CA1089573A - Method for treating waste water containing cyanide ion - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A method for treating a waste water containing cyanide ions, which comprises (1) adding a ferrous salt to the waste water to convert the cyanide ions in it to a precipitate of ferrous ferrocyanide and insoluble Turnbull's blue, (2) adding an alkali agent to the waste water to convert the remaining ferrous ion to Fe(OH)2, and (3) adding a ferric salt to this waste water to precipitate [Fe(CN)6]4- formed by addition of the alkali agent as insoluble Berlin blue. The method permits a very efficient removal of the cyanide ions from the cyanide ion-containing waste water. It is particularly suitable for the treatment of gas liquor which has been discharged from the step of quenching coke oven gas and treated with activated carbon and activated sludge.

Description

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B~CKG~OU~3 OE THE INVENTION

1. Field of the Invention This invention relates to a method for removing cyanide ions from a cyanide ion-containing waste water. More speci-fically, it relates to a method for removing cyanide ions from waste waters containing the cyanide ions in a low concentration, such as water treated by biological oxidation using activated sludge.

2. Description of the Prior Art As is well known, gas liquor discharged in the process of coke manufacture contains large quantities of noxious sub-stances such as phenols, thiocyanate compounds, ammonia, hydrogen sulfide and cyanide compounds. For example, the content of the cyanide compounds in the gas liquor is about 15 to 100 ppm. The gas liquor has previously been treated by a biolo-gical oxidizing method. But the treated gas liquor still con-tains the cyanide compounds in an amount greater than the water ., pollution standard value allowed for discharge water, and its -,.;
disposal has been a problem yet to be solved.
A cyanide ion-containing waste water discharged from the metal plating plants is usually a washing water having a concentration of 20 to 100 mg/liter ~as CN). Many of the CN ions form cyano complex ions with heavy metals such as Zn and Cd.
On the other hand, the concentrated waste liquid discharged to make the spent plating bath fresh has a CN concentration of 10,000 to 50,000 mg/liter.

~ A cyanide ion-containing waste water from plants for ~; heat-treating iron and steel is discharged from the cementating and washing process, and usually contains 100 to 500 mg/liter of ..
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1 cyanide ions (as CN), and at times, as much as 1,500 to 2,000 ' mg/liter of cyanide ions (as CN). In this process, most of the cyanide compounds undergo oxidative decomposition, and are contained as complex ions (iron cyano complex ions).
Other waste waters containing cyanide ions are, for example, a waste water from metal refining plants which has a concentration of 100 to 500 mg/liter (as CN), and a waste water from petroleum refineries which has a concentration of , 5 to 30 mg/liter (as CN).
Known methods for removing cyanide ions include an alkali chlorination method and a Prussian blue method. The alkali chlorination method, however, has the defect that the cost of chemicals used is high, and a cyano complex salt cannot be :~;
removed. The Prussian blue method can remove cyanide ions at relatively low cost, but the conventional procedures falling i; within this method (methods I to III described below) have their t~ own problems.

(I) Method for removing cyanide ions by a ferric compound~
~ This method involves reacting a ferric ion (Fe3+) with ~ -~ 20 a ferrocyanide ion ([Fe(CN)6] ) to form insoluble Berlin blue.
If the cyanide ion concentration in the waste water is high, the ferric salt must be added in large quantities in order to ~ obtain a satisfactory effect of removing the cyanide ion. Thus, '~; sludge is formed in large quantities, and the cost of operation ~¦ increases.
(II) Method for removing cyanide ions by a ferrous compound:-This method comprises reacting a ferrous ion (Fe2+) with ~ a ferricyanide ion ~[FetCN)6] ) to form insoluble Turnbull's hi30 blue, and reacting [Fe(CN)6]4 , which is formed by the reaction ~

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1 of a small amount of a free cyanide ion present in the waste water with Fe2+, and [Fe(CN)6]4 present in the waste water with Fe to form a precipitate o~ ferrous ferrocyanide -thereby to remove the cyanide ions. This method has a great effect of removing the cyanide ions, but Fe2 remains in the supernatant ; liquid (treated water) obtained by coagulation and separation.
When the treated water is left to stand, Fe2+ is oxidized to form a precipitate of ferric hydroxide [Fe(OH3]. In order to remove Fe2+ in the treated water, the reaction must be carried 10 out at a high pH. Addition of alkali in an attempt to maintain the pH high results in the dissolving of the precipitate of insoluble Turnbull's blue, and the efficiency of removing the , cyanide ions is reduced. Furthermore, the flock of ferrous hydroxide [Fe(OH)2] formed by this method is difficult to coagulate and separate since it has poor coagulability.
(III) Method for removing cyanide ions by a ferrous compound and a ferric compound:-;~ The method comprises adding a ferrous compound to the waste water to form a precipitate of insoluble Turnbull's blue 20 and ferrous ferrocyanide, then adding a ferric compound to form a precipitate of insoluble Berlin blue, ~inally adding an alkali to form Fe(OH)3 and Fe(OH)2, and coagulating and separating the resulting precipitates together. According to this method, s too, Fe2 remains in the treated water at a low pH as in the ~, method (II). Hence, on standing, a precipitate forms in the treated water. If the treatment is carried out at a high pH in order to avoid this disadvantage, the amount of alkali added increases and the cost of operation accordingly becomes hig~.
At the same time, the precipitates again dissolve. This causes 30 difficulty especially when the cyanide ions concentration of the waste water is high, and the amount of the ferrous compound added increases.

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SUMMARY OF THE INVENTION
It is an object of this invention to provide a method for removing cyanide ions from a cyanide ion-containing waste water surely and at low cost. Another object of the invention is to provide a method for removing cyanide ions from a cyanide ion-containing waste water, which is free from the redissolving of precipitates in the final treating step, requires only a small g amount of alkali for pH adjustment, yields precipitates having ; good coagulability, and does not permit the formation of pre-: 10 cipitates from the treated water after the end of the entire $ process.
The above objects can be achieved in accordance with this invention by a method for treating a waste water containing 3 cyanide ions, which comprises (1~ adding a ferrous salt to the waste water to convert the cyanide ions in it to a precipitate ;~
of ferrous ferrocyanide and insoluble Turnbull's blue, (2) adding an alkali-agent to the waste water to convert the remaining ferrous ion to Fe~OH)2, and ~3) adding a ferric salt to this waste water to precipitate [Fe~CN)6]4 formed by addition of the alkali agent, as insoluble Berlin blue.
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`; BRIEF DESCRIPTION OF THE ACCO~?ANYING DRAWING
`;;~ The drawing is a flowsheet showing one embodiment of the method of this invention.
'f. DETAILED DESCRIPTION OF THE INVENTION
,~ The cyano complexes, as used in this invention, denote ~, CN , [Fe~CN)6] , [Fe(CN)6]3 , and cyanide complex ions of Cd, ! Zn, Cu, etc. Generally, they are contained in waste waters as M(CN)l or 2 where M is H, K, Na, Cu, Zn, Cd, etc., XCN where X
is F, Cl, I, or Br, RCN where R is an alkyl group containing 1 ' to 17 carbon atoms or an aryl group containing 6 to 10 carbon ~

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The cyanide ion-containing waste waters include, for example, gas liquor discharged from the step of quenching coke oven gas in the coke manufacturing industry or coke oven gas :.
manufacturing industry, a product resulting from the biological ; oxidizing treatment of the gas liquor, and the waste waters discharged from the metal plating plants, iron and steel heat-10 treating plants, metal refining plants and petroleum refineries which are exemplified hereinabove. The treatment in accordance with this invention is possible whatever materials may be contained in the waste waters.
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~ Waste waters having any cyanide ion concentrations can :;
¦ be treated by the method of this invention. It is however especially effective for the treatment of waste waters having a cyanide ion concentration of less than 1,000 ppm, such as general industrial waste waters.
In step (1) of the method of this invention, a pre-20 determined amount of a ferrous compound is added according to the concentration of the cyanide ions in the waste water, and the mixture is optionally stirred. This causes the reaction of the cyanide ions in the waste water with the ferrous compound to form a precipitate of ferrous ferrocyanide (Fe2[Fe(CN)6]) and insoluble Turnbull's blue.
One example of the ion equation showing the formation of Turnbull's blue is shown as (a) below.
4Fe + K + 3[FetCN)6]

`~' > KFeII~FeIIIFe (CN)6]3............ (a) ,~ - 5 -,:~

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-i , 1 When the cyanide ion in the waste water is present as a cyano complex ion of Cu, Cd, Zn, etc., the pH of the waste , water is pre-adjusted to 3 or less, and the complex ion is dis-sociated to CN, after which the treatment with the ferrous salt mentioned above is performed.
Any water-soluble cerrous salts can be used in step (1).
The salts include, for example, FeC12, FeCL2.4H20, FeS04.nH20 (n = O, 1, 4, 5, 7), and (NH4)2So4.FeSo4.6H20. Generally, however, ferrous chloride or ferrous sulfate is used. The suitable amount of the ferrous salt to be added is such that the ~, amount of FeII is within the range of x' calculated from the ~; following equations.

y = 0.213x - 3.8 x' = x + 25 (mg/liter) wherein y is the concentration (mg/liter) of the cyanide ions in the influent waste water measured by the method shown in ~ Table 1, and x is the iron content tmg/liter) of the ferrous salt.
In step (2), Fe remaining in the waste water is con-verted to Fe~OH)2 which is removed as Fe(OH)3 by air oxidation.
Examples of the alkali agent used in this step are NaOH, KOH, CaC03, and Ca(OH)2. CaC03 and Ca(OH)2 are not preferred to the others because they form scales. The pH of the waste water ~,~ after the addition of the alkali agent is adjusted to 7.5 to 9.5, preferably to 8 to 9. As a result, Fe remaining in the waste water is converted to FetOH) and the insoluble Turnbull's blue ; 3 precipitate is decomposed to Fe(OH)2, Fe(OH)3 and [Fe(CN)6] .
The decomposition of the insoluble Turnbull's blue is ,; .
,~ performed, for example, as shown by equation (b) below.
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KE,eII [FeIIIFeTI (CN) ] + llOH---~ K + Fe (OH) 2 + 3FE (OH) 3 + 3 [Fe (CN) 6] . ... (b) , Step (2) can also be performed after separating and removing the precipitate formed in step (1). If this procedure is taken, one additional step is required, but the amount of the alkali agent can be reduced. In this case, the remaining precipitate is completely removed in step (2) and subsequent steps. Hence, in the precipitate removing step, it is not ' ~t 1 altogether necessary to remove the precipitate completely.
In step (3), a ferric compound is added in a predetermined $i amount to the waste water, and the mixture is stirred. As a result, [Fe~CN)6] dissolved by the addition of alkali reacts with Fe3+ to form insoluble Berlin blue as shown by equations (c) and (d).
~ Fe + [Fe(CN)6] -~ [Fe Fe I(CN)6]................. (c) ;~ [Fe Fe (CN)6] ~~~- FeIII[FeIIIFeII(C ) (insoluble Berlin blue) In step (3), any water-soluble f~rric salts can be used.
The salts include, for example, FeC13, FeC13.6H2O, Fe(N03)3.9H20, ; Fe2(SO4)3.nH2O(n = 0, 3, 6, 7, 7.5, 9, 10, 12), KFe(SO4)2.12H2O, NH4Fe(SO4)2.12H2O. Generally, ferric chloride or ferric sulfate is used. The amount of the ferric salt is generally such that S the FeIII/FeII weight ratio becomes 0.5 - 3, preferably 1 - 2.
Generally, each of the steps (1) to (3) is carried out at 15 to 25C.
The resulting precipitates of Berlin blue, Turnbull's `

blue, Fe(OH)3 and Fe(OH)2 are coagulated together and separated.
The precipitates (sludge) separated are suitably treated, and ., ~

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1 the supernatant liquid (treate~ water) left after the separation ~r of the precipit~tes is subjected to another treatment and then discharged into water courses.
Since according to the present invention, a ferrous compound is first added to a waste water containing cyanide ions, r then an alkali is added, and finally a ferric compound is added, it is possible to remove the cyanide ions and the residual Fe withoUt fail. With higher concentration of the cyanide ions in the waste water, the amount of the ferrous compound 10 to be added increases. Consequently, the amount of the alkali for removing the residual Fe2+ in the waste water naturally '; increases, and therefore, the redissolving of insoluble Turnbull's ~;~ blue formed by the addition of the ferrous compound increases.
In the method of this invention, the ferric compound is added in the last step, and therefore, the cyanide compounds dissolved by the addition of much alkali are surely removed as Berlin blue.
The present invention therefore achieves an efficient removal of the cyanide ions and Fe2+. The cyanide ions can be removed surely to below the water pollution standard value, and Fe2+ does not ~, 20 remain. Accordingly, even when the treated water left after ~ -the separation of precipitates is allowed to stand, no further precipitation occurs, and the purification degree of the waste water is excellent. The amount of the ferric compound used in this invention can be drastically reduced as compared with the case of the cyanide ion removing method using the ferric compound alone. Moreover, the amount of the alkali used for pH adjustment may be small. Hence, the cost of chemicals is low, and the treatment of waste waters can be performed at low cost. Further-more, as stated hereinabove, even when the ferrous compound 30 having a good removing effect is used, Fe2 does not remain in the . . '' ' ~ - 8 -,, ~Vb~3''i,'7;~

1 treated watcr. In addition, since the ferric compound is used in the final step, the coagulability of the precipitates is , good, and the precipitates can be easily sedimentated and separated. Waste water treatment is therefore performed with simplicity.
One conventional method for treating gas liquor comprises diluting the gas liquor to 2 to 4 times with industrial water ~ (water obtained by a treatment of sewage with an activated sludge, 5~ subterranean water or water from a river) or sea water, and 10 subjecting the diluted gas liquor to an activated sludge treatment and a post-treatment (coagulation and sedimentation ~ of cyanide ion and an adsorption treatment using granular S activated carbon)[see, for example, W.G. Gousins and A.~. Mindler, ¦ J. Water Pollution Federation, Vol. 44, No. 4, 607 (1972); Paul D. Xostenoader and John W. Flecksteiner, J. Water Pollution Federation, Vol. 41, No. 2, 199 (1969)]. According to this l; type of treatment, the treating efficiency in an activated sludge treatment device fluctuates greatly, and a stable treating performance with a high efficiency cannot be obtained.
20 Accordingly, such a method cannot meet rigorous legislative `~ environmental pollution standards. Moreover, the method which involves the dilution of gas liquor with industrial water is actually difficult to employ since industrial water is scarce nowadays. It has been desired, therefore, to establish a method for treating gas liquor stably at a high efficiency without the need for a dilution step.
The method of this invention is especially suitable for the treatment of the gas liquor described hereinabove. For example, it is suitable for removing cyanide ions of low con-i 30 centration tgenerally below 30 ppm) in a waste water in con-ii junction with a treatment process using microorganisms, i.e.
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t 1 biological activated sludge solids, activated carbon, or both.
An example of the combination of the treatment of gas liquor and ~ the method of the present invention comprises:
,, (A) a pretreatment step of treating gas liquor dis-charged from the step of quenching coke oven gas and containing ammonia, phenols, thiocyanide compounds, cyanide compounds, suspended solids and oils to reduce the content of ammonia to about 1,000 ppm or less, (B) a biological treatment step of treating the gas liquor treated in step (A) with microorganisms, or (B') a step of treating the gas liquor with activated carbon, (C) a biological treatment step of treating the gas liquor treated in (B) or (B') in an aeration tank including mixed liquor suspended solids (a liquor containing suspended solids) consisting of powdered activated carbon and activated sludge, ~-(D) the cyanide ion removing step in accordance with this invention, and (E) if desired, a step of treating the treated gas liquor with powdered activated carbon.
The gas discharged from a coke oven in a coke producing ~ plant and a coke oven gas producing plant is quenched by a primary ;:~ cooler to condense steam, tarry substances and ammonia, etc., in the gas. They are discharged as a condensed liquid. The condensed liquid is separated into crude tar and gas liquor in a tar decanter. The gas liquor contains large quantities of noxious and impure substances as shown in Table 1. `~

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' ~0~573 1 TABLE l_ Analyzing Method 1. pH 8.5 - 9.5 JIS K0102-1974 8 2. CODMn2,500 - 7,500 ppm JIS K0102-1974 14 3. CODCr3,300 - 9,500 ppm ASTM D 1252-1974

4. BOD51,500 - 4,000 ppm JIS K0102-1974 16

5. Phenols700 - 1,700 ppm JIS K0102-1974 20.1 ~; & 20.2

6. Thiocyanate 150 - 800 ppm Nitric acid decomposi-compounds tion method (as SCN) '~ 7. Cyanide15 - 100 ppm JIS K0102-1974 29.1.2 compounds (as CN) 8. NH33,000 - 4,000 ppm JIS K0102-1974 17.1.3 (as N) . 9. Suspended50 - 100 ppm JIS K0102-1974 10.2.1 solids 10. Oils 100 - 200 ppm JIS K0102-1974 18.2 In Table 1, CODMn is the chemical oxygen demand of polluting substances in gas liquor which is measured using ~7 potassium permanganate; CODcr 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 gas liquor for a period of 5 days at 20 C. Nitric acid decomposition method is shown below.
. The pH of an-aqueous liquid containing thiocyanate s compounds is adjusted to 1 - 2 with sulfuric acid. Cyanide ions in the liquid is removed from the thus obtained liquor by . .
~:, passing through gas or by distillation. Then thiocyanate ~ compounds in the liquid is decomposed with HNO3 to cyanide ions ~ and the amount of the cyanide ions is determined by, for example, the method prescribed in JIS K0102-1974 29.1.2. (This method is . described in, for example, H. Weisg "Mikrochim Acta" 1956, r 30 P.1225.).

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1 Phenols present include phenol, o-, m- and p-cresols, 3,5-xylenol, a- and ~-naphthols, oxine, catechol, pyrogallol, metal salts (e.g., ~a, K, Ca, Ba or Al salts) of these phenols, phenol-carboxylic aclds such as salicylic acid and benzoic acids (m- and p-), and the esters and ethers of mono-, di-, and tri-hydric phenols.
Thiocyanate compounds present include thiocyanic acid `~ (including isothiocyanic acid), ammonium salts of these acids, metal salts (e.g., Na or Fe salts) of these acids, and phenyl thiocyanate.
Cyanide compounds present include M(CN)l or 2 (where M is H, K, Na, Cu, Zn, Cd, etc.), XCN (where X is F, Cl, I, Br), RCN (where R is alkyl or aryl), and cyano complexes containing Ni, Fe, Cr, Mn, Cu, Hg, Cd, etc. [e.g., as disclosed in Encyclopedia Chimica, Vol. 7, p. 727, l9th Edition, published 'j on September 10, 1976 by Kyoritsu Shuppan, Tokyo].
The suspended solids present are insoluble inorganic or organic compounds such as carbon in the coal, corrosion products of the equipment ~for example, F~203), naphthalene, and 20 sulfur. Oils present include coal tar, pyridine, etc. ;~
Step (A) of the method achieves the removal of ammonia which is a major inhibiting factor in the decomposition or oxi-dation reaction of the polluting substances by microorganisms.
In steps (B) and (B'), phenols, suspended solids and oils are removed to reduce the BOD and COD ascribable mainly to the phenols.
In step (C), the phenols, thiocyanate compounds, suspended solids and oils are removed to reduce the COD and BOD further. In step (D), the cyanide compounds, suspended solids and oils are removed to reduce the COD and BOD of the gas liquor to extremely small values.
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1 In step (A), the reduction of the arQmonia, i.e. a stripping of the ammonia is performed generally by blowing air or steam into the gas liquor. The amount of ammonia removed , in this step should preferably be as large as possible, but preferably a part of the ammonia is left for use as a nitrogen source in the microbiological treatments. The optimum amount of ammonia to be left for this purpose is about 50 to about 200 ppm. In this case, stripping should be performed after adjusting the pH of the gas liquor to about 10 to about ll by adding an alkali such as sodium hydroxide (usually in the form of a concentrated aqueous solution of the alkali). Generally, however, it is sufficient for the ammonia to be removed such ~ that the residual amount of ammonia becomes about 800 to l,000 `~ ppm. At this level, there is no need to add the alkali. KOH, s CaCO3, and Ca(OH)2 can also be used as the alkali. But the use of CaCO3 or Ca(OH)2 is less preferred because a scale may be formed.
The ammonia stripping is generally performed at atmospheric pressure. Purther, the efficiency of the stripping 20 is better at high temperatures. Generally, the temperature ~ used for ammonia stripping is about 60 to about 100C, preferabIy ,~ 90 to 100C.
The pH of the gas liquor left after removal of the ~i~ ammonia is adjusted to pH values suitabl~ for microbiological --treatment i.e., a pH about 5 to about 8, preferably 5.5 to 7.5.
l~his pH adjustment is carried out generally by adding, e.g., "~' sulfuric acid of a concentration of about 10 to 80~ by weight.
t ~ Hydrochloric acid, nitric acid, and phosphoric acid can also ~ be used for neutralization, but sulfuric acid is most preferred.
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The gas liquor whose pH has been adjusted is then -subjected to a first biological treatment step (B) using micro-, ~ ~
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1 organisms, i.e. a biolo~ical activated sludge, e.g., as disclosed in, for example, Japanese Patent Application (OPI) No. 5949/69.
This step can be performed using a suspension process such as an activated sludge method, or a ~ixed bed method such as a rotating disc method, a contact oxidation method (or a submerged filter method, a tube method). However, since the concentration of organic matter of the influent gas liquor is high, it is preferred to employ a contact oxidation method using an aeration tank filled with a synthetic resin filling material lO which is resistant to variations in load.
' The filling material for the aeration tank used in the contact oxidation method may be a non-woven sheet having a three-dimensional network structure with irregularly interlaced fibers which is obtained by curling synthetic fibers such as those of nylon, polyvinylidene chloride or polyvinyl chloride by, for example, heat treatment, arranging the curled fibers in the form -of a web or a mat, and bonding these fibers into a sheet form using a bonding agent or using a melt-adhesion of the fibers themselves by heat treatment, or a foamed resin sheet formed by foaming a synthetic resin such as polyurethane or polystyrene.
i Generally, such filling materials having a thickness of about 20 to about 40 mm are aligned in parallel to one ~ ~
:.i :: ' another at intervals of about 20 to about 50 mm, and a large number of aerobic, facultative and anaerobic microorganisms are held and grown on the surfaces of the filling materials and in spaces in the interior thereof.
The pH inside the aeration tank in the first biological treatment step is adjusted usually to about 6.0 to about 7.5.
Depending on the character of the gas liquor, the pH of the gas ~ 30 liquor can be adjusted to the most suitable value experimentally.
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~ iU~5~3 1 The pH adjustment ~ay be performed prior to the introduction of the gas liquor i~to the aeration tank. Alternatively, the pH of the gas liquor may be roughly adjusted before introduction into the tank, and micro-adjusted in the tank by automatic control.
In the suspension process, the activated sludge con-centration in the aeration tank is usually about 2000 to about r 5000 ppm, preferably 3000 to 4000 ppm. The temperature is usually about 20 to about 40C, preferably 25 to 35C. Air is introduced into the tank so that the amount of dissolved oxygen i lO becomes usually about 1 to about 5 ppm, preferably 3 to 4 ppm.
,. .......................... .
In the contact oxidation method in the fixed bed system, the treatment is performed at a volume load of about 4 to about 8 kg CODMn/m3 day, preferably 5 to 7 kg CODMn/m3 day and a .~ surface area load of about 200 to about 400 g CODMn/m2 day, preferably 250 to 400 g CODMn/m day. The temperature and the '; pH may be the same as those used in the suspension process.
The amount of dissolved oxygen is about 2 to about 7 ppm, preferably 4 to 6 ppm.
In step (B), phenols and other polluting materials are 20 removed due to the action of microorganisms. Preferably, the polluting substances are removed in this step to an extent that ~ the CODMn is reduced by about 30~, so as to reduce the loads in~ -~
`~j the subsequent treatment with activated carbon and activated 1~ sludge and to perform the treatment in a stable manner and with i~ good efficiency. Removal of the polluting substances to reduce

7 the CODMn to more than about 90~ is not preferred for operation.
If the amounts of the polluting substances to be removed are ~-, small and the BOD and CODMn are high, the amount of sludge -generated in the second biological treatment step increases, and ;
30 this is undesirable from the standpoint of equipment cost, treating .
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1 efficiency, and treating effect. If, on the other hand, the rate of removal of the pollutlng substances is large and the reduction of the CODMn is more than about 90%, the amount of sludge ge-nerated in the second biological treatment step is small. Thus, the rate of addition of activated carbon is restricted depending , upon the absolute amount of excess sludge (activated sludge/
activated carbon mixture weight ratio). Hence, this is not preferred in the method of this invention. In order to maintain a fixed rate of addition of activated carbon and keep the concentration of activated carbon in the aeration tank at a fixed value, the amount of excess sludge generated should be within a certain fixed range. When the amount of excess sludge -I is too large, a large amount of activated sludge must be discharged ,~ from the system in order to maintain the concentration of acti-: ~ , ;~ vated sludge in the aeration tank at the desired value. As a ~` result, the amount of activated carbon in the excess sludge is ,l withdrawn in an amount larger than the desired amount, and in order to maintain the concentration of activated carbon in the ; ~-~
aeration tank at the desired value, the addition of more activated carbon becomes necessary. If, on the other hand, the amount of excess sludge generated is t:oo small, only a small -~ amount of activated sludge can be withdra~n in order to maintain .. ~
; the activated sludge concentration in the aeration tank ~ constant. If a fixed rate of addition of activated carbon is -~ maintained in such a situation, the amount of activated carbon in the aeration tank increases. Furthermore, in order to maintain the amount of activated carbon at the fixed value 1n the aeration tank, the rate of addition of activated carbon should be reduced. A decrease in the rate of addition of .;
activated carbon deteriorates the properties of the liquor being treated.

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1 In step (C), the excess sludge is treated with a device ~, for regenerating activated carbon by, for example, the wet air ~ oxidation method. (This method is described in, for example, 't U.S. Paten~ 3,442,798). The sludge is oxidized and burned, and the activated carbon is activated and regenerated for reuse.
Fresh activated carbon is supplied in an amount corresponding , to the loss during regeneration (which is about 4 to about 7%).
In order to add a predetermined amount of activated carbon while maintaining the composition of the activated carbon/activated sludge mixture weight ratio constant, the degree of decrease of CODMn in step (B) is preferably about 30 to about -90%, more preferably 50 to 80%.
The residence time of the liquor being treated in the treating tank is generally about 10 to about 15 hours ~hen the ~` amount of sludge returned is 100% by volume based on the volume of the starting liquor.
Step (B') may be carried out instead of step (B). It comprises treating the gas liquor, from which ammonia has been { removed, with powdery activated carbon. The activated carbon ;~
used has a particle size of usually 150 to 400 mesh, preferably -200 to 250 mesh. It is added in an amount of usually 3,000 to 10,000 ppm, preferably 5,000 to 8,00P ppm, and the mixture is :
stirred for about 0.5 to 2 hours to remove the phenols, ~
. .~. .
suspended solids and oils in the gas liquor and to reduce CODMn -by 20 to 80%, preferably by 30 to 70%. This can reduce the load in the subsequent biological treatment step.
, The gas liquor treated in step (B) or (B') is subjected to a solid-liquid separation, and the supernatant liquid is then ~ subjected to step (C). In step (C), phenols and thiocyanate L~ 30 compound etc. in the gas liquor are removed by the decomposition, 1~ - 17 -. 7' . ~` ' ' .

95'73 1 o~idation or decomposition-oxidation action of the microorganisms in the activated sludge and the adsorption action of the activated carbon. Hence, the BOD ~nd COD are reduced. In this step, activated sludge and activated carbon make up the mixed liquor suspended solids in the aeration tank.
The activated carbon used in this invention has a -particle size of usually about 150 to about 400 mesh, preferably 200 to 250 mesh. Activated carbon having too small particle ` size is difficult to separate in the solid-liquid separating ` 10 procedure, and an activated carbon having too large particle size has poor adsorbability and it is difficult to achieve good circulation within the tank.
The concentration of activated sludge in the aeration tank is usually about 2500 to about 5000 mg/liter, preferably 3000 to 4000 mg liter. The activated carbon concentration is usually about 10,000 to about 50,000 mg/liter, preferably 20,000 ~` to 40,000 mg/liter. The ratio by weight of the activated sludge to the activated carbon is about 1:2 to about 1:30, preferably ¦ 1:5 to 1:14. If the amount of activated carbon is less than about 10,000 mg/liter, the amounts of the polluting substances, the decomposition products and the oxidation products to be adsorbed decrease. If the amount of activated carbon is larger than about 50,000 mg/liter, it is difficult to separate the ` activated carbon with good efficiency in the solid-liquid sepa-rating operation.
The treatment in this step is carried out usually at about 20 to about 40C, preferably 25 to 35C. The amount of air fed into the tank is adjusted such that the amount of dissolved oxygen in the tank is usually about 2 to about 6 ppm, preferably , 30 3 to 4 ppm. The pH inside in the aeration tank is usually ~X - 18 -jr ~

F
~ ~ .

lO~gS73 1 adjusted to about 6 to about 7.5 by automatic control. The pH
can be adjusted to the most suitable range experimentally depending on the character of the gas liquor. The pH of the liquor can be adjusted with an inorganic acid which is described ~, hereinabove, such as sulfuric acid. In order to keep the weight ratio of the activated sludge and activated carbon constant, the activated carbon is added to the aeration tank in an amount of about 500 to about 2,000 mg/liter based on the liquor in-troduced. Regenerated activated carbon can be used for this purpose. The loss ~which is about 4 to 7~) of the activated carbon at the time of regeneration is replenished with fresh activated carbon. The residence time of the liquor in the aeration tank is usually about 80 to about 15 hours.
By mixing activated sludge and activated carbon in the step described above, an anaerobic zone is formed around the activated carbon, and an aerobic zone~ on outside of the anaerobic ~ zone. Substances adsorbed to the activated carbon are decomposed ¦ by anaerobic microorganisms, and oxidized by aerobic micro-organisms. Since the polluting substances are adsorbed on the activated carbon, the load of sludge and qualitative and quantitative shock loads (resistance to variation in load) can be reduced,and the treating efficiency can be stabilized. Further-more, the reactions within the system are promoted because the biological metabolites in the treating system are adsorbed.
The activated sludge-activated carbon mixture is separated and removed from the gas liquor treated in step (C), ,, and the residue is subjected to step ~D).
! The precipitate formed in step (D) is coagulated and separated. The supernatant liquid, if desired, is treated with powdered activated carbon in step ~E). Step ~E) can be performed 1 9 - ~ ~ ~

:,,.; :

':

; . , -: :

1 in quite the same way as in step (B'). The supernatant liquid ~ -obtained by solid-liquid separation after step (D) or (E) is discharged into water courses after, if desired, having been filtered through a bed of sand, for example.
, According to the method described above, main ingre- ~-dients which hinder biochemical reactions in step (C) are decreased or removed in step (B) or (B'), and the efficiency of the biological oxidation reaction in step (C) is increased.
Furthermore, since the biological treatment step is performed `~ 10 using activated carbon and activated sludge at a pH of 6 to 7.5, thiocyanate compounds, phenols and other polluting materials can be surely removed by a synergistic action of the biological oxidation by activated sludge and the adsorption by activated ( carbon, and BOD, COD can be reduced. After the biological ::t treatment step, the coagulating treatment using iron salts in accordance with this invention and the powdered activated carbon ~ -treatment (optionally) are carried out. Hence, the remaining polluting materials and impurities such as cyanide compounds, colour ingredients and residual suspended solids can be surely $s 20 removed, and CODMn can be reduced. By the effective combination of the aforesaid pre-treatment, biological treatment and the post-treatment of the invention, the gas liquor whose stable treatment has been regarded as difficult can be treated stably ; and completely to afford treated water of good quality. Further-; more, the effective combination of the pretreatment, the biological treatment and the post-treatment make it possible to treat the gas liquor easily and surely without diluting it with !~ industrial water, sea water, waste waters (domestic waste water and other process waste waters) or mixtures of these. Hence, ~s 30 the method is very effective for treatment of gas liquor.
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1 The above-described method is described below by reference to one specific embodiment as shown in the accompanying drawing which is a flowsheet illustrating the treatment of gas uor.
The process shown in the flowsheet comprises step (A) `, which can be considered a pretreatment step (an ammonia stripping step al, and a neutralization step a2), a biological treatment -~ step (~) (treatment with microorganism) or step (B') (treatment with activated carbon), a biological treatment step (C) (treatment with a mixture of activated sludge and activated carbon), a ., post-treatment step (D) (a coagulating-sedimentation step dl, and a final filtration step d2, and an activated carbon re-generating step (F). The flow of gas liquor is shown by the `~ boldface lines in the drawing. -~
First, gas liquor 16 is introduced into an ammonia stripper 1, and simultaneously, air or steam 17 is fed into the gas liquor 16 to remove ammonia 18 in the liquor. (ammonia stripping step A-al.) Then, the gas liquor from which ammonia has been removed is introduced into a pH adjusting tank 2~ and the pH of the gas liquor is adjusted to about 5 to about 8, e.g., with sulfuric acid. (neutralization step A=a2.) The gas liquor from which ammonia in a predetermined ~ amount has been removed in the pre-treatment step and for which `~,; the pH has been adjusted in the same step is then introduced into a first biological treatment aeration tank 3. Air 19 is introduced into the aeration tank 3. Due to the decomposition and oxidation action of microorganisms, the polluting sub-i~ stances in the gas liquor are partly removed. The pH of the liquor within the aeration tank 3 is adjusted using an automatic pH controller 29. When the above treating device is used with a l ~.
:

lf~
1 ixed bed-type 31010~ical treating method, although exhausted sludge from tank 3 may be returned to the tank, usually, it lS
not necessary. Tne gas liquor from which the polluting sub-stances have been partly removed in the aeration tank 3 is then introduced into a settling tank 4 and the liquor is sub-jected to a solid-liquid separating procedure. The supernatant liquid is introduced into an aeration tank 6. The pH of the liquid in tank 6 also adjusted as in tank 3 using an automatic pH controller 30. The sludge is sent to an activated carbon 10 reservoir tank 14 to be described hereinafter through a thickener 5, and the sludge is treated in an activated carbon regenerating device 15 simultaneously with the regeneration of the activated carbon. (first biological treatment step (B) and regeneration step (F).) The supernatant liquid introduced into the aeration tank 6 from the settling tank 4 is mixed in the aeration tank 6 with activated sludge (including return sludge 20) and activated ,- ~arbon (regenerated activated carbon 21 plus replenishing acti-vated carbon 22). Air 23 is introduced into the aeration tank 20 6. Due to the biological oxidation action of the microorganisms in the activated sludge and the adsorption action of the activated carbon, phenols and thiocyanate compounds etc. in the gas liquor are removed, and the BOD and COD are reduced. The ; regenerated activated carbon 21 may be activated carbon regenerated in the regenerating step (F). The gas liquor treated in the aeration tank 6 is introduced into a settling tank 7 where the activated sludge/activated carbon mixture is separated :~, ~, by sedimentation. The supernatant liquid is introduced into a ~ coagulation tank 9. A part of the sludge (the activated sludge~
-~ 30 activated carbon mixture) is returned to the aeration tank 6 as .
s Ps - 22 - -~ ~;
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1 return sludge 20. The remainder of the sludge is sent to a thickener 8 as excess sludge 24. (biological treatment step (C).) A predetermined amount of a ferrous compound 25 such as ferrous chloride is added to the supernatant liquid introduced , from the settling tank 7 into the coagulation tank 9, and, optionally, the mixture is stirred. Then, an alkali 26 such ' as sodium hydroxide or potassium hydroxide is added to adjust the pH of the mixture. Then, a predetermined amount of a ferric compound 27 such as ferric chloride is added. The mixture is 10 stirred to remove the cyanide co~pounds from the gas liquor, `~'f and the COD is reduced. The treated liquor is subjected to a t solid-liquid separating procedure in a settling tank 10. The ; supernatant liquid is introduced into a sand filtering device 13, and the sedimented sludge is supplied to a thickener 11.
The sedimented sludge is introduced into a sludge ~;j treating device 12 through the thickener 11, and separately 1`~., ~:
treated. (coagulating sedimentatlon step D-dl.) The super-natant liquid introduced into the same filtering device 13 is completely filtered, and released as treated liquor 28.
20 (final filtering step D-d2.) The sludge in the thickener 5 in the first biological ~ treatment step (B) and the sludge (the activated sludge/activated iii`~ carbon mixture) in the thicker 8 in the second biological treat-``' ment step (C) are each transferred to the activated carbon reservoir 14 in the activated carbon regenerating step (F), and are mixed in the activated carbon reservoir 14. The mixture -~
j'~ is introduced into an equipment 15 for regenerating activated carbon using a wet air oxidation method. The used activated carbon is reactivated and regenerated, and the excess sludge is 30 burned there. In the activated carbon regenerating step tF), the ~s - 23 -; : ' ~.
.

,'~: ' ' 1~'3'~73 1 regeneration of powdered activated carbon and the treatment of excess sludge are performed simultaneously. The activated carbon regenerated in the regenerating equipment 15 is returned to the aeration tank 6. In this way, the activated carbon is recycled, and the cost of treatment can be reduced. (regeneration step (F).) When step (B') is employed instead of step (B) and the treatment with activated carbon in step ~E) is also performed, the activated carbon used in step ~E) may be used directly in step ~B') to utilize its remaining adsorbability effectively.
The activated carbon used in step ~B') is generally concentrated and then sent to a regenerating device where it is treated - together with the activated carbon used in step tC). The regenerated activated carbon is recycled to step (E). When step (E) is not performed, the regenerated activated carbon is , recycled to step (C). Thus the cost of treatment can be reduced ~, when step (B') is employed, steps (A), (C) and (D) to be combined ;
with it are the same as in the case of employing step (B).
The following Examples and Comparative Examples speci-fically illustrate the present invention.

~ EXAMPLE 1 -~ FeC12 (100 ppm) was added to gas liquor containing 5.6 ppm of a cyanide ion (CN ) which had been subjected to a biolo-gical oxidizing treatment. The mixture was rapidly st1rred at 150 rpm for 2 minutes by a jar tester. The pH of the mixture was adjusted to 8.4 with sodium hydroxide, and it was rapidly stirred for 2 minutes. Furthermore, 150 ppm of FeC13 was addedr and the mixture was rapidly stirred for 2 minutes. Finally, ~; 30 the mixture was slowly stirred at a speed of 30 rpm for 10 minutes, and coagulated and separated. After the coagulation and ,:;

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10~ 3 s 1 separation, the supernatant liquid (treated water) had a pH of s 6.5. Analysis showed that it conta:ined 0.7 ppm of CN . Thus, the cyanide ion could be surely removed. The -treated water did s not form a precipitate on standing for a long period of time.
~ COMPARATIVE EXAMPLE 1 ,:
eC12 (100 ppm) was added to the same waste water as in Example 1, and after rapid stirring for 2 minutes, 150 ppm of FeC13 was added. The mixture was rapidly stirred for 2 minutes.
1 The pH of the mixture was adjusted to 6.5 with sodium hydroxide, and the mixture was rapidly stirred for 2 minutes. It was finally stirred slowly for 10 minutes, and then coagulated and ; separated. Analysis showed that the treated water contained 0.7 ppm of CN but on standing, a precipitate of Fe(OH)3 was ~; formed from the treated water.
When the procedure was repeated under the same conditions as set forth above except that the amount of sodium hydroxide was increased to adjust the pH of the mixture to 7.4, no precipitate was formed from the treated water but the CN concentration of the treated water was 1.1 ppm.
~ The amount of sodium hydroxide required to increase the Y~ pH to 8.4 in Example 1 was the same as that of sodium hydroxide .,~
required to raise the pH to 6.5 in Comparative Example 1.
A comparison of Example 1 (the method of the invention) with Comparative Example 1 shows that Example 1 required a smaller amount of alkali than Comparative Example 1, and in Example 1, the cyanide ions can be surely removed and the method can fully :~.
cope with an increase in the amount of FeC12 that is required ; with an increase in the cyanide ion content in the influent waste water in coagulating sedimentation.
~ 30 ; ~ - ' , - 25 -,`~.g,f '"' ~ ' ::. - - `

iOb~ '73 COMPARATIVE ~XAMPLE 2 To the same waste water as used in Example 1 was added FeC13 in an amount of 500 ppm, 1,000 ppm and 1,500 ppm, respecti-vely. The ~ixture was rapidly stirred for 2 minutes, and adjusted to pH 7 with sodium hydroxide. It was again rapidly stirred for 2 minutes, finally slowly stirred for 10 minutes, and coagulated and separated. Each of the treated waters was analyzed for cyanide ions, and the results are shown in Table 2.

TAsLE 2 Amount of FeC13 added CN concentration of the ; treated water (ppm) ~ppm) 500 2.1 1,000 1.5 .
s 1,500 1.3 ~, As can be seen from Table 2, the method of Comparative ; .
Example 2 requires a large amount of FeC13 in order to remove the cyanide ions without fail. When the amount of FeC13 increases, '~ the amount of sludge formed increases accordingly and leads to ~20 a high cost of operation.-.~;' . ~ .
.;,. .
FeC12 (250 ppm) was added to the same waste water as used in Example 1, and the mixture was rapidly stirred for 2 minutes. Then, its pH was adjusted to 7 with sodium hydroxide, and the mixture was stirred rapidly for 2 minutes and then slowly stirred for 10 minutes. It was then coagulated and separated.
But since the coagulability of the flock was poor, the coagula-tion and separation could not be effected well. Hence, 1 ppm of a polyacrylamide coagulant was added, but complete coagulation and separation were neither possible.

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~ ~ ' i~'3'~'73 1 The treated ~ater left after the separation of the flock was filtered through a No. 5 filter paper (JIS T-3801 standards).
The filtrate was found to have a CN concentration of 0.8 ppm, but on standing, a brown precipitate of Fe(OH)3 formed in the ~, filtrate.
It was ascertained that the pH at which no precipitate formed from the filtrate on standing was 9.2. When the waste `~ water was treated at this pH, it had a CN concentration of 1.8 ppm.
Thus, in Comparative Example 3, the ratio of removal of CN was good, but coagulation and separation were difficult.
Moreover, Fe2 remained, and an attempt to perform treatment at such a high pH as to prevent the remaining of Fe2+ resulted `,i in the dissolving of CN .

ExAMæLE 2 ~ FeC12 (200 ppm) was added in the same way as in Example 1 '1 to gas liquor containing 15 ppm of cyanide ions which had been subjected to a biological oxidizing treatment. The pH of the ~;
~ 2C mixture was adjusted to 8.4 with sodium hydroxide,and then 150 ppm -~ of FeC13 was added. The treated water had a CN concentration of 0.6 ppm. No precipitate was formed from the treated water.
The pH of the treated water was 7.3 and the water had a residual iron content of 0.4 ppm. Thus, good treatment of the gas liquor could be performed.

.
~ i .
~ A gas liquor as shown in Table 5 below was treated under ¦~ the conditions shown in Table 5 below using the process, that ~;

,~ is, process (A) - (B) - (C) - (D) as shown in the flowsheet F.' 30 shown in the Figure. The biological treatment steps were performed r i r ~ 2 7 ~/ :

10b~35'73 '~ 1 continuously, and the pre-treatment and post-treatment steps ` were performed batchwise.
' The biological treatment steps were performed as described below. The specifications of the test unit used are shown in Table 4.

:j ,; Specifications of the Testing Unit Biological Step Biological Step (B) (C) Fixed bed type Treatment with biological activated sludge treatment and activated carbon , Raw Waste Storage Tank 200 liters Aeration Tank 2.5 liters (2 tanks) 10 liters Settling Tank 5 liters 10 liters ,' Treated Liquor Storage 5~ liters 50 liters ~,' Tank ' Pump for Supplying 0 - 30 ml~min 0 - 30 ml/min `' Starting Liquor ~ Pump for Returning Sludge - 0 - 30 ml/min . . .
~ir Pump 15 N liters/min 15 N liters/min -~, Air Flow Meter 0-5 N liter/min 0 - 10 N liters/min ~ (2 air flow meters) ,~ 20 Surface Area of Filling ~,~ Material 0.11 m2 J Material of Filling Polyvinylidene '' Material chloride non-woven ' sheet :;~
~' The gas,liquor which had been subjected to the pre-treatment step (ammonia stripping and neutralization wit~ sodium ,~
~' hydroxide) was fed into the aeration tank of the first biological ~'~ treatment step at a flow rate of 12 liters/day. Air was introduced into the aeration tank at a flow rate of 2 to 4 N
~ liters/min. The amount of dissolved oxygen was maintained at 3 ;~ to 6 ppm, and the pH of the liquor in the aeration tank was ., ~

~ ~ - 28 -.

:s .

10~ '7~
1 maintained at 6 to 7 using an automatic pH adjuster. While the gas liquor was present in the aeration tanks (two tanks each with a capacity of 2.5 liters) for 10 hours,the gas liquor underwent ~e decomposition and oxidation actions of aerobic, facultative, and anaerobic microorganisms held and grown on the surface of the filling material and the interior spaces inside ~ the filling material. AS a result, the CODMn was reduced by ;~ about 60%.
Air was fed into the aeration tank of the second bio-10 logical treatment step at a flow rate of 2 to 3 N liters/min, and the amount of dissolved oxygen was maintained at 2 to 4 ppm.
T The pH of the liquor in the aeration tank was maintained at 6 to 7 using an automatic pH adjuster. The concentrations of the activated sludge and activated carbon in the aeration tank were 4,100 and 39,000 ppm, respectively. The weight ratio of the activated sludge to the activated carbon was 1:9.5. The ~' rate of addition of regenerated activated carbon was 1,520 ppm and flesh activated carbon was 80 ppm based on the raw waste. ;
While the gas liquor was present in the aeration tanks for 12 20 hours, the gas liquor was purified and clarified by the synergistic combination of the biologicaL oxidation action by the activated sludge and the physical adsorbing action by the ~, activated carbon. The amount of return sludge was 100% by volume based on the amount of the influent liquor fed.
In the coagulating and sedimenting step, 200 ppm of ~, ferrous chloride was added to the treated liquor of biological treatment step (C), and the mixture was rapidly stirred at 150 rpm for 2 minutes, and then sodium hydroxide was added to adjust the pH of the mixture to 8.5. Then, 100 ppm of ferric chloride 30 was added, and the mixture was rapidly stirred at 15 rpm for 2 minutes, and then slowly stirred at 30 rpm for 10 minutes. The ; - 29 :~ ' . ,.

, . , ' - : . ~ ::

10~S73 1 liquor was then filtered ~Jith a filter paper (NO 5-C by JIS
standards).

; EXAMPLE 4 . _ A gas liquor as shown in Table 5 below was treated using the same procedures as in Example 3 under the conditions , shown in Table 5 below.
In this Example, the gas liquor was immediately sub-jected to an activated sludge treatment after the pretreatment step, and then subjected to the post-treatment step.
The results obtained in the Example 3 and Example 4 are also shown in Table 5 below.

. .
~; TABLE 5 ;~ Example 3 Example 4 Ammonia Ammonia ~,~ Pretreatment stripping stripping Step adjustment adjustment ~,i Riaw OWrste Gas pH 9.5 9.5 BOD5 (ppm) 2960 2830 ~,, Mn (ppm) 4500 4300 SCN Compounds (ppm) 680 655 CN Compounds (ppm) 30 25 Phenols (ppm) 1020 980 NH3 (ppm) 3100 3300 Biological Treatmen _ St~
Ouent Gas pH 6.1 6.5 BOD5 (ppm) 1850 1700 Mn (ppm) 3000 3000 SCN Compounds (ppm) 670 650 CN Compounds (ppm) 20 20 Phenols (ppm) 622 500 NH3 (ppm) 810 450 ,~

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10~ 3 TABLE 5 (continued) Example_3 Example 4 . Fixed bed type bio- -First Biological logical ~,~ Treatment Step treatment Conditions COD Volume Load . (kg/m3.D) 7.2 COD Surface Area Load (g/m2.D) 327 Aeration Time (hours) 10 ~' Effluent Gas pH 6.7 Liquor BOD5 (ppm) 300 Mn (PP ) 1270 SCN Compounds (ppm) 580 '~ CN Compounds (ppm) 18 ., Phenols (ppm) lO
, Treatment ~; with Acti-vated sludge ~i Second Biological and activated Activated `~ Treatment Step carbon sludge Conditions COD Volume Load ,j (kg/m3.D) 1.27 1.0 ~,` COD-SS Load (kg~.D) 0.31 0.25 Sludge Concentration ~,~ (ppm) 4100 3S50 ¦~ Activated Carbon Con- 39000.~ 20 centration (ppm) '.
~mount.of Activated 1600(regenera- -, Carbon Added (ppm) ted: 1520 .. flesh: 80) Aeration Time (hours) 12 36 Example 3 Example 4_ ;, Treatment with.acti-vated sludge , Second Biological and acti-Activated Treatment Step _ vated carbon sludge Effluent Gas BOD5 (ppm) 3.8 30 ~ Liquor CODMn (ppm) 20 350 r SCN Compounds (ppm) 0.0140 (trace) ., 30 CN Compounds (ppm) 15 18 Phenols (ppm) 0.015 . (trace) , ~ - 31 -! :
, :

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1~ 3 ;
1 TABL~ 5 (continued) Floccula-, tion and precipi-tation, and Post-Treatment filtering r Step through sand Effluent BOD5 (ppm) less than 2 20 ,r Liquor (trace) CODMn (ppm) 12 115 SCN Compounds (ppm) less than 40 r O.1 (trace) ~ CN Compounds Ippm) 0.6 0.8 `~ Phenols (ppm~ less than 0.5 ~r 10 0 ~ 01 (trace) Total Aeration Time in Biological Treatment 22 36 Steps (hours) .
Ratio of Sludge Returned: 100% by volume based on the raw waste gas liquor volume.
., COD Volume Load: COD of the influent liquor per day per '~ - cubic meter in the aeration tank.

COD Surface Area Load: COD of the influent liquor per day per square meter of the filling material in the aeration tank.
,~ COD-SS Load: COD of the influent liquor per day per ! ~ kilogram of suspended solids in the aeration tank.
i 20 In Example 3, the gas liquor was treated in the same way except using ferrous sulfate and ferric sulfate instead of the ferrous chloride and ferric chloride. The treating con-ditions and the results obtained are shown in Table 6 below together with the results obtained in the case of using iron chlorides in Example 3.

~:.'., 1::,,,. :.

~ --10b~ 7~3 1 T~LF 6 Coaqulating-Sedimerting Step Iron Chlorides Iron Sulfates Conditions Ferrous Salt (ppm) 200 300 As Fe tppm) 88 84 pH (using NaOH) 8 . 5 8 . 4 Ferric Salt (ppm) 100 150 As Fe (ppm) 34 55 Influent CODMn (ppm) 20 22 (effluent BOD5 (ppm) 3 . 8 4 . 7 ; liquor from SCN Compounds (ppm) less than 0.01 less than 0.01 the second (trace) (trace) biologi- CN Compounds ~ppm) 15 13 ment step) Phenols (ppm)less than 0.01 less than 0.01 ~ ~trace) (trace) r Effluent CODMn (ppm) 12 14 the Coagu- BOD5 (ppm) ~trace) less than 2 menting SCN Compounds (ppm) less than 0.01 less than 0.01 Step (trace) (trace) CN Compounds (ppm)0.6 0.7 : Phenols (ppm)less than 0.01 less than 0.01 (trace) (trace) :
. All values in Table 6 were measured in the same manner as in Table 1.

Gas liquor shown in Table 7 was treated under the :
.~ ~
conditions shown in Table 7. Only the biological treatment was performed continuously, and the pretreatment and the post-treatment were carried out batchwise.
The biological treatment step was performed in the following manner.
The gas liquor which had been pretreated was treated using a flow-type activated sludge treating device composed of an aeration tank having a capacity of 10 liters and a settling tank having a capacity of 10 liters connected to each other. The :~:
'' :
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~CJ~95~3 .. .

! 1 concentrations of activated sludge and activated carbon in the aeration tank were 3780 and 16540 ppm, respectively. The mixing weight ratio of the former to the ]atter was 1:4.4.
The gas liquor which had been subjected to ar~onia strip-;5 ping and a pretreatment of adsorption with powdered activated carbon was adjusted to pH 6.5 with sulfuric acid, and then fed into the aeration tank at a flow rate of 10 liters/day. Air was fed into the aeration tank at a flow rate of 4 - 5 N liters/min ; to maintain the amount of dissolved oxygen at 2 to 4 ppm. The "t 1 gas liquor was caused to reside for 12 hours in the aeration tank, and during this time, was purified by a synergistic action of the biological oxidative decomposition by activated sludge and adsorption by activated carbon. It was then flowed into the subsequent settling tank, and subjected to solid-liquid separation. The supernatant liquid was flowed into a treated water tank, and a part of it was sampled for analysis. On the other hand, a part of the separated sludge was withdrawn as an excess sludge from the bottom of the settling tank. The remainder was returned to the aeration tank. The amount of the return sludge was 100~ by volume based on the amount of the influent j, lr gas liquor.
, ~ .
In the pretreatment step of adsorption with powdered ~ activated carbon, the activated carbon discharged from the ,~:/- post-treatment step of adsorption with powdered activated carbon was used, and added in an amount of 4,000 ppm to the gas liquor, followed by stirring the mixture for 60 minutes.
In the post-treatment step (D), FeC12 ~the amount in each Example is shown in Table 8) was added to the gas liquor, and the mixture was rapidly stirred at 150 rpm for 2 minutes by a jar tester. Then, sodium hydroxide was added to adjust the pH

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1 to 8.5. FeC13 ~the amount in each Example is shown in Table 8) , was added, and the mixture was stirred rapidly at 150 rpm for 2 minutes. Finally, the mixture was slowly stirred at 30 rpm for 10 minutes, followed by coagulation and separation.
In step (E) (adsorbing treatment with powdered activated . carbon~, powdered activated carbon which was used and has been `~ regenerated by wet air oxidation method was used. 4000 ppm of the activated carbon was added to the gas liqucr and the liquor was stirred for 60 minutes.
,. 10 Gas liquor shown in Table 7 was treated in the same , manner as in Examples 6 - 13 except that post-treatment step (D).
In the post-treatment step ~D), 500 ppm of FeC13 (172 ppm as FeIII) was added to the gas liquor, and the mixture was rapidly stirred at 150 rpm for 2 minutes, and then slowly stirred at 30 rpm for 10 minutes. ;
~; The results obtained in Examples 6 - 13 and Comparative Examples 4 - 11 are shown in Table 7.

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; 30 ' - 35 -'~' ' ' i ' ~ .

` ~0~'35i'~3 ., Treating Conditions Example 6 Comparative Example 7 Comparative . and Items of Analysis Exc~ple 4 Example 5 .
.~ Pretreatment Step : .
Ammonia Stripping ~ Step _ yes r. Powdered Activated ~ Carbon Adsorption ~ Step _ _ ~ Type of Biological : Treatment Step AS AS
~' 10 Dilution Ratio in the Biological Treatment Type of Diluting $ water Low Wa te Gas Liq~r :~ P~- 9-4 9.5 .;~ BOD, ppm 1,480 1,840 CODMn, ppm 2,500 2,800 ~l SCN Compound, ppm650 650 ~ CN Compound, ppm6.2 10.5 , .
r Phenols, ppm 500 700 .. 20 NH3, ppm 3,300 3,500 Influent Water in the Biolo~ical Treatment pH 9.4 8.5 BOD, ppm 1,480 1,480 Mn' ppm 2,500 2,500 SCN Compound, ppm650 650 ~ r~ CN Compound, ppm 6.2 6.1 ;~ Phenols, ppm500 500 I ~r NH3, ppm 3,300 450 Effluent Water from the Biological Treatment . 30 BOD, ppm 300 50 DMn, ppm 800 - 350 , j",~ . .

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TABLE 7 continued Treating Conditions Example 6 Comparative Example 7 Comparative and Items of Analysis Exam~le 4 Example 5 Effluent Water from the Biological- Treatment cont.
i . SCN Compound, ppm 450 70 ' CN Compound, ppm 4.8 3 Phenols, ppm 50 5 Discharge Water from the Post-Treatment ., _ BOD, ppm 200 200 30 30 CODMn' ppm 260 260 80 80 lO SCN Compound, ppm 220 220 40 40 CN Compound, ppm 0.7 2.5 0.5 1.4 Phenols, ppm 10 10 0.2 0.2 ~- Treatment Conditions in the Aeration Tank .~ COD Volume Load, kg-COD~m day 1.20 1.20 COD-SS Load, kg-COD/kg-SS day 0.29 0.30 Concentration of Activated , Sludge, ppm 4,100 3,950 Concentration of Activated : Carbon, ppm .. (Note) AS: activated sludge .
~' 20 AS ~ AC: activated sludge + activated carbon .:~
~ The amounts in the above table were all determined by : the same methods as in Table 1.
l Treating Conditions Example 8 Comparative Example 9 Comparative `~ and Items of Analysis ___ Example 6 ___ _ Example 7 : `
Pretreatment Step Ammonia Stripping Step yes yes Powdered Activated Carbon Adsorption Step yes yes Type of Biological ~ ~ ::
Treatment Step AS AS + AC -~
~: Dilution Ratio in the . Biological Treatment 1 1 Type of Diluting Water , ~ .

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i. :

.. 10~3,t.'i'3 - TABLE 7 continuecl Treating Conditions Example 8 Comparative Example 9 Comparative ~'. and Items of Analysis Example 6_ _ Example 7 Low Waste Gas Liquor pH 9.5 BOD, ppm 2,100 DMn, ppm 3,400 SCN Compound, ppm 700 CN Compound, ppm 7.5 Phenols, ppm 900 :~ lO NH3, Ppm Influent Water in the Biological Treatment pH 6.5 BOD, ppm 710 ~ CODMn, ppm 1,500 : SCN Compound, ppm700 CN Compound, ppm 5.3 Phenols, ppm 270 ~: NH3, ppm 910 :~ Effluent Water from the Biological Treatment 20 BODj ppm 15 4.3 DMn, ppm 150 40 SCN Compound, ppm 30 0.01 CN Compound, ppm 2.7 2.1 J', Phenols, ppm 3 0.01 ~ Discharge Water from the Post-Treatment BOD, ppm 11 11 3.1 3.1 A Mn~ ppm 60 60 10 10.0 SCN Compound, ppm 20 20 0.1 0.1 CN Compound, ppm 0.4 1.2 less than 0.3 0.8 ~ 30 Phenols, ppm 0.1 0.1 less than 0.01 less than 0.01 :''.~ ' ,5 - 38 -$
~, ~ ' - ' lV~ 3 1 T~.3LE 7 continued Treating Conditions Ex~ple 8 Comparative Example 9 Comparative and Items of Analysis Example 6 Example 7 Treatment Conditions in the Aeration Tank COD Volume Load, .' kg/COD/m3 day 1.50 1.47 COD-SS Load, kg-COD/kg-SS day 0.370 0.390 Concentration of Activated Sludge, ppm 4,050 3,780 Concentration of Activated Carbon, ppm _ 16,540 Treating Conditions Example 10 Comparative Example ll Comparative and Items of Analvsis Example 8 Example 9 .
Pretreatment St~
Ammonia Stripping Step yes yes Powdered Activated Carbon Adsorption Step ~,~ Type of Biological ~ Treatment Step AS AS + AC
: Dilution Ratio in the :~l Biological Treatment 23 23 ~ Type of Diluting Water Industrial Water Industrial Water ¦~., Low Waste Gas Liquor ::
' 20 pH 9.2 , BOD, ppm 2,530 : CODMn, ppm 3,450 SCN Compound, ppm 650 CN Compound, ppm 25 li Phenols, ppm 750 NH3, ppm 3,500 Influent Water in the Biological Treatment , pH 7.2 ~! BOD, ppm 992 ¦' 30 CODMn' ppm 1,521 t _ 39 -, , -', 1~, .

10~ 73 s, ~. T~.BL~ 7 continued .~ 1 T-eatiny Conditlons ~ample 10 Comparative Example 11 Comparative and Items of Analysis E:xample 8 _ _ Example 9 Influent Water ln the siological Treatment continued:
SCN Compound, ppm 310 `'; CN Compound, ppm 8.2 I Phenols, ppm 360 i N~3, ppm 300 ~ Effluent Water from the Biological Treatment ., _ .
' BOD, ppm 8.5 5.9 , 10 ' CODMn' ppm 250 40 S SCN Compound, ppm 10 0 CN Compound, ppm 5.2 3.4 Phenols, ppm 0.5 0.01 f Discharge Water from the Post-Treatment '~ BOD, ppm 5.7 5.7 4.5 4.5 Mn~ ppm 80 80 15 15 SCN Compound, ppm 7 - 7 0.01 - 0.01 .~- CN Compound, ppm 0.7 2.8 0.5 0.9 ~Phenols, ppm 0.2 0.2 0.01 0.01 Treatment Conditions in the Aeration Tank , COD Volume Load, ,. kg-COD~m3 day 1.51 1.50 COD-SS Load, kg-COD/kg-SS day 0.398 0.403 Concentration of Activated Sludge, ppm 3,790 3,720 ~ Concentration of Activated : -;~ Carbon, ppm _ 16,500 - ~
. .
I; . ~, .

~; 30 t ~ - 40 -, ".~
:~ .. : .. :

:- ; .:: .
-:.' - : - -lV~ '73 1 TA~LE 7 continued Treating Conditions Example 12 Comparative Example 13 Comparative and It_ms of Analvsis _ Example 10 Example 11 Pretreatment Ste~
, Ammonia Stripping Step _ _ Powdered Activated Carbon Adsorption Step Type of Biological Treatment Step AS AS + AC
Dilution Ratio in the Biological Treatment 1.82 1.89 . lO Type of Diluting Water Industrial Water Industrial Water :
Low Waste Gas Liquor pH 9.2 BOD, ppm 2,100 CODMn, ppm 3,000 :~ :
SCN Compound, ppm 650 CN Compound, ppm 28 Phenols, ppm 750 NH3, ppm 3,500 Influent Water in the Biological Treatment pH 7.4 7.4 BOD, ppm 1,210 1,150 . .
~ CODMn, ppm 1,650 1,580 SCN Compound, ppm360 340 ~.
CN Compound, ppm 15.3 14.8 Phenols, ppm 410 400 NH3, ppm 1,925 1,850 ., ~ !
~ 30 .

.!

57;3 1 _ABLE 7 continued Treatircr Cor.ditions E.Ya~.P1e 12 Comparative Example 13 Comparative a~d Items of Analysis _~ample 10 Example 11 s Effluent Water fro~ the Biological Treatment BOD, ppm 48 25 CODMn, ppm 310 250 SCN Compound, ppm 180 100 CN Compound, ppm 13.2 10.5 Phenols, ppm 20 8 s Dischar~e Water from the Post-Treatment : BOD, ppm 20 20 13 13 ODMn ppm 95 95 75 75 SCN Compound, ppm 80 8060 60 CN Compound, ppm 0.8 8.5 0.6 7.1 Phenols, ppm 2.0 2.0 0.5 0.5 : Treatment Conditions in the Aeration Tank ~, .
COD Volume Load, ~i kg-COD/m3 day 1.42 1.48 COD-SS Load, 0.356 0.361 kg-COD/kg-SS day Concentration of Activated Sludge, ppm 3,975 4,100 ~ Concentration of _ 16,300 s Activated Carbon, ppm .,.

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108"~5~3 Ti~LE 8 Fe-rous Salt (ppm) Ferric Salt (ppm) E~ample No. FeC12 as Fe I FeC13 as Fe . . _ . .

8 75 33 150 50

9 100 44 150 50 , 10 100 44 150 50 '1 11 75 33 150 50 ., , 12 200 88 300 100 :~:
' 13 200 88 300 100 ' While the invention has been described in detail ;~ and with reference to specific embodiments thereof, it will be :~ apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

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Claims (17)

The embodiments or the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for treating a waste water containing cyanide ions, which comprises (1) adding a ferrous salt to the waste water to convert the cyanide ions in the waste water to a precipitate of ferrous ferrocyanide and insoluble Turnbull's blue, (2) adding an alkali agent to the waste water to convert a ferrous ion remaining in the waste water to Fe(OH)2, and (3) adding a ferric salt to the waste water to precipi-tate [Fe(CN)6]4-, which is formed by addition of the alkali agent to the waste water, as insoluble Berlin blue.

2. The method of claim 1, wherein the ferrous salt is ferrous chloride or ferrous sulfate.

3. The method of claim 1, wherein the ferric salt is ferric chloride or ferric sulfate.

4. The method of claim 1, wherein the amount of the ferrous salt to be added is such that the amount of FeII is within the range of x' calculated from the following equations, y = 0.213x - 3.8 x' = x ? 25 (mg/liter) wherein y is the concentration (mg/liter) of the cyanide ion in the influent water, and x is the iron content (mg/liter) in the ferrous salt, and the amount of the ferric salt added is such that the weight ratio of FeIII/FeII becomes 0.5 - 3.

5. The method of claim 1, wherein an alkali agent is added to the waste water to adjust its pH to 7.5 - 9.5.

6. The method of claim 1, wherein the treatment of step (2) is carried out after the precipitate formed in step (1) has been separated and removed.

7. The method of claim 1, wherein the waste water is gas liquor discharged from the step of quenching coke oven gas, said gas liquor having been subjected successively to (A) a step of treating the gas liquor to reduce its ammonia content to about 1,000 ppm or less, (B) a step of treating the gas liquor using microorganisms, and (C) a step of treating the gas liquor is an aeration tank including powdered activated carbon and activated sludge in liquor.

8. The method of claim 7, wherein in the aeration tank, the concentration of the activated sludge is 2,000 to 5,000 mg/
liter, the concentration of the activated carbon is 10,000 to 50,000 mg/liter, and the mixing weight ratio of the activated sludge to the activated carbon is 1:2 to 1:20.

9. The method of claim 1, wherein the waste water is gas liquor discharged from the step of quenching coke oven gas, said gas liquor having been subjected successively to (A) a step of treating the gas liquor to reduce its ammonia content to about 1,000 ppm or less, (B') a step of treating the gas liquor with activated carbon, and (C) a step of treating the gas liquor in an aeration tank including powdered activated carbon and activated sludge in liquor.

10. The method of claim 7, wherein the precipitate is separated and removed after the treatment with the ferric salt, and then the treated water is treated with activated carbon.

11. The method of claim 9, wherein the precipitate is separated and removed after the treatment with the ferric salt, and then the treated water is treated with activated carbon.

12. The method of claim 1, wherein the cyanide ion is derived from a cyano complex ion of Cu, Cd or Zn which has been in the waste water.

13. The method of claim 12, wherein the cyanide ion is derived from by dissociation of the cyano complex ion by adjusting the pH of the waste water to 3 or less than 3.

14. The method of claim 7, wherein the method includes recovering the activated carbon used in treatment of the gas liquor, regenerating the recovered activated carbon and recycling the activated carbon.

15. The method of claim 14, wherein said regeneration treatment of said activated carbon is carried out by a wet air oxidation method.

16. The method of claim 9, wherein the method includes recovering the activated carbon used in treatment of the gas liquor, regenerating the recovered activated carbon and recycling the activated carbon.

17. The method of claim 16, wherein said regeneration treatment of said activated carbon is carried out by a wet air oxidation method.