Charles Banks

8/2/2019 Charles Banks

1/26

Mass and energy balance around theLudlow food waste digester

Charles BanksBioenergy and Organic Resources Group

University of Southampton

25 November 2010


2/26

Study period 1 st June 2007 to 31 st July 2008

2


3/26

Feedstock Source segregated

food waste fromdomestic properties

3936 tonnes over the14-month


4/26

Sample measurement and analysis Quantification of input waste and other materials

Weighbridge and water meters Biogas production and composition

Gas meter, infrared analyser, STP (273.15 oK and 101.325 kPa) Waste input parameters

TS, VS, NPK, metals

Digester and digestate parameters TS, VS, Ammonia, VFA, alkalinity, pH, NPK, metals, temperature

Power production and utilisation

Supply and export meters


5/26

Feedstock characteristics

5

Biowaste input Unit Domestic CommercialSamples analysed no 547 114Average DM g g -1 0.277 0.278Min DM g g -1 0.139 0.080Max DM g g -1 0.439 0.467

Average ODM g g-

0.244 0.243Min DM g g - 0.122 0.072Max DM g g - 0.374 0.403DM:ODM 87.9% 87.5%

0.0

0.1

0.2

0.3

0.4

0.5

0 100 200 300 400Day

D o m e s

t i c f o o d w a s

t e T S a n d

V S

,

g g -

1 TSVS21-day TS21-day VS


6/26

Feedstock nutrient content Average TKN 8.9, P 1.9, K 3.3 kg tonne -1 wet weight for

domestic, commercial similar

6

0

2

4

6

8

10

12

1 - 1 7 O c t

1 8 - 3 0 O c t

1 - 1 6 N o v

1 9 - 3 0 N o v

1 - 1 3 D e c

2 - 1 4 J a n

1 5 - 3 1 J a n

1 - 1 4 F e b

1 5 - 2 8 F e b

1 - 1 5 M a r

1 - 1 4 A p r

1 6 - 3 0 A p r

1 - 1 6 M a y

1 9 - 3 0 M a y

1 - 1 2 J u n

1 6 - 3 0 J u n

N u t r i e n t c o n c e n t r a

t i o n

k g t o n n e -

1 w e t w e i g h

t

Nitrogen (TKN) Phosphorus (P) Potassium (K)


7/26

Digester operational parameters 2.5 kg ODM m -3 day -1 based on digester volume 900 m 3

Average HRT 80 days

7


8/26

Digestate characteristics Some variation, ratio TS:VS constant

Average TS 4.5%, VS 2.9%

0.00

0.02

0.04

0.06

0.08

0.10

01/06/2007 10/08/2007 19/10/2007 28/12/2007 07/03/2008 16/05/2008 25/07/2008

D i g e s

t a t e

D M a n

d O D M

,

g g -

1

DM ODM


9/26

Digestate metals

9

0

100

200

300

400

1 - 1 7 O c t

1 8 - 3 0 O c t

1 - 1 6 N o v

1 9 - 3 0 N o v

1 - 1 3 D e c

2 - 1 4 J a n

1 5 - 3 1 J a n

1 - 1 4 F e b

1 5 - 2 8 F e b

1 - 1 5 M a r

1 6 - 3 0 M a r

1 - 1 4 A p r i l

1 - 1 6 M a y

1 9 - 3 0 M a y

M e t a l c o n c e n

t r a t

i o n ,

m g

k g - 1

d r y w e i g h

t

Lead (Pb) Nickel (Ni) Zinc (Zn) Copper (Cu) Chromium (Cr)


10/26

Digestate nutrients TKN 5.6, P 0.4, K 2.3 kg tonne -1 wet weight

Mass balance 86.1, 32.8, 96.4%

10

0

2

4

6

8

10

1 - 1 7 O c t

1 8 - 3 0 O c t

1 - 1 6 N o v

1 9 - 3 0 N o v

1 - 1 3 D e c

2 - 1 4 J a n

1 5 - 3 1 J a n

1 - 1 4 F e b

1 5 - 2 8 F e b

1 - 1 5 M a r

1 6 - 3 0 M a r

1 - 1 4 A p r i l

1 - 1 6 M a y

1 9 - 3 0 M a y

1 - 1 6 J u n e

N u t r i e n t c o n c e n t r a

t i o n

k g t o n n e -

1 w e t w e i g h

t

Nitrogen (TKN) Phosphorus (P) Potassium (K)


11/26

Biogas output

11

0

5000

10000

15000

0 100 200 300 400Day

W e e

k l y g a s p r o d u c

t i o n m

3

biogasCH4

CO2

45

55

65

75

85

0 100 200 300 400Day

C H 4 % Daily

CH4

AverageCH4


12/26

Biogas output

12

Gas production parameters during mass and energy balance periodItem Unit Value %Methane m 3 STP 385,488 62.6Carbon dioxide m 3 STP 229,984 37.4

Biogas m3

STP 615,472 100.0kg WW 3,936,504 -Food waste inputkg VS 959,209 -m3 tonne -1 WW 156 -Specific biogas yieldm3 tonne -1 VS 642 -

m3

tonne-1

WW 98 -Specific methane yield m3 tonne -1 VS 402 -Volumetric biogas yield a m3 m -3 reactor 1.59 -Volumetric methane yield a m3 m -3 reactor 1.00 -

a Based on volume of digester only


13/26

Digestion parameters pH 7.24 8.64, average 8.13

IA: PA ratio average 0.4, maximum 2.74

Ammonia maximum 5000 mg l -1 VFA maximum 15000 mg l -1

Propionic acid 11500mg l -1

13


14/26

VFA profiles

14

0

5000

10000

15000

20000

0 100 200 300 400Day

T o t a l V F A m g

l - 1

Acetic Propionic Iso-Butyric n-Butyric Iso-Valeric Valeric Total


15/26

pH and alkalinity

15

7.0

7.5

8.0

8.5

9.0

0 100 200 300 400Day

p H

0

5000

10000

15000

20000

0 100 200 300 400

Day

P A a n

d I A m g

C a C

O 3

l - 1

0.0

0.5

1.0

1.5

2.0

2.5

3.0

I A / P A

Partial Intermediate IA/PA


16/26

Mass balance Calculated in 2 ways: wet weight and volatile solids basis

Wet weight

Water additions for both process and facilities supplies Methane and CO 2 corrected to STP Stored materials based on tank volumes and estimated

fibre quantities stored on site No account of evaporative loss from gas mixing system No account of fugitive emissions (gas or liquid) from site

16


17/26

Cumulative mass balance (wet weight)

17

-1000

0

1000

2000

3000

4000

5000

6000

0 100 200 300 400

Day

C u m u l a t

i v e w e t

t o n n e s

input output output + change in storage balance


18/26

Wet weight mass balance

18

Mass balance for study period (wet weight)Parameter Unit ValueFood waste input kg 3,936,504Water input (washwater) kg 1,490,000Total input kg 5,426,504

Methane kg 275,177Carbon Dioxide kg 451,473Water vapour kg 12,526Digestate a kg 3,969,080Fibre a kg 39,240All waste leaving site kg 35,820Total output kg 4,783,315Wet tanks kg 92,433Stored material kg 30,000Total storage kg 122,433

kg 520,756Balance accounted for% 90.4%

a Any liquid digestate produced is recirculated through the process and leavesthe site as whole digestate


19/26

Mass balance Volatile solids

VS taken from average of lab determinations VS of reject stream assumed equal to incoming food

waste Stored materials based on tank volumes and VS assumed

equal to that in digestate storage

No account of volatiles lost in VS determination (VFA,ammonia)

19


20/26

VS mass balance

If volatile losses aretaken into account,mass balance is95.7%

Mass balance for study period (VS)Parameter Unit ValueFood waste input kg WW 3,936,504Food waste VS kg VS kg -1

WW 0.244

Total input kg VS 959,209Methane kg VS 275,177Carbon Dioxide kg VS 451,473

kg WW 3,969,080kg VS kg -1 0.029

Digestate (includesseparated and wholedigestate) kg VS 115,521

kg WW 39,240

kg VS kg-1

0.179

Fibre

kg VS 7,040kg WW 35,820kg VS kg -1 0.244

Reject

kg VS 8,728Total output kg VS 857,938

kg WW 92,433kg VS kg -1 0.029

Wet tanks

kg VS 2,690kg WW 30,000kg VS kg -1 0.179

Stored material

kg VS 5,382Total storage kg VS 8,072Balance kg VS 93,198

% 90.3%


21/26

Electrical and heat balance from CHP

21

Parameter Unit Value %CHP gross energy a kWh 2,781,48

1100.0%

CHP gross electrical output kWh 890,074 32.0%CHP parasitic electrical requirement kWh 37,728 1.4%CHP net electrical output kWh 852,346 30.6%CHP gross heat output kWh 1,891,40

768.0%

CHP recoverable heat output kWh 1,474,18

5

53.0%

CHP waste heat kWh 417,222 15.0%

a Calculated as electrical output divided by conversion efficiency taken as 32%


22/26

Process energy requirements

22

Parameter Unit ValueCHP electrical parasitic kWh 37,728Rest of plant parasitic kWh 232,694Total electrical parasitic a kWh 270,422

% of gross electrical output 30.4%Heat requirement to raise feedstocktemperature

kWh 202,674

Heat requirement for pasteurisation kWh 150,709Heat requirement to maintain tanktemperatures

kWh 92,951

Total parasitic heat requirement kWh 446,334% of recoverable heat 30.3%

a Total electrical parasitic, divided by CHP gross electrical output from Table 4


23/26

Overall energy balance

23

Parameter Unit ValueCHP net electrical output kWh 852,346Parasitic electrical requirement of process plant kWh 232,694Net energy output as electricity kWh 619,652Recoverable heat output from CHP kWh 1,474,185Parasitic heat requirement of plant kWh 446,334Net energy output as heat kWh 1,027,851CHP natural gas used kWh 18,413Energy required for digestate use kWh 34,350Total potentially recoverable energy (heat and electricity) a kWh 1,594,740Total potentially recoverable energy per wet tonne of foodwaste

kWh 405

a Includes heat energy generated but not used at the time of the study


24/26

Conclusions Specific methane yield of food waste was 98 m 3 tonne -1 wet weight or

402 m 3 tonne -1 ODM, and productivity remained high throughout thestudy period.

Nitrogen content led to high ammonia concentrations that buffered VFA accumulation.

Net recoverable energy 405 kWh tonne -1 wet weight, includingdigestate transport and utilisation.

Mass balance 90.4% (wet weight), and 95.7% (VS basis) allowing forloss of volatile components.

Since study ended the plant has continued in successful commercialoperation and provides a sustainable route for recovery of productsfrom domestic food waste.

24


25/26

Further information Banks C. J., Chesshire M, Heaven S., Arnold R, (2010).

"Anaerobic digestion of source segregated domestic food waste: performance assessment by mass and energy balance." Bioresource Technology DOI: doi:10.1016/j.biortech.2010.08.005

Arnold, R., Banks C.J., Chesshire, M., Foxall, M., Stoker, A.(2010). Defra Demonstration Project: Biocycle South

Shropshire Biowaste Digester. Defra New TechnologiesProgramme. www.defra.gov.uk/environment/waste/residual/newtech/demo/documents/Biocycle-final.pdf.

25
http://dx.doi.org/doi:doi:10.1016/j.biortech.2010.08.005http://dx.doi.org/doi:doi:10.1016/j.biortech.2010.08.005http://dx.doi.org/doi:doi:10.1016/j.biortech.2010.08.005http://dx.doi.org/doi:doi:10.1016/j.biortech.2010.08.005


26/26

Acknowledgements Funding for this project was provided by Advantage West

Midlands and by Defra from the New TechnologiesDemonstrator Programme.

The support and assistance of Biocycle South ShropshireLtd is gratefully acknowledged, with especial thanks to co-authors Michael Chesshire, Rebecca Arnold and SoniaHeaven.

26

Documents

Charles Banks