JPS5990693A - Method for controlling injection of chemical in water purification plant - Google Patents

Abstract

PURPOSE:To maintain treated water under an oxidizable atmosphere by injecting chlorine or an oxidative chlorine compound at the point downstream from an ozone injection point and upstream from a rapid filtration basin, and keeping the oxidizability of drainage at the downstream from filtration basin and at the filtration basin. CONSTITUTION:The water quality at the point 14 upstream from the injection point 20 of chlorine or the like is measured by a water quality tester 13, and on the other hand the treated water after injection of chlorine or the like at the point 16 downstream from the injection point of chlorine or the like is examined by the water quality tester 15. The injection rate of an oxidant such as chlorine or the like injected at point 20 upstream from a rapid filtration basin 5 is decided, calculating the analytical value of the oxidant such as chlorine or the like by a computer 17. The injection rate is converted to the injection volume by an operator 18 in proportion to the filtration flow rate measured by a flowmeter 12, and a prescribed quantity of chlorine is injected by controlling the opening of the valve of a chlorine injection quantity controller 19. The computer 17 also has a function capable of setting up the injection rate by the manual operation from an operation disc or the like.

Description

[Detailed Description of the Invention] This invention relates to a chemical injection control method that injects an oxidizing agent such as chlorine at a point before the rapid filtration oil in a water purification plant where ozone is injected near the landing well. At the water treatment plant that serves as the water source, sterilization and disinfection of the raw water taken,
It is also excellent in oxidizing manganese and iron compounds, etc. in raw water, oxidizing organic and inorganic pollutants, and decomposing ammonia nitrogen, and remains in water for a long time to maintain its bactericidal effect. However, in recent years, chlorine treatment has introduced trihalomecnes (T), including chloroform, into the treated water.
It has been discovered that a large number of organochlorine compounds exist, such as x). The public health maximum concentration level for dihalo/tan was announced as o, t my / t. In addition, in Japan, the control target value for total trihalomethane in tap water was set at o, 1 my /
Administrative guidance is being given to keep the number below 1. As described above, it has become clear that chlorine treatment at water treatment plants produces harmful chlorine compounds such as trihalomethane, and countermeasures are being researched in various fields.

Among these, several water purification processes using ozone as an oxidizing/sterilizing agent to replace chlorine have been proposed.

The water purification method using ozone not only prevents the formation of trihalomethanes, etc., but also deodorizes and improves the taste of tap water sources, where water quality continues to deteriorate.
It is a treatment method that is expected to become more widespread in the future, as it can also be used for purposes such as decolorization.

A comparison and summary of the characteristics of the chlorine method and ozone method in the water purification process is shown in the table below.

Table Comparison of treatment characteristics of chlorine and ozone As is clear from the four-layer table, the two disadvantages of the ozone method compared to the chlorine method are that there is no residual effect in the treated water and that ammonia nitrogen cannot be oxidized and decomposed. can be mentioned.

As described above, chlorine and ozone have advantages and disadvantages in their treatment effects, so when changing chlorine treatment to ozone treatment, there is a problem in applying the conventional chlorine injection method to the ozone injection method.

First, regarding the fact that ozone has no residual effect, even if ozone is injected near the receiving well, the residual ozone concentration will become zero as the treated water progresses through the chemical mixing pond, floc formation pond, and settling pond. When the residual ozone disappears, the oxidation state of the treated water or rapidly filtered oil is no longer maintained, and manganese oxides, iron oxides, etc. that should be captured by the rapidly filtered oil are reduced and become solubilized again and leak out from the rapidly filtered oil. There is a possibility that this will happen.

Second, since ozone has almost no ability to oxidize and decompose ammonia nitrogen in the vicinity of neutrality, the ammonia nitrogen contained in the raw water that is taken will proceed through the water purification process as it is.
It is not decomposed until post-chlorine is injected before the water purification pond. Therefore, maintaining the post-chlorine injection rate appropriately is an important factor in decomposing ammonia nitrogen and maintaining the residual @ element concentration in the treated water.

If the post-chlorine injection rate here is lower than the amount required to decompose anthonia nitrogen, free residual chlorine will be zero, which may cause sanitary problems such as contamination with bacteria and viruses during water distribution. occurs.

As mentioned above, if the chlorine injected near the landing well is replaced with ozone, there is no residual effect of ozone, so the K-filtered oil is not necessarily kept in an oxidized state, so it is difficult to replace manganese, iron, etc. There is a possibility of leakage from slowly flowing oil and the growth of bacteria and microorganisms, and there are disadvantages such as the ammonia nitrogen contained in the raw water is not decomposed.

This invention was made in order to eliminate the above-mentioned drawbacks and operate the water purification process safely when introducing ozone treatment to water purification plants. An object of the present invention is to provide a chemical injection control method characterized by constantly maintaining rapidly filtered oil in an oxidizing atmosphere and oxidizing and decomposing ammonia nitrogen.

In a water treatment plant where ozone is injected as an oxidizing/sterilizing agent near a receiving well, chlorine or an oxidizing chlorine compound is injected downstream from the point where the ozone is injected and upstream from the rapid filtration oil. The invention resides in a chemical injection control method for a water purification plant which performs at least one of maintaining the oxidizing power of treated water after filtration dissipation and filtration and reducing the oxidation content m of ammonia nitrogen.

Injection of chlorine or oxidizing chlorine compounds can be carried out at the points mentioned above, but is preferably carried out in the settling tank, more preferably before the rapid oil filtration. In addition, the injection amount of chlorine or oxidizing chlorine compounds can be controlled by
The injection rate is determined based on the water quality of the settling tank and the quality of the treated water exiting the rapid filtration station, and the amount of injection is changed according to the filtration flow rate of the rapid filtration station to maintain the residual chlorine in the treated water at the set value of 0 degrees. To do this.

When ozone is injected near the landing well, iron, manganese, etc. contained in the raw water are oxidized and become suspended iron hydroxide and manganese dioxide, some of which are incorporated into flocs and separated and removed. . However, in order to prevent iron and manganese from eluting in the filtrate where residual ozone has disappeared, it is necessary to maintain the filtrate in an oxidized state by adding an oxidizing agent such as chlorine. The following equation is known as the oxidation reaction of divalent iron ions and divalent manganese ions by chlorine.

xFd++ Hczo+,tH,o→2Fe (OH%
+ -tH" + CJ-...= (1) In addition, ammonia nitrogen that was not decomposed by ozone is oxidized and decomposed by injecting a sufficient amount of chlorine that is necessary for oxidative decomposition beyond the break point point, as shown in the following equation. be done.

, 2NH+JCI-=Nko+AHCJ...-(
3) In this case, if the injection amount is below the breakpoint point, ammonia can be left in the treated water in the form of combined chlorine as chloramine.

Hereinafter, this invention will be explained in detail with reference to FIG.

The figure is a schematic diagram showing a chemical injection control system for a water purification plant according to the present invention. In the figure, ozone is injected into raw water taken from a river, etc. at a landing well L to perform oxidation, sterilization, deodorization, etc. The ozone injection method is similar to the current chlorine injection method, and the ozone injection rate determined by the calculator 7 is converted into the ozone injection amount according to the water intake amount measured by the flowmeter 6 at the calculator. This control method generates a preset amount of ozone by adjusting the discharge voltage of the ozone generator io, and injects it from an ozone injector.

After the flocculant and coagulation aid are injected in the chemical mixing tank 2, most of the suspended matter is sedimented and separated in the sedimentation tank via the flocculation tank 3. Subsequently, a small amount of suspended matter contained in the supernatant water is removed by a rapid filtration cell S, but prior to this, an oxidizing agent such as chlorine is injected at a point 20 in front of the filtration cell 5.

Next, the chemical injection control method of the present invention will be explained based on the drawings.

The water quality at a point /g upstream of the injection point of chlorine etc. is measured by a water quality meter 13. Water quality meter/3 is a water quality meter related to the amount of chlorine injection, such as an oxidation-reduction potential (ORP) meter, a residual ozone n meter, an ultraviolet absorbance (Uv) meter, and a potassium permanganate consumption meter. This water quality meter/
According to 3, for example, when using an ORP meter, if the liquid property of the water shifts to the reducing side, the chlorine injection rate is increased,
In the opposite case, feed feed control is performed to reduce the chlorine injection rate.

On the other hand, the water quality meter 13 measures the treated water after injection of chlorine, etc. at point /6 on the downstream side of the injection point θ. The water quality meter 15 is a water quality meter, such as a residual chlorine concentration meter or an ORP meter, which is related to the amount of chlorine consumed, the oxidation-reduction state of filtration power, and the like. For example, when using a residual chlorine concentration meter, this water quality meter 13 performs feedback control such as increasing or decreasing the chlorine injection rate in P operation (proportional operation) or PI operation (fat operation) according to the increase or decrease of residual chlorine in the treated water. .

The injection rate of oxidizing agents such as chlorine to be injected at point Q on the upstream side of the rapid filtration power supply is determined by calculating the analytical values of both chlorine and other oxides obtained above using the calculator 17. shall be. This injection rate is converted into an injection amount by a calculator /j according to the filtration flow rate measured by the flow meter 12, and a predetermined amount of chlorine is injected by adjusting the opening degree etc. with a valve in the chlorine injection amount regulator 17. The computer also has a function that allows the injection rate to be manually set from the CRT or operation desk.

As mentioned above, it is possible to stably control the filtration current and the quality of the treated water by installing the water quality meter/3 and the water quality meter/2, but even if the water quality meter/J is not installed, the filtration current can be maintained in an oxidized state. Therefore, the basic requirements of preventing the elution of iron and manganese and the proliferation of bacteria and microorganisms, and oxidizing and decomposing ammonia nitrogen can be satisfied.

In addition, in this method, the filtration temperature! Since the subsequent treated water quality is sampled in Step 4 and feedback control is performed to achieve the set water quality, conventional filtration is not possible! It is possible to omit the injection of chlorine after it has been injected in the chlorine mixing pond further downstream.Although the above example describes a rapid filtration cell, the same method can be applied to an activated return light tower, etc. can. Further, although this example describes a water purification plant, the method of the present invention can be similarly applied to other water treatment plants. The oxidizing/sterilizing agent to be injected into the vicinity of the water receiving well/liter is not limited to ozone, but may also be applied to a chemical having a small residual effect like ozone, such as hydrogen peroxide.

As described above, according to the present invention, the ozone injected near the landing well deodorizes, improves the taste, and decolorizes the treated water, and the oxidizing agent such as chlorine injected at a point before the rapid filtration Even if the ozone injected near the landing well does not remain in front of the filtration oil, it is possible to maintain the filtration current and the treated water after the filtration site in an oxidizing atmosphere, and remove iron and manganese from the filtration current. In addition to preventing elution and inhibiting the growth of bacteria and microorganisms, it also has the effect of oxidizing and decomposing ammonia nitrogen. In addition, most substances other than ammonia nitrogen are oxidized and decomposed by ozone injected near the landing well, so the amount of chlorine injected before rapid filtration is slightly greater than the amount that can decompose ammonia nitrogen. Since this is sufficient, it has the effect of reducing the amount of harmful chlorine compounds such as trihalomethanes produced.

[Brief explanation of the drawing]

The figure is a schematic diagram showing a chemical injection control system for a water purification plant according to the present invention. In the figure, l...water landing well, 2...chemical mixing pond, 3...floc formation pond, ψ...sedimentation basin, 5...rapid filtration current, 6...flow meter,
ri...calculator, za...ratio calculator, ?・・Ozone injection machine, lθ・・Ozone generator, /l・・Ozone injection point, /・・Flowmeter, 13・・Water quality meter, /F・・Water sampling point, 1
3...Water quality meter, 16...Water sampling point, /ri...Calculator,
/1...Ratio calculator, l?・・Chlorine injection amount regulator, KO
...Chlorine injection point. Agent Shin Kuzuno −

Claims (3)

[Claims] (1) In water treatment plants where ozone is injected as an oxidizing/sterilizing agent near the receiving well, chlorine or oxidizing chlorine compounds are injected downstream from the point where the ozone is injected and upstream from the rapid filtration basin. A method for controlling chemical injection in a water purification plant, characterized by performing at least one of maintaining the oxidizing power of treated water after oil passing and filtering, and oxidizing and decomposing ammonia nitrogen. (2) The injection rate of chlorine or oxidizing chlorine compounds is determined based on the water quality of the settling tank and the water quality of the treated water exiting the rapid filtration oil, and the injection amount is changed according to the filtration flow rate at the rapid filtration oil inlet. 2. A method for controlling chemical injection in a water purification plant according to claim 1, wherein the residual chlorine concentration in the treated water is maintained at a set value. (3) A chemical injection control method for a water purification plant according to claim 2, wherein the oxidation state of the treated water is detected using an oxidation-reduction electrometer.