JPH08294693A - Treatment of waste water by lime milk - Google Patents

Abstract

PURPOSE: To obtain coloress clarified treated water by decoloring orange waste water after biochemical treatment such as activated sludge treatment. CONSTITUTION: The whole of waste water is stirred and mixed in such a state that lime milk is allowed to be present in waste water in a saturated amt. or more and impurities such as chromatic matter or the like in waste water are adsorbed on lime milk to be flocculated and sedimented to obtain clarified treated water. The treated water is neutralized by the addition of aq. sulfuric acid and the dissolving action of carbon dioxide in the atmosphere. Therefore, waste water of a beverage factory of coffee or teas and other every kind of waste water can be easily and cerainly decolored and clarified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to wastewater of a beverage food manufacturing plant, wastewater of a paper mill, other industrial wastewater containing organic matter,
It also relates to wastewater treatment of general miscellaneous wastewater, and also to environmental conservation related to water.

[0002]

2. Description of the Related Art Organic wastewater is treated by BOD or C in a conventional biochemical treatment method.
It is relatively easy to reduce the OD value to a certain level for purification if the operation management of the processing plant is proper.
However, it is very difficult to finish the treated water that is colored brown into a completely colorless and transparent treated water. Therefore, even if there is no real harm to the environment, it is customary to compromise with the suboptimal final treatment, such as condensing and diluting with other cooling water drainage to reduce the degree of coloring and discharging it to public water. It has become.

Such brown waste water is remarkable in the case of water treated by the activated sludge process at a paper manufacturing factory, a chemical agar factory, a coffee / tea beverage manufacturing factory and the like. As decoloring measures, ozone oxidation, ultraviolet irradiation, oxidative bleaching with sodium hypochlorite, reduction bleaching with sodium hyposulfite, etc. can be considered, but the size and safety management of the required equipment, the amount of harmful chemicals and harmfulness, or It is not practical in terms of reaction temperature conditions that require heating. In addition, satisfactory results have not always been obtained even in small-scale experiments using those physicochemical means.

Furthermore, even if a high-performance flocculant such as polyaluminum chloride (commonly known as PAC) is used, it is technically difficult to decolorize the activated sludge treated water colored in brown, and the decolorizing effect may be recognized. Even if it exists, it is not practical in terms of toxicity to the activated sludge biota and economical efficiency. That is, especially in the water-use manufacturing industry, the decolorization of brown wastewater is considered to be almost impossible industrially.

[0005]

Generally, a higher temperature promotes a chemical reaction. However, the operation that requires heating in the treatment of a large amount of industrial wastewater is not realistic. A treatment method that uses a considerable amount of chemicals is not only economically disadvantageous, but also an unintended technical measure that newly increases the concentration of another dissolved inorganic substance. The method of utilizing electric energy for the main principle is still unsuitable for the treatment of a large amount of wastewater. And
Even if the decolorization purpose can be fulfilled, another clarification secondary treatment operation is required if the turbidity is increased. In view of the above, the present invention aims at the development of a new technology with a focus on the colorless clarification of waste water that is still brown under the conditions such as after the treatment with the activated sludge method.

[0006]

Means for Solving the Problems According to the present invention, by adding calcium oxide or calcium hydroxide to brown-colored waste water or treated waste water and stirring and mixing the whole solution, a suitable amount of lime milk having a solubility or higher is obtained. Change to the state of. During the emulsification and stirring process at this time, the brown component substance is adsorbed by the lime milk, aggregates and precipitates with the lime content, and the upper layer other than the bottom lime milk becomes colorless and transparent water. This aggregation / precipitation proceeds rapidly.

Calcium hydroxide is poorly soluble in water,
The aqueous solution exhibits alkalinity with a pH of about 12. When neutralization is required, a small amount of an appropriate amount of sulfuric acid, an appropriate acid such as liquefied carbonic acid is added to the supernatant water obtained by solid-liquid separation by an appropriate means to obtain neutral treated water. However, when a considerable amount of sodium is present in the waste water, the use of hydrochloric acid in this neutralization treatment produces salt, which is not preferable for discharge to public water.

[0008]

The brown treated water of the activated sludge method, which is almost transparent to the naked eye, does not change its chromaticity even when filtered with a paper filter. However, according to the present invention, as a result of the brown component material being adsorbed and aggregated by the lime milk, No. It becomes an agglomerate of a size that does not pass through the No. 2 paper. In addition, since the specific gravity of the lime component is also large, the agglomerates settle in a short time of minute unit, and all the aqueous solution components become colorless and transparent. Moreover, solid-liquid separation is easy by any method.

Even if the above reaction system is left outdoors under open conditions, for example, for one week, the clarified water quality state does not change and is stable. Then, discard most of the clear water,
Alternatively, when the amount of the supernatant water is left as it is, new brown wastewater is replenished to the solution, and the same aggregation / precipitation reaction occurs by stirring and standing as described above to obtain colorless transparent water. That is, in general, a sufficient amount of lime milk is present with respect to a minute amount of brown component substance, so that the desired target reaction is continued up to the adsorption capacity limit. By the way, the solubility of calcium hydroxide is 2
At 0 ° C., 1.26 g remain for 1 kg of water.

Even if an acid is added to the supernatant water which has been solid-liquid separated to neutralize it, the colorless and transparent property no longer changes, and a stable clear water state is maintained over time. As a result of the treatment of the present invention, the decolorizing effect as well as the fact that the COD value further decreases further endorses the stability of water quality due to neutralization.

[0011]

[Example 1] The final discharged water discharged from the activated sludge method treatment facility of a beverage factory for coffee, tea, various fruit juices, etc. is clarified but always brownish. About 10 g of calcium oxide was added to this brown discharged water 11 (1 kg) to generate a white emulsified precipitate. Then, when the whole liquid phase was stirred so as to be uniformly suspended, it was clearly macroscopically recognized that an aggregation reaction had occurred. As the stirring motion of the liquid phase stopped, the agglomerates settled to the bottom in a few minutes,
The liquid phase changed to colorless and transparent. The precipitated portion became a reddish lime milk due to the adsorption of the brown component material.

A comparison of the water quality before and after the decolorization reaction is shown in Table 1.

In addition, 10 to 100 ml of saturated calcium hydroxide aqueous solution was added to the same brown discharged water 11 (1 kg) and stirred, but some aggregation and precipitation effect was observed, but clarification was insufficient.

[0014]

Example 2 The colorless transparent water after the decolorization reaction of Example 1 was decanted into 500 ml and neutralized with an aqueous sulfuric acid solution. There was no change in the properties as colorless and transparent water after the neutralization treatment, and no discoloration or precipitate formation was observed even after holding at room temperature for 1 week. The COD value of the decolorized neutralized water decreased as shown in Table 2.

[0015] The increase in electrical conductivity indicates an increase in the amount of inorganic salt that accompanies the decolorization / neutralization treatment.

[0016]

[Embodiment 3] Same as Embodiment 1, the final process facility for the activated sludge process of the factory waste water, the brown water of the upper layer of the clarifier is about 10
Pump 1 l into a plastic container and
When 0 g was added and the lime milk was formed on the bottom of the vessel and the whole solution was stirred, an agglutination reaction occurred immediately and the solution settled after a few minutes, and the brown color of the liquid phase disappeared completely and became colorless and transparent. did.
When this was left to stand outdoors in an open state, colorless and transparent water quality was maintained even after 1 week. Next, about 2/3 of the supernatant water was decanted and removed, and the brown water in the upper layer of the clarifier was added again, and when the whole solution was stirred, the same aggregation and precipitation as before occurred and the whole liquid phase It was confirmed that the sample became colorless and transparent and that it did not change with time.

When the supernatant water separated by tilting is left outdoors as described above, the pH of the clear water decreases with the passage of time,
The pH dropped to 11 or below 11. It is considered that this is a phenomenon due to the dissolution of carbon dioxide in the atmosphere, and it was recognized that the numerical degree of influence changed depending on the temperature, water temperature and wind conditions.

[0018]

[Example 4] A chemical agar factory wastewater for producing powder agar by treating seaweed Ogonori with alkali was treated from an activated sludge treatment agitation tank. It was collected in the state. This wastewater 1.8
1 in a PET bottle, submerge an air stone connected to a small air pump, and continue the exposure for 24 hours. When the dissolved components and suspended substances of agar and seaweed, which are indigestible organic substances, are further decomposed. Then, about 5 g of calcium oxide was added, and the exposure was stopped after 10 minutes. Table 3
The effect is shown in.

[0019]

The control test group to which calcium oxide was not added had a normal sludge sedimentation property, that is, a sludge volume after 30 minutes (SV ₃₀ ) of 50%, and a normal supernatant liquid color, that is, a yellowish brown color. On the other hand, in this test section to which calcium oxide was added, sedimentation of sludge was extremely fast, the sludge volume after 10 minutes was about 25%, and the supernatant became almost colorless and transparent.

[0021]

[Embodiment 5] When a sufficient amount of slaked lime is added to the saponified water that is semianaerobically and semiaerobically biologically treated in the three-tank type simple septic tank of general domestic wastewater, and the whole liquid is stirred and mixed and left to stand. In a few minutes, the suspension was coagulated and precipitated, and odorless and colorless clear water was obtained.

[0022]

Since the present invention is configured as described above, it has the following effects.

After biological treatment such as activated sludge method, decolorization of industrial wastewater which is still colored brown is effectively achieved by a chemically and physically simple method and operation, resulting in colorless and transparent discharged water. be able to. Moreover, it contributes to further reduction of COD value and complete deodorization of wastewater and environment.

Since the lime used is a daily chemical substance, there is no problem in safety, it is a low-priced product, and it is a compound with low solubility, so the economical burden is low. Further, by utilizing the dissolution of carbon dioxide in the atmosphere for the neutralization treatment after decolorization, the required acid amount can be reduced by about 1 to 1 or more in terms of pH value. This is also very effective in reducing processing costs.

Since calcium sulfate (commonly known as gypsum) and calcium carbonate which are likely to be produced in the neutralization reaction are hardly water-soluble compounds, the concentration of inorganic salts in the final treated water should be as high as natural water with high hardness. stay.

This is an epoch-making treatment method especially for drinking factory wastewater such as coffee and tea, but it can also be applied to decolorization and clarification of various industrial wastewater, and further, contaminated water connected to public water areas. It is also a method that can be used for purification.

Claims (3)

[Claims] 1. Calcium oxide or calcium hydroxide is added to wastewater, and the mixture is stirred and mixed with all liquids in the presence of lime milk in a saturated amount or more, and allowed to stand, whereby impurities such as coloring component substances in wastewater are mixed. A wastewater treatment method in which lime milk is adsorbed and coagulated and precipitated, and processed into clear treated water. 2. The clear supernatant water obtained by the method of claim 1 is subjected to solid-liquid separation by an appropriate method, and an acid such as sulfuric acid is added to neutralize the solution to process it into clear, neutral treated water. Wastewater treatment method. 3. Before or after the step of the neutralization treatment of claim 2, by exposing the supernatant water to the atmosphere, the carbon dioxide in the air is naturally dissolved or semi-forced to be dissolved,
A wastewater treatment method that lowers the pH of alkaline water to be neutralized.