In the last few classes we were discussing
about advanced wastewater treatment and we
also started discussing about industrial wastewater
treatment. We have also seen what all are
the major sources of industrial wastewater.
They are originating from either the extraction
or transportation of raw renewable resources
and second one is the wastewater or the waste
generated from the production itself and third
source is when we use the products that itself
can produce some waste and fourth one is ultimate
discard of the products.
For example, if you take the case of a pesticide
the production itself will be generating so
much of waste. The reason is it will be involved
in so many chemical processes and many separation
processes.
Now, coming to the product use we know that
pesticides are sprayed to the plants and other
places so what will happen is a portion of
that one will be entered into the atmosphere
and something will be getting adsorbed on
the plants and a part will be going to the
soil and ultimately this one will be coming
to the surface and ground water sources. Moreover,
it will be getting accumulated in the plant
itself and when we consume it will be entering
in our body. And the last one is when we discard
the used products for example the pesticide
bottles definitely when we throw it away some
pesticide will be there in the bottle so that
also be creating environmental pollution or
environmental degradation. These are the major
sources of industrial pollution and at each
and every stage it will be creating so much
of problems.
We also discussed about the nature or the
types of pollutants present in industries
those include inorganic salts, acids and alkalis,
organic matter, suspended solids, floating
solids and liquids, heated water, color, toxic
chemicals, microorganisms and foam producing
matter. These components present in the wastewater
will be depending upon the process and the
product because for each product the raw material
required is entirely different.
We also discussed about what is the difference
between the industrial and municipal waste
or when we discuss about the wastewater treatment
what is the difference between industrial
wastewater treatment and municipal wastewater
treatment. In municipality wastewater treatment
is taken as a public service because public
will be generating the domestic waste and
that institutes the responsibility to treat
the waste and protect the environment.
But when it comes to the industry what is
happening the major objective of the industry
is to reduce the cost of production because
they have to survive in the market so if the
same quality of the product if they can supply
at a lower cost that will be much more beneficial
for the industry so wastewater treatment or
the waste treatment that cost involved is
not at all going to improve the product's
quality. So, if they wanted to cut down the
product cost one way is to cut down the waste
treatment cost so they will be seeing the
waste treatment as imposed criteria on them
because through the waste treatment they are
not going to achieve much.
Now the concept is entirely changing because
the industry itself is realizing that the
waste whatever they can treat or use that
is the resource conservation because waste
is nothing but the resource out of its place.
Now we will see what all are the different
theories which we can apply for the industrial
wastewater treatment.
The first one is it is always advisable to
minimize the waste generation instead of generate
the waste and treat it. because once you generate
the waste resources whatever is present either
in the raw material form or the product form
it is going out of the place and that itself
will be causing some economic loss and again
if you want to treat the wastewater or the
solid waste to meet the standards definitely
the treatment will be incurring some cause
so it is always advisable to minimize the
waste generation than generate waste and treat
it.
Second one is to minimize the effect of industrial
wastes on receiving streams and treatment
plants. We know that it is impossible to reduce
the wastes to almost zero so there will be
some waste generated in the industries so
it is always better to reduce the volume of
waste so that the effect of wastes on the
environment or the receiving streams will
be minimum.
First we will see how the industry can reduce
the volume of waste. There are different methods
by which the volume of waste generated in
the industry can be reduced.
• classification of wastes
• conservation of wastewater
• changing production to decreasing wastes
• reuse both industrial and municipal wastes
and
• elimination of batch and slug discharges
Now we will discuss each one in detail. First
one is classification of wastes.
Waste classification is nothing but segregation
of manufacturing process wastes from cooling
water. That is the major one taking place
because we know that in industry various processes
are taking place so the water will be used
as processed water, product water, cleaning
water, cooling water etc. So naturally from
the point of view of wastewater management
the waste whatever is coming out of the processed
plants or after the product recovery that
waste will be containing maximum concentration
and maximum number of pollutants but the waste
whatever is coming out after washing the raw
materials or washing the floors or the wastewater
coming out of the cooling plant those wastewater
will not be having much problems because the
concentration of the pollutant will be very
less. So, if you mix all the wastes together
or in the industry all the waste is coming
together and we are collecting them together
then what will happen is you will be getting
a large volume of waste with lot of pollutants
so naturally what will happen is the treatment
cost will be very very high. But if you can
segregate the waste for example you segregate
the waste from manufacturing process from
waters used as cooling agents in industrial
processes and waste from sanitary use we can
reduce the volume of the waste considerably.
The reason is the water used for cooling will
not be containing much of the pollutants so
this water can be reused for many different
purposes. So the total waste whatever is coming
for the treatment will be reduced.
Similarly the waste from sanitary use, we
know what is the characteristics of sanitary
wastewater. So, if you can segregate this
one by giving a lesser extent of treatment
we can reuse it for gardening and other purposes.
So it is always advisable to classify the
wastes so that will be reducing the volume
of the waste that will be reducing the cost
of the wastewater treatment. This is a very
very important point as far as the industrial
wastewater treatment is concerned, the segregation
of waste or segregation of the process and
depending upon the wastewater characteristics
and its extent of pollution we classify the
waste accordingly.
Second one is conservation of water. Whenever
we talk about industrial pollution water conserved
is water saved. The thing is it will be saving
the wastewater treatment cost as well as the
water charges so how can we do the conservation
in an industry. Conservation begins when the
industry changes from an open to a closed
system. So, what most of the industries do
is that if the water is available in plenty
the water used for once will be just discharged
out so naturally volume of the wastewater
coming out of the industrial process will
be very very high and naturally the treatment
cost will be high. But if the industry can
segregate the wastewater and reuse a portion
of that wastewater for other purposes then
definitely the volume of the waste generated
can be reduced.
Some of the examples I have given here. One
example is recycling of the white water in
a paper mill.
What is this white water? It is nothing but
the water passing through a wire screen upon
which paper is formed. This water will not
be having much of the pollutants so the industry
can reuse this water much easily. Similarly
the cooling water, the only pollutant coming
out of the cooling water is the high temperature
and another one is because of the high temperature
what will happen some evaporation losses will
be there so the concentration of the solids
will be getting increased because of the evaporation
that is the only pollution present in cooling
water. So, if you can dissipate the heat energy
then we can recycle the cooling water so many
times. The only thing is whatever is the evaporation
loss if we can make it up with fresh water
the solid concentration will not be increasing
drastically and it will not be causing any
problem for the heat exchanges.
Now coming to the textile mills it is shown
that if the water availability is not there
if water is available cheaply then enforcing
conservation is difficult and in textile mills
it is shown that whenever there was a water
scarcity the total use of water has come down
to fifty percentage. That means if they do
the process properly whatever the effluent
coming down that itself can be reduced to
almost fifty percentage. But this conservation
is very very difficult if the water is available
cheaply because people will not be thinking
about the reuse of the water at all.
Now the third one is changing the production
to decrease waste. By changing the process
itself we can decrease the waste. This is
an effective method but it is difficult to
put in practice because everybody resists
change. So how can we do this one?
For example, if you have a wet process existing
in your industry so if you change from the
wet process to a dry process definitely the
water consumption will be less and the waste
generated will be also less. Then another
one is changing the raw materials itself.
Some raw materials require lot of water so
if we can replace such raw materials with
some other raw materials then also we can
reduce the water consumption very easily.
But as I have already mentioned this is very
difficult to practice in industries because
always the change is difficult unless they
think by themselves. So, if we change this
one it is going to bring us so much of profit
otherwise it is very very difficult to implement
the change in an existing industry. The other
option is reusing both industrial and municipal
effluents for raw water supplies. As I have
already mentioned it is applicable only where
water scarcity is existing.
For domestic wastewater reuse is the most
reliable source because we know that the industrial
processes will be varying day by day. Because
depending upon the production cycle or production
pattern the quantity and the quality of the
wastewater that will be coming will be varying.
So if you want to reuse the industrial wastewater
the processed wastewater as such the source
may not be reliable. But in most of the industries
what is happening they will be having their
own estate where all the employees are staying
so if you want to reuse the water it is always
advisable to reuse the domestic wastewater
because we know that the quantity of that
wastewater will be remaining almost a constant
and we know what is the fluctuations and variations
happening and moreover characteristics of
the wastewater is also well known and it is
not going to change drastically. So it is
always better to rely on the domestic wastewater
source for recycling purpose. Many industries
hesitate to reuse the wastewater. The reasons
are as follows:
First one is the lack of adequate information
on part of industrial managers because they
won't be having enough information. What are
the advantages they are going to get if they
can reuse the wastewater so it is one major
problem. Second one is difficulty of negotiating
contracts satisfactory to both municipalities
and industrial users. In many places the municipalities
are doing water treatment, they are putting
so much effort and money to treat the municipal
wastewater or municipal sewage and they usually
supply this treated wastewater to the industries.
But in most of the cases what is happening
is it is difficult to come on satisfactory
contracts with the municipality and the industry
that is another problem.
The third one is technical problems such as
hardness; color etc because if you reuse the
water it will be having many pollutants that
will adversely affect the industrial processes.
This is another problem.
Another issue is aesthetic reluctance to accept
effluents as a potential source of water for
any purpose because after treatment also we
will be having some color, some odor etc so
people will have some reluctance to reuse
the water.
Another thing is irregular operations of treatment
plants and slug discharges from industries
affect the treated water quality. We know
that the quality of wastewater whatever is
coming out of the industries is not a constant
one and we are designing our treatment plants
based upon the average characteristics and
average flow of the wastewater. So what will
happen is if the industry is not operating
uniformly or if the wastewater characteristics
and the quantity varies drastically the treatment
plants will not be achieving the desired treatment
efficiency so definitely the treated water
whatever is coming out will not be satisfying
the requirements for the purpose of reuse,
that is another problem.
But all the above the resistance to change
in practice is the most severe problem because
they are using fresh water so if there should
be some changes in the process and the industrial
layout or industrial process itself that requires
some changes or resistance to change in practice
is the most important problem or the biggest
problem. As we are telling we can reuse the
treated water what is the difference between
sewage plant effluent and fresh water. Definitely
the industries are bothered about this one.
The treated effluents will be having high
color and higher nitrogen content, high BOD
and high total dissolve solids and the presence
of phosphate etc due to detergents. These
components will be present so we should be
careful when we use the treated effluents
for the processes as it may adversely affect
the product.
How can the industry do the conservation of
water?
They can conserve water by following these
steps as listed below.
First one is install meters in each department
to make operators cost and quantity conscious.
So, if you know that what is the amount of
water we are using then definitely they will
be having some feeling when they waste the
water. Second one is regulate pressure to
prevent needless waste. If the water supply
system is having high pressure so little opening
can waste lot of water so regulate the pressure
to prevent needless waste. Third one is use
thermostatic control to save water and increase
efficiency. Fourth one is installing automatic
valves to prevent water shortage and the next
one is use spring closing sanitary fixtures
to prevent constant or intermittent flow of
unused water. Sixth one is De-scale heat exchangers
so that cooling water quality quantity can
be reduced because if the heat exchangers
are not working properly then the industry
might need more and more cooling water. The
seventh one is insulate pipes so that water
is not left running to get it cold or hot.
What will happen during summer times?
Naturally in the overhead tank will be getting
heated up. If some people want to wash their
face or something like that they will be coming
and opening the tub so immediately whatever
water is coming from the overhead tank will
be very hot. Therefore, what they will do
is they will allow the water to flow for sometime
so that they will get some cold water. Similarly
in winter the case is the reverse. Initially
whatever water is coming will be very very
cold and after sometime it will become relatively
cold. So in that process we will be wasting
lot of water so if you can insulate the pipe
then we can avoid such water loss.
The eighth point is instigate leak surveys
as a routine measure. In industries lot of
pipe networks are there so unless we easily
locate the leaking points lot of water will
be getting lost just like that. Thus, instigate
leak surveys as a routine measure then use
centralized control to prevent wastages from
improper connections, re-circulate cooling
water, reuse water, use high pressure, low-volume
rinse for more efficiency and the last one
is recondition wastewater.
These are the ways by which the industry can
conserve the water use.
Once you conserve the water the water is saved
so naturally the wastewater volume whatever
is coming out of the industry will be reducing
drastically so definitely the treatment cost
will be reducing and its adverse effect on
the environment also will be reducing.
The last one is elimination of batch or slug
discharges of processed water. So first we
will see what this slug discharge is. In a
wet manufacturing of a product one or more
steps may be repeated. The production of significantly
higher strength and high volume waste is very
common in such cases. If this waste is discharged
in a short period of time that is know as
slug discharge.
I will explain once again.
In wet manufacturing process, wet manufacturing
process means the raw materials are coming
in contact with water so the process is wet.
Most of the processes will be operated in
batch mode. So sometimes by some mistake the
mixing may not be proper or whatever quantity
we have added to the raw material may not
be proper so definitely whatever product is
generated by the process will not be meeting
the required standards. Hence after they realize
that something has gone wrong they will be
discharging that entire batch of chemicals
and the water to the effluent discharged pipeline
so that will be increasing the volume of wastewater
and all the chemicals or all the raw materials
present in the process which are intended
to convert to product so everything will become
a waste.
If the industry discharges it immediately
then it is coming as a slug discharge. So
it is always advisable to eliminate such slug
discharges because if you go for this slug
discharge definitely the volume of the wastewater
will be increasing and the strength of the
wastewater will be increasing moreover you
are losing so much of raw materials and that
will be causing loss to the industry and sometimes
it will be unavoidable.
So how can we reduce the effect of such slug
discharges?
One is to alter the process and the other
one is retention of slug wastes in holding
tanks and allow to flow continuously and uniformly
over an extended period. if you allow the
slug discharge as such to the effluent stream
then the volume will be increasing drastically
for a short period of time and the concentration
will be very very high so that will be affecting
the treatment unit. So what we can do is hold
it for sometime and allow it to go out uniformly
at a constant rate so that the volume variation
and the strength variation can be reduced.
Till now we were discussing about how the
industry can reduce the volume of the wastewater.
Not only the volume but also the strength
of the wastewater is very very important.
For example, if you have a small volume of
water but it is having such a high concentration
of pollutants then in such a case the treatment
will be very very difficult and the cost involved
also will be very very high. So apart from
reducing the volume of the wastewater it is
essential to reduce the strength of wastewater
because the strength of wastewater if we can
reduce the pollutant whatever is coming in
the wastewater is nothing but the raw materials
used in the production or the products whatever
is generated which was not able to recover
from the system so these are coming as waste.
So if we can reduce the strength of the wastewater
in the industry itself then industry is saving
either the raw materials or the products so
it is very very essential.
Now we will see how the industry can practice
this strength reduction. This is what I have
already mentioned. Waste generated is nothing
but the resources wasted.
So the strength of wastewater in the industry
can be reduced by following methods:
• process change
• equipment modifications
• segregation of wastes
• Equalization of wastes
• By-product recovery
• proportioning wastes
• monitoring waste streams
We will see one by one in detail. First one
is process change.
How can a process change reduce the strength
of wastewater?
We will take the case of tanning or tanneries.
We know what a tannery is. This is the treatment
used for leather manufacturing. In the tannery
they will be using different types of chemicals.
So if we can replace the chemicals like lime
and sulfides with other chemicals like amines
and enzymes the strength of the wastewater
can be reduced drastically thus the amount
of lime and sulfides used in tanneries are
very very high. But if you can replace this
lime and sulfide by amines and enzymes the
quantity required will be very very less.
The only thing is the raw material cost will
be high. But if the industry is concerned
about the environmental safety or concerned
about the environment so they don't mind changing
the process.
Similarly if you talk about the textile industry
they use lot of starch. So if you can replace
the starch with substituted cellulosic compounds
like carboxy methyl cellulose the strength
of the wastewater can be reduced drastically
because whatever starch that is used in the
textile industry only a very small portion
is being used by the product and all the remaining
is coming out as the waste, that will be increasing
the COD or Chemical Oxygen Demand of the waste
drastically. But if you can remove the starch
with this carboxy methyl cellulose the strength
of the wastewater or the COD of the wastewater
can be reduced drastically. These are other
examples of process change.
Coming to the metal plating industry this
is another large group of industries which
cause lot of pollution, change copper cyanate
solution to copper acid solution because in
most of the industries cyanide is used as
a complexing agent. If cyanide is present
the copper solubility can be increased drastically
because the cyanide will be making a complex
with copper like this copper cyanate complex.
So instead of this one if you can make acid
copper solutions at acidic pH all the metals
will be having high solubility. So, with the
copper if you make acidic solution definitely
it will be giving you high solubility and
reduce the strength of waste.
Similarly copper CN2 strike can be replaced
with nickel strike that is another way. Another
one is if you are using a molten cyanide bath
it can be replaced by a carbo-nitriding furnace
because we know that if cyanide is present
in the wastewater the treatment will be very
very difficult. These are some of the process
modifications and I have listed some more
here.
Use shot blast instead of H2SO4 in pickling
of steel and substitute phosphoric acid for
sulphuric acid in pickling because if sulphuric
acid is there we know that it is a very very
strong acid so if you can replace it with
phosphoric acid the treatment will be much
easier. Use alkaline de-rusters that means
if you want to remove the dust go for alkaline
de-rusters instead of acid solution and another
one is replace soluble oils with cold cleaners.
If you see the industrial processes we can
write hundreds of replacements as these. By
using this type of replacement we can reduce
the strength of the wastewater considerably.
Now we will see the next point. If you want
to reduce the strength of the wastewater it
can be achieved by equipment modification.
Change in the equipment can reduce the strength
of the wastewater. I can give a very simple
example.
For example, let us take the dairy industry.
In dairy industry we know that the milk is
stored in various types of containers. So
instead of a rough surface container if you
make the container design in such a way that
everything is very smooth then whatever milk
is there in the container when we empty it
everything will be coming to the tank and
whatever milk left over in the container will
be very very less and after emptying of the
container the container will be going for
cleaning so if some milk is left over in the
container then definitely the washed water
will be having lot of milk definitely the
strength of the waste will be very high. But
if you make a slight variation in the design
of that container the waste strength can be
reduced drastically.
Similarly there are different ways. By changing
the equipment or by modifying the equipment
the strength of the wastewater can be reduced.
Third one is segregation of wastes. This we
have already seen when we were discussing
the volume reduction. So segregation also
helps to reduce the strength and/or the difficulty
of treating final waste from industry.
What will happen if we mix up all the waste
together? For example, if you mix up the electro
plating wastewater, for example copper cyanide
with a domestic wastewater what will happen
is we cannot go for biological treatment process
immediately because cyanide is very very toxic
and copper is very toxic and when we mix it
with organic matter that also will be forming
complexes with this heavy metal so it is always
advisable to segregate the waste so that will
be reducing the strength of the waste as well
as it will be increasing the treatability
of the waste. When we mix all process waste
together the waste will become so complex.
But if you can segregate the waste separately
the treatment will be much easier. Industrial
waste can be classified into strong wastes
in small volumes, weaker wastes in large volumes.
For example, we can take the case of textile
industry, metal plating industry etc.
In metal plating industry the plating time,
whatever waste is coming out will be very
very strong but the waste coming from the
cleaning time will be relatively weaker. So
it we can segregate this waste then the volume
of waste can be reduced as well as the strength
of the waste can be reduced.
Next one is equalization of wastes. Sometimes
the waste will be having high pollutant concentration
and at other times it will be having low pollutant
concentration. If we can equalize the waste
we may not be reducing the overall strength
of the waste but for a particular time if
you see we will not be getting a very high
strength wastewater we will be equalizing
the effluent. So, equalization of the waste
also can reduce the strength of the wastewater.
It will not be reducing the overall quantity
of the pollutant present in the system but
at a particular time if you take the concentration
of the pollutant will be reducing.
Next one is by-product recovery. We have already
seen that waste is nothing but resources out
of its work place. So if we can replace the
resources into its original place that is
nothing but waste treatment or resource recovery.
If you can recover the resource so definitely
the strength of the waste will be decreasing.
Waste is nothing but resources out of place.
If we can put the resources back waste minimization
and economic benefits can be achieved.
For example, in the tanneries they will be
using lot of chromium for the tanning purpose.
So if we can recover this chromium because
you know that this chromium is a toxic heavy
metal we are not supposed to discharge chromium
containing wastewater to land or existing
water bodies the minimum discharge level is
0.5 milligrams per liter or so. So if you
can recover this chromium using lime or magnesium
hydroxide then the strength of the wastewater
will be reducing moreover the chromium thus
recovered can be reused for the process again.
That will be giving some economical gain also.
The next one is proportioning of wastes.
• Proportioning the discharge of concentrated
wastes to the mainstream
• Especially for toxic hazardous wastes
• To prevent the adverse effect on treatment
plants
Sometimes what will happen is some processes
will be generating lot of toxic chemicals
so if you allow that waste immediately to
the treatment plant then the toxic concentration
will be raising in the treatment plant and
if it is a biological system definitely the
system will be getting affected.
In chemical system the process will not be
getting affected but the efficiency of the
system will be coming down. But in biological
system the microbes as such will be affected
and to regain the original efficiency it will
be taking much time. So what we can do is
store it and proportion it so that the strength
of that particular pollutant will be constant
throughout and it will not be creating as
much adverse effect as if it is discharged
once for all.
The next one is monitoring of waste streams.
It is always advisable to go for remote sensing
devices for the operator. Sometimes we know
that the waste quantity will be very high
or the strength will be very high so by seeing
the characteristics of the wastewater the
operator can either stop the waste flow or
reduce the volume of flow or redirect the
flow depending upon the characteristics.
Therefore, it is always advisable to have
a remote sensing device with the operator
of the wastewater treatment plant. In industries
accidental spills is a common phenomena. It
is always advisable to avoid these accidental
spills. How can we avoid such things?
Make certain that all pipelines and valves
in the plant are clearly identified. If some
spillage is taking place or some leak is taking
place then if we know which valve that is
then we can just close it immediately. By
doing this one can avoid such type of an incident.
Second one is allow only certain designated
and knowledgeable persons to operate the valves.
Third one is install indicators and warning
systems and provision for detention of spilled
wastewater in holding basins or lagoons. Thus,
even if the spill is taking place if you have
proper provision so that the spill will not
be getting spread then the accident or the
concentration of the waste can be reduced.
Another one is monitor effluent quality and
quantity. The last one is establish a regular
maintenance program because most of the time
the accidental spills, leaks etc happens because
of improper maintenance. So, if we can establish
a regular maintenance program most of these
incidents can be avoided.
The third important point in industrial wastewater
treatment is the neutralization. We have seen
that industry can go for volume reduction
strength reduction. But we know that different
processes will be using different types of
chemicals and they will be using acids and
alkalis in different processes.
Therefore if industrial wastewater is coming
and if you want to discharge it to the municipal
wastewater treatment system and if it is an
acidic waste of alkaline waste it will be
having adverse effect on the treatment system.
So before sending it to the treatment system
it is always advisable to neutralize the waste.
How can they neutralize the thing? If the
industry is using acid waste in some process
and alkali waste in some other process if
they can mix it properly that itself will
be taking care of the neutralization.
What is the purpose of this neutralization?
Excessive acid or alkaline wastes should not
be discharged without treatment. Methods of
treatment include:
• Mixing wastes so that the next effect
is a neutral pH
• Passing acid wastes through beds of limestone
so that it will be getting neutralized
• Mixing acid wastes with lime slurries
or
• Adding proper quantities of sodium hydroxide
or sodium carbonate to acid wastes so that
it will be getting neutralized or
• Blowing waste boiler flue gas through
alkaline wastes. The waste boiler flue gas
will be containing lot of carbon dioxide.
When carbon dioxide mixes with water it will
be generating carbonic acid and that carbonic
acid will be reacting with the alkaline waste
and it will be neutralizing it
• Adding compressed carbon dioxide to alkaline
wastes
These are the various methods that can be
practiced to neutralize waste. These are the
chemical reactions involved .
If sulphuric acid is there if you add calcium
carbonate or pass this acid waste through
limestone then the calcium sulphate and carbonic
acid will be formed depending upon the pH.
If the pH is low carbon dioxide will be escaping
to the system otherwise it will be getting
converted to bicarbonate and carbonate.
This is the other reaction . Similarly, if
sodium hydroxide is there if you pass carbon
dioxide it will be forming sodium carbonate
and if you have acid waste and alkali waste
if you combine both of them then you will
be getting a salt and water.
This is another process . We have seen that
neutralization can be achieved by adding either
alkali or acid or if you have acid waste and
alkali waste mix then it properly according
to the proportion so that it will be getting
neutralized.
We have discussed in detail that the industrial
process will not be uniform throughout so
definitely the waste quantity and quality
will be varying with respect to time. But
whenever we discuss about or talk about the
treatment plant we always design it for the
average wastewater characteristics both in
quality and quantity. So if you want to treat
the industrial wastewater what should we do
is we should have some equalization mechanism
by which you can maintain the quality and
quantity of the wastewater almost uniform
before sending it to the treatment plant.
That is the purpose of this equalization and
proportioning.
Equalization is retaining wastes in a basin
so that the effluent discharge is fairly uniform
in its characteristics. Once again, equalization
is the retaining of wastes in a basin so that
the effluent discharge is fairly uniform in
its characteristics. So, apart from holding
because only holding will be giving you a
proper equalization, proper mixing is also
essential because some wastes will be containing
certain chemicals and other wastes will be
having something else so if you want to have
a uniform nature we have to mix it properly.
This is the graph showing how the pH variation
is in a plating bath waste when we average
it for twenty four hours, eight hours and
instantaneous discharge.
If it is an instantaneous discharge then pH
variation is like this. It is going up and
going up and down like this . Sometimes the
pH is up to 10 and sometimes it will be coming
below two so that is the instantaneous discharge.
But if you take eight hour retention then
the thing is like this. This red line shows
that the variation is somewhat damped but
even then you can see the peaks. But if you
can hold it for twenty four hours you will
be getting almost uniform flow characteristics.
So this is the purpose of equalization chamber.
I told you that not only holding but mixing
also is essential. Mixing can be achieved
by
• proper distribution and baffling
• mechanical agitation
• aeration and
• combination of all the three
This is a system of baffles. the baffles is
put over and under baffles so that the flow
will be going like this from underneath then
it will be overflowing like this so proper
mixing will be taking place. this is another
type of mixing paddle and motor assembly,
whatever we do in coagulation flocculation
we have seen in detail that type of mixing
also can be practiced. We have seen how we
can reduce the volume strength and what is
the purpose of neutralization and equalization.
Once this is done we will know the characteristics
of the waste and quantity of the waste. We
have also seen the entire treatment options
that are available. Depending upon the waste
characteristics we can go for the physiochemical
processes or biological process or even advanced
wastewater treatment to meet the effluent
discharge standards. Any of these treatments
namely the physiochemical processes, biological
processes or advanced wastewater treatment
can be employed for industrial wastewater
treatment depending upon the characteristics
of the wastewater.
Now we will be discussing about another important
aspect about the industrial waste management.
Nowadays this concept is coming up the industrial
complexing for zero pollution attainment.
This is an important concept.
Here what we are doing is make environmentally
balanced industrial complexes.
So first we will see what is an environmentally
balanced industrial complexes. It is a selective
collection of compatible industrial plants
located together in one area to minimize both
environmental impact and industrial production
cost.
Once again, an environmentally balanced industrial
complex is a selective collection of compatible
industrial plants located together in one
area to minimize both environmental impact
and industrial production cost. How can we
achieve that one? We have to use raw materials.
In any industry there will be raw materials,
there will be products and by-products. the
waste or the by-products of one industry is
being used as a raw material for another industry
or the wastewater of one industry is being
used as the water for other industry then
what will happen is we can reduce the waste
treatment and we can reduce the cost of the
raw material that is the basic concept of
this environmentally balanced industrial complexes.
The objective of complexes is to reduce the
environmental impact of the industries and
to reduce the cost. So if you want to meet
the objective this can be met by utilizing
the waste materials of one plant as the raw
materials for another with a minimum of transportation,
storage and raw material preparation. Because
if we can keep the industries in the same
place what will happen is the raw materials
of one industry are the waste materials from
one industry so we can reduce the transportation
cost, storage cost and raw material preparation
cost and when a manufacturing plant neither
treats its wastes nor stores or pretreats
certain of its raw material the overall production
cost will reduce significantly.
So this is the advantage of these environmentally
balanced industrial complexes. Neither they
have to treat the waste nor they have to store
it or they have to pretreat the raw material
so definitely the cost of production will
be reducing so the benefit will be increasing.
Industrial complex principles and concerns:
Pollution control cost will be very less compared
to overall production cost because whatever
waste is generated is used by other industries.
But if you see each industry separately the
pollution control cost will be very very high.
What will happen? The industry may think that
why should I go for producing this product
and incur loss so it is better to stop that
one. But if you have an environmentally balanced
industrial complex what will happen is this
type of a thought will not come because the
waste generated will be used by our industry
as its resources.
So, how can we take care of these industrial
complexes? By proper environmental management
the decision can be reversed. Whenever we
go for the industrial complexes it is advisable
to have this large water consuming industries
like tanneries, fertilizer industry etc because
these industries will be having large water
treatment costs. But if this water can be
utilized by other industries definitely the
cost of production will be coming down drastically.
But when we talk about establishing this environmentally
balanced industrial complexes their will be
some difficulties. The most important one
is compatibility because we have to select
the industries in such a way that one raw
material is used by other industry's raw material
which is known as the compatibility.
Then we have to think about the labor availability,
marketing of the products and what are the
taxes involved and optimal mass balance. We
have to select the industry in such a way
that all the waste generated by one industry
is used as the raw material by other industry
so optimal mass balance is also very very
essential. I will give one or two examples
of these complexes. First we will discuss
about a sugarcane industry.
This is a sugarcane refinery so you want to
have water, you want to have wet cane and
we want to have lime and lot of power is essential
so everything is coming here this is the sugarcane
refinery. It is having a capacity of thousand
tons per day. So, first one is we will be
getting refined sugar. If we use thousand
tons of sugarcane we will be getting around
hundred tons of sugar so this is your product
one. As a result what will happen is you will
be having so much of waste; one is bagasse
and another one is cachaca, this is nothing
but the insoluble sugar in the lime, this
one will be going for the anaerobic digestion,
this is one of the treatment. Here lot of
gas will be generated. This can be used by
a boiler for the generation of power and from
the anaerobic digestion the filtered cake
will be coming. That means the stabilized
sludge which can be used for agriculture purpose
and whatever filtrate is there will be the
liquid waste that will be going back to this
system again.
Here we can see that the bagasse is coming
and from here it is going to another boiler,
this bagasse can be utilized by that boiler
and lot of energy is recovered. Here we can
see that 1990 MKJ heat energy is released
and here again in this agricultural area we
are using this anaerobic sludge as the manure
and whatever be the area here it will be giving
so much of sugarcane so that can be used for
the alcohol fermentation. The same thing can
be used as sugarcane for the sugar industry.
Therefore as we can see here nothing is getting
wasted, whatever is the raw material or the
waste materials coming out of this one is
being used by other processes and the resources
or the products are generated. This is an
example of environmentally balanced industrial
complex. Similarly, for a fertilizer plant
we can make the same type of an arrangement.
Similarly we can show many examples of these
environmentally balanced industrial complexes
so that the total waste production will be
almost zero. That is the concept of this zero
polluting industrial complexes. Another important
point we have to consider is the common effluent
treatment plants whenever we talk about the
industries. Then the main objective is to
reduce the treatment cost to be borne by an
industrial unit to a minimum while protecting
the water environment to a maximum.
It is because whenever we talk about the small
scale industryfor them it is very very difficult
to have their own treatment plants, the cost
involved will be so high and their scale of
production is small. So when they have the
waste treatment plant the overall product
cost will be increasing too much and they
will not be able to survive in the market.
In such cases these common effluent treatment
plants are very very useful. Here what they
do is all the waste from various industries
will be collected and treated centrally.
What all are the advantages?
It will be reducing the capital and operating
cost and advantage of having trained personnel
to take care of the unit, avoiding land constraints
in individual industries because if individual
industries go for separate treatment plants
lot of land requirement is there so that can
be avoided and so much of domestic wastewater
will be coming to such plants so this domestic
wastewater can contribute nutrients and dilution
potential making an industrial wastewater
more amenable to degradation. This is another
advantage and the last one is domestic wastewater
provide a continual seed source to the biological
unit
This is because most of the industrial wastewater
will be containing hazardous waste that will
be adversely affecting the biological treatment
system. But if we can supply domestic wastewater
then the microorganism will be continuously
getting seeded so that the system efficiency
will be more.
Now, if you want to go for such type of a
treatment system, common effluent treatment
plants, who will be paying for that because
many industries are contributing to the pollution
to that treatment plant so who will be taking
care of that one. For example, in a municipal
wastewater treatment plant the residents of
the municipality will be paying the taxes
so they will be paying for the treatment plant
also. But when we are putting up a Common
Effluent Treatment Plant that will be bearing
the cost, definitely the industry has to bear
the cost. But many industries are involved;
many types of wastes are coming so how can
we proportion the cost of this treatment.
There are various methods for that one. One
is equitable sharing of the financial burden.
If many industries are present each industry
will be sharing equal amount. For example,
if the waste generated by each industry is
of same quantity and quality this is acceptable.
But if the quantity generated by various industries
is different then nobody will be accepting
this method.
In such cases we can go for quantity method.
This is applicable only for low strength wastewater.
So we will be charging the industry, the industry
which is producing maximum waste have to pay
more and the industry which is producing low
volume have to pay less. So based on the quantity
of production we can proportion the financial
burden. In certain cases what will happen
is some industry will be producing low volume
but the strength of the waste will be very
very high and vice versa. In such cases we
how to go for quantity quality method both
quality and quantity are taken into account
then only it will be possible.
In most of the cases this is what is practiced.
Both quantity and quality are taken care and
all the CETPs Common Effluent Treatment Plants
are based on PPP which is Polluters Pay Policy.
Whoever is generating pollution will have
to pay for that one. Here we have seen that
based on the quality and quantity we have
to proportionate the financial burden.
How can we find out the quality? The term
used for the load of industrial wastewater
is population equivalent so we know the total
waste whatever is coming into the system so
we will be converting it into population equivalents.
We know that what is the waste generated by
a single person whenever we talk about the
municipal wastewater treatment plants and
so on so industrial waste also will be converted
in population equivalents so based on that
one we can charge the industries.
Now we will see what all are the reference
books we have used for this course.
One is Peavy, H. S. Rowe and Tchobanoglous.
This is environmental engineering, TATA McGraw
- Hill edition.
Second one is Metcalf and Eddy, Wastewater
Engineering, treatment and reuse.
So this will be giving you the details about
the wastewater treatment process and this
will give overall picture of environmental
engineering that means water, wastewater etc.
Nemerow, N.L and Dasgupta, A is industrial
hazardous wastewater treatment.
So whatever I was talking in the last few
classes is covered in this textbook and another
one is Fair Geer and Okun Water and Wastewater
Engineering so this is very useful for water
treatment and another one is Weber Physiochemical
processes for water quality control, this
is John Wiley and Sons publication. This will
be giving you the details of the process mechanism,
each and every process involved, what are
the physiochemical processes, whatever we
are using in water and wastewater treatment.
It gives a good picture about the process
mechanisms or the concepts. Another one is
Manual on Water Supply and Treatment, Ministry
of Urban Development, New Delhi.
This manual gives you water distribution network
designs and water treatments unit designs
and all related aspects of water supply and
treatment. It is good for design purposes.
And the other one is Manual on Sewerage and
Sewage Treatment, this is also Ministry of
Urban Development, New Delhi. This gives you
the details of sewerage systems and sewage
treatment plants design.
