JP2010274180A - Water treatment method and water treatment system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method capable of effectively performing water treatment of water to be treated which contains ferrous ions. <P>SOLUTION: The water treatment method includes: a first step of oxidizing the ferrous ions contained in the water to be treated; a second step of giving carriers into the water to be treated, depositing iron oxyhydroxide after oxidation onto surfaces of the carriers and stripping the iron oxyhydroxide from the surfaces of the carriers by means of flow of the water to be treated; a third step of injecting an inorganic coagulant into the water to be treated; a fourth step of quickly stirring the water to be treated; and a fifth step of introducing the water to be treated into a sedimentation pond involving an upward stream and causing the water to be treated to pass between a plurality of inclined plates arranged in routes of the upward stream. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a water treatment method for treating water to be treated such as groundwater containing ferrous ions.

  Groundwater contains a larger amount of iron than surface water, and most of the iron is present as ferrous ions. When groundwater is treated with water, it is necessary to remove ferrous ions, and for example, there is a method described in Patent Document 1.

Japanese Patent Laid-Open No. 9-1157

  Generally, in order to remove ferrous ions from the water to be treated, a method of injecting chlorine into the water to be treated to oxidize the ferrous ions to form iron hydroxide and then remove the ferrous ions may be employed. Many. Although this method has the advantage that the oxidation rate is high and the oxidation equipment can be made compact, the iron hydroxide particles formed by this method become coarse and low-density, while remaining fine. Since there are many particles, there was a problem that the removal rate of iron hydroxide particles in the coagulation sedimentation was low. In addition, since a large amount of aggregating agent is injected to improve the removal rate of fine particles during the precipitation treatment, there is a problem that the flocs formed become coarser and less dense. Therefore, even if the oxidation method that can form fine-grained and high-density iron oxyhydroxide, which has been used in filtration treatment, is adopted, flocs after agglomeration treatment become coarse-grained and low-density. The oxidation method has not been applied to coagulation precipitation. In addition, the number of fine flocs remaining in the precipitated water is large, which not only increases the amount of fine flocs leaking into the filtered water, but also lowers the manganese removal effect because it coats the filter medium surface of the sand layer. There was a problem of becoming. As a result, the frequency of washing the filtration pond increased and the sedimentation concentration rate of the generated sludge was extremely poor. Therefore, the sludge treatment is difficult and the treatment cost is increased.

  This invention is made | formed in order to solve the said problem, and it aims at providing the water treatment method which can perform the water treatment of the to-be-processed water containing a ferrous ion effectively.

  The water treatment method according to the present invention includes a first step of oxidizing ferrous ions contained in water to be treated, a carrier provided to the water to be treated, and oxidized iron oxyhydroxide on the surface of the carrier. A second step of separating the iron oxyhydroxide from the surface of the carrier by the flow of the water to be treated, a third step of injecting an inorganic flocculant into the water to be treated, and a step of rapidly stirring the water to be treated. In 4 steps, water to be treated was introduced into a sedimentation basin with an upward flow, and in the sedimentation basin, a sludge / blanket layer in which fine grains and dense mother floc were accumulated at a high concentration, and a clarification separation zone were arranged. And a fifth step for allowing passage between a plurality of stages of upward-flow inclined plates or upward-flow inclined pipes.

Conventionally, rapid stirring intensity G _R value low, taking short rapid stirring time T _R values, have relied particles and fine flocks agglomeration only adhesion during coarse, low densification coagulant particles It was. As a result, many of the problems such as coarse and low floc flocs, fine iron hydroxide particles and fine floc remaining in the precipitated water are caused by the aggregation conditions of the third and fourth steps. To solve the problem, it is important to keep the Me / SS ratio low and strengthen the stirring conditions.

  In the water treatment method, the fifth step is a cross-flow sedimentation basin that separates the flocs formed in the conventional third and fourth steps under free settling, or a sludge / blanket type that accumulates coarse and low-density mother flocs. Instead of a high-speed coagulation sedimentation basin, it is possible to realize a sludge / blanket type high-speed coagulation sedimentation basin that accumulates fine grains and dense mother floc in high concentration.

  In the water treatment method, in the second step, water to be treated can be performed in a water tank with an upward flow.

  The fine and high-density iron oxyhydroxide precipitated on the support in the second step is fine while maintaining the fine and high density in the aggregation process of the third and fourth steps and the precipitation separation process of the fifth step. Agglomerated fine flocs can be highly separated.

  In the water treatment method, in the fourth step, the water to be treated can be divided into two or more sections in series and passed through a rapid stirring tank so that the water can be sequentially transferred.

  In the third step, the Me / SS ratio, which is the ratio of the metal content Me in the inorganic flocculant and the SS concentration in the water to be treated flowing into the rapid stirring tank, is 0.1 or less, and further after rapid stirring. The inorganic flocculant can be injected so that STR, which is an index indicating the residual amount of flocculant particles, is 2.5 or less.

Further, rapid agitation intensity _{G R} value in the fourth step is set to 150s ^-1 over rapid stirring time _{T R} value can be 3 minutes or more.

  The upward flow inclined plate in the fifth step may have a mounting pitch of 50 mm or less, which is the interval between the inclined plates.

  Moreover, 10 mg / L or less inorganic flocculant can be reinject | poured with respect to the rapid stirring tank exit water in a 5th step.

  The index SDI value indicating the concentration of the mother floc of the sludge / blanket in the fifth step can be 4.0 mg / mL or more, preferably 6.0 mg / mL or more.

  Moreover, the water treatment system according to the present invention includes an oxidizing means for oxidizing ferrous ions contained in the water to be treated and a support, and deposits oxidized iron oxyhydroxide on the surface of the support. A fluid tank for peeling iron oxyhydroxide from the surface of the carrier by the flow of the treated water, an inorganic flocculant injecting means for injecting the inorganic flocculant into the treated water, a rapid stirring tank, A sedimentation basin having a sludge blanket layer in which mother floc is accumulated at a high concentration and a clarification separation zone, and a plurality of upwardly inclined plates or upwardly inclined tubes in the clarification separation zone. Yes.

  In the water treatment system, an upward flow that causes the water to be treated to flow upward may flow in the fluid tank.

  The said water treatment system shall be provided so that the said rapid stirring tank may be divided | segmented into two or more divisions in series, and it can transfer to it sequentially.

  In the water treatment system, in the inorganic flocculant injection means, the Me / SS ratio, which is the ratio between the metal content Me in the inorganic flocculant and the SS concentration in the water to be treated flowing into the rapid stirring tank, is 0. The inorganic flocculant can be injected so that the STR, which is an index indicating the residual amount of the flocculant particles after rapid stirring, is 2.5 or less.

The water treatment system, wherein the rapid agitation tank, and the rapid agitation intensity G _R value 150s ^-1 or more, rapid stirring time T _R values may be not less than 3 minutes.

  In the water treatment system, the upward flow inclined plate may have an attachment pitch which is an interval between the inclined plates of 50 mm or less.

  The water treatment system may further include injection means for reinjecting 10 mg / L or less of the inorganic flocculant with respect to the rapid stirring tank outlet water.

  In the water treatment system, the index SDI value indicating the concentration of sludge blanket mother floc in the sedimentation basin may be 4.0 mg / mL or more, preferably 6.0 mg / mL or more. .

  The water treatment method according to the present invention enables effective water treatment.

It is explanatory drawing which shows the water treatment system in one Embodiment of this invention.

  Hereinafter, an embodiment of a water treatment method according to the present invention will be described. FIG. 1 is a schematic configuration diagram of a system that performs a water treatment method according to the present embodiment.

  As shown in FIG. 1, this system treats water to be treated such as ground water containing ferrous ions. Here, water treatment of groundwater containing ferrous ions will be described. First, air 2 is injected into the inflow pipe 1 into which groundwater to be treated flows (oxidation means). Thereby, in the gas-liquid contact tank 3 of the first tank to which the inflow pipe 1 is connected, ferrous ions are oxidized. The treated water that has been oxidized is introduced into the catalytic oxidation tank (fluid tank) 4 of the second tank. An upward flow is formed in the catalytic oxidation tank 4 of the second tank, and the water to be treated is introduced from below the catalytic oxidation tank 4 of the second tank and moves upward. In this process, the catalyst oxidation tank 4 of the second tank is filled with the carrier 5. The carrier can be, for example, sand particles having a specific gravity of 1 or more, synthetic resin, glass or the like. Further, it is preferably a spherical or irregular shaped particle having a large surface area per unit volume, as long as it can flow by upward flow. Oxidized iron oxyhydroxide precipitates on the surface of the support due to the catalytic action of the support. In the process in which the water to be treated is upward, the carrier under flow is subjected to a mutual shearing action, and as a result, the iron oxyhydroxide on the surface of the carrier is peeled off. Thus, the water to be treated containing the separated iron oxyhydroxide is discharged from the upper part of the catalytic oxidation tank 4 of the second tank. It should be noted that iron oxyhydroxide is iron rust itself, while ferric hydroxide is a flocculent floc and has a large difference in density.

  Subsequently, the inorganic flocculant 6 is injected into this water to be treated (inorganic flocculant injection means) and then introduced into the third tank 7. Examples of the inorganic flocculant used here include iron-silica inorganic polymer flocculant (PSI), which is a combination of aluminum sulfate, iron and polymerized silicic acid (silica), which is an inorganic anionic polymer, and polyaluminum chloride flocculant ( Examples thereof include inorganic flocculants such as PAC). Furthermore, in addition to the use of these inorganic flocculants, organic polymer flocculants can be used in combination.

  The third tank 7 is a rapid stirring tank, and is composed of three processing tanks (sub-processing tanks), each having a stirring blade that is rotated by a motor 8. In this example, three treatment tanks are provided, but two or more are preferable. This is because, under the same volume and stirring strength, the number of fine particles can be reduced as the number of tank divisions is increased. Here, the inorganic flocculant is injected into the raw water before being introduced into the rapid stirring tank 7, but the inorganic flocculant may be injected into the water to be treated after being introduced into the rapid stirring tank 7.

  Then, when the rapid stirring is performed after adjusting the injection amount of the inorganic flocculant, the suspended particles present in the water to be treated collide with the flocculant particles in the inorganic flocculant, and a predetermined amount of about 1 to 60 μm is obtained. A fine floc having a particle size distribution is formed. Furthermore, in this embodiment, the injection rate of the inorganic flocculant and the rapid stirring strength are controlled so that the STR indicating the residual amount of the flocculant particles in the water to be treated is 2.0 or less at the outlet of the rapid stirring tank. . STR is Suction Time Ratio: When the same filter paper is aspirated with the same temperature and the same amount of distilled water as the treated water, the suction time of treated water is Ts, and distilled water Is the index expressed by Ts / Tv.

  Here, when the injection rate of the inorganic flocculant is increased, even if a high rapid stirring strength is adopted, the STR after the rapid stirring becomes high, and the flocculant particles in the subsequent sludge / blanket layer are coarse / low density. It will become. Since the flocculant particles are reduced by being incorporated into the fine flocs during the agglomeration of the suspended particles present in the water to be treated, the injection rate of the inorganic flocculant is limited as much as possible, rapid stirring strength, By increasing the stirring time, the STR is preferably set to a lower value of 2.5 or less.

  The effect of removing suspended particles present in the water to be treated is expressed by the following collision frequency formula.

dn _i / dt = α × β × n _i × n _j (1)
Here, α: collision efficiency, β: collision frequency, n _i : number of inflowing particles, n _j : number of existing flocs The removal speed of inflowing i particles is the number of collisions β of inflowing particles i with existing floc j and the number of collisions It is determined by the rate α that adheres to the product and is proportional to the product of four factors. Adhesion was given by the flocculant particles, and conventionally, rapid stirring for improving the collision frequency β was not performed or even if installed, the rapid stirring strength GR value and the rapid stirring time TR value were low. Since the increase in the number of existing flocs n _j in the rapid agitation tank cannot be substantially expected, conventionally, an operation method that relies only on the increase of the coagulant injection rate and the adhesion force, that is, the collision efficiency α has been taken. For this reason, the subsequent sludge and blanket mother flocs are inevitably coarse and low in density. Therefore, there is no significance of forming fine-grained and dense iron oxyhydroxide, and there was a background that a simpler chlorine oxidation method was adopted.

As a calculation method of STR, for example, 500 mL of sample water and distilled water having the same temperature and the same amount as this are respectively used for membrane filter paper of 45 mm in total (filter paper manufactured by ADVANTEC having an average pore diameter of 0.45 μm and a porosity of 38%). The suction time with the attached suction device (specifically, a device equipped with a vacuum container, a filter folder, and a suction pump with a vacuum reach of 26.7 kPa) was defined as T _s (sec) and T _v (sec), respectively. STR = T _s / T _v ratio in the case.

  As described above, when an inorganic flocculant is injected so that the STR is 2.5 or less and rapid stirring is performed, the fine suspended particles contained in the water to be treated are simultaneously reduced and the fine flocs are reduced. Agglomeration and densification are achieved.

  Next, the water to be treated containing the fine flocs is allowed to flow into a sludge / blanket layer in which fine grains / high density mother flocs are highly accumulated, and fine grains / high density fine flocs formed in the rapid stirring process are used as mother substances. Detain in Flock.

The inflection of the fine flock by the mother flock here can also be explained by the collision frequency formula. First, STR is 2.5 or more, coagulant particles are coarse, low densification in the sludge blanket layer, depositing a fine-dense mother floc mutually to coarsening, the mother flock number n _j Decrease. At this time, the concentration of the mother floc decreases.

  If the fine flocs and dense flocs formed during the rapid stirring process are retained in the mother floc and the STR is kept low at 2.5 or less, the mother floc retains a large sedimentation rate and high concentration even though it has a small diameter. become. The difference between the sludge blanket layer and the rapid agitation process is that an extremely high mother floc is accumulated. Moreover, since the gap between the mother flocs is narrowed, an extremely high collision frequency β is given to the inflowing fine floc passing through the periphery, and the removal rate is improved.

In other words, the sludge / blanket layer has a particle separation characteristic that can obtain a high collision efficiency α without requiring high adhesion force from the high concentration mother floc number n _j and high collision frequency β in the collision frequency formula. is doing. This tendency becomes higher when the inflowing particles have a diameter of 3.0 μm or more. Therefore, agglomeration during the rapid stirring process is important.

  However, the condition for keeping the STR as low as 2.5 or less is intended to maintain the mother floc finely and densely, but a part of the mother floc is destroyed by the shearing force in the fluidized bed, and the mother floc fragments Will flow into the sedimentation water.

  Conventionally, it has been considered that the agglomeration conditions as described above should not be adopted as increasing the turbidity of the precipitated water. However, the fine flocs originally containing the mother floc fragments are particles that have been separated in subsequent filtration processes. Therefore, when the mounting pitch of the upward flow inclined plate is narrowed, the formation of a vortex toward the inclined plate retaining surface is confirmed by the shearing action of the lower end of the inclined plate, and the fine flock including the mother flock fragments transported by the eddy current is It collides with existing flocs on the inclined plate retaining surface and becomes highly separable by the same separation mechanism as sand filtration. That is, fine grains and high-density fine flocs do not have a large adhesive force, and thus have such a shape and a large sedimentation speed. The fine flock, which gradually increases in diameter by colliding with the existing floc on the inclined plate retaining surface, can easily slide down because of its low adhesive force with the inclined plate. At that time, a fine flock restrained downward is taken up, and the diameter is further increased to obtain a larger settling velocity, which is collected in the sludge / blanket layer.

  In other words, the present invention has been devised by changing all the disadvantages in agglomeration, which should be avoided in the past, from rapid stirring to separation in an upward flow inclined plate.

Further, rapid agitation is carried out in each processing tank, it is preferable that the 150 sec ^-1 or more _{G R} value is rapid stirring intensity. At this time, T _R value is rapid stirring time is preferably 1 minute or more, more preferably be at least 3 minutes. Incidentally, _{G R} value, the agitation coefficient C, and the area of the stirring blade A (m ^2), the peripheral speed of the stirring blade v (m / sec), the kinematic viscosity γ (m ² / sec), stirred tank When the volume (capacity) of V is V (m ³ ), it is calculated by the following formula.

In general, in each treatment tank that performs rapid stirring, the first condition for obtaining a fine floc with a high density is to employ a low coagulant injection rate. In the same conditions, to increase the agitation intensity G _R, yet by increasing the stirring time T _R, coagulant particles, since it is consumed while providing adhesion upon impact of the suspended particles and fine flocks, STR decreases As a result, the density of fine flocs is further increased. However, when a high flocculant injection rate is employed such that the STR exceeds a predetermined value and a large amount of inorganic flocculant remains after rapid stirring, coarsening of flocculant particles in the subsequent flocking step, Since the reduction in density is inevitable, fine flocs that have been refined and densified by rapid stirring inevitably become coarser and lower in density. Therefore, by setting the STR to 2.5 or less, it is possible to prevent the floc from being coarsened and reduced in density.

  The inorganic flocculant injected prior to the rapid stirring is preferably as follows. That is, the Me / SS ratio, which is the ratio of the metal content Me in the inorganic flocculant and the SS concentration in the water to be treated flowing into the rapid stirring tank, is 0.1 or less, and further the flocculant particles after rapid stirring It is preferable to inject the inorganic flocculant so that the STR, which is an index indicating the residual amount, is 2.5 or less.

  Thus, the water to be treated treated in the rapid stirring tank 7 is introduced into the sludge / blanket type high-speed coagulation sedimentation basin 9. An upward flow is formed in the sedimentation basin, and the water to be treated is introduced from below and discharged from above. A plurality of inclined plates 11 are arranged in the clarification separation zone at the upper part of the path of the water to be treated in the settling basin. The interval between the inclined plates 11 is preferably 50 mm or less, for example. As described above, in the rapid agitation tank 7, flocs with finer and higher density are formed, and these can be effectively removed by the inclined plate 11. The high-speed sedimentation basin 9 can generally follow a known device shape, and is provided with a concentrator 12, a sludge extraction pipe 14, and a sedimentation water outflow pipe 13. However, it can be said that the actual situation is completely different. In other words, in the conventional coagulation sedimentation treatment, 1) it was premised on the formation of flocs having a large diameter: “The attempt to improve the removal rate by increasing the sedimentation velocity V of the floc is as large as possible, and the sedimentation velocity is as high as possible. It is intended to make large flocs, and research on flocculants and coagulants, research on the state of coagulation operations, etc. has been carried out. ”2) Since flocs with large diameters cannot withstand shearing forces, stirring strength There is an upper limit: “In the flock formation stage, increasing the G value increases the floc growth rate, but on the other hand, the increase in shear force causes the floc to break, so increasing the G value There is a limit. " These two ways of thinking have resulted in low efficiency of the conventional coagulation-precipitation treatment, which has been a factor in increasing the treatment cost.

  The inventor confirmed that the agglomeration treatment is a technique for removing the smallest suspended particles contained in the water to be treated, and that the agglomeration characteristics and the separation characteristics both depend on the collision frequency formula of the above formula (1). did. The conventional coagulation-precipitation method has suppressed the G value because floc breakage occurs, but in the same formula, the collision frequency β is kept low, and the coagulant injection rate is increased, thereby improving the collision efficiency α related to the adhesion force. It can be pointed out that the driving method was strongly dependent. Moreover, the existing number of flocs nj in the agitation tank decreases as the agglomeration progresses, and hardly contributes to the improvement of the floc formation rate (dn / dt).

  However, if the agglomeration conditions that can give a low flocculant injection rate and high collision frequency are adopted, individual fine flocs cannot be separated under free settling, but sludge blankets in which the existing flocs are accumulated at high concentrations. Suppresses fine flocs with a diameter of 3.0 μm or more at a high rate of 97% or more, and the fine and dense fine flocs formed at that time form fine and dense mother flocs, It has been found that it has a large group sedimentation rate far exceeding that of high concentration. That is, by increasing the number of existing flocs and the collision frequency β in the collision frequency formula, the retention, that is, the separation efficiency is dramatically improved, and precipitation separation can be realized without forming a floc having a large diameter.

Note that this agglomeration condition uses a rapid agitation tank that is divided in series into two or more compartments so that it can be sequentially transferred, and adopts a low coagulant injection rate of Me / SS of 0.1 or less. _R value 150s ^-1 or more, at T _R value 3 minutes or more, is achieved by achieving a reduction in water residual amount of minimum suspended particle number and the aggregating agent particles contained in the water to be treated (STR). As a result, the index SDI value indicating the concentration of the mother floc increases.

  In this flocculation condition, in the case of the conventional sludge blanket type high-speed flocculation sedimentation basin, the clarification zone is separated by free sedimentation, so by outflow into the sediment water such as mother floc fragments that flow out along with the destruction of the mother floc, Precipitation water turbidity increases. Therefore, it led to the explanation that “an increase in stirring strength destroys the floc”. In addition, inclined plates or inclined tubes are usually used in the fining zone, but the mounting pitch (interval between inclined plates) is wide and the separation effect is not high.

  However, when the mounting pitch of the inclined plate is reduced, the vortex generated by the shearing action of the lower end of the inclined plate is directed toward the inclined plate retaining surface, and the mother floc fragments, which have been caused by the conventional breakage and cause the increased sediment water turbidity, The inventors have found that there is a collision with the existing detained micro flocs, and the detained and separated without flowing into the precipitated water. More specifically, a fine floc having a diameter of 3.0 to 7.0 μm cannot be separated under free settling, and the removal rate is only 9% at a mounting pitch of 50 mm, but about 60% at 24 mm and 75% at 11 mm. It becomes. Further, when the fine floc has a diameter of 7.0 μm or more, the removal rate is 50% at a mounting pitch of 50 mm, and the removal rate is 85% or more at both 24 mm and 11 mm.

  The separation effect here is based on the collision frequency equation of equation (1) and based on the same separation mechanism as the collision and detention of the mother flock and the inflow fine floc. In other words, instead of the conventional method of coagulation sedimentation that separates flocs under free sedimentation, a new concept of aggregation that introduces two contact floc formation functions of a mother floc with a large group sedimentation speed and an inclined plate with a narrow mounting pitch. By providing a precipitation method, it was possible to adopt the “iron oxyhydroxide method” that has been employed only by filtration.

  As described above, according to the present embodiment, it is possible to efficiently oxidize ferrous ions in the water to be treated, and fine-grained and dense iron oxyoxide can be formed. In addition, the inorganic flocculant is injected into the fine-grained, high-density iron oxyoxide with the Me / SS ratio limited to 0.1 or less, and then rapidly stirred, so the iron oxyhydroxide is finely divided. Fine particles and high density fine flocs can be formed while keeping the grains and high density, and for example, the number of iron oxyhydroxide particles of 3.0 μm or less can be reduced.

  Furthermore, in the high-speed coagulation sedimentation basin, high-density mother flocs are highly accumulated, so that an extremely high collision frequency can be given between the mother flocs and the fine flocs, resulting in a high flocculant injection rate. There is no need to do. Therefore, the fine floc can be restrained at a high rate. In the high-speed coagulation sedimentation basin, an inclined plate 11 having a narrow mounting pitch is provided in the upper clarification zone. For this reason, the fine flocs of each diameter including the mother floc fragments that flow out with the destruction of the mother floc due to the low flocculant injection rate can be separated with high efficiency, and very good precipitated water can be obtained.

  And since the number of fine flocs remaining in the precipitated water is small and the fine particles are dense, it is possible to reduce the amount of fine floc leakage into the filtered water. As a result, the quality of filtered water can be dramatically improved, and the frequency of washing the filtration pond can be reduced. In addition, since the mother floc of the sludge blanket 10 is maintained at a high density, the treatment and disposal of the generated sludge can be greatly reduced. Furthermore, since the coagulation sedimentation efficiency is extremely high, the sedimentation basin can be made compact and the construction cost can be reduced. Moreover, the reduction in the frequency of washing the filter basin and the reduction in treatment and disposal of the generated sludge will lead to a reduction in the cost of water purification.

  Examples of the present invention will be described below. However, the present invention is not limited to the following examples. Here, this example and two comparative examples are examined.

  Comparative Example 1 in Table 1 uses sodium hypochlorite as the oxidizing agent for ferrous hydroxide. Therefore, the oxidation treatment was carried out without installing the catalyst oxidation tank 4 shown in FIG. Moreover, the conventional low and short stirring conditions were employ | adopted for the agglomeration process, and 0.3% as a Al / SS ratio was inject | poured and flocculation process was performed. However, as the suspended particles, particles having a minimum diameter of 0.5 to 1.0 μm remained in a large amount of 213,000 particles / mL, and the precipitated water turbidity was as high as 0.24 degrees. In Comparative Example 1, not only the ferric hydroxide formed in the oxidation process already has a high water content, but the flocculant particles injected in the coagulation process are represented by 3.4 of the precipitated water STR. Thus, the mixture remained after rapid stirring, and became coarse and thin in the sludge / blanket layer. As a result, the SDI value indicating floc concentration was as low as 2.21 mg / mL, and subsequent filtration treatment and sludge treatment were extremely difficult.

  In Comparative Example 2, air was used for the oxidation treatment of ferrous hydroxide, and iron oxyhydroxide was formed by the gas-liquid contact tank 3 and the catalyst oxidation tank 4 of FIG. Therefore, the density of iron oxyhydroxide at this stage is high. However, in the agglomeration process, the number of divisions in the tank was 1, the residence time was 1 minute, and the conventional low rapid stirring conditions were adopted, and the agglomeration process was performed by injecting PAC still having a high Al / SS ratio of 0.2. As a result, a large number of particles of 0.5 to 1.0 μm remain in the precipitated water, and the turbidity of the precipitated water is still high at 0.16 degrees, and the reduction is not sufficient. Therefore, as indicated by 2.6 of the precipitated water STR, coarse and low density flocculant particles remaining after rapid stirring are inevitable. That is, it can be seen that the SDI value indicating floc concentration is slightly higher at 3.82 mg / mL than Comparative Example 1, but it is not sufficient. As described above, even when high-concentration iron oxyhydroxide is formed, the coarse and low-density flocculant particles spoil it. Therefore, the difficulty of subsequent filtration treatment and sludge treatment was not significantly different from that of Comparative Example 1.

  In contrast, the high-efficiency separation method of the example uses the system of FIG. 1 and uses air for the oxidation treatment of ferrous hydroxide as in Comparative Example 2, and uses the gas-liquid contact tank 3 and the catalytic oxidation tank of FIG. In 4, iron oxyhydroxide was formed. Next, the experiment was conducted by adopting a rapid stirring condition with a high GT value of 3 tank divisions and a residence time of 6 minutes and a low flocculant injection rate of 0.08 as the Al / SS ratio in the coagulation treatment process. Moreover, it processed so that it might comprise the 5th step which passes between the several steps of upward flow inclination boards arrange | positioned in the clarification separation zone of a sludge blanket layer. As a result, the number of particles of 0.5 to 1.0 μm was first reduced in the aggregation process, and the same particles in the precipitated water were reduced to 86900 particles / mL, and the precipitated water turbidity was decreased to 0.08 degrees. Moreover, since the residual amount of flocculant particles after rapid stirring was reduced so that the precipitated water STR was lowered to 1.20 in addition to adopting a low Al / SS ratio, the density of the mother floc was kept high and concentrated. The SDI value indicating sex was improved to 6.24 mg / mL. By the way, if the residual amount of the flocculant particles after rapid stirring is reduced in this way, the mother floc cannot be given sufficient adhesion to maintain its diameter, and the mother floc breaks out into the sediment water due to the destruction of the mother floc. However, since the mounting pitch, which is the interval between the inclined plates, is narrowed, it was possible to prevent the mother floc fragments from flowing out into the settling water. As a result, filtration treatment and sludge treatment can be greatly reduced, and treatment costs can be reduced.

3 Gas-liquid contact tank 4 Catalytic oxidation tank 7 Rapid stirring tank 9 High-speed sedimentation tank 11 Upwardly inclined plate

Claims (16)

A first step of oxidizing ferrous ions contained in the water to be treated;
A second step of providing a carrier to the water to be treated, precipitating the oxidized iron oxyhydroxide on the surface of the carrier, and peeling the iron oxyhydroxide from the surface of the carrier by the flow of the water to be treated;
A third step of injecting an inorganic flocculant into the water to be treated;
A fourth step of rapidly stirring the water to be treated;
The treated water is introduced into a sedimentation basin with an upward flow, and in the sedimentation basin, a sludge / blanket layer in which fine grains and dense mother floc are concentrated at a high concentration, and a plurality of stages arranged in the clarification separation zone A water treatment method comprising: a fifth step of passing between a counterflow inclined plate or an upward flow inclined pipe.   The water treatment method according to claim 1, wherein the second step is performed in a water tank with upward flow of water to be treated.   The water treatment method according to claim 1 or 2, wherein the fourth step is performed by passing the water to be treated through a rapid stirring tank divided in series into two or more sections so as to be sequentially transferred.   In the third step, the Me / SS ratio, which is the ratio of the metal content Me in the inorganic flocculant and the SS concentration in the water to be treated flowing into the rapid stirring tank, is 0.1 or less, and more rapidly The water treatment method according to any one of claims 1 to 3, wherein the inorganic flocculant is injected so that STR, which is an index indicating the residual amount of flocculant particles after stirring, is 2.5 or less. The rapid agitation intensity G _R value in the fourth step is at 150s ^-1 or more, rapid stirring time T _R value is more than 3 minutes, the water treatment method according to any one of claims 1 to 4.   6. The water treatment method according to claim 1, wherein the upward flow inclined plate in the fifth step has an attachment pitch which is an interval between the inclined plates of 50 mm or less.   The water treatment method according to any one of claims 1 to 6, wherein an inorganic flocculant of 10 mg / L or less is reinjected with respect to the rapid stirring tank outlet water in the fifth step.   The index SDI value indicating the concentration of the mother floc of the sludge blanket in the fifth step is 4.0 mg / mL or more, preferably 6.0 mg / mL or more. Water treatment method. Oxidizing means for oxidizing ferrous ions contained in the water to be treated;
A fluid tank filled with a carrier, depositing oxidized iron oxyhydroxide on the surface of the carrier, and peeling iron oxyhydroxide from the surface of the carrier by the flow of water to be treated;
An inorganic flocculant injection means for injecting an inorganic flocculant into the water to be treated;
A rapid stirring tank;
A sedimentation basin with a sludge / blanket layer and fine clarification zone with high concentration of fine-grained and dense mother floc and a clarification separation zone. When,
A water treatment system.   The water treatment system according to claim 9, wherein an upward flow that causes the water to be treated to flow is flowing in the fluid tank.   The water treatment system according to claim 9 or 10, wherein the rapid stirring tank is divided into two or more sections in series and is provided so as to be able to move sequentially.   In the inorganic flocculant injection means, the Me / SS ratio, which is the ratio of the metal content Me in the inorganic flocculant and the SS concentration in the water to be treated flowing into the rapid stirring tank, is 0.1 or less, The water treatment system according to any one of claims 9 to 11, wherein the inorganic flocculant is injected so that STR, which is an index indicating the residual amount of flocculant particles after rapid stirring, is 2.5 or less. Wherein in the rapid agitation tank, and the rapid agitation intensity G _R value 150s ^-1 or more, rapid stirring time T _R value is greater than or equal to 3 minutes, water treatment system according to any of claims 9-12.   The water treatment system according to any one of claims 9 to 13, wherein the upward flow inclined plate has an attachment pitch that is an interval between the inclined plates of 50 mm or less.   The water treatment system according to claim 9, further comprising injection means for re-injecting 10 mg / L or less of the inorganic flocculant with respect to the rapid stirring tank outlet water.   The index SDI value indicating the concentration of the sludge blanket mother floc in the sedimentation basin is 4.0 mg / mL or more, preferably 6.0 mg / mL or more. Water treatment system.

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