REMOVAL OF COLOUR AND TOXIC POLLUTANTS FROM BIOLOGICALLY
TREATED COKE PLANT WASTEWATER
FIELD OF INVENTION:
The present invention relates to a pro@ss for removal of colour and toxic pollutants
from biologically treated coke plant waste water.
The present invention also relates to the treatment of biologically treated coke plant
wastewater by using indigenous low cost adsorbent.
BACKGROUND OF THE INVENTION
Coal is transformed by carbonization in to a hard porous mass, devoid of volatile
mafter called coke. During coking period, the coke oven gas is collected from the top
of the oven and scrubbed with weak ammonia liquor to remove tar. The scrubbed
liquid used in by-product recovery operation.
Heavily polluted wastewater is generated in this process. The wastewater generated
during the by-product recovery process is very complex in nature which contains
various organic and inorganic pollutants and toxic substances along with acute
colour bodies. Due to their toxic effects, coke plant effluents cannot be discharged
without detoxification into the environment.
Destruction of the pollutants present in coke plant wastewater can be done by
physico-chemically or biologically. However, physic-chemical process is more
expensive than biological process. Use of biological process is a proven and viable
technology for the treatment of coke plant wastewater for the removal of nihogenous
and carbonaceous toxic pollutants. However, this biological treatment cannot reach
the discharge standards imposed by various environmental agencies. Therefore'
further treatment is required to remove residual pollutants and acute colour bodies
present in biologically treated crke plant wastewater (BTCPW)'
Addition of chemicals (oxidative agents) to remove these residual pollutants and
colour bodies after biological treatment is a very crmmon practice. But, there are
some shortcomings of the existing physico-chemical treatment methods for BTCPW
such as-
(1)TheexistingtreatmentmethodofBTCPWrequireshighinvestment'high
operating costs.
(2) The existing treatment method of BTCPW considers only the removal of primary
pollutant. However, it creates secondary pollutants which are very difficult to remove
and effects environment badlY.
(3) ln the existing treatment method of BTCPW, the company has only invested,
cannot produce benefits for the organisation.
1. lndustrial effluents such as coke plant wastewaters often contain high levels
of ammonia as well as phenols, cyanides, sulfides, thiocyanates, thiosulfates, and
other compounds.
2. With respect to coke plant wastewaters, removal of the above pollutants has
normally been achieved by means of biological treafnent process.
3. However, this biological treatment cannot reach the discharge standards
imposed by various environmental agencies. Therefore, further treatment is required
to remove residual pollutants and acute colour bodies present in biologically treated
coke plant wastewater (BTCPW).
4. while the addition of oxidative agents to remove these residual pollutants and
colour bodies are a very common practice. But, the main shortcoming of the existing
chemical treatment methods for BTCPW is high operating cost'
5. Yet another problem inherent in conventional chemical treatment is that the
generation of secondary pollutant and thereby unusable treated liquid for high end
application.
6.Finally,althoughpriortreatmentprocesseshavereferredtotheuseof
biological treatment steps followed by physico-chemical treatment, such treatments
have been associated with high operating cost and generation of secondary
pollutants. Therefore, this patent seeks to overcome the above mentioned problems
by using an adsorption technique with indigenous adsorbent which reduces the
operating cost and does not produce any secondary pollutants'
4-
OBJECTS OFTHE INVENTION:
An object of the present invention is to propose a process for removal of colour and
toxic pollutants from biologically treated coke plant waste water'
Another object of the invention to propose a tertiary wastewater treatment process
which is highly compatible with a secondary biological treatment of the coke plant
wastewater.
Yet another object of the invention is to propose a treatment system for removing
colour bodies and toxic pollutants from biologically treated coke plant wastewater
(BTCPW) which is both economical and commercially feasible as compared to
currently used physico-chemical treatment.
Further object of the invention is to propose a pro@ss and apparatus which avoids
generation of secondary pollutants that is difficult to remove thus, reducing further
expense
Yet another aspect of the invention relates to treating a coke plant wastewater by
using ingenious adsorbent material present in integrated steel plant'
Further object of the invention is to propose a process and apparatus which, by
virtue of the treatment process, can be easily and accurately monitored and
controlled with a minimum of supervision to meet stringent government regulations
relating to water pollution standards.
Still another object of the invention is to propose a process of using of exhausted
adsorbent for some other purpose. Thereby, to develop a complete close loop unit
which leads to sustainable and environment friendly "zero discharge" coke making
process.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a process for removing colour and toxic
pollutants from biologically treated coke plant wastewater comprising:
mixing the biologically treated coke plant wastewater (BTCPW) with the desired
quanti$ of crushed and screened adsorbent,
separating adsorbent from treated wastewater and using the absorbent for energy
generation,
subjecting the said treated wastewater to the step of filtration to remove the
remaining colloidal and suspended solids.
BRIEF DESCRIPTION OF THE ACCOMP NGD NGS:
Brief flow chart depict in Figure 1 illustrating the present invention. Unit 't- Biological
treatrnent of coke plant wastewater generated during the recovery of the by-product
from coking process; Unit 2- Preparation of adsorbent for the treatment of
biologically treated coke plant wastewater (BTCPW); Unit 3- mixing of BTCPW with
indigenous adsorbent for the removal of colour bodies and residual pollutants; unit
4- Decanter centrifuge for the separation of adsorbent from the reusable treated
water; Unit 5- Pressure sand filter for the final treatment of centrifuge effluent Unit 6-
Dry adsorbent with 15 % moisture content used for energy generation in sinter plant'
DET D cRl ON OF THE I
The object of the invention to provide a cost effective treatrnent method for c,oke
oven wastewater after biological treatment, colour and other toxic pollutants have
reached the permissible level for discharge or reuse. The method comprises the
following stePs of-
Biological Treatment of Coke Oven Wastewater:
coking wastewater is generated from coal coking, coal gas purification and byproduct
recovery processes of coking. lt contains complex inorganic and organic
pollutants, such as ammonium, sulfate, cyanide, thio-cyanate, phenolic compounds,
poly-nucleararomatichydrocarbonsandpolycyclicnitrogen-containingacyclic
compounds, most of which are refractory, toxic, mutagenic and carcinogenic.
Conventional treatment of coking wastewater includes solvent extraction of phenolic
compounds, steam stripping of ammonia, and biological treatment (mostly the
activated sludge process). However, biological process is not efficient for the
complete removal of removal of colour and toxic pollutants. Therefore, advanced
and cost effective adsorption process has been developed for the final treatment of
biologically treated coking wastewater.
Treatment of Biologically Treated coking wastewater:
ln this process an adsorbent was developed for the treatment of biologically treated
coking wastewater. The size distribution of adsorbent is one of the important factors
that play an important role in achieving efficient treatment. Therefore, the effects of
size distribution of adsorbent on removal performance are investigated'
Experimental results show that o to -3.15 mm size of adsorbent gives best results'
There should be a balance of fines and course particle of adsorbent. The size
distribution of adsorbent should be 60% of -lmm, 250/o of 1to -3 mm, 15% of +3 to
-3.15 mm to get optimum results. Therefore the indigenous adsorbent needs proper
pulverisation and screening. The adsorbent with the density of 1.9 g/cm3, bulk
density of 0.4 to 0.65 g/cm3, porosity of 51 to 73%, specific surface area of 3 to 5
m2lg and pore size distribution 0.52 pm or less showed best results for the removal
of intense colour bodies and residual pollutants present in BTCPW'
Mixing of BTCPWwith Adsorbent:
Desired quantity of adsorbent is mixed with BTCPW in a mixing tank. According to
the invented process, 80 g/L of adsorbent is required for the treatment of BTCPW.
The materials are stirred for a time, for example, about 30 minutes, to produce a
uniform mix and to cause intimate contact between the adsorbent and BTCPW' The
optimum stirring intensity is 80 to 90 rpm'
Separation of Adsorbent from Treated Wastewater:
The mixed slurry from the mixing tank is hansferred to a two-phase decanter
centrifuge by either flow under the influence of gravity or is pumped for solid liquid
separation. This decanter centrifuge is a solid bowl, scroll discharge centrifuge, with
counter current flow design. The unit is built to operate continuously at a maximum
bowl speed ot 42OO rpm, which equates to 3549 x G-force, at a wet cake density of
1.2gm/cm3.Howeverthecentrifugehasgivenoptimumresultatabowlspeedof
3500 rpm. The differential speed is controlled by varying the speed of the back drive
motor, with a variable frequency drive, using a Basic core controller' A flocculent
dosing system is devised which discharge a desired amount of flocculent in to the
inlet of the centrifuge.
Final Treatment:
Pressure sand (PSF) is used as final treatment unit for the removal of remaining
colloidal and suspended solids present in the liquid discharge from centrifuge. The
PSF consist of coarse and fine media mixed together in a fixed proportion. Raw
water flows down words through the filter bed with adequate pore dimensions for
retaining both large and small suspended particles, doing so it reduces turbidity.
Used adsorbent for Energy Generation:
The utilized adsorbent generated in this process is collected and sends to respective
plant unit for energY generation'
According to the above method the colour bodies and the residual pollutants present
in BTCPW adsorbed on the surface of adsorbent thus cleaner effluents is produced
which can be reused as ahernate source of industrial water'
Homogenised mixing of adsorbent and BTCPW is essential to achieve optimum
removal of colour bodies and toxic pollutants. The continuous mixing is essential to
avoid the settling and deposition of solid adsorbent in the mixing tank'
The process removes all the colour bodies from the BTCPW along with considerable
amount of residual pollutants and produces colourless and transparent treated water
with no smell. This process does not produce any secondary pollutant or products
therefore no safe disposal required.
D(AMPLE:
Removal of colour and cyanide from biologically treated coke plant wastewater
(BTCPW

This example represent the removal of colour compound from biologically treated
coke plant wastewater (BTCPW obtained from the clarifier of the biological orygen
treatment plant treating wastewater generated from of a metallurgical cokeproducing
plant. ln this tertiary treatment plant, about 5 m3/h of wastewater was fed
continuously in the apparatus shown in the drawing. The adsorbent having particle
size in the range of +0 mm to -3.15 mm was added continuously to the mixing tank
by controlling the conveyer belt speed.
with a ratio (by weight) of the wastewater to the adsorbent of about 8:1, the
following results were obtained-
Reduction of the colour from 1680 Hazen to 45 Hazen and reduction of the
cyanide content from 3.5 mg/l to 0.24 mg/l respectively (Figure 2a and Figure
2b).

WECLAIM:
1. A process for removing colour and toxic pollutants from biologically treated coke
plant wastew€ter comprising :
mixing the biologically treated coke plant wastewater (BTCP\A/) with the desired
quantity of crushed and screened adsorbent,
separating adsorbent from treated wastewater and using the absorbent for energy
generation,
subjecting the said treated wastewater to the step of filtration to remove the
remaining colloidal and suspended solids.
2. The process as claimed in claim 1, wherein the said crushed and screened
adsorbent has a size distribution of 60% of 1mm,25o/o of 1 to 3 mm, 15% of + 3 to
3.15 mm of particle size.
3. The process as claimed in claim 1, wherein the said adsorbent has a densi$ of
1.9 g/cm3, bulk density of 0.4 to 0.65 g/cm3, porosity of 5'l to 73% specific area of 3
to 5 m?g and pore distribution of 0.52 pm or less.
4. The process as claimed in claim 1, wherein the ratio between the adsorbent and
biologically treated coke plant wastewater (BTCPW) is ranging from 1:6 to 1:12 in a
continuously stirred tank reactor system with mixing time of 30 minutes.
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5. The process as claimed in claim 1, wherein for the step of separation of the
adsorbent from the treated waste water a two-phase decanter centrifuge is used.
6. The process as claimed in claim 1, wherein in the step of filtration to remove
colloidal and suspended solids a final gravel filtration unit is used.
7 . The process as claimed in claim 6, wherein the final gravel filtration unit
comprises of pressure sand having coarse and fine media mixed together in a fixed
proportion and the raw water flows down words through the filter bed with adequate
pore dimensions for retaining both large and small suspended particles.