FIELD OF THE INVENTION
The present invention relates to a process for pre-treatment of waste water generated
from coke making in steel plant using an ultrasonic generator. More particularly, the
present invention is directed to a process for pre-treatment of coke oven effluent using
sonication of reaction solution adapted to reduce/ eliminate the toxicity level, along with
associated recalcitrance of the wastewater, that remain either in dissolved ionic level or
very low size range of suspension, through reduction in concentration of normative
constituents for easier biodegradation. Importantly, sonication of coke plant effluent is
carried out in a batch reactor using an ultrasonic transducer coupled with ultrasonic
generator and of 100W power and frequency of 40kHz at a temperature in the range of
35-40°C maintaining selective pH level of influent/reaction solution. Advantageously, the
sonic process according to the present invention for treatment of effluent generated from
coke making can reduce recalcitrance of coke oven wastewater without needing recurrent
consumables. The system and method of the pre-treatment process according to the
present invention achieved under optimal process and operating conditions 50%
degradation in cyanide level and 25% degradation in COD level. The Coke oven effluent
pre-treatment process thus favour oxidation of target radical without dosing of any
conventional chemical or coagulant making it a cost effective, reliable and efficient
process for waste water pre-treatment with the possibility of wide application in industry.
BACKGROUND ART
It is well known in the field of waste water treatment that chemical method has been the
principal method used to prevent water pollution and remove specific pollutants. These
methods employ chemicals added to the process fluid, usually solid or water based.
These additives control a large number of pollutants. However, it is very expensive in the
long run, and additionally there are secondary pollution problems associated with it.
Since removal of dissolved constituents through physico-chemical treatment is an
expensive proposition, biological treatment is adopted for the same which is most cost
effective and widely adopted for effluent treatment process. However, presence of
recalcitrant toxic constituents as well as high level of normative constituents in influent
often affect the performance of biological treatment process.
Most of the biological wastewater treatment plants were earlier designed based on
principle of sewage treatment. However, there is a fundamental difference between
sewage treatment plants and Coke oven effluent treatment plants- whereas sewage
mostly consists of food and natural wastes which are easily biodegradable, the same is
not true for Coke Oven effluent. Besides, when these plants were designed these were
based on hydrological principles, which assume that at pre-treatment stage only
suspended solids needs to be taken care off . So waste treatment systems initially
installed in Steel Plants have clarifiers/settling chambers as major pre-treatment units.
However, scientific development in last few decades indicate that Coke oven effluent
consists of compounds which are difficult to degrade (i.e, to be used as food by bacteria )
either because of high toxicity or because of presence of recalcitrant (or inhibitory)
compounds. For effective pre-treatment these compounds either need to be removed or
broken down into simpler compounds. Standard methods of Dissolved Solids removal like
ion-exchange are applicable for removal of inorganic compounds; Select Chemical Pre-
treatment (e.g, Fenton's, Alkaline chlorination) methods are available which create
secondary pollution and need to be replaced from sustainability perspective.
Therefore, in order to enhance effectiveness of biodegradation, a pretreatment process is
required which reduces the toxicity level, along with associated recalcitrance of the
wastewater through reduction in concentration of normative constituents for easier
biodegradation. Existing physico-chemical treatment processes generally target reduction
in suspended solids concentration before biological treatment. However, most of the
recalcitrant toxic constituents remain either in dissolved ionic level or very low size range
of suspension which cannot be removed by traditional processes of suspended solids
removal.
It is scientifically known that ultrasonic irradiation of liquids causes acoustic cavitations:
the formation, growth and implosive collapse of bubbles. The cavitation generates sites
of locally high temperatures and pressures for short periods of time, which are
responsible for sonochemical effects.
Therefore chemical effects of ultrasound derive from formation, growth and implosive
collapse of cavitation bubbles in a liquid. Extreme temperatures of several thousand
degrees and pressures of several hundred atmospheres are developed locally within the
bubbles during their collapse with these bubbles serving as hot spot microreactors in an
otherwise cold liquid. It is generally believed that there are three potential sites for
chemical reactions in ultrasonically irradiated aqueous solutions, namely: a) the bubble
itself where pyrolysis of volatile species takes place in the gas phase, while water
decomposes thermally to form hydrogen and hydroxyl radicals, b) the interface between
the bubble and the surrounding liquid where the temperature is lower than that in the
bubble but is still high enough to cause thermal decomposition. Moreover, reactive
radicals formed through water decomposition in the bubble accumulate at high
concentrations in this site and may mediate free radical decomposition reactions, and c)
the solution bulk, where reactions of hydrogen or hydroxyl radicals, which escape from
the interface, may occur.
Organic compounds may be destroyed either at the first two sites upon combined effects
of pyrolytic decomposition and hydroxylation, or in the solution bulk via oxidative
degradation by hydroxyl radicals and hydrogen peroxide. The beneficial effect of
ultrasonic irradiation on the removal of several target compounds from model aqueous
solutions has been reported in literature. Such compounds include, amongst others,
phenol, chlorophenols, nitrophenols, polychlorinated biphenyls, pesticides, polycyclic
aromatic hydrocarbons and surfactants.
As per literature, typical treatment conditions include relatively dilute aqueous solutions
of initial concentrations in the micromolar to millimolar range (such concentrations are
typical of refractory compounds found in natural waters or in already treated effluents),
low to medium ultrasound frequencies from 20 to 500 kHz and irradiation times from
several minutes to several hours.
Coke making process also generates significant quantity of cyanide in the effluent. Coke
making and associated activities consume large amounts of water and resulting water
effluents always contain cyanide that must be treated before disposal to the natural
environment. A large number of procedures have been proposed for treatment of
cyanides: physical (dilution, membranes, hydrolysis/distillation), adsorption (minerals,
activated carbon, resins), complexation (acidification/volatilization, metal addition,
flotation, solvent extraction), and/or chemical (catalytic, electrolytic) methods. There are
several methods in which chemical oxidants (oxygen, ozone, hydrogen peroxide,
chlorine, sodium hypochlorite, and sulphur dioxide) are used, with or without catalysts.
However, both physical and chemical method require recurrent consumables which limits
their use. Therefore a minimally invasive method is required which can reduce
recalcitrance of coke oven wastewater without needing recurrent consumables.
There has been therefore a growing need in the prevailing art of coke oven waste water
treatment to developing an effective pre-treatment process which would work at
dissolved compound level. The system and method of wastewater pre-treatment
according to the present invention, particularly encompassing treatment of coke oven
effluent for driving out recalcitrant toxic constituents including cyanides, would aim to
solve the limitations of the existing physico-chemical treatment processes particularly
eliminating toxic constituents by selectively sonicating the reaction solution without
needing repeated use of any chemicals/consumables.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to providing a system and
method for pre-treatment of coke oven effluent using sonication adapted to
reduce/eliminate the toxic recalcitrant constituents including cyanides from the
wastewater, that remain either in dissolved ionic level or very low size range of
suspension, to achieve reduction in concentration of normative constituents for easier
biodegradation.
A further object of the present invention is thus directed to providing a system and
method for pre-treatment of coke oven effluent using sonication of reaction solution
which would be a minimally invasive method able to reduce recalcitrance of coke oven
wastewater without needing recurrent consumables.
A still further object of the present invention is thus directed to developing a system and
method for pre-treatment of coke oven effluent using sonication of reaction solution so
that the water effluents containing cyanides are efficiently treated before safe disposal to
the natural environment.
A still further object of the present invention is thus directed to developing a system and
method for pre-treatment of coke oven effluent using sonication of reaction solution
wherein recalcitrant toxic constituents are reduced/eliminated based on the principle of
Sonochemical degradation of constituents performed in a batch-type reactor involving
ultrasonic transducer.
A still further object of the present invention is thus directed to developing a system and
method for pre-treatment of effluent of coke making plant using sonication of reaction
solution wherein maximum degradation level would be achieved by selectively adjusting
the pH value of any particular reaction solution.
A still further object of the present invention is thus directed to developing a system and
method for pre-treatment of effluent of coke making plant using sonication of reaction
solution wherein oxidation of target radical is achieved without dosing of any
conventional chemical or coagulant.
A still further object of the present invention is thus directed to developing a system and
method for pre-treatment of effluent of coke making plant using sonication of reaction
solution wherein recirculation rate and level of dissolved oxygen has been experimentally
established to achieve desired maximum degradation of cyanide level and COD level in
effluent.
SUMMARY OF THE INVENTION
The basic aspect of the present invention is thus directed to a process for pre-treating
coke oven effluent comprising subjecting the coke oven effluent to sonication treatment
involving ultrasonic wave under controlled conditions to thereby achieve desired
degradation of cyanide level and /or COD level in the effluent .
A further aspect of the present invention is directed to said process wherein said
sonication treatment is carried out maintaining a pH level in the range of 8.3-8.7.
A still further aspect of the present invention is directed to said process which comprises
controlling the pH level involving appropriate pH regulator preferably including sulphuric
acid or sodium hydroxide solutions.
Further in said process, said sonication treatment was carried out in the temperature
range of 30-40°C .
Importantly also in said process comprises carrying out said sonication maintaining
recirculation rate and level of dissolved oxygen in the level of 40 to 50 litres/hr and 6 to
7 mg/l respectively.
A further aspect of the present invention is directed to said process wherein said
sonication is carried out involving an ultrasonic generator with ultrasonic transducer
operated under controlled operating parameters power supply in the range of 100 to 300
KW preferably about 100 W ( lowest ), frequency in the range of 25 to 40 preferably
about 40 kHz (highest) .
According to yet another aspect of the present invention is directed to said process
wherein said sonication is carried out at:
Frequency/Power - 40 KHz/ 100W
pH - 8.3-8.7
Temp-35-40°C
Conductivity - 200-300 µS
O2 saturation level- 6-7 mg/l
Residence time - 35-40 mins
Advantageously, said process for pre-treating coke oven effluent is carried out free of
any chemical or coagulant dosing.
Yet another aspect of the present invention is directed to a system for carrying out the
process of pre-treating coke oven effluent to thereby achieve desired degradation of
cyanide level and /or COD level in the effluent comprising:
a reactor means for containing the effluent to be treated having a transducer
operatively connected to an ultrasonic generator;
means for maintaining desired pH level, recirculation rate and level of dissolved
oxygen;
said reactor provided with a cooling jacket adapted for supply of coolant for
maintaining desired reaction temperature.
The various other objects and advantages are described in greater details with reference
to the following accompanying non limiting illustrative drawings.
BRIEF DSECRIPTION OF THE ACCOMPANYING FIGURES
Figure l: is the photographic image of the complete experimental set up for sonic pre-
treatment process of coke oven effluent according to the present invention, including the
power source, control panel etc.
Figure 2: is the photographic image of the batch-type reactor for performing
sonochemical degradation experiments for pre-treatment of coke oven effluent according
to the present invention.
Figure 3: is the schematic illustration of the experimental set-up for sonic pre-treatment
process of coke oven effluent according to an embodiment of the present invention
involving ultrasonic generator and ultrasonic transducer with provision for recirculation of
reaction solution and reactor cooling.
Figure 4: is the graphical presentation of the percent degradation cyanide level achieved
by the process according to the present invention for an effluent sample plotted against
exposure time in minutes.
Figure 5: is the graphical presentation of the degradation of COD level in mg/l achieved
by the process according to the present invention for an effluent sample plotted against
exposure time in minutes.
Figure 6: is the graph showing the time vs temperature plot of batch sonication according
to the present invention.
Figure 7: is the graph showing the time vs temperature plot of sonication with
recirculation of reaction solution.
Figure 8: is the graph showing the change in pH with time during sonication.
Figure 9: is the graph showing % CN degradation over time with pH adjustment.
Figure 10: is the graph showing % CN degradation at different dissolved oxygen levels.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS
The present invention is directed to a system and method for pre-treatment of effluent of
coke making plant using sonication of reaction solution which would be able to reduce
recalcitrant constituents of coke oven wastewater without needing recurrent
consumables. The various objects and advantages are described hereunder in details
with the help of following illustrative example:
Example I:
To ascertain the effectiveness of the process, an experimental set up comprising
ultrasonic generator, an ultrasonic transducer, a batch reactor with other supporting
facilities were developed and sonication of effluent samples were performed in the said
reactor with and without recirculation to establish the optimum parameter values which
ensure maximum degradation of cyanide and COD levels.
Accompanying Figure 1 shows a photographic image of the complete experimental set
up for sonic pre-treatment process of coke oven effluent according to the present
invention. Sonochemical degradation experiments were performed in a batch-type
reactor made of stainless steel, at the bottom of which an ultrasonic transducer of rating
power: 100 W, frequency : 40 kHz , is placed. The volume of the reactor is 750 ml and
recirculating water tank volume is 5 litre. The temperature inside the reactor is
controlled/maintained by circulation of cooling water. Accompanying Figure 2 is a
photographic image of the batch-type reactor for performing sonochemical degradation
experiments for pre-treatment of coke oven effluent and accompanying Figure 3 shows
the schematic line diagram of the complete sonicator system used in the experimentation
according to the present invention.
Sonication of the effluent sample has been carried out with the ultrasonic generator.
The degradation efficiency of the sonication process was evaluated for different effluent
samples over selected residence time to determine the optimum values of variable
parameters like the temperature, pH, Dissolved Oxygen level etc. A constant
temperature of 25±2°C is maintained as and when desired during the sonication by
circulating water through a jacket around the sonication cell. However, for the
experimental purpose, considering the actual operating plant conditions, temperature
control has not been implemented and an actual operating temperature regime(30-35°C)
has been established.
The pH value of each reaction solution is adjusted to the desired level using appropriate
concentrations of sulphuric acid or sodium hydroxide solutions during experimental
stages where pH adjustment is required. Based on experiments an optimal pH level
( 8.3-8.5 ) level has been established to achieve maximum degradation. At different time
intervals, samples are withdrawn from the reactor for evaluation. Other operating
conditions and process conditions established are recirculation rate and level of dissolved
oxygen. These parameters have also been studied and best ranges detected which
corresponds to achieving maximum degradation.
Samples periodically drawn from the reactor vessel have been analysed by means of
selective ion analyzer to follow concentration profiles of the original organic substrate
through the marker of cyanide.
The above experimental observations are reflected graphically in the accompanying
Figures 6-10.
Figure 6 is the graph showing the time vs temperature plot of batch sonication according
to the present invention which indicate that during batch operation temperature rises fast
and therefore batch operation to be avoided.
Figure 7 is the graph showing the time vs temperature plot of sonication with
recirculation of reaction solution which indicate that with continuous recirculation
temperature rises slowly and therefore can be controlled and residence time is a
parameter for optimization.
Figure 8 is the graph showing the change in pH with time during sonication which
indicate that sonic treatment shows pH dependent behavior and optimal pH range need
to be ascertained.
Figure 9 is the graph showing % CN degradation over time with pH adjustment which
indicate that cyanide degradation improves when pH is maintained at desired range.
Figure 10 is the graph showing % CN degradation at different dissolved oxygen levels
which indicate that cyanide degradation is a function of oxidation.
Under Optimal process and operating conditions as given below, 50% degradation in
cyanide level and 25% degradation in COD level have been achieved following the
sonication process for pretreatment of coke oven effluent according to the present
invention:
Frequency/Power - 40 KHz/ 100W
pH -8.3-8.7
Temp-35-40°C
Conductivity - 200-300 uS
O2 saturation level- 6-7 mg/l
Residence time - 35-40 minutes
It is thus possible by way of the present invention to providing a system and method for
pre-treatment of coke oven effluent using sonication of reaction solution which would be
able to reduce recalcitrant constituents including cyanides of coke oven wastewater to
desired levels without needing recurrent consumables, in a reliable and cost effective
manner for further processing/safe disposal.
We Claim:
1. A process for pre-treating coke oven effluent comprising subjecting the coke oven
effluent to sonication treatment involving ultrasonic wave under controlled
conditions to thereby achieve desired degradation of cyanide level and /or COD
level in the effluent .
2. A process as claimed in claim 1 wherein during said sonication treatment was
carried out maintaining a pH level in the range of 8.3-8.7.
3. A process as claimed in anyone of claims 1 or 2 comprising controlling the pH
level involving appropriate pH regulator preferably including sulphuric acid or
sodium hydroxide solutions.
4. A process as claimed in anyone of claims 1 to 3 wherein said sonication treatment
was carried out in the temperature range of 30-40°C .
5. A process as claimed in anyone of claims 1 to 4 comprising carrying out said
sonication maintaining recirculation rate and level of dissolved oxygen in the level
of 40 to 50 litres/hr and 6 to 7 mg/l respectively.
6. A process as claimed in anyone of claims 1 to 5 wherein said sonication was
carried out involving an ultrasonic generator with ultrasonic transducer operated
under controlled operating parameters power supply in the range of 100 to 300 W
preferably about 100 W ( lowest level ), frequency in the range of 25 to 40 kHz
preferably about 40 kHz ( highest level ) .
7. A process as claimed in anyone of claims 1 to 6 wherein said sonication is carried
out at:
Frequency/Power - 40 KHz/ 100W
pH - 8.3-8.7
Temp-35-40°C
Conductivity - 200-300 uS
O2 saturation level- 6-7 mg/l
Residence time - 35-40 mins
8. A process as claimed in anyone of claims 1 to 7 which is carried out free of any
chemical or coagulant dosing.
9. A system for carrying out the process of pre-treating coke oven effluent to
thereby achieve desired degradation of cyanide level and /or COD level in the
effluent comprising:
a reactor means for containing the effluent to be treated having a transducer
operatively connected to an ultrasonic generator;
means for maintaining desired pH level, recirculation rate and level of dissolved
oxygen;
said reactor provided with a cooling jacket adapted for supply of coolant for
maintaining desired reaction temperature.
10. A process for pre-treating coke oven effluent and a system for carrying out such
process substantially as hereindescribed and illustrated with reference to the
accompanying figures.

ABSTRACT

The present invention is directed to a process for pre-treatment of coke oven effluent
using sonication of reaction solution adapted to reduce/ eliminate the toxicity level, along
with associated recalcitrance of the wastewater. Importantly, sonication of coke oven
effluent is carried out using an ultrasonic generator and ultrasonic transducer of 100W
power and frequency of 40kHz at a temperature in the range of 35-40°C maintaining pH
level of 8.3-8.7 of influent/reaction solution. Advantageously, the sonic process for
treatment of effluent generated from coke making can reduce recalcitrance without
needing recurrent consumables. The system and method of the pre-treatment is capable
of achieving under optimal operating conditions 50% degradation in cyanide level and
25% degradation in COD level. The process favours oxidation of target radical without
dosing of any conventional chemical or coagulant making it a cost effective, reliable and
efficient process for coke oven wastewater pre-treatment with the possibility of wide
application in industry.