Thermal hydrolysis for biosolids stabilization

Neptune workshop: Technical Solutions for Nutrient and Micropollutants Removal in WWTPs

Université Laval, Québec, March 25-26, 2010

Thermal hydrolysis for

biosolids stabilization

Pretreatment for Anaerobic Digestion

Damien Batstone

Advanced Water Management Centre, The University of Queensland

Neptune Workshop, Université Laval, Québec, March 25-26, 2010

Sludge Steams from WWT

Aeration Basin Clarifier

Influent

Return activated sludge

Effl.

Waste sludge

Digester 40-50% removal

gas

Primary sludge

Thickener


The Scale of Biosolids/Sludge

• People produce 50 g dry (400g wet) biosolids per

day each

• In Australia, 5 million wet tonnes per day

• Equivalent to 150,000x40 tonne trucks

• Costs $50-$100 per wet tonne

• 30%-60% of overall wastewater treatment plant

costs

• 1M people produce enough “energy” to power

10,000 homes (2% of energy demand)

And that’s only from people! What about

everything else??


Classical Treatment Methods


Emerging trends with BNR

Aeration Basin Clarifier

Influent

Return activated sludge

Effl.

Waste sludge

Digester 40-50% removal

gas

Primary sludge

Thickener

0%

10%

20%

30%

40%

50%

60%

5 10 15 20 25 30 35 40

Activated Sludge Age (d)

Deg

rad

ab

ilit

y (

%)

Long Sludge Age = Low

Degradability!


Pretreatment – Thermal Hydrolysis


Key Outcome 1 – Neptune

Thermal hydrolysis is cost neutral but

greenhouse negative. Costs are shifted to

capital expense instead of operating

expense.

Batstone, DJ, Keller, J., and Darvodelsky, P.S. (2008) “Trends in Biosolids Handling

Technologies: Economics and Environmental Factors” AWA Biosolids Conference June 7-10,

Adelaide.


Centralised Plant Case Study


-0.5 0 0.5 1 1.5 2 2.5 3

Landfill

Current Combined

Decentralised Aerobic

Centralised Anaerobic

Centralised Thermal

Hydrolysis + Anaerobic

kg COD emitted/kg dry biosolids handled

CO2

Greenhouse Gas Emissions


Mesophilic Income (option b)

2016 per tonne wet biosolids

Cogen

electrical,

$4.32

Biosolids

charges,

$52.50

Mesophilic Expenditure (option b)


Polymer, $3.40

Disposal, $29.20

Maintenance,

$3.36

Staffing, $1.19

Depreciation

Civils, $4.31

Depreciation

M&E, $4.97

Alum, $1.76

Nitrogen-

Carbon, $3.40

Nitrogen

Aerators, $1.25

Engineering

Overheads,

$3.25

Cost – Mesophilic Alternative


Thermal Hydrolysis Expenditure (option f)


Polymer, $2.40

Potable water,

$0.15

Maintenance,

$6.01

Staffing, $1.19

Depreciation

Civils, $7.31

Depreciation

M&E, $9.29

Engineering

Overheads,

$5.79

Nitrogen

Aerators, $2.11Nitrogen-

Carbon, $5.77

Alum, $2.99

Disposal, $6.05

Thermal Hydrolysis Income (option f)


Cogen

electrical,

$6.67

Biosolids

charges,

$43.12

Cost – Thermal Hydrolysis



Thermal hydrolysis produces coloured

compounds. Colour production is

dependent on temperature. Anaerobic

degradability is not.

Dwyer J, Starrenburg D, Tait S, Barr K, Batstone DJ, Lant PA. (2008). The impact of thermal

hydrolysis operating temperature on colour production and biodegradability of waste activated

sludge. Wat Res. 42(18): 4699-4709.


Colour from THP is in effluent

• Advanced BNR with UV

disinfection

• Downstream membrane

filtration

• Compounds identified as

large humics by Ex-Em

Spec

• Failed quality measures

during thermal

hydrolysis operations


Results variation in temperature

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 5 10 15 20 25

THP 145C


Results variation in temperature

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 5 10 15 20 25

Time (d)

THP 165C


Other Impacts



Thermal hydrolysis greatly increases

degradability, but there is still a basic

dependency on sludge age.

Batstone DJ, Tait S, Starrenburg D. (2009) Estimation of hydrolysis parameters in full-scale

anerobic digesters. Biotech. and Bioeng. 102(5): 1513-1520.

Batstone, DJ, Balthes, C., and Barr, K. (2010) “Model Assisted Startup of Anaerobic Digesters

Fed with Thermally Hydrolysed Activated Sludge”. Submitted Wat. Sci. Tech Feb 2010.


Model Based Analysis

0

1000

2000

3000

4000

5000

6000

7000

0 50 100 150 200 250 300 350 400 450

Ga

s F

low

(N

m3 d

-1)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

fd

Digester 1


On Both Digesters

0

1000

2000

3000

4000

5000

6000

7000

0 50 100 150 200 250 300 350 400 450

Time (d)

Ga

s F

low

(N

m3 d

-1)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

fd

Digester 2


Indicated a relationship

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0.65

0.7

5 10 15 20 25 30

Upstream Sludge Age (d)

De

gra

da

bility

Activated

Sludge

Hydrolysed


Conclusions

Thermal hydrolysis is cost neutral but greenhouse

negative. Costs are shifted to capital expense

instead of operating expense.

Thermal hydrolysis produces coloured compounds.

Colour production is dependent on temperature.

Anaerobic degradability is not.

Thermal hydrolysis greatly increases degradability, but

there is still a basic dependency on sludge age.


Acknowledgements

• Brisbane City Council (and many people there)

• Gold Coast City Council

• Cambi AS

• DIISR International Science Linkage (ISL) project

CG110007

• Neptune FP6 EU project Contract-No. 036845

Thermal hydrolysis for biosolids stabilization

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