mixed solution, the treated water W3, and the discharged water W4. Even if the amount of excess sludge generated due to fluctuations in water quantity, water quality, and temperature fluctuates, the amount of ozone used should be controlled so as to stably meet the discharged water quality standards and obtain the optimum sludge volume reduction effect. Is possible.

In addition, since the appropriate amount of ozone used is determined based on the sludge concentration and water quality data of the mixed solution, it is possible to prevent an excessive supply of ozone. Further, the ozone treatment efficiency is improved by controlling the value of G / L in the ejector 17 to be the minimum value based on the determined sludge extraction flow rate and the amount of ozone used. As a result, the discharge water quality standard can be satisfied with a small amount of ozone used, the optimum sludge volume reduction effect can be obtained, and the running cost can be suppressed.

Embodiment 2.
FIG. 3 is a schematic view showing the configuration of the wastewater treatment system according to the second embodiment of the present invention. In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals. The wastewater treatment system according to the second embodiment includes an ozone concentrator 13 and an ozone gas pressure gauge 15 in the ozone injection pipe 14a. The ozone generator 12 and the ozone concentrator 13 are connected by a pipe 14c for returning oxygen gas. The other configurations and the treatments and operations in each part are the same as those in the first embodiment, and thus the description thereof will be omitted here.

The ozone concentrator 13 can concentrate the ozone generated by the ozone generator 12 to generate high-concentration ozone of 400 mg / L or more and a maximum of 2000 mg / L. The ozone concentrator 13 includes an adsorption tower containing an adsorbent such as silica gel cooled by the refrigerant, and a refrigerator for cooling the refrigerant. The ozone concentrator 13 mainly exhausts oxygen from the adsorbent that has adsorbed ozone by the suction force of the ejector 17, and increases the ozone concentration in the adsorption tower. The ejector 17 may be replaced by a vacuum pump. The high-concentration ozone generated by the ozone concentrator 13 is introduced into the gas suction port of the ejector 17 via the ozone injection pipe 14a. Further, the oxygen gas not adsorbed by the ozone concentrator 13 is returned to the ozone generator 12 via the pipe 14c and reused.

In the second embodiment, the data storage device 19 includes a sludge concentration measuring device 4, a water quality measuring device 5a, 5b, 5c, a sludge flow meter 10a, 10b, an ozone gas pressure meter 15, an ozone gas flow meter 16, and an ozone concentrator 13. Signals are connected to thermometers (not shown) provided in the adsorption tower of the above, and data including those measured values are accumulated.

Further, the calculation and control device 21 is signal-connected to the data storage device 19, the experimental data input device 20, the sludge extraction pump 11a, the sludge circulation pump 11b, the ozone generator 12, and the ozone concentrator 13, respectively. The calculation and control device 21 acquires the data necessary for the calculation from the data storage device 19 and the experimental data input device 20, and determines the sludge withdrawal flow rate and the amount of ozone used to satisfy the discharged water quality standard and obtain the optimum sludge volume reduction effect. decide.

Further, the calculation and control device 21 controls the sludge extraction pump 11a, the sludge circulation pump 11b, the ozone generator 12, and the ozone concentrator 13 so as to obtain the determined withdrawal sludge flow rate and ozone usage amount. For example, the calculation and control device 21 acquires the temperature of the adsorption tower of the ozone concentrator 13 and the measured values of the ozone gas pressure gauge 15 from the data storage device 19, and determines the convergence value of the ozone injection amount into the ejector 17. Feedback control is performed so as to be. As a result, the optimum adsorption and desorption conditions of the ozone concentrator 13 can be obtained, and ozone of a desired concentration can be generated.

FIG. 4 shows the results of experiments on the relationship between the concentration of ozone injected into sludge-containing treated water and the convergence value of the ozone injection amount. In FIG. 4, the horizontal axis is the ozone gas concentration (mgO ₃ / L), and the vertical axis is the convergence value of the ozone injection amount (mgO ₃ / gSS). The convergence value of the ozone injection amount on the vertical axis is a relative value when the convergence value of the ozone injection amount at an ozone _{gas concentration of 50 mgO 3 / L is 1.} As a result of the experiment, it was confirmed that the higher the concentration of ozone to be injected, the smaller the convergence value of the ozone injection amount, and the smaller the required ozone usage amount.

From this experimental result, the calculation and control device 21 provided 6 g of pipes so that the gas-liquid flow rate ratio in the ejector 17 became the minimum value and the ozone concentration became the maximum value based on the determined sludge withdrawal flow rate and ozone usage amount. It is desirable to control the flow rate of the circulating sludge-containing treated water and the concentration and flow rate of ozone injected into the ejector 17.

According to the second embodiment, in addition to the same effect as that of the first embodiment, the use of high-concentration ozone in the ozone treatment further improves the ozone treatment efficiency as compared with the first embodiment, and ozone. It is possible to reduce the amount used. As a result, the initial cost including the ozone generator 12 and the running cost of ozone generation and injection can be suppressed. Further, since the oxygen gas not adsorbed by the ozone concentrator 13 is returned to the ozone generator 12 and reused, the running cost can be further reduced.

Embodiment 3.
FIG. 5 is a schematic view showing the configuration of the wastewater treatment system according to the third embodiment of the present invention. In FIG. 5, the same parts as those in FIG. 1 are designated by the same reference numerals. The wastewater treatment system according to the third embodiment includes a plurality of ejectors 17a, 17b, 17c (collectively referred to as ejectors 17) having different nozzle diameters, and an ejector liquid line switching valve 22 and an ejector connected to each ejector 17. A gas line switching valve 23 is provided. The other configurations and the treatments and actions in each part are the same as those in the first and second embodiments, and thus the description thereof will be omitted here.

In the third embodiment, the calculation and control device 21 is signal-connected to the ejector liquid line switching valve 22 and the ejector gas line switching valve 23, respectively. Similar to the first embodiment, the calculation and control device 21 acquires sludge concentration and water quality data of the mixed liquid in the biological treatment tank 1 from the data storage device 19, and stores the correlation in the experimental data input device 20. With reference to the data, the appropriate sludge treatment ratio and convergence value of ozone injection amount are calculated, and the sludge withdrawal flow rate and ozone usage amount are determined to satisfy them.

Further, the calculation and control device 21 determines the optimum ejector 17 for the sludge extraction flow rate and the ozone usage amount determined from the plurality of ejectors 17a, 17b, and 17c, and the circulating sludge and ozone are supplied to the ejector 17. The ejector liquid line switching valve 22 and the ejector gas line switching valve 23 are switched so as to be so.

According to the third embodiment, in addition to the same effects as those of the first and second embodiments, the flow rate of circulating sludge that can be dealt with by providing a plurality of ejectors 17a, 17b, and 17c having different nozzle diameters. The range of is widened. As a result, even when the amount, water quality, temperature, etc. of the wastewater W1 flowing into the biological treatment tank 1 fluctuates greatly and the amount of excess sludge generated fluctuates greatly, the sludge that stably meets the discharge water quality standard and is optimal sludge. Volume reduction effect can be obtained. In the present invention, each embodiment can be freely combined, and each embodiment can be appropriately modified or omitted within the scope of the invention.

INDUSTRIAL APPLICABILITY The present invention can be used as a wastewater treatment system for reducing the volume of excess sludge generated during biological treatment of organic wastewater by using ozone.

1 Biological treatment tank, 2 Air diffuser, 3 Air supply device, 4 Sludge concentration measuring device, 5a, 5b, 5c Water quality measuring device, 6a, 6b, 6c, 6d, 6e, 6f, 6g piping, 7 Solid-liquid separation tank , 8 disinfection pond, 9 ozone reaction tank, 10a, 10b sludge flow meter, 11a sludge extraction pump, 11b sludge circulation pump, 12 ozone generator, 13 ozone concentrator, 14a, 14b, 14c piping, 15 ozone gas pressure gauge, 16 Ozone gas flow meter, 17, 17a, 17b, 17c ejector, 18 exhaust ozone decomposition device, 19 data storage device, 20 experimental data input device, 21 calculation and control device, 22 ejector liquid line switching valve, 23 ejector gas line switching valve

Claims (16)

A biological treatment tank that biologically treats organic wastewater under aerobic conditions to produce sludge-containing treated water containing activated sludge.
A solid-liquid separating section for separating the sludge containing treated water produced by the biological treatment tank to treatment water a concentrated sludge,
Performs ozone treatment is withdrawn the biological treatment the sludge-containing treated water produced by the vessel, or the concentrated sludge separated by the solid-liquid separation unit at a predetermined sludge withdrawal rate, after processing the sludge-containing process water or an ozone reaction unit to return the concentrated sludge to the biological treatment tank,
An ozone generator that generates ozone and supplies it to the ozone reaction unit,
Sludge concentration measuring means for measuring the sludge concentration in the mixture containing the sludge-containing treated water of the biological treatment tank,
The mixed solution, wherein the treated water, and each of the discharge water which has been disinfected the treated water, and water quality measuring means for measuring the water quality data except sludge concentration,
The mixture based on the sludge concentration to determine the sludge withdrawal rate, the determining ozone usage in the ozone treatment on the basis of a product of the sludge concentration and sludge withdrawal rate of the mixed solution, respectively measured by the quality measuring means it has been the mixed solution, the treated water, and wastewater treatment, characterized in that it comprises an arithmetic and control unit for adjusting the sludge withdrawal rate and ozone usage based on any one or more of the water quality data of the discharged water system. The sludge concentration measuring means, characterized after stirring the mixture of the biological treatment tank at a timing immediately before withdrawing the sludge-containing treated water from the biological treatment tank, making measurements of sludge concentration in the mixed solution The wastewater treatment system according to claim 1. Said arithmetic and control device, and characterized in that to ozone usage was determined based on the product of sludge concentration and sludge withdrawal rate of the mixture to determine the amount of ozone added, based on the quality data of the mixed solution The wastewater treatment system according to claim 1 or 2. Any one of claims 1 to 3, further comprising an ozone concentrator for concentrating ozone generated by the ozone generator, wherein the ozone concentrator supplies the concentrated ozone to the ozone reaction unit. The wastewater treatment system described in the section. 4. The calculation and control device is characterized in that the pressure of the ozone adsorption tower of the ozone concentrator and the flow rate of ozone injected into the ozone reaction unit are determined based on the determined ozone usage amount. The described wastewater treatment system. The ozone-reactive part, a pipe for circulating the concentrated sludge is withdrawn from the sludge-containing treated water or the solid-liquid separation unit is withdrawn from the biological treatment tank, wherein disposed on the pipe the sludge-containing treated water or the The wastewater treatment system according to any one of claims 1 to 5, further comprising an ejector for injecting ozone into concentrated sludge. The ozone reaction unit has a plurality of ejectors having different nozzle diameters, and the calculation and control device determines an ejector to be used from the plurality of ejectors based on the determined sludge extraction flow rate and ozone usage amount. The wastewater treatment system according to claim 6, wherein the wastewater treatment system is characterized. Said arithmetic and control device based on the determined sludge withdrawal rate and ozone consumption, as the gas-liquid flow rate is the minimum value in the ejector, the sludge-containing treated water or the concentrated sludge circulating the pipe The wastewater treatment system according to claim 6 or 7, wherein the flow rate and the concentration and flow rate of ozone injected into the ejector are controlled. A data storage device for storing data used for calculation by the calculation and control device is provided, and the data storage device includes at least the sludge concentration measuring means, the water quality measuring means, a sludge flow meter for measuring sludge extraction flow rate, and the sludge flow meter. The wastewater treatment system according to any one of claims 1 to 8, wherein data including a measured value of an ozone gas flow meter for measuring the flow rate of ozone injected into the ozone reaction unit is stored. .. The wastewater treatment system according to claim 9, wherein the data stored in the data storage device is collected online. The wastewater treatment system according to claim 9, wherein a part or all of the data stored in the data storage device is input by an operator. The calculation and control device obtains a convergence value of the sludge treatment ratio and the ozone injection amount based on the data acquired from the data storage device, and automatically sets a parameter that satisfies the obtained convergence value of the sludge treatment ratio and the ozone injection amount. The wastewater treatment system according to any one of claims 9 to 11, wherein the wastewater treatment system is calculated. The calculation and control device is provided with an experimental data input device for storing experimental data including correlation data between sludge concentration and ozone usage or sludge volume reduction effect, and correlation data between water quality and ozone usage or sludge volume reduction effect. 9. The sludge extraction flow rate and the amount of ozone used are adjusted with reference to the experimental data stored in the experimental data input device with respect to the sludge concentration and water quality data acquired from the data storage device. The wastewater treatment system according to any one of claims 12. The arithmetic and control unit, to meet the quality standards of the effluent water quality data of the discharged water is set in advance, according to claim claim 1, characterized in that to adjust the sludge withdrawal rate and ozone consumption 13. The wastewater treatment system according to any one of 13. The calculation and control device according to any one of claims 1 to 14, wherein the calculation and control device determines the time and interval for injecting ozone into the ozone reaction unit based on the determined ozone usage amount. Wastewater treatment system. A biological treatment process in which organic wastewater is biologically treated under aerobic conditions to produce sludge-containing treated water containing activated sludge.
A solid-liquid separation step of separating said sludge-containing treated water generated in the biological treatment step in the process water and concentrated sludge,
A water quality data acquisition step of acquiring water quality data excluding sludge concentration of each of the mixed solution containing the sludge-containing treated water produced in the biological treatment step, the treated water, and the discharged water obtained by disinfecting the treated water.
And a reforming step of the pulling out biological treatment the sludge-containing treated water produced in step, or the concentrated sludge separated by the solid-liquid separation step at a predetermined sludge withdrawal rate performing ozone treatment,
Wherein in the reforming step, based on the sludge concentration in the mixture was determined sludge withdrawal rate, and determines the ozone consumption in the ozone treatment on the basis of a product of the sludge concentration and sludge withdrawal rate of the mixed solution, the mixture, the treated water, wastewater treatment method characterized by adjusting the sludge withdrawal rate and ozone usage based on any one or more of the water quality data of the及beauty release water.

Images