JPS6257400B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a useful treatment method for purifying oil-containing wastewater in which surfactants, emulsifiers, etc. are dissolved, which is discharged from, for example, a cold rolling mill for thin steel sheets, and obtaining high-quality treated water. The present invention will be mainly described below with reference to examples of treatment of cold-rolled soluble oil-containing wastewater. Conventionally, for soluble oil wastewater discharged from cold rolling mills, metal acid salts (aluminum chloride, aluminum sulfate, ferric chloride, ferric sulfate, etc.) are added as flocculants, and neutralizing agents such as caustic soda are added. The method of injecting wastewater and coagulating and separating it in a neutral pH range is widely used, but the wastewater discharged from factories contains various surfactants and extreme pressure additives, etc. Although the oil content (n-hexane extracted material) of the treated water shows a low value (10 ppm or less), the COD value is high (100 + ppm to several +
ppm). In recent years, with the strengthening of environmental regulations (such as the introduction of total volume regulations in closed water bodies), measures to reduce COD in various types of wastewater have been intensively studied. Currently, there is no suitable treatment method for this, and the development of a new treatment method is desired. In addition, as a method for reducing COD in the above-mentioned soluble oil wastewater, the application of biological treatment has been considered to remove hydrophilic organic substances in the wastewater. The current situation is that it is extremely difficult to treat because it is a substance that inhibits biological metabolism. In general, soluble oil wastewater discharged from the cold rolling process absorbs heat generated when rolling steel plates, and
It is oil-containing wastewater used for the purpose of preventing seizure of rolls and reducing rolling pressure, and emulsified soluble oil is usually used as the oil. Emulsified soluble oil contains various surfactants, with the main ingredient being one or a mixture of mineral oil, beef tallow, palm oil, and the like. Surfactants include anionic fatty acid soda salts, higher alcohols or fatty acid sulfonates, and alkyl sulfate soda salts, nonionic surfactants such as sorbitan monoalkyl ethers, alkyl ethoxylates, and glycol ethers, and cationic surfactants such as fatty acid amines and high-grade surfactants. Contains amines, quaternary ammonium salts, etc.
In addition, as a vacuum additive, chlorinated paraffin,
It may contain a naphthyl compound as an antioxidant. Thus, the composition of soluble oil is complex, and its wastewater has a high concentration of organic matter. When such wastewater is treated using the conventional coagulation separation method, it is impossible to maintain the COD value of the treated water at a low value (below 30 ppm to 50 ppm). In addition, the application of biological treatment methods has been considered to remove hydrophilic organic substances from this soluble oil wastewater, but treatment is difficult due to the presence of biological metabolism inhibitors in the wastewater. This is the current situation. Under such circumstances, the inventors of the present invention have conducted extensive research, and have found that, for example, biological metabolism inhibitors in cold-rolled soluble oil wastewater can be efficiently coagulated and floated away using weak alkalinity, and that this treated water can be used for biofilm fixation using biofilm fixation methods. The present invention was completed by discovering a method for scientific treatment. That is, the present invention adds a flocculant and a PH regulator to the water to be treated to adjust the pH of the water to a weak alkaline range, flocculates and separates biological metabolism inhibitors in the water, and then performs the flocculation treatment step. A method for treating oil-containing wastewater, characterized in that the water to be treated is sequentially treated through a biological treatment process using a biofilm fixation method, which is arranged in two stages in series downstream of the coagulation treatment process, The purpose is to drain cold-rolled soluble oil.
To provide a method for treating oil-containing wastewater that can treat COD stably at low cost. To explain in detail a preferred embodiment of the present invention, first, in order to coagulate cold-rolled soluble oil wastewater, a metal acid salt is added and slaked lime is added to make the pH slightly alkaline at 8 to 10, preferably 1 to 9. By adjusting the concentration within this range, mineral oil, fat, surfactant, etc. in the waste water can be stably precipitated together with metal hydroxide flocs. It is not clear how the addition of slaked lime along with the addition of metal acid salts produces cohesive properties, but the addition of slaked lime neutralizes the electric charge of the emulsion particles, making them more likely to coagulate, or the interface The activator hydrophilic group is substituted with calcium,
It is presumed that hydrophobicity increases and aggregation becomes easier. The precipitated flocs are removed by separation means such as sedimentation or flotation, but in the present invention, a polymer flocculant is added and the flocs are separated and removed by a flocculation pressure flotation method. The obtained treated water is sent to the next biological treatment process, but biological metabolism inhibitors such as mineral oil and fats and oils are removed, and foam contamination in the biological treatment process or interfaces that cause suspended solids to flow out due to foam are removed. As the activator is removed, the amount of organic pollution load is greatly reduced, and the COD in the wastewater is lower, but this is because the wastewater contains biodegradable substances such as lower fatty acids, alcohols, and glycol ethers. , Biological treatment is performed as an advanced treatment. Usually, a fluidized bed method such as an activated sludge method is used as a biological treatment method, but due to the characteristics of the organic substances contained in the cold-rolled soluble oil wastewater, the microorganisms that appear on the substrate are susceptible to Sphaerocilus. Since filamentous bacteria are the main components, the activated sludge method causes bulking and is difficult to treat. Therefore, biological treatment using biofilm fixation (fixed bed biological treatment), i.e., sprinkled bed method, catalytic oxidation method, etc. , the rotating disk method is advantageous. In addition, cold-rolled soluble oil wastewater lacks nitrogen and phosphorus necessary for biological treatment, and in particular, phosphorus is almost completely removed by the previous coagulation treatment, so BOD:N:P=100:5 : It is necessary to supply so that it becomes 1. Biological treatment using the biofilm fixation method can reduce the COD of cold-rolled soluble oil wastewater by: to include. (b) The operating status of each line in the cold rolling mill is inconsistent. Due to factors such as this, the amount of coagulated water fluctuates widely.
COD also fluctuates, and single-stage biological treatment does not necessarily provide a satisfactory treatment effect. According to the present invention, in the biological treatment of cold-rolled soluble oil wastewater, two stages of biological treatment using the biofilm fixation method are connected in series, and the total COD area load of the two stages is 1.
It has been found that by treating in the range of g·CCD/m ² ·day to 10 g·COD/m ² ·day, the effects of fluctuations in raw water can be completely absorbed and the COD of the treated water can be reduced. Furthermore, if the COD area load is maintained within this range, the sedimentation properties of the sludge that separates and falls off the biofilm are extremely good. In the biologically treated water obtained in this way, Ca ²⁺ ions are converted to calcium carbonate due to carbon dioxide gas generated during the process of microbial decomposition, and NH ₃ −N is generated.
Therefore, the pH of the treated water is around 7 to 8 and has buffering properties. Therefore, re-neutralization of the treated water is not necessary. As mentioned above, in the advanced treatment of cold-rolled soluble oil wastewater, this process, in which coagulation flotation treatment is performed as a pretreatment, and then biological treatment using a biofilm fixation method is combined, has mutually complementary treatment effects. The processing method is extremely excellent in practical terms. FIG. 4 shows an example of the apparatus used for carrying out the present invention, in which 1 is a coagulation and pressurized flotation tank, 2 is a coagulation tank, 3 is a pressurization tank, 4 is a separation tank, and 5 is a scum pit. , 6 is a scum skimmer. In addition, 7 indicates an adjustment tank, 8 indicates a first-stage watering bed, and 9 indicates a second-stage catalytic oxidation tank in the biological treatment process. Note that 10 is a settling tank. Further, A indicates cold-rolled soluble oil wastewater, B indicates pressurized water, C indicates air, and D indicates treated water. In the following examples of the present invention carried out using such an apparatus, FIG. 1 shows the results of Example 1, and FIGS. 2 and 3 show the results of Example 3. Example 1 Cold-rolled soluble oil wastewater (PH6.3, COD363ppm,
Oil content: 660ppm) and polyaluminum chloride: 800ppm
At the same time as addition, the pH was changed to 7, 8, 9, and 10 using slaked limestone to coagulate, and anionic polymer flocculant Himoroku OK-307 (trade name) was added to the mixture to produce 5 kg/cm ²
When 25% of air-dissolved pressure water was added to carry out pressurized flotation separation, the results shown in Figure 1 were obtained. That is, it is preferable for both CDO and turbidity to have a pH in the range of 8 to 10, and a pH of 10 or higher is not preferable because re-neutralization is required in the subsequent production process. Example 2 800 ppm of polyaluminum chloride was added to the same cold-rolled soluble oil wastewater as in Example 1, slaked lime was added at the same time to adjust the pH to 9.7, and then 1 ppm of an anionic polymer flocculant was added to remove the resulting flocs. The separated clear liquid is subjected to coagulation and pressure flotation treated water (PH
When a two-stage fixed bed treatment using a sprinkled bed and a catalytic oxidation bed acclimated to 9.8, 3 ppm oil, 97 ppm COD, and 250 ppm BOD was carried out under the conditions shown in Table 1, the treatment effects shown in Table 2 were obtained. In other words, the oxygen consumption potential such as BOD and COD is significantly reduced, and the PH satisfies the quality of the effluent water.

【table】

[Table] Example 3 The coagulation and pressurized flotation treated water of cold-rolled soluble oil waste water was acclimatized in the same manner as in Example 2, and the two-stage fixed bed treatment using sprinkled bed and catalytic oxidation was performed to obtain the total COD.
When biological treatment was performed with an area loading of 1 to 10 g COD/m ² · day (first stage COD area loading 0.5 to 8 g COD/m ² · day, second stage COD area loading 0.5 to 2 g COD/m ² · day), The results shown in FIG. 2 were obtained.
i.e. total COD area load 1-10g
Even within the range of COD/m ² ·day, the first-stage treated water shows a clear tendency to fluctuate as the COD of the raw water changes, but the second-stage treated water shows a very stable treatment effect. Furthermore, the batch concentration curve of detached organisms (SS 2690 ppm) when the first stage biofilm was forcibly detached is shown in FIG. 3A. In other words, the concentrated sludge concentration after 30 minutes of standing was 15,000 ppm, and the activated sludge treatment (SS load 0.2 Kg-COD/Kg-SS) operated at the same time.
The sedimentation property is significantly better than the concentration curve of Fig. 3B of the sludge (MLSS 2500ppm) (Japan).

[Brief explanation of the drawing]

The drawings show an example of the implementation of the present invention. Figure 1 is a graph showing the relationship between agglomerated PH and COD (ppm), and Figure 2 is a graph showing the relationship between time (days) and COD (ppm). , FIG. 3 is a graph showing the relationship between time (minutes) and interface height (cm), and FIG. 4 is a schematic diagram showing an example of the device used. 1... Coagulation pressurized flotation tank, 2... Coagulation tank, 3...
Pressurized tank, 4... Separation tank, 5... Scum pit, 6
... Scum skimmer, 7 ... Adjustment tank, 8 ... Sprinkling bed, 9 ... Contact oxidation tank, 10 ... Sedimentation tank, A ...
...Cold-rolled soluble oil wastewater, B...pressurized water, C...air, D...treated water.

Claims (1)

[Claims] 1 Adding a flocculant and a PH adjuster to the water to be treated to adjust the PH of the water to be treated to a weak alkaline range,
After the biological metabolism inhibiting substances in the water to be treated are flocculated and floated, the water to be treated that has undergone the flocculation treatment process is sequentially subjected to a biological treatment process using a biofilm fixation method in which two stages are arranged in series in the downstream area of the flocculation treatment process. A method for treating oil-containing wastewater, which is characterized by treating oil-containing wastewater through the process.