DK143064B - PROCEDURE FOR THE REMOVAL OF ORGANIC POLLUTIONS FROM INDUSTRIAL WATER - Google Patents

Description

VRbl / (11) PUBLICATION WRITING 1 ^ 306 * 4 · ---- DENMARK wmt.a> o 02 f o / oo • (21) Application No. 5585/75 (22) Filed on 28 Jun. 1975 (24) Race day 28 Jun. 1975 (44) The application presented and the petition published on 23 * Π1 & Γ. 1981

DIRECTORATE OF

PATENT AND TRADE MARKET (3 °) As requested by the

June 28 1972, 267231, US

(71) ESSO RESEARCH AND ENGINEERING COMPANY, Linden, New Jersey, US.

(72) Inventor: Ronald Victor Trense, 66 Clive Street, Metuchen, New Jersey, US: Allen Clamen, 131 CoTtage Place, Westfield, New Jersey, US: John Matthew Ferrib, 1701 Lobdell Avenue, Baton Rouge, Louisiana, US * (74) Plenipotentiary in the proceedings:

The engineering firm Lehmann & Ree. _____ (54) Process for removing organic pollutants from industrial * wastewater.

The invention relates to a method for removing suspended and dissolved organic pollutants from industrial wastewater, whereby the wastewater is pre-treated to remove suspended contaminants therefrom and then passed through a layer of activated carbon to remove dissolved organic pollutants, passing through the layer of activated carbon if the found desirable, periodically interrupted by backwashing of the coal layer by passing water up through the layer at a sufficient rate of 3 to reduce the amount of biological growth accumulated on the activated carbon.

The most common method for removing impurities from wastewater consists first of a primary precipitate in which a large part of the solids suspended in the wastewater is removed with or without chemical flocculants. Another treatment step, in which the residual suspended solids, which are usually present in an amount of approx. 50 to ea. 150 ppm, decomposed, can then be carried out. Furthermore, the second treatment step usually involves vigorous aeration to further degrade the dissolved organic materials by bacterial action. The starting stream from this biological treatment step is precipitated to remove the bacteria in the form of sludge. The sludge is then recycled to the second treatment zone. This biological treatment of wastewater was primarily developed for the treatment of toilet or household wastewater. In the treatment of toilet or household wastewater, which typically contains waste contained in a public wastewater pipeline, the process has generally seemed quite satisfactory. Recently, however, industrial plants have discharged their wastewater into public sewerage systems. This has resulted in serious difficulties given that industrial wastewater also contains a significant amount of non-biodegradable contaminants. These non-biodegradable contaminants often, together with other toxic materials in industrial wastewater, cause the bacteria to be killed in the aforementioned secondary biological treatment steps, rendering the treatment plant inactive during the period of purification of the toxic materials and new bacterial growth being established. In addition, conventional biological oxidation has not demonstrated the ability to generate uniformly high-quality effluent streams in the treatment of wastewater from crude oil refining processes and petrochemical manufacturing processes.

In determining the amount of pollutants in a wastewater stream, certain recognized indications have been developed. These include: Biochemical oxygen requirement (BOD), which is the amount of oxygen in milligrams per minute. liters or parts per million used for biochemical oxidation over a period of 5 days at 20 ° of the organic matter contained in the water; and chemical oxygen requirement (COD), which is the amount of oxygen, expressed in milligrams per minute. liters consumed under specific oxidation conditions with strong chemical oxidizing agents such as sodium chromite (see Method of Examination of Water and Waste Water, 12th Edition, Public Health Association, New York (1965), pp. 510-51 ** ·) Generally is the acceptable minimum standard expressed as BODej and COD, respectively, for a purified wastewater stream, respectively. 0 and approx. 100 mg per liter.

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Accordingly, there is a need to treat the output stream of such biological secondary treatment plants, as well as an improved method of treating industrial waste water to remove biodegradable as well as non-biodegradable contaminants, i.e. bio-resistant contaminants, from this water to avoid the above unwanted results.

To remove the organic pollutants from wastewater, especially industrial wastewater, it has recently been proposed to treat the industrial wastewater as well as the effluent stream from the secondary activated carbon treatment stage. Eg. methods are described in U.S. Pat. U.S. Patent Nos. 3,244,621, 3,455,820 and 3,658,697 to the removal of organic soluble pollutants from wastewater by passing the wastewater through a bed of activated charcoal. However, it has also been described (see Hopkins, C.B., Weber, W.J., Jr., Bloom, R., Jr., U.S. Department of the Interior Federal Water Pollution Control Administration Report No. TWRC-2, Dec. 1968) that by treatment of public and industrial wastewater with granular activated charcoal, biological activity occurs in the carbon beds during extended operation, which results in a significant build-up of sludge in the carbon bed. The formation of this aerobic biological sludge, in addition to giving rise to a problem of removal and deposition of the sludge, results in clogging of the carbon beds so that frequent flushing to restore and thus regenerate the absorbed capacity of the activated charcoal is necessary. This biological activity, which is found in the activated carbon bed, also results in undesirable formation of hydrogen sulfide flowing from the carbon bed (see U.S. Patent No. 3,658,697) ·

However, these deficiencies in the methods used heretofore are remedied by the process according to the invention, which is characterized in that the waste water is passed through the layer of activated carbon together with oxygen in such an amount that a controlled aerobic biological oxidation of the pollutants adsorbed is obtained. on the activated charcoal, where this amount of oxygen is 0.09-0.15 kg per COg contaminants removed from the wastewater, unless the layer of activated charcoal in connection with the flushes is treated with an oxygen-containing gas stream, in which case the amount of oxygen dissipated with the wastewater is 0.05-0.12 kg per liter. kg of COD contaminants removed from the wastewater.

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When the amount of oxygen added to and consumed in the activated carbon bed is kept within the critical limits stated above, a balance of anaerobic and aerobic biodegradation of the contaminants adsorbed on the activated carbon is provided. Thus, the evolution of hydrogen sulfide that would occur as a result of uncontrolled, anaerobic biological growth on the carbon is suppressed. Furthermore, the amount of sludge which is naturally formed during the aerobic biological oxidation is minimized so as to avoid clogging of the contact system, i.e. activated charcoal (s). In addition, the controlled aerobic oxidation achieved by the practice of the invention results in a significant increase in the effective carbon of the activated carbon with regard to the removal of organic pollutants relative to the capacity obtained by physical adsorption alone.

In another embodiment of the invention, it has surprisingly been found that the use of a activated clay coagulant in the wastewater pretreatment to remove the suspended oil and suspended solids remaining after sedimentation prevents contamination of the activated charcoal. in the bed, which contamination is known to occur using soluble inorganic coagulants. In another preferred embodiment of the invention, it has been discovered that conducting the wastewater up through an undefined activated charcoal bed is preferred over conventional downward flow of the wastewater into a activated charcoal packed bed. The technique of flowing up through an expanded bed requires less flushing and maintains a constant pressure drop across the bed, allowing better control of the dissolved oxygen concentration in the bed.

The wastewater treated according to the invention is first cleared by settling before being contacted with the activated charcoal in the columns or zones intended for contact with the carbon. The wastewater which can be purified according to the invention comprises toilet, municipal or industrial wastewater streams containing dissolved organic pollutants such as aliphatic, aromatic and phenolic hydrocarbons. The process of the invention is particularly useful for removing bio-resistant contaminants such as aromatic compounds, halogenated and nitrated hydrocarbons and the like, which are bio-resistant contaminants characteristic of refining crude oil and producing organic chemicals. These bio-resistant contaminants, which generally give the recipients a very distinct taste and odor, are substantially completely removed by the activated carbon adsorption of the invention, although substantially unaffected by conventional biological treatment. While the untreated wastewater stream is usually initially pretreated to remove suspended solids and oils, it should be noted that the activated carbon causes a filtration by physical adsorption of the remaining suspended solids into the wastewater in addition to removing dissolved organic matter by adsorption and concurrently break down the pollutants on the activated charcoal biologically.

Coagulating polymers can be used in the precipitation step to increase the total removal of suspended solids and oils. Usually, the untreated wastewater contains which must be purified, e.g. from an oil refinery, significant amounts of oil and other suspended solids. These suspended, small oil droplets and solids can advantageously be removed in the primary settling zone by coagulants. In addition to using both organic and inorganic coagulants, which are known to be suitable for increasing the total removal of suspended solids and oils, other techniques such as dissolved air flotation, solids contact filtration and filtration techniques may using two or more media also be useful in separating the suspended solids and oils from the untreated wastewater. While all of these techniques may be used in the practice of the invention, it has surprisingly been found that the use of activated clay, especially in connection with filtration by means of two media as a final pretreatment process, is an effective pretreatment method for the aforementioned carbon sorption system. The use of soluble inorganic coagulants such as alum with a polyelectrolyte in connection with flotation using dissolved air often over a period of time leads to contamination of the activated carbon bed. This is believed to be due to the dissolved aluminum compounds remaining in the outlet stream precipitating on the activated charcoal, which causes severe clogging problems when the wastewater is either directed up or down through the activated charcoal bed, which also significantly reduces the efficiency. of the activated charcoal for removal of organic pollutants from the wastewater after thermal regeneration. The activated clay, which has surprisingly been found to be suitable for the initial primary treatment of the untreated wastewater, consisting of a sodium montmorillonite in association with an organic cationic agent such as an amine or a glycol, the aforementioned clogging issues and the permanent carbon deactivation. Sodium montmorillonite clay can be activated by a variety of cationic agents comprising primary, secondary and tertiary amines, as well as the so-called ethyleneamines such as tetraethylene pentamine. The activated clay coagulants suitable for use in this form of treatment comprise all such clay types specifically described in U.S. Pat. U.S. Patent No. 3,487,928. A flocculation coagulation solution containing sodium montmorillonite in conjunction with a cationic activator is preferably added to the wastewater in an amount of about 10 - 50 ppm clay in conjunction with 1 to 5 ppm of the activating agent to promote precipitation of suspended oils and solids in the primary treatment zone.

Furthermore, it has been discovered that the critical amount of oxygen to be added and consumed is affected by the particular after-rinse technique used. Rinse is required when the accumulation of solids causes an increase in pressure drop when the wastewater is led down through the activated charcoal bed or when a particularly large expansion of the bed occurs when wastewater is led through the activated charcoal bed. When the flushing technique performed by either pumping the pretreated effluent stream or the carbon effluent effluent from the wastewater treatment process up through the bed of activated charcoal at a rate of approx. 400 to approx. 800 liters per per minute square meters, intermittently interrupted to conduct a gas flow, such as air, through the activated charcoal bed to "air purify" the activated charcoal, it has been discovered that the critical amount of oxygen to be added to the activated charcoal bed (s) for to achieve the above results, ranges from approx. 0.05 to approx. 0.12 kg oxygen per kg of COD contaminants removed from the wastewater. It must be assumed that the reduction of the addition and consumption of the critical oxygen amount from approx. 0.09 kg of oxygen per kg of COD contaminants removed from the wastewater to approx. 0.05 kg of oxygen per kg of COD contaminants removed from the wastewater is due to the fact that the air purification effectively reduces the thickness of the biological sludge layer on the activated charcoal so that the amount of oxygen required to maintain an aerobic anaerobic balance in the bed (s) of coal, reduced. Furthermore, this reduction in oxygen demand is also caused by oxygen being absorbed by the activated charcoal during air purification.

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Addition of this critical amount of oxygen to the activated charcoal bed can be accomplished by either adding air, a gas stream containing oxygen, or oxygen in an amount sufficient to control the aerobic biological oxidation of the contaminants adsorbed on the coal, thereby suppressing the evolution of hydrogen sulphide from the activated charcoal bed (s) as well as minimizing the aerobic biological sludge which is necessarily formed due to the addition of oxygen to the bed (s). The above-mentioned critical oxygen amounts can be added directly to the bed or to the wastewater stream to be fed into bed (s). If the latter method is used, the oxygen-containing gas can be bubbled into the wastewater at the inlet to the bed (s), so that oxygen gradually dissolves in the water flowing through bed (s). This method makes a controlled amount of oxygen available to all parts of the bed, the top included where biological sludge may be present. The capacity of the activated charcoal obtained by the practice of the invention was about 3 times the capacity obtainable by pure physicochemical adsorption, i.e. 1.0 kg of COD per kg of coal against 0.3 kg of COD per kg of coal.

Accordingly, when the untreated wastewater is passed through an activated charcoal bed that is regularly rinsed without air purification, the amount of oxygen supplied to the bed is of the order of approx. 0.09 to approx. 0.15 kg per kg of COD contaminants removed from the effluent stream. If it is envisaged to purify the carbon during the rinse step, as mentioned above, it is essential that the amount of oxygen supplied to the bed is in the range of approx. o, 05 to approx. 0.12 kg per kg of COD contaminants removed from the wastewater.

Many different types of activated charcoal can be used in the practice of the invention. The activated charcoal preferably has a large surface area, preferably in the range of from approx. 300 to approx. 1200, or better in the range of approx. 400 to approx. 1000 m 2 per g. Because it is preferable to direct the wastewater, i.e. flow upwardly through the activated charcoal bed, it is further preferred that the activated charcoal has a low frictional resistance to prevent the formation of large amounts of very fine particles when operating with upward flow to form an expanded bed. Furthermore, it is also preferred to avoid activated charcoal which deposits into gas bubbles formed in the expanded bed of activated charcoal using the upward flow characterized technique, given that such gas which is chargeable to gas bubbles , is transported out of the contact zone constituted by the activated ball bearing.

The most preferred types of activated charcoal that can be used in the practice of the invention are compositions of activated fluid coke as described in Danish Pat. 3586/73. These new compositions of activated fluid coke are peculiar in that they have a surface area of at least 400 m per minute. grams and a pore volume of at least 0.20 ccn. gram. The activated fluid coke is prepared by contacting fluid crude oil coke with a gas mixture containing steam at a temperature of at least 815 ° C for such a time that at least 35% by weight of the coke particles are converted into gaseous products, new activated coke composition is formed which exhibits really good properties as absorbent.

A more detailed description of a preferred embodiment of the invention will now be given, with reference to the accompanying drawing, in which is shown a schematic diagram of apparatus suitable for use in the practice of the invention.

Untreated industrial waste water with a COD of approx. 800 mg per per liter and containing contaminants which may be adsorbed, such as aromatic, aliphatic and phenolic hydrocarbons, etc., as well as suspended oils and solids are passed through pipeline 1 into pretreatment zone 2. cannot pass through a 0.45µ Millipore® filter so that a concentration less than 25 ppm by weight, preferably less than 15 ppm by weight, is achieved. The pretreatment processes that can be used can be very diverse and include, but are not limited to, the following: flotation using dissolved air, sedimentation, solids contact with solids, filtration using two or more media, and sand filtration using of upward flow. The preferred pretreatment process involves using an activated clay coagulant, as described above, in connection with filtration by two media, thereby reducing suspended material to less than 15 ppm by weight.

The pretreated wastewater is then fed via pipeline 3 into a storage tank 4, to provide uniform feed to the carbonate bed bearings and flush water to the filters and carbonate bed bearings. Thereafter, the pretreated wastewater is fed via pipeline 5 into the bottom of the first activated coal treatment zones 7 via pipeline 8. In the tanks 7, 9 and 11 used for activated coal treatment there is a bed of activated charcoal, preferably activated, fluid. coke as described above. The waste water is led up via pipeline 8 through contact charcoal 7 with activated charcoal, causing an expansion of the activated charcoal bed. The activated charcoal bed has such physical properties that the volume of the adsorption beds is expanded at least 10 # but not more than 100 # at wastewater flow rates between 163 and 285 liters per liter. per minute square meters of the bearing cross-sectional area.

It is essential that the above-mentioned critical oxygen amounts be added to activated carbon contact zones 7, 9 and 11. This can be accomplished by various methods which include, but are not limited to, the following: injection of air, oxygen-enriched air or oxygen in pipeline 8, injection of air, oxygen-enriched air or oxygen in contact zone 7 with activated carbon and / or injection of air, oxygen-enriched air or oxygen in the free space over contact zone 7 with activated carbon. The preferred technique consists of supplying air, oxygen-enriched air or oxygen through pipeline 13 into the wastewater which is passed through pipelines 8, 10 or 12, to obtain maximum utilization of the oxygen-containing gas, to minimize the cost of feed materials. of the oxygen-containing gas and to obtain a satisfactory distribution of oxygen over the coal contact zones 7, 9 and 11.

The economical operation of the activated carbon treatment process often requires that the carbon be contacted stepwise with the wastewater. Practice of the invention comprises operating the coal contact areas or bearings using an upwardly expanding bed as described above, wherein critical oxygen amounts are added to each of contact zones 7, 9 and 11 at a rate corresponding to the rate at which COD is removed. in each of the series connected contact zones. P.eks. is added and consumed approx. 45 ppm of oxygen in the carbon sorbent bed 7, where the waste water COD is reduced from 800 to 300. The partially treated starting stream having a COD concentration of approx. 300, is removed from carbon contact vessel 7 via pipeline 10 and fed to the bottom of carbon contact vessel 9 via pipeline 10. A sufficient amount of oxygen is then fed via pipeline 13 into pipeline 10 so that 18 ppm of oxygen is consumed in carbon adsorption bed 9 while COD - the concentration of the wastewater is reduced from 300 to approx. 100. Thereafter, the output current is conducted from vessel 9 to coal contact vessel 11 via pipeline 12, wherein 143064 approx. 9 ppm of oxygen is introduced via pipeline 13, while the remaining COD in the wastewater is removed in coal contact vessel 11. The effluent stream of treated wastewater is removed from contact zone 11 by activated charcoal via pipeline 14. In all three activated coal bearings 7, 9 and 11 it was added to the bed. amount of oxygen kept at 0.09 kg of oxygen consumed per kg of COD contaminants removed from the wastewater treated in each activated charcoal bed. The flow of industrial wastewater between series-connected contact vessels can be accomplished either by using pumps or by arranging the contact zones so that flow using the gravity between the steps is made possible. The pressure in the bearing (s) is kept in the range from approx. 100 to approx. 310 kPa abs., And preferably around atmospheric pressure. Determining the most economically advantageous number of coal treatment steps is obvious to one skilled in the art of activated charcoal wastewater treatment.

At intervals, the build-up of biological sludge on the activated coal causes excessive expansion of the activated coal bed. A flushing technique is used to partially remove the sludge that deposits to the carbon grains by conducting from ca. 400 to approx. 800 liters per per minute square meter of the output stream from the pretreatment through pipeline 15, marked by a dotted line, up through the contact vessels 7, 9 and 11. It is preferred to interrupt the passage of this pretreated output stream by passing an oxygen-containing gas stream such as air through pipeline 16 the activated coal bed (s) in order to clean the granules of activated carbon and reduce the thickness of the biological sludge layer which accumulates on the activated coal. Usually, each absorption column is rinsed with coal for approx. every other day, the time needed for the post-rinse is from approx. \ to approx. 1 hour. The rinsing is typically interrupted about 3 or 4 times to air-purify the activated charcoal, preferably under pressure, for a period of from ca. 10 to approx. 30 seconds to run air through the ball bearing.

In the following Examples 1-5, refinery wastewater with a COD contamination level in the range of approx. 400 to 1500 mg per day liters passed through a filter consisting of two media, e.g. anthracite and sand, which removes suspended oils and solids, resulting in a filtrate with a COD contaminant level of 300 to 1400 mg per day. liter. This filtrate was produced at a rate of 0.25 liters per liter. per minute continuously passed through 12 consecutive columns of diameter 5 cm and height 1.8 meters, each column containing a load of activated charcoal. The flow of the wastewater was directed through each vertical column and the exit stream from the top of each column was introduced at the bottom of the next column. With a flow rate of 0.25 liters per per minute (or 122 liters per minute per square meter) the beds with activated granular coal expanded approx. 10¾ in height. Oxygen was supplied to the activated coal bed by introducing the oxygen-containing gas stream into the wastewater introduced into the first column, and also at the top of the activated coal bearings in the 2nd, 4th, 6th, 8th and 10th columns. Dissolved oxygen determinations were made on the water flowing from each column and determination of the total amount of organic carbon was made at the top of each other column, starting with the second column. COD determinations were made on the output current from the last column.

The amount of oxygen consumed in each column was varied by enriching the air introduced into columns 2, .4, 6, 8 and 10 with oxygen.

Example 1 In Example 1, air was introduced into the columns as described above, enriched and at 1 atmosphere. In all five columns, i.e. columns 2, 4, 6, 8 and 10 were the total amount of oxygen added to the wastewater and consumed, thus 35 mg per ml. liter. The output current from the last column showed a removal of COD, which remained at approx. 90% over a 2-week period in which these conditions were maintained. During this 2-week period, biological sludge formation was low, with no cumbersome accumulation in any of the columns. Rinse only required approx. 1 time every four days. After one week of operation, the presence of hydrogen sulfide was detected both by odor and chemical analysis of the exit stream from the top of the anterior column and was determined to be in the range of approx. 20 to approx. 50 ppm hydrogen sulfide. After 2 weeks of operation, hydrogen sulphide was also determined in the last column exit stream in an amount in the range of approx. 2 ppm.

Example 2 In Example 2, oxygen was added to the activated charcoal bed in the same manner as described in Example 1, except that the air was enriched to an oxygen content of 60 ° and the pressure in column U3064 was increased to 207 kPa. overpressure, resulting in a dissolved oxygen concentration of approx. 40 ppm in the places where it was introduced into the wastewater. The removal of GOD, as evidenced by determinations on the output column from the last column, was on the order of approx. 90% over the 2 week period during which this trial ran. The formation of sludge was greatly increased, necessitating more frequent flushing to avoid excessive contamination and expansion of the bed. However, the presence of hydrogen sulfide could not be determined by odor or chemical analysis on the front columns or the exit stream from the last column during the experiment.

Example 3 In Example 3, oxygen was fed in the same manner as described in Examples 1 and 2. However, the concentration of oxygen added was reduced to 35% at 138 kPa overpressure, so that the dissolved oxygen concentration at the introductory sites was about. 12 ppm, whereby the total amount of oxygen consumed was approx. 50 ppm. The removal of COD remained at the 90% level over the seven day period during which this trial ran. Furthermore, hydrogen sulphide was not detected, either in the front columns or in the last stream exit stream. In addition, the volume of biological sludge formed during this seven-day period was significantly reduced. Air purification of the ball bearing was used during the rinsing to partially remove the sludge attached to the carbon grains during this cycle.

Example 4 In Example 4, oxygen was introduced into the system in the same manner as described in Examples 1-3, with un enriched air at a pressure of 1 atmosphere being introduced into the system so that the total amount of oxygen added to the water and consumed all the columns were approx. 35 mg per liter. During the three-week period during which this trial ran, the removal of COD in the mean was approx. $ 75. The formation of biological sludge was low, and flushing was only needed approx. every six days during this period. However, the evolution of hydrogen sulphide was uncontrolled and unsatisfactory considering that hydrogen sulphide was detected in the starting stream at concentrations of the order of ca. 4 to 50 ppm after three weeks of operation.

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Example 5 In Example 5, oxygen was again introduced in substantially the same manner as described in previous Examples 1 to 4, with oxygen being introduced as un enriched air at a slightly increased pressure, so that the wastewater passing through the carbon columns was oxygenated. . During this trial, the COD removal was approximately ca. 90%. Rinse was performed approx. every other day and included the air purification technique. During this experiment, the formation of biological sludge was not violent and there was no remarkable content of hydrogen sulfide in the front columns or in the exit stream of the last column.

Example 6 In Example 6, activated fluid coke as described above was used as the activated charcoal material. The refinery wastewater treated had a mean CQD concentration of 700 mg. per. liter. The wastewater became at a rate of approx. 61 liters per liter. per minute square meter passed continuously through six consecutive columns of diameter 5 cm and with bearings consisting of activated fluid coke, which had a height of 60 cm after the material had settled. Oxygen was introduced into the system by introducing the oxygen-containing gas stream into the wastewater in the same manner as described above in Example 1. Air was used to oxygenate the wastewater in the same way as described in the previous examples, the wastewater being saturated with oxygen in equilibrium with air. at a pressure which varied from atmospheric pressure to 207 kPa overpressure in a manner similar to that of commercially activated coal described in Example 1. Medium was added per day. liter of 50 mg of oxygen to the wastewater and was consumed in all the columns for the four weeks that this experiment lasted. The removal of COD by this system averaged approx. $ 80. Air purification technique was used during the rinse operation to partially remove the biological growth that accumulated on the activated fluid coke. During the four weeks during which this experiment was conducted, there was no evidence of the development of hydrogen sulphide in the effluent stream from the last column at any point during the experiment. Furthermore, the resistance produced by the biological sludge was within acceptable limits, as no overwhelming 14

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the rampant accumulation in the bearing (s).

An overview of the operating conditions used in the examples described above as well as of the total effects is given in Table 1 below.

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Claims (2)

As seen from the results in Table 1, the amount of oxygen consumed per Critically, CO 2 removed COD to control the aerobic biological oxidation of the activated charcoal adsorbed contaminants, thus preventing excessive sludge production which would clog the bed and at the same time suppress the development of hydrogen sulfide. When air purification during the rinsing is not used, experiments 1 and 2 clearly show that it is essential to keep the amount of oxygen supplied to the bearings at a level from ea. 0.09 to approx. 0.15 kg oxygen per kg COD removed to suppress the evolution of hydrogen sulfide from the bed as well as to minimize biological sludge formation on the activated charcoal. Further, it can be seen that when air purification is used in the post-rinse technique, e.g. In experiments 3, 5 and 6, smaller amounts of oxygen can be used, i.e. 0.05 to approx. 0.12 kg of oxygen consumed per kg of COD removed, and preferably in the range of approx. 0.08 to approx. 0.12 kg oxygen per kg of COD removed to obtain the advantages of the invention. Claims. A process for removing suspended and dissolved organic pollutants from industrial wastewater, thereby pretreating the wastewater to remove suspended contaminants therefrom and then passing through a layer of activated carbon to remove dissolved organic pollutants, passing through the activated carbon layer, if present desirably, intermittently interrupted by flushing of the coal layer by passing water up through the layer at a sufficiently high rate to reduce the amount of biological growth accumulated on the activated carbon, characterized in that the wastewater is passed through the layer of activated carbon together with oxygen in such an amount that a controlled aerobic biological oxidation of the pollutants adsorbed on the activated charcoal is obtained, where this amount of oxygen is 0.09 to 0.15 kg per liter. kg COD contaminants removed from the wastewater unless the layer of activated charcoal in connection with the flushes is treated with an oxygen-containing gas stream, in which case the amount of oxygen dissipated together with the wastewater is 0.05-0.12 kg per kg of COD contaminants removed from the wastewater.