Upload
others
View
16
Download
3
Embed Size (px)
Citation preview
1
Activated Sludge Process Control
by R. Dale Richwine, P.E.
Richwine Environmental, Inc.
Session Overview
» Sludge Quality – Visual Observations – Use of Settlometer
» Sludge Quantity – System Inventory – Solids Management
2
Sludge Quality
» Visual Observations
» Use of Settlometer
Sludge Quality Visual Observations
» Aeration Basins – Foam Color – Diffuser Pattern
» Secondary Clarifiers – Quantity of Foam – Effluent Quality
3
Visual Observations Aeration Basin Foam
Fresh Crisp White Foam
Visual Observations Aeration Basin Foam
Excessive Billowing White Foam
4
Visual Observations Aeration Basin Foam
Thick, Scummy, Dark Brown Foam
Nocardia Foam (200X)
Visual Observations Aeration Basin Foam
Proper Foam
5
Visual Observations Diffuser Pattern
Fine Bubble Coarse Bubble
Visual Observations Diffuser Pattern
Diffuser Problems Can Cause Dead Spots
6
Visual Observations Clarifier Foam
Visual Observations Effluent Quality Problems
Poor Treatment
7
Visual Observations Effluent Quality Problems
Sludge Bulking
Visual Observations Effluent Quality Problems
Sludge Solids Washout
8
Visual Observations Effluent Quality Problems
Clumping Clumping
Visual Observations Effluent Quality Problems
Ashing
Ashing may be a symptom of overoxidized
(overaerated) mixed liquor.
9
Visual Observations Effluent Quality Problems
Straggler Floc
Straggler floc is indicative of a low SRT
Visual Observations Effluent Quality Problems
Pin Floc
– Carryover of very fine material in final effluent
– Turbid or milky appearance of final effluent
Possible Causes of Pinpoint Floc
– Old sludge with poor floc-forming
characteristics – Excessive turbulence shearing the
floc.
10
Sludge Quality Use of Settlometer
Settlometer Test – Sample Aeration
Basin Effluent – Run test
immediately following sampling
– Handle sample with care
Use of Settlometer Settlometer Test
» Original Test – 1 liter graduated
cylinder » Mallory Settlometer
– 2-liter container – Graduated to 1000 ml/L
11
Use of Settlometer Settlometer Test
Sample Handling – Collect sample in wide-mouth bottle – Start test immediately – Minimize agitation of sample
Use of Settlometer Settlometer Test
Four Phases of Settling – Flocculation – Blanket Formation – Settling – Compaction
12
Use of Settlometer Settlometer Test
What to watch for
Settling Rate
Characteristics of Interface
Clarity of Supernatant
Use of Settlometer Settlometer Test
Take Readings – Every 5-minutes – Up to 30-minutes – Every 10-minutes – Up to 60-minutes – After 4-hours
Note Observations – Supernatant
quality – Type of interface – Surface
13
Use of Settlometer Settlometer Test
Settled Sludge Volume – SSV
Cleanwater Treatment Plant
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60
Sludge Settling Time (minutes)
SSV (cc
/L)
0
2
4
6
8
10
12
14
16
SSC (mg/L)
Use of Settlometer Settlometer Test
» Settled Sludge Concentration
– SSC
SSV/MLSSSSC=
Cleanwater Treatment Plant
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60
Sludge Settling Time (minutes)
SSV (
cc/L)
0
2
4
6
8
10
12
14
16
SSC (mg/L)
MLSS = 2500mg/L
Calculation
14
Use of Settlometer Settlometer Test
Fast Settling Sludge
Cleanwater Treatment Plant
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60
Sludge Settling Time (minutes)
SSV (
cc/L)
0
2
4
6
8
10
12
14
16
SSC (mg/L)
MLSS = 2500mg/L
Cleanwater Treatment Plant
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60
Sludge Settling Time (minutes)
SSV (
cc/L)
0
2
4
6
8
10
12
14
16
SSC (mg/L)
MLSS = 2500mg/L
Slow Settling Sludge
Use of Settlometer Sludge Volume Index (SVI)
Data Required – The SSV30 from Settlometer Test – MLSS concentration of the sample
15
Use of Settlometer Sludge Volume Index (SVI)
)(MLSS)/(1000)/(SSV)/(SVI 30
mg/LgmgLmLmlg ×
=
Target range: 75 - 150 mL/g
but IT DEPENDS!
The volume occupied by 1 gram of MLSS after 30 minutes of settling.
Sludge Quantity
System Inventory – Mass of solids in system
Solids Management – Return Sludge Rate – Wasting Rate
16
System Inventory
» Aeration Basin MLSS » Clarifier Solids (Blanket)
Goals – Manage Inventory to Match Optimum Growth Rate – Maintain Consistent Inventory of Solids
System Inventory
Manage Inventory to Match Optimum Growth – Determine optimum F/M or Growth Rate
Growth Rate – Sludge Age – Age – MCRT
17
System Inventory
Aeration Basin Solids
Clarifier Solids
System Inventory Maintain Consistent Inventory
Inventory Management Tools – Return Sludge Rate – Wasting Rate
18
System Inventory Return Sludge Rate
Cleanwater Treatment Plant
0
200
400
600
800
1000
1200
0 10 20 30 40 50 60
Sludge Settling Time (minutes)
SSV (
cc/L)
0
2
4
6
8
10
12
14
16
SSC (mg/L)
MLSS = 2500mg/L
Optimum Return Sludge Concentration is determined
by Quality of MLSS
Desired RAS Concentration
System Inventory Return Sludge Rate
RAS Rate Calculation
)MLSSSSC()MLSSRAS(RateRASCurrent(gpm) Rate Flow RAS Desired
−−×
=t
Conc
Where: • Desired RAS Flow Rate (gpm) = Optimum RAS Flow (gpm) • Current RAS Rate = Current RAS Flow (gpm) • RAS Conc = Return Sludge Concentration (mg/L) • MLSS = Mixed Liquor Suspended Solids (mg/L) • SSCt = Settled Sludge Concentration at desired time
19
System Inventory Maintain Consistent Inventory
Sludge Wasting – Change rate slowly – Use 5-day average
Control Process Using Sludge Age
Out SolidsInventory Age Sludge −=
System Inventory Sludge Age
Data Required – Solids under aeration in the aeration basin, pounds
(lbs) – Clarifier Solids (lbs) – Secondary effluent suspended solids (SESS) from
previous day, lbs/day – Solids intentionally wasted from the process (WAS),
pounds per day (lbs/day)
20
System Inventory Sludge Age
(lbs/day) SESS (lbs/day) WAS(lbs)Inventory Basin Aeration (days) SRT
+=
(lbs/day) SESS (lbs/day) WAS(lbs)Inventory Clarifier (lbs)Inventory Basin Aeration (days) MCRT
++
=
Sludge Retention Time, Sludge Age, Age
Mean Cell Residence Time (MCRT)
System Inventory Wasting
Data Required – Solids under aeration in the aeration basin (inventory),
pounds (lbs) – Secondary effluent suspended solids from the previous
day (SESS), pounds per day (lbs/day) – Desired sludge residence time (SRT), days
21
System Inventory Wasting
/day)((days) SRT Desired
(lbs)Inventory Solids System (lbs/day) AS lbsSESSW −=
Where: • System Solids Inventory = Aeration Basins Inventory (lbs)
+ Clarifier Inventory (lbs) *** Clarifier Inventory only used if desired • Desired SRT (days) = Sludge Age Set as Process Goal • SESS (lb/day) = Secondary Effluent TSS (mg/L) * 8.34 * Plant Flow (mgd)
System Inventory Food to Microorganism Ratio (F/M)
Data Required – Primary effluent flow (Q), mgd – Primary effluent cBOD, mg/L – MLVSS concentration, mg/L – Aeration basin volume, million gallons
22
System Inventory Food to Microorganism Ratio (F/M)
)/( 8.34)/( MLVSS)( VolumeBasin Aeration )/( 8.34)/( cBOD PE)( Q PEF/M
gallbLmgMGgallbLmgmgd
××××
=
(lbs)Aeration Under Biomass(lbs)Basin Aeration Into cBODF/M =
)/( MLVSS)( VolumeBasin Aeration )/( cBOD PE)( Q PEF/M
LmgMGLmgmgd
××
=
System Inventory Food to Microorganism Ratio (F/M)
Interpretation of F/M Values
0.04 – 0.15 Extended Aeration 0.20 – 0.50 Convention Activated Sludge 0.50 – 1.50 High-rate Processes
23
Session Summary
Sludge Quality – Visual Observations – Use of Settleometer
Sludge Quantity – System Inventory – Solids Management
Activated Sludge Process Control
» Basics – BOD update rate = Bacterial Growth Rate
» Growth Factors » Sludge Quality
– Visual Observations – Use of Settlometer
» Sludge Quantity – System Inventory – Solids Management
24
One Thing to Remember
Rate of Removal = Rate of Biomass Growth