Greengas Research Outlook Sweden23-25 March 2015

Making food waste digestion areality

Charles Banks

University of Southampton

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Greengas Research Outlook Sweden23-25 March 2015

Food waste digestersNuance

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Greengas Research Outlook Sweden23-25 March 2015

A short history2003 – First pilot scale study,mesophilic and thermophilic

2006 – 2009 Laboratory studies confirmingearlier observations

2006 – 2010 commissioning of firstdemonstration plant, and problems at alarge scale

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Greengas Research Outlook Sweden23-25 March 2015

Facts to hypothesis

• Ammonia toxic to acetoclastic methanogens lesstoxic to hydrogenotrophic methanogens

• Propionic acid accumulation is due to insufficient capacityof hydrogenotrophic methanogens to synthesis formatedehydrogenase enzyme

• Requirement for Se as part of this enzyme complex

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Greengas Research Outlook Sweden23-25 March 2015

Batch screening tests

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Greengas Research Outlook Sweden23-25 March 2015

Semi-continuous anaerobic digestion trials

Supplemented with:

• Trace element

combinations

• Single trace

element

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Greengas Research Outlook Sweden23-25 March 2015

Organic loading rate (OLR)

0,0

1,0

2,0

3,0

4,0

5,0

0 50 100 150 200 250 300 350

OL

R(k

gV

Sm

-3d

ige

ste

rd

ay

-1)

Time (days)

Control OLR=2

Control OLR=3

Se, Mo

Se, Mo, Co, W

Se, Mo, Co, W, Fe, Ni (supplementation ceased from day 112onwards)Se, Mo, Co, W, Fe, Ni, Zn, Cu, Mn, Al, B

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Greengas Research Outlook Sweden23-25 March 2015

0

6000

12000

18000

24000

30000

36000

0 50 100 150 200 250 300 350 400

VFA

(mg

l-1)

Time (days)

Control OLR=2

Control OLR=3

Se, Mo

Se, Mo, Co, W

Se, Mo, Co, W, Fe, Ni

Se, Mo, Co, W, Fe, Ni, Zn, Cu, Mn, Al, B

Sesupplementedaccidentally

Volatile fatty acid profiles

Trace elementsupplementationstopped inSe,Mo,Co,W,Fe & Ni

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Greengas Research Outlook Sweden23-25 March 2015

Digestion efficiency

0,000

0,200

0,400

0,600

0,800

1,000

0 50 100 150 200 250 300 350

SB

P(S

TP

m3

kg

-1V

S)

Time (days)

Specific biogas production (SBP)

Control OLR=2

Control OLR=3

Se, Mo

Se, Mo, Co, W

Se, Mo, Co, W, Fe, Ni

Se, Mo, Co, W, Fe, Ni, Zn, Cu, Mn, Al,B 0,00

1,00

2,00

3,00

4,00

5,00

0 50 100 150 200 250 300 350

VB

P(S

TP

m3

m-3

dig

este

rd

ay

-1)

Time (days)

Volumetric biogas production (VBP)

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Greengas Research Outlook Sweden23-25 March 2015

Other digestion parameters

6,00

6,50

7,00

7,50

8,00

8,50

0 50 100 150 200 250 300 350

pH

Time (days)

pH

Control OLR=2

Control OLR=3

Se, Mo

Se, Mo, Co, W

Se, Mo, Co, W, Fe, Ni

Se, Mo, Co, W, Fe, Ni, Zn, Cu, Mn, Al, B0,00

0,50

1,00

1,50

2,00

2,50

3,00

0 50 100 150 200 250 300 350

IA:

PA

Time (days)

Intermediate alkalinity (IA) : partialalkalinity (PA)

0

1000

2000

3000

4000

5000

6000

7000

0 50 100 150 200 250 300 350

TA

N(m

gN

H3-N

l-1)

Time (days)

Total Ammonia nitrogen (TAN)

Control OLR=2

Control OLR=3

Se, Mo

Se, Mo, Co, W

Se, Mo, Co, W, Fe, Ni

Se, Mo, Co, W, Fe, Ni, Zn, Cu, Mn, Al, B

30,0

35,0

40,0

45,0

50,0

55,0

60,0

65,0

0 50 100 150 200 250 300 350

Me

tha

ne

(%)

Time (days)

Methane percentage

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Greengas Research Outlook Sweden23-25 March 2015

Selected publications

More information onwww.bioenergy.soton.ac.ukwww.valorgas.soton.ac.uk

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Greengas Research Outlook Sweden23-25 March 2015

Microbial communitystructure analysis

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Greengas Research Outlook Sweden23-25 March 2015

FISH images

Probe name Target group Probe sequence (5’-3’) Fluorescent dye Fluorescent colour Formamide (%)EUB338 Bacteria GCTGCCTCCCGTAGGAGT Cy5 blue 20~50ARC915 Archaea GTGCTCCCCCGCCAATTCCT 6-Fam green 20~50MG1200 Methanomicrobiales CGGATAATTCGGGGCATGCTG Cy3 red 20MS1414 Methanosarcinaceae CTCACCCATACCTCACTCGGG Cy3 red 50MSMX860 Methanosarcinales GGCTCGCTTCACGGCTTCCCT Cy5 blue 45

Methanomicrobiales (food waste digestion) Methanosarcinaceae (vegetable waste digestion)

Archaea ArchaeaMethanomicrobiales Methanosarcinaceae

Bacteria Methanosarcinalesand Bacteria

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Greengas Research Outlook Sweden23-25 March 2015

Testing the maximum digester loading

0.000

0.100

0.200

0.300

0.400

0.500

0.600

900 1000 1100 1200 1300 1400 1500

SM

P(S

TP

m3

CH

4k

g-1

VS

)

Time (days)

Weekly average specific methane production (SMP)

Control

High load test

0.00

1.00

2.00

3.00

4.00

5.00

900 1000 1100 1200 1300 1400 1500

VM

P(S

TP

m3

CH

4m

3d

ay-1

)

Time (days)

Weekly average volumetric methane production (VMP)

Control

High load test

0

500

1000

1500

2000

2500

900 1000 1100 1200 1300 1400 1500

To

talV

FA

(mg

-1)

Time (days)

Total volatile fatty acids (VFA)

Control

High load test

0.00

0.10

0.20

0.30

0.40

0.50

0.60

900 1000 1100 1200 1300 1400 1500

IA:P

A

Time (days)

Intermediate alkalinity:partial alkalinity (IA:PA)

Control

High load test

4.0

5.0

6.0

7.0

8.0

9.0

900 1000 1100 1200 1300 1400 1500

pH

Time (days)

pH

Control

High load test

Digestate RMPcompared tocontrol

Performance of high load digester(OLR up to 8 kg VS m-3 day-1)

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Greengas Research Outlook Sweden23-25 March 2015

Testing operation under variable load conditions

OLR = 5.0 ± 3 kg VS m-3 day-1

Daily methane production (litres day-1)

Specific methane production(30-day rolling average)

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Greengas Research Outlook Sweden23-25 March 2015

Dilute-outexperiments

OLR 3 kg VS m-3 day-1 OLR 4 kg VS m-3 day-1

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Greengas Research Outlook Sweden23-25 March 2015

Trace elements requirement

• Selenium and cobalt are the key trace elements needed forlong-term stability of food waste digesters in Europe, butare likely to be lacking in the food waste

• Minimum recommended concentrations in food wastedigesters for selenium and cobalt are ~0.2 and ~0.35 mg l-1respectively, when running at moderate loading rate

• A total selenium concentration >1.5 mg l-1 is likely to betoxic to the microbial consortium

• Food waste is likely to have sufficientAl, B, Cu, Fe, Mn, Zn,Ni, Mo and W, but always check!

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Tolerance toammonia

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Full-scale digesters

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Greengas Research Outlook Sweden23-25 March 2015

After addition of micronutrients• VFA reduced from >30000 to <1000 mg l-1• SMP increased from 380 to 420 m3 tonne-1 VS• OLR increased to 3.2 kg VS m-3 day-1

Biocycle 900 m3 digester

Andigestion 300 m3 plant

DS% WW

VS% WW

CODg l-1

N-totalmg l-1

Comg l-1

Semg l-1

Nimg l-1

18.6 16.7 22.9 6877 0.07 0.04 0.52

Average composition of food waste asreceived at the Waterbeach plant

Substantial reduction in VFAfollowing Se and Co addition

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Greengas Research Outlook Sweden23-25 March 2015

Conclusions from mesophilic digester studies

• With proper trace element supplementation,stable operation of food waste digesters ispossible with low VFA concentrations at a loadingrate of 8 kg VS m-3 day-1 with volumetric biogasproduction >4 m3 m-3 day-1 and specific biogasproduction of 0.76 m3 kg-1 VS. Higher loadingsmay be possible.

• Prevention of VFA accumulation in the digester bytrace element supplementation is necessary, asrecovery of a severely VFA-laden digester is not arapid process even when supplements are added.

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Greengas Research Outlook Sweden23-25 March 2015

Thermophilicdigestion

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Thermophilicdigesters fed on‘high’ nitrogen

food waste

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Thermophilicdigestion fed on

‘low’ nitrogenfood waste

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Greengas Research Outlook Sweden23-25 March 2015

Thermophilicdigestion with

dilution of ‘high’nitrogen food

waste

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Greengas Research Outlook Sweden23-25 March 2015

Conclusions from thermophilic digestion studies

• Threshold inhibition concentration for totalammonia nitrogen (TAN) is ~2.5 g N l-1

• Failure of digester occurs at ≥ 3.5 g N l-1

• Trace element supplementation is noteffective in controlling VFA accumulation inthermophilic digesters

• Food waste can be digested thermophilicallyby dilution with water, but the ratio must besuch as to reduce TAN ≤ 2.5 g l-1 which is abouta 1:1 dilution

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Greengas Research Outlook Sweden23-25 March 2015

Continuing work• Ammonia removal in a side stream stripping

process successful

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Greengas Research Outlook Sweden23-25 March 2015

Thanks to:

Dr Yue Zhang, Dr Sonia Heaven and Prof Michael Chesshire

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