JPH0117433B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating oil-containing wastewater. Various types of oil are used in automobile, machining, and metal processing factories, and cutting oil is especially used during cutting processes, and wastewater containing these oils and emulsifiers that emulsify and disperse the oil components is discharged. Such oil-containing wastewater (hereinafter referred to as concentrated wastewater) exhibits a large pollution load, and hexane extractable substances, BOD, and COD can all reach tens of thousands of mg/ml, making it a significant source of pollution. Further, in the above-mentioned factories, cleaning wastewater containing cleaning agents is also discharged, and the pollution load of this cleaning wastewater is large. Conventionally, when treating this kind of wastewater, mineral acid is added to concentrated wastewater or a mixture of concentrated wastewater and washing wastewater to adjust the pH to 1 to 3, the oil emulsion is destroyed, the oil is floated and separated, and then coagulated and precipitated. Water treatment is carried out using appropriate combinations of treatment, microbial oxidation treatment, filtration, activated carbon adsorption treatment, etc., to make the water quality suitable for discharge. However, in such processing methods, if the type of oil or emulsifier contained changes, the emulsion cannot be broken sufficiently, which often causes fatal problems in subsequent processing, and the processing lacks stability. There were even cases in which the discharge standard water quality could not be achieved. An object of the present invention is to provide a method for treating oil-containing wastewater that eliminates the drawbacks of the prior art described above, that can be treated stably and reliably, and that can easily meet the standard discharge water quality. This objective is achieved according to the invention by destroying the oil emulsion by oxidative decomposition. In the method of the present invention, wastewater is oxidized with hydrogen peroxide and ferrous sulfate at a pH of 3 to 5, and the oxidized water is
It is characterized by coagulation and precipitation treatment in steps 6 to 8, followed by solid-liquid separation. Hydrogen peroxide and ferrous sulfate are strong oxidizing agents, known as Fenton's reagent, but their use in treating oil-containing wastewater has not been known. According to the present invention, when this oxidizing agent is added to the concentrated wastewater, most of the emulsifier in the concentrated wastewater is
The emulsion is oxidized and decomposed regardless of its type, that is, its emulsifying power, and the emulsion is destroyed and the oil is removed. In the method of the present invention, most of the oil in the concentrated wastewater may be removed by permeation treatment using an ultrafiltration device in advance, and then the emulsifier leaking into the permeated water may be decomposed and removed by the method of the present invention. Hydrogen peroxide and ferrous sulfate are added to concentrated wastewater or permeated water obtained by ultrafiltering concentrated wastewater, and if necessary, mineral acid or alkali is added to maintain the pH at 3 to 5.
Oxidize. The oxidized water is then adjusted to pH 6-8 using alkali.
and add a flocculant to precipitate and flocculate oxidation products, iron hydroxide, etc. At this time, washing waste water may be mixed with the oxidized water and coagulated together. According to the method of the present invention, since the emulsion is sufficiently destroyed by the oxidation treatment, the aggregation treatment can be carried out efficiently. The precipitated and aggregated solids can be separated into solid and liquid by a conventional method. By the above treatment, organic pollutants expressed as hexane extractables, BOD and COD in wastewater can be removed very efficiently. The treated water thus obtained has reached the discharge standard water quality and can be discharged as is, but if a higher quality water quality is desired, it is further subjected to adsorption treatment using an adsorbent such as activated carbon. As described above, according to the method of the present invention, oil-containing wastewater can be treated stably and reliably, and discharge standard water quality can be easily achieved. Next, the present invention will be explained in detail based on examples.
The present invention is not limited to this. In addition,
The wastewater used in the examples is concentrated wastewater containing concentrated cutting oil and washing wastewater discharged from an automobile manufacturing factory, and has the water quality shown in Table 1 below.

[Table] Example 1 Collect concentrated wastewater with the water quality shown in Table 1, and add 5000 mg of hydrogen peroxide and ferrous sulfate to the wastewater 1.
After adding 11,000 mg/ml, the pH was adjusted to 3 and oxidation treatment was performed. After mixing this oxidized water with the washing wastewater shown in Table 1, caustic soda was added to bring the pH to 6.
~8, add a polymer flocculant to flocculate, leave to stand, filter the supernatant water using No. 5A paper,
The quality of the perfused water was measured and the results are shown in Table 2 below as treated water A. 25,000 mg of powdered activated carbon was added to this treated water A, and after shaking for 15 hours, it was filtered through No. 5C paper.
The quality of the treated water was measured, and the results are similarly shown in Table 2 below as treated water B.

[Table] As can be seen from Table 2, according to the method of the present invention,
It was possible to purify wastewater containing high concentrations of organic pollutants very easily and bring the water quality within the effluent standard. Example 2 Concentrated wastewater with the water quality shown in Table 1 was processed using an ultrafiltration device using a polyolefin membrane at a pressure of 1.7 kg/kg.
cm ² at a flow rate of 1.5 m/sec, 3000 mg of hydrogen peroxide and 5400 mg of ferrous sulfate were added to the permeated water 1, and the pH was adjusted to 3 for oxidation treatment. Mix the oxidized water with washing wastewater and adjust the pH to 6~6 with caustic soda.
8, then add a polymer flocculant to flocculate, leave to stand, and filter the supernatant water through No. 5A paper.
The quality of the overwater was measured and the results are shown in Table 3.
Shown as Add 25,000 mg of powdered activated carbon to treated water C,
After shaking for 15 hours, it was filtered through No. 5C paper and the quality of the supernatant water was measured, and the results are shown in Table 3 as treated water D.

[Table] As can be seen from Table 3, most of the organic pollutants except for the emulsifier can be removed by ultrafiltration, and the remaining emulsifier is very well treated by hydrogen peroxide and ferrous ions. The activated carbon adsorption treated water was of extremely good quality.

Claims (1)

[Claims] 1. In order to purify wastewater containing oil and an emulsifier for emulsifying and dispersing the oil, the wastewater is oxidized with hydrogen peroxide and ferrous sulfate at a pH of 3 to 5, and the oxidized water is oxidized to a pH of 6. 8. A method for treating oil-containing wastewater, which comprises performing a coagulation-sedimentation treatment and solid-liquid separation. 2. The method according to claim 1, wherein the wastewater is wastewater containing cutting oil. 3. The method according to claim 1, wherein the wastewater is subjected to ultrafiltration in advance and then subjected to oxidation treatment.