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![Page 1: Clarifier General overview of plant components Secondary Sludge P rimary Sludge Clarifier Raw Wastewater Influent PRIMARY DISINFECTION Biological Treatment.](https://reader036.fdocuments.us/reader036/viewer/2022081718/551555a155034685568b56cf/html5/thumbnails/1.jpg)
Clarifier
General overview of plant components
Secondary Sludge
Primary Sludge
Clarifier
Raw Wastewater Influent
PRIMARY
DISINFECTION
BiologicalTreatment
System
SECONDARY
Clean Wastewater EffluentDischarge to Receiving Waters
Preliminary Residuals(i.e., grit, rags, etc.)A
B
C
WastewaterTreatmentResiduals
BiosolidsProcessing
and Disposal
(e.g., attached-grwoth Suspended-Growth, Constructed Wetland, etc.)
Clarifier
PRELIMINARY
Usually to Landfill
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Biological wastewater (WW) treatment
• To remove the suspended solids & the dissolved organic load from the WW by using microbial populations.
• The microorganisms are responsible for– degradation of the organic matter – they can be classified into
• aerobic (require oxygen for their metabolism)• anaerobic (grow in absence of oxygen) • facultative (can proliferate either in absence or presence of
oxygen).
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Biological wastewater (WW) treatment
• If the micro-organisms are suspended in the WW during biological operation– suspended growth processes
• Recycling of settled biomass is required.
• While the micro-organisms that are attached to a surface over which they grow– attached growth processes
• The biomass attached to media (ex. rock, plastic, wood)
• Recycling of settled biomass is not required.
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Attached Growth Process
What can this process do?
1. Remove Nutrient
2. Remove dissolved organic solids
3. Remove suspended organic solids
4. Remove suspended solids
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Cross-section of an attached growth biomass film
Wastewater
Oxygen (the natural or forced draft)
Organic/ nutrient
filter media
Biomass : viscous, jelly-like substance containing bacteria
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Attached Growth Process
• Trickling filter (TF)
• Rotating biological contactor (RBC)
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Trickling Filter (TF)- side view
Wastewater
rotating distributor arms
Packing media
Underdrain
– TF consists of:• A rotating arm that sprays
wastewater over a filter medium.
• Filter medium: rocks, plastic, or other material.
– The water is collected at the bottom of the filter for further treatment.
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Trickling Filter Process
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Design consideration
• Influent wastewater characteristics• Degree of treatment anticipated (BOD & TSS removal). • Temperature range of applied wastewater• Pretreatment processes• Type of filter media• Recirculation rate • Hydraulic and organic loadings applied to the filter• Underdrainage and ventilation systems
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Trickling Filter (TF)- side view
Wastewater
rotating distributor arms
Packing media
Underdrain
– TF consists of:• A rotating arm that sprays
wastewater over a filter medium.
• Filter medium: rocks, plastic, or other material.
– The water is collected at the bottom of the filter for further treatment.
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Design consideration - Pretreatment
• Trickling filters shall be preceded by primary clarifiers equipped with scum and grease collecting devices, or other suitable pretreatment facilities.
• If fine screening is provided the screen size shall have from 0.03 to 0.06 inch openings.
• Bar screens are not suitable as the sole means of primary treatment.
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Design consideration
• Influent wastewater characteristics• Degree of treatment anticipated (BOD & TSS removal). • Temperature range of applied wastewater• Pretreatment processes• Type of filter media• Recirculation rate • Hydraulic and organic loadings applied to the filter• Underdrainage and ventilation systems
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Filter media
• Crushed rock– Durable & insoluble– Locally available– But, reduce the void spaces for passage of air– Less surface area per volume for biological growth
• Plastic media – Random packing media– Modular packing media
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Filter media
Schematic diagrams of modular and random packed media used in fixed-film treatment systems (Source: Bordacs and Young, 1998)
Cross-flow Tubular Pall rings
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Design consideration - Filter media
The ideal filter packing is material that• has a high surface area per unit of volume• is low in cost• has a high durability• has a high enough porosity so that clogging is
minimized • provides good air circulation
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Design consideration
• Influent wastewater characteristics• Degree of treatment anticipated (BOD & TSS removal). • Temperature range of applied wastewater• Pretreatment processes• Type of filter media• Recirculation rate • Hydraulic and organic loadings applied to the filter• Underdrainage and ventilation systems
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Flow Diagram for Trickling Filters
Recycle
Primaryclarifier Trickling
filter
Finalclarifier
Wastesludge
FinaleffluentInfluent
Q
Qr
Recirculation= A portion of the TF effluent recycled through the filterRecirculation ratio (R) = returned flow (Qr)/ influent flow (Q)
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Trickling Filter Process
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Design consideration - Recirculation
• Why is recirculation required?– maintain constant wetting rate – dilute toxic wastes – increase air flow – recirculation flow dilutes the strength of raw
wastewater & allows untreated wastewater to be passes through the filter more than once.
• A common range for recirculation ratio– 0.5~3.0
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Single stage
PC SCTF
PC SCTF
PC SCTF
a.
b.
c.
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Two stage
PC SCTF
PC SCTF
TF
TF SC
PC SCTFTF SC
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Design consideration
• Influent wastewater characteristics• Degree of treatment anticipated (BOD & TSS removal). • Temperature range of applied wastewater• Pretreatment processes• Type of filter media• Recirculation rate • Hydraulic and organic loadings applied to the filter• Underdrainage and ventilation systems
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Underdrain System
Two purposes:• (a) to carry the filtered wastewater and the biomass
lump (sloughed solids) from the filter to the final clarification process
• (b) to provide for ventilation of the filter to maintain
aerobic conditions. • The underdrain system is generally designed to flow one-
third to one-half full to permit ventilation of the system.
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Ventilation systems
• In TF system,
– Air is supplied by natural draft or forced draft fan.– The forced draft fans have been applied in order
to provide the adequate oxygen.
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Stone media filter
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Stone media TF design
• Organic (BOD) loading rate:– Expressed as kg/m3/d – Typically, 0.320-0.640 kg/m3/d for single-stage filters– Typically, 0.640-0.960 kg/m3/d for two-stage filters
• Ex) Influent BOD =200mg/L, influent flow = 1.8 ML/d, diameter of the filter is 16 m & the depth of the filter is 2m. Calculate the organic loading rate.
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Stone media TF design
• Hydraulic loading rate:– m3 wastewater/m2 filter*d – the rate of total influent flow is applied to the surface of
the filter media– Total influent flow = the raw WW + recirculated flow– Typically, 9.4 m3/m2/d– Maximum, 28 m3/m2/d
• Ex) Influent flow = 8.5ML/d, the recirculation ratio is 2:1. Diameter of the filter is 16 m & the depth of the filter is 2m. Calculate the hydraulic loading rate.
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Stone media TF design
• NRC (national research council) formula
where:
E1 = BOD removal efficiency for first-stage filter at 20oC, %
w1 = BOD load applied, kg/dayV = volume of filter media, m3
F = recirculation factor
VFw
E1
1
4432.01
100
First stage or single stage
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Stone media TF design
• NRC formula
Where:E2 = BOD removal efficiency for second-stage filter at 20oC, %
E1 = fraction of BOD removal in the first-stage filter
w2 = BOD load applied, kg/day
V = volume of filter media, m3
F = recirculation factor
VFw
E
E2
1
2
14432.0
1
100
Second stage
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Stone media TF design
• NRC formula
where:F = recirculation factorR = recycle ratio
2)10/1(
1
R
RF
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Stone media TF design
• The effect of temperature on the BOD removal efficiency
where:
ET = BOD removal efficiency at ToC, %
E20 = BOD removal efficiency at 20oC, %
2020 )035.1( T
T EE
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Stone media TF design
• Example 1– Calculate the BOD loading, hydraulic loading, BOD
removal efficiency, and effluent BOD concentration of a single-stage trickling filter based on the following data:
– Design assumptions:• Influent flow =1530 m3/d• Recirculation ratio = 0.5• Primary effluent BOD = 130 mg/L• Diameter of filter = 18 m• Depth of media = 2.1 m• Water temperature =18oC
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Stone media TF design• Example 2
– A municipal wastewater having a BOD of 200 mg/L is to be treated by a two-stage trickling filter. The desired effluent quality is 25 mg/L of BOD. If both of the filter depths are to be 1.83 m and the recirculation ratio is 2:1, find the required filter diameters. Assume the following design assumptions apply.
– Design assumptions:• Influent flow =7570 m3/d• Recirculation ratio = 2• Depth of media = 1.83 m• Water temperature =20oC• BOD removal in primary sedimentation = 35%• E1=E2
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Stone media TF design
• Example 2
Primary Clarifier
Secondary ClarifierTF2TF1
BOD=200mg/L BOD=25mg/L
VFw
E1
1
4432.01
100
VFw
E
E2
1
2
14432.0
1
100
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Plastic media
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Plastic media
Schulze formula
• The liquid contact time (t) of applied wastewater
Where:t = liquid contact time, minD= depth of media (m)q = hydraulic loading, (m3/m2/h)C, n = constants related to specific surface & configuration of media
nq
CDt
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Plastic media
• hydraulic loading (q)
Where:
Q= influent flow rate L/min
A=filter cross section area m2
A
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Plastic media TF design
Schulze formula
Where:Se= BOD concentration of settled filter effluent, mg/LSo= influent BOD concentration to the filter, mg/Lk=wastewater treatability and packing coefficient, (L/s)0.5/m2
D=packing depth, mq= hydraulic application rate of primary effluent, excluding recirculation, L/m2*sn=constant characteristic of packing used (assumed to be 0.5).
)/( nqkD
o
e eS
S
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Plastic media TF design• Example 3
– Given the following design flow rates and primary effluent wastewater characteristics, determine the following design parameters for a trickling filter design assuming 2 reactors at 6.1 m depth, cross-flow plastic packing with a specific surface area of 90 m2/m3, a packing coefficient n value of 0.5, & a 2-arm distributor system. The required minimum wetting rate=0.5L/m2*s. Assume a secondary clarifier depth of 4.2m and k value is 0.187.
– Design conditions
Item unit Primary effluent Target effluent
Flow m3/d 15,140
BOD mg/L 125 20
TSS mg/L 65 20
Temp oC 14
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Plastic media TF design
• Example 3–Using the information presented in
the previous slide, determine:• Diameter of TF
• Volume of packing required.
• Recirculation rate required