JP2008036517A - Wastewater treatment apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment apparatus which combines a ditch of an oxidation ditch method and an anaerobic treatment means to remove organic matter, nitrogen, and phosphorus in raw water and to provide a method. <P>SOLUTION: The wastewater treatment apparatus comprises an endless water passage (a ditch 11) which includes an aerobic zone 14 and an anoxic zone 15 and the ditch 11 which controls an oxygen supply means (an aeration device 13) and a circulation flow generation means (an underwater propeller 12) from the upstream side dissolved oxygen concentration and downstream side dissolved oxygen concentration of the aerobic zone 14, the anaerobic means (an anaerobic tank 19) installed in a raw water inflow passage 18 for making the raw water flow into the ditch 11, a solid-liquid separation means (a final settling basin 17) for performing the solid-liquid separation of treated liquid treated in the ditch 11, and a return sludge passage 21 for returning sludge separated by the solid-liquid separation means 17 to the anaerobic tank 19 to mix the sludge with the raw water. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wastewater treatment apparatus and method, and more particularly to a wastewater treatment apparatus and method for removing organic matter (BOD), nitrogen and phosphorus in raw water with a wastewater treatment apparatus including an oxidation ditch.

  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, a dissolved oxygen meter (DO meter) is installed at an appropriate position in the aerobic region, and the flow rate of the circulating fluid and the supply amount of oxygen are adjusted based on the measured value (DO value) of the DO meter. The balance between the aerobic region and the anoxic region is appropriately maintained (see, for example, Patent Document 1).

On the other hand, as a method for removing phosphorus in sewage and wastewater, conventionally, when microorganisms ingest an organic substance in an anaerobic state, the phosphorus accumulated in the body is released into the water, and more phosphorus than the amount released in the anaerobic state is favored. Biological removal of phosphorus from water is carried out by utilizing the excessive intake of microorganisms in the air state. Combining this method with the oxidation ditch method, an anaerobic tank (flow control tank) is placed in front of the ditch (aeration tank), and the inflow raw water and return sludge are mixed in the anaerobic tank to release phosphorus from microorganisms. A method described above has been proposed (see, for example, Patent Document 2).
JP 2005-52804 A JP-A-7-290086

  However, as described in Patent Document 2, simply adding an anaerobic tank to the oxidation ditch cannot keep the anaerobic tank in a predetermined anaerobic state due to a state change in the ditch due to daily fluctuations. When a large amount of nitrate nitrogen flows into the anaerobic tank together with the returned sludge, the release of phosphorus from microorganisms cannot be sufficiently performed and the removal of biological phosphorus is hindered. It was necessary to take measures, and the apparatus became complicated, which was a major factor in increasing costs. Furthermore, in Patent Document 2, intermittent aeration is performed in the ditch to increase nitrification / denitrification efficiency. However, when intermittent aeration is performed, the concentration of nitrate nitrogen in the returned sludge changes greatly, which is anaerobic. It also has a great influence on the release of phosphorus in the tank and becomes a factor of reducing the phosphorus removal efficiency.

  Therefore, the present invention effectively uses the advantage of the oxidation ditch method for controlling the flow rate and aeration amount of the circulating fluid based on the measured dissolved oxygen value on the upstream side and the measured dissolved oxygen value on the downstream side, An object of the present invention is to provide a wastewater treatment apparatus and method that can reliably remove not only nitrogen but also phosphorus.

  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 And a control means for adjusting the supply amount of oxygen by the oxygen supply means and the flow rate of the circulating fluid by the circulating flow generation means based on the dissolved oxygen concentration measured by the upstream dissolved oxygen meter and the downstream dissolved oxygen meter. An anaerobic treatment means provided in the raw water inflow path for allowing raw water to flow into the endless water channel, a solid-liquid separation means for performing solid-liquid separation of the treatment liquid treated in the endless water channel, Solid-liquid separation hand In is characterized in that the separated sludge and a return sludge passage to be mixed with the raw water and returned to the anaerobic treatment means.

  Further, the wastewater treatment method of the present invention includes a circulating flow generating means and an oxygen supply means provided in an endless water channel, and an aerobic region downstream from the oxygen supply means, and the oxygen supply means from the end of the aerobic region. An oxygen-free region is formed between each of them, and an upstream dissolved oxygen concentration and a downstream dissolved oxygen concentration in the aerobic region are respectively measured, and the oxygen supply means is based on a measured value of each dissolved oxygen concentration. In the wastewater treatment method for adjusting the oxygen supply amount by the circulating flow and the flow rate of the circulating fluid by the circulating flow generating means, the treatment liquid treated in the endless water channel is separated into solid and liquid, and the separated sludge flows into the endless water channel Anaerobic treatment is performed by mixing with raw water, and the mixed solution of raw water and sludge subjected to the anaerobic treatment is caused to flow into the endless water channel.

  According to the present invention, by adjusting the supply amount of oxygen and the flow rate of the circulating fluid based on the dissolved oxygen concentrations measured respectively upstream and downstream of the aerobic region in the endless water channel (ditch), Even if the load of water fluctuates greatly, the ditch is kept in a constant aerobic / anoxic condition. By mixing the sludge and the inflowing raw water and maintaining the anaerobic state for a certain period of time, the intake of organic substances by microorganisms and the release of phosphorus are ensured, and the aerobic treatment in the aerobic region of the ditch will exceed the released amount When microorganisms ingest phosphorus excessively, phosphorus can be biologically removed from water. That is, by keeping the state in the ditch constant, the anaerobic state in the anaerobic treatment means can also be kept constant, so that phosphorus in the raw water can be reliably removed.

  FIG. 1 is an explanatory view showing an embodiment of the wastewater treatment apparatus of the present invention, FIG. 2 is a view showing an example of the fluctuation state of nitrate nitrogen concentration and ammonia nitrogen concentration in the returned sludge when intermittent aeration is performed, FIG. 3 is a diagram showing an example of fluctuation states of nitrate nitrogen concentration and ammonia nitrogen concentration in the return sludge when the flow rate of the circulating fluid and the supply amount of oxygen are adjusted.

  This waste water treatment apparatus is provided with an underwater propeller 12 as a circulation flow generating means and an aeration device 13 as an oxygen supply means in a ditch 11 comprising an endless water channel, and forms a circulation flow in the direction indicated by an arrow in the ditch 11. Thus, an aerobic region 14 is formed between the aeration device 13 and a predetermined distance, and an anoxic region 15 is formed between the end of the aerobic region 14 and the aeration device 13 with a predetermined balance.

  A final sedimentation basin 17 is provided at the end portion of the aerobic region 14 via an outlet channel 16, and a raw water inflow path 18 is provided in an upstream portion of the anoxic region 15, and the middle of the raw water inflow path 18. Is provided with an anaerobic tank 19 which is an anaerobic treatment means. 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 sludge separated and separated is returned, and a sludge extraction path 22 through which part of the sludge is extracted as excess sludge. And are 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.

  The aerobic region 14 includes an upstream dissolved oxygen meter (first DO meter) 23 and a downstream dissolved oxygen meter (second DO meter) 24 for measuring the dissolved oxygen concentration in the circulating fluid upstream and downstream. Are respectively provided, and based on the dissolved oxygen concentration measured by the first DO meter 23 and the second DO meter 24, for adjusting the supply amount of oxygen by the aeration device 13 and the flow rate of the circulating fluid by the underwater propeller 12, respectively. Control means 25 is provided.

  The raw water flowing into the anaerobic tank 19 from the raw water inflow path 18 is mixed with the sludge returned from the final sedimentation basin 17 through the return sludge path 21 and held in an anaerobic state in the anaerobic tank 19. In this anaerobic state, microorganisms in the sludge ingest organic substances in the raw water and release phosphorus from the body. After being kept in an anaerobic state for a predetermined time, the mixed liquid of the released sludge containing phosphorus and raw water flows into the upstream portion of the anoxic region 15 of the ditch 11 and joins the circulating fluid. By maintaining the oxygen-free state, nitrate nitrogen is denitrified and nitrogen is removed from the circulating fluid.

  When the circulating fluid passes through the aeration device 13 through the underwater propeller 12, it comes into contact with the air pumped from the blower and ejected into the circulating fluid, so that oxygen is taken into the fluid and becomes an aerobic state. While the organic substance is decomposed and ammonia nitrogen is nitrified while flowing through the zone 14, an excessive intake of phosphorus by microorganisms is performed, the organic substance and phosphorus are removed from the circulating liquid, and ammonia nitrogen is nitrified.

  A part of the circulating liquid 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 liquid mixture is separated in the final sedimentation basin 17. The supernatant liquid separated in the final sedimentation basin 17 flows out 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 liquid that has not been extracted to the final sedimentation basin 17 becomes oxygen-free due to a decrease in dissolved oxygen, and joins the mixed liquid from the anaerobic tank 19 in the upstream portion of the oxygen-free zone 15, and the inside of the ditch 11 Circulate.

  On the other hand, the control means 25 controls the aeration apparatus 13 and the underwater propeller 12 based on the dissolved oxygen concentrations measured by the first DO meter 23 and the second DO meter 24 so that the ditch 11 can be used even if the inflow load varies. The balance between the aerobic region 14 and the anoxic region 15 is kept constant.

  For example, the dissolved oxygen concentration measured by the first DO meter 23 (hereinafter referred to as upstream measurement value) is within an appropriate range due to fluctuations in the load of the inflow raw water, and the dissolved oxygen concentration measured by the second DO meter 24 (hereinafter referred to as downstream measurement). (Referred to as “value”) exceeds the proper range, the underwater propeller 12 is decelerated to reduce the flow rate of the circulating fluid so that the downstream measurement value falls within the proper range. When the downstream measurement value falls below the appropriate range, the downstream measurement value falls within the appropriate range by increasing the underwater propeller 12 and increasing the flow rate of the circulating fluid.

  On the other hand, when the upstream measurement value exceeds the appropriate range, it is an oxygen excess state. Therefore, after the aeration amount by the aeration apparatus 13 is decreased so that the upstream measurement value falls within the appropriate range, the downstream measurement value is As described above, the underwater propeller 12 is accelerated or decelerated so as to adjust the flow rate of the circulating fluid.

  On the contrary, when the upstream measurement value falls below the appropriate range, it is in an oxygen-deficient state. Therefore, after the aeration amount by the aeration device 13 is increased so that the upstream measurement value falls within the appropriate range, the downstream measurement is performed. As described above, the underwater propeller 12 is accelerated or decelerated to adjust the flow rate of the circulating fluid so that the value falls within the appropriate range.

  In this way, the balance between the aerobic region 14 and the anaerobic region 15 in the ditch 11 is kept constant by controlling the underwater propeller 12 that is the circulating flow generating means and the aeration device 13 that is the oxygen supplying means. And stable processing can be performed.

  And since the process in the ditch 11 is stabilized, the state of the liquid mixture extracted from the ditch 11 to the final sedimentation tank 17 is also stabilized, and the concentration of nitrogen contained in the liquid mixture is also stabilized.

  For example, FIG. 2 shows an example of the fluctuation state of the nitrate nitrogen concentration (A) and the ammonia nitrogen concentration (B) in the return sludge when the aeration apparatus 13 is intermittently operated without performing the control. Since the inside of the ditch 11 is in an aerobic state at the time of aeration, the nitrate nitrogen concentration (A) in the sludge extracted and separated into the final sedimentation basin 17 rises, and the ammonia nitrogen concentration ( B) decreases. When aeration is stopped, the nitrate nitrogen concentration (A) decreases and the ammonia nitrogen concentration (B) increases. Furthermore, since the change in both nitrogen concentrations is greatly influenced by the inflow load, nitrate nitrogen may become high in the return sludge returned from the final sedimentation tank 17 to the anaerobic tank 19, and phosphorous from microorganisms. The release of phosphorus is inhibited, and phosphorus cannot be sufficiently removed.

  On the other hand, as described above, when the flow velocity and the aeration amount are controlled based on the upstream measurement value and the downstream measurement value, as shown in FIG. The nitrogen concentration (A) is in a substantially constant low concentration state, and the ammoniacal nitrogen concentration (B) is also in a substantially constant state regardless of the inflow load because the aerobic region 14 is stably formed. Accordingly, since the nitrate nitrogen concentration in the sludge returned to the anaerobic tank 19 becomes stable at a low concentration, the release of phosphorus from the microorganisms in the anaerobic tank 19 can be performed stably.

  Further, by operating the interior of the ditch 11 in a high load state, it is possible to suppress the self-decomposition of the sludge as compared with the low load state, so that the phosphorus concentration in the sludge extracted from the sludge extraction path 22 can be increased, It becomes possible to further reduce the phosphorus concentration in water.

  Furthermore, phosphorus released in the anaerobic tank 19 is taken into sludge when the ditch 11 is in an aerobic state or anoxic state, and in particular in an aerobic state, the intake rate of phosphorus is fast, so the aeration apparatus 13 is intermittently operated. By appropriately controlling the underwater propeller 12 and the aeration device 13 during aeration operation to bring the entire ditch 11 into an aerobic state, intake of phosphorus by sludge is promoted and phosphorus removal efficiency is improved. be able to.

  In this way, compared to the case where an anaerobic treatment means such as an anaerobic tank is simply combined with the conventional oxidation ditch method, the oxidation for controlling the flow velocity and the amount of aeration based on the upstream measurement value and the downstream measurement value. By combining an anaerobic treatment means such as an anaerobic tank with the ditch method, phosphorus can be stably removed, and phosphorus removal efficiency can be greatly improved.

It is explanatory drawing which shows one example of the waste water treatment apparatus of this invention. It is a figure which shows an example of the fluctuation | variation state of nitrate nitrogen concentration and ammonia nitrogen concentration in the return sludge when performing intermittent aeration. It is a figure which shows an example of the fluctuation | variation state of the nitrate nitrogen density | concentration in the returned sludge, and ammonia nitrogen density | concentration when adjusting the flow rate of circulating fluid, and the supply amount of oxygen, respectively.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Ditch, 12 ... Underwater propeller, 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 (first DO meter), 24 ... downstream dissolved oxygen meter (second DO meter), 25 ... 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 and a downstream dissolved oxygen meter for measuring the dissolved oxygen concentration in the circulating fluid are provided on the upstream side and the downstream side in the aerobic region, respectively, and the upstream dissolved oxygen meter and the downstream dissolved oxygen meter are provided. In the wastewater treatment apparatus provided with control means for adjusting the amount of oxygen supplied by the oxygen supply means and the flow rate of the circulating fluid by the circulating flow generation means based on the dissolved oxygen concentration measured in step 1, the raw water is supplied to the endless water channel. Anaerobic treatment means provided in the raw water inflow path to be introduced, solid-liquid separation means for performing solid-liquid separation of the treatment liquid treated in the endless water channel, and sludge separated by the solid-liquid separation means are returned to the anaerobic treatment means Raw water Wastewater treatment apparatus characterized by and a return sludge path to be mixed.   An aerobic zone is formed on the downstream side of the oxygen supply means and an anoxic zone is formed between the end of the aerobic zone and the oxygen supply means by the circulating flow generating means and the oxygen supply means provided in the endless water channel. And measuring the upstream dissolved oxygen concentration and the downstream dissolved oxygen concentration in the aerobic region, respectively, and based on the measured values of each dissolved oxygen concentration, the oxygen supply amount and the circulation flow generation by the oxygen supply means In the wastewater treatment method for adjusting the flow rate of the circulating fluid by each means, the treatment liquid treated in the endless water channel is subjected to solid-liquid separation, and the separated sludge is mixed with the raw water flowing into the endless water channel to perform anaerobic treatment. A wastewater treatment method characterized by causing the mixed solution of raw water and sludge subjected to the anaerobic treatment to flow into the endless water channel.

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