JPS6034792A - Treatment of waste water containing oil - Google Patents

Abstract

PURPOSE:To obtain easily waste water having quality permissible with respect to standard for final effluent by oxidizing waste water contg. oil and emulsifier with H2O2 and ferrous sulphate at pH3-5, performing then flocculation and settling at pH6-8 to separate solid from liquid. CONSTITUTION:H2O2 and ferrous sulphate are added to concentrated waste water or permeated water obtd. by ultrafiltration of concentrated waste water to perform oxidation by adding if necessary mineral acid or alkali and maintaining at pH3-5. The pH of oxidized water is adjusted to 6-8 with alkali, and oxidation product and hydroxide of iron, etc. are settled by flocculation by adding flocculant. In this stage, waste water produced by washing may be mixed with the oxidation treated water and flocculated together. Since, emulsions are destructed sufficiently by oxidation in this process, the flocculation is performed effectively, and deposited flocculated solid can be subjected to solid/liquid separation by the conventional process.

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 contains hexane extractables, BO
D,, COD are all wrong mg/I! , and is 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 broken, the oil is floated and separated, and then coagulated and precipitated. If appropriate combinations of treatment, microbial oxidation treatment, 'RF filtration, activated carbon adsorption treatment, etc. are used, Emulsilon will not be destroyed sufficiently, which will often cause fatal problems in subsequent treatments, resulting in a lack of processing stability. There were even cases where the discharge water quality standards 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 emulsicone of the oil by oxidative decomposition.

The method of the present invention is characterized in that wastewater is oxidized with hydrogen peroxide and ferrous sulfate at a pH of 3 to 5, and the oxidized water is subjected to cohesive root treatment at a pH of 6 to 8, followed by solid-liquid separation.

Although hydrogen peroxide and ferrous sulfate are strong oxidizing agents and are known as Fenton's reagents, their use in treating oil-containing wastewater has not been known. According to the present invention, when this oxidizing agent is added to concentrated wastewater, most of the emulsifier in the concentrated wastewater is oxidized and decomposed regardless of the type of emulsifying agent, that is, the difference in emulsifying power, and the emulsion is destroyed.
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 ultra-8R filtration 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 the concentrated wastewater or the permeated water obtained by treating the concentrated wastewater in an ultracentrifugal manner, and if necessary, #L acid or alkali is added to maintain the PL (3 to 5), followed by oxidation treatment. do.

Next, the oxidized water is adjusted to p) 16 to 8 using alkali, and a flocculant is added to precipitate and flocculate oxidation products, iron hydroxide, and the like. 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.

Through the above treatment, hexane extractables, BOD
Organic pollutants indicated by COD and COD can be removed very efficiently. The treated water obtained in this way has reached the discharge standard water quality and can be discharged as is.
Even higher quality water can be treated stably and reliably, and discharge standard water quality can be easily achieved.

Next, the present invention will be described in detail based on Examples, but the present invention is not limited thereto. 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 1 Example 1 Concentrated wastewater with the water quality shown in Table 1 was collected, and the wastewater 11 was mixed with 5000 μ/l of hydrogen peroxide and 11000 μl of ferrous sulfate.
After adding /l, it was adjusted to pna and oxidized. After mixing this oxidized water with the cleaning wastewater shown in Table 1,
Add caustic soda to adjust the pH to 6 to 8, add a polymer flocculant to flocculate, leave to stand, and convert the supernatant water to Na 5
The water was filtered for 1 hour using Ai paper, and the quality of the filtrated water was measured, and the results are shown in Table 2 below as treated water.

25,000 μ/l of powdered activated carbon was added to this treated water A,
After shaking for 15 hours, it was filtered with No5Cir paper,
``The quality of the treated water was measured, and the results are similarly shown in Table 2 below as treated water B.

As can be seen from Table 2, according to the method of the present invention, wastewater containing high concentrations of organic pollutants could be purified extremely easily, and the water quality could be brought to within the effluent standard water quality. .

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/d and a flow rate of 1.
．． Passed at 5 m/sec, and added 3000 ml of hydrogen peroxide to 1 liter of permeated water.
■/j2 and 5400 ■/l of ferrous sulfate were added, and the pH
was adjusted to 3 and oxidized.

The oxidized water was mixed with washing waste water, the pH was adjusted to 6 to 8 with caustic soda, then a polymer flocculant was added for flocculation treatment, left to stand, and the supernatant water was washed with No. 5 A'tP paper. The water quality of the 2R perfused water was measured, and the results are shown in Table 3 as treated water C.

Powdered activated carbon 25,000 μ/β was added to treated water C, and 15
After shaking for an hour, filter through 3.5 C'r paper, and
The quality of the treated water was measured and the results are shown in Table 3 as treated water.

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

patent applicant Hitachi Plant Construction Co., Ltd.

Claims (3)

[Claims] (1) In order to purify wastewater containing oil and an emulsifier that emulsifies and disperses the oil, the wastewater is oxidized with hydrogen peroxide and ferrous sulfate at pH 3 to 5, and the oxidized water is pl+
A method for treating oil-containing wastewater, which comprises performing coagulation-sedimentation treatment and solid-liquid separation in steps 6 to 8. (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.