Importance of industrial waste treatment:
• Industries use water that is obtained from the water treatment system for a
variety of purpose such as for manufacturing goods, for heating, for cooling, as
carrier of raw material, as carrier of waste matter, as a solvent etc.
• The resulting water is then classified as waste water.
• The indiscriminate discharge of these waste water into streams, the environment
can render soils sick, pollute the receiving bodies of water, and cause air pollution
by generating obnoxious gases.
• Discharge untreated waste water into the domestic sewer system makes the tasks
of treating domestic sewage a very difficult and costly exercise.
• To prevent any health hazards caused by discharging waste water into the
environment and protect domestic sewage, the waste water must be treated
before discharge.
• Important contaminants of concern in waste water treatment are: suspended
solids, nutrients, priority pollutants, refractory organics, heavy metals, dissolved
inorganic etc
Waste Volume Reduction
Volume of waste generated by an industry can be
reduced by
1. Segregation
2. Conservation
3. Reuse, recycle
4. In plant control measures
5. House keeping
1. Segregation
1. It is cheaper to treat low volume of concentrated
waste water than large volume of dilute waste waters.
2. Cooling water is generally free from pollution.
3. Waste water from process, cooling boiler blow down,
sanitary waste, waste water from canteen and storm
water should be segregated and treated separately.
4. In the process, waste waters from some sections are
stronger than those from the other sections.
5. All these waste waters have to be sewered separately,
if necessary
Segregation(classification of waste)
• If waste are classified so that manufacturing
process water are separated from cooling
waters, the volume of water requiring
intensive treatment may be reduced
considerably.
• Some time it is possible to classify and
separate the process water themselves, so
that only the most polluted ones are treated
and the relatively uncontaminated are
discharged without treatment.
Segregation(classification of waste)
• The three main classes of wastes are
1. Waste from manufacturing process
2. Water used as cooling agents in industrial
process
3. Waste from sanitary use.
2. Conservation of water
There is lot of scope for conservation of water in many industries like
tanneries, textiles, paper mills etc.
In many industries, in summer the consumption of water is less.
In water scarce areas the amount of water is used is less per unit of product
than in industries in other area.
It is therefore possible to reduce water consumption in many industries
without affecting the quality of the product, Important steps included
(a) prevention of running taps, leaks, spills
(b) alarm at overflow position
© spill collection system
(d) preventive maintenance
(e) no overloading
Modification of equipments and process automation has in many cases
minimizes operational errors, reduced spills and reduced waste generation.
3. Reuse and Recycle of water
• First preference is reuse of waste water
without treatment like reuse of textile mill
wash waters.
• Second preference is reuse of waste water
after partial treatment like reuse of paper
machine waste water.
• Third preference is reuse of waste water after
complete treatment.
3. Reuse and Recycle of water
• Improved operations routines like cleaning routines,
analysis and prevention of spills (accidental discharges)
and internal treatment of separated effluent streams
which can result in process water clouser (recycling)
and raw material recycling are important.
• Reclaiming water from sewage is being practiced using
tertiary treatment methods in many countries.
• In many countries water reclaimed from sewage is
being used in industries for various purposes like
cooling, washing etc.
4.In Plant Control Measures
• In a sugar mill, for example, cooling oil used in roller
mills for tandem cooling can be selected in a sump
filled with bagasses, solid waste from the same
industry.
• Bagasse absorbs large quantities of cooling oil which
can later be used in boilers.
• The overflow from evaporators can be collected in a
sump and recycled to clarification section. Press mud
can be uses as a soil conditioner and should not be
allowed in to drains.
• Proper storage of molasses is very important.
Molasses spills have high BOD and COD.
4.In Plant Control Measures
• In a pulp and paper mill, leakages and spillage
of black liiquor can be collected in a sump and
pumped to soda recovery section.
• Chemical and process water recycling will
result in less effluent flow and less discharge
of pollutants.
5.House Keeping
• Preventive maintenance prevention of leaks
and spills, cleaning schedule and clean
environment are important house keeping
measures required to reduce the volume of
waste water generated.
• Good house keeping practices are very
important and involve alteration of existing
system to limit unnecessary generation of
wastes attributable to human intervention.
Strength reduction:
• Waste strength reduction is the second major objective for
the industrial plant. The following are the methods which
help in reducing the strength which include:
• Process change
• Equipment modification
• Segregation of waste
• Equalization
• Proportioning of waste
• Monitoring of waste stream
• Deduction in accidental spills
• By-product recovery.
• Process change The production engineer can be asked to change the
manufacturing process by providing options either by change in
manufacturing intermediate chemicals or change in certain raw materials
or change in some equipment.
• In reducing the strength of waste through process changes, the wastes that
are most troublesome from a pollutant point of view should be considered.
• Equipment modification: The change in equipment can reduce the amount
of contaminant entering the waste stream and thereby reducing the
strength.
• Segregation of waste Segregation of waste reduces the strength and a
difficulty of treating the final waste in an industrial plant. It results into 2
waste:1) one is strong and small in volume 2) Another bigger and more in
volume with almost the same volume as the original unsegregated waste.
• Equalization: Description provided in same module.
Waste Strength Reduction
• Strength of waste water generated from an
industry can be reduced by
1. Equipment change
2. Process change
3. Equalization and Proportioning
4. By product recovery.
Process change
• In reducing the strength of wastes through
process changes, the sanitary Engineer is
concerned with wastes that are most trouble
some from a pollution standpoint.
Equipment Modification
• Changes in equipment can effect a reduction in the
strength of the waste, usually by reducing the
amounts of contaminants entering the waste
stream.
• An outstanding example of waste strength
reduction occurred in dairy industry.
• The new cans were constructed with smooth necks
so that they could be drained faster and more
completely.
• This prevented a large amount of milk waste from
entering streams and sewage plants.
Segregation wastes
• Segregation of wastes reduces the strength and or the
difficulty of treating the final waste from an industrial
plant.
• It usually results in two wastes one strong and small in
volume and the other weaker with almost the same
volume as the orignal unsegregated waste.
• The small volume strong waste can then be handled
with methods specific to the problem it presents.
• In terms of volume reduction alone, a segregation of
cooling waters and storm waters from process waste
will mean a saving in the size of the final treatment
plant.
