DE2753401C2 - Process for the treatment of gas water resulting from the production of coke - Google Patents

Description

2. The method according to claim 1, characterized in that in step (D)

25th

(1) an iron (II) salt is added to the wastewater and thereby the cyanide ions in the wastewater as Iron (II) ferrocyanide and Turnbull's insoluble Blue precipitates,

(2) an alkaline agent is added to the wastewater, converting the iron contained therein into Fe (OH) ₂ and

(3) by adding an Ev ^ nOIIJsalzes to the Wastewater forms insoluble Berlin blue.

35

3. The method according to claim 2, characterized in that the amount of iron (II) salt added is so large that the amount of Fe "is within the range of x ' , which from the following equations

x '

0.2: 13 * -3.8 * d: 25 (mg / 1)

is calculated where y is the concentration (mg / 1) of cyanide ions in the inflowing water and χ is the iron content (mg / 1) in the ferric salt, and that the amount of ferric salt added is so large that the weight ratio of Fe ¹¹¹ ZFe "is 03 to 3. so

4. The method according to claim 1, characterized in that the concentration in the ventilation tank of activated sludge is 2000 to 5000 mg / 1, the concentration of activated carbon is 10,000 to 50,000 mg / 1 and that the mixing weight ratio of activated sludge to activated carbon is 1: 2 to 1:20.

b. Process according to Claim 1, characterized in that the activated carbon used in the treatment of the gas water is recovered and the recovered activated carbon is regenerated and returned to the circuit.

It is known that the gas water which is produced in the production of coke, large amounts of harmful Substances such as phenols, thiocyanate compounds, ammonia, hydrogen sulfide and cyanide compounds gen, contains The content of cyanide compounds in the For example, gas water is around 15 to 100 ppm. Up to now, gas water has been processed using a biological oxidation process. But the treated gas water still contains cyanide ions in quantities which are higher than the standard value allowed for a waste water, and therefore it is problematic, to release such wastewater into the environment.

From DE-AS 12 86 463 a process for the detoxification of cyanide-containing wastewater is known, in which the wastewater is aerated in the presence of carbon-containing catalysts. The increasing demands on the purity of waste water to be given off into the environment, however, requires the content of cyanide ions to be reduced to a greater extent than is possible with such a process. From Chemisches Zentralblatt 1967/48, Referat 2183, it is also known to reduce cyanide-containing chemical wastewater by anaerobic fermentation and subsequent aerobic decomposition of the anaerobic product to less than 0.1 ppm of cyanide ions. Furthermore, from procedural reports 6624/124, 1197 the reduction of the cyanide content in wastewater through the combination of an activated sludge process and treatment of the end product with CoCl ₂ and (NHj) ₂ PO * is known from DE-OS 23 53 562 it is known by means of activated carbon and aeration Purify wastewater 2U and treat it biologically.

In a common method for treating gas water, the gas water is 2 to 4 times with Industrial water (water obtained by treating wastewater with activated sludge, spring water or river water) or diluted sea water, and the diluted gas water is subjected to an activated sludge process and post-treatment (coagulation and sedimentation of cyanide ions and an absorption treatment using granular activated carbon) (see W. G. Gousins and A. B. Mindler, J. Water Pollution Federation, Vol. 44, No. 4,607 (1972); Paul D. Kostenoader and John W. Flecksteiner, J. Water Pollution Federation, Vol. 41, No. 2,199 (1969)). With this type of treatment, the treatment effect in the activated sludge device varies considerably and stable treatment performance with high efficiency cannot be obtained. Consequently Such a procedure cannot meet the strict legal requirements with regard to the prevention of environmental pollution. About that In addition, in this method, one has to dilute the gas water with industrial water and it is industrial water even scarce. Therefore, there is a need to have a method of treating gas water that operates with high efficiency, not one Dilution level required.

The object of the invention is to provide a method for treating gas water produced during coke production which is safe and inexpensive and which enables cyanide ions to be removed to such an extent that the gas water can be released into the environment after the treatment .

According to the invention, this object is achieved in that one obtained in the coke production Gas water

(A) the ammonia content by blowing with air or water vapor to about 1000 ppm or less decreased

(B) about 30 to about Ai-Vb of the organic ingredients removed biologically or with activated carbon in the wastewater treated according to stage (A),

(C) the gas water treated according to step (B) in an aeration tank with pulverized activated carbon; and activated sludge treated in the liquid, and

(D) the gas water treated in step (C) is precipitated by adding an iron salt

Step (D) in the process according to the invention is preferably carried out in such a way that

15th

(1) adding an iron (l l) salt to the wastewater and thereby the cyanide ions in the wastewater as iron (II) ferrocyanide and insoluble Turnbull's blue settles down,

(2) Adds an alkaline agent to the waste water, converting the ferrous ions contained therein in Fe (OH) J and

(3) Forms insoluble Prussian blue by adding an iron (III) salt to the wastewater

It is preferred that the amount of ferrous salt added is so large that the amount of Fe "is within the range of x 'given by the following equations

25th

x '

0.213x-3.8
x ± 25 (mg / 1)

is calculated where y is the concentration (mg / 1) of cyanide ions in the inflowing water and χ is the iron content (mg / 1) in the ferrous salt, and that the amount of ferric salt added is so large that the weight ratio of Fe ¹¹ VFe "is 0.5-3

It is preferred that in step (C) in the aeration tank the concentration of activated sludge 2000 to 500C mg / 1 is the concentration of activated carbon 10,000 to 50,000 mg / 1 and that the mixing weight ratio of activated sludge to activated carbon 1: 2 to 1:20 is

The activated carbon used in the treatment of the gas water can be recovered and returned to your home Regeneration can be brought back into the cycle.

The stages (A) to (D) and their order and necessity result from the following considerations:

(1) In the biodegradation of thiocyanate compounds f ammonia alone is the inhibiting factor in the decomposition of the thiocyanate compounds represent.

(2) Becomes ammonia, the only inhibiting factor in the decomposition of thiocyanate compounds is tolerated in an amount of less than 1000 ppm, this can be ammonia effectively serve as a nutrient source for the activated sludge.

(3) If a mixture of powdered activated carbon and activated sludge is used, the oxidative decomposition of thiocyanate compounds and phenols by microorganisms considerable be accelerated.

(4) By having a stage in which 30 to 80 or 90% of the organic components are removed with a coagulate mis-sedimentation is connected, can water be good ·: Owlity from gas water received, even if the gas water u: itfrsi.-niediiche Amounts of impurities are contained and in between without having to use this gas water beforehand must dilute. The combination according to the invention enables an economical cleaning process for the gas water.

Compared to the prior art, the method according to the invention achieves considerable advantages:

a) The combination of stage (A) with stage (C) removes 100% of thiocyanate compounds. In addition, activated carbon is absorbed in large quantities by the activated sludge in the aeration tank, and this increases the specific weight of the activated sludge at the same time This increases the settling speed Since the density of the precipitated sniff also increases, it is easier to do this in an ejector handle.

b) By performing step (B) it becomes possible to treat a gas liquid without that a dilution stage takes place, and that means that the aeration tanks can be kept correspondingly small, which in turn is a is an economically important factor

c) Through the step (D) the cyanide ions which are not removed by a biological treatment can could be removed with certainty to 1 ppm or less.

The gas water contains large amounts of harmful compounds as shown in Table 1

Table 1

l.pH
2.CSB _M "

3.CSBcr

4. BOD ₅

5. Phenols

6. Thiocyanate compounds

7. Cyanide compounds

8. NH ₃

9. Suspended solids
10. Oils

8.5-9.5

2500-7500 ppm
3300-9500 ppm
1500-4000 ppm

700-1700 ppm

150-800 ppm

15-100 ppm

3000-4000 ppm

50-100 ppm

100-200 ppm

In Table 1, COD _Mn means chemical oxygen demand of the impurity in a gas water. This is measured using potassium permanganate. COD _Cr is the chemical oxygen demand of the polluting substances, which is measured using potassium dichromate, and BOD5 is the biological oxygen demand of the polluting substances in a gas water over a period of 5 days at 20 ° C.

In step (A) ammonia is removed, which is the most critical factor in the decomposition or oxidation reaction of contaminating substances by microorganisms. In stage (B) phenols, suspended solids and oils are removed and the BS3 ηκκ \ COD, which is mainly attributable to the phenols, is reduced. In step (C) phenols, ^'r' are iiiocyanatverbindungen, '! Spendierte solids and oils decreases with further reduction of the COD and DSB. Be in stage (D)

Cyano compounds, suspended solids and oils removed and thereby the COD and BOD values in the gas water are extremely low reduced.

In stage (A), part of the ammonia is left in the microbiological treatment as a nitrogen source return. The optimal amount of ammonia left for this purpose is about 50 to 200 ppm. In general, however, it is sufficient that the ammonia up to a residual amount of ammonia of about 800 to 1000 ppm removed. At this level there is no need to add alkali.

The ammonia stripping is generally carried out at atmospheric pressure. Stripping efficiency is better at high temperatures. Therefore, the temperatures are generally in the stripping of ammonia at about 60 to 100 ° C, preferably 90 bii 100 ⁰ C.

After the ammonia has been removed, the pH of the gas water is reduced to a microbiological level Treatment adjusted to a suitable value, for example to a pH of about 5 to about 8. preferably 5.5 to 7.5. This pH adjustment is generally carried out by, for example Sulfuric acid is added at a concentration of 10 to 80% by weight. You can also neutralize Use hydrochloric acid, nitric acid, and phosphoric acid, but sulfuric acid will do most preferred.

The gas water with adjusted pH is then in a first biological treatment stage (B) a Subject to activated sludge process. This step can be carried out using a suspension process carried out as in the activated sludge process or according to a fixed bed process, a contact oxidation process (or a submerged filter procedure). When the concentration of organic substances in the inflowing gas water is high, the application of a contact oxidation method is used an aeration tank in which a synthetic resin is filled as a filler is preferred.

The pH in the aeration tank in the first biological treatment stage (B) is usually on about 6.0 to about 7.5 adjusted Depending on the type of gas water one can adjust the pH value of the gas water to set the most suitable value. The pH treatment can be carried out before the gas water is introduced into the Aeration tank. Alternatively, the pH of the gas water can also be roughly adjusted before it is introduced into the Tank can be set, the exact setting then in the tank by an automatic device he follows.

The temperature is 20 to about 40 ⁰ C, preferably 25 to 35 ° C, air is introduced into the tank in such amounts that the amount of dissolved oxygen can be about 1 ppm to about 5, preferably from 3 ppm to 4, constitutes

In step (B) about 30 to 90% phenols and other contaminating organic materials are due the action of the microorganisms removes the contaminating substances in this stage are up removed to such an extent that the CODMn is around about 30 to 90% is reduced. If the amounts of contaminating substances to be removed are low and the BOD and CSD are high, take the crowd of the sludge formed in the second biological treatment stage undesirably. If on the other hand the degree of removal of the contaminants is high and the COD by more than about 90% is reduced, then the amount of sludge formed is in the second biological treatment stage too low.

To add a predetermined amount of activated carbon and the composition of the activated carbon / Keeping the activated sludge mixture in stage (C) at a constant weight ratio is the degree ίο the decrease in BOD in stage (B) preferably about 30 to about 90% and in particular 50 to 80%.

The residence of the liquid to be treated in

the treatment tank is generally around 10 up to about 15 hours if the amount of recirculated sludge is 100% by volume based on the volume of the Starting liquid.

Step (B) may also treat the gas water from which ammonia has been removed with pulverized water Be activated carbon. The activated carbon used has a particle size of 0.105 mm to 0.037 mm, preferably 0.074 to 0.063 mm. It is used in an amount of 3,000 to 10,000 ppm, preferably 5,000 to 8,000 ppm added, and the mixture is stirred for about 0.5 to 2 hours to remove the phenols, suspended solids-2ϊ to remove fe and oils in the gas water and to increase the COD by 20 to 80%, preferably 30 to 70% Reduce. This can reduce the stress in the subsequent biological treatment stage will.

The gas water treated in stage (B) is subjected to a solid-liquid separation process and the supernatant Liquid is fed to stage (C). In stage (C) there are phenols and thiocyanate compounds and the like by the activated sludge microorganisms and by the Adsorp; ionswirAj; .fr der Activated charcoal removed. lr; f, oigf-! i-; en become BSB and COD reduced.

The concentration of activated sludge in the aeration tank is preferably 3000 to 4000 mg / 1. The concentration of activated carbon is preferably from 20,000 to 40,000 mg / l. The weight ratio of activated sludge to activated carbon is preferably 1: 5 to 1:14.

Treatment will generally be at about 20 to about WC at this stage. preferably carried out at 25 to 35 ° C. The ^N: -; length of the introduced air in the tank is adjusted so that the amount of dissolved oxygen in the tank about 2 to et'.va 6 ppm. preferably from 5 ppm to 4, constitutes The pH'A'ert inside of the aeration tank is generally from 6 to 7 is adjusted by an automatic adjustment in order to keep the weight ratio of activated sludge and activated carbon constant, the activated carbon in the aeration tank in an amount is from about 500 to 2000 mg / 1, based on the amount of liquid introduced.

The residence time of the liquid in the aeration tank is generally about 8 to 15 hours.

The activated sludge-activated charcoal mixture is separated after stage (Q and the remainder goes to stage (D) subject. The precipitate formed in stage (D) is coagulated and separated off. The supernatant If desired, the liquid can also be treated with powdered activated charcoal.

One embodiment of the process according to the invention is described by the following flow sheet.
The process in the flow sheet includes the step

A, which can be seen as a pre-treatment stage (an ammonia removal stage a * and a neutralization stage a2), a biological treatment stage B (treatment with microorganisms or with activated carbon), a biochemical treatment stage C (treatment with a mixture of activated sludge and activated carbon), an aftertreatment stage D, a coagulation sedimentation mfe di and a final filtration stage d ₂ . The flow of the gas water is indicated in the drawing by the direction of the arrow.

First, gas water 16 is introduced into an ammonia wiper I and at the same time air or Steam 17 in the gas water 16 to remove ammonia 18 in a predetermined amount in the Liquid introduced (ammonia stripping stage A-ai). π

Then, the gas water from which the ammonia has been removed is put into a pH adjusting tank 2 and the pH of the gas water is adjusted to about 5 to about 8, for example with Sulfuric acid (neutralization mare A-a?).

The gas water, the pH of which has been adjusted in the same stage, is then put into a first aeration tank 3 for biological treatment or a Activated carbon treatment performed. Air 19 is fed into the ventilation container 3. Due to the decomposition and the oxidizing action of the microorganisms or the activated carbon will remove the pollutants in the Gas water partially removed. The pH of the liquid in the aeration tank 3 is using an automatic pH adjuster 29 jo set. The gas water from which the pollutants have been partially removed in the aeration tank 3 is then passed into a settling tank 4. the Supernatant liquid is introduced into an aeration tank 6. The pH of the liquid in the Aeration tank 6 is as in aeration tank 3 using an automatic pH adjuster 30 set. The sludge is placed in a receptacle 14 through a thickener 5, and the sludge is in a device for regenerating the activated carbon 15 simultaneously with the Regeneration of activated carbon treated.

The Füssigkeii in the ventilation tank 6 is with Activated sludge, to which recycled sludge can be added, and activated carbon, which can be made from regenerated Activated charcoal and further activated charcoal may exist, air 23 is mixed into the ventilation container 6 initiated due to the biological oxidizing effect of the microorganisms in the activated sludge and the adsorbing effect of the activated carbon, pheno-Ie and thiocyanate compounds and the like are in the Gas water removed The BOD as well as the COD is reduced as a result The regenerated activated carbon 21 can be activated carbon that has been regenerated in a regeneration stage (F). The gas water that is in the Aeration tank 6 was treated, is passed into a settling tank 7, in which the mixture from activated sludge and activated carbon by sedimentation sfcs? * 7t The supernatant liquid is in a Coagulation Behajiw? «'^' Ct. Fin part of the mud (Activated sludge / activated charcoal mixture; will .Ii ^ - aeration tank 6 fed in as return sludge 20 D ~ the rest of the sludge becomes a thickener 8 as Passed excess sludge 24 (biochemical treatment stage (C)).

A pre-best amount of soluble iron (II) compound 25, like Esen (II) chloride, is added to the supernatant fluid that flows into the Coagulation container 9 is introduced, and, if desired, the mixture is stirred. Then there alkali 26, such as sodium hydroxide or potassium hydroxide, is added to adjust the pH of the mixture to adjust. Then a predetermined amount of a soluble iron (III) compound 27, such as Iron (III) chloride, added. The mixture is used to remove the cyanide components from the gas water touched. This reduces the COD. Dk: treated liquid becomes in the settling tank 10 a Subject to solid-liquid separation. The protruding ": liquid is passed into a sand filter 13 and the sedimented sludge is fed to a thickener It.

The sedimented sludge is passed into a sludge treatment device 12 through the thickener 11 and treated there separately (coagulation sedimentation stage D-di). The supernatant liquid that is introduced into the sand filter bed 13 is completely filtered and discharged as waste water 28 · ;: Filter level Dd ₂ ).

The sludge in the thickener 5 in the biological treatment stage B and the sludge (the mixture from Activated sludge and activated carbon) in the thickener 8 in the second biochemical treatment stage (C) each led to the receptacle 14 at the regeneration stage (F) for the activated carbon and into the: Activated carbon reservoir 14 are mixed. The mixture is in a device 15 for regeneration initiated by means of wet oxidation. The used activated carbon is reactivated and regenerated, and de · Excess sludge is burned there. In the activated carbon regeneration stage (F) the regeneration the powdered activated carbon and the treatment of the excess sludge carried out at the same time. The activated carbon regenerated in the regeneration device 15 is returned to the aeration tank 6 fed. This will keep the activated carbon in circulation and the cost of the treatment are reduced (regeneration level (F)).

Examples 1 to 6
Examples 1, 2 and 6 not according to the invention

Gas water according to Table 2 was treated under the conditions given in Table 3. Only the biological treatment (C) was carried out continuously, while steps (A), (B) and (D) were made in paragraphs.

The biological treatment stage (C) was carried out in the following way:

The gas water pretreated in step (B) was prepared using an activated sludge device of the flow type in an aeration tank with a capacity of 101 and a settling tank with a Capacity of 101 interconnected The concentration of activated sludge and activated carbon in the aeration tank was 3780 and 16,540 ppm. The weight ratio of the activated sludge to the activated carbon was 1: 4.4

The gas water that was previously used in stage (A) ^ .fe ^ iung the ammonia had been treated and treated in stage (B) mh pulvonükrtar activated carbon was adjusted to pH 6.5 with sulfuric acid and then poured into the Aeration tank introduced at a flow rate of 10 l / day. Air was introduced into the aeration tank in a flow rate of 4 to 5 N l / min.

tet so that the amount of dissolved oxygen was kept at 2 to ppm. The gas water was left! 2 Linger in the aeration tank for hours and during this time it was due to the synergistic action the biological oxidative decomposition through activated sludge and absorption through activated carbon cleaned. It then flowed into a subsequent settling tank and underwent a solid-liquid separation there subject. The supernatant liquid was poured into a water tank and a part of it became collected for analytical purposes. On the other hand, part of the separated sludge became excess sludge withdrawn from the bottom of the settling tank. The rest was returned to the aeration tank.

The amount of recirculated sludge was 100%. based on the volume of the inflowing Gas water.

In the step (B), the absorption was carried out with powdered activated carbon, with a Activated carbon was used which originated in the step (C) and which was in an amount of 4000 ppm dem Gas water was added, followed by stirring the mixture for 60 minutes.

In stage (D) *, FeCl ₂ (the amount is given in Table 3 in each case) is added to the gas water, and the mixture is rapidly stirred at 150 rpm for 2 minutes. Sodium hydroxide is then added to adjust the pH to 8.5. FeCli is then added (the amount used in each case is shown in Table 3) and the mixture is stirred vigorously at 150 rpm for 2 minutes. Finally, the mixture is slowly stirred at 30 rpm for 10 minutes and then coagulated and separation carried out.

Table 2

Treatment conditions and analysis data

at at at at at at game 1 game 2 game 3 game 4 game 5 game 6 Yes Yes Yes Yes Yes - Yes Yes - - - AS AS AS + AC AS AS + AC AS 1 1 1 23 23 1.82

Pre-treatment stage
Ammonia stripping stage

Absorption stage with powdered activated carbon

Type of biological treatment stage Dilution ratio at the
biological treatment

Type of dilution water

Raw gas water
pH
BOD, ppm

COD _Mn , Ppm

SCN compounds, ppm
CN compounds, ppm
Phenols, ppm
NH ₃ , ppm

Incoming water

in biological treatment

BOD, ppm

COD _Mn , ppm

SCN compound, ppm

CN compound, ppm

Phenols, ppm

NH ₃ , ppm

Drained water

from biological treatment BOD, ppm
CODmo, ppm
SCN compound, ppm
CN compound, ppm
Phenols, ppm

Industrial industrial industrial water water water

9.5 15th 4.3 8.5 5.9 7.4 1840 150 40 250 40 1210 2800 30th 0.01 10 0 1650 650 2.7 2.1 5.2 3.4 360 10.5 3 0.01 0.5 0.01 15.3 700 410 3500 1925 8.5 48 1480 310 2500 ISO 650 13.2 6.1 20th 500 450 50 350 70 3 5

11th

12th

continuation

Treatment Conditions "nd Analysis Caieri

example

Example!

Example 3

Example A.

Example p

Example!

30th 11th 3.1 5.7 4.5 20th 80 60 10 80 15th 95 40 20th O ₁ I 7th 0.01 SO 0.5 0.4 fewer
than 0.3 0.7 0.5 0.8 0.2 0.1 fewer
than 0.01 0.2 0.01 2.0

Released water after post-treatment BOD, ppm COD _Mn , ppm SCN compound, ppm CN compound, ppm

Phenols, ppm

Treatment conditions in the aeration tank COD volume loading, kg-COD / nr / Tac COD-Beladurs, kg-COD / kg / day Activated sludge concentration, ppm Activated carbon concentration, ppm Note:

AS: activated sludge.

AS + AC: activated sludge + activated carbon.

The values given in the table were determined in the same way as in table 1.

Tabel

1.50

1.47

1.51

1.50

1.42

0.30 0.370 0.390 0.398 0.403 0.356 3950 4050 3780 3790 3720 3975 _ _ 16 540 _ 16 500 _

example Iron (II) salt (ppm) as Fe " Iron (III) salt (ppm) No. FeCl ₂ 33 FeCl ₃ as Fe ¹ " 1 75 33 150 50 2 75 44 150 50 3 100 44 150 50 4th 100 33 150 50 5 75 88 150 50 6th 200 300 100

2. Effect of level (A) .... , ,,,., ..,., .... , " _{V. n,,}

biological treatment gerrsab level (Cj with B> ! ebi-

In Examples 2, 4 and 6 results will be subjected to 45 mud. The properties of the shown in which gas water with an ammonia from this biological treatment flow off Contents of 910 ppm, 300 ppm and 1920 ppm of a water are shown in Table 4 below.

Table 4 Example 2 Example 4 300 ppm Discharge Beisjie: ί Distance rZIB * S Plague Removal rest 2, jfach degree of efficiency rest degree of efficiency salary grades salary (%) salary (%) (ppm) (%) (ppm) 99.1 (ppm) 96.0 15 97.9 8.5 Ul kg / 3 83.6 48 81.2 BSB 150 90.0 250 Yes 96.8 310 50.0 CODm ₀ 30 95.7 10 36.6 180 13.7 SCN 2.7 49.0 5.2 99.9 13 ^ 95.1 CN 3 98.9 0.5 20th 1725 ppm Phenols 910 ppm l, 82 times NII ₃ in the water iach Degree of dilution (no ver thinning) 1.42 Se | 1.50 kg / m ³ «/ no COD loading Yes Ammonia stripping

From Table 4 it can be seen that with a decrease in the ammonia content, there is an improvement in the removal of the contaminants takes place and in particular the removal of SCN is to a considerable extent due to the ammonia content causes.

Example 6 shows the results that can be achieved When treating gas water in the usual way, Um is retained by ammonia in this process to reduce to 1000 ppm, one would have to increase the dilution ratio still further and thereby one would bring in very large amounts of dilution water, which is of course uneconomical. According to the invention, these disadvantages are to be avoided. According to Example 2, it is possible to obtain high treatment efficiency without being diluted is done by stripping the ammonia in the gas water to a level of 1000 ppm or less, followed by the absorption treatment using activated carbon or a biological fixed bed treatment

The reasons why the biodegradation of SCN is improved when using ammonia according to

Table 5

Grade (A) is reduced to 1000 ppm or less probably the following:

Bacteria that decompose thiocyanate compounds require inorganic nutrient sources (thiocyano-

5 oxidase). So you need N to live and grow. There is generally ammonia in wastewater the main supplier for N. Therefore, if ammonia is reduced in the wastewater, the thiocyanate must decomposing bacteria to another nitrogen source

ίο fall back and then use N from the SCN as the Nutrient source and this accelerates the decomposition of SCN

The numerical limitation of the ammonia content through the measures of stage (A) is therefore not one arbitrary measure, but essential for the removal of SCN in the overall process.

Effect of level (B)

In example 1, stage (B) is carried out in the example 2, step (B) is carried out using pulverized activated carbon. The properties of the in Step (C) water obtained in Examples 1 and 2 are shown in Table 5 below

example 1 no Distance Example 2 Yes Distance Residual salary 1.20 kg / m ³ · «/ Degree Residual salary 1.50 kg / m ³ · «/ Degree Yes (%) Yes (%) (ppm) 48 h 96.7 (ppm) 24 hours 97.9 BSB 50 2400 ppm 86.0 15th 1,500 ppm 90.0 COD _Mn 350 89.2 150 95.7 SCN 70 50.8 30th 49.0 CN 3 99.0 2.7 98.9 Phenols 5 3 Level (B) COD loading Ammonia stripping Ventilation time COD _{Mn of} the inflowing Water

These results show that the aeration time in step (C) in Example 2 is shorter and that the achieved Effect is better The reason for the better effect by applying stage (B) is to be seen in the fact that the organic substances were previously removed in this stage, so that the loading in stage (C) is much lower

Table 6 Effect of level (C)

so In Example 2, stage (C) is carried out in the customary manner using an activated sludge process, while in Example 3 in stage (C) according to the invention pulverized activated carbon and activated sludge is used (AC + AS). In the following table 6 Example 2 and Example 3 are compared:

Example 2 Distance Example 3 Distance Remaining hall Degree Residual salary Degree (%) (%) (ppm) 97.9 (ppm) 99.4 15th 90.0 4.3 97.3 150 95.7 40 100 30th 0.01

BOD COD _Mn

SCN

continuation

Phenols
COD loading
Level (A)
Level (B)
Level (C)

Example 2 1.5 kg / m ³ -a 'Distance f Example 3 1.47 kg / m ³ Distance ■ d Residual salary Yes Degree Residual salary Yes Degree Yes <%) Yes CA) common 49.0 (ppm) 60.4 according to the invention 2.7 98.9 2.1 100 3 0.01

Example 2 reproduces the case in which, although step (A) and step (B) are carried out according to the invention were, however, a complete decomposition of SCN is not achieved because it remains! 30 ppm SCN left. In Example 3, however, SCN is practically 100% removed. When treating gas water from the It is important that thiocyanate compounds are completely through a biological scrubbing process of coke oven gas Treatment can be removed. 1 ppm SCN theoretically corresponds to a COD of 03 / · Die Invention makes it possible to 100% remove SCN by biological means. In example 3 this is showed that it is compulsory to check the monia level to be removed beforehand to 1000 ppm or less in step (A) and to carry out step (C) according to the present invention. Only by combining (A) and (C) can thiocyanate compounds be removed 100%.

1 sheet of drawings

Claims (1)

Patent claims: 1. A method for the treatment of gas water obtained in the production of coke, characterized in that one (A) the ammonia content in the gas water by blowing it out with air or water vapor to about Decreased 1000 ppm or less, (B) about 30 to about 90% of the organic constituents in the wastewater treated according to stage (A), biologically or with activated carbon removed, (C) the gas water treated according to step (B) in an aeration tank with pulverized activated carbon and activated sludge in the liquid treated, and (D) in the gas water treated according to step (C) carries out a precipitation by adding an iron salt.