Characterization and measurement of sewage flow rates

Characterization of Sewage
UCE-601: Sewerage and Sewage
Treatment
Thapar University

Characterization of Sewage
• Flow rate and flow variations
• Solids (TSS, VSS and biodegradable VSS)
• Organic matter (TOC, COD and BOD)
• Nutrients (nitrogen and phosphorus)
– Nitrogen: TKN (Organic –N and Ammonical –N), Nitrate -N and
Nitrite –N
– Phosphorus (ortho and total phosphorus)
• Biological water quality (MPN or coliform count)
• Oil and grease
• pH, Acidity and Alkalinity
• Chlorides, Sulfates, Sulfides and Phenols
• VFA analysis

Why flow measurement?
• To quantify flows of
– water in streams in streams and rivers
– wastewater in sewers and wastewater drains
• To facilitate flow proportionated sampling of water
• To provide daily flow records required by regulatory agencies
• To determine
– Sizes of water and wastewater treatment plants and the
constituent treatment units
– Chemical dosage to the treatment units
• Interest may be to know instantaneous flow rates, cumulative
flows and variations in flow rates (peaking factor)
4

Flow proportionated sampling and
composite sample collection
Flow
Time
Base Flow
5

Basic requirements of flow meters
• Ability to calibrate
• Ability to integrate integrate flow fluctuations
• Ease of integration with piping system
• High accuracy
• High turn down ratio
• Low cost
• Low sensitivity to dust particles
• Low pressure loss
• Resistant to corrosion and erosion

Basic types of flow meters
• Differential pressure flow meters
• Velocity flow meters
• Positive displacement flow meters
• Mass flow meters
• Open channel flow measurement
• Miscellaneous type flow meters
7

Differential pressure flow meters
• Based on bernoullis equation
– Pressure drop over an obstruction inserted in the flow is used as
basis for flow measurement
• Used for flow measurement under pipeflow conditions
• Orifice meters, venturi meters and flow nozzles
– Orifice meter: a sharp edged orifice plate is introduced as
obstruction to flow – a simple and cheap but poorly accurate
specially at low flows - but can cause significant pressure drops
– Venturi meter: Flow cross section is gradually reduced to generate
pressure difference, and then increased for pressure recovery (low
pressure drops) – Preferred for accurate flow measurements and
for high turn-down rates (10:1)
– Flow nozzles: used usually for gas flow measurement - simple and
cheap - turn down rate and accuracy are comparable to orifice
plates - pressure drop across constricted area is maximum for
orifice plates & minimum for venturi tubes
8

Venturi meter
9
Consists of a conical contraction, a short cylindrical throat and a
conical expansion
P
1
P
2
V1 V2
Bernoulli equation between 1 and 2:
Continuity equation between 1 and 2: 2211 VAVAQ 
0
2
)VV()PP( 2
1
2
212





])/(A-[1
)(2
C 2
12
21
d,2
A
PP
V ideal


 Cd is discharge coefficient

Orifice Meter
A thin flat plate with a circular hole drilled in its center.
])/(A-[1
)(2
C 2
12
21
2
A
PP
V d


 Where Cd is the discharge
coefficient
P
1
P
2
A1, V1
1 2
Front view of
orifice plate
A2, V2

Nozzle Meter
P
1
P
2
])/(A-[1
)(2
C 2
12
21
2
A
PP
V d



• A Venturi meter without the diverging recovery section
• Less expensive than Venturi meter but higher head loss
• Accuracy: < ±1%; Range (turn-down ratio): 4:1
11
A1,V1 A2,V2

Velocity flow meters
• Flow is calculated by measuring flow velocity at one or more
points across the flow cross section
• Typical velocity flow meters
– Pitot tube
– Turbine flow meter (flow current meter)
– Electromagnetic flow meter
– Ultrasoic flow meter, etc.
• With the known flow velocity, flow rate is obtained using flow
cross sectional area

Turbine Flow meters
• Uses a multiple-bladed rotor
(turbine) mounted within a pipe,
perpendicular to flow
• The rotational speed is a direct
function of volume flow rate.
• The meter factor K is found by
direct calibration.
• Limited to pipes running full,
under pressure, and liquids low
in suspended solids
• Excellent accuracy (±0.25%)
and a good range of flows (turn
down ratio): 10:1

Measurement of flow rate
StageorDepth
Discharge, Q
Rating Curve
14

The Pitot Tube
P1 is a Static pressure: It is
measured by a device (static
tube) that causes no velocity
change to the flow. This is
usually accomplished by drilling
a small hole normal to a wall
along which the fluid is flowing.
P2 is a Stagnation pressure: It is
the pressure measured by an
open-ended tube facing the
flow direction. Such a device is
called a Pitot tube.
15
P1,V1 Stagnation
Point V2=0
1 2P2
2/1
12
1
)PP(2
V 















 

f
fm
XgV


21
ρm and ρf are fluid and manometic fluid densities
ΔX is manometric fluid level difference

Electromagnetic flow meter
Faraday’s law: Voltage produced by a
conducting fluid through a magnetic
field is proportional to fluid flow
velocity
• Advantages: Turn down ratio is quite
large (10:1); No head loss; and
Unaffected by temperature,
conductivity, viscosity, turbulence, &
suspended solids
• Problems: High initial cost and need
of trained personnel to handle
routine O&M
16
E=BDVx10-8
E=voltage, volts
B=magnetic flux density, gauss
D= length of the conductor, cm
V=velocity of the conductor, cm/sec

Ultrasonic flow meters
Ultrasonic Doppler flow meter:
• Frequency of a reflected signal is
modified by the velocity and
direction of the fluid flow
– If the fluid is moving towards a
transducer frequency of the
returning signal is increased and
otherwise it is decreased
– Frequency difference (reflected
frequency minus originating
frequency), known as ‘Doppler
effect’, is used to find flow velocity







C
V
FF SourceDoppler
‘V’ Flow velocity between source and receiver
‘C’ Speed of sound
‘Fsource‘ Transmitted frequency.

18
Time-of-travel flow meters
Have 2 transducers mounted on each
side of the pipe
The transducers function as both as
sound wave transmitters and
receivers – operate alternatively as
transmitters and receivers
Sound wave is transmitted in the direction of the fluid flow and in the
opposite direction of flow and time of flight is measured
Differential in the time of flight is used to know the flow velocity and flow
measurement
Ultrasonic Flow meters

Positive displacement flow meters
Devices that isolate fixed volumes of fluid flowing into them in
sealed compartments and discharge to the outlet.
These may be passive (operate on the power from flowing fluid) or
active (metering pumps - driven by external power source)
Leakage and pressure loss are two problems associated with the PD
flow meters
Volume flow rate is calculated from the size and number of
compartments delivered per unit time
PD meters can be classified as rotary, reciprocating, or nutating
PD meters for liquids: Nutating disk meters, reciprocating-piston
meters, rotary-piston meters, rotary-vane meters, rotor meters
PD meters for gases: Roots-type meters, diaphragm-type meters,
liquid-sealed drum-type meters

Nutating disk meters
(a disk nutates in a dual conical housing)
Reciprocating – single piston meters
Plunger or piston is driven by a cam

Rotary-vane flow meters
Flat vanes are inserted into matching
slots around the perimeter of a
cylindrical drum.
Cylindrical drum is located eccentrically
within the housing
Rotary-(oscillating) piston flow meters
A cylindrical drum mounted
eccentrically inside a cylindrical
housing

Rotor meters: Oval Gear Meters
Rotor meters: Gear flow meters

Rotor meters: Helical gear flow meter
Roots-type flow meters
Lobe Rotary Piston

Diaphragm-type meters
Liquid-sealed wet gas flow meters (liquid provides sealing action)
Liquid ring pump

Mass flow meters
• These are also known as inertial flow meters
• If density is variable (temperature, pressure and fluid
composition influence density) mass flow rate can not be
obtained from volumetric flow rate
• Includes
– Coriolis flow meters
– Thermal flow meters
• Capillary tube type thermal mass flow meter
• Constant temperature differential method
• Constant current method
densityfluid
rateflowmass
rateflowvolumetric 

Coriolis mass flow meters
• with the help of an actuator the
inlet arm and the outlet arm are
vibrated at the same frequency
• when there is fluid flow, the inlet
arm and the outlet arm vibrate
differently and a phase shift
occurs
• The (measured) degree of phase
shift is proportional to the mass
flow in the tube


2
2
2Kd
IK
Q uu
m


Qm is fluid mass flow rate
Ku is temperature dependent tube stiffness
K is shape dependent factor
‘d’ is width, τ is time lag
ω is vibration frequency
Iu is inertia of the tube

Thermal mass flow meters
• Thermal dispersion or immersible mass flow meters
– Fluid mass flow rate is measured through measuring the heat
convected from a heated surface to the flowing fluid
– Commonly used for the gas flow measurement
– Heat is introduced into the flow stream and the heat dissipated is
measured by sensors
– Heat dissipated depends on the sensor design and the thermal
properties of the fluid
• Constant temperature differential method: two sensors, a heated
sensor and a gas temperature sensor are used - Power required for
maintaining constant temperature difference between the two sensors
is measured and used
• Constant current method: also have two sensors – power used to heat
the sensor is kept constant – temperature difference between the two
sensors is measured and used for flow measurement
• Capillary tube type of thermal mass flow meter
– Heat is transferred to the flowing fluid from a small heated
capillary tube carrying fluid
– Used for measuring smaller flows of cleaner gases and liquids

Rotameter, variable area flow meter
Fluid flowing moves the float/bob
upwards and maintains in a equilibrium
position when
 










tan2
1
.
.Re
min
2
22
22
hmor
D
DD
mwhere
gm
RnoRuppel
DU
Rnoynold
gVgVgVF
flowturbulentforUDCF
flowarlaforUDCF
buoyancyBobweightBobforceDrag
b
b
b
b
u
bin
e
bbbbbd
bTd
bLd
















Fd is drag force
ρb and ρ are bob density and fluid density
Vb is volume of the bob
Db is maximum bob diameter
D is tube diameter at the bob height
U is flow velocity at the annular gap around the bob

 
 
 
 
 
4
4
4
4
4
44
2
2
2
2
2
222
b
T
bb
b
bTbb
L
bbb
b
bLbb
b
bb
mD
C
gV
Q
mD
Q
DCgV
C
mDgV
Q
mD
Q
DCgV
mD
Q
U
UmDUDDQ
























 Q is volumetric flow rate
--- for laminar flow conditions
--- for turbulent flow conditions
Rotameter, variable area flow meter

Flow meters for open channel flow
Weirs and flumes: used as flow meters for open channel flow
Weirs:
• Elevated structures in open channels used for flow
measurement
• Can be sharp crested weirs (thin plates set vertically across
the width of the channel) and board crested weirs
• Can be contracted weirs or suppressed weirs
– Contracted weirs: Nappe is open to atmosphere at the edges; Nappe
width is slightly lesser than the weir width
– Suppressed weirs: Channels sides are also the sides of the weir
opening; Nappe is not open to atmosphere, but usually some type of
air vent is provided beneath the nappe)
• Weirs for flow measurement
– Rectangular weirs
– Cipolletti weirs
– Triangular (V-notch) weirs

Rectangular weirs
  2
3
2
3
2
3
2.083.1
83.1
075.0611.0
2
3
2
HHbQ
bHQ
H
H
C
HbgCQ
w
d
d




Discharge for suppressed rectangular weir
Discharge for contracted rectangular weir
Applicable for H/Hw is <5
‘b’ is width at the weir crest
H is water depth above the crest at 4H to 5H
distance upstream side
Cd according to Rouse (1946) & Bievins (1984)
Hw is weir crest height from channel bottom
For H/Hw <0.4 Cd is 0.62 & Q is
Acceptable for b≥3H

Cipoletti weir and V-notch weir
Cipoletti or trapezoidal weir
• Side slope is 1:4 (H:V)
• Corrections for end contractions not needed
• Can be used when the H is >6 mm (for <6
mm the nappe does not spring free of crest)
V-Notch weir
• Has V shaped opening with θ = 10° to 90°
• Cd value decreases with increasing angle
• Minimum Cd value is 0.581
• 0.58 can be used as Cd for θ = 20° to 100°
2
3
859.1 HbQ  ‘b’ is bottom weir width
2
5
2
tan2
15
8
HgCQ d 







Weirs cause high head losses and suspended
solids tend to accumulate behind the weirs

  













3
2
2
3
2
97.4
5.0
5.0
a
hgabCQ
a
hbaQ
d














 
5.0
1
tan
2
1
a
y
bx

.max
.max
.min
5.0
.max
.min5.1
.max
.max
262.0
H
Q
Q
a
Q
Q
gH
Q
b








Cd value is 0.6 to 0.65
b is taken as ‘channel width – 150 mm’!
Proportional weir (Sutro weir)

Broad crested weirs
• Very robust flow measurement device used in rivers/canals
• A broad rectangular weir with a level crest and rounded edges
• Works on the principle that the flow over the weir occurs at
critical depth
– Flow at critical depth occurs when the weir height is above a
specific value
– Uptill critical depth occurs, raising the crest level will not affect
the upstream water level
– Once critical depth is achieved, any further rise of crest height
also rises the upstream water level
• For a proper broad crested weir used for flow measurement
– Upstream flow is sub-critical
– Flow over the crust is critical flow
– Super critical on the downstream side
– On the downstream side a super critical flow turns back to a sub-
critical flow after a hydraulic jump
• Hydraulic jump in the downstream side is in fact an evidence
for critical flow on the crest

Broad crested weirs
• Problems associated with broad crested weirs
– Accumulation of silt and debris in the region of dead water on the
upstream side
– Loss of energy from the downstream side hydraulic jump formation
• A solid weir has no hydraulic jump (!)
• Crump weir can to a great extent solve the above problems
– Crump weirs have an upstream slope of 1 in 2 and a
downstream slope of 1 in 5 to reduce the region of dead water
on the upstream side
• For critical depth of flow over the crest of the weir, unique
relationship exists between the head above the crest and the
flow rate/discharge

Broad crested weir
Discharge equation/formula
5.1
5.1
5.1
705.1
6.1
LHQ
LHQ
CLHQ



L is weir length
H is head over the crest
H is actually height of the total energy line
from the crest of the weir
It is measured usually in a stilling chamber a
few meters upstream the weir where the
water level is affected by draw-down
C is weir coefficient, its value is taken as 1.6
C is estimated from the total energy or bernouli’s equation as 1.705
From this the coefficient of discharge can be calculated as 0.94
Critical depth of flow should occur on the crest for the discharge
formula to work
The discharge formula is based on the critical flow on the crest and
does not be influenced by the weir shape
Value of ‘C’ however can be influenced by the weir shape

Flumes
• Flumes are specially shaped fixed hydraulic structures that
force flow to accelerate through in such a way that the flow
rate becomes related to the liquid level
– Converging side walls or raising bottom or both are used in
shaping the special hydraulic structures
• Flumes usually have 3 sections: converging section, throat
section and diverging section
– All the sections do not necessarily be present in all the flumes -
Cutthroat flume has no throat
• Compared to weirs, head loss for flumes is lesser (it is just
1/4th of a sharp crested weir)
• Flumes have no dead zones on the upstream side where
sediment and debris can accumulate
• Types of flumes commonly used:
– Parshall flumes
– Palmer-Bolus flumes

Parshall flume
• Consists of a converging section, a throat section and a
diverging section
– Crest of the throat section is tilted to the downstream side
– In channels of < 2.44 m width, inlet of the converging section
may be rounded
• Parshall flumes are constructed for standard dimensions
defined by the width of the constriction
• Parshall flumes operate on the venturi principle
– Narrow throat causes water level to raise on the upstream side
• Flow rate is obtained by measuring water depth in the
converging section of the parshall flume
n
KHQ 
H is water depth at point h1
K is a constant (function of the constriction and of the
units chosen for the measurement – value increases with
the increasing flume width)
‘n’ is a constant of exponent (function of the constriction’s
dimensions – value is between 1.522 - 1.607

Standard dimensions
W 305±0.8
A 1372
2/3A 914
B 1343
C 610
D 845
E 914
F 610
G 914
H ----
K 76
M 381
N 229
P 1492
R 508
X 51
Y 76Parshall flume of standard dimensions

Parshall flume (submerged conditions)
• When downstream water depth is higher than the crest level
of the flume (floor level of the converging section), a second
water depth measurement (h2) is needed for the flow
measurement
• If h2/h1 is crossing 50% to 80% (50% for smaller flumes and
80% for larger flumes) then flow is said to be submerged
• Flow measurement for submerged flow conditions is possible
when h2/h1 is <0.95
 
2
1
1
2
211
log
n
n
h
h
hhC
Q









C1 is a constant – its value increases with the
increasing width of the flume
‘n1’ and ‘n2’ are constants – their values also
increase with increasing flume width
‘h1’ and ‘h2’ are water depths against a
reference level in the converging section and
at the downstream of the throat

Parshall flume
• Parshall flume must be located in the straight section of the
channel for flow measurement
• Crest level of the flume must be higher than the channel
bottom
– The crest level is raised at 1 in 4 slope from the channel
• Parshall flume is extremely effective for flow measurement
when the water contains suspended solids
• Parshall flume creates very little head loss
• Turndown ratio is >100
– A feet wide standard parshall flume can measure a minimum
flow of 0.00439 m3/sec. (h1 is 31 mm) and a maximum flow of
0.4568 m3/sec. (h1 is 762 mm)
• Margin of error is ±3%

Palmer-Bolus flume
• It is a venturi type flume
– High velocity critical flow is produced in the throat by flow
constriction
• Usually prefabricated - designed to install in existing channels
– Installed in sewers or in manholes or in open, round or
rectangular bottom channels
• Advantages
– Easy to install
– Minimum restriction to flow, less energy loss, less cost and low
maintenance
– Less sensitive to upstream disturbances
– Can be used in submerged flow conditions (80-90%
submergence is no problem
– Does not require upstream or downstream crest differential
– Water containing solids can be measured

Palmer-Bolus flume
• Size may range from 100 mm to 1000 mm
– Dimensions of the flume depend on the diameter or size of the
channel in which installed
• Throat is trapezoidal in shape
– Has a flat bottom and inclined sides (20°)
– Length of the throat is usually equal to the diameter
• The flume is elevated from the channel bottom by D/6
• Inclined section from channel to flume has 1 in 3 slope
• Length of the base of the flume is D+2P where P is length of
the inclined section (D/2)
• Turndown ratio is relatively small (9 or 10:1)
– Difference between the minimum flow and the maximum flow
that can be measured is relatively small
– For a 12’’ flume (D=12’’) the minimum and the maximum flow
measured is 0.0056 m3/Sec. and 0.0158 m3/Sec. respectively

t = D/6
B = W = D/2 or 5D/12
m = D/4
mm

PALMER-BOWLUS FLUME – STANDARD DIMENSIONS

Palmer-Bolus flume
 
 mz
mzgz
DQ
8.41
4.21
12
5
33
2
5



Q is flow rate
D is diameter of the channel
‘g’ is acceleration due to gravity
‘z’ is dc/D where ‘dc’ is depth of flow
‘m’ is vertical constrictions base projection (D/4)
Flow measurement equation
Flow rate is determined by measuring water depth upstream
from the flume
Liquid depth is measured at a point D/2 distance from the
flume on the upstream side
Within the normal range of flow (10% to 90% of the flume
capacity) error in flow measurement is <3%

Acoustic Meter
• Use sound waves to measure
the flow rates
• Sonic meter or ultrasonic meter
depending on whether the
sound waves are in or above
audible frequency range
• Determine the liquid levels,
area, and actual velocity
• Advantages: low head loss,
excellent accuracy (2~3%),
usable in any pipe size, no
fouling with solids, and wide
flow ranges (10:1)
• Disadvantages: High initial cost
and need for trained personnel
to handle routine O&M 50

Miscellaneous Flow
Measurement Devices
• Depth Measurement
– Need to measure the flow depth and sewer slope and use
Manning equation for flow estimation
– Frequently used for interceptor flow estimation
• Open Flow Nozzle
– Crude devices used to measure flow at the end of freely
discharging pipes.
– Must have a section of pipe that has a length of at least six
times the diameter with a flat slope preceding the discharge.
– Examples: Kennison nozzle and the California pipe
51

Suspended Solids
(TSS, VSS, Biodegradable VSS, SVI
and Colloidal solids )

Suspended Solids
• Total solids (TS): Material residue left behind after
evaporation of a sample and its subsequent drying in a oven
at a defined temperature to constant weight
• Total dissolved solids (TDS): Portion of the material residue of
a sample that passes through a filter
• Total suspended solids (TDS): Portion of the material residue
of a sample retained by a filter
– Settlable solids: Material settling out within a defined period
• Fixed suspended solids: Residue of TSS left after ignition for a
specified time at a specified temperature
• Volatile suspended solids: weight loss on ignition of total
suspended solids
– Biodegradable volatile suspended solids: volatile suspended
solids lost through biodegradation
• Colloidal solids: cause turbidity and measured as turbidity
(NTU or JTU)

Suspended Solids
• Regulatory limits are imposed on TSS for sewage disposal
– Water with high suspended solids may be aesthetically
unsatisfactory (for bathing!)
• Removal of TSS is one of the sewage treatment objectives
– Primary treatment is mainly concerned with it
• Sludge generation calculations in biological treatment require
the knowledge of TSS, VSS and biodegradable VSS
– All VSS is not biodegradable, and biological treatment can
hydrolyze only the biodegradable VSS
• Biological treatment involves generation of suspended solids
(biosolids)
– These biosolids are monitored as MLSS (TSS) and MLVSS (VSS)
• Maintenance of higher levels of biosolids (activated sludge) is
important in biological treatment
– MLVSS is often used as a measure of active biomass/sludge
• SVI used in the design, operation and control of secondary
clarifiers require MLSS (TSS) monitoring

Total suspended solids (TSS)
TSS and MLSS are one and the same
Two alternate ways for TSS measurement
• Filter the sample through a weighed ash free filter paper, dry
the filter paper along with the residue retained on it to
constant weight at 103-105C, and gravimetrically find the TSS
– High measurement uncertainty values – in case of low TSS larger
volumes need sampling
– In case of samples with high TDS thoroughly wash the filter
paper with TDS free water to remove the dissolved material
• Find TS and TDS for the sample and take difference of TS and
TDS as TSS
– In case of the filter paper clogging and prolonged duration of
filtration this method is followed
Often settlable solids rather than TSS is measured as an
alternative
• Centrifugation for TSS measurement?

Volatile Suspended Solids
• VSS and MLVSS are one and the same
• Weight loss on ignition of the TSS represent the VSS
• Ash free filter paper leaves no residue on ignition
• Negative error is introduced from the loss of volatile matter
during drying
• Estimation of low concentrations of volatile solids in the
presence of high fixed solids concentration can be more
erroneous
• Dried residue left on the ash less filter paper is ignited to
constant weight at 550±50C in a muffle furnace to remove
volatile matter and obtain fixed or non-volatile matter
– Difference of TSS and NVSS (fixed solids) is taken as VSS

Solids in Samples with Solids > 20,000 mg/L
The methods used for samples with lower solids levels are not
used – can be associated with negative error
If the sample is a sludge, stir to homogenize and place it in a
evaporation dish, evaporate to dryness on a water bath, and
dry at 103-105C for 1 hour to find % solids
For finding fixed and volatile solids ignite the residue in muffle
furnace for one hour at 550±50C
– If the residue left in the evaporation dish contains large
amounts of organic matter then ignite it first over a gas burner
and then in the muffle furnace
 
BC
BA
solidstotal



1000
%
 
BA
DA
solidsvolatile



1000
%
 
BA
BD
solidsfixed



1000
%
A - weight of dish with residue
B - weight of the dish
C - weight of dish with wet sample
D - weight of dish with residue after ignition

Settlable Solids
• Determined on either volume (mL/L) or weight (mg/L) basis
• Measurement on volume basis requires an Imhoff cone
– Fill the cone to 1 L mark with sample and settle for 45 min.
– Gently stir sides of the cone with a rod by spinning and settle for
another 15 minutes
– Record volume of the settled solids in the Imhoff cone
• Measurement on weight basis
– Determine TSS of well mixed sample
– Pour >1-L of sample into a glass vessel of >9 cm dia. to depth
>20cm and let it stand quiescent for one hour
– Without disturbing the settled and floating material siphon out
water from the vessel center and determine TSS as non-
settlable TSS
Settlable solids = TSS – non-settlable TSS

Sludge Volume Index (SVI)
• Volume in mL occupied by 1 g of a suspension after 30 min.
settling
• Used to monitor settling characteristics of activated sludge
and other biological suspensions
– Determined for the mixed liquor of the aeration tank of the ASP
• Determine TSS concentration of a well mixed mixed-liquor
sample
• Use Imhoff cone for settling 1 L of well mixed mixed-liquor for
30 min. time and measure the settled sludge volume in mL
– Gently stir the sample during settling
• Calculate SVI as
)/(
1000)/(
Lgionconcentratsolidssuspended
LmLvolumesludgesettled
SVI



Colloidal Solids and Turbidity
• Colloidal matter causes turbidity
• Turbidity is an optical property caused by scattering of light,
and indicates clarity of water
• Biological treatment removes colloidal solids/turbidity
through bioflocculation
• Nephelometers are used for measurement and the results are
reported in Nephalometric Turbidity Units, NTU
– Intensity of light scattered by the sample is compared with the
standard reference suspension under the same conditions
• Formazin polymer suspension is used
• A light source and a photoelectric detector are used in the
measurement

Organic Matter
• TOC
• ThOD
• COD
• BOD
– DO
– BOD3 and BOD5
– BODu
• BOD kinetics
– Serial BOD test
– BOD kinetic parameters

Measurement of Organic Matter
Organic matter in wastewater is heterogeneous
– Suspended (VSS), colloidal (turbidity) and dissolved organic
matter
– Carbohydrates, proteins, fats, etc.
Organic matter is biodegradable and non-biodegradable
Single direct method for the measurement of organic matter is
not feasible – so indirect methods – these depended on
• Total organic carbon –TOC:
• Organic matter invariably has carbon, and the Organic Carbon
(OC) content is proportional to the Organic Matter (OM)
content
• Samples also have inorganic carbon (carbonates, bicarbonates,
etc.) and these interfere in the measurement of organic carbon
• Samples are first treated for the removal of inorganic carbon,
and then treated to convert organic carbon into carbon dioxide
and the amount of CO2 formed is measured

Measurement of Organic Matter
• Oxygen Demand (ThOD, COD and BOD)
– Organic matter is reduced substance and it can be completely
oxidized and transformed into inorganic end products and this
demands oxygen
– Amount of oxygen demanded is proportional to the organic
matter present – the oxygen demanded is measured and
related to organic matter
– Oxygen demand of the sample’s organic matter is measured as
• Theoretical Oxygen Demand (ThOD): If chemical formula of the
organic matter is known, oxygen demand of the sample’s organic
matter can be theoretically found through stoichiometry
• Chemical Oxygen Demand (COD): Organic matter of a sample is
chemically oxidized, and oxygen demand of the sample’s OC is
measured in terms of the amount of oxidizing agent consumed
• Biological Oxygen Demand (BOD): Microorganisms are made to
use the organic matter as food and aerobically oxidize into
inorganic end products, and oxygen utilized is measured as BOD

Theoretic Oxygen Demand
Empirical formula of organic matter present in the sample is
used and a balanced equation of oxidation is written
Amount of oxygen required (for complete oxidation of one
unit mass of organic matter) is stoichiometrically
estimated
The oxygen demand equivalent to the organic matter
presented
3222
2
3
24
3
24
cNHOH
ca
nCOO
cba
nNOHC cban 












oxygengrequireseglugofOxidation
OHCOOOHC
192cos180
666 2226126 

Chemical Oxygen Demand (COD)
• Measures oxygen equivalent of organic matter provided the
latter is susceptible to oxidation by potassium dichromate
• Oxidation (wet) is brought about under acidic conditions
(created by H2SO4 reagent) at high temp. (150ºC± 2oC) for 2
hrs., and can be shown by:
CnHaObNc+dCr2O7
-2+(8d+c)H+ nCO2+ {(a+8d-3c)/2}H2O+cNH4
++2dCr+3
d is moles of dichromate consumed
One mole of dichromate = 1.5 moles of COD/oxygen
• Not a good measure for biodegradable organic matter and not
capable of oxidizing all the organic matter
• Widely used because real time/reasonable time results are
possible
• In case of anaerobic treatment COD is preferred over BOD for
organic matter concentration measurement
2363
2 cban
d 

Biochemical Oxygen Demand (BOD)
• Acclimatized microorganisms are used to oxidize the organic
matter aerobically under favourable conditions of pH,
temperature, osmotic pressure and nutrients
• Sample is incubated with acclimatized microorganisms at a
specific temperature (20/27°C) for specified period (5/3 days)
• Organic matter is used by organisms as food and oxidize –
only the matter that can be consumed as food (biodegradable
fraction) can be measured
• O2 is also demand by microorganisms for the nitrification of
ammonical-N into nitrite-N and Nitrate-N (introduces positive
error in the measurement)
• COD on the other hand measures both biodegradable non-
biodegradable organic matter

COD
• Measure of oxygen equivalent of organic matter content of a
sample
• Oxidation of organic matter occurs under acidic conditions at
elevated temperature (150±2C) for about 2 hours
• Oxidation can be shown by
• Hexa-Cr is orange colored and Tri-Cr is greenish blue in color
– As a consequence of conversion of haxa-Cr into Tri-Cr, color of
digestion mixture changes from orange to greenish blue
• Amount of dichromate consumed is basis for COD estimation (one
mole dichromate consumption is equivalent to 1.5 moles of COD)
• Oxidation is not complete - measures only the organic matter
susceptible to oxidation by potassium dichromate
     3
422
2
72 22/388 
 dCrcNHOHcdanCOHcdOdCrNOHC cban
2363
2 cban
d 

COD
• Pyridine (and related compounds) and aromatic hydrocarbons are
not completely oxidized
• VOCs (originally present or formed during oxidation) are oxidized
only to the extent of their contact with oxidant (at elevated temp.
may escape oxidation)
– Silver sulfate is used as catalyst for the effective oxidation of VOCs
– Halides of the sample form silver halides and make catalyst ineffective
– Mercuric sulfate is used at 10:1 ratio for preserving the effectiveness
(not appropriate when the halides level is >200 mg/l)
• Use of reflux condensers or closed reflux (or sealed digestion
containers), minimize escape of VOC from oxidation
• Oxidation at elevated temps, results in thermal decomposition of
the dichromate used and introduces positive error
– For estimating the error and making correction, a blank is digested
along with the sample
• Nitrite (NO2-), reduced inorganic species (like chloride, ferrous iron,
sulfide, manganous manganese) and ammonia (from organic mater
oxidation!) can also be oxidized and introduce positive error

COD
• Interference caused by chloride ions can be shown by
– Oxidation of ammonia requires presence of significant levels of free
chloride ions
– Addition of excess mercuric sulfate prior to addition of other reagents
can eliminate chloride ion interference by making ions non-available
• Nitrite level is rarely >1-2 mg/l and hence insignificant interference
– Remove interference by adding 10 mg sulfamic acid per mg of nitrite
• Error introduced by other inorganic species, if significant, is
stoichiometrically estimated and necessary corrections are made
• Collect samples in glass bottles, and test preferably immediately
– If delay is unavoidable, acidify samples with H2SO4 to 2 pH and store
– If stored at room temperature, test within 7 days, and if stored at 4C,
then test within 28 days
– If sample has settlable solids, then homogenize the sample in a
blender prior to testing
• Two alternate methods (open reflux and closed reflux methods) are
used in the COD meaurement
OHCrClHOCrCl 2
3
272 723146  

COD by Open reflux method
• Sample and blank are refluxed in strongly acidic solution in the
presence of known excess of standard K2Cr2O7 solution for 2 hours
• A reflux apparatus, comprising of an Erlenmeyer flask, a vertical
condenser and a hot plate/heating mantle, is used for refluxing
• During refluxing
– Hexa-Cr of the K2Cr2O7 is reduced to tri-Cr and supplies oxygen
– Some fraction of the added dichromate is thermally decomposed
• Residual dichromate of the sample and of the blank are measured
by titrating against standard ferrous ammonium sulfate (FAS)
– Ferroin is used as indicator
– Titration involves conversion of residual hexa-Cr into tri-Cr
– Once all the Hexa-Cr is converted into Tri-Cr, Fe+2 ions of FAS form a
complex (of intense orange brown colour) with ferroin indicator
– Color change from greenish blue to orange brown is end point
– Redox potentiometer can also be used to detect the end point

 3362
33 CrFeCrFe

COD by Open reflux method
• COD of the sample is calculated by:
• Open reflux method is associated with
– Consumption of costly and hazardous chemicals, like, silver sulfate,
mercuric sulfate etc.,
– Generation of hazardous waste with chromium, mercury, silver, etc.
• To reduce cost and minimize hazardous waste generation, instead
of 50 ml, use smaller sample size (10 ml!)
– Smaller size samples demands proper homogenization of samples in
blender prior to use
• Refluxing time less than 2 hours can be employed provided the
results obtained are same as those obtained from 2 hour refluxing
8000
).(
/( 2
usedsampleofml
MBA
OaslmgCOD


‘A’ is ml FAS consumed in blank titration
‘B’ is ml FAS consumed in sample titration
‘M’ is molarity of FAS

COD by Closed reflux method
• Amount of sample used is small (2.5-10 ml) - for avoiding errors
from uneven distribution of suspended solids, the sample is
homogenized by a blender prior to testing
• Method has a cost advantage, generates minimum of hazardous
waste, and VOCs are more completely oxidized
• Sample and blank are digested for 2 hours in a closed system of
culture tubes with tight caps or of sealed ampules placed in a block
digester or in an oven preheated to 150±2ᵒC.
• Digested samples are cooled and tested for COD by
• Titration with FAS (Titrimetric closed reflux method)
• Measuring color change (Colorimetric closed reflux method)
• Basis for the colorimetric method
• Hexa-Cr is orange colored and Tri-Cr is greenish blue in color
• As a consequence of conversion of haxa-Cr into Tri-Cr, color of
digestion mixture changes from orange to greenish blue
• Fading of orange color (at 400 nm) or appearance of greenish blue
color (at 600 or 620 nm) is measured and compared against standards

COD by closed reflux method
Titrimetric method
• Remove caps of the culture tube and transfer contents into a
conical flask
• Add 1 or 2 drops of ferroin indicator and titrate against FAS.
• Record the amount of FAS consumed
• Calculate the sample’s COD from the results by
Colorimetric method
• Invert the cooled culture tubes for thoroughly mixing the
contents and allow proper settling of suspended solids
• Read absorbance (color intensity) either at 400 nm or at 600 nm
with the help of a spectrophotometer
• Through using the readings obtained for the standards, construct
a calibration curve
• Through using the calibration curve find COD of the sample
corresponding to its absorbance
8000
).(
/( 2
usedsampleofml
MBA
OaslmgCOD


‘A’ is ml FAS consumed in blank titration
‘B’ is ml FAS consumed in sample titration
‘M’ is molarity of FAS

Dissolved Oxygen (DO): Winkler Method
• Can be measured by either Winkler method (iodometric method!)
or Membrane electrode method
• BOD bottle containing the sample is added with Manganous sulfate
and alkaline potassium iodide solutions
• DO present in the sample oxidizes an equivalent amount of divalent
manganese ions to higher valency states (forms oxides)
• Rest of the manganese ions form divalent hydroxide precipitate
• On acidification with sulfuric acid, the higher valency manganese
ions are reduced into divalent ions (by iodide ions), and iodine,
equivalent to the sample’s DO content, is liberated
• All precipitates formed (both oxides and hydroxides) get solubulized
• Amount of iodine liberated is measured by titrating with standard
sodium thiosulfate solution, while using starch as indicator
• For detecting end point more precisely, in place of using starch
indicator, electrometric method can also be used
• If interferences (suspended solids, color and chemicals) are absent,
spectrophotometer can also be used to measure the iodine liberated

Winkler method for DO
NaIOSNaIOSNa
OHMnHOHMnb
OHMnIHIMnOa
OHMnOHMnc
OHMnOOOHMnb
OHMnOOOHMna
22.3
22)(.2
242.2
)(2.1
5.0)(.1
5.02.1
6422322
2
2
2
2
2
22
2
2222
222
2










• Reactions involved in the Winkler method of DO testing are
• Sources of error:
• Presence of Nitrite (more than 50 g/L as N) introduces positive error
• Nitrite can oxidize the iodide ions back into iodine and introduce the
error (a chain reaction)
– Biologically treated effluents, incubated BOD bottle samples, and
stream samples may have nitrite interference
– For eliminating, instead of alkaline-iodide solution, alkaline-iodide-
azide solution is used – the azide added reacts with NO2¯ and removes
it as N2 and N2O gases




HNOOHOON
OHONIHINO
225.0
422
22222
22222
OHONNHNOHN
NaHNHNaN
22223
33





Winkler Method for DO
• For avoiding errors, the sample should not come in contact with air
during sampling and testing (at least till the sample’s DO is fixed)
• Samples with iodine demand can be preserved for 4-8 hours by
adding 0.7 mL conc. H2SO4 and 1.0 mL of 2% azide (NaN3) prior to
actual analysis by usual procedure
• Permanganate modification
• Permanganate modification is needed if ferrous iron level is > 1.0
mg/L
• To the sample collected add 0.7 mL conc. H2SO4, 1.0 mL KMnO4 and
1.0 ml of KF below the surface, and stopper and mix the contents
• KMnO4 addition may be increased if the resulting violet tinge do not
persist for at least 5 minutes
• Decolourize the sample by adding 0.5 to 1.0 mL of potassium oxalate
(K2C2O4) and mixing the contents

Winkler Method for DO
• Ferric iron interference can be overcome by addition of 1 ml
of KF and Azide provided titration is done immediately after
acidification
• Addition of 1.0 mL of KF solution prior to acidification is needed
for samples with 100-200 mg/L of ferric iron (acidified sample
should be immediately titrated)
• Copper sulfate-sulfamic acid flocculation modification
– Used for biological flocs having high oxygen utilization rates
– Fill aspirator bottle with the sample from the bottom by a tube
near the bottom while allowing overflow of 25-50% volume
– Add 10 ml of copper sulfate-sulfamic acid inhibitor solution to
1.0 L aspirator bottle with glass-stopper.
– Stopper the bottle, mix the contents by inverting the bottle and
allow the bottle to stand and siphon out sample into the BOD
bottle for DO measurement

Membrane Electrode Method for DO
• Membrane electrode is composed of two solid metal electrodes and an
electrolyte solution forming a bridge between them
• The electrodes and the electrolyte solution are separated from the sample
by a molecular oxygen permeable membrane
• The membrane electrode system (DO probe) is either a polarographic
system or a galvanic system
• Because of the permeable nature, a dynamic equilibrium is established
(through oxygen diffusion) between the DO of the electrolyte solution and
that of the sample
• Oxygen present in the electrolyte is reduced at the cathode and electrons
required are produced at the anode and transported to the cathode
• Current resulting from the required electron transport is proportional to
the DO concentration in the electrolyte solution (indirectly in the sample)
• Current in the circuit is measured and related with the DO of the sample

Calibration: Establishing relationship between DO of the sample
and current in the circuit
• Calibration of membrane electrode system involves use samples of
known DO
• Samples with known DO can be prepared by aeration, bubbling
nitrogen gas, addition of sodium sulfite and traces of cobalt chloride
• The membrane electrode (DO probe) is placed in water saturated
air, and current generated in the circuit is taken as proportional to
the DOs at that temperature and pressure
• When calibrated in saturated air, necessary compensation for altitude
(or atmospheric pressure) should be made (Manufacturer provides a
standard table for altitude correction)
• Distilled water (or unpolluted water with known conductivity/
salinity/ chlorinity) saturated with DO can also be used for calibration
• Samples with known DO can also be used for the calibration
• Winkler method is used for knowing DO with precision and accuracy
• Manufacturer of DO probe and DO meter provides a written
calibration procedure and it should be strictly followed

• Membrane permeability is both temp. and salt conc. sensitive.
– Temp and salt conc. of the sample should be monitored and necessary
corrections be made to the probe sensitivity
– Nomographic charts available from the manufacturer can be used
– Certain DO meters may include facilities for automatic temp. and salt
conc. compensation
– For confirming the corrections made by nomographic charts,
sensitivity of the DO probe is frequently cross-checked at one or two
temp. and salt conc.
• With time membrane looses its properties, and hence, it is
frequently changed and the electrode system is calibrated afresh
• Precision and accuracy of membrane electrode method (± 0.1 mg/l
and ± 0.05 mg/l) is not very good
• Precision of Winkler method is ± 50 µg/l, but being a destructive
test, can not be used for continuous DO monitoring in samples

BOD Bottle Method for BOD Estimation
A BOD bottle filled with diluted sample with acclimatized
seed and stoppered is incubated at constant temperature
for a fixed duration
– Dilution of the sample
– Acclimatized seed
– Favourable nutrient and osmotic conditions
– No air bubble entrainment
– known initial DO
5 days incubation at 20°C (3 days at 27°C)
– only partial oxidation of the organic matter occurs
– complete oxidation needs incubation for longer time (60 to 90
days)
Measurement of final DO
– Difference between initial and final DO is oxygen demand of the
diluted sample during the incubation period

5-day BOD Test by BOD Bottle Method
• BOD is a bioassay test used to measure biodegradable organic
matter concentration
– Amount of oxygen required to biooxidise organic matter of the sample
is measured
• Diluted sample is incubated with appropriate microbial populations
for 5 days at 20ºC
– Distilled water (or tap water or water collected from receiving water, if
having negligible BOD) is used for diluting the sample
– Water should not have bio-inhibitory substances like chlorine, heavy
metals etc.
• Aerobic bio-oxidation of biodegradable organic matter consumes
DO of the sample
• Change in DO of the incubated sample is measured and reported as
BOD5 at 20°C
• Experimental results to become acceptable
– Residual DO of the sample should be >1.0 mg/l
– DO difference between initial and final should be >2.0 mg/L

Sources of Error
Seed added is organic matter and undergoes bio-oxidation exerting
oxygen demand during incubation
– Positive error introduced is measured through incubating a blank
containing seed in dilution water but no sample
– Measured error is then subtracted from the overall oxygen demand for
obtaining oxygen demand of the sample
Oxygen demand is denoted as BODt at X°C (BOD5 at 20°C, BOD3 at
27°C, etc.)
– Units for BODt at X°C are mg/L (BODt is oxygen demand when the
sample is incubated for ‘t’ days at X°C
Testing gives oxygen demand of diluted sample - multiplication of this
with dilution factor gives sample’s oxygen demand
NH3-N added (as nutrient supplement) and NH3-N released during
incubation are prone to nitrification and introducing positive error
• To eliminate this error, either inhibit the nitrification or quantify and
subtract from the measurement
– In 5-day BOD test, use of nitrification inhibitor chemical is preferred
– In BODu test quntification and subtraction of error is preferred

Expression for BODt from test results
BODt at X°C of a sample can be written as
Dilution Factor ‘Df’ is the factor by which original sample is
diluted for obtaining diluted sample - can be defined as:
OD of diluted sample:
Error introduced by the seed
– Oxygen demand of dilution water is almost negligible
– But, seeded dilution water has significant oxygen demand
– Add known volume of seed (5 times or more to that added to diluted
sample) to dilution water to raise the OD to > 2 mg/l
– Test the seed control for OD through incubating parallel with the
diluted sample for the same duration































Factor
Dilution
ionnitrificat
byerror
-
aterdilution wand
seedbyerror
-
samplediluted
theofOD
BODt
)(
1000
sampledilutedofliteronepreparingforusedsampleofml
Df 
sfsi DODOOD 
DOsi & Dosf are initial & final DO of diluted
sample before & after ‘t’ days of incubation

F)DO-(DOaterdilution wseededofOD cfci
preparedcontrolseedofliterperseedofml
preparedsampledilutedofliterperseedofml
F 
f
f
cfcisfsi
o
t DF
D
DODODODOCXatBOD

















1
1)()(
cfci DO-DOseedofOD  DOci & DOcf are initial & final DO of
the seed control incubated for ‘t’ days
F
D
DODOwaterdilutionseededofOD
f
cfci 








1
1)(
Expression for BODt from test results
bottleBODinwaterdilutionseededoffractionvolumeis
Df









1
1
Error by nitrification: Nitrification reaction is inhibited by adding
nitrification inhibition chemical and hence no correction needed.

Incubation conditions
• Favourable pH conditions
– Micro-organisms are pH sensitive - 7.2 is considered as optimum
– pH of incubated sample can change from production of CO2
– Phosphate buffer is used to adjust the pH to optimum and to
maintain pH during incubation
• Favourable nutrient conditions
– Bio-oxidation of organic matter involves synthesis of new
microbial biomass
– This synthesis requires nitrogen (NH3-N or NO3-N), phosphorus
(orthro) and other inorganic nutrients
– Insufficient nutrients make bio-oxidation nutrient limiting
– The sample is supplemented with nutrient formulations
(phosphate buffer has KH2PO4, K2HPO4, Na2HPO4 and NH4Cl)
– Salts added for maintaining osmotic conditions (FeCl3, CaCl2 and
MgSO4) may also contribute
• Favourable osmotic conditions:
– Maintaining osmotic conditions is important for ensuring this
FeCl3, CaCl2 and MgSO4 salts are added

Incubation conditions: Constant
temperature throughout
• 5/3 day incubation bio-oxidizes only a fraction of organic matter
(OM)– total oxidation requires infinite time – BOD kinetics model is
used estimating the total OM by extrapolating BODt results
– BOD kinetics model involves a reaction rate constant (K) which is
temp. sensitive
– BOD kinetics model can not be applied to the results obtained from a
test where the sample is not incubated at constant temperature
• The BOD test results are always reported along with temperature
and period of incubation (BOD5 at 20°C).
• By conviction incubated for 5 days at 20C (annual average temp. of
UK and time taken by the Thames to reach the ocean) – CPCB
recommends 3 days at 27°C (annual average temp. of India!)
• 5 days incubation has an advantage - nitrogenous BOD in many
cases will not interfere with carbonaceous BOD measurement
– One can adapt any temp. within the range that will not affect the
microbial metabolic activity
– Incubation period giving BODt = 60-70% of BODu can be adapted
• For ensuring incubation at constant temp., samples are incubated
either in BOD incubators or in water baths set at desired temp.

Acclimatized seed
• For the bio-oxidation of OM, the incubated sample should
have appropriate microbial populations
• During initial period of incubation, selection among the
populations and their size increase occurs – this results in
initial lag in oxygen demand pattern and consequently
• Cumulative demand may not follow first order kinetics
• Negative error may be made in BOD5 measurement, and in the
BODu estimation
• Municipal sewage, biologically treated effluents and samples
collected from receiving water bodies are supposed to have
these populations
• Many industrial wastewaters may not have (w/w generated at
elevated temp. and w/w containing toxicants above the
threshold limits)

Acclimatized seed
• Microbes have preferences as to the OM they can bio-oxidize
• seed added may not have appropriate microbial populations in
significant size
• W/w not having appropriate microbial populations require
addition of these populations as seed
• The initial lag can be eliminated through use of acclimated
seed.
• What can be used as seed
– Settled domestic sewage, clarified and undisinfected effluents of
biological treatment units, and clear water from receiving
waters
– Effluent from the biological treatment plant, treating the
wastewater being sampled (most appropriate)
– Clear water collected from the water body, which is receiving
the wastewater in question, at a point 3 to 8 KM down stream
– Seed, specially, developed in laboratory

Aclimatized Seed
• Can be developed from
• Settled domestic sewage
• Suspension prepared from wastewater contaminated soil
• Prepared through continuously aerating for a few days and
adding small daily increments of the wastewater in question
• Preparation of acclimatized seed:
• Take mixed liquor or secondary sludge of a STP and start aeration
• While continuing aeration, gradually replace the mixed
liquor/secondary sludge with the wastewater in question over a
period of two days or more
• Settle the contents and use the supernatant as seed

Dilution factor (Df)
• Oxygen is sparingly soluble in water and depends on altitude,
temperature and salinity
Altitude (in
meter)
Saturated
DO (in
mg/l)
Temperat
ure (in
C)
Saturated
DO (in
mg/l)
Chlorini
ty
Saturated DO
(in mg/l)
sea level 9.2 0.0 14.62 0.0 9.09 (20C)
305 8.9 5.0 12.77 7.56 (30C)
610 8.6 10.0 11.29 6.41 (40C)
914 8.2 15.0 10.08 5.0 8.62 (20C)
1219 7.9 20.0 9.09 .. 7.19 (30C)
1524 7.6 25.0 8.26 .. 6.12 (40C)
1829 7.4 30.0 7.56 10.0 8.17 (20C)
2134 7.1 35.0 6.95 .. 6.85 (30C)
2438 6.8 40.0 6.41 .. 5.84 (40C)
2743 6.5 45.0 5.93 15.0 6.51 (30C)
3048 6.3 50.0 5.48 20.0 6.20 (30C)

Dilution factor (Df)
• Diluted sample is aerated to rise DOi closer to DOS
• At 20°C, DO level can rise to about 8 mg/l level - diluted sample’s
initial DO: about 8 mg/l
• At  0.5 mg/l DO, bio-oxidation rates are influenced by DO and
assumption of first order kinetics (BOD kinetics) becomes invalid
• DO in incubated samples should be >1.0 mg/L – final DO should be
>1.0 mg/L
• DO available for bio-oxidation can be about 7 mg/L
• Sample needs dilution so as its cumulative OD is  7 mg/L.
• For finding Df, an idea of range of expected BOD for the sample
should be known (Published literature or past experience can help)
• COD of the sample can also help
• Take upper limit of the range and divide by 7 mg/l to get Df.
• If no idea on expected BOD range, then test at a series of dilutions
• For acceptable results, OD should be >2 mg/L and residual DO
should be >1 mg/L
• A geometric progression of Df (1, 3, 9, 27, 81, …, so on) can be used
in the test

Standard BOD Bottle Method: Limitations
• Sample dilution introduces error in measurement and affect
reproducibility
• Can not be successfully used for the measurement of BOD
contributed by suspended organic matter
– Must first undergo hydrolysis - takes time (2 to 3 days or more), BOD
exertion may not follow first order kinetics (BOD model assumption)
– Very difficult to ensure uniform distribution of the TSS among the BOD
bottles - consequence is erroneous BOD measurement.
• Testing requires long time (5 days) - results become less relevant
(for operation and control of, specially, biological treatment units)
– Attempt to reduce the time required: increase the incubation
temperature (to 27°C to reduce time to 3 days).
• Dilution of sample with nutrient rich buffer solution may not reflect
the conditions existing in the treatment processes
• Inaccuracy of BODt measurement: 15 to 50% (18% SD)

Interferences
• Secondary effluent samples and samples seeded with secondary
effluents, and polluted water samples collected from surface water
bodies show significant nitrification rates
– Nitrification inhibitor chemicals: TCMP (2-chloro, 6-trichloro methyl
pyridine)
– Whenever nitrification inhibitor chemical is used, results are reported
as CBOD5 (not as BOD5)
• Dilution water used can also introduce positive error
– Good quality dilution water exerts < 0.1 or 0.2 mg/l of oxygen demand
during 5-day incubation at 20°C.
• Sulfides and ferrous iron can be oxidized during incubation and
introduce positive error
• Residual chlorine if present can inhibit biological activity and bio-
oxidation of organic matter
– Samples with residual chlorine are first dechlorinated
– Keeping under light for 1 to 2 hours can dechlorinate the sample
– Addition of predetermined quantity of sodium sulfite can dechlorinate
– Dose of sodium sulfite required: Take 200 ml sample, add 2 ml of 1:1
acetic acid or 1:50 H2SO4 and 2 ml of 1% KI, and titrate against Na2SO3,
use starch as indicator - Na2SO3 consumed is the dose

Serial BOD test by BOD bottle method
• Needed for finding out BOD kinetics parameters
• Involves measurement of BOD1, BOD2, …, BODi, …, BODn
• Similar to 5 day or 3 day BOD test, but daily BOD is measured
• Large number of diluted sample bottles are incubated and daily 2
or 3 bottles are taken out for measuring DO and BODi estimation
• For acceptable results, the conditions, DOf >1.0 mg/L and DOi-Dof
>2.0 mg/L should be satisfied in all the cases
• For ensuring this, the sample may be incubated at different dilutions
(shorter the incubation period lesser will be the dilution)
• If X is dilution factor for 5 day BOD, the following dilution factors
may be used in the serial BOD test
– X/4 dilution factor for BOD1, and BOD2 measurement
– X/2 dilution factor for BOD2, BOD3 and BOD4 measurement
– X dilution factor for BOD4, BOD5 and BOD6 measurement
– 2X dilution factor for BOD6, BOD7 and BOD8

Fate of organic matter of the sample in the BOD test
Organic Matter
(dissolved)
Non-biodegradable
& residual organic matter
Suspended & colloidal
organic matter
oxygen
CO2, H2O, NH3, Energy, etc.
New heterotrophic
Microbial biomass
Auto-oxidation
CO2, H2O, NH3, Energy, etc.
ammonia
oxygen
nitrite nitrate
oxygen
(Nitrogenous BOD)
BOD is sum of oxygen utilized during biooxidation of the organic matter
and during autooxidation of the microbial biomass
(Carbonaceous BOD)
oxygen
Nitrification
Residual biomass
Cell debris
hydrolysis

Conclusions drawn from the analysis of the
fate of organic matter during BOD test
• Oxygen demand exerted is having
– Demand for biooxidation of organic matter and for autooxidation
of microbial biomass (carbonaceous BOD)
– Demand for the nitrification of the ammonia generated or already
present (nitrogenous BOD) – chemical inhibition of nitrification
– Demand of the seed and of the dilution water used
• Because of non-biodegradable organic matter, residual organic
matter, and residual biomass, BOD is always lesser than ThOD
• Unless some of the biodegradable organic matter is resistant to
chemical oxidation BOD is lesser than COD
• Complete biodegradation of organic matter needs infinite time
• BOD includes two components: Carbonaceous BOD and
Nitrogenous BOD

Ultimate BOD (BODu)
BODt is the sample’s oxygen demand when it is incubated for ‘t’ time
(3 or 5 days) at XᵒC temperature
• Higher the temperature lower will be the time
Only a portion of the biodegradable organic matter is oxidized -
oxidation of total matter requires >25 d (60-90 days)
BODu test wherein the sample is aerated at regular interval and
incubated till daily demand becomes <1 or 2% of the cumulative
demand is used for finding
• Nitrification demand of oxygen is parallelly quantified and subtracted
Incubating and waiting for that long period for the results is not
desirable but knowing ultimate BOD (BODu) is considered
important
For this the BODt results are extrapolated through using BOD kinetics
model which assumes that the BOD exertion follows first order
decreasing rate of increase

Oxygen demand exertion pattern of a sample during incubation

BOD kinetics
Oxygen demand exertion pattern is first order decreasing rate of
increase and can be shown as
ttou LBODLBOD
''

ttimegivenanyat
exp(-k.t)}-{1LBOD
BOD
ot
t

aswrittenbecan
 20
20T kk 
 T

T is temp. in °C
 is constant - taken as 1.056 for
20-30°C and as 1.135 for 4-20°C
kL-dL/dt
L0

 tt LBOD
exp(-k.t)LL ot 
dL/dt is rate of oxygen demand exertion
Lt is oxygen demand that is yet to be exerted at
after incubation time ‘t’
L0 is oxygen demand to be exerted by the sample
at incubation time ‘zero’ (also known as BODu)
k is BOD reaction rate constant (per day units)
K and L0 are known as BOD kinetics parameters
Use of BOD kinetic model requires knowledge of BOD kinetic parameters

BOD Kinetics Parameters and their
Estimation
• K and L0 are BOD kinetics parameters
• Use of BOD kinetics model requires values of these
parameters
• Results of a serial BOD test for n days can be used for
finding the BOD kinetic parameter values
• Methods used to determine BOD kinetics parameters
• Method of least squares
• Method of moments (Moore et al. 1950)
• Log difference method (Fair, 1936)
• Fugimoto method (Fujimoto, 1961)
• Daily difference method (Tsivoglou, 1958)
• Rapid ratio method (Sheehy, 1960)
• Thomas method (Thomas, 1950)

Method of least squares for BOD kinetics parameters
 
n
BOD
Kn
dt
BODd
BOD
BODBODn
dt
BODd
BODBOD
dt
BODd
n
K
tt
BODBOD
dt
BODd
BODKLKLK
n
i i
n
i
i
u
n
i i
n
i i
n
i
n
i
i
n
i ii
i
ii
ii


 



 




















1
1
2
11
2
1 11
11
11
0
.
)(
.
)(
..
)(
.
)(
...
dt
d(BOD)
Time (day) BOD BOD2 dBOD/dt (dBOD/dt).BOD
1
2
…
I
…
n
Results of serial BOD test for n days are needed

Method of Moments for BOD kinetic parameters
• Moore’s diagram (a nomograph relating K with BOD/L0 and
BOD/(BOD.t)) is needed
– Moore’s diagram is different for different n value
• Results of serial BOD test for n days are used to find BOD and
BOD/ (BOD.t)
• BOD/(BOD.t) value is used to read k value and BOD/L0 value
from the Moore’s diagram
• From BOD/L0, since BOD is known, L0 is found
• Using the following formulae Moore’s diagram can be constructed
  
 
 
  
 
  



























n Kin
K
KnK
n
n
K
KnK
n
ii
n
tBOD
BOD
n
L
BOD
1
.
1
.
1
1
.
0
1
exp.
1exp
1expexp
.
1exp
1expexp

k 4 days 5 days 6 days 7 days 8 days
value Y/L0 Y/tY Y/L0 Y/tY Y/L0 Y/tY Y/L0 Y/tY Y/L0 Y/tY
X- axis Y1-axis Y2-axis Y1-axis Y2-axis Y1-axis Y2-axis Y1-axis Y2-axis Y1-axis Y2-axis
0.001 0.01 0.333 0.01 0.273 0.02 0.231 0.03 0.200 0.04 0.177
0.01 0.10 0.334 0.15 0.273 0.21 0.231 0.27 0.201 0.35 0.177
0.025 0.24 0.335 0.36 0.274 0.50 0.232 0.66 0.201 0.84 0.178
0.05 0.46 0.336 0.69 0.276 0.94 0.234 1.24 0.203 1.57 0.179
0.1 0.86 0.339 1.26 0.278 1.71 0.237 2.21 0.206 2.76 0.182
0.15 1.21 0.341 1.74 0.281 2.33 0.239 2.98 0.209 3.68 0.185
0.2 1.51 0.344 2.14 0.284 2.84 0.242 3.60 0.211 4.40 0.188
0.25 1.77 0.347 2.49 0.286 3.26 0.245 4.09 0.214 4.96 0.190
0.3 2.00 0.349 2.78 0.289 3.61 0.247 4.49 0.216 5.40 0.193
0.35 2.20 0.351 3.03 0.291 3.91 0.249 4.82 0.218 5.76 0.195
0.4 2.38 0.354 3.24 0.294 4.15 0.251 5.09 0.221 6.05 0.197
0.45 2.53 0.356 3.43 0.296 4.36 0.254 5.32 0.223 6.29 0.199
0.5 2.67 0.358 3.59 0.298 4.54 0.256 5.51 0.224 6.49 0.200
0.55 2.79 0.360 3.72 0.300 4.69 0.258 5.67 0.226 6.65 0.202
0.6 2.89 0.362 3.84 0.302 4.82 0.259 5.80 0.228 6.79 0.203
0.7 3.07 0.366 4.04 0.305 5.03 0.262 6.02 0.231 7.02 0.206
0.8 3.22 0.369 4.20 0.308 5.19 0.265 6.19 0.233 7.19 0.208
0.9 3.33 0.372 4.32 0.311 5.32 0.268 6.32 0.235 7.32 0.210
1 3.43 0.375 4.42 0.313 5.42 0.270 6.42 0.237 7.42 0.211

Moore's Diagram for n = 5 days
2.779476
0.295758
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 0.2 0.4 0.6 0.8 1
'k' value
CumulativeBOD
0.27
0.275
0.28
0.285
0.29
0.295
0.3
0.305
0.31
0.315
CumulativeBOD.t
Moore's Diagram (for n = 8 days)
4.955678
0.198616
0
1
2
3
4
5
6
7
8
0 0.2 0.4 0.6 0.8 1
k value
CumulativeBOD
0.175
0.18
0.185
0.19
0.195
0.2
0.205
0.21
0.215
CumulativeBOD.t
Moore's Digram (for n = 7 days)
4.491721
0.224454
0
1
2
3
4
5
6
7
0 0.2 0.4 0.6 0.8 1
'k' value
CumulativeBOD
0.2
0.205
0.21
0.215
0.22
0.225
0.23
0.235
0.24
CumulativeBOD.t
Moore's Diagram (for n = 6 days)
3.264788 0.251606
0
1
2
3
4
5
6
0 0.2 0.4 0.6 0.8 1
'k' value
cumulativeBOD
0.23
0.235
0.24
0.245
0.25
0.255
0.26
0.265
0.27
CumulativeBOD.t
0
1
L
BOD
n

0
1
L
BOD
n

0
1
L
BOD
n

0
1
L
BOD
n

 

n
n
tBOD
BOD
1
1
.  

n
n
tBOD
BOD
1
1
.
 

n
n
tBOD
BOD
1
1
. 

n
n
tBOD
BOD
1
1
.

Methods for BOD Kinetic Parameters
Fujimoto method
• Serial BOD test results for n number of days are used
• BODt+1 is plotted against BODt in a graph
– On the same graph another plot with slope=1 is plotted
– Point of intersection of the two plots is taken as BODu
• Using the BODu obtained, with the help of BOD kinetics model K
value is found
Rapid ratio method
• Serial BOD test results for n number of days is used
• Ratio of BODt+1 to BODt is plotted against BODt+1 in a graph
– On the same graph another plot with slope=1 is plotted
– Point of intersection of the two plots is taken as BODu
• Using the BODu obtained, with the help of BOD kinetics model K
value is found

Methods for BOD Kinetic Parameters
Thomas method
• Serial BOD test results are needed
• The kinetic parameters determination is based on the following
equation (Thomas equation)
• (t/BOD)1/3 is plotted against t
• (KL0)1/3 is obtained as intercept and K2/3/6L1/3 as slope
• Form the slope and intercept K and L are calculated
  t
L
K
LK
BOD
t
.
6
.
3
1
0
3
2
3
1
0
3
1







• Nitrogen
– Kjeldahl nitrogen
• Ammonical nitrogen (NH3-N)
• Organic nitrogen (Organic-N)
– Nitrite nitrogen (NO2-N)
– Nitrate nitrogen (NO3-N)
– Total nitrogen
• Phosphorus
– Ortho phosphorus
– Total phosphorus
110

Total Kjeldahl Nitrogen
Organic-N
• Organically bound nitrogen is in the trinegative state
• Natural materials like proteins, peptides, nucleic acids and urea, and
many synthetic organic materials have organic-N
Ammonical-N
• Deamination of organic-N and hydrolysis of urea produce
ammonical-N
• Ammonical-N encountered in waters is <10 µg (in ground waters) to
>30 mg/l (in some wastewaters)
– Groundwater has low ammonical-N (soil absorbs and does not allow
leaching)
• Ammonia is often added to water in WTPs for forming combined
residual chlorine
Analytically organic-N and ammonical-N can be determined
together and referred to as Total Kjeldahl Nitrogen (TKN)
112

Methods of Analysis
Ammonical-N can be measured by:
– Nesslerization method (sensitive to 20 µg/l and used for <5 mg/l)
– Phenate method (sensitive to 10 µg/l and used <500 µg/l)
– Titrimetric method (preferred for higher levels, >5 mg/l)
– Ammonia selective electrode method (good for 0.03 to 1400
mg/l levels)
Usually samples need preliminary distillation
– When samples are turbid or coloured or having hydroxide
precipitates of calcium and magnesium (interfere with direct
methods)
– When samples are preserved with acid
When concentration is low, drinking water or clean surface
waters or good quality nitrified wastewater samples can be
tested by direct nesslerization or direct phenate methods - Still
for greater precision preliminary distillation is required 113

Organic-N of the sample can be measured from
– The residual left after preliminary distillation of the sample for
ammonical-N measurement or
– Sample after the removal of ammonical-N from it
• Measurement of organic-N involves
– Conversion of organic-N into ammonical-N through digestion
– Estimation of ammonical-N by one of the Ammonical-N
estimation methods
• Depending on the concentration, either macro-kjeldahl or
semi-micro-kjeldahl method is used for organic-N analysis
A sample is directly tested, without the preliminary distillation,
for TKN (ammonical-N plus organic-N) measurement
Methods of Analysis
114

Sampling and analysis for ammonical-N and organic-N or TKN
involves
• Sample collection, preservation and storage
– If residual chlorine is present, immediately after sample collection
destroy it (for preventing ammonical –N oxidation)
– As far as possible analyze fresh samples
– Preserve samples by acidifying with conc. H2SO4 to 1.5 to 2.0 pH, and
store at 4°C – neutralize to 7 pH with NaOH /KOH prior to testing
• Preliminary distillation and collection of the distillate in boric
acid or sulfuric acid solutions
– Estimation of ammonical-N by any of the methods
• Kjeldahl digestion to convert organic-N into ammonical-N
• Kjeldahl distillation and collection of the distillate in boric
acid or sulfuric acid solutions
– Estimation of organic-N as equivalent to ammonical-N
Method of Analysis
115

Preliminary distillation: interferences
Glycine, urea, glutamic acid, cyanates and acetamide if present in
samples can hydrolyze on standing and introduce + error
– Sample is buffered at 9.5 pH with borate buffer to decrease
hydrolysis of cyanates and organic nitrogen compounds
Volatile alkaline compounds like hydrazines and amines
influence titrimetric results
Some organic compounds, ketones, aldehydes, alcohols and some
amines, cause yellowish/greenish colour even after distillation
– Glycine, hydrazine and some amines give characteristic yellow
colour on nesslerization
– Boiling the distillate at low pH before nesslerization can remove
formaldehyde like interferences
116

• Steam out the distillation apparatus
– Take water into distillation flask, add borate buffer, adjust pH
to 9.5 with NaOH and steam out
• Distillation of the sample
– Take 500 ml sample, or a fraction of it diluted to 500 ml, or 1 L
if ammonical-N is <100 µg/l, into the distillation flask, adjust pH
to 9.5 with 6N NaOH and add 25 ml borate buffer solution
– Disconnect steaming out flask and connect sample distillation
flask and distill at 6-10 ml/min. rate
– Collect distillate in 500 erlenmeyer flask into 50 ml of boric acid
or sulfuric acid solution - submerge condenser outlet tip in acid
– After collecting 200 ml distillate, free condenser outlet tip from
absorbent acid and continue distillation for 1-2 min to clean
condenser and its delivery tube
• Analyse the distillate for ammonical-N
Preliminary distillation
118

Kjeldahl digestion
Meant to convert organic-N into ammonical-N while not
affecting the other forms of nitrogen
– Fails to influence azide, azine, azo, hydrazone, nitrate, nitrite,
nitrile, nitro, nitroso, oxime and semi-carbazone nitrogens
Macro or semi micro kjeldahl digestion method is used
– Macro-kjeldahl method for samples with low organic-N
– Semi-micro-kjeldahl method for samples with high organic-N
In the presence of H2SO4, K2SO4 and (mercuric sulfate) catalyst
(all present in the digestion reagent) organic-N is converted
into ammonium sulfate
– During digestion ammonium complex is formed with mercury
and this is decomposed by sodium thiosulfate
– Even the free ammonia of the sample is converted into
ammonium sulfate
119
Hands on Training Program on Water and Wastewater Analysis (24-29th June, 2013)

Nitrate can prove both a + and a - interference
– At >10 mg/l, it can oxidize some fraction of the ammonical-N
during digestion
– In the presence of sufficient organic matter, nitrate can be
reduced to ammonical-N
The acid and the salt of the digestion reagent are meant for
producing 360-370°C temperature for digestion
– Higher salt concentration can raise the temp. to >400°C during
digestion and this can result in the pyrolytic loss of nitrogen
– Higher salt levels demand more acid for maintaining the desired
acid-salt balance (1 mL H2SO4 per gram of salt is needed)
– Too much acid can reduce digestion temp. to <360°C and this
can lead to incomplete digestion
– Higher levels of organic matter in the sample can consume more
acid – this can increase salt to acid ratio and the digestion
temperature (every 3 grams of COD requires 10 mL of acid)
Kjeldahl digestion: Interferences
120

Digestion reagent:
• Dissolve 134 g K2SO4 in 650 ml water and 200 ml of conc. H2SO4.
• While stirring add 25 ml mercuric sulfate solution (8 g of mercuric
oxide in 100 ml of 6N H2SO4)
• Makeup the volume to one liter and keep the reagent at 20°C
– Toxicity and residues disposal are problems when mercuric sulfate is
used as a catalyst
– 10 ml of copper sulfate solution (25.115 g/L of CuSO4) per 50 ml
digestion reagent can be used in place of mercuric sulfate
– Selenium can also be a catalyst (but it is highly toxic and also acts as an
interference)
Sodium hydroxide-sodium thiosulfate reagent:
• Dissolve 500 g NaOH and 25 g Na2S2O3.5H2O in water and dilute to
one liter
Kjeldahl digestion
121

• Take measured volume of sample in 800 ml capacity digestion
flask and diluted to 500 ml
Volume of the sample should be such that it has 0.2 to 2 mg of
TKN in it
• 500 ml when organic-N is 0.1-1 mg/l
• 250 ml when organic-N is 1-10 mg/l
• Take 1 L sample when organic –N is <0.1 mg/L and use bigger
Kjeldahl flask
• Remove ammonia by distillation after adding 25 ml borate
buffer and adjusting pH to 9.5 with 6N NaOH
– Distillate can be collected into boric acid or sulfuric acid for
determining ammonical-N of the sample
– Residue left behind after preliminary distillation of sample for
ammonical-N can be used for organic-N measurement
Kjeldahl digestion and distillation
122

• Cool the sample after distillation removal of ammonical-N,
add 50 ml digestion reagent and glass beads, and mix contents
• Heat the digestion flask under hood with suitable ejection
equipment to briskly boil until the volume is reduced to 25-50
ml and release of copious white fumes
• Continue digestion for another 30 min. till the sample turns
clear or straw-coloured
• Cool the flask contents, dilute to about 300 ml, and add 50 ml
of hydroxide-thiosulfate reagent along the walls so as it forms
an alkaline layer at the flask bottom
• Connect the flask (with diluted digested sample and bottom
alkaline layer) to a steamed out distillation system
• Mix the contents and distillate (similar to the preliminary
distillation) and collect distillate into boric acid/ sulfuric acid
Run reagent blank parallel to the sample through all the steps and
apply necessary corrections to the results on the basis of the
blank results
Kjeldahl digestion and distillation
123

Semi-micro Kjeldahl method
• Take measured volume of the sample, adjust to 50 mL, add 3
ml borate buffer and adjust pH to 9.5 with 6N NaOH
– 50 ml for 4-40 mg/l concentration
– 25 ml for 8-80 mg/l
– 10 ml for 20-200 mg/l
– 5 ml for 40-400 mg/l
• Transfer the contents to 100 mL semi-micro kjeldahl flask and
boil off 30 mL of the contents for remove the ammonical-N
• Add 10 ml digestion reagent and a few glass beads, heat till the
sample becomes clears and copious fumes come out, and
continue heating, at maximum heating, for 30 minutes more.
• Cool the contents and transfer into a micro-kjeldahl distillation
apparatus while ensuring the total volume <30 mL
• Add 10 mL hydroxide-thiosulfate reagent, turn on distillation,
and collect 30-40 ml distillate in 10 ml H3BO3/H2SO4 solution
124

125

Nesslerization method
• Undistilled samples
– Add 1 ml ZnSO4 solution (100 g ZnSO4.7H2O in 1 liter) to 100
mL of sample, mix, adjust pH to about 10.5 with 6N NaOH and
allow the sample to stand
– Clarify the supernatant by centrifuging or filtering prior to
nesslerization
• Can remove calcium, iron, magnesium, etc. (which form turbidity
on nesslerization) and suspended solids & colour
• Samples with >10 mg/l of NH3-N may loose some ammonia from
higher pH
– To 50 ml of the filtered/centrifuged (or a portion of it diluted to
50 ml) sample add a drop of EDTA reagent or 1 or 2 drops of
Rochelle salt solution, mix and then nesslerize
• Addition of EDTA or Rochelle salt solution inhibits precipitation of
calcium, iron, magnesium, etc., when nesslerized (but EDTA
demands additional nessler reagent)
126

• Distilled samples
– Prepare standard solution (1 mL = 10 µg NH3-N) from stock
ammonium solution ((1 mL = 1 mg of NH3-N)
– Distill samples, standards and reagent blanks and collect distillate for
nesslerization
– Dilute the distillate plus boric acid solution to 500 mL volume and take
50 mL for nesslerization
• Nesslerize the sample with 2 mL Nessler reagent (if the sample
is already neutralized with NaOH use only 1 mL)
– For the reaction to occur allow at least 10 min. (when NH3-N is very
low use 30 min. reaction time)
– Keep temperature and reaction time same for samples, blanks
and standards
127

• Measure transmittance or absorbance of samples and standards
against reagent blank by spectrophotometer
– For low NH3-N levels (0.4 to 5.0 mg/l) measure colour at 400-
425 nm and use light path of 1 cm (5 cm light path allows
measurements as low as 5-60 µg/L)
– For NH3-N levels approaching 10 mg/l use 450-500 nm
wavelength
– Measurements for standards are used for calibration
• Visual comparison against standards can be alternative to
spectrophotometer
– Temporary standards prepared from standard NH4Cl in the range
of 0-6 ml in 50 mL water and nesslerized by adding 1 ml of
Nessler reagent can be used
– Permanent standards prepared from potassium chloroplatinate
and cobaltous chloride solutions and calibrated against
temporary standards can also be used
128

– EDTA reagent: dissolve 50 g of ethylene diamine tetra
acetate dihydrate in 60 ml water containing 10 g NaOH
(heat to dissolve if needed and cool to room temp.) and
dilute to 100 mL
– Rochelle salt solution: dissolve 50 g of potassium sodium
tartrate tetra hydrate in 100 ml water, boil out to reduce
volume to 30 ml, cool and dilute 100 ml
– Stock ammonium solution: dissolve 3.819 g anhydrous
NH4Cl (dried at 100°C) in water and adjust volume to 1
liter (1 mL = 1 mg of NH3-N)
– Nessler reagent: dissolve 160 g NaOH in water, cool,
slowly add mixer of 100 g of mercuric iodide (HgI2) and 70
g potassium iodide (KI) dissolved in water, and adjust
volume to 1 liter
129

Titrimetric method
• Distillate collected into boric acid solution is used
– Sample size: 250 ml for 5-10 mg/l of NH3-N; 100 ml for 10-20
mg/l; 50 ml for 20-50 mg/l and 25 ml for 50-100 mg/l
– Indicating boric acid: dissolve 20 g of H3BO3 in water, add 10 ml
of mixed indicator and adjust volume to 1 liter
– Mixed indicator: dissolve 200 mg of methyl red in 100 mL of
95% ethyl or isopropyl alcohol and 100 mg of methylene blue in
50 mL of 95% ethyl or isopropyl alcohol and mix the two
• Titrate the distillate with 0.02N H2SO4 to pale lavender colour
end point (1ml titrant used = 280 µg of NH3-N)
• Run blank through all the steps and correct results
130

Phenate method
• Method is good for 10 to 500 µg/l
• Preliminary distillation of sample and collection of distillate
• Alkalinity >500 mg/l, acidity >100 mg/l and turbidity can
interfere with direct phenate method
• Distillate is collected into 0.04N H2SO4
• Ammonia is made to react with hypochlorite and phenol in
the presence of manganous salt catalyst to form indophenol
(an intensely blue coloured compound)
• Concentration of indophenol is measured by
spectrophotometer at 630 nm at path length of 1cm
131

Ammonia selective electrode method
Uses hydrophobic gas permeable membrane to separate sample
from an electrode internal solution (NH4Cl)
• By raising pH to 11 NH3-N is converted into gaseous form
• Gaseous NH3 diffuses through membrane and changes pH of the
internal solution
• This changes the millivolt reading of the meter proportional to NH3-
N concentration
Measurement
• 100 ml sample is taken, and ammonia selective electrode is
immersed in it
• While mixing with magnetic stirrer pH of the sample is adjusted to
11 by adding 10N NaOH
• After stabilization take millivolt reading for the sample
132

Ammonia selective electrode method
Calibration
• Prepare standards with 1000, 100, 10, 1 and 0.1 mg/l levels
• Take millivolt reading for each of the standards in a way similar to
that of sample
• Plot readings on semi-log plot (take concentrations on the log axis
and millivolt readings on linear axis)
Method is applicable for measurement of 0.03 to 1400 mg/l
The sample does not require distillation
Interference
• High concentration of dissolved ions affect the measurement but
color and turbidity do not
• Amines introduce positive error
• Mercury & silver through complexing introduce negative error
133

Nitrite nitrogen and Nitrate
nitrogen

Nitrite and Nitrate Nitrogen
• Oxidized Nitrogen may be present in water mainly in two
forms: nitrite and nitrate
• Nitrite
• Represents an intermediate oxidation state and present
usually in very low concentrations
• Often used as corrosion inhibitor in industrial process water
• Nitrate
• Occurs in trace quantities in surface water (however,
wastewaters of biological nitrifying treatment plants can
have upto 30 mg/L), but ground waters have higher levels
• High levels of nitrate in water can be problematic
– thought to be toxic to humans, particularly to babies –
contributes to methemoglobinemia
– oxidized nitrogen is a factor in the eutrophication of waters
• All forms of nitrogen (reduced and oxidized) can be digested
and converted into nitrate for measuring as total nitrogen 135

Sample preservation and storage
• Samples for nitrate
– Samples should be promptly analyzed
– Store at 40C up to 2 days (24 hr.!)
– Unchlorinated samples can be preserved with 2 mL/L conc
H2SO4 and stored at 40C
• Samples for nitrite
– Analyse promptly, if not nitrite can be converted into
nitrate/ammonia by bacteria
– Freeze sample at –20°C for preservation or store at 4°C for
short-term preservation (1 to 24 hrs.)
• For acid preserved samples nitrate and nitrite can not be
determined as individual species
136

Methods of analysis
• Nitrite
– Colorimetric method – suitable for 5 to 1000 µg/L – acid
preservation for samples should not be used
– Ion-chromatography
• Nitrate
– UV Spectrophotometric Method – used for screening
uncontaminated water low in organic matter
– Cd-reduction Method (range 0.01 – 1.0 mg/L)
– Ion Chromatography or capillary ion electrophoresis
– Nitrate electrode method (0.14 – 1400 mg/L)
• Total nitrogen
– Measured through conversion of all (reduced and oxidized)
forms of nitrogen into nitrate and estimation of nitrate
– Persulfate/UV digestion or persulfate digestion is used
• Not effective for wastes with high (suspended) organic loadings
• Recovery of some industrial nitrogen containing compounds is low137

Nitrite -N: Colorimetric method
Good for 10 to 1000 g/L levels (light path of 5 cm allows
measurement in the 5-50 g/L range)
Nitrite forms reddish purple azo dye at 2-2.5 pH by coupling diazotized
sulfanilamide with N-1(1-naphthyl)-ethylene diamine dihydro
chloride (NED dihydrochloride)
Interferences
– NCl3 imparts false red colour
– Sb3+, Au3+,Bi3+,Fe3+,Pb2+,Hg3+,Ag3+, chloroplatinate (PtCl6
2-) and
metavanadate can precipitate under test conditions and interfere
– Cupric ion can catalyze decomposition of the diazonium salt and
introduce negative error
– Colored ions and suspended solids can also interfere
Use nitrite free water during sample analysis for nitrite
138

Nitrite -N: Colorimetric method
• Filter the sample through 0.45 m pore membrane filter and adjust
pH to 5-9 with HCl or NH4OH
• Take 50 ml or a portion diluted to 50 ml (dilution when conc. is >1.0
mg/L) and add 2 ml colour reagent and mix
• After 10 min but before 2 hrs measure absorbance at 543 nm
• Treat standards also with colour reagent and measure absorbance
– Plot absorbance of standards against NO2
- concentration for obtaining
a standard/calibration curve
• Read sample’s nitrite concentration from the standard curve
Colour reagent: add 100 ml of 85% phosphoric acid to 800 ml water,
dissolve 10 g of sulfanilamide, then dissolve 1 g of N-(1-naphthyl)-
ethylenediamine dihydrochloride, and adjust volume to 1 liter – can
be stored upto a month in dark bottle in refrigerator
Standard stock solution : dissolve 1.232 g NaNO2 in water and dilute to
1000ml: 1 mL = 250µg Nitrite -N
139

Nitrate: Cd reduction method
• Range: 0.01 to 1 mg/L Nitrate-N
• Nitrate-N is almost quantitatively reduced to Nitrite-N in the
presence of cadmium (Cd).
• Nitrite thus produced is diazotized with sulfanilamide and
coupled with N-(1–naphthyl)-ethylene diamine dihydro
chloride to form colored azo dye
• The colour intensity is measured spectrophotometrically
• Correction is needed for the nitrite-N originally present in the
sample
– Testing the sample for nitrite without subjecting it to nitrate
reduction step is used for the correction needed
140

Handling interferences
• Turbid samples need filtering through 0.45 µm pore (nitrate
free) membrane filter
– Suspended solids will restrict sample flow so pre filtration is
needed
• EDTA is added to remove interference from iron, copper or
other metals
• Residual chlorine if present is removed by dechlorination with
sodium thiosulfate
• If oil and grease are present the sample is pre-extracted with
organic solvent.
• Chloride ions can significantly decrease the rate of reduction
141

Cd reduction column 142

Cd reduction column
Cd reduction column
• Constructed from two pieces of tubing (3.5 mm ID and 2 mm ID
tubing) joined end to end
• 3 cm ID and 10 cm long tube is fused on the top of 25 cm long and
3.5 mm ID tubing
• Stopcock arrangement is made to allow control of flow rate
Activation
• Wash the column with 200 mL dilute NH4Cl-EDTA solution
• Activate the column by passing >100 mL of a solution (of 25% 1.0
mg/L nitrate standard and 75% NH4Cl-EDTA solution) through the
column at 7 to 10 mL/min, rate.
Ammonium chloride-EDTA solution: dissolve 13 g NH4Cl and 1.7 g
disodium ethylene diamine tetra acetate (EDTA) in 900 mL water,
adjust pH to 8.5 with NH4OH and dilute to 1L.
143

• Screen the sample and adjust the pH between 7 and 9.
• To 25.0 mL sample (or a portion diluted to 25.0 mL), add 75
mL NH4Cl- EDTA solution, mix and pass through the column
at 7 to 10 mL/min. rate - discard the first 25 mL, and collect
the rest in original sample flask.
• Within 15 min after reduction, add 2.0 mL color reagent to 50
mL sample and mix, and within 10 min. to 2 hours measure
absorbance at 543 nm
• From the stock solution, prepare (100 mL) standards in the
range 0.05 to 1.0 mg/L nitrate-N
• Carry out cadmium reduction of the standards exactly as has
been done for the sample.
Stock nitrate solution (1.00mL = 100µg NO3
- -N): dissolve 0.7218 g
dry potassium nitrate in water and dilute to 1000 mL – preserve the
stock solution with 2mL CHCl3 /L.
– Intermediate stock nitrate solution (of 1.0 mL = 10 µg NO3
- -N
strength) is prepared from this stock for routine use 144

Nitrate: Ion electrode method
Interferences
• Chloride and bicarbonate ions interfere when their weight
ratios to nitrate-N are >10 and >5, respectively
• NO2–, CN–, S2–, Br–, I–, ClO3–, and ClO4– are also
potential interferences (but do not normally occur at
significant levels in potable waters)
• Electrodes function satisfactorily in buffers over 3 to 9 pH
range – but for avoiding erratic responses pH is held constant
• Since the electrode responds to nitrate activity, ionic strength
must be constant in all the samples and the standards
• A buffer solution containing
a) Ag2SO4 to remove Cl–, Br–, I–, S2–, and CN–,
b) sulfamic acid to remove NO2–,
c) a buffer at pH 3 to eliminate HCO3– and to maintain a constant
pH and ionic strength, and
d) Al2(SO4)3 to complex organic acids is used 145

Preparation of calibration curve
• Transfer 10 mL of 1 mg/L nitrate -N standard to a 50-mL
beaker, add 10 mL buffer, and stir with a magnetic stirrer
– Immerse the electrode tip and record millivolt reading when
stable (after about 1 min)
– Remove the electrode, rinse, and blot dry
• Repeat this for 10 mg/L and 50 mg/L nitrate-N standards
• Plot potential measurements against nitrate -N concentration
on semilog graph paper (nitrate-N on the log axis and potential
on the linear axis)
– A straight line with a slope of +57 ±3 mV/decade at 25°C should
result
• Recalibrate electrodes several times daily (check potential
reading for 10 mg/L nitrate-N standard and adjust the
calibration control until the reading plotted on the calibration
curve is displayed again 146

Measurement of sample:
• Transfer 10 mL sample to a 50-mL beaker, add 10 mL buffer
solution, and stir (for about 1 min) with a magnetic stirrer
• Immerse electrode tip in sample and record potential reading when
stable (after about 1 min).
• Measure standards and samples at about the same temperature.
• Read concentration from calibration curve.
The electrode responds to nitrate ion activity corresponding to
0.14 to 1400 mg/L nitrate –N
Buffer solution: Dissolve 17.32 g Al2(SO4)318H2O, 3.43 g
Ag2SO4, 1.28 g H3BO3, and 2.52 g sulfamic acid (H2NSO3H),
in 800 mL water. adjust to pH 3.0 by 0.10N NaOH, makeup
volume to 1000 mL and store in a dark glass bottle
147

Nitrate: UV Spectrophotometric Method
• Used for samples having low organic matter
• Nitrate ion and organic matter absorb at 220 nm and only
organic matter absorbs at 275 nm
• Interferences
– Dissolved organic matter, surfactants and Cr6+
– Acidification with 1N HCl can prevent the interference from
hydroxide or carbonate concentration
• Procedure
• Filter the sample and add 1 mL of 1 N HCl to 50 mL sample.
• Prepare 50 mL each of NO3
- calibration standards in the range
from 0 to 7 mg/L NO3
- -N from the stock
• Read absorbance at 220 nm and 275 nm
• Construct a standard/calibration curve by plotting concentration
against corrected absorbance.
• Discard the method if correction value is more than 10% of the
reading at 220nm 148

Sample
Standards
NO3
- -N/L
Absorbace
at 220 nm
( R )
Absorbance
at 275 nm
(S)
T = 2S U=R-T
0.2
0.4
0.8
1.4
2
7
Nitrate: UV Spectrophotometric Method
Discard the method if correction value is more than 10% of the
reading at 220nm
149

Total Nitrogen
Chemicals
• Borate buffer solution: Dissolve 61.8 g boric acid, H3BO3, and
8.0 g NaOH in water and dilute to 1000 mL.
• Copper sulfate solution: Dissolve 2.0 g CuSO4˜5H2O in 90 mL
water and dilute to 100 mL.
• Ammonium chloride solution: Dissolve 10.0 g NH4Cl in
water, adjust to pH 8.5 by adding NaOH pellets or NaOH
solution and make up volume to 1 L (stable for 2 weeks when
refrigerated)
• Color reagent: Combine 1500 mL water, 200.0 mL conc.
H3PO4, 20.0 g sulfanilamide, and 1.0 g N-(1-naphthyl)-
ethylene diamine dihydro chloride, dilute to 2000 mL, add 2.0
mL polyoxyethylene 23 lauryl ether and store at 4°C in the
dark (stable for 6 weeks)
151

Total Nitrogen
• Calibration standards: Prepare nitrate calibration standards
(100 mL) in 0 to 2.9 mg/L range, and treat the standards in the
same manner as samples.
• Digestion check standard: Prepare glutamic acid digestion
check standard of 2.9 mg N/L by diluting the stock, and treat
the digestion check standard in the same manner as samples.
• Blank: Carry a reagent blank through all steps of the procedure
and apply necessary corrections to the results
Stock glutamic acid solution: Dry glutamic acid,
C3H5NH2(COOH)2, in an oven at 105°C for 24 h. Dissolve
1.051 g in water and dilute to 1000 mL; 1.00 mL = 100 Pg N.
Preserve with 2 mL CHCl3/L.
– Intermediate glutamic acid solution (1.00 mL = 10.0 Pg N)
152

Total Nitrogen
Digestion:
• Samples should not be preserved with acid for digestion
• To a culture tube (20 mm OD and 150 mm long), add 10.0 mL
sample (or a portion diluted to 10.0 mL) or standard, add 5.0 mL
digestion reagent, cap tightly, mix by inverting twice
– In case of reagent blank, 10 mL water is taken in place of sample
• Heat for 30 min in autoclave/ pressure cooker at 100 to 110°C
• Slowly cool to room temperature, add 1.0 mL borate buffer solution,
mix by inverting twice
Nitrate measurement: Determine by cadmium reduction
Digestion reagent: Dissolve 20.1 g low nitrogen (<0.001% N)
potassium persulfate, K2S2O8, and 3.0 g NaOH in water and
dilute to 1000 mL just before use
Borate buffer solution: Dissolve 61.8 g boric acid, H3BO3, and
8.0 g NaOH in water and dilute to 1000 mL.
153

Chemicals
• Colour reagent: add 100 ml of 85% phosphoric acid to 800 ml
water, dissolve 10 g of sulfanilamide, then dissolve 1 g of N-(1-
naphthyl)-ethylenediamine dihydrochloride, and adjust volume to 1
liter – can be stored upto a month in dark bottle in refrigerator
• Standard stock solution : dissolve 1.232 g NaNO2 in water and
dilute to 1000ml: 1 mL = 250µg Nitrite -N
• Ammonium chloride-EDTA solution: dissolve 13 g NH4Cl and 1.7 g
disodium ethylene diamine tetra acetate (EDTA) in 900 mL water,
adjust pH to 8.5 with NH4OH and dilute to 1L.
• Stock nitrate solution (1.00mL = 100µg NO3
- -N): dissolve 0.7218 g
dry potassium nitrate in water and dilute to 1000 mL – preserve the
stock solution with 2mL CHCl3 /L.
– Intermediate stock nitrate solution of 1.0 mL = 10 µg NO3
- -N
strength is prepared from it used
154

Characterization and measurement of sewage flow rates

Characterization and measurement of sewage flow rates

Recomendados

Recomendados

Más contenido relacionado

La actualidad más candente

La actualidad más candente (20)

Similar a Characterization and measurement of sewage flow rates

Similar a Characterization and measurement of sewage flow rates (20)

Más de Akepati S. Reddy

Más de Akepati S. Reddy (20)

Último

Último (20)

Characterization and measurement of sewage flow rates