DE2461727A1 - METHODS FOR TREATMENT AND PURIFICATION OF OILY WASTE WATER - Google Patents

Description

PATENTANWÄLTE O / R 1797

DR.-ING. VON KREI5IER i>: L-ING. BEAUTIFUL FOREST ^ DR.-ING. TH. MEYEiI D *. FUtS DIPL-CHEM. ALEK VON KREISLER DIPL-CHEM. CAROLA KELLER DR.-ING. KLOPSCH DIPL-ING. SELTING

5 COLOGNE 1, DEICHMANNHAUS

Cologne, December 27th Pu / Ax

The British Petroleum Company Limited, Britannic House, Moor Lane, London EC2Y 9BU (England). Process for the treatment and purification of oily

sewage

The invention relates to a method for treating waste water which has been contaminated with petroleum and petroleum products and in particular comes from oil refineries.

Operations in oil refineries use "water, e.g. in the desalination plant. After being used in the refinery, the wastewater is eventually turned into a . recirculated to natural public water. In the refinery contaminates the water, and before returning the wastewater to public water or the contaminating oil must be removed before being discharged into a sewer system to meet certain regulations.

Where the regulations require the water to contain less than about 5 ppm oil is a wastewater treatment process Commonly used where the wastewater is passed through an oil separator to remove the bulk of the Oil passed and the remaining oil is flocculated. This is often done in conjunction with a biological one Treatment. To flocculate, a water-soluble

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Lich salt, e.g. an aluminum or iron (III) salt is added to the water, and at the correct pH value the hydroxide formed is precipitated, absorbing the oil and taking it with it. This has the formation of an oily one Sludge which must be disposed of and is usually destroyed by incineration.

This oily sludge is commonly used in refineries Incinerator burned which is costly to install, operate and maintain. The incinerator is not normally suitable for treating sludge that contains and accumulates salt (sodium chloride), ■ if saline wastewater is treated, because the ι Sodium content in the sludge damages the furnace lining. . '

In addition to the oil, the refinery wastewater contains suspended solids or particulate matter and other contaminants, which absorb oxygen when discharged into public waters. The strength of this other Impurities are usually measured as the BOD (Biological Oxygen Demand) of the wastewater.

Biological wastewater treatment processes are used to reduce the biological oxygen demand of the wastewater reduce. They are used to purify refinery wastewater when the biological oxygen demand of the untreated Wastewater above an acceptable level

lies. j

Biological wastewater treatment processes are more effective in the absence of oil. To improve the efficiency of the To increase biological wastewater treatment, the oil content of refinery wastewater is often flocculated lowered during or before feeding to a biological cleaning system. The oil content of the biological Liquid leaking from the cleaning system

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can also be through a subsequent flocculation treatment, by which the oil content is reduced to an acceptable level is lowered, lowered.

A commonly used biological cleaning process is the activated sludge process used in domestic wastewater treatment plants and in oil refineries Widely used, although its particular advantages are in the cleaning of aqueous Outflows with high biological oxygen demand etc. are more obvious. In the case of activated sludge systems, however Excess sludge is formed, which further disposal systems, e.g. Incineration plants, requires which are costly to build and operate.

As an additional means for biological purification of wastewater trickling filters are used, but they have not yet been used on a large scale because they are not very effective in cleaning oily wastewater such as refinery wastewater.

Where there is no combined clogging and activated sludge stage is present, the oil content of the liquid that the "Biological purification plant is supplied to be lowered to a level that after the biological treatment is acceptable in a final departure. . ;

The type of wastewater treatment plant intended for a refinery depends on the type and nature of the wastewater and the required final concentration limits away.

The final oil content and biological oxygen demand achieved in the wastewater from a refinery depend on the final disposal of the wastewater. If the sewage in a public municipal sewage system for cleaning in a conventional sewage treatment plant is initiated

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the allowable concentrations of oil and other contaminants are higher than when the refinery wastewater can be directed into a body of water from which drinking water is taken. . i

In order to achieve a low oil concentration of "for example less than 5 mg / 1 and a low value of" biological oxygen demand, it was previously normally necessary to block and separate the sludge either in combination with an activated sludge treatment or with subsequent activated sludge treatment with simultaneous formation of large amounts of sludge To use amounts of oily sludge which requires costly disposal, usually by incineration. '

It has now been found that some of the oil in refinery wastewater is released during biological purification is oxidized quickly, but that the rest of the oil is more slowly oxidized and mainly in that normally formed excess sludge appears. For the purification of refinery wastewater, the Sand filtration applied, however, sand filters alone as a result of soluble oils are not sufficient to achieve very low levels To achieve total oil concentrations. Sand filters do not remove soluble or emulsified oil, however oily sludge, suspended solids or particulate matter and - under the right conditions - one

large proportion of the insoluble oil. !

Surprisingly, it has now been found that the oil content which are or are not removed by biological trickling filter and sand filtration, each other largely supplement, i.e. each treatment is able to absorb a large proportion of the oil fraction that after the other method is not removed, remove it.

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The subject of the invention is the treatment or cleaning, supply of refinery wastewater by a process that enables an oil content of less than 5 mg / 1 without reaching a flocculation stage, without the need for an incinerator is required, and this is applied to almost all refinery wastewater and similar wastewater can be. ;

According to the invention, oily wastewater after a Process, which is characterized in that one.das wastewater first through a sand filter and then passes through a biological trickling filter. One. Reversing the order of the stages is

not as satisfying or effective. :

It has been found that a biological trickling filter ' Filtration after sand filtration can surprisingly be sufficient to achieve the required oil concentration and to achieve the required value of biological oxygen demand, and contrary to expectations is in some respects superior to activated sludge treatment. For example, in the process according to the invention surprisingly little humus sludge compared to the excess sludge from one Activated sludge process formed. It has been shown that biological trickling filters compared to activated sludge systems Advantages, e.g. a higher resistance to shock loading, especially with alkali, due to the Neutralizing effect of the high COp concentrations towards the upper layers of the filter bed, good oxidation of ammonia in the lower layers and temperature reduction warm waste water.

The term biological trickling filter systems includes submerged and partially submerged biological Trickling filter. Instead of a biological trickling filter, several can be connected in series or in parallel 35. trickling filters are used. This system is particularly

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2A6J727

This is well suited for wastewater from an oil separator in refineries, e.g. any shape from parallel Plates existing separators or settling basins etc. or an API separator as described in "Manual on Disposal of Refinery Wastes ", 1969, issued by. ' American Petroleum Institute, above

equivalent separators.

The term "sand" includes all granular media. Both sand filters used according to the invention, the sand preferably has a particle size of 0.5 to 5 mm, e.g. about 1 mm.

The dimensions of the sand filters and the particle size depend on the flow rate and the type of sewage and the required final quality of the wastewater. Instead of one sand filter, several sand filters arranged in parallel can be used.

To regenerate a sand filter, it can be used backwashed by combinations of air and / or warm water. The oily water that arises which may contain up to 1 to 2 wt .- $ oil is preferred returned to the oil separator. It is very surprising that in this cycle management there is a A satisfactory equilibrium is reached, which makes it possible to apply the process without affecting the oil content of the water exiting the sand filters to a

unacceptable concentration increases. j

In the method according to the invention and in the cycle, all of the oil that is removed from the sand filters is separated, finally recovered as usable oil by the oil separator, and none are produced new oily by-products that would otherwise have to be disposed of, for example by incineration.

In a preferred embodiment of the invention

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a single pumping station is used to divert the oil contaminated water exiting the oil separator through the sand filters and to the top of a biological trickling filter. The static Pressure head of the liquid between the sand filters and the trickling filter system helps to maintain a constant Maintain back pressure on the pumps and make it easier to control the drainage from the sand filters Amount of liquid. The regulation of the liquid flowing out of the sand filters takes place normally - alternatively through an automatically adjustable non-return control valve. Such a regulation is necessary for correct

■ operation of the pumps required. . . !

The usual biological trickling filters are followed by a settling basin, which is used for settling and removing of the formed urnus sludge is provided.

It has surprisingly been found that when using sand filters after the process has passed Removal of the humus sludge is not necessary through the trickling filter system, since the content of Suspended solids in the liquid emerging from the biological trickling filter system is low enough, to enable direct derivation.

Biological trickling filters are designed by L. Klein in ' "River Pollution" 3: Control, Butterworth, London 1966,

Page 101. |

The relative size of the sand filter and the trickling filter [ ■ is selected depending on the flow rate and the 'composition of the refinery wastewater or other oily wastewater and the quality of the purified water to be achieved. :

Although both sand filters and biological cleaning systems are independent for the treatment of refinery wastewater

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Sern are used, it is very surprising that it can be achieved by using sand filters with subsequent biological cleaning by trickling filters is possible, a low oil content and a low biological vision To achieve oxygen demand with such a low content of suspended solids that it is not necessary to separate the existing small amounts of humus sludge.

If large amounts of rainwater or other runoff water can run through the system, a sump can be used or a sump that temporarily absorbs the excess water, for example and preferably in the form of a combination of a storm and water basin with a pump sump for the sand filter, into the system

be included. . ' j

The invention is described below with reference to the figure which shows an embodiment of the The method according to the invention is shown schematically, the receiving container 1, of which the oil-containing Wastewater is supplied, are connected to an API separator 2 for the removal of oily sludge. That Water from the API separator is supplied by a battery. of pumps 6 of a series of parallel sand filters 3 fed. With the sand filters 3, a backwash line 4 is connected, with which the sand filters individually and can be backwashed one after the other. The backwash water is fed through line 5 to the API separator. The water running through the sand filter is controlled by a pressure control valve 7 of a biological trickling filter fed. The water from the trickling filter system 8 passes through line 9 to a pond or equilibrium basin 12, from which it finally passes through outlet 10 can be derived.

The API separator 2 is connected to the pond or the same

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weight basin 12 connected by an emergency gravity overflow 11. Through an emergency bypass line 14, the water from the sand filters 3 can bypass the trickling filter system 8 in the event that a toxic material, for example a mineral acid, leaks. The waste water from the tanks 1 is fed to the API separator 2, where most of the oil is removed. After emerging from the API separator, the water is pumped through the sand filter 3, where the non-deductible suspended oil removed _o tray exiting the Sahdfiltern 3 then passes the water to the trickling filter system 8. The back pressure on the pump is controlled by the pressure regulating valve 7 regulated. In the biological trickling filter system 8, the soluble oil content and the BOD value are reduced to the prescribed limits, and the purified water is then fed to the equilibrium basin 12 before the final discharge.

When the backwashing of the sand filter · 3 is due, will they are backwashed with water, and the oil etc. separated off by the backwashing is passed through line 5 to the API separator 2 supplied.

example

A sand filter with a particle size of the sand of; 1 to 2 mm and a maximum nominal flow rate of 460 m / h was with a biological trickling filter connected, which was filled with random filling material made of plastic of 5 cm piece size. I.

A refinery wastewater which, after exiting an API separator, had an oil content of 22 mg / 1 (measured by extraction with chloroform, evaporation at room temperature and weighing) and a BOD content of 100 mg / L , was passed through the sand filter and then through the trickling filter at a rate of 80 nP / hour. After exiting the trickling filter system, the

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treated wastewater has an oil content of 4 mg / 1 and one -Value of 10 mg / 1.

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Claims (7)

- v \ - AA Claims Process for the treatment and purification of oily wastewater , characterized in that the wastewater is first passed through a sand filter and then through a biological trickling filter. 2) Method according to claim 1, characterized in that the effluent from an oil separator is used as waste water at an oil refinery. 3) Method according to claim 1 or 2, characterized in that one uses a sand filter whose Particles have a size of 0.5 to 5 mm. 4) Method according to claim 1 to 3, characterized in that that one uses a single pumping stage to pump the wastewater through the belt filter and above to give up on the trickling filter system. 5) Method according to claim 1 to 4, characterized in that the wastewater through several in parallel; arranged sand filter and then to the trickling filter system directs. j 6) Method according to claim 1 to 5, characterized in that after a certain time of implementation of the process interrupts the flow of waste water through the sand filter and the sand filter with ' backwashed with a mixture of air and water and the backwashing water to the oil separator of an oil refinery: feeds. j 7) Method according to claim 1 to 6, characterized in that that one works in such a way that it comes from the trickling filter system escaping water has an oil content of less than 5 mg / l. 5 0 9828/0871 Blank page