JP2013027821A - Sand filtration device, and method for producing filter sand therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and effectively remove COD (chemical oxygen demand) by filtration without needing special facilities.SOLUTION: In a moving bed type upflow sand filtration device 2, a filter sand supporting metals is used. Raw water flows upward from raw water dispersion device 9, and is filtered while passing a filter layer 6 to become treated water. A filter sand flows gradually through the filter layer 6 from top down. While the filter sand exists below from the raw water dispersion device 9, the COD component adsorbed to the filter sand undergoes biolysis though its speed is slow. Further, a microbial group which can decompose the persistent COD is formed by mixing a backwash effluent.

Description

  The present invention relates to a sand filtration device capable of reducing COD in water to be treated such as waste water and a method for producing filter sand used therefor.

  In recent years, water pollution in public water bodies has been improved with the development of sewers. However, the COD concentration in closed water areas (Tokyo Bay, Ise Bay, Seto Inland Sea, or lakes such as Lake Biwa) has not decreased. Although this may require removal of nutrient salts such as nitrogen and phosphorus, a major reason is that COD that cannot be decomposed by ordinary water treatment remains in the treated water. The term COD (chemical oxygen demand) is an indicator of water pollution, but in the following description, it may be used to mean a substance such as an organic substance contained in treated water.

  Conventionally, as a technique for removing COD, a method using coagulation sedimentation, a method using ozone treatment, a method using biological activated carbon, and the like are known. There is also a biofilm filtration technique for removing COD by attaching a biofilm to a carrier for filtration (Patent Documents 1 and 2). Furthermore, the technique which combined ozone treatment and biofilm filtration is also proposed (patent document 3, nonpatent literature 1).

JP 2004-237219 A Japanese Patent Laid-Open No. 11-128968 JP-A-9-29285

Keiichi Sone et al., “Sewage Reclaimed Water Production System Combining Ozone and Separation Membrane”, Proceedings of Sanitary Engineering Symposium, November 1, 2001, p. 220-224

However, in the method using coagulation and precipitation, the cost of the drug is expensive, and in the method using ozone treatment and biological activated carbon, the equipment cost and the running cost are expensive, which is a bottleneck when introducing it. Moreover, in the method using biofilm filtration, there is a problem that maintenance and management are complicated and the effect is low, for example, it is necessary to pay attention to prevention of performance degradation due to biofilm accumulation.
For this reason, it is desired to build a system that can remove COD at low cost.

  The present invention has been made in view of the above-described problems, and provides a sand filtration device capable of realizing COD removal processing by filtration effectively and inexpensively without requiring special equipment. And it aims at providing the manufacturing method of the filtration sand used for the sand filtration apparatus collectively.

In order to achieve the above object, the sand filtration device according to the first invention comprises:
In the sand filtration device that passes the raw water through the filtration sand filled in the filtration tank and performs filtration treatment,
Soluble COD is removed by using filtration sand carrying metals as the filtration sand.

  Here, the sand filtration device is preferably a moving bed upward flow sand filtration device in which the raw water supplied from the lower part of the filtration tank becomes an upward flow, passes through the filtration sand and becomes treated water (first). 2 invention).

  In the second invention, it is preferable that the backwash waste water discharged from the sand filter is mixed into the raw water (third invention).

Moreover, the manufacturing method of the filtration sand by 4th invention is as follows.
A method for producing filtration sand used in the sand filtration device according to any one of the first to third inventions,
A step of dissolving a metal nitrate in a nitric acid solution and adjusting the pH, a step of adding untreated filtration sand into the solution and then adding NaOH again to readjust the pH, and stirring the solution followed by centrifugation A filtration sand carrying metals is obtained by performing a separation step and a step of washing a solid content obtained by centrifugation with pure water, followed by a drying step.

  In the fourth aspect of the invention, the cleaning with pure water is preferably performed until the electrical conductivity of the supernatant is 1000 μS / cm or less (the fifth aspect).

  Here, the metal nitrate may be iron nitrate or aluminum nitrate (sixth invention).

  According to the present invention, since the filtration sand carries metals, the surface of the filtration sand can be charged to a positive charge. On the other hand, among organic substances dissolved in water, especially organic substances such as humic substances contained in sewage treated water are often negatively charged, so the COD adsorption capacity of positively charged filtration sand is Becomes drastically increased, and the adsorption removal effect of COD can be maintained. Therefore, soluble COD removal that has been impossible until now can be performed simultaneously with filtration.

The flowchart which shows the manufacturing method of the filtration sand which concerns on one Embodiment of this invention. The flowchart which shows the manufacturing method of the filtration sand which concerns on other embodiment of this invention. Schematic diagram of system in which adsorption test of Example 1 and Comparative Example 1 was performed The graph which shows the adsorption test result of Example 1 and Comparative Example 1 Sectional drawing of the moving bed type upward sand filter of Example 2 and Comparative Example 2

  Next, specific embodiments of the sand filtration device according to the present invention and the method for producing the filtration sand used therein will be described with reference to the drawings.

  The present invention is based on the knowledge that the ability to adsorb COD charged to a negative charge is drastically improved by carrying a metal on the surface of the filter sand and charging the surface to a positive charge. In addition, although adsorption of COD by filtration sand reaches breakthrough while continuing the treatment, it is gradually subjected to biodegradation while being adsorbed and fixed, and can be continuously removed.

  The metal to be supported on the filter sand is not particularly limited as long as it becomes a cation, but typical metals such as alkaline earth metals and transition metals are preferable. Of these, iron, manganese, and aluminum are preferable.

  FIG. 1 and FIG. 2 exemplify flowcharts representing a method for producing metal-carrying sand (filtered sand). FIG. 1 shows an example in which iron is supported, and FIG. 2 shows an example in which aluminum is supported.

<Method for supporting iron on the surface of the filtration sand (FIG. 1)>
S1: hydrate of iron nitrate _{(Fe (NO 3) 3 ·} 9H 2 O) are weighed 25.25 g.
S2: Dissolve the weighed iron nitrate hydrate in 0.1 N (N) nitric acid (HNO ₃ ), and make up to 10 L with MQ water (ultra pure water). This solution is colorless and has pH = 1.0.
S3: A commercially available filter sand is put into the solution.
S4: Re-adjust to pH = 2.5 with 1N (N) nitric acid (HNO ₃ ), and add 5N (N) sodium hydroxide (NaOH) to the solution containing sand left for 1 hour. Add until 0. This solution changes its color to yellow brown.
S5: While stirring the solution, 1N (N) sodium hydroxide (NaOH) is added dropwise until pH = 8.0.
S6: Continue stirring for 3 hours and readjust to pH = 8.0 with 1N (N) sodium hydroxide (NaOH). At this time, the color of the solution becomes brown.
S7: Stir in the dark for 24 hours and centrifuge at 7000 g for 15 minutes.
S8 to S9: The solid content obtained by centrifugation is washed with MQ water. This washing is performed until the electrical conductivity of the supernatant of the solution becomes 1000 μS / cm (micro Siemens) or less.
S10: When the supernatant liquid has a predetermined electrical conductivity, it is dried and stored in a dark place.

<Method for supporting aluminum on the surface of the filtration sand (FIG. 2)>
T1: Weigh aluminum nitrate hydrate _{(Al (NO 3) 3 ·} 9H 2 O) 7.50g.
T2: The weighed aluminum nitrate hydrate is dissolved in 0.1 N (N) nitric acid (HNO ₃ ) and made up to 10 L with MQ water (ultra pure water).
T3: in solution, the addition of sodium silicate _{(Na 2 SiO 3 · 9H 2} O) 5.684g. This solution has pH = 3.0.
T4: Commercially available filter sand is put into the solution.
T5: readjusted to pH = 2.5 with nitric acid (HNO ₃ ) of 1N (N), and 1N sodium hydroxide (NaOH) was added to the solution containing sand left for 1 hour at pH = 7 Add dropwise until 0. This solution is first confirmed to have turbidity at pH = 4.5, and becomes considerably cloudy at pH = 7.0.
T6: If stirring is continued for 24 hours, the pH settles down to 6.5, so readjust to pH = 7.0 with 1 N sodium hydroxide (NaOH).
T7: Continue stirring for 1 month (10 minutes / 24 hours) and centrifuge at 7000 g for 15 minutes.
T8 to T9: The solid content obtained by centrifugation is washed with MQ water. This washing is performed until the electrical conductivity of the supernatant of the solution becomes 1000 μS / cm (micro Siemens) or less.
T10: When the supernatant liquid has a predetermined electrical conductivity, it is dried and stored in a dark place.

  Note that, in steps S10 and T10 described above, the purpose of drying and storing in the dark is to prevent alteration during storage. As a drying method, drying with hot air is unsuitable because the tempered sand is altered, and freeze drying or aeration drying at room temperature is preferable. In the case of long-term storage, it is preferable to keep the dry state (for example, in a desiccator if the amount is small, or in the drying chamber if the amount is large).

<Example 1, comparative example 1>
Next, in order to confirm the effect of the filtered sand carrying iron as shown in FIG. 1, water in which commercially available sodium humate is dissolved is used as raw water, and the column 1 as shown in FIG. An adsorption test was conducted by contacting the raw water with the filter sand filled. The sand used at this time is filtered sand having an effective diameter of 1.0 mm and a uniformity coefficient of 1.4 or less. As Example 1, what carried | supported iron on the said filtration sand was used, and as the comparative example 1, commercially available filtration sand was used as it was. Then, the raw water was continuously flowed into the column 1, and the evaluation was performed by measuring the COD concentration of the raw water and the treated water. In addition, the back washing | cleaning of the filter layer was not implemented.

  The result of the adsorption test is shown in FIG. As is clear from FIG. 4, in Comparative Example 1, the ratio between the raw water concentration and the treated water concentration is approximately 1, and no change is seen in the COD concentration, whereas in Example 1, the COD adsorption capacity is remarkably high. You can see that it has improved. As a result, it has been clarified that the COD adsorption ability of the filter sand can be greatly increased by loading the metal such as iron on the filter sand. Therefore, it is clear that the sand filtration apparatus using such filtration sand can remove the soluble COD component together with the filtration by the filtration layer.

<Example 2, comparative example 2>
As Example 2, the filtration layer 6 of the moving bed type upward flow sand filtration device 2 as shown in FIG. 5 is filled with the filtration sand carrying the iron described above, and the continuous operation is performed on the sewage secondary treated water. Carried out. At that time, the backwash waste water of the sand filtration device 2 was mixed with 10% of the raw water and supplied from the raw water inflow pipe 7. As a result, it was confirmed that the soluble COD removal rate was about 40%. On the other hand, as Comparative Example 2, the above-mentioned moving bed type upflow sand filtration device 2 was filled with commercially available filtration sand, and continuous operation was carried out for sewage secondary treated water. As a result, soluble COD could not be removed.

  Here, in the moving bed type upward flowing sand filtration device 2, the filtration sand (sand layer) 6 is formed by filling the container 5 in which the lower part of the cylindrical part 3 is the bottom part 4 having an inverted cone shape with the filtration sand. It is comprised so that. The raw water is supplied from the raw water inflow pipe 7 to the lower part of the filtration layer 6 through the guide pipe 8 and the raw water dispersing device 9. The raw water dispersion device 9 is a pipe having a plurality of (4 to 8) lower surfaces opened. Thus, the raw water flows out from the lower part of the raw water dispersing device 9 and is filtered by the filtration layer 6 while flowing through the filtration layer 6 to the upper part, and the treated water after the filtration overflows from the upper part and flows to the water collecting trough 10, Sent to the process. On the other hand, an air lift pipe 11 is inserted in the lower part of the container 5. By blowing air into the air lift pipe 11, the circulation force due to the specific gravity of the internal air + sand + raw water and the specific gravity of the surrounding sand + water is reduced. Due to the occurrence, dirty sand and raw water rise inside the air lift pipe 11. During this ascent, the sand is agitated and washed with air and water. The ascending air, sand and water are separated by the separator 12, and the sand is washed by the sand washer 13 in a counter flow with the filtered water and returned to the filtration layer 6 again. The water flows into the cleaning drainage pipe 15 through the holes of the orifice plate (holed plate) 14 as cleaning drainage.

  In this moving bed type upward sand filter 2, the raw water flows upward from the raw water dispersing device 9 and is filtered while passing through the filtration layer 6 to become treated water. On the other hand, the filtration sand gradually flows from the top to the bottom of the filtration layer 6, and the portion below the raw water separator 9 is a time that does not contribute to the filtration. In Example 2, the COD removal effect was greatly improved as compared with Example 1. The reason why the COD component adsorbed on the filter sand while the filter sand was below the raw water separator 9 was slow. It is also considered that a microorganism group capable of decomposing hardly decomposable COD was formed by receiving biodegradation and mixing backwash waste water. Therefore, it can be said that the moving bed type upward sand filter is an apparatus suitable for filtration for removing COD.

  In the present invention, soluble COD removal can be performed simultaneously with filtration at a low cost and effectively, so that the industrial utilization effect is great.

DESCRIPTION OF SYMBOLS 1 Column 2 Moving bed type upward flow sand filtration apparatus 6 Filtration layer (sand layer)
7 Raw water inflow pipe 9 Raw water disperser 10 Water collection trough 11 Air lift pipe 12 Separator 13 Sand washer 15 Washing drain pipe

Claims (6)

In the sand filtration device that passes the raw water through the filtration sand filled in the filtration tank and performs filtration treatment,
A sand filtration apparatus characterized in that soluble COD is removed by using filtration sand carrying metals as the filtration sand.   The sand filtration according to claim 1, wherein the sand filtration device is a moving bed type upward flow sand filtration device in which the raw water supplied from the lower part of the filtration tank becomes an upward flow and passes through the filtered sand to become treated water. apparatus.   The sand filtration apparatus according to claim 2, wherein the backwash waste water discharged from the sand filtration apparatus is mixed into raw water. It is a manufacturing method of the filtration sand used for the sand filtration device according to any one of claims 1 to 3,
A step of dissolving a metal nitrate in a nitric acid solution and adjusting the pH, a step of adding untreated filtration sand into the solution and then adding NaOH again to readjust the pH, and stirring the solution followed by centrifugation A method for producing filtration sand, characterized by obtaining filtration sand carrying metals by washing the solid content obtained by centrifugation and washing with pure water and then drying the solid. .   The method for producing filtered sand according to claim 4, wherein the washing with pure water is performed until the electrical conductivity of the supernatant is 1000 μS / cm or less.   The method for producing filtered sand according to claim 4 or 5, wherein the metal nitrate is iron nitrate or aluminum nitrate.

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