JP2000263049A - Method and apparatus for cleaning barn effluent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for cleaning barn effluent whereby a large amount of effluent can be treated; humic substances can be oxidatively decomposed economically; and the concentration of trihalometanes as a by-product is kept low enough to meet the effluent standard by adding a chloride and causing electricity to flow through while the pH is being adjusted to a specified value with an alkali agent when decomposing organic substances contained in an effluent formed by the activated sludge treatment of a barn sewage. SOLUTION: A barn effluent 2 after an activated sludge treatment is transferred to a filtration vessel 4 to be adsorbed by a filtering material 5 and then is put into an electrolysis vessel 6 and a reaction vessel 13. An aqueous halogen compound solution, e.g. an aqueous common salt solution, from a chemical liquid vessel 9, is injected into the effluent 2 to be treated; some alkali agent is added to an aqueous solution adjusted so that the concentration of common salt is kept higher than 3% to prevent an electrode from being damaged, thus adjusting the pH to 6-7; and a rectifier 12 is switched on. After 30 min of electrolysis, an electrolytic solution 8 is injected into 10-50 times as much effluent 2, which is transferred from the filtration vessel 4 and stored in a reaction vessel 13, and is stirred with a stirrer 17 to be homogeneously mixed. Sodium hypochlorite synthesized in the electrolysis vessel 6 emits nascent oxygen as an oxidizing agent to oxidatively decolor huminic substances, a coloring component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an organic substance contained in wastewater, which is oxidatively decomposed by irradiating ultraviolet rays in the presence of sodium hypochlorite to remove coloring components in the wastewater and to produce by-products in the present process. The present invention relates to a process for decomposing and removing trihalomethane on a photocatalyst solid surface irradiated with ultraviolet rays.

[0002]

2. Description of the Related Art Sewage discharged from barns such as cows and pigs is
Generally, it is discharged after purification treatment with activated sludge. However, in recent years, such discharge after treatment has been greatly regarded as a problem in terms of environmental pollution and living safety.

[0003] Wastewater from a livestock sewage purification treatment facility has a pale yellow or brownish color depending on the concentration. The main cause of this coloring is the humic substances (final compounds of organic matter) contained in the water, and when treated water containing this humic substance is discharged into rivers, it not only destroys the natural environment and natural ecosystem, It also affects the way people live. In other words, if there is a water purification plant downstream of the river, it will be chlorinated for disinfection, but humic substances and chlorine will react to produce harmful trihalomethane. Naturally, it is not permissible for the wastewater itself from the purification treatment facility to contain a large amount of trihalomethane.

[0004] Therefore, in the future, the treated water from the purification facility for livestock barn sewage will have (1) a very low content of humic substances and no coloring of the wastewater, and (2) very little trihalomethane. It is required socially that there is not.

[0005] Regarding the decolorization of wastewater (1), many methods have been tried so far. For example, a coagulation sedimentation method, an activated carbon adsorption method, a separation membrane method, an ozone treatment method, a hydrogen peroxide method, an ultraviolet oxidation method, a chlorine-based oxidant method and the like are known.

First, the coagulation precipitation method is a method in which a coagulant such as aluminum sulfate, polyaluminum chloride, ferrous sulfate or ferric sulfate is mixed and reacted with waste water to coagulate and precipitate coloring components, and the supernatant is discharged. However, there is a disadvantage that the number of steps for treating the aggregated precipitate increases.

[0007] The activated carbon adsorption method is a method of adsorbing coloring components by passing waste water through activated carbon. However, the short life of the activated carbon is limited because the adsorption capacity of the activated carbon is limited. Therefore, there is a problem that the used activated carbon is frequently replaced and the used activated carbon is discarded, and it is not practical including economy.

[0008] The separation membrane method is a technique for filtering and removing substances as coloring components. However, in livestock sewage treatment with a high concentration of coloring components and a large amount of filtration, clogging is likely to occur, and reprocessing of the coagulated liquid is necessary, which makes it practical. Is not preferred in terms of

[0009] The ozone treatment method is a method in which a high concentration of ozone is generated by an ozonizer, aerated in wastewater and decolorized by the oxidizing power of ozone. Since ozone is required, it is not economical, and high-concentration ozone has a disadvantage that a new ozone treatment is required.

[0010] The hydrogen peroxide method is a method of oxidatively decomposing coloring components with hydroxy radicals generated by decomposition of aqueous hydrogen peroxide, but the treatment speed is considerably slow. Therefore, the use of ultraviolet rays or the combination with other chemicals or technologies has been studied, but the capacity is inferior to large-scale livestock drainage.

The ultraviolet oxidation method is basically based on irradiating organic substances in wastewater with ultraviolet rays having a short wavelength in the wavelength range of 254 nm to decompose them. Therefore, studies are being made to use it in combination with other methods, and to use a lamp that also emits a short wavelength of 185 nm that generates ozone. However, this method is also difficult to treat a large amount of wastewater in a short time.

The chlorine-based oxidizer method is known as a method for chemically oxidizing organic substances with sodium hypochlorite or the like, and it is effective to oxidize organic substances and chromaticity components that cause COD and BOD. Widely known. However, it is not generally used when the running cost is considered high and the amount of treated water is large. In addition, harmful trihalomethane is generated in the treated water due to the reaction with organic substances, and is not considered to be a preferable process.

[0013]

Each of the above methods has a decolorizing effect on livestock sewage, but requires a large amount of processing capacity in a short time, is economically problematic, or requires secondary treatment. It has advantages and disadvantages as by-products of harmful substances. The present invention considers the method having a large amount of decoloring effect in a short time among the above-mentioned methods as the highest priority, taking up the chlorine-based oxidizing method as the most preferable method, and reducing the running cost from the technical process side. Another object of the present invention is to provide a condition in which harmful trihalomethane caused by a chlorine-based oxidizing agent is difficult to be formed and to decompose the formed product.

The present invention has an object to determine what process can be used to make the economy as running cost reasonable, and to decompose and reduce harmful halides such as trihalomethane which are naturally produced. It is an object of the present invention to provide a wastewater treatment method and apparatus.

[0015]

Means for Solving the Problems The present invention has been intensively studied in order to achieve the above object. (1) In a method of treating livestock sewage, a halide is added to a part of the sewage, and after electrolysis, excess Injected into a reaction tank with livestock drainage,
The solid photocatalyst fixed in the waste liquid is irradiated with ultraviolet rays while being stirred at room temperature to perform decolorization, and at the same time, photodecomposes by-product chlorine compounds such as trihalomethane.

(2) A halogen compound is added and dissolved in a part of the wastewater filtered in advance in a livestock wastewater treatment apparatus, and a current is passed through an electrolytic cell using a platinum-plated titanium electrode as an anode and a stainless steel electrode as a cathode. I do. The pH of this is adjusted with an alkaline agent, poured into a reaction tank having excess livestock wastewater, and stirred at normal temperature to oxidize and decolor excess livestock wastewater. At this time, trihalomethane, etc., which is thought to be produced by reacting with the humic substances in the liquid, comes into contact with the photocatalyst fixed in the net cage in the liquid in the reaction tank, and is decomposed by the light of the low-pressure mercury lamp irradiated on the catalyst surface. Is done. After the completion of the reaction, the filtered water containing residual chlorine after filtration is aerated before being discharged to obtain low residual chlorine-containing water.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the accompanying drawings. In FIG. 1, 1
Reference numeral denotes a wastewater storage tank after activated sludge treatment, in which livestock wastewater 2 after activated sludge treatment is stored. The livestock sludge wastewater 2 after the activated sludge treatment is moved to a filtration tank 4 by a wastewater supply pump 3 and adsorbed by a filter material 5 which is a ceramic ball having adsorption performance, and then put into an electrolytic tank 6 and a reaction tank 13.

The anode of the electrode plate 7 of the electrolytic cell 6 is a platinum-plated titanium mesh plate, and the negative plate is SUS304.
An alkaline agent is slightly added to the aqueous solution adjusted so that the salt concentration does not become 3% or less so that an aqueous solution of a halogen compound, for example, a saline solution is injected into the processing solution from the chemical solution tank 9 so as not to damage the electrodes, and the pH is adjusted to 6 to 8. To turn on the power of the rectifier 12. The electrolysis temperature is preferably maintained at 50 ° C. or lower. If necessary, a cooling coil is provided in the electrolysis tank 6 for cooling. Preferably, the pH is maintained between 6 and 8,
with less l _2, the distribution of hypochlorous acid and hypochlorite ions with oxidation ability is because the largest occupying area. (Humio Fumio, Electrochemical Reaction Operation and Electrolyzer Engineering, Doujinshi) The voltage during electrolysis is around DC12V and the current density is 1
About 0 A / dm ² and the distance between the electrodes are 50 mm.

Thirty minutes after the electrolysis, the electrolytic solution 8 is injected into the storage where the processing solution 2 in an amount of 10 to 50 times is moved from the filtration tank 4 to the reaction tank 13 and stored. Stir at room temperature with stirrer 17,
Mix evenly. The sodium hypochlorite (NaClO) synthesized in the electrolytic cell 6 releases nascent oxygen (O) as an oxidizing agent, and oxidizes and decolorizes humic substances as coloring components.

However, since Cl ₂ and ClO ⁻ are present in the electrolytic solution 8, they react with humic substances contained in the livestock sewage wastewater 2 after the activated sludge treatment to form harmful so-called trihalomethane such as chloroform. Therefore, it is necessary to decompose and remove this trihalomethane.

It was conceivable to add titanium dioxide as a powder under ultraviolet irradiation for the purpose of decomposing the organic halogen. In this case, however, the aqueous solution became cloudy and the light hardly penetrated, and the effect was not recognized. . (JP-A-5-26937
8).

However, if the titanium dioxide 15 or the like 15 is solidified and fixed in a liquid and the ultraviolet lamp 16 is set very close, the photocatalyst trihalomethane attached to the surface of the titanium dioxide can be photodecomposed. The wavelength is preferably 385 mm, but an effect of 254 mm is effective.

When the reaction solution 14 having a chromaticity of 300 to 400 becomes chromaticity 1 to 50, it is transferred to a filtration tank 20 by a reaction solution pumping pump 19, and suspended matter is removed by a filter medium 21 to overflow. Then, it moves to the discharge monitoring tank 23.

In the discharge monitoring tank 23, air is aerated from the air diffuser 25, and any residual chlorine is removed by aeration.

The processing liquid 24 overflows from the discharge monitoring tank 23 and is sequentially discharged.

[0026]

The present invention will be described in more detail with reference to examples.
In the case of using a chlorine-based oxidizing agent alone to oxidize colored wastewater, 60 liters of activated sludge treatment liquid is placed in an electrolytic tank, and 1.8 kg of sodium chloride and 2.5 g of caustic soda are added thereto, followed by stirring and uniformity of pH 7.2. In phase. 9.7 at 18 ° C
Electricity was supplied at Ａ11.5 V, 190 A for 30 minutes. The current density was 9.05 A / dm ² and the distance between the electrodes was 50 mm.
The electrodes used were a platinum-plated titanium mesh plate for the anode and a stainless steel plate for the cathode. The liquid obtained by energizing is colorless and transparent. A part of this solution was taken out, diluted with a 10-fold amount of colored wastewater having a chromaticity of 350, and subjected to a stirring reaction under various conditions at room temperature for 30 minutes.

[0027]

[Table 1]

As is clear from Table 1, the decomposition of trihalomethane is not recognized only by stirring and irradiation with ultraviolet rays, but the decomposition is confirmed by using a photocatalyst.

In Experiment 1, the chromaticity is large because the reaction is slow, but the chromaticity tends to decrease with time. The COD of Experiment 3 was 8.6, which was 1 of the starting stock solution.
It was reduced to 1/0.

[0030]

According to the present invention, it is possible to produce a hypochlorous acid component effective for oxidation without damaging the electrode and to discharge a large amount of liquid, as compared with the conventional sodium hypochlorite method as a chlorine-based oxidizing method. Therefore, the humic substance can be oxidatively decomposed economically with a large amount of treatment. Furthermore, the amount of harmful trihalomethanes produced as by-products cannot be so large, and even if they are formed, they are photodegraded by the use of solid photocatalysts, so that they are below the range that can sufficiently comply with the emission regulations of trihalomethanes.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a processing apparatus for implementing the present invention.

[Explanation of symbols] ··· Wastewater storage tank after activated sludge treatment · · · Livestock drainage after activated sludge treatment · · · Drainage supply pump · · · Filtration tank · · · Filter material · · ·・ Electrolyzer ・ ・ ・ ・ Electrode plate ・ ・ ・ ・ Electrolyte ・ ・ ・ ・ Chemical solution tank ▲ 10 ▼ ・ ・ ・ ・ Temperature meter ▲ 11 ▼ ・ ・ ・ ・ pH meter ▲ 12 ▼ ・ ・ ・ ・ Rectifier ▲ 13 ▼・ ・ ・ ・ Reaction tank ▲ 14 ▼ ・ ・ ・ ・ Reaction liquid ▲ 15 ▼ ・ ・ ・ ・ Photocatalyst ▲ 16 ▼ ・ ・ ・ ・ Ultraviolet lamp ▲ 17 ▼ ・ ・ ・ ・ Stirrer ▲ 18 ▼ ・ ・ ・ ・ Chromaticity meter ▲ 19 ▼ ・ ・ ・ ・ Reaction liquid pump pump ▲ 20 ▼ ・ ・ ・ ・ Filtration tank ▲ 21 ▼ ・ ・ ・ ・ Filter material ▲ 22 ▼ ・ ・ ・ ・ Filtrate ▲ 23 ▼ ・ ・ ・ ・ Discharge monitoring tank ▲ 24 ▼・ ・ ・ ・ Treatment liquid ▲ 25 ▼ ・ ・ ・ ・ Aeration tube ▲ 26 ▼ ・ ・ ・ ・ Treatment liquid recovery pump

Continued on the front page F-term (reference) 4D028 AB00 4D037 AA13 AB14 BA18 CA04 CA07 CA11 4D050 AA14 AB03 AB11 BB06 BC04 BC09 CA10 CA17 4D061 DA08 DB19 EA02 EA03 EB01 EB12 EB17 EB19 EB30 EB31 ED13 FA07 FA11 A15 A15 FA15 FA15 FA15 FA15 FA15 CA07 CA10 CA15 DA06

Claims (3)

[Claims] 1. An electrolytic treatment of organic matter in wastewater obtained by subjecting sewage discharged from a livestock bar to activated sludge treatment, wherein a chloride is added, and then the pH is adjusted to 6 to 8 with an alkali agent, and then electricity is supplied. Processing method. 2. When oxidizing organic matter in wastewater obtained by subjecting sewage discharged from a livestock bar to activated sludge treatment, an amount of chloride of 3% or more which does not damage electrodes is added, and 10% is added to the electrolytically treated liquid. What is claimed is: 1. A method for treating wastewater, comprising mixing and agitating a 50-fold volume of an electroless wastewater. 3. A photocatalyst is placed in a net basket during the oxidation reaction to decompose and remove trihalomethane by-produced after electrolytic oxidation of organic matter in wastewater obtained by subjecting sewage discharged from livestock to activated sludge treatment. A method for treating wastewater, comprising immersing and irradiating ultraviolet light from near the surface.