reduce excess sludge by over 50 percent with ozone sludge by over 50... · · 2008-08-25¾sludge...

Copyright © 2001, Praxair Technology, Inc. All rights reserved.

Reduce Excess Sludge By Over 50 Percent with OzoneReduce Excess Sludge By Over 50 Percent with Ozone

Malcolm Fabiyi, PhD., Richard Novak, PE., Randall B. Marx, PhD PE

Praxair R&D 2008

© Praxair, Inc. 2008

2Copyright 2008 © Praxair Technology, Inc. All Rights Reserved.

Agenda

Overview

The challenge of excess sludge generation

Sludge ozonation

Prior approaches vs. Praxair approach

Case Study

Conclusions


Sludge Costs: Understanding the Problem/Opportunity

Sludge handling & disposal make up 40-60% of WWT costs ($200-$900/Dry tons)

Costs increasing due to:Increasingly stringent regulations (emissions & toxins)Increasing sludge handling input costsShrinking landfill capacityUrbanization (increasing distances from landfill)Public concerns over safety/odorReplacing aging equipment/infrastructure

Target strategies that minimize sludge generation

Praxair’s patented Lyso™ process offers optimal solutionCost effectiveMinimal footprintSignificant side benefits – SVI, Foaming Control, DO augmentation, enhanced operational control

Sources: WERF, EPA Estimates, Town of Greenwich, CT


Options for Sludge Reduction

Long Sludge Age SystemsLagoons and Ponds – SRT of 30+ daysMBR – Operation of ASB at 10-20 g/L

LysisMechanical – Grinders, ComminutionChemical – Ozonation, AlkaliUltrasoundThermal methods

Praxair uses a Lysis approachApplied to secondary (excess) sludgeExpose excess sludge to ozoneOzone “attacks” cell wallCells contain ~90-95% liquid cellular compounds (COD)COD is released from lysed cellsCOD is (Bio)oxidized in the basin


Effect of SRT on Yield

Excess Sludge vs. SRT

y = 0.7324x-0.3245

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 10 20 30 40 50 60

Solids Retention Time, days

Slud

ge y

ield

, kgS

S/kg

CO

D

Doubling of sludge age = 20% reduction in waste sludge

High Solids → High SRT → Low Yield

Source: Eckenfelder (2004)


How Sludge Ozonation Works

Ozone penetrates cell wallBacterial cell to be ozonated in contactor

O3 contacts cell wall

Lysed cell – returned to basin

Cell with lysis ‘pockets’ after contact with ozone

Ozone oxidizes cellular compounds causing lysis

Lysed cells are returned to basin, where COD is released

Solid waste effectively transformed to “FOOD” for biomass in BasinSource: http://www.lenntech.com/ozone/ozone-disinfection-mechanism.htm


Mineralization vs. LysisOxidation with Ozone (Mineralization)

CO2+

H2O

Lysis ONLY is the Goal of Sludge Ozonation

Sludge ozonation approach must provide SELECTIVITY

Lysis with Ozone

1-4 C moleculesBacterial cell

Polysacchs, phospholipids, proteins, RNA, DNA, etc

Lysis ‘pockets’formed

COD leaks out into treatment

basin

Bacterial cell

Ozone attacks cell wall


Bacterial Cell


Comparison of Prior Art vs. Praxair Approach

Prior Art Approach Praxair Approach

ASBO3

Gen.

O3 contactor(CSTR)O3

Gen.

RAS Line

Sidestream pump

O2 reuse 10% O3 in O2

Single point injection

To Basin

RAS Line

Multi-staged injection


Process ConceptReduction of Waste Activated Sludge by Ozonation

Activated SludgeBasin

Activated SludgeBasin ClarifierClarifier

Waste Flow: 0.03 MGDSludge: 890 kgs/dayWaste Flow: 0.03 MGDSludge: 890 kgs/day

Waste Flow: 0.2 MGDSludge: 4,452 kgs/dayWaste Flow: 0.2 MGDSludge: 4,452 kgs/day

Influent Flow: 10 MGD BOD in: 218 mg/LBOD in: 7,420 kg BOD/dayYield: 0.6 kg Sludge/kg BODExcess sludge: 4,452 kgs Sludge/day

Influent Flow: 10 MGD BOD in: 218 mg/LBOD in: 7,420 kg BOD/dayYield: 0.6 kg Sludge/kg BODExcess sludge: 4,452 kgs Sludge/day

Effluent Flow: 9.97 MGDBOD out: 22 mg/LSolids: <10 mg/L

Effluent Flow: 9.97 MGDBOD out: 22 mg/LSolids: <10 mg/L

O3 Gen.

Praxair Sludge Ozonation Process

Return Sludge from clarifier

Current

Praxair

Effluent

Sludge

Influent

80% Reduction


Reactor operation mode impacts dosage rates

0.17

0.08

0.03

0.21

0.10 0.10

0.00

0.05

0.10

0.15

0.20

0.25

CSTR Sparger Injectors

g O

3/g(

CO

D/V

SS)

gO3/gVSSgO3/gCOD

0.17

0.08

0.03

0.21

0.10 0.10

0.00

0.05

0.10

0.15

0.20

0.25

CSTR Sparger Injectors

g O

3/g(

CO

D/V

SS)

gO3/gVSSgO3/gCOD

Plug flow approach with injection gives optimal O3 dosage

VSS & COD impacts of various approaches are differentInjection + Plug Flow provides enhanced dosage properties


Praxair Injection Scheme Reduces Ozone Requirement

Injection approach gives higher VSS reduction than alternatives for same O3 dosage

Experiments carried out at near “pilot” scale – 800L Tank

However a previous chemicals (Dye decolorization) based mass transfer study had showed injection mode had no real impact

Dosage to achieve 50% VSS Reduction

0.17

0.08

0.03

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

CSTR-Sparger Plug Flow - Sparger Plug Flow Injectors

g O

3/g

VSS

Rem

oved

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70

Tim e (m ins)

VSS

(mg/

L)

Plug Flow Injector

Plug Flow Sparger


Comparison of Volatile Suspended Solids* Removal

(Dosage = 0.2 g O3/min)

Comparative VSS Removal

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35 40

Time (mins)

VS

S R

emov

ed (g

m)

gVSS - Praxair InjectorsgVSS - CSTRgVSS - Diffusers

Comparative VSS Removal

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35 40

Time (mins)

VS

S R

emov

ed (g

m)

gVSS - Praxair InjectorsgVSS - CSTRgVSS - Diffusers

Praxair Approach provides superior lysisPraxair Approach provides superior lysis

* Refers to Bacterial cellsCSTR = Wedeco Approach; 2 gpm Flow through


Significant Foam formation occurs as Lysis proceeds

Significant foaming in CSTR approach

High sCOD content in foamExcessive O3 consumptionCommon problem with Kurita approach

VSS better measure of O3 lysis impact

VSS measures direct impact of O3 on cellsCOD measures primary lysis + secondary COD oxidation

Close-up on foam at 60 mins. 400-600L of foam generated from 400L of Sludge

5 LPM, 80% O3 Power; 2 Injectors.


Treatability of Lysis Product

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25

Time (hrs)

Mg

O2/

L

Synthetic

Blank

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25

Time (hrs)

Mg

O2/

L

Synthetic

Blank

0

50

100

150

200

250

0 5 10 15 20 25 30 35

Time (hrs)

Mg

O2/

L

St Charles_9_8Lysis_ALysis_B

0

50

100

150

200

250

0 5 10 15 20 25 30 35

Time (hrs)

Mg

O2/

L

St Charles_9_8Lysis_ALysis_B

Typical Substrate Composition (%)

Substrate Sample ID

Reactive Phosphorus (mg/L PO4

3-)

Nitrate (mg/L NO3-)

Total Nitrogen (mg/L N)

NH3 (mg/L) COD (mg/L)

Foam Sample A (Bottle #3) 7% 1% 11% 6% 100%Foam Sample B (Bottle #9) 6% 0% 13% 8% 100%Synthetic Raw Influent 5% 1% 16% 11% 100%St. Charles Raw Influent 8% 1% 35% 20% 100%

• Lysis product has high treatability• Biokinetic rates similar to plant

influent• Work being done to completely

characterize lysis products

• Lysis product has high treatability• Biokinetic rates similar to plant

influent• Work being done to completely

characterize lysis products


Lysis Product Has High Biodegradability

Lysis product composition has optimal nutrient distribution i.e., COD:N:P = 100:10-15:5-8

Lysis product has high treatability

Biokinetic rates similar to Municipal plant primary effluent

0

50

100

150

200

250

0 5 10 15 20 25 30 35

Time (hrs)

Mg

O2/

L

Municipal Primary EffluentLysis_ALysis_B


Case Study – Sludge Ozonation

Location: Italy

25,000 m3/day (7 MGD)

22,000 Lbs COD removed/day

50% Municipal, 50% Textile waste


Reduction in Excess SludgePILOT PLANT ~50% OF FULL SCALE

Cumulative Excess Sludge

0

50

100

150

200

250

300

350

400

17 18 19 20 21 22 23 24 25 26 27 28 29 30

Week #

Exce

ss s

ludg

e (to

n/w

eek)

Historical dataDuring piloting with O3

35-40% Sludge reduction

Pilot startup


Significant Reduction of Filamentous Bacteria


Filamentous Organisms are Effectively Controlled by Ozone

Sludge ozonation reduces filamentous populations

Large surface area = High vulnerability to Ozone


Effect on Filamentous Bacteria

Significant reduction in Nocardia, Parvicella, Thiotrix sp, etc.

Effects observed within 1-2 weeks

Effective for types 0041 and 0675

No impact on other biomass – Ciliates, Heterotrophs, AOBs, NOBs

Sludge reduction effects are sustained


Sludge Ozonation – Results Summary

Pre-Ozonation Post-Ozonation

Sludge Generated

2 Dry Tons/day 0.4 Dry Tons/day

% Dry solids 18% 22%

SVI (mL/g) 80-100 50-60

O3 Usage 0 0.07 kgs O3/kgs SS Removed (70 kgs O3/Dry ton)

Foaming 20 cm above liquid Nil

Treatment Capacity

80% COD removal

60% TN removal

80% COD removal

60% TN removal

*Pilot scale was for 80% sludge reduction of half plant sludge generation


Economical Ozone Usage vs. Alternatives

Reference Ozone Usage kg O3/kg SS reduced

Scale

Yasui et al (1996) 0.165 Lab Scale

Sakai et al (1997) 0.133 - 0.178 Lab Scale

Kobayashi et al (2001) 0.250 Lab Scale

Ried et al (2002) 0.395 Full Scale

WERF 2004 Sludge Minimization Study*

0.2-0.4 Full Scale

Praxair’s Lyso™ 0.05 - 0.10 Full Scale

*Praxair’s sludge ozonation technology has been included in WERF’s current review


Cost competitive vs. Alternatives

$/Dry ton Sludge

0

200

400

600

800

1000

1200

WERF SludgeOzonation

Praxair SludgeOzonation

Kady Process CannibalDigestion

$/Dry ton Sludge

0

200

400

600

800

1000

1200

WERF SludgeOzonation

Praxair SludgeOzonation

Kady Process CannibalDigestion

*Sources: WERF Sludge ozonation from 2004 Sludge Minimization Report; Cannibal Process economics from literature sources (Rickermann, J. H., & Johnson, B. R. Cannibal as a Cost Effective Biosolids Alternative. WEF/AWWA Joint Residuals and Biosolids Management Conference, Denver CO, 2007). Assumptions $0.06/kWh power cost, 20 year equipment life, 6% Rate.


Cost comparison

Rickermann, J. H., & Johnson, B. R. Cannibal as a Cost Effective Biosolids Alternative. WEF/AWWA Joint Residuals and Biosolids Management Conference, Denver CO, 2007.


Sludge Ozonation Process

Reduced sludge

Small footprint

Optimum ozone use

Foam elimination

Enhanced dewatering

Improved operations

Control of filamentous bacteria

Improved effluent quality

Improved settling (SVI)

No supplemental O2 required

Patented (US 7,309,432)


Conclusions

Sludge ozonation is an effective process for minimizing excess sludge generation

Small footprintHighly biodegradable lysis productsSludge reductionSVI improvementFoaming & Bulking control

No impact on N, COD removal; P release could increase

Plug flow process is the most cost effective approach for sludge ozonation (US Patent 7,309,432)

reduce excess sludge by over 50 percent with ozone sludge by over 50... · · 2008-08-25¾sludge...

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