Operation-Based Improvements through the Use of

Trommel Screens for Processing and Contaminant

Reduction across Various Seasons

Ali Rajabpour, Ph.D. Candidate

Daryl McCartney, Ph.D., P.Eng.

1

17 September, 2015

The National Compost Conference

Gatineau, Québec

Background: Rotary Screen (Trommel)

• Originally adapted from

mineral processing

– Diameter

– Length

– Inclination angle

– Rotational velocity

– Shape and size of apertures

– Feed rate

• Screening of organic fines

• Final screening of compost

product

• … 2

ω

R

h

1

3

2

Background: North American Case Studies

3

CA

LA

MD

AB

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec-20

-10

0

10

20

30

Ave

rag

e T

em

pe

ratr

e (

oC

)

Month

Baltimore, MD

Bereckley, CA

New Orleans, LA

Edmonton, AB

Case Studies

Berkeley, CA (Glaub et al.,1982)

New Orleans, LA (Glaub et al.,1982)

Baltimore, MD (Hannon et al.,1983)

Edmonton, AB (Rajabpour et al., 2015)

Integrated Processing and Transfer Facility (IPTF)

4

Note: The flow of ferrous metals separated by overhead magnets from both undersize

waste streams are not shown for simplicity

<2 inch

2 to 5 inch

5 to 9 inch

>9 inch

2

2

2

2

5 to 9 inch

MSW

<2 inch

>9 inch 2nd Hand

Sorting

1

2 to 5 inch

2 to 9 inch

D D

D

D

To ECF To RDF

C- 502

C- 401

C- 700C- 600

Recyclables,

Rejects and

bulky items

1st Hand

Sorting

D

Trommel

Disc Screen

Pre-processing Line #1

Pre-processing Line #2

Common conveyors and belt-scales

2

1

D

Weekly variation of <2” in 2013

5

Winter Spring Summer Fall

Areas of improvement

• Variation in recovery of <2” waste stream over time

• Feed rates exceeding the designed throughput (summer)

• Clogging of 2” apertures (especially in winter)

• Non-biodegradable contaminants in compost feedstock

• Available options:

– Increase the screen size

– Control the feed rates

6

Objectives

• To assess the effectiveness of screening with larger

screen size (i.e., 3”)

• To quantify the feed rate that:

1. Maximizes the screening of the organic-rich fines (<2”); and/or

2. Maximizes the waste processing throughput

7

Methodology (1): Trials and feed rate calibration

• Preliminary trials: three full-day tests at minimum,

average and maximum feed rates (i.e., 40, 55, 70-tph)

with 2” screen in March

• 4 trials were scheduled in June-July:

– Feed rate: 40 and 70 tph (nominally)

– Screen size (of 1st stage): 2 and 3 inch

• Trial duration: 4 hours in summer

• Feed rate calibration:

– Random sampling from waste pile for scoop measurement

– Setting time intervals between waste loads

8

Methodology (2): Data collection and sampling

• Data collection: – Data recording in every 15 minutes

– Operation downtime

• calculation of feed rate, system availability and

recovery ratios

• A single sampling (ASTM D5231) from: – First unders (<2″ WS): 15-kg

– Second unders (2 to 9″ WS): 75-kg

– Overs (>9″ WS): 20-kg

9

Methodology (3): Waste characterization

• Particle size distribution (PSD) analysis – 9, 7, 6, 5, 3.5 (or 3) and 2 inch sieves

– Further sieving of <2” fraction into 35 mm (1.4”) and

15 mm (0.6”).

• Composition of post-sieved size fraction: – 1) Paper & cardboard; 2) rigid plastics; 3) film plastic;

4) yard; 5) food; 6) other combustible; 7) glass; and,

8) non-combustible wastes.

10

0 60 120

180

240

300

360

420

480

540

600

660

0

10

20

30

40

To

tal re

co

ve

ry (

%,

by w

et w

eig

ht)

Operation Time (min)

Min rate (41 tph)

Mean rate (60 tph)

Max rate (75 tph)

Recovery of <2” at different feed rates in March-14

11

-20°C

+7°C

~0°C

Rosin-Rammler PSD of combined feed in summer

season (June-July 2015)

12

0.01 0.1 1 10 1002" 3"

0

20

40

60

80

100 96%

66%66%R

2= 0.993

Cum

ula

tive P

assed (

%, w

et w

eig

ht)

Particle Size (inch)

Ave

Max

Min

52%

0 60 120 180 2400

10

20

30

40

50

60R

eco

ve

ry (

%, w

et w

eig

ht)

Operation time (min)

T1 @ 2" & 82.4 tph

T2 @ 2" & 45.8 tph

T3 @ 3" & 75.9 tph

T4 @ 3" & 55.2 tph

Recovery of <2” and <3” waste streams

13

2" Screen 52% 3" Screen 66%

0 60 120 180 2400

10

20

30

40

50

60

70R

eco

ve

ry (

%, w

et w

eig

ht)

Operation time (min)

T1 @ 2" & 82.4 tph

T2 @ 2" & 45.8 tph

T3 @ 3" & 75.9 tph

T4 @ 3" & 55.2 tph

Recovery of 2-9” and 3-9” waste streams

14

2" Screen 44% 3" Screen 30%

0 60 120 180 2400

5

10

15

20R

eco

ve

ry (

%, w

et w

eig

ht)

Operation time (min)

T1 @ 2" & 82.4 tph

T2 @ 2" & 45.8 tph

T3 @ 3" & 75.9 tph

T4 @ 3" & 55.2 tph

Recovery of >9” waste stream

15

2" Screen 4% 3" Screen 4%

Composition of <2” and <3” streams

16

NS: Not significantly different

S: Significantly different

Size Sample # Paper Rigid

Plastic Film

Plastic Yard Food

Diap. & Nap.

Other Comb.

Glass Non-

Comb. Biodeg. Non-Biodeg.

2"

Scre

en

1 4% 3% 3% 42% 20% 8% 13% 2% 6% 74% 26% 2 7% 4% 2% 47% 12% 10% 12% 1% 4% 76% 24% 3 10% 7% 4% 36% 15% 11% 12% 1% 4% 72% 28% 4 7% 4% 4% 45% 9% 14% 11% 1% 6% 74% 26%

Average 7% 4% 3% 42% 14% 11% 12% 1% 5% 74% 26%

3"

Scre

en

5 8% 5% 6% 29% 14% 19% 12% 1% 6% 70% 30% 6 8% 4% 4% 41% 16% 9% 8% 1% 9% 74% 26% 7 9% 5% 5% 39% 8% 12% 15% 1% 6% 68% 32% 8 13% 5% 5% 37% 14% 7% 12% 1% 6% 71% 29%

Average 10% 5% 5% 37% 13% 12% 12% 1% 7% 71% 29%

T-Test results NS NS S NS NS NS NS NS S NS NS

Composition of <2” and <3” streams

17

NS: Not significantly different

S: Significantly different

Size Sample # Paper Rigid

Plastic Film

Plastic Yard Food

Diap. & Nap.

Other Comb.

Glass Non-

Comb. Biodeg. Non-Biodeg.

2"

Scre

en

1 1% 1% 0% 54% 23% 6% 5% 4% 6% 83% 17% 2 2% 1% 0% 69% 12% 4% 6% 2% 4% 87% 13% 3 2% 1% 0% 71% 9% 4% 5% 3% 5% 87% 13% 4 2% 0% 0% 88% 1% 2% 2% 2% 4% 93% 7%

Average 2% 1% 0% 70% 11% 4% 4% 3% 5% 87% 13%

3"

Scre

en

5 2% 4% 0% 42% 21% 11% 10% 3% 7% 75% 25% 6 3% 1% 0% 57% 19% 6% 6% 3% 5% 85% 15% 7 6% 1% 0% 63% 9% 9% 7% 3% 3% 86% 14% 8 4% 2% 1% 53% 17% 8% 11% 1% 3% 81% 19%

Average 4% 2% 1% 54% 16% 8% 8% 2% 5% 82% 18%

T-Test results NS NS S S NS S S NS NS NS NS

Maximum Foreign Matter Particles Allowed in

Composts

18

Country Recommended levels (% of dry weight)

Australia < 0.5% foreign matter (glass, metals, plastic) for

>2mm fraction

US: Los Angeles, CA 0.1% film plastic

US: Portland, OR 0.5% film plastic

Germany < 0.5% for >2mm of foreign matter

Italy <3 % in total

Switzerland: 1) < 0.5% for >2mm fraction; 2) max 0.1% plastic

United Kingdom 1) < 1% > 2mm; 2) < 0.5% if plastic

Contamination level in the final compost produced in June & July of 2015

was 0.14% DW of plastic (average of 3 tests)

20 30 40 50 60 70 80 90

65

70

75

80

85

90

95

100S

yste

m A

va

ilab

ility

(%

)

Feed Rate (tph)

R2=0.7

Correlation between feed rate & system availability

19

Availablity % =Net peration time

Total Time× 100

40 50 60 70 80 90 100

200

300

400

500

600

700A

mo

un

t o

f w

aste

pro

cesse

d (

tpd)

Feed Rate (tph)

8 hpd

9 hpd

10 hpd

Maximum achievable processing throughput

20

Processing Throughput tpd = Feed rate tph × Duration (hpd) × Aavailability %

Summary

• Challenges of studying at full-scale operation.

• Effectiveness of larger screen size vs. lower feed rate

on screening performance

– Larger screen more consistent screening

– Lower feed rate higher recovery ratios

• The practical feed rate to be applied was between 45

and 75 tph.

– What’s the objective? Priority?

• Concerns on quality of compost product

– Which facility to target?

21

Acknowledgements

22

Thank you!

Questions?

23