JPH0587320B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a method for treating wastewater, and more specifically, to wastewater treatment methods that are difficult to biologically treat, such as those discharged from pulp wastewater and other various chemical factories, such as petrochemical factories and oil and fat manufacturing factories.
Concerning methods for treating wastewater containing COD components.

Conventional technology Conventionally, in the treatment of this type of wastewater, COD components cannot be removed by biological treatment alone.
The treatment standards are satisfied by installing tertiary treatment equipment such as coagulation-sedimentation treatment, sand filter treatment, activated carbon treatment, and ozone treatment at the subsequent stage, but this has the following drawbacks.

(i) The processing process becomes multi-stage and complicated.

(ii) A large area is required.

(iii) Higher processing costs.

Problems to be Solved by the Invention The present invention has been made for the purpose of eliminating the above-mentioned conventional problems.

Means for Solving the Problems As a result of extensive research in order to solve the problems of the conventional wastewater treatment methods described above, the present inventor found that when discharging COD component-containing wastewater in water as a pretreatment, normal biological organisms It was discovered that treated water quality that can be discharged could be obtained through treatment alone, and this led to the completion of the method of the present invention.

That is, the present invention relates to a wastewater treatment method characterized by pre-treating COD component-containing wastewater by underwater discharge to improve the BOD/COD ratio and improving it into wastewater that is easily biodegradable, and then biologically treating the wastewater. .

Examples of wastewater treated by the method of the present invention include pulp wastewater and wastewater discharged from various chemical factories, such as petrochemical factories and oil and fat manufacturing factories. Such wastewater generally has a low BOD/COD ratio of around 0.5, for example, and contains large amounts of components that are difficult to decompose biologically. If this is simply treated with a normal biological treatment method, such as an activated sludge method, rotating disk method, or sprinkled bed method, the COD components of the treated water will hardly be decomposed. Also, depending on the type of wastewater, some wastewater is colored brown.

The present invention is characterized in that such wastewater is pretreated by underwater discharge to improve water quality so that it is suitable for biological treatment. The discharge conditions applied to the wastewater as a pretreatment can be selected from a wide range;
If this is too low, it will not contribute much to water quality improvement, and if it is ^too high, it may lead to unfavorable results in terms of equipment and operation.
Discharge conditions are adopted that provide discharge energy of about 10,000 KJ to 500,000 KJ. Also discharge voltage
500V or more is suitable. Such pretreatment of wastewater by underwater discharge is carried out using a pretreatment tank equipped with a discharge device 3 having electrodes 3a and 3b in the middle of a supply line 2 that leads wastewater to a biological treatment tank 1, as shown in FIG. 4 may be installed and the treatment may be carried out in the pretreatment tank 4. Further, as shown in FIGS. 2 and 3, when a direct discharge device 3 is provided in the middle of the wastewater supply line 2, the installation of the pretreatment tank 4 can be omitted.
In the figure, 5 is a stirrer.

Effect In the present invention, since wastewater is pretreated by underwater discharge, the COD components in the wastewater, especially biologically undegradable polymer substances, are reduced to low molecular weight by underwater discharge. become.

Therefore, underwater discharge treated water indicates biological treatment.
The BOD value will be higher than before treatment, but if this is treated with normal biological treatment, the treated water will not only have a BOD value.
The COD value also decreases, making it possible to obtain treated water properties for wastewater such as sewage and food wastewater that are easy to treat.
It becomes possible to release water only by biological treatment.

Example Examples of the present invention are listed below.

〔Example〕

Parv waste liquid (contains difficult-to-decompose substances such as lignin) was used as raw water.

The properties of the raw water were as follows: the BOD/COD ratio was low at 0.48, and it contained components that were difficult to decompose biologically.

Raw water properties COD 1250g/BOD 600mg/g PH adjusted to 8.0 When this is treated with activated sludge under the conditions of BOD sludge load 0.5Kg/BOD/kgss.day, the treated water is colored brown and its COD The components were hardly decomposed.

Treated water properties COD (COD removal rate 32.8%) 840mg/ BOD (BOD removal rate 87.8%) 73mg/ This wastewater is transferred to pretreatment tank 4 (capacity 1.5, retention amount 1, made of stainless steel) as shown in Figure 1. At that,
Discharge voltage 1KV, discharge energy 1KJ, discharge interval 3
When pre-treated by underwater discharge under the conditions of 12 seconds, discharge gap 3C50mm, and supply rate 12/hr, the properties of the COD ranged from 1250mg/ to 1700mg/or
The BOD increased from 600mg/ to 3000mg/, and the BOD/COD ratio also increased from 0.48 to 1.76, confirming that the wastewater was improved to be more easily biodegradable.

This pretreated wastewater was led to the biological treatment tank 1 and treated with the same BOD sludge load as the conditions described above, making it possible to treat the water to a quality that could be directly discharged into rivers and sea areas. The properties of this treated water are as follows.

Treated water properties COD (COD removal rate 98%) 25 mg / BOD (BOD removal rate 97.7%) 14 mg / Color Colorless effect According to the treatment method of the present invention, when biologically treating wastewater, pretreatment by submerged discharge is only required. The treated water can be discharged as is, and there is no need for any post-treatment using tertiary treatment such as activated carbon, which not only simplifies the equipment and operations, but also reduces the amount of land required. , which has the feature of reducing processing costs as a whole.

[Brief explanation of the drawing]

FIG. 1 is a flow chart showing one example of the treatment method of the present invention, FIG. 2 is a flow chart showing another example of the treatment method of the present invention, and FIG. 3 is an enlarged detailed view of the discharge device portion of FIG. 2. In the figure, 1 is a biological treatment tank, 2 is a wastewater supply line, 3 is a discharge device, 3a and 3b are its electrodes, 4 is a pretreatment tank, and 5 is a stirrer.

Claims (1)

[Claims] 1. A wastewater treatment method characterized by pre-treating COD component-containing wastewater by underwater discharge to increase the BOD/COD ratio and improving it into wastewater that is easily biodegradable, and then biologically treating the wastewater.