Sludge Bulking - Causes, Control Strategies and Options for ......2019/06/03  · Sludge Bulking - Causes, Control Strategies and Options for Domestic and Industrial Systems David

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