improving anaerobic conversion of pulp mill secondary sludge to

Improving Anaerobic Conversion Improving Anaerobic Conversion of Pulp Mill Secondary Sludge to of Pulp Mill Secondary Sludge to

Biogas by Pretreatment Biogas by Pretreatment

Nicholas Wood, Honghi Tran and Emma MasterUniversity of Toronto

TAPPI EPE ConferenceMemphis, TN, October 12-14, 2009

Wastewater TreatmentWastewater Treatment

PrimaryTreatment

Waste Water

PrimarySludge

TreatedEffluent

SecondarySludge

Dewatering/Incineration/

Disposal

SecondaryTreatment

O2 CO2

2

EffluentDegassing Unit

Gas-liquid-solidseparator

Anaerobic granulesludge blanket

Influent distributionWastewater

Biogas

UpflowUpflow Anaerobic Sludge Blanketing Anaerobic Sludge Blanketing ((UASBUASB) Digester) Digester

3

Wastewater

Biogas(CH4, CO2)

Aerobic TreatmentUASB

Digester

TreatedEffluent

SecondarySludge

Dewatering/Incineration/

disposal

UASBDigesterUASB

Digester

CO2O2

Treatment System IncorporatingTreatment System IncorporatingUASBUASB DigesterDigester

4

Wastewater

Biogas(CH4, CO2)

Aerobic TreatmentUASB

Digester

TreatedEffluent

SecondarySludge

Dewatering/Incineration/

disposal

UASBDigesterUASB

Digester

Pretreatment

CO2O2

Treatment System Incorporating Treatment System Incorporating UASBUASBDigester and Sludge PretreatmentDigester and Sludge Pretreatment

5

ObjectiveObjectiveTo investigate the effectiveness of several pretreatment methods in increasing the anaerobic digestibility and biogas yield of pulp mill secondary sludge

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Sludge SamplesSludge SamplesKraft Sludge (KS)

Bleached kraft pulp millUses an aerobic stabilization basin system to treat its effluent.

Sulphite Sludge (SS)Ammonium based sulphite pulp millUses an activated sludge system and an up-flow anaerobic sludge blanket (UASB) digester to treat several mill wastewater streams prior to aerobic treatment.

Methanogenic culture for SS and KSMicrobial granules formed in the UASB digester at the sulphite mill. Samples stored at 4oC in sealed plastic bagsAnaerobic granules stored at 4oC in glass serum bottles

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Pretreatment MethodsPretreatment MethodsThermal Pretreatment:

170oC for 1 hour

Caustic Pretreatment:NaOH pellets were dissolved in the sample slurry (pH 12)140oC for 1 hour, pH adjusted to 7.

Sonication Pretreatment: Sonicated at 20 kHz to induce cavitation at an intensity of 1 kW/L, using a tubular sonication unit

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Sludge CharacterizationSludge CharacterizationChemical compositionTSSVSSCODProteinBiogas Production

Biochemical methane potential (BMP) assay

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Sludge AnalysisSludge AnalysisSulphite

Sludge (SS)Kraft

Sludge (KS)TSS, g/L 8.7 17.9VSS, g/L 7.3 13.9COD, g/L 12 27Soluble COD, % of total 12 1.1Carbohydrates, g/L 0.8 2Soluble carb., % of total 7.4 0.5Protein, g/L 3.9 4.6Soluble protein, % of total 0.43 0.13pH 7.4 7Sulphate, g/L 0.2 0.6Calcium, g/L 0.19 0.89Iron, g/L 0.18 0.04

10

0

20

40

60

80

100

Thermal Caustic Sonication

Red

uctio

n in

VSS

(%)

Sulphite SludgeKraft Sludge

Effect of Pretreatment on Effect of Pretreatment on VSSVSS

11

0

20

40

60

80

100

Untreated Thermal Caustic Sonication

Solu

ble

CO

D (%

)

Sulphite SludgeKraft Sludge

Effect on Soluble CODEffect on Soluble COD

12

0

20

40

60

80

Untreated Thermal Caustic Sonication

Solu

ble

Car

bohy

drat

es (%

)

Sulphite SludgeKraft Sludge

Effect on Soluble CarbohydratesEffect on Soluble Carbohydrates

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Sulphite SludgeKraft Sludge

Effect on Soluble ProteinEffect on Soluble Protein

0.0

0.4

0.8

1.2

1.6

2.0

Untreated Thermal Caustic Sonication

Solu

ble

Prot

ein

(g/L

)

14

Biogas Produced from SSBiogas Produced from SS

0

0.05

0.1

0.15

0.2

0.25

0.3

0 5 10 15 20 25 30 35Time (days)

Cum

ul. B

ioga

s Pr

oduc

ed(L

/gC

OD

)

Untreated

Thermal

Caustic

Sonication

15

Biogas Produced from KSBiogas Produced from KS

Thermal

Caustic

0

0.05

0.1

0.15

0.2

0.25

0.3

0 5 10 15 20 25 30 35Time (days)

Cum

ul.B

ioga

sPr

oduc

ed(L

/gC

OD

)

Sonication

Untreated

16

Effect on Biogas ProductionEffect on Biogas Production

Sulphite Sludge

Kraft Sludge

0.0

0.1

0.2

0.3

0.4

Untreated Thermal Caustic Sonication

Tota

l Bio

gas

Prod

uctio

n(L

/gC

OD

)

17

Biogas Production vs. Soluble Biogas Production vs. Soluble CarbCarb. .

0

5

10

15

20

25

30

0 1 2 3 4Soluble Carbohydrates Added (mg)

Tota

l Bio

gas

Prod

uctio

n (m

L)

y = 6.02x + 3.63R2=0.96

y = 4.52x + 1.49

R2=0.90

Sulphite Sludge

Kraft Sludge

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SummarySummaryEffects of thermal, caustic and sonication pretreatment methods on anaerobic conversion of SS and KS to biogas were investigated. Biogas production from untreated SS was four times higher than that from untreated KS

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SummarySummaryThermal pretreatment was the most effective in improving the rate and extent of biogas yield of SS and KS sludges; followed closely by caustic pretreatment; sonication was the least effectiveSoluble carbohydrate content may be used as an indicator for the biogas production potential

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! Alberta Pacific! Alberta Research Council/AFRI! DTE Petcoke! FPInnovations! Jammbco! Kiln Flame Systems! Zellstoff Celgar! Members of Research Consortium “Increasing Energy &

Chemical Recovery Efficiency in the Kraft Process”! NSERC

AcknowledgementsAcknowledgementsMembers of Research Consortium on

“Alternative Fuels for Lime Kilns”

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