WASTE WATER ENGINEERING : PART 1
QUALITY OF WASTE WATER/SEWAGE
Wastewater
is the combination of water and liquid originated from the different
activities.
Sewage can
be classified into three types
1- Domestic Sewage
2- Industrial Sewage
3- Drainage discharge/Storm water
/Drainage Sewage
DOMESTIC SEWAGE
It is mixer of water and liquids originated from domestic activities
like cocking , bathing , washing etc.
INDUSTRIAL SEWAGE
Waste waster originated from industrial activities like manufacturing is
termed as industrial sewage.
Combination
of domestic and industrial sewage is termed as the sanitary sewage.
Combination
of kitchen and bathroom waste is termed as the sullege
STORMWATER
It is
sewage that is originated due to rainstorms water.
SEWERS:-
Pipes are used
for transporting sewage from one point to another are called sewers.
SEWERAGE SYSTEM
It is the
method of collection ,treatment and disposal of the treated sewage.
Sewerage
system are generally of three types:-
1- Separate sewerage system
2- Combined sewerage system
3- Partially separate system
PHYSICAL WASTEWATER PARAMETERS
All physical water quality parameters are
applicable here also such as Total solids , Dissolved solids , Suspended
solids.
(a) 80% of water supplies are goes into
the sewers
(b) Sewage consist of both organic and
Inorganic particles.
(c) Organic particles are decomposed by
the chemicals and the biological action
(d) Organic matter are decomposed by
biological action is known as the Biodegradable organic matter.
(e) This biological decomposition can be
carried out either in the presence or absence of oxygen. If it is carried out in
the presence of O2 is termed as aerobic and if carried out in absence of O2 are
called anaerobic .
The method of treatment for employed for sewage
depends on the condition whether it is carried out anaerobically or aerobically.
Methods based on the aerobic condition
-
TRICKLING
FILTER
-
ACTIVATED
SLUDGE PROCESS
-
OXIDATION
POND
-
ROTATIMG
BIOLOGICAL CONTRACTOR
Methods based on the anaerobic condition:-
-
Septic
tank
- Emhoff
tank
-
Anaerobic
lagoons
-
Upflow
anaerobic sludge blanked reactor (UASBR)
Sewage consist of more than 99.9% of water and less .1% of solids .
SETTLABLE SOLIDS :-
The solids settled at the base of the Emhoff cone when sewage is allowed
to stand in this cone for 120 minutes are termed as the settleable solids.
CHEMICAL WASTE WATER QUALITY PARAMETERS
1- Dissolved oxygen (DO)
At a particular temperature max quality of o2
present in water is termed as dissolved oxygen .
Any efficiency observed in the value of DO
indicates the presence of biological activity in water.
A minimum of four DO is required at all the
temperature for survival of fishes in water. The DO in water can be computed
by the Winkler’s method.
CHEMICAL OXYGEN DEMAND
It is the amount of oxygen required to
decompose both biodegradable and non-biodegradable organic matter.
It can be calculated by adding potassium dichromate K2Cr2O7 along with sulphuric acid and noting down the amount of oxygen consumed for decomposition of organic matter.
NOTE
As potassium dichromate is strong oxidizing
agent it carries out decomposition of some inorganic matter present in water
,hence it is also known as dichromate demand.
THEORETICAL OXYGEN DEMAND
If exact formula and concentration of organic
matter present in waste water is known then quality of oxygen demand required
for decomposition of organic matter can be computed theoretically and is termed
as theoretical oxygen demand.
TOTAL ORGANIC CARBON
Total organic carbon is just another method for
expressing organic matter present in the water in form of its carbon content
BIOLOGICAL OXYGEN DEMAND
It is the amount of oxygen required by the
microorganism to carry out the decomposition of biodegradable organic matter
present in wastewater.
Biological oxygen demand of water during 5 days
at 20 degree celcius as taken as the standard
biological oxygen demand and is approximately equals to 68% of ultimate
Biological oxygen demand.
Important
notes
Waste water
sample consist different types of organic matter , hence required different
microorganism.
Micro
organism obtain carbon for their growth. Micro organism which utilizes organic
carbon for their growth are heterotrophs .
Conversion of
carbon from carbon dioxide through cellular carbon required reduction process ,
hence autotrophic micro organism utilizes more of their energy to extent
carbon from carbon dioxide resulting into lower cell moss growth.
Nitrogen BOD
is obtained by Autotrophs while the biochemical oxygen demand is
by heterotrophs.
For municipal
sewage biochemical oxygen demand is in
the range at 100-500 Mg/L.
THE RATIO OF BOD AND COD
This BOD/COD
ratio represents quality of sewage entering in the treatment plant .hence
decides the method of treatment adopted for removal of organic impurities.
BOD/COD ≤ 0.68
If BOD and
COD ratio is less than 0.8 or BOD/COD ratio is less than 0.5 sewage is consumed
to be treated non biologically.
THE RATIO OF COD AND TOC
COD/TOC =5.33
If it is zero for those organic compound which cannot be oxidized by K2Cr2O7 thus giving COD =0
COD/TOC
ratio signifies quality of sewage and the method of treatment.
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