JP5725869B2 - Waste water treatment apparatus and operation method thereof - Google Patents

Description

  The present invention relates to a wastewater treatment apparatus and an operation method thereof, and more particularly, to a wastewater treatment apparatus that performs purification treatment of wastewater including removal of nitrogen by a biological wastewater treatment method using an endless water channel and an operation method thereof.

  The oxidation ditch method is widely known as a biological wastewater treatment method. This oxidation ditch method forms an aerobic region and an anoxic region in the ditch by aerating part of the water in the endlessly formed ditch (endless water channel) while circulating it. In addition to decomposition, nitrogen is also removed by a nitrification reaction in an aerobic region and a denitrification reaction in an anoxic region.

  The oxidation ditch method is suitable for small-scale treatment plants that have large daily fluctuations compared to large-scale treatment plants, but the load in the ditch varies greatly due to daily fluctuations. It is important to adjust the supply amount (aeration amount) and maintain a proper balance between the aerobic region and the anoxic region. For this reason, dissolved oxygen meters (DO meters) are installed at appropriate positions on the upstream side and downstream side of the aerobic region, respectively, and the flow rate of the circulating fluid and the oxygen concentration are measured based on the measured values (DO values) of each DO meter. By adjusting the supply amount, the balance between the aerobic region and the anaerobic region is appropriately maintained by so-called two-point DO control (see, for example, Patent Document 1).

  Regarding the removal of nitrogen (ammonia nitrogen, nitrate nitrogen) in the waste water, the concentration difference between the two is adjusted by measuring the ammonia nitrogen concentration and nitrate nitrogen concentration and adjusting the rotation speed of the aeration rotor. It is controlled within a certain range (for example, refer to Patent Document 2), and the ratio between the aerobic region and the anaerobic region is controlled and the ratio between the nitrate nitrogen concentration and the ammonia nitrogen concentration is controlled (for example, Patent Document 3), and proposals have been made such as switching between aeration operation and non-aeration operation by measuring ammonia nitrogen concentration and nitrate nitrogen concentration (for example, see Patent Document 4).

JP 2005-52804 A JP-A-8-1184 JP-A-8-323384 JP-A-2005-715

  However, in the method described in Patent Document 1, it is necessary to change the set value of each DO meter in order to obtain optimum processing performance with respect to a large fluctuation in the inflow ammonia load. In addition, in the methods described in Patent Documents 2 to 4, the ammonia nitrogen concentration and the nitrate nitrogen concentration are measured and controlled. However, both methods are extremely difficult to control and can be controlled. However, it is difficult to sufficiently remove the nitrogen content.

  Then, this invention aims at providing the waste-water-treatment apparatus which can remove a nitrogen content effectively, utilizing the advantage of the said 2 point | piece DO control, and its operating method.

In order to achieve the above object, the waste water treatment apparatus of the present invention comprises a circulation flow generating means and an oxygen supply means in an endless water channel, and includes an aerobic region downstream of the oxygen supply unit and an end of the aerobic region. Forming an oxygen-free region leading to the oxygen supply means, and an upstream dissolved oxygen meter and a downstream dissolved oxygen meter for measuring the dissolved oxygen concentration in the circulating liquid on the upstream side and the downstream side in the aerobic region, respectively An oxygen supply amount control means for controlling the supply amount of oxygen by the oxygen supply means based on the upstream dissolved oxygen concentration measured by the upstream dissolved oxygen meter; and the downstream dissolved oxygen meter measured by the downstream dissolved oxygen meter. A flow rate controlling means for controlling the flow rate of the circulating fluid by the circulating flow generating means based on the oxygen concentration, and an ammonia / nitric acid concentration measuring means for measuring the concentrations of ammonia and nitric acid in the circulating fluid. When ammonia concentration measured by the nitric acid concentration measurement means is below a preset ammonia concentration lower limit, regulate upstream oxygen concentration target value and the downstream oxygen concentration target value to respective low values, the ammonia concentration measured preset When the ammonia concentration upper limit value is exceeded, at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value is adjusted to a high value, and the measured ammonia concentration is not more than the ammonia concentration upper limit value, and Provided with a target value control means for adjusting at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value to a low value when the measured nitric acid concentration exceeds a preset upper limit value of nitric acid concentration It is characterized by.

Further, the operating method of the wastewater treatment apparatus of the present invention comprises a circulation flow generating means and an oxygen supply means in an endless water channel, and an aerobic region downstream of the oxygen supply means, and the oxygen from the end of the aerobic region Forming an oxygen-free region leading to the supply means, and providing an upstream dissolved oxygen meter and a downstream dissolved oxygen meter for measuring the dissolved oxygen concentration in the circulating liquid on the upstream side and the downstream side in the aerobic region, An oxygen supply amount control means for controlling an oxygen supply amount by the oxygen supply means based on an upstream dissolved oxygen concentration measured by the upstream dissolved oxygen meter, and a downstream dissolved oxygen concentration measured by the downstream dissolved oxygen meter And a flow rate control means for controlling the flow rate of the circulating fluid by the circulating flow generating means, and an ammonia / nitric acid concentration measuring means for measuring the concentrations of ammonia and nitric acid in the circulating fluid. A target value for adjusting the upstream oxygen concentration target value of the oxygen supply amount control means and the downstream oxygen concentration target value of the flow rate control means based on at least one of the ammonia concentration and the nitric acid concentration measured by the measuring means a method of operating is provided a control means the waste water treatment apparatus, the oxygen supply amount control means, by the oxygen supply means so that the upstream side of dissolved oxygen concentration measured becomes the upstream oxygen concentration target value set in advance to control the supply amount of oxygen, the flow rate control means controls the flow rate of the circulating liquid by the circulating flow generation means such that the downstream side of dissolved oxygen concentration measured becomes the downstream oxygen concentration target value set in advance, When the measured ammonia concentration is lower than the ammonia concentration lower limit value set in advance, the target value control means is configured to set the upstream oxygen concentration target value. Each of the downstream oxygen concentration target values is adjusted to a low value, and when the measured ammonia concentration exceeds a preset ammonia concentration upper limit value, at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value. When either one is adjusted to a high value and the measured ammonia concentration is equal to or lower than the ammonia concentration upper limit value and the measured nitric acid concentration exceeds the preset nitric acid concentration upper limit value, the upstream oxygen concentration target value and the downstream It is characterized in that at least one of the side oxygen concentration target values is adjusted to a low value.

  According to the present invention, by adjusting the upstream oxygen concentration target value of the oxygen supply amount control means and the downstream oxygen concentration target value of the flow rate control means based on the measured ammonia concentration and nitric acid concentration, ammonia nitrogen and nitric acid Nitrogen can be controlled.

It is explanatory drawing which shows one example of the waste water treatment apparatus of this invention. It is explanatory drawing of the control which lowers a target value. It is explanatory drawing of the control which raises a target value.

  The wastewater treatment apparatus shown in the present embodiment is a set of water flow generation device 12 and oxygen supply means that are circulation flow generation means in the ditch 11 that performs wastewater purification treatment including nitrogen removal by a biological wastewater treatment method. By providing an aeration device 13 and forming a circulating flow in the direction indicated by the arrow F in the ditch 11, the aerobic region 14 is moved from the end of the aerobic region 14 to a predetermined distance from the aeration device 13. The oxygen-free region 15 is formed in a predetermined balance between the aeration device 13 and the aeration device 13.

  A final sedimentation basin 17 is provided in the downstream portion of the aerobic region 14 via the outlet channel 16, and a raw water inflow passage 18 is provided in the upstream portion of the anoxic region 15, and the middle of the raw water inflow passage 18 Is provided with an anaerobic tank 19. Further, in the final sedimentation basin 17, a treated water outflow path 20 through which the separated supernatant water flows out, a return sludge path 21 through which the settled and separated sludge is returned to the anaerobic tank 19, and sludge that extracts a part of the sludge as excess sludge. An extraction path 22 is provided. The anaerobic tank 19 mixes the raw water flowing into the anaerobic tank 19 and the sludge returned from the return sludge path 21 and keeps them in an anaerobic state for a predetermined time.

  An upstream dissolved oxygen meter (DO1) 23 for measuring the dissolved oxygen concentration in the circulating fluid and a downstream dissolved oxygen meter (DO2) are disposed upstream and downstream in the circulating fluid flow direction in the aerobic region 14. 24, and the concentration of ammonia (ammonia nitrogen) and nitric acid (nitrate nitrogen) in the circulating liquid is measured at an appropriate position in the ditch 11, preferably in the vicinity of the outlet channel 16. An ammonia / nitric acid concentration measuring means 25 is provided.

  Furthermore, the oxygen supply amount control means 26 for controlling the oxygen supply amount by the aeration apparatus 13 based on the upstream dissolved oxygen concentration measured by the upstream dissolved oxygen meter 23 and the downstream dissolved oxygen meter 24 measured. The flow rate control means 27 for controlling the flow rate of the circulating fluid by the set of water flow generators 12 based on the downstream dissolved oxygen concentration, and the oxygen concentration based on the ammonia concentration and nitric acid concentration measured by the ammonia / nitric acid concentration measurement means 25. A target value control means 28 for adjusting the upstream oxygen concentration target value of the supply amount control means 26 and the downstream oxygen concentration target value of the flow rate control means 27 is provided.

  The raw water flowing into the anaerobic tank 19 from the raw water inflow path 18 becomes a mixed liquid mixed with the sludge returned from the final sedimentation basin 17 through the return sludge path 21 and is kept in an anaerobic state in the anaerobic tank 19. 11 flows into the oxygen-free region 15 and joins the circulating liquid, and is maintained in an oxygen-free state in the oxygen-free region 15, so that nitrate nitrogen is denitrified and nitrogen is removed from the circulating liquid.

  When the circulating fluid passes through the aeration device 13 via the water flow generator 12, it comes into contact with the air pumped from the blower B and jetted into the circulating fluid, so that oxygen is taken into the fluid and becomes an aerobic state. While flowing through the aerobic region 14, organic matter is decomposed and ammoniacal nitrogen is nitrified, and organic matter and ammoniacal nitrogen are removed from the circulating fluid.

  A part of the circulating fluid flowing through the end portion of the aerobic region 14 is extracted to the final sedimentation basin 17 through the outlet channel 16, and the circulating fluid is subjected to solid-liquid separation in the final sedimentation basin 17. The supernatant liquid separated in the final sedimentation basin 17 is discharged from the treated water outflow path 20, a part of the settled sludge is extracted as excess sludge from the sludge extraction path 22, and the remaining sludge passes through the return sludge path 21. And returned to the anaerobic tank 19. In addition, the circulating fluid that has not been withdrawn into the final sedimentation basin 17 becomes oxygen-free due to a decrease in dissolved oxygen, and merges with the mixed solution from the anaerobic tank 19 in the upstream portion of the oxygen-free zone 15 to enter the interior of the ditch 11. Circulate.

  The oxygen supply amount control means 26 controls the oxygen supply amount by the aeration apparatus 13 so that the measured upstream dissolved oxygen concentration becomes a preset upstream oxygen concentration target value. For example, if the upstream dissolved oxygen concentration falls below the appropriate range set as the upstream oxygen concentration target value due to fluctuations in the load of the inflow raw water, the amount of aeration by the aeration device 13 is increased because the oxygen is insufficient. The upstream dissolved oxygen concentration is controlled so as to fall within the appropriate range. If the upstream dissolved oxygen concentration exceeds the appropriate range, it is an oxygen excess state. Therefore, the amount of aeration by the aeration device 13 is reduced so that the upstream dissolved oxygen concentration falls within the proper range. Control to enter.

  The flow rate control means 27 controls the rotational speed of the water flow generator 12 so that the measured downstream dissolved oxygen concentration becomes a preset downstream oxygen concentration target value. For example, when the downstream dissolved oxygen concentration measured by the downstream dissolved oxygen meter 24 becomes higher than the appropriate range set as the downstream oxygen concentration target value due to fluctuations in the load of the inflow raw water, water flow is generated. By reducing the flow rate of the circulating fluid by decelerating the device 12, it is controlled so that the downstream dissolved oxygen concentration falls within the proper range, and when the downstream dissolved oxygen concentration falls below the proper range and becomes a low concentration, By controlling the water flow generator 12 to increase the flow rate of the circulating fluid, the downstream dissolved oxygen concentration is controlled to fall within an appropriate range.

  Then, when the ammonia concentration measured by the ammonia / nitric acid concentration measuring means 25 falls below a preset ammonia concentration lower limit value, the target value control means 28 sets the upstream oxygen concentration target value and the downstream oxygen concentration target value. At least one of them, preferably both are adjusted to a low value, and when the measured ammonia concentration exceeds the ammonia concentration upper limit value, at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value, Preferably both are adjusted to a high value.

  That is, when the ammonia concentration of the circulating fluid in the ditch 11 measured by the ammonia / nitric acid concentration measuring means 25 falls below the ammonia concentration lower limit value, the target value control means 28, as shown in FIG. The upstream oxygen concentration target value A is reduced to a target value AL that is a dissolved oxygen concentration lower than the upstream oxygen concentration target value A, or the downstream oxygen concentration target value B of the flow rate control means 27 is For example, the dissolved oxygen concentration is lowered to the target value BL lower than the side oxygen concentration target value B.

  Accordingly, when the oxygen supply amount control means 26 determines that the upstream dissolved oxygen concentration measured by the upstream dissolved oxygen meter (DO1) 23 exceeds the appropriate range set as the upstream oxygen concentration target value AL. Then, the amount of aeration by the aeration device 13 is decreased so that the upstream dissolved oxygen concentration falls within the appropriate range of the upstream oxygen concentration target value AL.

  Similarly, when the flow rate control means 27 determines that the downstream dissolved oxygen concentration measured by the downstream dissolved oxygen meter (DO2) 24 exceeds the appropriate range set as the downstream oxygen concentration target value BL, The water flow generator 12 is decelerated to reduce the flow rate of the circulating fluid, so that the downstream dissolved oxygen concentration is controlled to fall within the appropriate range of the downstream oxygen concentration target value BL.

  In this way, by controlling at least one of the upstream oxygen concentration target value of the oxygen supply amount control means 26 and the downstream oxygen concentration target value of the flow rate control means 27 to the target values AL and BL, control is performed by the ditch 11. The dissolved oxygen concentration in the circulating fluid is controlled to be low as a whole, and the region of the aerobic region 14 decreases and the region of the anoxic region 15 increases. Thereby, the oxidizing action of ammonia by nitrifying bacteria is suppressed, and the ammonia concentration in the circulating fluid gradually increases. In addition, it is possible to prevent nitrifying bacteria from undergoing auto-oxidative decomposition due to excessive dissolved oxygen, and it is possible to reduce power consumption of the aeration apparatus 13 and the water flow generation apparatus 12.

  Conversely, when the ammonia concentration of the circulating fluid in the ditch 11 measured by the ammonia / nitric acid concentration measuring means 25 exceeds the ammonia concentration upper limit value, the upstream oxygen concentration target of the oxygen supply amount control means 26 as shown in FIG. The value A is raised to a target value AH which is a dissolved oxygen concentration higher than the upstream oxygen concentration target value A, or the downstream oxygen concentration target value B of the flow velocity control means 27 is changed to the downstream oxygen concentration target value B. Or higher to the target value BH with a higher dissolved oxygen concentration.

  As a result, when the oxygen supply amount control means 26 determines that the measured upstream dissolved oxygen concentration falls below the appropriate range set as the upstream oxygen concentration target value AH, the oxygen supply amount control means 26 increases the aeration amount by the aeration device 13 to increase the upstream amount. Control is performed so that the side dissolved oxygen concentration falls within an appropriate range of the upstream oxygen concentration target value AH.

  Similarly, in the flow rate control means 27, when it is determined that the measured downstream dissolved oxygen concentration falls below the appropriate range set as the downstream oxygen concentration target value BH, the water flow generator 12 is accelerated to increase the circulating fluid flow rate. By increasing the flow rate, the downstream dissolved oxygen concentration is controlled to fall within the appropriate range of the downstream oxygen concentration target value BH.

  In this manner, by controlling at least one of the upstream oxygen concentration target value A of the oxygen supply amount control means 26 and the downstream oxygen concentration target value B of the flow rate control means 27 to the target values AH and BH, The dissolved oxygen concentration in the circulating fluid in the ditch 11 is controlled to be high as a whole, and the region of the aerobic region 14 increases and the region of the anoxic region 15 decreases. As a result, the oxidizing action of ammonia by nitrifying bacteria is promoted, and the ammonia concentration in the circulating fluid is gradually lowered by changing the ammonia to nitrous acid or nitric acid.

  In any control, when the ammonia concentration measured by the ammonia / nitric acid concentration measuring means 25 becomes equal to or higher than the ammonia concentration lower limit value or lower than the ammonia concentration upper limit value, the upstream oxygen concentration target value and By returning the downstream oxygen concentration target value to the original target values A and B set in advance, the waste water treatment can be performed efficiently by performing the preset normal control.

  Furthermore, even if the ammonia concentration measured by the ammonia / nitric acid concentration measuring means 25 is not less than the ammonia concentration lower limit value and not more than the ammonia concentration upper limit value, and the ammonia concentration is within an appropriate range, the ammonia / nitric acid concentration measuring means. When the nitric acid concentration measured in 25 exceeds the preset nitric acid concentration upper limit value, at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value is adjusted to low target values AL and BL. Thus, as described above, the amount of aeration by the aeration device 13 decreases or the water flow generation device 12 decelerates, so that the region of the anoxic region 15 increases and the denitrification reaction in the anoxic region 15 is promoted. The nitric acid concentration gradually decreases. Also in this case, when the nitric acid concentration falls below the nitric acid concentration upper limit value, the upstream oxygen concentration target value and the downstream oxygen concentration target value are returned to the original target values A and B.

  Thus, in order to control the ammonia concentration in the circulating fluid to a certain concentration range between the ammonia concentration lower limit value and the ammonia concentration upper limit value, and to control the nitric acid concentration in the circulating fluid below the nitric acid concentration upper limit value, Since the upstream oxygen concentration target value of the oxygen supply amount control means 26 and the downstream oxygen concentration target value of the flow rate control means 27 are adjusted based on the ammonia concentration and the nitric acid concentration, respectively, the oxygen supply amount control means 26 and The dissolved oxygen concentration in the ditch 11 can be reliably controlled by the flow rate control means 27, and the ratio of the aerobic region 14 and the anoxic region 15 is controlled to an optimum ratio according to the ammonia concentration and the nitric acid concentration. Can do.

  That is, the balance between the aerobic region 14 and the anaerobic region 15 is larger than in the conventional case where these concentrations are directly controlled based on the measured nitrate nitrogen concentration and ammonia nitrogen concentration. Since it does not collapse, the state of the circulating fluid extracted from the ditch 11 to the final sedimentation basin 17 is stable, the concentration of nitrogen contained in the circulating fluid is also stable, and wastewater treatment efficiency can be improved. It is also possible to reduce power consumption.

  Furthermore, when it is necessary to keep the ammonia concentration in the effluent water as low as possible, it is possible to perform reliable control only by reducing the upper limit value of the ammonia concentration. Similarly, the nitric acid concentration in the effluent water is as low as possible. When it is necessary to suppress this, it is possible to perform reliable control only by reducing the upper limit value of the nitric acid concentration. In addition, when it is necessary to keep the nitrogen content in the effluent water as low as possible, the sum of ammonia concentration and nitric acid concentration is calculated as the total nitrogen concentration, and the upstream side is calculated based on the ratio of ammonia concentration and nitric acid concentration set in advance. It is possible to control the total nitrogen concentration to be the minimum by adjusting the oxygen concentration target value and the downstream oxygen concentration target value, respectively. By reducing the area, it is possible to reduce the power consumption of the blower B of the aeration apparatus 13 that is an oxygen supply means and the motor of the water flow generation apparatus 12 that is a circulation flow generation means.

  The upper limit, lower limit, and target value for control can be set in multiple stages, the target value can be raised or lowered in two or more stages, and the width of the appropriate range for the target value can be set arbitrarily. be able to. It is also possible to continuously change the upstream oxygen concentration target value and the downstream oxygen concentration target value with respect to the measured value of the ammonia concentration.

  The ammonia / nitric acid concentration measuring means is preferably one that can simultaneously measure ammonia ions and nitrate ions with a single sensor, but it can also be used for ammonia and nitric acid, respectively. Any circulating flow generating means and oxygen supplying means can be used depending on conditions such as the configuration of the ditch and the amount of treated water. Furthermore, the anaerobic tank can be omitted depending on the state of the raw water and the treatment target, and an aerobic tank can be installed instead of the anaerobic tank.

  DESCRIPTION OF SYMBOLS 11 ... Ditch, 12 ... Water flow generator, 13 ... Aeration apparatus, 14 ... Aerobic area, 15 ... Anoxic area, 16 ... Outlet flow path, 17 ... Final sedimentation basin, 18 ... Raw water inflow path, 19 ... Anaerobic tank, 20 ... treated water outflow route, 21 ... return sludge route, 22 ... sludge extraction route, 23 ... upstream dissolved oxygen meter (DO1), 24 ... downstream dissolved oxygen meter (DO2), 25 ... ammonia / nitric acid concentration measuring means , 26 ... oxygen supply amount control means, 27 ... flow rate control means, 28 ... target value control means

Claims (2)

A circulation flow generating means and an oxygen supply means are provided in the endless water channel, and an aerobic area downstream of the oxygen supply means and an anoxic area from the end of the aerobic area to the oxygen supply means are formed, An upstream dissolved oxygen meter that measures the dissolved oxygen concentration in the circulating fluid and a downstream dissolved oxygen meter are provided on the upstream and downstream sides in the aerobic region, respectively, and the upstream dissolved oxygen measured by the upstream dissolved oxygen meter. An oxygen supply amount control means for controlling the oxygen supply amount by the oxygen supply means based on the concentration; and a flow rate of the circulating fluid by the circulation flow generation means based on the downstream dissolved oxygen concentration measured by the downstream dissolved oxygen meter. And a flow rate control means for controlling the concentration, and ammonia / nitric acid concentration measurement means for measuring the concentration of ammonia and nitric acid in the circulating fluid,
When the ammonia concentration measured by the ammonia / nitric acid concentration measuring means falls below a preset ammonia concentration lower limit value, the upstream oxygen concentration target value and the downstream oxygen concentration target value are adjusted to low values, respectively, and the measured ammonia concentration When the ammonia concentration upper limit value set in advance is exceeded, at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value is adjusted to a high value, and the measured ammonia concentration is less than the ammonia concentration upper limit value. And a target value control means for adjusting at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value to a low value when the measured nitric acid concentration exceeds a preset upper limit value of nitric acid concentration. A wastewater treatment apparatus characterized by being provided. A circulation flow generating means and an oxygen supply means are provided in the endless water channel, and an aerobic area downstream of the oxygen supply means and an anoxic area from the end of the aerobic area to the oxygen supply means are formed, An upstream dissolved oxygen meter that measures the dissolved oxygen concentration in the circulating fluid and a downstream dissolved oxygen meter are provided on the upstream and downstream sides in the aerobic region, respectively, and the upstream dissolved oxygen measured by the upstream dissolved oxygen meter. An oxygen supply amount control means for controlling the oxygen supply amount by the oxygen supply means based on the concentration; and a flow rate of the circulating fluid by the circulation flow generation means based on the downstream dissolved oxygen concentration measured by the downstream dissolved oxygen meter. A flow rate control means for controlling the ammonia concentration, and an ammonia / nitric acid concentration measurement means for measuring the concentrations of ammonia and nitric acid in the circulating fluid. Based on one of a concentration of at least one of the concentration of the waste water treatment apparatus in which a target value control means for regulating the downstream oxygen concentration target value of the upstream oxygen concentration target value and the flow rate control means of said oxygen supply quantity control means Driving method,
Said oxygen supply quantity control means controls the supply amount of oxygen by the oxygen supply means so that the upstream side of dissolved oxygen concentration measured becomes the upstream oxygen concentration target value set in advance, the flow rate control means measures and the downstream side of dissolved oxygen concentration by controlling the flow rate of the circulating liquid by the circulating flow generation means so that the downstream oxygen concentration target value set in advance with the target value control means, the ammonia concentration measured preset When the ammonia concentration lower limit value is less than the lower limit, the upstream oxygen concentration target value and the downstream oxygen concentration target value are adjusted to lower values, respectively, and when the measured ammonia concentration exceeds a preset ammonia concentration upper limit value, Measured by adjusting at least one of the side oxygen concentration target value and the downstream oxygen concentration target value to a high value When the ammonia concentration is equal to or lower than the ammonia concentration upper limit value and the measured nitric acid concentration exceeds the preset nitric acid concentration upper limit value, at least one of the upstream oxygen concentration target value and the downstream oxygen concentration target value is set. A method for operating a wastewater treatment apparatus, characterized by adjusting to a low value.

Images