Oil Refinery Waste water treatment Plant

Waste Water Treatment Plant
Pakistan Refinery Ltd

SCOPE OF DISCUSSION
 CLASSIFICATION OF WASTES
 REFINERY EFFULENT CHARACTERSTICS
 TREATMENT TECHNIQUES
 PROCESS DESIGN PHILOSPHY
 WASTE WATER TREATMENT PLANT IN
GENERAL

Water used by homes, industry, business must be
treated before released back to the environment
Waste Water Generation

Parameter Exist.Standard Into Land Into Sewage Into Sea
Temperature 40oC =<3oC =<3oC =<3oC
pH value 6-10 6-9 6-9 6-9
BOD5 80 80 250 80
COD 150 150 400 400
TSS 150 200 400 200
TDS 3500 3500 3500 3500
Oil & grease 10 10 10 10
Phenols 0.1 0.1 0.3 0.3
Chloride 1000 1000 1000 SC***
Fluoride 20 10 10 10
Cyanide total 2 1.0 1.0 1.0
An ionic
detergent
20 20 20 20
Sulphate 600 600 1000 SC***
Sulphide 1.0 1.0 1.0 1.0
Ammonia 40 40 40 40
Pesticides 0.15 0.15 0.15 0.15
Cadmium 0.1 0.1 0.1 0.1
Chromium 1.0 1.0 1.0 1.0
Copper 1.0 1.0 1.0 1.0
Lead 0.5 0.5 0.5 0.5
National Environmental Quality Standards

Mercury 0.01 0.01 0.01 0.01
Selenium 0.5 0.5 0.5 0.5
Nickel 1.0 1.0 1.0 1.0
Silver 1.0 1.0 1.0 1.0
Total Toxic metals 2.0 2.0 2.0 2.0
Zinc 5.0 5.0 5.0 5.0
Arsenic 1.0 1.0 1.0 1.0
Barium 1.5 1.5 1.5 1.5
Iron 2.0 8.0 8.0 8.0
Manganese 1.5 1.5 1.5 1.5
Baron 6.0 6.0 6.0 6.0
Chlorine 1.0 1.0 1.0 1.0
National Environmental Quality Standards

Parameter PRL Effluent NEQ’S WWTP Effluent
pH 8.5-9.5 6-9 7- 8.5
TDS 2000-3000 3500 <3500
TSS 50 200 <30ppm
Temperature 30 40 30- 35oC
Oil & grease 10-20 10 <0.1ppm
Sulphide 13 1 <0.1ppm
BOD5 120 80 <5ppm
COD 450 150/400* <50ppm
Ammonia 1 40 ---
Phenol 1-7 0.3 <0.05ppm
TREATED EFFLUENT QUALITY.

EXPLANATIONS:
1. Assuming minimum dilution 1:10 on discharge, lower ratio would attract
progressively stringent standards to be determined by the Federal
Environmental Protection Agency. By 1:10 dilution means, for example that for
each one cubic meter of treated effluent, the recipient water body should have
10 cubic meter of water for dilution of this effluent.
2. Modified Benzene Alkyl Sulphate; assuming surfactant as biodegradable.
3. Pesticides include herbicides, fungicides and insecticides.
4. Subject to total toxic metals discharge should not exceed level given at S.No.25
5. Applicable only when and where sewage treatment is operational and BOD5=80
mg/lit is achieved by the sewage treatment system.
6. Provided discharge is not at shore and not within 10 miles of mangrove or other
important estuaries.

ENVIRONMENTAL THREATS FROM INDUSTRIAL
WASTE
WATER POLLUTANTS
 Total Suspended Solid (TSS)
 Biochemical Oxygen Demand (BOD)
 Chemical Oxygen Demand (COD
 Oil and Grease
 Total Dissolve Solids (TDS)
 Toxic Chemicals

Size Classification Of Solids in Water
Dissolved
Colloidal
Suspended or
Non-filterable
10-5 µm
10-4 µm
10-3 µm
10-2 µm
10-1 µm
100 µm
10 µm
100 µm
Dissolved material consists of
molecules and ions that are held
by molecular structure of water.
Colloids are very small
particles that technically
suspended in water but often
exhibit characteristics of
dissolved solids.
Suspended materials consists
of particles larger than
molecular size that are
supported by buoyant and
viscous forces within water.

Suspended Solids
 Sources
Suspended materials are often natural contaminants in surface water
that come from the errosive action of water flowing over surfaces. Due
to filtration capability of soil SS seldom a constituent of ground water.
 Solids suspended in water may consists of inorganic and
organic particles of immiscible liquids.
 Inorganic solids such as clay ,slit and other soil
constituents are common in surface waters.
 Organic matters such as plant fibers and biological solids
(algae cells,bacteria. etc) are common constituents in
surface waters.
 Domestic waste water constrains SS mostly organic in
nature
 Industrial use water may result in variety of suspended
impurities of either organic or inorganic nature. Immiscible
liquids such as oils and greases are also constituents of
industrial waste water.

Suspended Solids continue…
 Impacts
Suspended solids may be objectionable in water for several
reasons:
 SS are aesthetically displeasing and provides adsorption
sites for chemical and biological agents.
Suspended organic solids may be biodegradable resulting in
objectionable by-products and also constitutes to BOD
Biological active SS may includes disease causing micro
organisms as well as organisms such as toxin producing
strains.

Biochemical Oxygen Demand (BOD)
“The amount of oxygen consumed during microbial
utilization of organics is called the biochemical oxygen
demand.”
Measurement: The BOD is measured by determining the oxygen
consumed from a sample placed in a air tight container and kept
in a controlled environment for a pre-selected period of time.
For a standard test a 300 ml BOD bottle is used and the sample
is incubated at 20 Co for 5 days. Light must be excluded from the
incubator to prevent algal growth that may produce oxygen
inside bottle.
BOD5 = DOi – DOf DOi---- Dissolve Oxygen initial
P DOf----- Dissolve Oxygen final
P ----- Fraction of sample in 300 ml.

Chemical Oxygen Demand (COD)
“COD is the amount of oxygen derived from a chemical
oxidizer such as potassium dichromate that is required to
fully convert the organic pollutants onto carbon dioxide ,
water and other oxidized end products.”
Measurement
Measured volume of dichromate is added to a measured
volume of sample then takes place in a concentrated sulfuric
acid environment at a temperature of 148 Co . The mixture boils
for 2 hr only. Sample is again titrated by ferrous ammonium
sulfate for remaining unconverted dichromate.
The method is more accurate than BOD analysis. It provides
a better reading of organic pollutants in the waste water. It
constitutes total oxygen demand that chemically required
however it does not give fraction of biodegradable substances.

Alkalinity-PH
Alkalinity: “The neutralization ability of solution against
acidic tendencies is called alkalinity”
Carbonates,bicarbonates,hydroxide etc. contribute to
total alkalinity of a solution.
PH: “ It is the measure of acidity or basisity of a
solution”
PH of a solution is a measure of H+ present.
Higher the concentration of H+ ions lower
the value of PH.
7 143.5 10.51.0
Acidity Basisity

Refinery Effluent Sources
Crude Tanks Drain Water
Process Area Water
Spent Caustic
Cooling Tower Blow-down
Wash Water CTC
Boiler Blow-down
Sour Water From 101-F
RO Rejected Water
1-2 m3/day
100-150 m3/day
5-6 m3/day
150-300 m3/day
40-50 m3/day
40-45 m3/day
130-140 m3/day
110-125 m3/day
Desalter Effluent 140-125 m3/day
Refinery Total Effluent 716 – 943 = 830 m3/day

Refinery Effluent Water Characterization
Parameter Unit Tank Process Spent
Caustic
Cooling
Tower
WWC Boiler 101-F RO
Rejected
Drain Drain BD Drain BD Sour
PH 7.3 8.8 13.3 9.9 6.2 11.6 6.7 6.9
TDS PPM 3685 3087 179900 1708 299 3315 195 12600
TSS PPM 22 28 337 59.5 55 12.6 11.6 7
T.Hardness PPM 680 560 532 520 160 1 10 630
Ca2++ PPM 280 272 280 120 0.8 8 360
Mg2++ PPM 400 288 240 100 0.2 2 270
Alkalinity PPM 530 352 650 100 280 60 320
CO3
2- PPM 112 352 330 Nil 184 Nil Nil
HCO31- PPM 418 Nil 320 100 96 60 320
OH-1 PPM Nil Nil Nil Nil Nil Nil Nil
Cl-1 (NaCl) PPM 2457 2105 420 70 1813 28.5 5600
BOD5
COD PPM 147 64 133000 136 765
Oil &
Grease
PPM 19.7 10.5 16.0 18.0 30.3

WASTE WATER TREATMENT PLANT
WWTP comprises of multiple treatment units for refinery
effluent to bring its pollutants down to the permissible
limits.
 Equalization
 Physio-chemical Pretreatment
 Aerobic Biological Treatment

Process Flow Block DIAGRAM
Holding Basin Buffer Tank
CPF
Pre-Selector-1Oxidation Basin
API
TPF
Sludge
Basin
Pre-Selector-2
Secondary
Clarifier-1
Secondary
Clarifier-2
Arabian Sea

Equalization
All refinery wastewater streams collect at API separator
where water and oil separates through
gravity difference. The oily water from API separator pit
transferred to equalization tank. This tank has a holding
capacity of 850 m3. Tank is equipped with an aerator, PH
sensor and acid dosing nozzle.
Working Principle: Tank serves as homogenizer for variety
of effluent discharge of the refinery. HCl is supplied to get its
PH down to 8.5 aerator strips out H2S gas from the water.
Thus sulphide level considerably decreased. That is beneficial
for biological process. This homogenized water free from
sulfide fed to Physio-chemical process.

BUFFER TANK
FRESH AIR IN
H2S EXHAUST STACK
HCl INJECTION
HOMOGENIZE WATER
TO TPF
MAN HOLE
Buffer Tank Internal Aeration System

Buffer Tank (The Equalizer)
H2S Stack
Flow In
Flow Out

Buffer Tank Feed Line
Buffer Tank Front View

EQUILIZATION BUFFER TANK CONTINUE…
CHEMICAL REACTIONS
S-2 + 2HCl H2S + Cl-1
CO3
-2 + 2H+ H2 CO3

PHYSIOCHEMICAL PRE-TREATMENT
Physiochemical pretreatment comprises of
chemical and physical separation processes.
 PH Control
 Coagulation
 Flocculation
 Flotation
 Sludge Separation
All above processes take place in Coiled Pipe Flocculater
(CPF) and Tilted Plate Flocculator (TPF)

Coagulation Theory
Coagulation: “It is the neutralization of charged suspensions
present in water.”
Suspended particles in water get charge due to frictional forces due
to this induce charge repulsion force generates that hinders in
suspensions coagulation.
High density charge radical neutralizes this induce charge from
suspensions allowing them to combine to form coagulates.
High density charge radicals are usually trivalent +ve metal ions like
Al3+,Fe3+ etc… These are called coagulant.

Coagulation Theory Continue…
Coagulation phenomena consists of following four steps:
 Ionic Layer Compression
 Adsorption
 Charge Neutralization or Destabilization
 Flock Formation

+ -
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+ -+ -
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+ -
+ -
+ -
+ -
+ -
- +
- +
- +
- +
- +
- +
+
- +
+
++
Electro negative particle
Surface Shear (Bounded
by water molecules)
Stern Layer
Diffuse Layer
Stern potential: Opposite charge surrounding charge particle causes a rapid drop in
potential called as stern potential.
Zeta Potential: Gradual drop in potential between shear surface of boundary water layer
and the point of neutrality in the solution.
Surface Charge on particle
that hinders in coagulation
Stable Colloidal Particle

 Ionic Layer Compression
The quantity of charge in the
water surrounding a colloid has
an effect on the decay function of
the electrostatic potential. A high
ionic concentration compresses
the layers predominantly of
counter ions towards the surface
of the colloid. If this layer is
sufficiently compressed then
vander wall forces will be
predominant across the entire
area of influence,so that net force
will be attractive and no more
repulsive energy barrier exits.
Co-ions
Counter ions
Bulksolution
Diffused Layer
Distance From Particle
NumberOfIons

 Adsorption and Charge Neutralization
The nature of ions, rather than quantity, is a prime
importance in the theory of adsorption and charge neutralization.
The ionization of aluminum sulfate in water produces sulfate ions
(SO4-2) along with aluminum cat ions Al+3. The aluminum ions
combine with water and forms a variety of aquometallic ions and
hydrogen proton.
 Al3+ + H2O AlOH2+ + H+
 Al3+ + 2H2O Al(OH)2
+ + 2H+
 7Al3+ +17H2O Al7 (OH)4+ + 17H+
 Al3+ + 3H2O Al(OH)3 + 3H+

 The aqua-metallic ions become part of
the ionic cloud, surrounding the colloid.
Due to high affinity for surfaces these
ions adsorbed onto the colloid surfaces
and neutralize the repulsive charge.
 Once the surface charge has been
neutralized ,the repulsive ionic cloud
dissipates and electrostatic charge
disappears. Particles becomes free to
combine/coagulate.
 Overdosing of coagulant can restabilize
suspensions. Excessive aqua-metallic
ions are formed and adsorbed they can
reverse the phenomena . Charge on
particles may reverse and regain cloud
of opposite charge.
Distance B/W particlesNet Force
vanderwallVsZ-Potential
Coagulation : Reduction of Net Force

PH
2 4 6 8 10
Log(AlumMolarCon.)
No CoagulationSlow Coagulation
Re-stabilization
-1
-2
-3
-4
-5
-6
Effective Coagulation

Flocculation Theory
Polymer Particle
De-stabilized Particle
Initial Adsorption At Optimum Polymer Dosage
Floc Formation
Secondary Adsorption Of Polymer
De-stabilized Particle Re-stabilized Particle
No contact with vacant sites on
another particle

Flocculation Theory Continue…
Initial Adsorption At Excess Polymer Dosage
Stable Particle No Vacant SiteParticle
Polymer
Rupture OF Floc
Floc Fragments

Al3+Al3+
Al3+
Coagulated Suspensions
Dispersed Suspensions
Flocculation

Jar Tests For Coagulant Dosage
 Coagulation is not yet an exact
science,therefore selection and
optimum dosage of coagulant is
determined experimentally.
 These experiments are determined
with a series of jars named as jar
test.
 Jar test must be performed for each
type of water that is to be
coagulated. Test results are used
to calculate type and quantity of the
coagulant to be used in the
treatment.
Apparatus
The jar test is performed
using a series of six glass
containers that hold at least 1liter
and are of uniform size and shape.
Stirrer device also required.

Jar Tests Continue…
Procedure:
Fill all six jars up to I lit mark. Add coagulant of different
dosage in each 5 jar. 6th Jar placed for reference.
Water is then mixed rapidly for about one min to
ensure complete dispersion of the chemical,then mix
slowly for 15 to 20 min to permit floc formation. The
water is then allowed to settle for approx. 30 min. or at
least clarification occurs. The portion of the settled water
are then removed and tested to determine the remaining
turbidly.

Coiled Pipe Flocculator
Working Principle
 CPF is a plug flow type piping construction in which all
stages of precipitation takes place sequentially.
 Influent water PH is controlled through PLC PH controller to
ensure coagulation process.
 Coagulant followed by flocculant are injected to have
precipitation of suspensions and flocculation.
 Intensive and instantaneous mixing of the PH correcting
chemicals ,coagulant and flocculant chemicals is achieved
by the turbulence created inside CPF.
 Flocculated suspensions mix with air saturated water to get
flotation effect caused by gravity difference
 The dosing rate of coagulant and flocculant are adjusted
manually according to the feed rate.

Sludge Basin
PH
PE Injection Alum Injection
R-Flow
HCl
Caustic

Coiled Pipe Flocculater CPF
CPF
 Coiled pipe floculator
equipped with injection points
for PH regulation Alum and PE
solutions injections for
coagulation and flocculation.
 CPF is a variable area pipes
sections with different lengths to
ensure necessary residence time
for completion of the process.
PH
DAF
Air Saturated
water injections
Alum
PE

Tilted Plate Flotator (TPF)
 In the TPF the destabilized and flocculated oil emulsions and colloid
suspensions are removed by means of the Dissolved Air Flotation
process.
 TPF based on the principle that by attaching tiny air bubbles with the
flocs provide intense flotation effect due to gravity difference.
 The sludge containing the air bubbles and contaminants floats readily on
the liquid surface. From where it is removed by means of pneumatic
driven skimmer.
 To dissolve the required amount of air ,a definite amount of air is mixed
with recycle water and is passed through a pump ,specially designed for
this duty, then release pressure into DAF. Here water saturates with air
and transferred into tiny bubbles 30 to 50 microns.
 Air saturated water is entered into CPF at 6 injections point partially. In
this way maximum contact of air bubbles with flocs occur.
 TPF is equipped with fiber tilted plates at angle of 45o. Water enters TPF
through inlet perforated nozzle. Nozzle drives centrifugally and sludge
floats outwards to the surface.
 Tilted plates provided maximum contact between waters of high density
(relatively pure) and of light water containing air-lifted sludge.

TPF Side View: Coagulated
water enters into TPF through CPF
line ending with a distributor
Tilted Plates: Tilted Plates placed
at 45o angle with the axis of TPF basin.
Water with lesser gravity flows
outwards while of higher gravity moves
downwards provides intimate contact.

Sludge At Surface
Clean Water Flows out
Perforated pipe
Tilted Plates
Air Injection
DAF
Re-circulation Pump 9 m3/hr,6 kg/cm2

The Skimmer
 Sludge floating at TPF is removed
through skimmer, top mounted on
TPF.
 Skimmer is equipped with
horizontal scrapper with air drive
pistons.
 Skimmer is operated through auto
PLC sequence. Play time adjusted
with reference to sludge
accumulation rate

Sludge Floating On TPF Surface

SS Free Water Flow-Out

Biological Treatment
 Biological Treatment is applied for digestion of biodegradable
impurities. Biodegradable matter is responsible for BOD, this parameter
is worth controlling to meet standards and to save marine life.
 Biological water treatment is achieved by naturally occurring species ;
microorganisms. In such a treatment environment is provided for
culture growth. Micro-organisms utilizes impurity as their food and
oxidize it producing water and carbon dioxide.
Biological Treatment comprises of the following units.
Preselctors
 Oxidation Basin
 Secondary Clarifiers

Control Parameters
MLSS: Mix liquor suspended solids
Suspended solids present in water temporarily mix with
help of mechanical means(agitation) are termed as
MLSS.
MLSS is determined by weight analysis in lab through
filtration and drying procedure.
MLSS in biological treatment is an important parameter
that provides the measurement of combine sludge in
oxidation basin. (Total suspensions)
3500 ppm of MLSS level is maintained in oxidation
basin through continuous recycling of activated sludge
Excessive MLSS is expelled into sludge thickener
compartment through activated sludge recycle stream.

MLVSS: Mix liquor volatile suspended solids
 The actual living organism in MLSS are reported as MLVSS.
 After MLSS analysis the dried sludge sample is heated in
furnace at temperature of 550 Co . The volatile species (organic
part) removes only ash remains. The quantitative difference
between MLSS and this remainder is claimed as MLVSS.
 MLVSS is maintained at level of 3500 ppm corresponding MLSS
level.
 MLSS and MLVSS can never be equal theoretically or practically
yet a close agreement is expected to assume quality of
activated sludge.
Sludge Volume
 Sludge volume in oxidation basin (ml/lit) is measured
 One liter sample from oxidation basin is kept quiescent for
30 min the level settled down is taken from graduated scale.
 Oxidation basin SV is maintained at 450 ml/lit

Sludge Volume Index: SVI
 It is also an important parameter to understand quality of
sludge.
 SVI is maintained 80-120 ml/gm
 SVI is proportional to the MLSS and SV by this formula
SVI =
SV * 1000
MLSS
(ml/gm)
Sulfide:
 Sulfide concentration is kept lesser than 0.1 ppm
whether CPF outlet is 100 ppm.
 Sulfide slight higher concentration can destroy
microorganism.
 Ferric chloride is added in preselector to oxidize
sulfide into sulfates.

Preselector (Bioreactor)
The first step of the aerobic biologic effluent treatment takes place in the preselector.
Preselector consists of 2 separate concrete tanks ,each equipped with a mixer device.
First preselector receive activated sludge recycle and effluent water from TPF. Water from
TPF considered to be free from suspensions only impurity present is dissolve substances.
 The activated sludge adsorbs at a quite high rate the dissolved organic
contaminants at their cell walls through both chemical and biochemical bonds.
 At the same time the microbes through variety of chemical bonds attach
themselves to oily and suspended particles that have passed the dissolved air
flocculation
 The microbes starts producing exo-enzymes which enables them to hydrolyze and
decompose the absorbed organic compounds.
 A preferential selection of microbes grows ,as only the microbes which are best
equipped for immediate adsorption of the organic contaminants ,can only well
survive. Types of microbes that adsorb organics at slower rate during the pre-
selection phase out due to starvation(food shortage).

 The types best equipped are those with a distinct polysaccharide layer around
their cell wall; the layer functions as the adsorbent for organic contaminants.
The same layer also ensure at a later stage in the settling basin,the flocculation
of microbes,through the process they become separable from water due to
gravity.
 The environment in the pre-selector is definitely adverse for hosts of
filamentous sludge species which leads to sludge bulking.
 The phenomenon of filamentous sludge leads to bulking.
 Sludge bulking decreases flocculation ability and tends to float over water
surface.
 The phenomenon of pre-selection is most useful tool to avoid sludge bulking as
it directly discourages the generation of filamentous sludge.
 In pre-selection the food is immediately adsorbed by activated sludge by itself.
There is nothing left for slower growing other species ( like filamentous
bacteria). Therefore in pre-selection process these species disappear.
Sludge Bulking

 The internal configuration of the pre-selector has been designed to minimize
the hydraulic short circuiting and back mixing in reactors.
 Total retention time in both the pre-selectors is 25 minutes, after that water
runs to the oxidation basin.
 First preselector receives recycle sludge form clarifiers. Phosphoric acid is
injected for microbes integration. Ferric chloride is injected to oxidize
sulfides to sulfates
 Both the pre-selectors are equipped with submersible motor driven mixers.
These mixers are designed for entire homogeneity of water and activated
sludge.
Submersible Mixer

TPF Out Flow
Preselectors
Oxidation Basin
Sludge Recycle
Phosphoric Acid
Ferric Chloride
Pre-selector Specification
 Volume = 15.5 m3
 Design Flow = 35 m3/hr
 Design Recycle Flow = 35 m3/hr
 Total Retention Time = 25 min

Activated Sludge Recycle To Preselector

Bacterial growth curve in a fix food environment
Exponential Rise and Exponential Fall

Element
%age
Dry- Wt.
Source Function
Carbon 50
Organic compounds
or CO2
Main constituent of cellular material
Oxygen
20
H2o , organic
compounds,CO2, N2
Constituent of cell material and cell water ; O2 is
electron accepter in aerobic respiration
Nitrogen 14
NH3,NO3,Organic
compounds, N2
Constituent of amino acids, nucleic acids,
nucleotides and coenzymes
Hydrogen 8
H2O, Organic
compounds, H2
Main constituent of organic compounds and cell
water
Phosphorus 3
Inorganic
phosphates (PO4)
Constituent of nucleic acids, nucleotides,
phospholipids
Sulfur 1
SO4, H2S, S , organic
sulfur compounds
Constituent of cysteine, several coenzymes
Potassium
1
Potassium salts
Main cellular cation and cofactor for certain
enzymes
Magnesium 0.5 Magnesium salts
Inorganic cellular cation, cofactor for certain
enzymatic reactions
Calcium 0.5 Calcium salts
Inorganic cellular cation, cofactor for certain
enzymes and a component of endospores
Component of cytochromes and certain nonheme
Major Elements, Sources and function in Bacteria Cell

 Microbes needs dissolve oxygen in water to intake for digestion, this
phenomenon is achieved in oxidation basin
 Oxidation basin equipped with aerators, internal baffle outlet mesh and
contained of volume 240 m3 that provides a hydraulic detention time of
70 hrs.
 Water overflows form second preselector to oxidation basin.
 High detention time ,70 hr, enables microbes to digest and metabolize
adsorbed substrates.
 Microbes derive their energy from oxidation digestion , a part of which
is utilized in re-synthesis of new cell tissue. This synthesis leads to an
increase of total cell population. Reported in activated sludge growth.
Remaining part of energy is expelled into surroundings.
 A sufficient amount of dissolved oxygen is provided by means of two
submersible ejectors type aerators.
 Continuous aeration support microbes to digest their food and to
promote new cell growth.
 PLC Control loop implies to maintains desirable dissolve oxygen
concentration
Oxidation Basin

Oxidation Basin
Pre-selector
Aerator P-32201Aerator P-32101
Air AtmosphereAir Atmosphere
D
O
P
H

Oxidation Basin Top View
Pre-selector

Secondary Clarifiers
 Two parallel secondary clarifiers are employed for the segregation of treated
effluent from activated sludge.
 Imhof type clarifiers are based on the principle of gravity settling by
affording ample time.
 Clarifiers bottom structure is steep like structure with an angle of 60o
 The design overflow of each clarifier is 0.5 m/hr, that provides stream like
quiescent flow helps in gravity settling of microbes flocks ( Activated
Sludge).
 First tranquilizing zone helps in re-coaglomeration of activated sludge
particles through their ability to auto flocculate. That ‘s due to
polysaccharide layer around the microbes cell wall.
 Surface load of suspended solids (SS) is 0.4 Kg/(m2/h)
 The flow rate of both the clarifiers is balanced by a set of outlet weirs. V-
notch is provided on the either side to measure over flow rate from each
clarifier.
 The clarified water is discharged directly into the clarified water basin.

Secondary Clarifiers
Arabian Sea
Knock Out Pit
Discharge Pit
Preselector-I
20m3/hr * Each
Sludge -
Thickener
Volume = 81.5 m3 * Each
Retention Time = 4 hr-37 min
Liquid Load = 70 m3/hr

Clarifiers Outflow Weir
 Secondary Clarifiers discharge though outlet
weirs. The final treated water to sea.
 Weir are mounted by sliding bolts,by which
flow can be balanced between both
compartments of the clarifier.
 Clean Water flow is spectacular over the
weirs any SS passing through water is quite
visible.
 V-notch is attached at out-way of both
compartments. Flow rate can be measured
through direct scale reading on V-notch.

CHEMICAL DOSE CONSUMPTION DOSINGPUMP
ALUM35% 200 480 l/day 20 l/hr
PE centrifuge0.1% 400 3.6 Kg/day 150 l/hr
PE DAF 0.1% 3.2 2.5 Kg/day 56 l/hr
HCL35% buffer tank 20 l/hr
HCL35% DAF 30 l/hr
NaOH50% DAF 20 ml/hr
FeCl3 40% 438 ml/hr
H3PO4 10% 0.5 mgP/l 13.3 l/day 554 ml/hr
CHEMICAL CONSUMPTION

Parameter Value
pH 7- 8.5
TSS <30ppm
Temperature 30- 35oC
Oil & grease <0.1ppm
Sulphide <0.1ppm
BOD5 <5ppm
COD <50ppm
Phenol <0.05ppm
TREATED EFFLUENT QUALITY.

Parameter Sample point Daily Twice weekly Weekly Target value
BOD CPF in X 120 mg/l--O2
TPF-out X 102 mg/l--O2
Scond. Clarifier out X <5 mg/l--O2
COD CPF-in X 450 mg/l--O2
TPF Out X 330 mg/l--O2
Second. Clarifier out X <50 mg/l--O2
Nkj CPF-in X 60 mg/l
Second. Clarifier out X 15 mg/l
NH4+ CPF-in X 25-50 mg/l
NO3 CPF-in X 5 mg/l
Ptol CPF-in X 0 mg/l
TPF out X 0 mg/l
Secon. Clarifiers out X 1 mg/l
MLSS Oxidation Basin X 3500 mg/l
MLVSS Oxidation Basin X 3500 mg/l
Control Parameters Their Targets and Testing Frequency

Control Parameters Their Targets and Testing Frequency
TDS CPF- in X 2000-3200 mg/l
TPF- out X 2000-3200 mg/l
Secon. Clarifiers out X 40-120 mg/l
TSS CPF- in 40-120
TSS Secon. Clarifiers out X <30 mg/l
TSS TPF- out X 5-10 mg/l
SV Oxidation Basin X 450 mg/l
SVI Oxidation Basin X 80-120 mg/l
DO Oxidation Basin X 1-2 mg/l
PH CPF-in X 8.5
PH TPF- out X 7-7.3
PH Oxidation Basin X 7-8.5
PH Second. Clarifier out X 7-8.5
Oil & grease CPF- in X 40 mg/l
Second. Clarifier out X 0.1 mg/l
Temperature CPF-in 30-35o
C
Second. Clarifier out 30-35o
C
Phenolic CPF- in X 3-5 mg/l
TPF- out X 2 mg/l
Sulphide CPF-in X 100 mg/l
TPF- out X 30 mg/l
Second. Clarifier out X 0.1 mg/l

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Oil Refinery Waste water treatment Plant

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