JPS62121688A - Method for treating oil-containing waste water - Google Patents

Abstract

PURPOSE:To perfectly remove floated oil while shortening the stagnation time of said oil in an oil separation tank, by providing a process for separating the floated oil in a pressure flotation tank to which no chemicals are added to the post-stage of a process for separating the floated oil in the oil separation tank. CONSTITUTION:Oil-containing waste water is supplied to an oil separation tank 1 and sent to a pressure flotation tank 4 from a raw water tank 2 by a pump 3. The waste water is recirculated in the pressure flotation tank 4 by a water recirculation pump 5 to be mixed with air during recirculation and subsequently mixed with inflow waste water through a stagnation tank 6. The waste water is supplied to a flocculation/pressure flotation/concn. tank 9 from the pressure flotation tank 4 through a mixing tank 7 and a reaction tank 8 and recirculated in the tank 9 by a water recirculation pump 10 to be mixed with air and subsequently mixed with inflow waste water through a stagnation tank 11. By this method, the injection amount of a flocculant can be reduced and the handling of conc. scum becomes easy.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for treating oil-containing wastewater, and for example, an oil-containing wastewater that can be suitably applied to a method for treating oil-containing wastewater generated from a cold rolling mill. This relates to a processing method.

C. Prior art] In cold rolling, rolling oil such as soliple oil, tallow, palm oil, vegetable oil, etc. and water are sprayed onto the rolls using a spray nozzle for cooling, anti-seizure, lubrication, etc., and the oil-containing wastewater is , has conventionally been processed using processing equipment as shown in FIG.

In FIG. 2, oil-containing wastewater is first sent to a separation tank 21, where molecules i of floating oil are removed, and then sent to a first-stage pressurized flotation separation device 22. Here, first in the rapid stirring tank 23, pH control by acid and alkali injection and emulsion breaking using an inorganic flocculant are performed, and then in the slow stirring tank 24.
The flocs are coarsened using an organic flocculant, and the grown flocs are made to float with fine air bubbles attached to them in the flotation separation tank 25, and the floated scum is sown and sent to the scum tank 26. In addition, to make the treated water clearer,
A second-stage pressure flotation separation device 27 having the same structure as the first-stage pressure flotation separation device 22 is provided, and the same process is performed again. After that, the treated water goes to the neutralization tank 28 to
The value is adjusted and released or reused. On the other hand, the scum in the scum tank 26 is disposed of by removing moisture in a concentrator 29 and incinerating it.

However, in such a treatment method, it is difficult to completely separate the floating oil using the separation tank 21 alone. Therefore, there is a problem that floating oil gets mixed into the wastewater of the next process, and a large amount of flocculant is required to break the emulsion.Furthermore, when floating oil gets mixed into the floating scum, it causes problems in dewatering and handling of the scum. It turns out.

In addition, since floating scum is normally discharged at a concentration of 1 to 2%, it is necessary to concentrate it as described above in order to perform incineration treatment, and when separating oil from scum by acid decomposition, it is necessary to concentrate it. This allows the amount of acid added to be reduced. Methods for concentrating floating scum for this purpose include: ■ Centrifugation using a decanter, ■ Gravity dehydration using filter cloth,
■There are sun drying methods using air-drying beds, etc., but the above method ■■ requires the addition of chemicals, and the above method ■ has problems with space and odor. There is a problem in that it requires problematic dehydration equipment.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned conventional problems, and is capable of completely separating and removing floating oil from oil-containing wastewater, reducing the amount of flocculant added for emulsion breaking, and The purpose of the present invention is to provide a method for treating oil-containing wastewater that can also concentrate scum without special dehydration equipment.

[Structure of the invention]

The method for treating oil-containing wastewater according to the present invention involves separating floating oil from oil-containing wastewater in an oil separation tank, and then further separating the floating oil in a pressurized flotation tank without using chemicals to remove the floating oil in two stages. After that, emulsion breaking is performed, a flocculant is added, and the separated oil is floated as scum in a coagulation pressurized flotation concentration tank, and is concentrated and removed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

First, the outline of the treatment equipment will be explained along the flow of oil-containing wastewater. Oil-containing wastewater is supplied to an oil separation tank 1 and sent from a raw water tank 2 to a pressurized flotation tank 4 by a pump 3. In this pressurized flotation tank 4, wastewater is circulated by a circulating water pump 5, and after being mixed with air during circulation, it is mixed with inflowing wastewater via a retention tank 6. The wastewater is supplied from this pressurized flotation tank 4 to a coagulation pressurized flotation concentration tank 9 via a mixing tank 7 and a reaction tank 8. In this coagulation pressurized flotation concentration tank 9 as well, the wastewater is circulated by the circulating water pump 10, and after being mixed with air during the circulation, it is mixed with the inflowing wastewater via the retention tank 11.

Next, a processing method using the above processing equipment will be explained.

Floating oil is separated from the oil-containing wastewater in an oil separation tank 1.

The residence time in this separation tank 1 is approximately 2 to 3 hours, which is dramatically shorter than the conventional 12 hours. The floating oil slightly remaining in the wastewater is separated and floated in the next pressurized flotation tank 4 without chemical injection, and the floating oil and emulsion oil are completely separated. In this pressurized flotation tank 4, pressurized flotation conditions are set such that the circulation rate is 20 to 50%, the pressure is 4 kg/cntg, and the amount of air is about 2 to 4% of the circulation amount. The floating oil separated and removed in the oil separation tank 1 and the pressurized flotation tank 4 is incinerated. Next, approximately 5 to 20 μ/l of organic emulsion break is injected into the wastewater from which the floating oil has been completely removed before entering the mixing tank 7.

As a result, the amount of inorganic flocculant to be injected next in the mixing tank 7 can be reduced to about one-third.

Furthermore, if the amount of inorganic flocculant injected is small, metal hydroxides such as AA(OH)3 and Fe(OH)+ will decrease when the scum is concentrated, and the oil content will become thicker, making it difficult to handle the concentrated scum. It becomes easier and saves energy. Mixing tank 7
Then, inject an inorganic flocculant to completely break the emulsion. At that time, add only an inorganic flocculant to adjust the pH to 4 to 6.
By slightly lowering the emulsion break 8
function can be promoted. The emulsion-broken wastewater is collected in a reaction tank 8 at a pH that can be discharged with an alkaline agent and a pH that is optimal for coagulation and oil treatment.
Adjusted to H6,0-7.0. The oil separated from water by emulsion breaking forms scum together with metal hydroxide as an inorganic flocculant, and air is attached to it in the coagulation pressurized flotation concentration tank 9 to form floating scum. In this coagulation pressurized flotation concentration tank 9, the circulation rate is 25 to 50% and the pressure is 4k.
g/crAg, and the air amount is 2 to 4% of the circulating water. Even under these conditions, an appropriate residence time (
The floating scum is concentrated to 10-30% by ensuring a sufficient scum thickness (50-500 HR) and scum thickness (50-500 HR). The scum thus concentrated is incinerated as it is, and the treated water is discharged.

〔Effect of the invention〕

According to the method for treating oil-containing wastewater of the present invention, as described above,
By installing a step in which floating oil is separated in a pressurized flotation tank without chemical injection after the process of separating the floating oil in an oil separation tank, the residence time in the oil separation tank is significantly reduced compared to conventional methods. In addition to being able to completely remove the floating oil, only the emulsified oil needs to be treated in the next step. This makes it possible to reduce the amount of emulsion break and coagulant injection.

Furthermore, when the scum is concentrated for this purpose, the amount of metal oxides caused by the coagulant decreases and the oil content becomes thicker, making it easier to handle the concentrated scum and saving energy during incineration.

Furthermore, the scum can be concentrated without the need for special scum concentration equipment and chemicals. Therefore, speeding up oil-containing wastewater treatment,
It has the effect of simplifying equipment, saving chemicals, saving energy, and saving space.

[Brief explanation of drawings]

FIG. 1 is a flowchart of an embodiment of the present invention, and FIG. 2 is a flowchart of a conventional example. 1 is an oil separation tank, 4 is a pressurized flotation tank, 7 is a mixing tank, 8 is a reaction tank, and 9 is a coagulation pressurized flotation concentration tank.

Claims (1)

[Claims] 1. After separating the floating oil from oil-containing wastewater in an oil separation tank, the floating oil is further separated in a pressurized flotation tank without chemical injection, and the floating oil is removed in two stages. After that, the emulsion is broken and a flocculant is removed. A method for treating oil-containing wastewater, which comprises adding the separated oil to the surface as scum in a coagulation and pressure flotation concentration tank, and concentrating and removing the oil.