JP4743100B2 - Fermentation waste liquid treatment method and fermentation waste liquid treatment apparatus - Google Patents

Description

  The present invention relates to a fermentation waste liquid treatment method and a fermentation waste liquid treatment apparatus for biochemically treating fermentation waste liquid such as nitrogen-containing wastewater.

  In recent years, a method of methane fermentation of organic waste such as garbage and surplus sludge from sewage and recovering energy as methane gas has been adopted as part of the resource-saving and recycling-oriented society formation.

  In methane fermentation, organic substances are decomposed into methane and carbon dioxide gas, but not 100% decomposed, and high concentration organic components remain in the fermentation waste liquid. Further, in the fermentation waste liquid, there is a sludge as a fermentation residue or a microbial cell grown in a methane fermentation tank, and this sludge contains a high concentration of nitrogen components. Ammonia, which is a decomposition product of organic matter, is also contained at a high concentration. Therefore, it cannot be discharged into sewers or rivers as it is, and a process for decomposing and removing organic substances and nitrogen components is necessary.

  FIG. 5 is a schematic diagram showing a main configuration of a conventional methane fermentation treatment system. The methane fermentation treatment system includes a methane fermentation tank 110 that inputs organic waste 100 and performs methane fermentation, and an activated sludge tank 120 that purifies the fermentation waste liquid 101 discharged from the methane fermentation tank 110 using activated sludge. And a final sedimentation basin 130 that obtains treated water by solid-liquid separation of activated sludge. Methane gas 102 generated in the methane fermentation tank 110 is used as an energy resource.

The fermentation waste liquid 101 contains a nitrogen content mainly composed of ammonia in addition to the organic matter. In the activated sludge tank 120, an aerobic process and an anaerobic process are temporally divided by performing intermittent aeration treatment, and are repeated alternately to remove organic matter and nitrogen in the fermentation waste liquid 101 (for example, Patent Documents). 1).
Japanese Patent Laid-Open No. 4-104896

  By the way, in the activated sludge tank 120, nitrogen is removed from the waste liquid by the action of nitrifying bacteria and denitrifying bacteria, but nitrification is caused by disturbances such as lack of aerobic conditions or anaerobic conditions, changes in water temperature, mixing of inhibitory substances, etc. The activity of bacteria or denitrifying bacteria may be reduced. When the activity of nitrifying bacteria or denitrifying bacteria decreases, the nitrogen concentration in the activated sludge tank 120 increases without being able to process the inflowing nitrogen, and the nitrification / denitrification reaction process by intermittent aeration may break down.

  When such a problem of decreased activity occurs, it is necessary to take measures to reduce the amount of waste liquid flowing into the activated sludge tank 120, but it is not possible to grasp the nitrogen removal ability in the activated sludge tank in real time by water quality analysis etc. There is a problem that it is difficult and countermeasures are delayed.

  The present invention has been made in view of such points, and without monitoring the nitrogen removal capability in the activated sludge tank in real time, if the activity of nitrifying bacteria or denitrifying bacteria decreases for some reason, nitrification / denitrification is performed. It is an object of the present invention to provide a waste liquid treatment method and a waste liquid treatment apparatus that can reduce the treatment load of the activated sludge tank and restore the normal state before the nitrogen reaction treatment breaks down.

The waste liquid treatment method of the present invention is a waste liquid treatment method for treating fermentation waste liquid flowing into an activated sludge tank by intermittent aeration in which air aeration and aeration stop are repeated in the activated sludge tank, and measuring the pH value in the activated sludge tank. When the difference between the pH value at the end of the current cycle in the intermittent aeration processing cycle and the pH value at the cycle start time in the processing cycle before the current cycle is calculated, and the absolute value of the calculated difference exceeds the threshold value In addition, the inflow amount of fermentation waste liquid to the activated sludge tank is reduced .

The waste liquid treatment apparatus of the present invention is a waste liquid treatment apparatus for treating fermentation waste liquid flowing into the activated sludge tank by intermittent aeration in which repeated air aeration and aeration stop are performed in the activated sludge tank. Waste liquid inflow means, measuring means for measuring the pH value in the activated sludge tank, taking in the pH value from the measuring means, and the pH value at the end of the current cycle in the intermittent aeration processing cycle and the processing before the current cycle Calculate the difference from the pH value at the cycle start time in the cycle, and control the waste liquid inflow means when the absolute value of the calculated difference exceeds the threshold value to reduce the inflow amount of the fermentation waste liquid to the activated sludge tank And a control means.

  According to these inventions, the inflow amount of the fermentation waste liquid into the activated sludge tank is based on the difference between the pH value at the end of the current cycle and the pH value at the start of the current cycle or at the start of the cycle in the treatment cycle before the current cycle. Thus, even if the activity of nitrifying bacteria or denitrifying bacteria decreases due to some factor, the processing load of the activated sludge tank can be reduced in units of one cycle, and the normal state can be quickly restored.

Further, the waste liquid treatment method of the present invention is a waste liquid treatment method for treating fermentation waste liquid flowing into the activated sludge tank by intermittent aeration that repeats aeration and aeration stop in the activated sludge tank, wherein the pH value in the activated sludge tank is adjusted. When the difference between the pH average value in the current cycle in the treatment cycle of the intermittent aeration and the pH average value in one cycle before the current cycle is calculated, and the absolute value of the calculated difference exceeds the threshold value The inflow amount of the fermentation waste liquid to the activated sludge tank is reduced .

The waste liquid treatment apparatus of the present invention is a waste liquid treatment apparatus for treating fermentation waste liquid flowing into the activated sludge tank by intermittent aeration in which repeated air aeration and aeration stop are performed in the activated sludge tank. Waste liquid inflow means, measuring means for measuring the pH value in the activated sludge tank, taking in the pH value from the measuring means, the pH average value in the current cycle in the treatment cycle of the intermittent aeration and before the current cycle Control which calculates the difference with the pH average value in 1 cycle, and controls the waste liquid inflow means when the absolute value of the calculated difference exceeds the threshold value to decrease the inflow amount of the fermentation waste liquid to the activated sludge tank And means.

  By these inventions, by adjusting the inflow amount of fermentation waste liquid to the activated sludge tank based on the difference between the pH average value in the current cycle and the pH average value in the treatment cycle before the current cycle, Even if the activity of nitrifying bacteria or denitrifying bacteria decreases, the processing load of the activated sludge tank can be reduced in units of one cycle, and the normal state can be quickly restored.

  According to the present invention, the activity of nitrifying bacteria or denitrifying bacteria decreases due to disturbances such as inadequate aerobic / anaerobic conditions, changes in water temperature, mixing of inhibitors, etc., without monitoring the nitrogen removal capacity in the activated sludge tank in real time. Even in this case, the processing load of the activated sludge tank can be reduced and the normal state can be quickly restored before the nitrification / denitrification reaction process fails.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a main configuration of a methane fermentation treatment system according to an embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the component similar to the methane fermentation processing system of FIG. 5 mentioned above, and duplication of description is avoided.

  The methane fermentation treatment system of the present embodiment includes a methane fermentation waste liquid supply pump 10 as a waste liquid inflow means for extracting the fermentation waste liquid 101 from the methane fermentation tank 110 and introducing it into the activated sludge tank 120, and the activated sludge tank 120. a pH meter 11 as a measuring means for measuring the pH value, and an influent waste liquid amount adjusting device 12 as a control means for controlling the methane fermentation waste liquid supply pump 10 using the measurement result of the pH meter 11 to adjust the waste liquid inflow amount; It has. The methane fermentation waste liquid supply pump 10, the pH meter 11, and the inflow waste liquid amount adjusting device 12 constitute a waste liquid treatment apparatus in the methane fermentation treatment system.

  The methane fermentation waste liquid supply pump 10 is provided in a pipe that guides the fermentation waste liquid 101 discharged from the methane fermentation tank 110 to the activated sludge tank 120, and is configured to be able to control the inflow amount by a command signal from the inflow waste liquid amount adjusting device 12. ing. The influent waste liquid amount adjusting device 12 includes a CPU, a nonvolatile memory such as a ROM storing a control program, a volatile memory such as a RAM used in the operation of the CPU, a measured value from the pH meter 11, and a methane fermentation waste liquid supply pump. 10 is composed of an interface for sending command signals. The inflow waste liquid amount adjusting device 12 determines the suitability of the inflow waste liquid amount using the measured value taken from the pH meter 11, and gives a command signal to the methane fermentation waste liquid supply pump 10 according to the determination result.

  In the activated sludge tank 120, an intermittent aeration operation that repeats air aeration (aerobic process) and aeration stop (anaerobic process) is performed. Since ammonia is consumed as the nitrification reaction proceeds in the aerobic process, the pH value decreases. In the anaerobic process, as the denitrification reaction proceeds, nitric acid is consumed and alkalinity is supplied, so that the pH value rises. Normally, if the nitrification / denitrification reaction proceeds without problems in the activated sludge tank 120, the alkalinity in the activated sludge tank 120 is balanced by the above-described increase / decrease in alkalinity and alkalinity supply from the methane fermentation waste liquid, The pH value at the start of each cycle is kept constant.

  By the way, for example, when the denitrification reaction is not completed during one cycle, the supply of alkalinity accompanying denitrification is insufficient, and the pH value at the end of one cycle is lower than the pH value at the start of one cycle. End up. If this state continues, the pH value gradually decreases, and the activities of nitrifying bacteria and denitrifying bacteria also decrease accordingly, so that nitrogen removal is further deteriorated.

  FIG. 2 is a graph showing the transition of the pH value change in the activated sludge tank 120 when nitrogen removal deteriorates in the waste liquid treatment experiment conducted by the inventors. In each treatment cycle, the state where the denitrification is not completed continues, and for this reason, the pH value at the start of aerobic gradually decreases. Along with this, the activity of nitrifying bacteria and denitrifying bacteria also decreased, and it was found that ammonia, nitrous acid, and nitric acid accumulated in the activated sludge tank 120.

  In the present embodiment, in order to prevent the above-described deterioration of nitrogen removal, the pH value in the activated sludge tank 120 is measured, and the pH value at the end of the current cycle and the pH at the start of the cycle in the treatment cycle before the current cycle. The difference with the value was calculated, and the inflow amount of the fermentation waste liquid 101 flowing into the activated sludge tank 120 was adjusted based on the difference value.

  Therefore, the inflow waste liquid amount adjusting device 13 takes in the measured value (pH value) from the pH meter 11 and is based on the difference between the pH value at the end of the current cycle and the pH value at the start of the current cycle for each cycle of the intermittent aeration process. Then, the inflow amount of the fermentation waste liquid 101 into the activated sludge tank 120 is controlled. That is, from the start of the aerobic process to the end of the anaerobic process (or from the start of the anaerobic process to the end of the aerobic process) as one cycle, the pH value at the start of one cycle and the end of the cycle (same as the start of the next cycle) The absolute value of the difference from the pH value is calculated, and the absolute value of the difference thus obtained is compared with a predetermined threshold pHs. When the absolute value of the difference is equal to or greater than the threshold pHs, it is determined that there is a risk that the balance of nitrification / vaginosis reaction is lost and the nitrogen is over, and the flow rate of the methane fermentation waste liquid supply pump 10 is decreased to activate activated sludge. The amount of methane fermentation waste liquid flowing into the tank 120 is reduced. The rate of decrease in the inflow amount is set, for example, in the range of 1 to 0.5 times the current inflow amount. For example, when the flow rate of the methane fermentation waste liquid supply pump 10 is decreased, the flow rate control for the next and subsequent cycles is performed at a flow rate obtained by multiplying the current flow rate of the methane fermentation waste liquid supply pump 10 by 0.8.

  By reducing the inflow amount of the fermentation waste liquid 101 flowing into the activated sludge tank 120, the absolute value of the difference between the pH value at the start of one cycle and the pH value at the end of the cycle becomes small. When almost no difference in pH value is observed, the nitrification / denitrification rate in the activated sludge tank 120 is measured by a known method, and the supply amount of the fermentation waste liquid 101 is gradually increased to supply the waste liquid during steady operation. Return to quantity. The threshold value is preferably set within a range of change in pH value from 0 to 1 cycle (0.25 in FIG. 2). Further, the pH value to be compared with that at the end of the cycle is not the current cycle as described above, but may be the pH value at the start of the aerobic cycle in the previous cycle (for example, the previous cycle, the cycle before the previous cycle, etc.).

FIG. 3 is a flowchart showing the operation of the influent waste liquid amount adjusting device 13.
The inflow waste liquid amount adjusting device 13 takes in the measured value pHa at that time from the pH meter 11 and stores it at the start of one cycle for each cycle. The pH value at the end of one cycle in a certain cycle is treated as the pH value at the start of the current cycle when determining the next cycle.

  The inflow waste liquid amount adjusting device 13 acquires the measurement result pHb of the pH meter 11 at the end of the current cycle and the measured value pHa of the pH meter 11 at the start of the current cycle (step S10), calculates the difference, and calculates the absolute value. Is obtained (step S11). As described above, the pH value (pHa) at the start of the current cycle may be compared with the pH value at the start of the previous cycle or the cycle before the previous cycle.

  Next, it is determined whether or not the absolute value | pHa−pHb | of the difference exceeds the threshold pHs (step S12). If the absolute value of the difference | pHa−pHb | exceeds the threshold pHs, the flow rate of the methane fermentation waste liquid supply pump 10 is decreased (step S13). For example, the flow rate of the current methane fermentation waste liquid supply pump is multiplied by 0.8, and the waste liquid is supplied in the next cycle at this flow rate. When the absolute value of the difference | pHa−pHb | is equal to or lower than the threshold pHs, the current state is maintained without changing the flow rate of the methane fermentation waste liquid supply pump 10.

  Thus, according to the methane fermentation treatment system of the present embodiment, the difference between the pH value at the end of the current cycle and the pH value at the start of the current cycle (or the pH value at the start of the previous cycle or the cycle before the previous cycle). When the absolute value of the difference obtained by calculating the absolute value is equal to or higher than a predetermined threshold pHs, the flow rate of the methane fermentation waste liquid supply pump 10 is decreased and the fermentation waste liquid 101 flows into the activated sludge tank 120. Since the amount is reduced, it is possible to prevent the failure of nitrogen removal even when the activity of nitrifying bacteria and denitrifying bacteria decreases due to disturbances such as inadequate aerobic and anaerobic conditions, changes in water temperature, and mixing of inhibitors.

  In addition, according to the methane fermentation treatment system of the present embodiment, since the pH value is only taken and calculated at the end (start) of at least one cycle, the measured value is always taken from the pH meter 11 and the water quality is analyzed in real time. Thus, the load on the inflow waste liquid amount adjusting device 12 can be greatly reduced as compared with the configuration for controlling the inflow amount of waste liquid.

  In the above embodiment, the absolute value of the difference between the pH value at the end of the current cycle and the pH value at the start of the current cycle (or the pH value at the start of the previous cycle or the previous cycle) is calculated. Is not limited to this. For example, the waste liquid inflow amount may be controlled using a difference between the pH average value in the current cycle and the pH average value in the previous cycle.

  FIG. 4 is a flowchart showing the operation of the influent waste liquid amount adjusting device for controlling the waste liquid inflow amount using the pH average value in each cycle.

  The pH value is acquired every predetermined time within one cycle (step S20). At the end of the current cycle, an average value of pH values in the current cycle is calculated from a plurality of pH values acquired in the current cycle (step S21). The difference between the pH average value pHaa of the current cycle and the pH average value pHab of the previous cycle is calculated to obtain an absolute value (step S22).

  Next, it is determined whether or not the absolute value | pHaa−pHab | of the difference exceeds the threshold value pHas (step S23). When the absolute value | pHaa−pHab | of the difference exceeds the threshold value pHas, the flow rate of the methane fermentation waste liquid supply pump 10 (see FIG. 1) is decreased (step S24). When the absolute value | pHaa−pHab | of the difference is equal to or less than the threshold pHas, the current state is maintained without changing the flow rate of the methane fermentation waste liquid supply pump 10.

  In this way, when the average value of pH values in cycle units is used and the absolute value of the difference between the average value pHaa of the current cycle's pH value and the average value pHab of the previous cycle's pH value exceeds the threshold pHas Even if the waste liquid flow rate is reduced, the failure of nitrogen removal can be prevented in the same manner as described above.

  The present invention can be applied to a methane fermentation treatment system for treating fermentation waste liquid with activated sludge.

The schematic diagram which shows the principal part structure of the methane fermentation waste liquid processing system which concerns on one embodiment of this invention. The figure which shows transition of the pH value change in the activated sludge tank when nitrogen removal deteriorates The flowchart which shows operation | movement of the inflow waste liquid amount adjustment apparatus in the said one Embodiment. The flowchart which shows operation | movement of the modification of an inflow waste liquid amount adjusting device in the said one Embodiment. Schematic diagram showing the main components of a conventional methane fermentation wastewater treatment system

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Methane fermentation waste liquid supply pump, 11 ... pH meter, 12 ... Inflow waste liquid amount control apparatus, 100 ... Organic waste, 101 ... Fermentation waste liquid, 102 ... Methane gas, 110 ... Methane fermentation tank, 120 ... Activated sludge tank, 130 ... Final sedimentation basin

Claims (4)

In the waste liquid treatment method for treating the fermentation waste liquid flowing into the activated sludge tank by intermittent aeration that repeats air aeration and aeration stop in the activated sludge tank,
Measure the pH value in the activated sludge tank and calculate the difference between the pH value at the end of the current cycle in the intermittent aeration treatment cycle and the pH value at the cycle start time in the treatment cycle before the current cycle. When the absolute value of the difference exceeds the threshold value, the amount of fermentation waste liquid flowing into the activated sludge tank is reduced . In the waste liquid treatment method for treating the fermentation waste liquid flowing into the activated sludge tank by intermittent aeration that repeats air aeration and aeration stop in the activated sludge tank,
Measure the pH value in the activated sludge tank, calculate the difference between the pH average value in the current cycle in the intermittent aeration treatment cycle and the pH average value in one cycle before the current cycle , and calculate the difference When the absolute value of exceeds the threshold, the inflow amount of the fermentation waste liquid to the activated sludge tank is reduced . In the waste liquid treatment apparatus for treating the fermentation waste liquid flowing into the activated sludge tank by intermittent aeration that repeats air aeration and aeration stop in the activated sludge tank,
Waste liquid inflow means for allowing fermentation waste liquid to flow into the activated sludge tank;
Measuring means for measuring the pH value in the activated sludge tank,
The incorporation of pH values from the measuring means, wherein the calculating the difference between the pH value at the cycle start point in pH value and the current cycle previous processing cycle of the current cycle at the end in the intermittent aeration process cycles, of the calculated difference Control means for controlling the waste liquid inflow means when the absolute value exceeds a threshold value to reduce the inflow amount of the fermentation waste liquid to the activated sludge tank;
A waste liquid treatment apparatus comprising: In the waste liquid treatment apparatus for treating the fermentation waste liquid flowing into the activated sludge tank by intermittent aeration that repeats air aeration and aeration stop in the activated sludge tank,
Waste liquid inflow means for allowing fermentation waste liquid to flow into the activated sludge tank;
Measuring means for measuring the pH value in the activated sludge tank,
Taking the pH value from the measuring means, calculating the difference between the pH average value in the current cycle in the intermittent aeration treatment cycle and the pH average value in one cycle before the current cycle, and the absolute value of the calculated difference Control means for controlling the waste liquid inflow means to reduce the inflow amount of the fermentation waste liquid to the activated sludge tank when the threshold is exceeded ,
A waste liquid treatment apparatus comprising:

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