Design of Spent Cutting Fluids Treatment Plant for

International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
Design of Spent Cutting Fluids Treatment
Plant for Ibadan Municipal
R.A. Kazeem, D.A. Fadare, N.C Ehumadu
Abstract - Cutting fluids are substances required in several industrial applications for lubrication of metallic parts and
engines. Considering the large amount of cutting fluids consumed and disposed irresponsibly without prior treatment in
Ibadan, Nigeria, we have detected the need to design a spent cutting fluid treatment plant for the city. With this view, a
treatment plant with a retaining capacity of 0.1 million gallons influent per day was designed. The design was carried
out using engineering principles with due consideration to cost, ease of operation, serviceability and durability. The
plant consists of primary clarifier, aeration tank, sedimentation tank, chemical treatment tank, oxygen cylinders,
sludgedigester and the control panel. The proposed design aimed at ensuring a safe re-use of treated waste and
recovered sludge for agricultural purposes. The characteristics of the influent and the expected effluent parameters are
outlined in the Design for Reactor Parameters.
Index Terms: Spent cutting fluids, treatment plant, sludge, influent, effluent and digester.
——————————  ——————————
without any prior treatmentinto rivers, storm
drainages and landfills, where they are exposed to
uncontrolled natural processes of destruction. A
field survey carried out among 103 metal
workshops in Ibadan reported that 23 of the
workshop operators dispose spent MWFs into
storm drainage, 42 dispose as landfills, 13 dispose
into the river(Kazeem et al, 2015). Spent MWFs are
highly visible form of water pollution, land
contaminations, health hazards and environmental
degradation. It harm plants and animals, destroys
rivers, ground waters and the soil. When machine
operators are not careful of properly disposing
spent MWFs, plants and animals suffer it. Many
animals are injured, become ill and die each year
due to machine operators’ carelessness with
contaminated fluids. Animals can swallow and get
entangled with the fluids and chips disposed in
their environment. If the spent fluids entered the
environment or water in small quantity, it can be
concentrated by bio- magnification (Kilgore, 1999).
Regrettably, this condition characterizes the
environmental culture of machine operators in
Ibadan. It is important to note that endanger public
health situation can curtails productivity and
worsen urban condition of health. This ugly
situation has persisted for several years and may
continue to be because of high rate of illiteracy,
ignorance, operators’ inability to maintain a clean
environment and reluctance of operators to
cooperate with authority by disposing spent
Metalworking fluids (MWFs) are used in the metal
cutting workshops as cooling and lubricating
agents (Vesnal et al, 2013). They also have
secondary functions, such as to reduce heat
generation, provide flushing action in washing off
the chips, to reduce friction and wear; and to
protect the newly machined surface from
environmental corrosion. MWFs also help to
increase the tool life by reducing the cutting
temperature during machining process.
MWFs provide numerous advantages but suffer
from serious drawbacks of environmental
problems. After utilization, the MWFs become less
effective due to their thermal degradation and
contamination by substances in suspension
therefore they must be replaced periodically,
generating a waste stream called spent cutting oil
(Sulaymon and Thuaban, 2010). Generally, spent
MWFs contain tramp oils (adulterant hydraulic
and lubricating oil from the machine), greases,
biocides, metal fines, other components of original
emulsified oil and the products of their
degradation. When irresponsibly and nonprofessionally handled, spent MWFs appear as
environmentally hazardous waste oil (Vesnal et al,
In Ibadan (largest city in West African), spent
MWFs are disposed from metal workshops
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
MWFs in illegal sites. Nigeria has a law banning
the disposal of toxic substances such as the
disposal of mineral oils. The pollution abatement
in industries and facilities generating waste
regulation 5.1.9 of 1991 among other things
imposes restrictions on the release of toxic
substances and stipulates requirements for
monitoring of pollution to ensure that permissible
limits are not exceeded while unusual and
accidental discharge contingency plans, generators
liability and strategies for waste reduction the
safety are put in place. Section (1) stipulates that
‘No oil in any form shall be discharged into public
drain, rivers, lakes, sea or underground injection
without a permit issued by the agency or any
organization designated by the Agency (Federal
Ministry of Environment)’ (Bamiro and Osibanjo,
Other factors that militate against descent disposal
of spent MWFs in Ibadan include; uncontrolled
number of increasing metal workshops, poor
planning and lack of waste treatment plants for
spent MWFs treatments.
The major objective of the study is to present a
complete design of spent cutting fluids treatment
plant for Ibadan city. The design will aim at
achieving a safe re-use of treated waste and
recovered sludge for agricultural purposes (such
asirrigation and fertilizers production).
 The designer must be sure of the maximum
number of metal cutting workshops and the
quantity of spent MWFs disposed in each
workshop weekly/monthly so as to determine
the capacity of spent cutting fluids treatment
plant to be designed. In determining the
capacity of the reactor tanks, the designer must
put into consideration the possibility of future
extension of the treatment plant. Special factors
causing influx of MWFs users should be
foreseen to a possible extent.
 Reactor tanks should be provided with stainless
steel ladders or step board for easy access to the
 Reactor tanks should be covered with a light
material e.g. stainless steel and aluminum alloy
open mesh flooring
The objective of the spent cutting fluids treatment
plant is to ensure that spent MWFs collected from
metal cutting workshops are properly collected,
transported, treated to the required level and
finally disposed of without causing any health or
environmental problems. Prior to the design of a
waste treatment plant, the following guidelines
must be followed by the designer:
 The location of site for the waste treatment
plants must be available. It is always advisable
that the location of site should be far from water
bodies, living environments, restaurants and
shops. This will make future operations easy
and reliable. In order to get a suitable location,
the designer can liaise with the state council
and environmental protection agency.
 Clean pipe borne water should be provided at a
convenient location in the treatment site for
pipes and hand washing.
 The material for air pipeline shall be steel with
zinc coating
 Air pipeline shall be installed above waste
cutting fluidslevel to prevent back flow of fluid
into the pipeline
 Valves shall be attached for check, flow
adjustment, back flow prevention and waste air
 Reactor tanks should have drain pipe, catch
basin and gutter on the side or bottom for
 Reactor tanks
 Reactor tank
 The number of air compressors (blowers) shall
be two or more. Capacity and number of air
compressors shall be decided by plant start- up
and future air in need considering diurnal
variation within a day.
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
Further design shall be guided by following basic
design considerations such as;
 Engineering (i.e. engineering drawing; design
of part/components, flow rates)
 Treatment Processes
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
2.1 Working Principles of the Proposed Treatment Plant
The operation of the waste cutting fluids plant is based on the fill-and-draw principle which consists of four main steps namely: Fill, React, Settle
and Draw stages. The fill stage is known as the primary clarifier stage whereby the influent (untreated spent cutting fluid) passes through a
screening where objects such as nylon, cans, bottles, rags and woods are being stopped from entering the aeration chamber. The primary clarifier
stage is important because it ensures the mechanical components such as stirrer, pipes and pumps from getting damage. After partial treatment
in this stage, the spent cutting fluid is transferred to the aeration tank (react stage) by means of a pump. Some sludge will remain in the primary
1: Shows the layout of the spent cutting fluids treatment plantto be designed
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
Fig. 2: Shows the conceptual drawing of the spent cutting fluids treatment plant to be designed.
As the waste cutting fluid enters the aeration tank, it mixes with the bacteria and other microorganisms known as mixed liquor or activated sludge. In
the aeration chamber, the stirrer aerator has two functions: (1) It continuously puts oxygen from the air into the mixed liquor, oxygen which is
necessary for the bacteria to live; and (2) Keeps the contents of the tank mixed and moving. While the waste cutting fluid flows into the aeration
chamber, mixed liquor flows over the adjustable weir and out of the channel to the sedimentation tanks (also known as settle stage). The
sedimentation tank is a specially designed tank which allows the mixed liquor solids (bacteria and inert inorganic material) settle to the bottom. When
the solids settle, they leave a clarified liquid, (fluid floating on the surface) which will pass over the clarifier effluent weir. The cleared fluid from the
sedimentation tank will be discharged to a tertiary treatment tank or a disinfecting chlorine contact chamber before discharging (draw stage) to the
stream. The sludge which has settled to the bottom of the sedimentation tank will continuously be removed by pump for return into the primary
clarifier to mix with new incoming waste cutting fluids. As the sludge accumulates in the hopper base of the primary clarifier, it will be necessary
from time to time to take excess activated sludge out of the process. The waste activated sludge will be removed by gravity to the sludge holding tank
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
The design was carried out using principles of
engineering design with due consideration to cost,
ease of operation, serviceability, durability and
performance. The design of this treatment plant
was separated into three distinct phases which
include: (1) Design of machine components (such
as tank volume, stirrer, pipes, electric power rating
and belts designs), (2) Design of biological kinetics
and (3) Design for fluid flow.
4.1 Design for Future Expansion of
Metalworking Workshops
This section includes designing a municipal waste
cutting fluids treatment plant for Ibadan city,
Nigeria for a projected period of 20years. A
recently completed survey to metalworking
workshops in Ibadan has showed that there are 103
considering future increase of the metalworking
workshops, we can determine the possible number
of workshops in 20 years as follows:
P˕ = P˳ + (K t Pₒ)
P = Future number of metalworking workshops
P˳ ⇒ Present number of metalworking workshops
= 103
t ⇒ Design period required for the plant = 20 years
K ⇒ Constant = 0.03
P₂ₒ = 164.8
Therefore, the proposed waste cutting fluids plant
will be designed for approximately 165
metalworking workshops for a 20 years design
The waste treatment plant has been designed
based upon the following design for reactor
Design Parameter
Average daily flow of waste cutting fluids (Mg d)
Maximum Yield Coefficient (Y), lb VSS/lb BOD 5
0.4 – 0.8
Endogenous Decay Coefficient (kd), day – 1
0.025 – 0.075
Mixed Liquor Suspended Solids (X), mg/L
1,000 – 6,500
Volatile Suspended Solids Fraction (Xa)
0.5 – 0.8
Decay Fraction (fd)
0.78 – 0.82
Density of mild steel material considered (kg/m3)
Acceleration due to gravity, g (m/s)
Sludge age in the reactor, θ c (days)
5 – 15
Influent substrate, BOD 5 concentrate (S o ) [mg/L]
Effluent substrate (BOD 5 ) concentrate (S) [mg/L]
Concentration of sludge in return line, Xr (mg/L)
Concentration of solids in effluent, Xe (mg/L)
Peaking factor
Surface loading rate in settling tank (gal/day/ft3)
Input waste sludge, (gal/day)
Thickened waste activated sludge (%)
Minimum liquid temperature for aerobic digestion (oC)
Maximum liquid temperature for aerobic digestion (oC)
Sludge concentration in the digester (%)
Volatile fraction of digester suspended solids
Specific gravity of digester sludge
Density of water (kg/m3)
Sludge cake solids
Sludge feed solids
Sludge centrate solids
Conversion factor from BOD5 to BOD L
Cake density (lb/ft3)
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International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
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The reactors have been calculated with several
design parameters. The reactors will be provided
with stirrer for mixing, oxygen delivery
requirements and a digester for dewatering of
sludge from the plant.
4.2 Designs for Machine Components
4.2.1 Reactor Tank Design
The reactor tank designed is a combination of two
shapes: a cylinder with a conical hopper at its base
to enable storage of spent cutting fluids.
reactor= [Volume of cylinder +
Volume of cone with a tip (frustum)]
Volume of cone with a tip (frustum) ⇒
[(R₁2 + R₁r₁ + r₁²) − (R₂² + R₂r₂ + r₂²)]
Where (R₁2 + R₁r₁ + r₁²) − (R₂² + R₂r₂ + r₂²) is
wall thickness of frustum
Let h be the height, R the radius of the upper base,
and r the radius of the lower base of the frustum.
Generally, volume, V, for a hollow cylinder is
given by:
V = Area x height = π(r₁2 − r²₂)h
Thickness of the cylindrical wall, t:
t = r₁- r₂
Weight of reactor tank = Volume of reactor tank x
Density of steel
Volume occupied by steel = Volume of the reactor
Density of material = 7850 kg/m3
Mass of reactor tank = volume of reactor tank x
Density of material to be considered
Weight of reactor tank = Mass of reactor tank x
Acceleration due to gravity
Fig 3: Conical Hopper with outlet size D and semi
included angle Ɵ
As commonly practiced, the coefficient of friction
is expressed as the angle of wall friction given by ∅
∅ = arc tan(µ)
With known values of semi included angleƟ, wall
friction ∅ and the effective angle of internal
friction, the flow factor (ff) can be determined from
the Jenike published charts for conical hopers.
For flow:
Assuming σy and σc are related by the material
flow function
σy = σc1.34
Thus, the criterion for flow becomes
4.2.2 Determination of Conical Hopper Outlet
The opening of the diameter for conical hoppers is
given by (Jenike, 1964)
D = H(θ)
H (θ) = 2 +
Where gc is gravity constant conversion factors to
convert the result from units of mass to units of
Ns 2
. Typical value for H is about 2.4 (Jenike,
1964). Therefore θ semi included angle of the
materials from equation (5) is 24°.
] >σ y
And so the critical value of unconfined yield stress
σ crit is found when
] = σ y(10)
ff = 1.54From the Jenike published chart for
conical hoppers. The angle θ was reduced by 3° as
a margin of safety (1964). Therefore θ used was 21°
throughout. Hence solving for σy from equation (1)
gives σ crit
By applying law of indices we have,
σ y (-0.34/1.34)= 1.54
Therefore σy equals to σcrit is 0.1823 kN/m2
2.4 x 0.1823 x 1000
D =
900 x 9.81
Minimum diameter of circular outlet D is 0.0495
4.2.3 Determination of Mass Flow Rate of
Conical Hopper
The mass flow rate or discharge rate of a conical
hopper was determined by the equation (Jenike,
2(m+1)Tan θ
Where A =
For conical hopper m = 1
The stress action on the hopper wall is given by:
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International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
�1 − exp �−
Where B is the hopper maximum diameter and z is
the cylinder height
To estimate the normal stress on the hopper wall
Jassen’s assumption was applied
Pw = KPv
The material that can withstand the maximum
stress acting on the wall of the hoppers should be
Pv =
Capacity Design for a Given Electric Motor
The design for motor output power enables
appropriate selection of a motor with enough
power to start and run the machine at full load.
Power = F x V
P = Power in watts
F = Rotational force acting on the shaft in Newton
V = Linear velocity of the shaft in meters/seconds
But F = ma
M = Mass of rotating shaft in kilogram (kg)
a = Angular acceleration of the motor in
radian/seconds square (rad/s2)
a = w²r
w = angular velocity of the motor in
w = v/r
Therefore v = wr
By putting equation (17) into (16)
F = mw2 r
By putting (18) and (19) into (20)
Vhc = volume of horizontal component of the
Vhc = 4 (lbh)(25)
For the vertical component of the stirrer
Vvc = Volume of vertical component of the stirrer
Vhc = 4 (lbh)(26)
By adding the horizontal and vertical components,
we obtain the volume of the stirrer. Density of
stirrer is material dependent. For example, density
of mild steel is 7.85 x 106kg/mm3
Mass = density x volume
The mass to be obtained from equation (27) will be
substituted into equation (22) to get the electric
power rating
πN 3
P = 8M � � r 2
P = electric motor power rating
M = mass of rotating stirrer
N = speed of the motor
r = radius of themotor pulley
Putting (21) into (20)
πN 3
P = 8M � � r 2 (22)
But w =
4.2.4 Calculation of the Mass of Rotating
Where D = Density of stirrer in kg/mm3
M = mass of stirrer in kg
V = volume of stirrer in mm3
But V = lbh
L = length of stirrer in mm
For horizontal component of the stirrer
4.2.5 Belt Selection and Design
There is need to select a belt that will surely
transmit the ron as required under a reasonable
tension without failure (cutting). Also the belt and
the pulley must also be designed to allow the two
to work together in harmony (to match each other
and to hold firmly to each other). The speed of the
driving pulley and the driven pulley can be
expressed as
DeNe = DsNs
De = Driving pulley diameters (mm)
Ne = Speed of driving pulley (rpm)
Ds = Driven pulley diameter (mm)
Ns = Speed of driven pulley (rpm)
The driving pulley can be determined from the
electric motor to be considered. For instance, if the
speed and diameter of the driving pulley are 600
rpm and 50 mm respectively, then to express the
diameter of the driven pulley by considering speed
input ratio 1:5, we transform equation (28).
Ds =
4.2.6 Center to Center Distance Design
The minimum distance between driving and
driven pulleys for appropriate belt tension is
obtained below
C = (D₁ + D₂) + D₂
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C = the minimum distance between the pulleys in
D 1 = Pitch diameter of the driving pulley (motor
pulley) in meters.
D 2 = Pitch diameter of the driven pulley
4.2.7 Design for Belt Length
The design generally specifies the type of standard
belt to be selected. Design length for belt is
obtained from
(D₂ − D₁)²
(D₂ + D₂) +
L = 2C +
L = Belt length
C = Minimum distance between the pulleys
D 1 = Pitch diameter of the driving pulley (motor
pulley) in meters
D 2 = Pitch diameter of the driven pulley
4.2.8 Tension in the Belt
The tension T 1 acting on the tight side of the belt
and the tension T 2 acting on the slack side of the
belt are calculated using the equation at Hall et al
4.2.9 Pipe Design
Cross – sectional inside area of a pipe can be
calculated as
di 2
A = π� � = π � �
A = cross sectional inside area of pipe (mm2)
di = inside diameter of the pipe (mm2)
Similarly, the cross – sectional outside area of the
pipe can be calculated as
do 2
A = π� � = π �
do = outside diameter (m)
Therefore, the cross-sectional wall area – or area of
piping material can be calculated as
do 2
di 2
Am = π � � − π � �
T₁ − mV²
= ℯ
sin 0.5θ
T₂ − mV²
Where m = mass of a unit length of the belt (kg)
V = linear velocity of belt (m/sec)
∝ = angle of wrap on pulley (rad)
f = coefficient of friction between belt & pulley.
T 1 = Tension in the tight side of belt (N)
T 2 = Tension in the slack side of (N)
θ = Groove angle for v – belt (degree).
The maximum tension in the tight side of the belt
depends on the allowable stress of the material.
Linear velocity V is given by
π x Ds x Ns
V =
The angle of wrap between on the small and large
pulleys for open belt is determined using Hall et al
do2 − di2
Am = cross – sectional wall area of pipe (mm2)
= π�
4.2.0 Shaft Design
To determine the diameter of the shaft by
neglecting bending moment we have:
α1 = 180° − 2sin−1 ⦋
T = Torque transmitted by shaft
P = Power transmitted by the electric motor
N = Number of revolution of shaft per minute
Torque transmitted by the shaft can also be
calculated in terms of the diameter of the shaft as:
π x τ x d³
τ = Allowable shear stress of the material
d = diameter of the shaft
The value of torque obtained in equation (38) can
be substituted into (39)
α₁ = angle of wrap on small pulley
α₂ = angle of wrap on large pulley
R = radius of large pulley (m)
r = radius of small pulley (m)
C = center distance of shaft (m)
4.3 Designs for Biological Kinetics
α2 = 180° + 2sin−1
⦌ (33)
⦌ (34)
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4.3.1 Volume of the Reactor
The volume of the reactor can be determined using
the following equation derived from Monod
θcQY (So − S)
Vr =
Xa (1 + Kdθc)
Vr = Reactor volume (M gal) (m3)
θc = the average time that the sludge remains in the
reactor (sludge age). θc ranges from 5 to 15days for
a complete mix activated sludge process. The
design of the reactor is based on θc on the
assumption that substantially all the substrate
(BOD) conversion occurs in the reactor.. A θc of 8
days will be assumed.
Q = Average daily influent flow rate (Mgd) = 0.1
Y = Maximum yield coefficient (mg VSS/mg
BOD 5 ). For the activated sludge process for
municipal treatment plant Y ranges from 0.4 to 0.8.
A Y of 0.6mg VSS/mg BOD 5 will be assumed.
Essentially, Y represents the maximum mg of cells
produced per mg organic matter removed.
Sₒ = Influent substrate (BOD 5 ) concentration
(mg/L) = 240 mg/L
S = Effluent substrate (BOD 5 ) concentration (mg/L)
= 10mg/L
Xa = Concentration of microorganisms in reactor
Mixed Liquor Volatile Suspended solids (MLVSS)
in mgL. It is generally accepted that the ratio
MLVSS/MLSS is 0.8, where MLSS is the Mixed
Liquor Suspended Solids concentration in the
reactor. MLSS represents the sum of volatile
suspended solids (organics) and fixed suspended
solids (inorganics). For a complete mix activated
sludge process, MLSS ranges from 1,000 to 6,500
mg/L. An MLSS of 4,500 mg/L will be assumed.
Kd = Endogenous decay coefficient (d-1) which is a
coefficient representing the decrease of cell mass in
the MLVSS. For the activated sludge process for
municipal wastewater Kd ranges from 0.025 to
0.075 d – 1 . A value of 0.06d – 1 will be assumed.
Vr = 0.021 M gal
θ = hydraulic retention time
Vr = Volume of reactor
Q = Influent flow rate
θ = 0.21 M gal
4.3.3 Determination of the Quantity of Sludge
The observed cell yield
1+Kd θc
Where, Yobs = Observed cell yield
Yobs= 0.41 mg/mg
Hence, 0.41 mg/mg represents the actual cell yield
that would be observed. The observed cell yield is
always less than the maximum cell yield (Y). the
increase of MLVSS is calculated using the equation
Px = Yobs Q (S˳ − S)(8.34 lb/Mgal/ mg/L)
Px is the quantity of the wasted sludge
Px = 78.65 lb/VSS/d
Therefore the increase in the mass of mixed liquor
suspended solids (MLSS)
= Px(ss) =
4.3.2 Determination of the Hydraulic
Retention Time
The hydraulic retention time (θ) is given by:
Px(ss) = 98.31 lb SS/d.
This is the total mass of sludge wasted from the
system each day
4.3.4 Determination of Oxygen Requirement
based on Ultimate Carbonaceous Oxygen
Demand (BOD L )
The theoretical oxygen requirements are
determined using the BOD 5 of the wastewater and
the amount of organisms (Px) wasted from the
system each day. If all BOD 5 were converted to
end products, the total oxygen demand would be
computed by converting BOD 5 to ultimate BOD
(BOD L ), using the appropriate conversion factor.
Therefore the theoretical oxygen requirements for
the removal of the carbonaceous organic matter in
wastewater for an activated sludged system can be
determined by the equation below:
�total mass of BODʟ utilized, � −
1.42 �mass of organisms wasted, �
For converting BOD 5 to BOD L , a conversion factor,
f is introduced. The most commonly used value of
f is 0.68. Therefore, the theoretical oxygen required
for the removal of the influent BOD 5 is calculated
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Q (S˳−S)(8.34) (lb /Mgal )/(mg /L))
lb O₂/d =
lb O₂/d = 270.9 lb O₂ /d
It is recommended that the aeration equipment be
designed with a safety factor of at least 2.
Therefore, in sizing aeration equipment a value of
(2) (270.9 lb O 2 /d) = 541.9 lb O 2 /d is to be used.
4.3.5 To Compute the Waste Activated
Sludge (WAS) and Return Activated Sludge
(RAS) Requirement
Control of activated sludge process is important to
maintain high levels of treatment performance
under a wide range of operating conditions. The
principle factors used in process control are (a)
maintaining dissolve oxygen levels in the aeration
tanks, (2) regulating the amount of return activated
sludge (RAS), and (3) controlling the waste
activated sludge (WAS). One of the methods of
calculating the waste sludge flow rate is as shown
X = Mixed Liquor Suspended Solids (MLSS) = 4500
as earlier stated
Q = Return activated sludge pumping rate (Mgd)
negligible, a mass balance around the settling tank
yields the following equation for RAS pumping
XQ − XrQw′
Qr =
Xr − X
Using values defined previously, the RAS
pumping rate is computed to beQr = 0.125 Mgd
The ratio of RAS pumping rate to influent flow
rate, or recirculation ratio (α), may now be
= 1.25 ⇒ OK
Recirculation ratio can vary from 0.25 to 1.50
depending upon the type of activated sludge
system used.
4.3.6 To Calculate the Growth of Biological
The growth of biological sludge over time period,
∆t, mg/L is given by:
Growth of biological growth is 11.81 kg/day
Xr = Concentration of sludge in the return line�
When lacking site specific operational data a value
commonly assumed is 8000 mg/L
Qe = Effluent flow are (Mgd)
Xe = Concentration of solids in effluent�
�. When
lacking sites specific operational data, this value is
commonly assumed to be zero.
Qw = Waste activated sludge (WAS) pumping rate
from the return line (Mgd). Therefore, the wasting
rate is calculated using the following:
θc =
Qw ′ Xr + QeXe
Assuming the concentration of solids in the
effluent from the settling tank is low, then the
above equation reduces to:
θc =
⇒ Qw ′ =
Qw = 0.0015 Mgd
To determine the waste activated sludge (WAS)
using this method, the solids concentration in both
the aeration tanks and the return line must be
Assuming that the sludge blanket level in the
settling tank remains constant and that the solids
in the effluent from the settling tank (Xe) are
4.3.7 To Design the Circular Settling Tank
Municipal waste cutting fluids with an average
daily flow of 0.1 Mgd exists the aeration tanks of a
standard activated sludge treatment process.
Design of circular settling tank to separate the
sludge from the effluent is to be designed. The
settling tank will work in conjunction with the
aeration tank. Assume a peaking factor of 2.5. The
following are of paramount importance in the
design of circular settling tank: (1) Determination
of the peak flow (2) Determination of the settling
tank surface area using surface loading criteria (3)
Determination of the settling tank surface area
using solids loading criteria (4) Determination of
the number of settling tanks.
4.3.8 To Calculate the Peak Flow
Using a peaking factor of 2.5. The daily peak flow
Qp is given by:
Qp = Peak flow x Average daily flow = 0.25 Mgd
4.3.9 To Calculate the Settling Tank Surface
Area Using Surface Loading Criteria
The recommended surface loading rates vary
depending upon the type of activated sludge
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
process used. However, surface loading rates
ranging from 200 to 800 gal/day/ft2(8.09 to 32.4 L/
m². d) for average flow, and a maximum of
1,000 gal/day/ft² (40.7 L/m². d) for peak flow are
Qp of 0.25 Mgd �250,000
� and a design surface
loading rate of 400 gal/ day /ft 2 at peak flow the
surface area (A) of a settling tank may be
Surface loading rate (gal/day/ft²)
Settling tank effluent flow (gal/day)
Settling tank area (m2 )
Therefore, A = 625ft2
4.3.0 To Calculate the Settling Tank Surface
Area Using Solids Loading Criteria
The total solids load on a clarifier consists of
contribution from both the influent and the return
activated sludge (RAS).
Qr = RAS flow rate = 1.25 (Q) = 0.125 Mgd
X = MLSS in aeration tank = 4500 mg/L
Therefore, the maximum solids loading occurs at
peak flow and maximum RAS flow rate. The
maximum solids entering the clarifier are
calculated using:
(Qp +
Qr)(X)(8.34 lb. mg. Mgal)
Using values given above;
Maximum solids = 14,073.75 lb/d = 586.41 lb/h =
of suspended solids
Therefore, using a solids loading rate of 2.0 lb/ft2 at
peak flow, the surface area of a settling tank may
be calculated:
(i) The minimum liquid temperature is 15oC and
the maximum liquid temperature is 30oC.
(ii) The system must achieve a 35 percent volatile
suspended solids (VSS) reduction
(iii) Sludge concentration in the digester is 70
percent of the incoming thickened sludge
(iv) The volatile fraction of digester suspended
solids is 0.8.
Factors to be considered in designing aerobic
digester include temperature, solids reduction,
tank volume (hydraulic retention time), oxygen
requirements and energy requirements for mixing.
The total mass of solids processed by the digester
will be 98.31 lb SS/d which is the total mass of
solids wasted from the treatment facility. The total
mass of VSS input to the digester is:
(0.8) Px(ss) = 78.65 lb/d
VSS reduction = (0.35) (Total mass of VSS input to
digester) = 27.53 lb VSS reduced/day
Maximum solids
= 293.2ft²
Solids loading rate
In this case, the solids loading dominate and
dictate the required settling tank area.
4.4 Design of an Aerobic Digester
An aerobic digester is to be designed to treat the
waste sludge produced by an activated sludge
waste water treatment plant. The input waste
sludge will be 3,300gal/d �5
. only� of thickened
waste activated sludge at 5.0 percent solids. The
following assumptions will be considered:
Digested sludge leaving the digester = (Px(ss) –
VSS reduction) lb/d = 70.78 lb/d (59)
4.4.1 To Calculate the Daily Volume of
Sludge for Disposal
The volume of sludge
to be disposed daily (Qi)
Qi = (3,300gal/day) � � = 2357gal/day
4.4.2 To Calculate the Volume of Digested
The volume of digested sludge is:
(ρ)(s. g)(% solids)
V = sludge volume (ft3) (m3)
Ws = weight of sludge (70.78)(lb( (kg)
ρ = density of water (62.4lb/ft3)
s.g. = specific gravity of digested sludge (assume
s.g. = 1.03)
% solids = percent solids expressed as a decimal
(incoming sludge: 5.0%)
Therefore, the volume of the digested sludge is:
V = 22.03ft3/d
4.4.3To Calculate the Volume of the Aerobic
Digester Volume
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
The volume of the aerobic digester is calculated
using the equation below, assuming the digester is
loaded with waste activated sludge only.
X (KdPv + 1/θc)
V = Volume of aerobic digester, ft2/d (m3/d)
Qi = Influent average flow rate to the digester, ft3/d
Xi = Influent suspended solids, mg/L
Kd = Reaction rate constant d-1, This may range
from 0.05 d–1 at 15oC to 0.14d–1 at 25oC (assume 0.08
d–1 at 15oC)
Pv = Volatile fraction of digester suspended solids
(expressed as a decimal) = 0.8 (80%) as stated in the
initial assumptions.
Θc = Solids retention time (sludge age), d assuming
20.8 d
V = 30.041 ft3
A recovery formula is used to determine the solids
capture, the equation for percentage solids
recovery is given by:
Cs F − Cc
R = 100 � � �
F Cs − Cc
R = Recovery, percent solids
Cs = Cake solids, percent solids (assuming 25%)
F = Feed solids, percent solids (assuming 5%)
Cc = Cenztrate solids, percent solids (assuming
Therefore, R = 95.14%
4.4.6 To Calculate the Dewatered Sludge
Cake Discharged Rate
The dewatered sludge (cake) discharge rate is
calculated using the following:
Cake discharge rate (lb/h) dry solids = (sludge
federate, lb/h) (solids recovery)
Cake discharge rate = 98.09 lb/h dry cake
The wet cake discharge in (lb/h) is calculated using
the following:
Wet cake discharge (lb/h)
Cake discharge rate, lb/h
Cake % solids
Therefore, wet cake discharge = wet cake
The volume of wet cake assuming a cake density of
60lb/ft3us calculated as follows:
Volume of wet cake (ft³/h)
Wet cake rate, lb/h
Cake density, lb/ft³
= 6.54 ft³/h wet cake
For a dewatering facility operation of 5 hr/day, the
volume of dewatered sludge cake to be disposed of
per day is:
(6.54 ft³/h)(5 hour/day) = 32.7 ft³/d
= 244.7 gal/day
4.4.4 To Determine the Sludge Feed Rate
Assuming the designed digester will be used to
produce 1200 gal/d of aerobically digested sludge 5
h/d, 3 d/wk, then the sludge fed rate is:
Sludge feed rate
Quantity of anerobic digested sludge
Operating time of facility daily
1200 gal /day
Therefore, sludge feed rate =
[(5 h/d) (60 min /h)
= 4.0 gal/min
By considering a feed sludge specific gravity of
1.03, the sludge feed in lb/h is calculated using the
equation below:
(V)(ρ)(s. g)(% solids)(60 min/hr )
7.48 gal/ft³
4.4.7 To Determine the Percent Reduction in
Sludge Volume
Ws = Weight flow rate of sludge feed, lb/h � �
The percentage reduction is sludge volume is then
calculated using the following:
% Volume Reduction
Sludge volume in − Sludge volume out
x 100% (69)
Sludge volume in
1200 gal/day − 244.7 gal/day
x 100%
1200 gal/day
% Volume Reduction = 79.61%
4.4.5 To Compute the Solids Capture
4.4.8 To Determine the Flow rate required for
Sludge Pump
V = Volume flow rate of sludge feed, gal/min (L/s)
s.g. = Specific gravity of sludge
% solids = Percent solids expressed as a decimal
ρ = density of water (62.4lb/ft3)
By using the values obtained above, the sludge
feed in lb/h is:
Ws = 103.1 lb/hof dry solids
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
The required flow rate for the sludge pump using 4
h.d, 7d/wk operation scheme is:
Flow rate (gal/min) =
(5 h/d)(60 min/hr)
= 4 gal/ min
The velocity of 4.0 gal/min in a 3 inch (76.3mm)
diameter pipe is:
4.0 gal/min
(7.48gal/ft) � � (3 inch⁄12 inch/ft)²(60s/min)
= 0.18ft/s
4.5 Designs for Fluid Flow
4.5.1 Detention Time
The theoretical (calculated) time required for a
given amount of waste fluid to pass through a tank
at a given rate of flow. The time required to fill a
tank at a given flow. The detention time in hours
can be calculated with the formula below:
Detention Time
(Clarifier volume, gal)(24 hr/day)
Flow, gal/day
Volume = 0.785 x Diameter of clarifier x Diameter
of clarifier x Depth x 7.48 gal/ft3 (73)
Project submitted to to the Building &
Construction Department of the University of
Vigneswaran, S., Sundaravedivel, M and
Chaudhary, Sequencing Batch Reactors: Principles,
Design/Operations and Case Studies D.S. Water
and Wastewater Treatment Technologies..
Jenike A.W (1964), Storage and Flow of Solids,
Bulletin No. 123, Utah Engineering Experiment
Station, University of Utah, Salt Lake City, USA
(Revised edition 1970)
Khurmi R.S., Gupta J.K., A textbook of machine
design. Paperback: 1230 pages Publisher.
Fadare, D.A (2004). Development of an Organomineral fertilizer processing plant.A Ph.D thesis,
Mechanical Engineering Department, University of
Ibadan, Ibadan, Nigeria.
Bamiro O.A and Osibanjo O (2004).Pilot study of
used oil in Nigeria.Conducted by Basel convention
regional coordinating center in Nigeria in
collaboration with secretariat of Basel convention,
Vesna, B.L, Ivan, M. K, Miodrag, L.L, Dragiša, S. S,
Dejan, U.S, Vlada, B.V. Scaling up the chemical
treatment of spent oil-in-water emulsions from a
non-ferrous metal-processing plant.SCIENTIFIC
PAPER Hem.Ind. 67 (1) 59–68 (2013).
Kilgore, M (1999), Litter and Pollution – Chintimini
Wildlife Rehabilitation Center.
Kazeem, R.A., Fadare, D.A., Ogundiran, M.B.
(2015). An Assessment of Metalworking Fluids
Utilization and Management Practices of
Machining Workshops in Ibadan.
Tyler G, Hicks, P.E (2006). Handbook of
Sulaymon, A.H, Thuaban, L.H (2010),
Demulsification of Cutting Fluid before Disposal
tothe Environment. Journal of Engineering, 16(1),
4580- 4592
Janssen, H.A (1985), Versucheüber, G, Verein, D,
Zeitschrift, Pages 1045-1049
Jenike, A.W., Storage and Flow of Solids, Bulletin
123, University of Utah Engineering Station, 1964
(revised, 1976).
4.5.2 Flow Rate of Waste Cutting Fluid
Travelling through a Pipe
Flow rate, Q = Velocity x Transverse internal area
of pipe A
Velocity = rate of wastewater travelling through a
Transverse internal area = 0.785dᵢ²
5.0 Conclusion
The design of a spent cutting fluids treatment plant
was carried out for Ibadan community, Nigeria.
Plant capacity of 0.1Mgd was designed using
engineering principles.The designed treatment
plant contained the major components such as
reactors, mixers, aeration gas, and a digester (to
dewater moisture content of sludge).
6.0 References
Fatima, H.A, Salah, F (2011). Design of Wastewater
Treatment Plant.Republic of Iraq Ministry of
Higher Education and Scientific Research. A B.Sc.
IJSER © 2016
International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August-2016
ISSN 2229-5518
Fig.4. Showing the third angle projection of the designed spent cutting fluids treatment plant.
IJSER © 2016
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