Minimising sludge production

by long SRT, trash and grit

removal from sludge

Yves Comeau1, Peter L. Dold2,

Alain Gadbois3, Stéphane Déléris4, Majdala M.-Geoffrion1,

Abdellah Ramdani1, Marc-André Labelle1

Neptune Workshop (FP6 Project)

Quebec, Canada

March 25-26, 2010

1 23 4

2

Outline

• WWT & sludge production

• Modelling sludge production

• Objectives

• Experimental units

• Trash and grit removal

• Biodegradation of « unbiodegradables »

• Conclusions and Perspectives

3

Wastewater Treatment (or WW Resource Management)

Effluent

2ry

Influent

Transformation

processes

water, org. fertiliser,

energy, C, N, P, K

Removal:

pathogens,

micropollutants

Prelim.(incl. solid-liquid

separation)

1ry Advanced(incl. UV, O3,

PAC)

Reuse:

waterSludge

disposal

(modelling)

(this project)(to favor)

(this project)

Costs of WWT Effect (+: positive/-: negative)

of reducing sludge production

• Capital costs:

+ size of bioreactors, settling tanks,

sludge treatment units

• Operating costs:

– aeration

+ sludge treatment & disposal

- increasing sludge disposal costs- Quebec: from 20 to >80 $/wet t. from 2000 to 2009

4

Reducing sludge production

• Chemical: ozonation, uncoupling

• Thermal: thermal disruption

• Physical: mechanical disruption, ultrasounds,

pressure drop, microscreening, hydrocycloning

• Biological: predation, anaerobic digestion,

fermentation, endogenous respiration (SRT)

5

Cannibal®

• Claims of « no » or minimal sludge production

• Limited data available – How does it work?

6

(hypoxic fermenter)

Sludge reduction: Effect of SRT

7

• Short SRT for BOD removal

• Longer SRT for N and P

removal at cold temperature

• Longest SRT for small-

medium WWTPs to minimize

sludge production (but

increased costs of aeration)

e.g. SRT 5 d to 30 d

25% less kg TSS/kg COD

•Thus, long SRT low sludge

production (WAS + effluent)

(nothing magical)

kgTSS/kg COD

kg VSS/kg COD

0.17TSS/COD

1000 d

for raw WW(fus=0.05

fup=0.13)

s l L

Mixed liquor components vs SRT

8

XTSS

XIg (XISS)

XVSS

XU,inf

XE

XH

with increasing SRT, leveling of XH

but continuous increase in XIg, XU,inf, XE

XTSS

XVSS

XU,inf

XIg; XE

XH

9

MLVSS fractions vs SRT

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60

SRT (d)

Bio

mass f

racti

on

s (

A,

E,

I, V

SS

)

(g V

SS

/g V

SS

)

VSS

active

inert

endogenous

1000

XU,inf

XE

XH

V

V

• at very high SRTs, the active biomass fraction becomes minimal

and the VSS are essentially composed of XU,inf and XE

Mixed liquor composition

10

ISS (XIg)

Particulate unbiodegr.

influent organics (XU,inf)

endogenous residue (XE)

active biomass (XH)

Example:

raw WW: 280 mg COD/L

aerobic AS, 20oC, 8 h HRT

SRT

5 d 20 d

18% 22%

23% 30%

9% 21%

48% 16%

1280 3720

mg TSS/L

TSS

ISS

VSS

from 5 to 20 d SRT, 2.9 times more sludge (but 3x less XH)

if 33% removal of grit (in XIg) and of trash (in XU,inf)

can be removed from sludge at an SRT of 20 d,

the capacity can be increased by 17% (7+10)

treatment capacity increased or reduced reactor size

Cannibal®Research questions

• Can grit (XIg) and trash (XU,inf) removal from the mixed

liquor be efficiently removed enough to increase

significantly the treatment plant capacity?

– what is the effect on sludge settleability?

• Can « unbiodegradable » XE (endog. residue) and

XU,inf (infl. partic. unbiodeg. org.) be biodegraded at long

SRTs and in the AN/OX fermentation reactor?

– can the lower sludge production savings compensate the extra

aeration costs?

11

12

Objectives

« Explain » the Cannibal® process by:

1) Modelling biological and unit processes

Characterizing the efficiency of:

2) physical removal from mixed liquor (or RAS) by:

2.1 microscreening (MS) of trash (XU,inf)

2.2 hydrocycloning (HC) of grit (XIg)

3) biodegradation of the mixed liquor components:

3.1 endogenous residue (XE)

3.2 influent « unbiodegrad. » partic. organics (XU,inf)

13

SB

XB

XB

XH

(NO3-)

O2

(N2)

H2O

SE

XE

biodegradable ?

Mixed liquor

XU,infXU,inf

biodegradable ?

Influent

XIg XIg « hydrocyclonable » ?

« microscreenable » ?

Cat+(Ca2+, Mg2+, Fe2,3+, Al3+)

An-(CO3

2-, PO43-, SO4

2-, S2-)CatAn (adsorbed)

Organic

Inorganic

2.1

3

4

5

6

2.2

7

9

8

10

11

hypoxic

conditions

1.1

1XN

NH4+

NO3-

WAS

1.2

12

13

« solubilisable » ?

Processes & objectives

Obj. 1Modelling

Obj. 3.1

Obj. 3.2

Obj. 2.1, 2.2

effluentSU

effluent

Methodology

• Lab tests

– MS and HC

– Biodegradation of XE

• Modelling

• Pilot testing

14

15

from 8 WWTPs near Montreal

0

20

40

60

80

100

A B C D E F G H

% In

du

stri

al l

oad

ing

Wastewater treatment plant (WWTP)

Coarse screening

Grit removal

Primary tr. Clarifier

Preliminary tr.8

4

2

16

ML & RAS

Microscreen

mixer above MS

Raw

sludge

Mic

rosc

reen

Screen

underflow

Screen

underflow

? P H ydrocyclone

U nderflowO verflow

Pit floor

Lab floor

200 L

200 L

40 L160 L

Ø: 10 cm

200, 300 & 500 µm

HC

Lab microscreening (MS) of

mixed liquor and RAS

17

Trash (organic) retained by MS: hygienic paper, vegetal (plants, wood) residues, hair, large filamentous flocs, etc.

(+ sand)

Direct removal: by size

Indirect removal: by dynamic filtration

18

wash trough

influent

screened effluent

wash water

50%

60%

70%

80%

90%

100%

50% 60% 70% 80% 90% 100%

i VT

scre

enin

gs (m

g V

SS/m

g TS

S)

iVT raw sludge (mg VSS/mg TSS)

ML RAS

average=89±4%

Effect of raw sludge iVT on screenings iVT

screenings iVT relatively constant (89 ± 4%) for ML and RAS

selective removal of organic matter of similar composition

is possible 19

vs 99±1% for toilet paper,

Kleenex, paper towel

3.6 ± 4.1 (n=8)

1.8 ± 1.3 (n=8)

0.64 ± 0.30 (n=4) 0.63 ± 0.70 (n=9)

0

1

2

3

4

CS CS+GR CS+PC CS+GR+PC

Vo

l. s

cre

en

ings

/vo

l sc

ree

ne

d s

lud

ge (

mL/

L)

Pre-/primary treatments at WWTP

LegendCS: coarse screeningGR: grit removalPC: primary clarifier

Improved pretreatment results in less screenings

that can be removed from the mixed liquor (or RAS) by MS

? g TSS/g COD & ? cost/kg TSS 20

Effect of WWTP pretreatment

on captured screenings

Hydrocycloning: grit removal (XIg)

from mixed liquor and RAS

Composition of XIg:

• inorganics associated to XH, XE XU,inf (~9% VSS)

• precipitates (mainly with Al, Fe, Ca)

• fine sand, silt, egg shells, etc.

21

22

(Svarovsky, 1984)

Apex

Vortex

Inlet

y = -0,002x + 0,332R² = 0,438

-20%

0%

20%

40%

60%

80%

0 20 40 60 80 100

E T' F

SSE

(gri

t)

Industrial loading (%)

Effect of %industrial loading

on XISS,Inf (FSSE) removal by the HC

Higher efficiency with a smaller industrial loading: sand from the municipality, not the industry

About 25 ±10% of ISS can be removed by HC23

(red

uced

eff

icie

ncy)

E’T = ET – Rf

1 – Rf

ET = mass recovery

Rf = flow recovery (20 ± 2%)

Endogenous residue (XE)

biodegradation

1. Production of mixed liquor containing only

(XH + XE) from a synthetic feed with acetate as

sole carbon source in an MBR (200 L)

- determination of the active fraction (FA)

2. Mixed liquor biodegradation under

2.1 anaerobic (AN) conditions

2.2 anaerobic-aerobic (AN-OX) conditions

24

MBR setup

MBR

selector

Feed stocks

Zenon hollow fibers (ZW-10, 0.04 μm)

25

Removal efficiency and mass balances

Hydraulic: 99.5 ± 0.4 (%)

COD: 98.4 ± 1.8 (%)

N: 101.9 ± 2.0 (%)

P: 102.8 ± 1.1 (%)

COD: > 97%

TKN: > 96%

SRT = 5.2 d

HRT = 11.7 h

Mass balances

Removal efficiency

MBR 200 L

SRT= 5.0 d

Selector

17.5 L Permeate

1525 mg VSS/L

26

influent

effluent

WAS

Active fraction (FA) determination

by 21 d endogenous respiration

0

5

10

15

20

25

0

500

1000

1500

2000

0 5 10 15 20 25

OU

R (m

g O

2/L

.h)

VS

S (

mg

/L)

TIME (d)

VSS measured

VSS predicted

OUR measured

OUR predicted

by VSS: bT = 0.272 d-1 (0.243 d-1@ 20°C); FA = 0.685 g XH/g VSS

by OUR.: bT = 0.263 d-1 (0.235 d-1 @ 20°C); FA = 0.683 g XH/g VSS

Temp = 24°C

SRT = 5 d

27

Batch digestion units

AN OX-AN 28

SELECTOR EFF.

HCl

NO EFF.

EFF. 1

WAS

MBR

AER - N. AER

ACETATE

Digestion Unit

- Simulations consider or not the biodegradation of XE

- Determination of the rate of XE biodegradation: kd,XE

Modelling with BioWin(OX-AN)

SLUDGE

WASTAGE

100% TSS

separation

29

(/CO2 in

the lab)

0

200

400

600

800

1000

1200

1400

1600

0 20 40 60 80 100

VS

S (

mg

/L)

TIME (d)

VSS sim. (decay)

VSS measured

VSS sim. (no decay)

ML biodegradation tests – AN-OX Results

AN-OX: kd,XE,35C,AN-OX = 0.012 d-1

(AN: kd,XE,35C,AN = 0.005 d-1)30

pH 7.2

Biodegradation of

« unbiodegradable » organics

• XE is very slowly biodegradable

– more rapid under AN-OX (0.012 d-1)

than AN (0.005 d-1) conditions at pH 7.2 and 35°C

– Arrhenius coefficient to determine

• XU,Inf is probably also similarly

« slowly biodegradable »

31

32

Demo scale MBR with MS and HC

Mobile WWTP unit (16 m long) at St-Hyacinthe WWTP

• Activated sludge basins (1, 3, 5 m3 + FST)

• MBR (membrane bioreactor – hollow fibers)

•(option: SBR or media for MBBR or IFFAS)

(Observation: essentially no grit and trash in sludge fed from a

primary effluent)

MS

HC

Conclusions

• Grit & Trash can be removed from mixed

liquor and RAS by hydrocycloning and

microscreening, respectively

increased treatment capacity or smaller reactor

size

– effect on settling to determine

– cost?

• XE (and probably also XU,Inf)

is very slowly biodegradable

under AN-OX or AN conditions

33

Conclusions

• Cannibal®: proposed mechanisms of low sludge

production:

– main factor: long SRT (e.g. 0.40, 0.27, 0.17 g TSS/g COD

at 3, 30 and 300 d SRT, respectively)

• extra aeration costs to evaluate

– other factors:

• grit and trash removal by MS and HC feasible

– MS screenings iVT = 89 ± 4%

– about 25 ± 15% grit removal by HC

– not useful if there is primary treatment

– effect on settling to determine

• very slow biodegradation of « unbiodegradable »

XE and XU,Inf in the bioreactor and the hypoxic fermenter

(0.005 to 0.012 d-1 for XE at 35°C)34

35

Wastewater Treatment (or WW Resource Management)

Effluent

2ry

Influent

Transformation

processes

water, org. fertiliser,

energy, C, N, P, K

Removal:

pathogens,

micropollutants

Prelim.(incl. solid-liquid

separation)

1ry Advanced(incl. UV, O3,

PAC)

Reuse:

waterSludge

disposal

(modelling)

(this project)

(to favor: energy via AD @ St-Hyac.)

(this project)

St-Hyacinthe WWTPConventional activated sludge

36

1ry

settling

AS

basins

2ry settling

St-Hyacinthe WWTP

37

La Presse, Feb 8, 2010

Completely mixed LIPP anaerobic digesters (german) & drying

+: energy from CH4, sludge reduction

-: odors, sludge disposal, transportation GHG

Future: agrofood waste to digest in 2 extra units

CH4 for municipal vehicles

Future: maximize AD by bCOD recovery at 1ry (CEPT)

and 2ry (high rate) treatment

Acknowledgments• Polytechnique

– Ph.D.: Marc-André Labelle, Reza Salehi

– M.Sc.A.: François Desjardins

– Techniciens: François Tremblay, Denis Bouchard, Mélanie

Bolduc (and undergraduate students)

• John Meunier

– Daniel Lamarre, Édith Laflamme (and others)

• City of St-Hyacinthe

– Pierre Mathieu, Robert Perry

• Natural Sciences and Engineering

Research Council

38