sludge densification, process intensification, and plant

Sludge Densification, Process Intensification, and Plant Resiliency

Belinda Sturm, PhDUniversity of Kansas

Steady Progression of Design for Settleability

2

1970s 1980s 1990s 2000s 2010s

Selector zone concept introduced to control bulking(Choduba et al. 1973)

Filaments shown to dominate based on bioreactor design and operation (Eikelboom, 1975)

Unified theory of filaments developed (Sezgin et al, 1978)

DO shown to impact selection of filaments versus flocs (Palm et al. 1980)

SVI correlations for settling curves became more standardized (Wahlberg and Keinath, 1998; Daigger, 1995; Ozinsky and Ekama, 1995)

Selector zone design became more formal (Marten and Daigger, 1997) and better understood (Martins et al, 2004)

WE&RF report on selector zone design guidelines (Gray et al, 2008)

Is aerobic granular sludge the natural evolution of good settling sludge development?

Five decades of settling theory evolution has been summarized in one key manual for operations

• Focus: settleability

• Select for good settling

•Low SVI

•Larger floc

•Limit filamentous growth

• Operating parameters

•SRT control

•F/M gradients

•Selector zones and plug flow

IWA Granule Workshop 2004

Granules making up aerobic granular activated sludge are to be understood as

aggregates of microbial origin, which do not coagulate under reduced hydrodynamic shear,

and which subsequently settle significantly faster than activated sludge flocs.

• SVI30 < 60 mL/g• SVI5 = SVI30 or SVI5 / SVI30 = 1• Settling velocities > 9 m/hr• Particle diameter > 200 µm

How Does Densified Activated Sludge Compare with Granular Sludge?

Compact AS(non-granular)

SVI30 80 to 120 mL/g SVI30 < 50 mL/g

Densified AS(granular)

AquaNEREDA™inDENSE™

non-patented ASConventional Selector

Design

non-patented AS*

Densified AS(non-granular)

SVI30 < 80 mL/g

Different types of aerated granules have been formed

1. EBPR – Enhanced biological phosphorus removal2. OHOs – Ordinary heterotrophic organisms3. PAOs – Phosphorus accumulating organisms4. GAOs – Glycogen accumulating organisms – may also grow

Parameter NIT Granules

OHOGranules

NDN-OHOGranules

NDN-PAO Granules*

Processes Nitrification (low COD/N feed)

COD oxidation (and possiblyNitrification)

Nitrification +Denitrification

Nitrification +Denitrification + EBPR1

Feeding condition

Aerobic Aerobic Anoxic Anaerobic

Denitrifying bacteria

N/A OHOs2 OHOs2 PAOs3 and GAOs4

Nitrogen removal method

N/A Assimilation w/ limited denitrification

Sequential anoxic and aerobic periods

Simultaneous nitrification and denitrification (SND) in aerobic period

Demonstrated Lab-scale Lab-scale Lab-scale Lab- and Full-scale

Figdore, B.A., Stensel, H.D., Winkler, M.K.H., Neethling, J.B. (2017) Aerobic Granular Sludge for Biological Nutrient Removal. Project No. NUTR5R14h. Water Environment and Reuse Foundation: Alexandria, VA.

Densifying Activated Sludge Is Key to Increasing Capacity at WRRFs

Lawrence WWTP Granular Sludge Pilot (70 L)

Flocculent Sludge– 5 mins Settling

Granular Sludge– 5 mins Settling

Flocculent Sludge – 30 mins Settling

Granular Sludge – 30 mins Settling

WERF U1R14 Project

Lawrence WWTP AGS Pilot Results -Settling Parameters

y = 19.4e-0.000413x

y = 9.8e-0.000459x

y = 12.6e-0.000471x

y = 15.1e-0.000395x

y = 17.6e-0.000397x

0

2

4

6

8

10

12

14

0 2000 4000 6000 8000 10000 12000 14000

Initi

al S

ettli

ng V

eloc

ity (m

/h)

MLSS Concentration (mg/L)100%GS 100%FS 25%GS,75%FS 50%FS,50%GS70%GS,30%FS Expon. (100%GS) Expon. (100%FS) Expon. (25%GS,75%FS)Expon. (50%FS,50%GS) Expon. (70%GS,30%FS)

100% GS

70% GS, 30% FS

50% GS, 50% FS

25% GS, 75% FS

100% FS

)(0

TSSXKS eVV ⋅−⋅=

SVI = 100 mL/g

SVI = 80 mL/g

SVI = 61 mL/g

SVI = 63 mL/g

SVI = 56 mL/g

Flux Curves for different levels of granulation

0

50

100

150

200

250

300

350

400

450

500

0 2000 4000 6000 8000 10000

Flux

(kg/

m2/

d)

MLSS Concentration (mg/L)

100% FS

0

50

100

150

200

250

300

350

400

450

500

0 2000 4000 6000 8000 10000

Flux

(kg/

m2/

d)


100% FS 50% GS,50% FS


0

50

100

150

200

250

300

350

400

450

500

0 2000 4000 6000 8000 10000

Flux

(kg/

m2/

d)


100% GS 100% FS 50% GS,50% FS


Note: Modeling assumed equal biomass concentrations for all ratios

Performed by Dr. José Jimenez and Dr. Alonso Griborio

Clarifier Capacity Modeling

Sludge Densification extends the same principles we learned from preventing bulking sludge

Five decades of settling theory evolution has been summarized in one key manual for operations

• Focus: settleability

• Select for good settling

•Low SVI

•Larger floc

•Limit filamentous growth

• Operating parameters

•SRT control

•F/M gradients

•Selector zones and plug flow

Floc Selection Theory and Filament Out-Selection

What are our key parameters for selecting for good settling activated sludge?

1. Plug Flow Conditions17

Number of Equivalent Tanks, N0 10 20 30 40 50

0

100

200

300

SS

VI 3.

5, m

L/g

N = 101

From E. J. Tomlinson and B. Chambers, The effect of longitudinal mixing on the settleability of activated sludge. Technical Report TR 122, Water Research Centre, Stevenage, England, 1978. Reprinted by permission of the Water Research Centre.)

Slide courtesy of Dr. Leon Downing, Black & Veatch




0

100

200

300

SS

VI 3.

5, m

L/g

N = 101


2. Anaerobic/Anoxic feed

From Gray et al (2006) Develop and Demonstrate Fundamental Basis for Selectors to Improve Activated Sludge Settleability





0

100

200

300

SS

VI 3.

5, m

L/g

N = 101


2. Anaerobic/Anoxic feed 3. Loading rate matters

From Sezgin et al (1978) A Unified theory of activated sludge bulking, Journal of Water Pollution Control Federation 50(2)

From Gray et al (2006) Develop and Demonstrate Fundamental Basis for Selectors to Improve Activated Sludge Settleability


High F/M and Metabolic Selection

Decreasing substrate concentration

Martins et al. (2003) Water Research 37, p.2555–2570

From Sezgin et al (1978) A Unified theory of activated sludge bulking, Journal of Water Pollution Control Federation 50(2)

Contacting with high rbCOD drives diffusion to granule interior

-Allows interior to be biologically active

Anaerobic feeding selects for PAOs for EBPR

Slow upflow feeding widely used in lab and full-scale SBRs

Slug feeding has also been used in lab systems

Slow upflow plug-flow feeding through settled

sludge bed

Treated effluent

displaced

Figdore, B.A., Stensel, H.D., Winkler, M.K.H., Neethling, J.B. (2017) Aerobic Granular Sludge for Biological Nutrient Removal. Project No. NUTR5R14h. Water Environment and Reuse Foundation: Alexandria, VA.

A high F/M anaerobic feeding regime is important to drive diffusion into granule and achieve metabolic selection

Substrate Utilization in SBR vs Plug Flow

Feeding Sludge Bed Height

rbCO

D (m

g/L)

22

Anx Aerobic

HRT

rbCO

D (m

g/L)

Continuous Flow configuration with high F/M selectorAnaerobicSelectors

Effect of F/M on EPS Formation

Scale = 100 µm

Cells – Red Polysaccharides - Blue Proteins Green

McSwain et al. (2005). Applied and Environmental Microbiology, 71(2), 1051-1057.

Jimenez (2015). Water research, 87, 476-482.

Effect of substrate utilization on EPS and granulation

Substrate Utilization Rate Utilization rate based on Monod-Based Kinetics𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅

= 𝒀𝒀𝒅𝒅𝒅𝒅𝒅𝒅𝝁𝝁𝑯𝑯𝒀𝒀𝑯𝑯

𝒅𝒅𝒔𝒔𝑲𝑲𝒔𝒔+𝒅𝒅𝒔𝒔

𝒅𝒅𝑯𝑯 - qEPS,HYD 𝒅𝒅𝒅𝒅𝒅𝒅𝒅𝒅

Formation rate Decay rate

Laspidou, C. S., & Rittmann, B. E. (2002). Water Research, 36(8), 1983-1992.

50

100

150

200

0.120 0.150 0.180 0.210 0.240 0.270 0.300E

PS-T

B (m

g C

OD

/g V

SS)

Substrate Utilization Rate (g sCOD / g VSS.d)

Modelled EPS mg COD/g VSSExp. EPS mg COD/g VSSPoly. (Modelled EPS mg COD/g VSS)

• Substrate utilization rate is one of the fundamental mechanisms driving EPS production and subsequent granule formation

• In principle, reactors must have a minimum substrate utilization rate to maintain EPS production and granule structure

Sludge densification may utilize a combination of biological and physical selection mechanisms

WRF Study Purpose: Granule Application in Continuous-Flow Systems

Plug flow conditions create necessary substrate selection

Granule selection performed separate from reactor and clarifier

Favor retention of larger, faster-settling granules over flocs

Short settling times <10 minutes widely applied in SBRs

-“Selective settling pressure”-“Hydraulic selection pressure”

Other approaches involving selective wasting-Screens / Sieves (Liu et al., 2014)-Hydrocyclones (Welling et al., 2015)-Surface wasting (Barnard 2015)

Sludge feed

Return sludge

Waste sludge

Screen.

..

..

.

...

Selective wasting using screening

Selective wasting using hydrocyclones

Sludgefeed

Granule return (underflow)

Waste sludge (overflow)

Figdore, B.A., Stensel, H.D., Winkler, M.K.H., NeethlingJ.B. (2017) Aerobic Granular Sludge for Biological Nutrient Removal. Project No. NUTR5R14h. Water Environment and Reuse Foundation: Alexandria, VA.

Liquid-solids separation design must retain granules

Water Research Foundation Project Overview

Particle SelectionCyclones installed at full-scale

Particle Selection

Pilot

Substrate Selection

Substrate & Settling Selection

A target F/M is maintained by wasting mixed liquor daily (both granules and flocs wasted)

A mixture of granules and flocs are maintained in reactor

North Reactor

South Reactor

Daily biomass wasting is performed through a 0.2 mm sieve, and granules are retained

Mainly granules are maintained in the reactor

Substrate Selection Only:

Substrate & Particle Selection:

Pilot Studies Manipulating F/M with Wasting

Effect of F/M on EPS and Granule Formation

50

70

90

110

130

150

170

190

210

230

0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24

Tota

l EPS

(mg

CO

D /

g V

SS)

F/M (g rbCOD / g VSS-d) (3 day ave)

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

0.10 0.12 0.14 0.16 0.18 0.20 0.22 0.24

Ave

Dia

met

er (m

m)

F/M (g rbCOD / g VSS-d) (3 day ave)

Effect of substrate utilization on EPS and granulation

0

0.1

0.2

0.3

0.4

0.5

0

50

100

150

200

0.13-0.15 0.15-0.20 0.20-0.25 0.25-0.30

Mea

n di

amet

er m

m

Tota

l E

PS m

g C

OD

/g V

SS

Substrate utilization rate (g sCOD/g VSS-d)

EPS Mean diameter

Anaerobic or Metabolic Selectors

0

10

20

30

40

50

60

70

80

90

0

50

100

150

200

250

< 5.20 5.20 - 5.94 5.94 - 6.68 6.68 - 7.42 > 7.42

SVI (

mL/g)

Diam

eter (

um) /

EPS

(mg C

OD / g

VSS

)

F/M (g COD / g MLSS-d)

Series1 EPS (mg COD/g VSS) Series3

Anaerobic F/M –Assuming COD Uptake in First Selector Zone

Diam.

EPS

SVI


rbCO

D(m

g/L)

507090

110130150170190210230

0.10 0.15 0.20 0.25

Tota

l EPS

(mg

CO

D /

g V

SS)

F/M (g rbCOD / g VSS-d) (3 day av

Aug. 15, 2015to Mar. 25, 2016

Mar. 25, 2016to Oct. 1, 2016

Granule formation and development

External selector implementation

Experimental Plan

Floc wasting0.2 mm screen

Sludge

Granule retaining

Granule selection through selective wasting of flocs Retained fraction

Wasted fraction

Selective Wasting

External selector

Impact of Selective Wasting on Sludge Structure

Increasing F/M Floc Granule transition

This graph shows the transition to mainly granule particles as the F/M > 0.21

Pilot Studies Manipulating F/M with Wasting

0102030405060708090100

05

101520253035404550

Am

mon

ia R

emov

al %

SRT

frac

tion

d

>0.2 mm <0.2 mm Ammonia removal

5.5 mg/L H2S found in feed bucket

External selector


0

0.5

1

1.5

2

2.5

3

3.5

4

Con

c (m

g/L)

Date (MM/DD/YY)

Eff PO4-P

Granule retention PAOs accumulation and phosphate removal improvement

15-20Lwasting

5-10Lwasting


Was

ted

frac

tion

Ret

aine

d fr

actio

n

Selectively Wasted

Selectively Retained

Microbial Community Selection through Wasting

Substrate Utilization in SBR vs Plug Flow


rbCO

D (m

g/L)

Anx Aerobic

HRT

rbCO

D (m

g/L)

Continuous Flow configuration with high F/M selectorAnaerobicSelectors

Anaerobic or Metabolic Selectors

0

10

20

30

40

50

60

70

80

90

0

50

100

150

200

250

< 5.20 5.20 - 5.94 5.94 - 6.68 6.68 - 7.42 > 7.42

SVI (

mL/g)

Diam

eter (

um) /

EPS

(mg C

OD / g

VSS

)

F/M (g COD / g MLSS-d)

Series1 EPS (mg COD/g VSS) Series3

Anaerobic F/M –Assuming COD Uptake in First Selector Zone

Diam.

EPS

SVI0

14

Stage 1

Stage 3Stage 2

7

80%68%

62%51%

35%29%

18%17%

15%10%

10%5.6%

3.3%1.3%

0.7%0.5%

0.0 2.0 4.0

HE1ID2

HE2ID1HW

Puy1CrCCMClC

Puy2WBSPDurPocKalBM

Anaerobic Stage HRT (hr)

F/M Ratio

Wei, S. P., Stensel, H. D., Nguyen Quoc, B., Stahl, D. A., Huang, X., Lee, P.-H., Winkler, M-K.H., 2020. Flocs in disguise? High granule abundance found in continuous-flow activated sludge treatment plants. Water Research

Summary

Metabolic selectors should be designed to achieve high rbCOD uptake rates, with virtually complete rbCOD removal

An anaerobic F/M ratio greater than 5.2 gCOD/gVSS corresponded to higher EPS production; Anaerobic F/M greater than 7 has been associated with granulation

Microorganisms subjected to high F/M may accumulate substrate as internal storage products

It is possible to form granular sludge in continuous flow systems

Administrative Experience

U1R14CBET-1512667

sludge densification, process intensification, and plant

Documents