JPH01266897A - Continuous moving bed type iron removing method for utilizing iron bacteria - Google Patents

Abstract

PURPOSE:To remove iron continuously with high efficiency by moving layered fine carrier having deposited iron bacteria thereon continuously to below an aq. phase, and feeding water contg. Fe<2+> from below countercurrentwise to the movement of the carrier. CONSTITUTION:Water contg. Fe is fed from a feeding port of feed water 4 through plural passages 10 into a filtration layer 3. Clogging of the passages 10 is prevented with a roof member 11 having an annular shape of the whole body and an inverted V shape of the section. Thus, the opportunity for causing contact of the feed water with the filtration layer 3 increases. The feed water flows through the filtration layer 3 upwards, and divalent Fe in the feed water is oxidized during this stage by the effect of iron bacteria, forming thus insoluble compds., and caught in the filtration layer 3. The feed water freed of Fe is partly utilized as purified water, but almost the whole part thereof is discharged from an outlet port 7 provided to a top of a main body 1 of a tank.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for removing iron from raw water, such as groundwater, in which iron is dissolved in the form of Fe3+, using iron bacteria.

[Prior art] Iron is a necessary component for the human body, but it gives water a metallic taste and colors it yellow-red or reddish-brown, making such water not only unsuitable for drinking but also unsuitable for various industrial uses. . A typical example of water in which a relatively large amount of iron is dissolved is groundwater, where iron is dissolved in a reducing state at 2
It is dissolved in raw water as a valent ion. Therefore, when raw water containing dissolved iron, such as groundwater, is used as industrial water or drinking water, it is necessary to remove the iron dissolved in the raw water.

One way to remove iron from raw water is to immerse an oxidizing agent such as chlorine into the raw water to oxidize dissolved iron (Fe
There is a method of binding 3+ and converting it into an insoluble compound and accumulating it. Alternatively, a method of oxidizing and removing iron by aeration is also known. In response to these, a method has been developed in which such oxidizing action is performed by iron bacteria (Water Association Journal No.

213, p19, 1952). In this method, raw water containing iron bacteria is poured into a water tank and sand filtered at a constant flow rate to develop an iron bacteria layer on the surface of the filtration layer. The iron bacterial layer that has grown and accumulated on the sand surface is scraped off before the filtration is blocked, and then restored after a period of -4. Since this method uses microorganisms, PAC (Poly A
It does not require flocculants such as luminium chloride (luminium chloride) or sulfuric acid clay, and has various excellent advantages such as stable function, easy operation, and low cost.

[Problems to be Solved by the Invention] Since the effectiveness of the above method in removing iron from groundwater by iron bacteria was revealed, many reports have shown that the method has excellent iron removal efficiency, stability, low cost, etc. It has been proven and introduced.

However, the reality is that this method has not been widely adopted except in extremely small-scale private treatment facilities.

The reasons for this are: ■mA clogging occurs quickly, ■removal of the bacterial membrane is hard work, and ■backflow method is frequently used as a means of cleaning sand in the filtration layer.
During this time, filtration is not possible, ■ Control to maintain a constant amount of water and water quality is complicated, and ■ A large area of land is required because the amount of water treated per unit area is small.

The present invention has been made in view of the above-mentioned problems, and its purpose is to improve the iron removal method using iron bacteria, and to improve the iron removal method so that raw water of Oe can be treated continuously and efficiently. The point is to provide a removal method.

[Means for solving the problem] The method of the present invention that has achieved the above object is to treat raw water in which Fe''''' is dissolved with iron bacteria to convert Fe'' to F.
When oxidizing to Fe3+ and removing it as an insoluble compound, the fine carrier is continuously moved downward while maintaining its layered structure.
At the same time, a configuration is adopted in which the raw water is supplied from below so as to oppose the movement of the fine carriers, the iron bacteria are supported on the fine carriers, and the raw water is passed through the fine carrier layer. Fe2+ in water is converted to Fe
3'' insoluble compound, and the fine carrier is circulated and supplied to the upper part of the fine carrier layer after separating the insoluble compound.

[Function] The present inventor has conducted various studies in consideration of the superiority of the iron removal method using iron bacteria and from the viewpoint that it can be an effective iron removal method if the drawbacks listed above can be overcome. As a result, when performing iron removal by iron bacteria, by adopting the above configuration (so-called countercurrent type continuous 8-filter method) in place of the conventional gravity sand filtration method, iron removal efficiency was maintained and compared. We have discovered that processing capacity can be dramatically increased in a small space. Further, according to the present invention,
■It does not cause filtration clogging, and special techniques and expenses for labor, equipment, and maintenance are not required; ■The amount and quality of treated water is stable; ■The amount of washing water is reduced. All of the drawbacks of the conventional technology have been overcome.

Although not all details of the iron removal mechanism in the method of the present invention have been elucidated, the following has been clarified through experiments conducted by the present inventor.

Microscopic observation of the inside of the first layer of sand used for filtration and the surface of the first layer of sand revealed that the sand grains function as microscopic carriers for iron bacteria, but the morphology of microorganisms during BOD measurement and organic matter removal is different. The biofilm formed on the sand surface and inside the carrier showed a different morphology. In other words, iron bacteria reproduce in a form in which colonies rich in filamentous sheaths fill the gaps between sand grains (the voids in the four layers), and the entire four layers are thought to form one huge colony. I was disappointed. Therefore, even if the raw water passes through the filtration layer in a short period of time, the raw water can come into contact with a very large number of iron bacterial colonies. It is thought that most of the dissolved iron undergoes oxidation and is incorporated into the colony. Taking these points into consideration, when implementing the present invention, the filtration rate should be determined as "the first rate of iron bacteria".
It is necessary to set the speed at a speed that does not exceed the iron oxidation capacity and a speed at which the filtration layer does not become fluidized (that is, a speed that maintains the layered state). However, it is also effective to optimize the porosity and pore structure in the filtration layer by changing the grain size and shape of the sand, and there is room for even more efficient operation by changing the filtration speed and other factors. The conditions may be set as appropriate depending on the situation.

The above explanation has mainly been based on the assumption that the filtration layer is formed from sand, but the material that forms the filtration layer is not limited to sand, but may also be made of synthetic resin or other material as long as it functions as a fine carrier. I don't care. The type of iron bacteria used in the present invention is not particularly limited as long as the invasive species forms a filamentous sheath; examples of filamentous iron bacteria include, for example, the genus Leptothrix.

Examples include Ga1lionella genus, Toxothrix genus, etc., as well as 5iderocyst, is genus, S
It may also contain granular particles such as those of the genus 1derocapsa.

Hereinafter, the present invention will be explained in more detail with reference to examples, but the following examples are not intended to limit the present invention.
Any design changes for the purposes described below are included within the technical scope of the present invention.

[Example] Fig. 1 is a schematic explanatory diagram showing an example of a self-flowing continuous moving bed type filtration device configured to carry out the method of the present invention. In the figure, 1 is a tank body, and 2 is a funnel-shaped bottom. , 3 is a filtration layer formed by fine carriers.

4 is a raw water supply port, 5 is a separation section, 6 is a transport pipe, 7 is a treated water take-out port, and 0.8 is a wash water discharge port. The basic structure of such a device is well known, as can be seen in, for example, Japanese Patent Publication No. 56-staoa.

The present invention is carried out using the above apparatus as follows. Iron bacteria are supported on the fine carriers housed in the tank body 1, and the filtration layer 3 is formed by the fine carriers.

Raw water containing iron, such as groundwater, is supplied into the filtration layer 3 through the raw water supply port 4 and the plurality of pipes 10. A roof member 11 having an annular overall shape and an inverted V-shaped cross section is installed near the upper end of the conduit 10.
This prevents clogging of the pipe line 10 and increases the chance of raw water coming into contact with the filter layer 3. The raw water flows upward through the filter 13, during which time 2
The valent iron is oxidized by the action of iron bacteria, becomes an insoluble compound, and is taken into the filter layer 3. A portion of the raw water after iron removal treatment (hereinafter referred to as treated water) is used as washing water, but most of it is taken out from the treated water extraction lower provided above the tank body 1.

On the other hand, the fine carriers below the filtration layer 3 are sent to the separation section 5 above from the lower opening 6a of the transport pipe 6, with the iron in the raw water taken in, by air as a transport medium. Therefore,
The filtration layer 3 as a whole moves downward while maintaining its layered shape.

A cleaning pipe 15 formed to cover the outer periphery of the transport pipe 6 is provided near the upper part of the transport pipe 6 as a part of the separating part 5. As the sent fine carriers descend, a portion of the treated water is used as cleaning water from below the cleaning pipe 15 (hereinafter simply referred to as cleaning water), and the fine carriers are washed in the cleaning pipe 15. The insoluble compounds and the like are separated. The washed fine carriers are then circulated and supplied to the upper part of the filtration layer 3 to be used again. After washing the fine carrier, the washing water is discharged from the washing water outlet 8 together with the separated insoluble compounds. Note that 16 in the figure indicates the upper surface of the filter layer 3.

The present inventor conducted the following experiment using the apparatus shown in FIG. 1 and according to the method of the present invention.

The device used at this time has an inner diameter of tank body 1: 38
On+m, the length of the effective filtration layer 3 (the filtration layer from the end of the pipe 10) was 800 mm.

First of all, raw water is sourced from 10 wells at Katayama Water Purification Plant in Suita City (
Depth 150-250m, total pumping capacity 12000 t/d
Water pumped from the collective water landing well of AY was used (see Table 2 below for the quality of raw water), and the amount of treated water was adjusted using a valve. The raw water flow rate per unit volume of the filtration layer was set in five stages within the range of 12 to 37 t/m3·hr (i.e., filtration rate of 260 to 8 o m/day), and the water flow rate per unit volume of the filtration layer was set in five stages for approximately 10 consecutive days at each stage. Water was sampled and analyzed (see Table 2 below for analysis items). For the measurement of water efficiency and filtration rate, the flow rate per unit time of IA-treated water washing wastewater was actually measured.

The fine carrier has an effective diameter of 0.85 mm and a uniformity factor of 1.
No. 50 silica sand was used for the experiment after being sufficiently washed with sample raw water.

The dominant species of iron bacteria has a branched stalk, a spiral and elongated shape, and a cell diameter of 0.6 to 1.3μ.
Ga1lionella has morphological characteristics such as approximately m.
It was consistent with that of ferrugena Ehrenberg, and was estimated to be Galionella sp.

Four days after water flow started, the iron removal rate exceeded 90%, so the experiment was started. As a result, the iron removal rate at each stage was as shown in FIG.

As is clear from the results shown in Figure 2, the method of the present invention
It is understood that even under high-speed filtration conditions of 0 m/day, iron removal efficiency of around 90% is stably exhibited. Further, at a filtration speed of 800 m/day, a decrease in iron removal efficiency was observed, but the iron removal efficiency was still approximately 70% without causing filtration clogging.

In the above experiment, in order to keep the cleaning cycle and cleaning drainage volume constant even if the amount of treated water fluctuated, the air supply to the transport pipe 6 was adjusted and the opening of the drainage volume control valve (not shown) was controlled. did.

Under the above control conditions, the filtration speed was increased from 260 m/day to 6.
Even when increasing the flow rate to 60 m/day, the amount of drainage of the washing water could be kept constant, and the ratio of the amount of drainage (relative to the amount of treated water) at this time could be suppressed from 13 to 14% to 5%.

Table 1 below shows examples of results reported using the conventional iron bacteria method (5th National Institute of Water Science and Technology Presentation Summary Collection, 1954)
. Table 1 shows that the filtration rate in the method of the present invention is 660
The results are also shown in the case of m/day. As is clear from the results in Table 1, it can be seen that according to the method of the present invention, the processing capacity can be increased by more than 20 times without reducing the iron removal efficiency.

Table 1 and Table 2 show the raw water and treated water used in the experiment (filtration rate 500
This shows the analysis results of the main water quality items (in the case of m/day). The raw water quality is very stable throughout the year, with almost no fluctuations in water temperature, weakly acidic, low in organic matter, and low in dissolved oxygen (DO). The concentration of iron is almost constant at 3.0 mg/u, and its form in the receiving well is 90-93% dissolved iron (passed through a 0.45 μm membrane filter).
It becomes. Also, many floc-like colonies of iron bacteria are floating in Wakamizu well throughout the year.

When the above-mentioned raw water is treated by the method of the present invention, alkalinity, acidity, KMn○4 consumption, Do, etc. are reduced, which are consistent with the trends reported in treatment examples using conventional methods.

Table 2 *(-) is not measured [Effect of the invention] As described above, according to the present invention, by adopting the above-described configuration, it is possible to continuously and efficiently treat the entire raw water. A method for removing iron has been realized.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a continuous moving bed type filtration apparatus constructed to carry out the method of the present invention, and FIG. 2 is a graph showing the results of an experiment conducted according to the method of the present invention. 1...Tank body 3...Filtration layer 5...Separation section 6...Transport pipe Figure 1

Claims (1)

[Claims] Fe^2^+ is oxidized to Fe^3^+ by allowing iron bacteria to act on the raw water in which Fe^2^+ is dissolved.
In removing ^+ as an insoluble compound, a configuration is adopted in which the fine carriers are continuously moved downward while maintaining a layered structure, and raw water is supplied from below so as to oppose the movement of the fine carriers, By supporting the iron bacteria on the fine carrier and passing the raw water through the fine carrier layer, Fe^2^+ in the raw water becomes an insoluble compound of Fe^3^+, and the fine carrier separates the insoluble compound. A continuous moving bed type iron removal method using iron bacteria, which is characterized in that iron bacteria are circulated and then supplied to the upper part of a fine carrier layer.