Co-digestion of Used Cotton Clothing

Allison Kelly 2012 BioEnergy and Sustainability School

August 7, 2012

Summary of Problem

• Used cotton clothing commonly sent to landfill

• Wasted energy source

- ~90% cellulose

• Possibility of anaerobically digesting discarded clothing

Donate clothing 43%

Landfill 9%

Give to others 25%

Repurpose 15%

Sell 8%

Survey on the Disposal of Used

Clothing

N=130

Composition of Cotton

cellulose-94%

protein-1.3%

pectic substance-.95%

wax-0.6%

mineral matters-1.3%

acid-0.8%

sugar-0.3%

Cellulose

• Cellulose

-Hard to break down

-Hydrolysis limited

• Need for pretreatment!

Objectives

• Assess biodegradability of cotton fabric by using cellulase enzyme

• Test if cotton fabric can produce biogas using co-digestion in a Biomethane Potential Assay

Assessment of Cotton Fabric Biodegradability

-

• Test biodegradability

-Factory enzyme Kerry Biocellulase

• Compare biodegradability

-Filter Paper (control)

-Cotton T-shirt

-Biocellulase (blank)

Methods • Microscopic examination of

sample before and after

• Chemical Oxygen Demand (CODT)= indirectly measures organic material

- measured liquid portion

• Soluble Chemical Oxygen Demand (CODs)= measures dissolved organic material

Effect of Treatment with Cellulase

Before After

Total Chemical Oxygen Demand (CODT)

0

20000

40000

60000

80000

100000

120000

140000

160000

Cellulase Cellulase+ CotonFabric

Water + CottonFabric

Cellulase +FilterPaper

Water+ Filterpaper

CO

D m

g/L

Soluble Chemical Oxygen Demand (CODS)

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

Cellulase+Water

Cellulase+Cotton Fabric

Water + CottonFabric

Cellulase +FilterPaper

Water + FilterPaper

CO

D m

g/L

Downside of Factory Cellulases

• Very expensive!

• Need a lot to be fully effective

• Possible Solutions: natural enzymes

- Food waste

Possible Solution: Co-digestion with Food Waste

• Food waste is an efficient feedstock

• Food waste has low C: high N quickly acidifies inhibition

• Cotton has high C: low N longer to produce methane

• Both feedstocks balance each other out

Possible need for Different Temperatures

• Different enzymes have different optimal temperatures

• Kerry Biocellulase= 55 °C

• Food Waste BMP= 35 °C

• 35, 45, 55 °C

Measurement

• Tested by measuring Biochemical Methane Potential (BMP)

-100% Cotton T-Shirt (TS)

-100% Food Waste (FW)

-50% Cotton TS, 50% FW

-25% Cotton TS, 75% FW

-Blank

Results-BMP 35 °C

0

50

100

150

200

250

300

350

400

450

500

0 5 10 15 20

Cu

mu

lati

ve C

H4 m

L/g

of

VS

Days of incubation

100% cotton

100% foodwaste

50/50 %

25/75 %

Results-BMP 45 °C

0

50

100

150

200

250

300

350

0 5 10 15 20

Cu

mu

lati

ve C

H4

mL/

g o

f V

S

Days of incubation

100% cotton

100% foodwaste

50/50%

25/75%

Results-BMP 55 °C

0

50

100

150

200

250

300

350

400

450

0 5 10 15 20

Cu

mu

lati

ve C

H4

mL/

g o

f V

S

Days of incubation

100% Cotton

100% food waste

50/50

25/75

Comparing Temperatures

0

50

100

150

200

250

300

350

400

450

500

100% cotton 100% Food waste 50/50 25/75

Cu

mu

lati

ve C

H4

mL

/g o

f V

S

35° C

45° C

55° C

Conclusion

• Cotton clothing can be a feedstock for anaerobic digestion

• Food waste aids clothing in methane production and vice versa

• 35°C is most efficient temperature with the tested inoculum

Future Studies • Test for any other

possible natural pretreatments

-septic system treatment

-natural digestion enzymes

• Create digester with food waste and used clothing

• Test if effluent is efficient fertilizer

• Test effects of dyes and detergents

Thank you!

Questions or Comments?