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Sludge Bulking - Causes, Control Strategies and Options for Domestic
and Industrial Systems
David Jenkins University of California at Berkeley
Operation and Control of Activated Sludge Processes
using Microbiological Analysis
Ljubljana, Slovenia June 5-7, 2019
Activated Sludge Bulking • Many types of filaments can occur in activated sludge • Each filament type has its own preferred set of growth conditions • Filament type(s) present can be used to diagnose cause of settling problems
Bulking sludge effects • Settling rate in clarifier decreases • Clarifier sludge blanket level rises • RAS/WAS becomes dilute • Solids handling process hydraulic load increases • Recycle stream volumes increase • Sludge blanket overflows clarifier leading
to high effluent TSS, BOD, process failure
Filamentous bulking causes • Nutrient deficiency • Sulfide (septic sewage) • Low DO • Low pH • Soluble readily biodegradable organics
(septic sewage) • Microthrix parvicella
Nitrogen limitation
• Indicated by: type 021N, Thiothrix, often with rosettes, gonidia, and intracellular PHB granules
Rosettes
Gonidia
Correction of nitrogen limitation
Requirements: • Influent COD/N ratio 1 mg/L • MLSS > 7%N/TSS
Add a readily available N source: • Aqueous ammonia • Anhydrous ammonia • Urea
Phosphate limitation Indicated by: type 021N, Nostocoida limicola, Haliscomenobacter hydrossis, Sphaerotilus natans
Correction of phosphate limitation
• Influent COD/P 0.3-0.5 mg/L • MLSS >1.5%P/TSS • Add readily available phosphate
source, H3PO4
Micronutrient limitation
Effect of micronutrients on performance
Sulfide • Indicated by: Thiothrix, type 021N, type
0914, Beggiatoa (fixed film) with intracellular sulfur granules
Sulfur granules
Correction of sulfide bulking • Eliminate dissolved sulfide by Oxidation: O2, H2O2, Cl2, NaOCl Precipitation: Fe(II), Fe(III) salts Prevention: NO3 salts • Beware of anaerobic zones
Low DO • Indicated by: S. natans, type 1701, H. hydrossis
Sphaerotilus natans
Sphaerotilus natans covered with slime
type 1701
Haliscomenobacter hydrossis
Low DO bulking • Low DO is a relative term.
• Limiting DO value is a function of F/M
or, more correctly, DO uptake rate
• Limiting DO, F/M combinations apply to completely mixed aerobic basins or to the first aerobic zone following anoxic or anaerobic zones
Low DO
SVI and DO uptake rate, pulp and paper waste activated sludge
Correction of low DO bulking • Raise DO and/or lower F/M (DO uptake
rate) • Install initial anoxic or anaerobic zones
and ensure that the first aerobic zone meets the DO concentration, F/M (DO uptake rate) criterion
Competitive factors between floc formers and filaments
• Dissolved oxygen concentration (DO) • Soluble substrate uptake rate • Substrate storage capacity • Surface trapping
Dissolved oxygen concentration
• General Observation: In a well mixed aeration basin filaments do not predominate at DO concentrations below about 2 mg/L
Completely mixed activated sludge (CMAS)
AB SC
Inf Eff
WAS RAS
AB SC
Inf Eff
WAS RAS
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5 6
Gro
wth
rate
, 1/d
ay
DO concentration, mg/L
Growth Rate of S. natansand Citrobacter as a Function of DO Concentration
Citrobacter
S. natans
0.4 mg DO/L
Chart1
0.0020.002
0.0040.004
0.0060.006
0.0080.008
0.010.01
0.020.02
0.030.03
0.040.04
0.050.05
0.060.06
0.070.07
0.080.08
0.090.09
0.10.1
0.120.12
0.140.14
0.160.16
0.180.18
0.20.2
0.30.3
0.40.4
0.50.5
0.60.6
0.70.7
0.80.8
0.90.9
11
22
33
44
55
Citrobacter
S. natans
0.4 mg DO/L
DO concentration, mg/L
Growth rate, 1/day
Growth Rate of S. natans and Citrobacter as a Function of DO Concentration
1.0833333333
0.1210526316
1.8571428571
0.238961039
2.4375
0.3538461538
2.8888888889
0.4658227848
3.25
0.575
4.3333333333
1.0823529412
4.875
1.5333333333
5.2
1.9368421053
5.4166666667
2.3
5.5714285714
2.6285714286
5.6875
2.9272727273
5.7777777778
3.2
5.85
3.45
5.9090909091
3.68
6
4.0888888889
6.0666666667
4.4413793103
6.1176470588
4.7483870968
6.1578947368
5.0181818182
6.1904761905
5.2571428571
6.2903225806
6.1333333333
6.3414634146
6.6909090909
6.3725490196
7.0769230769
6.393442623
7.36
6.4084507042
7.5764705882
6.4197530864
7.7473684211
6.4285714286
7.8857142857
6.4356435644
8
6.4676616915
8.5581395349
6.4784053156
8.7619047619
6.4837905237
8.8674698795
6.4870259481
8.932038835
Sheet1
s (DO mg/L)u S. natansu Citrobacter
0.0021.08333333330.1210526316
0.0041.85714285710.238961039
0.0062.43750.3538461538
0.0082.88888888890.4658227848
0.013.250.575
0.024.33333333331.0823529412
0.034.8751.5333333333
0.045.21.9368421053
0.055.41666666672.3
0.065.57142857142.6285714286
0.075.68752.9272727273
0.085.77777777783.2
0.095.853.45
0.15.90909090913.68
0.1264.0888888889
0.146.06666666674.4413793103
0.166.11764705884.7483870968
0.186.15789473685.0181818182
0.26.19047619055.2571428571
0.36.29032258066.1333333333
0.46.34146341466.6909090909
0.56.37254901967.0769230769
0.66.3934426237.36
0.76.40845070427.5764705882
0.86.41975308647.7473684211
0.96.42857142867.8857142857
16.43564356448
26.46766169158.5581395349
36.47840531568.7619047619
46.48379052378.8674698795
56.48702594818.932038835
Sheet2
Sheet3
Sheet4
Sheet5
Sheet6
Sheet7
Sheet8
Sheet9
Situation in Flocs
Floc
Bulk Liquid
DO Conc
Readily biodegradable soluble organics
Indicated by: • type 021N • Thiothrix • N. limicola • type 0914, • type 0411 • type 0961 • type 0581 • type 0092
type 021N
Nostocoida limicola (Neisser stain)
Readily biodegradable soluble organics
Filaments prefer: • Soluble readily bidodegradeable
organics conc. • Continuous dissolved organics supply • Usually aerobic conditions
Readily biodegradable soluble organics
Filaments cannot tolerate: • Intermittent organics supply (feed then starve) • Anoxic or anaerobic conditions (some exceptions)
Completely mixed activated sludge
AB SC
Inf Eff
WAS RAS
Selector activated sludge
Inf AB SC
Eff
WAS RAS Selector
Soluble COD uptake by activated sludges
DO uptake rate of activated sludges
Aerobic selector, selector zone
Aerobic selector, aeration basin
Anoxic selector, selector zone
Anoxic selector, aeration basin
Anaerobic selector, anaerobic zone (Bio P bacteria)
Anaerobic selector (Bio P), aeration basin
Anaerobic selector, anaerobic zone (G bacteria)
Anaerobic selector (G bacteria), aeration basin
Hamilton, OH: original aeration basin (T3)
RAS PE
To Secondary Clarifiers
Hamilton, OH: original flowsheet
Hamilton, OH: selector flowsheet 1
Hamilton, OH: selector flowsheet 2
Hamilton, OH: SVI
Hamilton, OH: selector performance
Davenport, IA: aeration basin configuration
ICZ PE
RAS To secondary clarifiers
Davenport, IA: selector performance
Tri-City, OR: anoxic/aerobic selector
Tri-City, OR: selector performance
23rd Ave. Phoenix AZ, original step feed
23rd Ave. Phoenix AZ anoxic selector
23rd Ave. Phoenix AZ, results of anoxic selector
Microthrix parvicella, 1000x, phase contrast
M. parvicella, 1000x, Gram stain
M. parvicella, 1000x, Neisser stain
Microthrix parvicella
Favored by: • Initial unaerated zones • Fats/oils (grease) • SRT >12d • Low temperature • Surface trapping and foam recycle
M. parvicella control • Reduce SRT • Surface wasting • Eliminate unaerated zones • Chlorination • Add PAX 14 (doses 0.5-1.5g/kg MLSS)
Effect of temperature on M. parvicella population and SVI (Fusina plant, Venice , Italy
Effect of PAX on M. parvicella counts and foam coverage (Fusina plant, Venice, Italy)
Rapid non-specific methods
• Manipulate influent/RAS feed points to reduce clarifier solids load
• Polymer flocculation • Selectively kill extended filaments
Plug–flow mode
Step-feed mode
Rationale of Cl2 addition • Add sufficient Cl2 to kill microorganisms
exposed to bulk liquid but not those inside the flocs
• Since the filamentous organisms causing
bulking are exposed to the bulk liquid while most floc-forming organisms are not, the addition of Cl2 selectively kills exposed filamentous organisms
Cl2 dose points
• Usually to RAS
• Sometimes to aeration basin
• Dose point determined by “frequency of exposure” of solids inventory to the Cl2 dose point
Cl2 dose points
• Add figure
Cl2 dose points
• Usually to RAS
• Sometimes to aeration basin
• Dose point determined by “frequency of exposure” of solids inventory to the Cl2 dose point
Cl2 dose points
• Add figure
Frequency of exposure, typical municipal plant
Frequency of exposure, high HRT plant
Typical Cl2 doses 2-3 kg Cl2/t SS, d: maintenance dose 5-6 kgCl2/t SS, d: will reduce SVI over
several days with little effect on effluent quality
10-12 kgCl2/t SS, d: will reduce SVI very
rapidly but effluent deterioration during dosing can be expected
Mixing at dose point
• Needs to be excellent • Consequences of poor initial mixing: No SVI control Turbid effluent
Examples of good dose points
• Into RAS piping at pump inlet, pump
discharge, elbow in piping • Into aeration basin close to surface
aerator and below water surface
Examples of poor dose points
• Into wet wells or open channels
• Into aeration basins where there is a high Cl2 demand from influent wastewater or where the initial mixing is poor,
e.g. between surface aerators, into anoxic /anaerobic zones)
Effects of initial mixing on SVI control
Effect of Cl2 dose point
Comparison of Cl2 dose points
1979 1984 Ave BOD load,103 lb/d 22 23 Cl2 dose point RAS Basin Polymer cost,103$/ y 63 1.5 Cl2 cost, $103/y 3.6 7.3 Total cost, $103/ y 66.6 8.8 Ave SVI, mL/g 285 156
Target SVI
• Establish an SVI value that can be tolerated
• Use target SVI to control Cl2 addition
• Add Cl2 when the SVI increases to the target value
• Stop adding Cl2 when the SVI decreases to the target value
Use of target SVI
Chlorination factoids
• Can use NaOCl: dilute 15% NaOCl to approx 0.5-1% before adding
• H2O2: expensive • No THM’s are produced • Works on all filaments • Can be a long-term solution • Can observe Cl2 effects on filaments
microscopically
Sludge Bulking - Causes, Control Strategies and Options for Domestic and Industrial SystemsActivated Sludge BulkingBulking sludge effectsFilamentous bulking causesNitrogen limitation�RosettesGonidiaCorrection of nitrogen limitationPhosphate limitationCorrection of phosphate limitationMicronutrient limitationEffect of micronutrients on performanceSulfideSulfur granulesCorrection of sulfide bulkingLow DOSphaerotilus natansSphaerotilus natans covered with slimetype 1701Haliscomenobacter hydrossisLow DO bulkingLow DOSVI and DO uptake rate, pulp and paper waste activated sludgeCorrection of low DO bulking Competitive factors between floc formers and filamentsDissolved oxygen concentrationCompletely mixed activated sludge (CMAS)Slide Number 28Situation in FlocsReadily biodegradable soluble organicstype 021NNostocoida limicola (Neisser stain)Readily biodegradable soluble organicsReadily biodegradable soluble organicsCompletely mixed activated sludge Selector activated sludgeSoluble COD uptake by activated sludgesDO uptake rate of activated sludgesAerobic selector, selector zoneAerobic selector, aeration basinAnoxic selector, selector zone Anoxic selector, aeration basinAnaerobic selector, anaerobic zone (Bio P bacteria)Anaerobic selector (Bio P), aeration basinAnaerobic selector, anaerobic zone (G bacteria)Anaerobic selector (G bacteria), aeration basinHamilton, OH: original aeration basin (T3) Hamilton, OH: original flowsheetHamilton, OH: selector flowsheet 1Hamilton, OH: selector flowsheet 2Hamilton, OH: SVIHamilton, OH: selector performanceDavenport, IA: aeration basin configurationDavenport, IA: selector performanceTri-City, OR: anoxic/aerobic selectorTri-City, OR: selector performance23rd Ave. Phoenix AZ, original step feed23rd Ave. Phoenix AZ anoxic selector 23rd Ave. Phoenix AZ, results of anoxic selectorSlide Number 60Slide Number 61M. parvicella, 1000x, Neisser stainMicrothrix parvicellaM. parvicella controlEffect of temperature on M. parvicella population and SVI (Fusina plant, Venice , ItalyEffect of PAX on M. parvicella counts and foam coverage (Fusina plant, Venice, Italy)Rapid non-specific methodsPlug–flow modeStep-feed modeRationale of Cl2 additionCl2 dose pointsCl2 dose pointsCl2 dose pointsCl2 dose pointsFrequency of exposure, typical municipal plantFrequency of exposure, high HRT plantTypical Cl2 dosesMixing at dose pointExamples of good dose pointsSlide Number 80Slide Number 81Slide Number 82Slide Number 83Examples of poor dose pointsEffects of initial mixing on SVI controlSlide Number 86Effect of Cl2 dose pointComparison of Cl2 dose pointsTarget SVI�Use of target SVIChlorination factoids�Slide Number 93Slide Number 94