JP5940435B2 - Coagulation sedimentation activated sludge treatment system and operation method thereof - Google Patents

Description

  The present invention relates to a coagulation sedimentation activated sludge treatment system and an operation method thereof.

  Activated sludge treatment of organic wastewater in the aeration tank, the treated water from this aeration tank is solid-liquid separated in the sedimentation tank to settle the sludge to obtain supernatant water, and a part of the settled sludge is sludge in the aeration tank. An activated sludge treatment system that returns to maintain the concentration at a predetermined level is widely known, but in this system, the sludge settling property may deteriorate.

  Therefore, as described in Patent Document 1 below, in the process of biologically treating organic wastewater, an aggregation floc is generated by adding an inorganic flocculant and a polymer flocculant to the activated sludge, and the sludge settling property in the settling tank is generated. There is a known method for increasing this.

JP-A-11-156368

  However, in the so-called coagulation sedimentation activated sludge treatment system as described above, the period from the system start-up to the stable operation is long, and it is desired to shorten the period. It is desired.

  The present invention has been made in view of the above, and an object of the present invention is to provide a coagulation sedimentation activated sludge treatment system and an operation method thereof that enable early stable operation and reduce the amount of coagulant.

  Here, the present inventors diligently studied and arrived at the present invention through the following considerations. That is, the mechanism of the coagulation sedimentation activated sludge treatment system is considered as follows. Activated sludge in an aeration tank (biological reaction tank) decomposes and grows organic components (BOD) in organic wastewater, and metal components of inorganic flocculants (such as sulfate bands) added as a flocculant added later (For example, Al) reacts electrochemically with activated sludge. Specifically, the metal component (+ charge) of the inorganic flocculant and activated sludge (-charge) react electrochemically to generate floc ( The flocs are coarsened by adding a polymer flocculant as a flocculant to the flocs, and the flocs are coarsened (coarse flocs). Solid-liquid separation. Part of the sludge that has settled and separated is returned to the aeration tank in order to maintain the sludge concentration in the aeration tank, and the remaining sludge is discharged out of the system as excess sludge. The added inorganic flocculant is discharged out of the system by the amount of excess sludge, but newly added inorganic flocculant reacts electrochemically with the sludge, and this action is repeated, so that the activity gradually increases. The metal component derived from the inorganic flocculant in the sludge accumulates, the metal ratio (metal component concentration) increases and the sedimentation improves, and eventually the metal ratio reaches the equilibrium value, so that the most improved and stable sludge sedimentation is achieved. As a result, the mixing of SS (Suspended Solids) into the supernatant water is suppressed and the quality of the treated water is improved. As a result, a stable operation state is obtained.

  Here, when the sludge in which the metal component is not accumulated in the aeration tank at the start of operation is used as the seed sludge, the amount of the inorganic flocculant to be added to increase the metal component concentration to the equilibrium value is increased. Therefore, by using the metal component-containing agglomerated sludge as seed sludge from the start of operation and efficiently promoting the mixing with the metal component of the inorganic flocculant, the accumulation of metal components in the sludge efficiently proceeds, and the metal ratio is increased. It was considered that the amount of the inorganic flocculant could be reduced by the shortened period as the period until the equilibrium value was reached.

  Therefore, the coagulation sedimentation activated sludge treatment system according to the present invention has an activated sludge, a biological reaction tank for biologically treating the introduced organic waste water, and an inorganic flocculant in the treated water from the biological reaction tank. Inorganic flocculant adding means to be added, treated water to which the inorganic flocculant is added by the inorganic flocculant adding means is introduced, and a part of the sludge settled and separated in the settling tank And a return line for returning the bioreactor as a return sludge. The bioreactor is filled with seed sludge to which an inorganic flocculant is added at the start of operation.

  Further, the operation method of the coagulation sedimentation activated sludge treatment system according to the present invention includes an activated sludge, a biological reaction tank for biologically treating the introduced organic waste water, and inorganic treatment water from the biological reaction tank. Inorganic flocculant adding means for adding a flocculant, treated water to which the inorganic flocculant is added by the inorganic flocculant adding means is introduced, and the sludge settled and separated in the settling tank A coagulation sedimentation activated sludge treatment system comprising a return line for returning a part of the bioreactor as a return sludge, and at the start of operation, seed sludge to which an inorganic flocculant has been added is the biological reaction. It is characterized by being put in a tank.

  According to the above-described coagulation sedimentation activated sludge treatment system and its operation method, seed sludge having a coagulation sludge floc formed by adding an inorganic coagulant in advance in the biological reaction tank from the start of operation is introduced. Compared with the conventional case, accumulation of metal components with respect to activated sludge is performed efficiently. Accordingly, it is possible to reduce the time required for the operation of the coagulation sedimentation activated sludge treatment system to be stabilized as the metal component becomes a desired accumulation amount, and it is possible to reduce the amount of the inorganic coagulant to be introduced until the stable operation. .

  Here, as a configuration that effectively exhibits the above-described action, specifically, the seed coagulant charged into the biological reaction tank is added with the inorganic flocculant so as to neutralize the surface charge. An embodiment is mentioned.

  ADVANTAGE OF THE INVENTION According to this invention, while enabling the stable operation of early, the coagulation sedimentation activated sludge processing system which can reduce the quantity of a coagulant | flocculant, and its operating method are provided.

It is a block diagram which shows the coagulation sedimentation activated sludge processing system which concerns on embodiment of this invention. It is a figure which shows the result of having measured the initial sedimentation rate of the sludge at the time of throwing the seed sludge to which the inorganic flocculant was added into the aeration tank. It is a figure explaining an initial sedimentation speed. It is a figure which shows the result of having measured the change of the initial sedimentation rate at the time of changing the density | concentration of the inorganic flocculant added to the seed sludge, and the colloid titration value.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram showing a coagulation sedimentation activated sludge treatment system that employs the coagulation sedimentation activated sludge treatment method according to the embodiment of the present invention.

  As shown in FIG. 1, the coagulation sedimentation activated sludge treatment system 100 includes an aeration tank 1 to which organic wastewater is introduced, a reaction tank 2, and a high speed coagulation sedimentation tank 3 connected in this order, and a high speed coagulation sedimentation tank 3. And an aeration tank 1 are provided with a sludge return line L1 and an excess sludge discharge line L2 branched from the sludge return line L1.

  The aeration tank 1 decomposes organic components (BOD) by introducing organic waste water and performing activated sludge treatment (aerobic treatment) by aeration.

  In the reaction tank 2, treated water containing activated sludge from the aeration tank 1 is introduced through the line L 3, and an inorganic flocculant is added by the inorganic flocculant adding means 4. A floc is generated by electrochemically reacting the metal component of the inorganic flocculant with the sludge.

  Here, as the inorganic flocculant, Al-based such as sulfuric acid band and PAC is used, but for example, Fe-based inorganic flocculant may be used, in short, a metal component that electrochemically reacts with activated sludge. (Al or Fe) may be included.

  The high-speed coagulation sedimentation tank 3 introduces treated water containing flocs from the reaction tank 2 through the line L4 and is added with a polymer flocculant to generate coarse flocs with coarse flocs.

  Specifically, the high-speed coagulating sedimentation tank 3 introduces treated water containing flocs from the reaction tank 2 into a mixing chamber 3b disposed in an upright state in the tank 3a, and at the same time introduces high water into the mixing chamber 3b. A polymer flocculant is added by the molecular flocculant addition means 5, and in this state, the polymer is stirred by rotation of a rotary mixer (polymer flocculant stirring blade) 3c disposed in the mixing chamber 3b. The contact between the flocculant and the floc is enhanced to collect coarse flocs to generate coarse flocs, and the treated water containing the coarse flocs in the mixing chamber 3b is horizontally and radially extended from the rotating distribution pipe 3d. A uniform sludge layer is formed in the bottom of the tank 3a by dispersing and supplying the tank 3a evenly and forming a uniform upward flow in the tank 3a to settle and separate coarse flocs. In, onto the concentrated sludge layer to form flocs layer, a clear layer is the supernatant in order.

  The sludge return line L1 is for returning a part of the metal component-containing agglomerated sludge, which is the agglomerated sludge of the concentrated sludge layer of the high-speed agglomerated sedimentation tank 3, to the aeration tank 1 as the returned sludge, and the excess sludge discharge line L2 In order to discharge surplus sludge, which becomes surplus in the system, out of the system.

  According to such an agglomerated sedimentation activated sludge treatment system 100, organic wastewater is introduced into the aeration tank 1 and treated with activated sludge, and treated water containing activated sludge from the aeration tank 1 is introduced into the reaction tank 2 and inorganic. By adding the flocculant, the activated sludge and the metal component of the inorganic flocculent react electrochemically to produce a metal component-containing primary flocculent sludge that is floc. The treated water is introduced into the high-speed coagulating sedimentation tank 3 and the polymer coagulant is added to produce a coarsened metal component-containing coagulated sludge, and this metal component-containing coagulated sludge is evenly distributed and supplied into the tank 3a. As a result, a concentrated sludge layer, an agglomerated floc layer, and a clarified layer are formed in order from the bottom to the top, and a part of the agglomerated sludge containing metal components of the concentrated sludge layer is returned to the aeration tank through the sludge return line L1. Sludge concentration of the returned the aeration tank 1 while being maintained, excess sludge is discharged from the system through the excess sludge discharge line L2 to.

  Here, the operation start time of the coagulation sedimentation activated sludge treatment system 100 will be described. Usually, after the operation of the coagulation sedimentation activated sludge treatment system 100 is started, the inorganic coagulant is added from the inorganic coagulant addition means 4. According to this method, immediately after the operation is started, activated sludge in which the metal component of the inorganic flocculant is not accumulated is introduced into the aeration tank 1. After that, until the stable operation state is reached, the aeration tank 1 is a mixture of activated sludge flocculation flocs with insufficient metal components and sludge not containing metal components (unreacted component + breeding sludge by BOD component decomposition). There is a need to accumulate the metal component of the inorganic flocculant with respect to both, and the amount of the inorganic flocculant added needs to be increased. And when it becomes a stable operation state, since the fluctuation | variation of the ratio of the metal component containing aggregation sludge in the aeration tank 1, the reaction tank 2, the high-speed coagulation sedimentation tank 3, and the return line L1 decreases, the organic thrown into the aeration tank 1 The inorganic flocculant is reduced in accordance with the amount of wastewater discharged. That is, when the required time from the start of operation to the stable operation becomes longer, the amount of the metal component contained in the excess sludge discharged from the excess sludge discharge line L2 also increases, so the amount of the inorganic flocculant input also increases.

  In contrast, in the coagulation sedimentation activated sludge treatment system 100 according to the present embodiment, sludge containing activated sludge aggregation flocs generated by adding an inorganic flocculant at the start of operation is used as seed sludge in the aeration tank 1. The operation starts with the power being turned on. Thereby, compared with the case where the sludge in which the metal component is not accumulated is added, the accumulation of the metal component in the sludge is promoted, and the aeration tank 1, the reaction tank 2, the high-speed coagulation sedimentation tank 3, and the return line L1 The inorganic flocculant added before the metal component concentration of sludge shifts to the stable operation state is reduced and the time required to shift to the stable operation state is shortened.

  As the sludge containing activated sludge flocculation floc to be put into the aeration tank 1 at the start of operation, it is preferable that the surface charge of the sludge is in a neutralized state. Here, as a method for evaluating the surface charge of the colloidal particles, there are a colloid titration method and a zeta potential method, and any method may be used.

  Moreover, the method of producing the seed sludge which added the inorganic flocculant is not specifically limited. For example, seed sludge may be created by mixing sludge and an inorganic flocculant in an aeration tank, or sludge to which an inorganic flocculant has been added in advance may be introduced into the aeration tank.

  Hereinafter, the effects of the present invention will be described with reference to examples. FIG. 2 shows the results of verifying the effect of shortening the time required to reach a steady state by introducing sludge containing activated sludge aggregation floc into the aeration tank 1. Specifically, activated sludge added with sulfuric acid band, which is an Al-based inorganic flocculant so as to have a concentration of 5000 mg / L, is introduced as seed sludge into the aeration tank 1 to start sludge sedimentation in the aeration liquid. As a property, the initial sedimentation property of sludge is measured. The sludge to which the inorganic flocculant is not added (raw sludge) has an initial sedimentation rate of 0.45 m / hr (triangle mark on the 0th day in the figure), and the initial sedimentation rate of the seed sludge after adding the sulfuric acid band is 1 It was 0.52 m / hr (circle on the 0th day in the figure). Here, the initial settling speed indicates the initial settling speed (0 to 5 min) of the sludge settling curve. Specifically, the sedimentation speed in the initial linear portion of the sludge sedimentation curve as shown in FIG. 3 is shown. As shown in FIG. 2, the initial settling velocity gradually increased after the start of operation, and after about 15 days, the initial settling velocity reached equilibrium at about 5 m / hr, resulting in stable operation. When the seed sludge that is put into the aeration tank at the start of operation is changed to the sludge to which no inorganic flocculant is added as in the prior art, it takes 1 to 2 months before stable operation is achieved. Therefore, by using the sludge to which the inorganic flocculant is added as in this embodiment as the seed sludge, the time required from the start of operation to the steady state can be greatly shortened, and the amount of the inorganic flocculant used in the meantime can be reduced. It was confirmed that it was reduced.

  FIG. 4 is a diagram showing the results of studies on the amount of inorganic flocculant added to the sludge to be introduced as seed sludge. Specifically, the results of measuring the initial sedimentation rate and the surface charge (colloid titration value) when the addition rate of the sulfuric acid band is changed to 5000 mg / L, 10000 mg / L, and 20000 mg / L are shown. As shown in FIG. 4, it was confirmed that the initial sedimentation rate was decreased and the colloid titration value was increased by increasing the input amount (addition rate) of the sulfuric acid band. According to the result of FIG. 4, when the concentration of the inorganic flocculant is set to 5000 mg / L, which has the highest initial sedimentation rate, the colloid titration value is almost zero, that is, a charge neutralized state. In other words, by adding an inorganic flocculant so that the surface charge of the seed sludge is in a charge neutralized state, the initial sedimentation rate can be increased, and the time required from the start of operation to the steady state is shortened. be able to. In addition, the charge neutralization state said by this embodiment means -0.1 + 0.1 meq / g-MLSS in a colloid titration value.

  Although the present invention has been specifically described above based on the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made.

  For example, in the above embodiment, the high-speed coagulation sedimentation tank 3 is used as being particularly preferable, but a normal sedimentation tank (precipitation tank) by gravity sedimentation can also be used.

  In the above embodiment, the application to the coagulation sedimentation activated sludge treatment system in which the polymer flocculant is further added to coarsen the floc after addition of the inorganic flocculant is described, but at least the metal component-containing inorganic flocculant It is applicable to the coagulation sedimentation activated sludge treatment system to which is added.

  Moreover, in the said embodiment, although the biological reaction tank to biologically treat is used as the aeration tank 1, it can also be set as a nitrification / denitrification tank, for example.

DESCRIPTION OF SYMBOLS 1 ... Aeration tank (biological reaction tank), 2 ... Reaction tank, 3 ... High speed coagulation sedimentation tank (precipitation tank), 4 ... Inorganic flocculant addition means, 100 ... Coagulation sedimentation activated sludge processing system, L1 ... Return line.

Claims (3)

A biological reaction tank having activated sludge and biologically treating the introduced organic waste water;
An inorganic flocculant addition means for adding an inorganic flocculant to the treated water from the biological reaction tank;
A treatment tank into which the inorganic flocculant is added by the inorganic flocculant addition means is introduced, and a settling tank for settling and separating sludge,
A return line for returning a part of the sludge settled and separated in the settling tank as a returned sludge to the biological reaction tank;
With
The biological reaction tank is filled with seed sludge to which an inorganic flocculant is added at the start of operation.   The coagulation sedimentation activated sludge treatment system according to claim 1, wherein the inorganic flocculant is added to the seed sludge charged into the biological reaction tank so as to neutralize the surface charge. A biological reaction tank having activated sludge and biologically treating the introduced organic waste water;
An inorganic flocculant addition means for adding an inorganic flocculant to the treated water from the biological reaction tank;
A treatment tank into which the inorganic flocculant is added by the inorganic flocculant addition means is introduced, and a settling tank for settling and separating sludge,
A return line for returning a part of the sludge settled and separated in the settling tank as a returned sludge to the biological reaction tank;
A method for operating a coagulation sedimentation activated sludge treatment system comprising:
An operation method, wherein seed sludge to which an inorganic flocculant is added is put into the biological reaction tank at the start of operation.

Images