Golnaz Arab & Daryl McCartneyEWMCE & University of Alberta

Composting Council of Canada Annual Conference, Niagara Falls

27 September 2016

Digestate as Composting Feedstock:

Benefits to Decomposition Rates

2

• Capital of Alberta.

• Population: 880,000.

• GDP = $80,000 per year.

• Residential waste diversion goal of 90% by 2017.

Current situation

• Capacity issues.

• Wish to treat more biosolids.s

• Growth to ICI sector.

• Installing AD capacity.

Anaerobic

digester

(40,000 t y-1)

SSO from ICI

OFMSW

Manure

Digestate

Biogas

Final productsInputs

• Co-composting of digestate with fresh organics will reduce

MRT of composting.

• Controlled variable:

• Digestate portion ranged from 0 to 100%.

Background

Simplified Full-scale Material Flow

Co-Composting

(active phase)

Co-Composting

(curing phase)

OFMSW (2” & 3 to 5”), biosolids

Mature compost

Anaerobic digestion

Composting

(active phase)

OFMSW (<2 or <3”), ICI

SSO, horse manure,

woodchips, water

Digestate

Composting

(curing phase)

Mature compost

12

4

Background

Digestate Co-composting

Why Co-compost? Common MO in composting & AD processes.

Extracellular enzymes in digestate.

Nutrient addition, e.g. N, P, Mg, Fe.

Physical amendment: BD & MC.

May result in: Shorter lag phase.

Shorter retention times or more stable product.

Decrease in energy needs.

Lower costs??

5

Key Objective for Today

6

Highlight potential of

digestate co-composting.

Digestate preparation

• 500 L HSAD pilot-scale facility.

• With the same feedstock materials used in the full scale:

a. Pretreated OFMSW (-2”), 48%

b. ICI SSO, 51%

c. Horse manure, 1%

d. Woodchips, as needed.

7

8

2 to 5” material Digestate

Composter Feedstock

5”

• 2 to 5” material in spring 2015.

• Mostly yard waste, grass, & thatch.

Composter feedstock

Digestate As Inoculum

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Main feedstocks Amendments

Composter ID Digestate

(%, ww1)

OFMSW

(%, ww)

WC 2

(kg)

Water

(kg)

C0 0 100 0 1.22

C10 10 90 0 1.04

C20 20 80 0 1.02

C30 30 70 0 1.04

C40 40 60 0 1.00

C50 50 50 0 0.50

C75 75 25 0.59 (5%) 0.00

C100 100 0 1.57 (15%) 0.00

1 Wet weight.2 Woodchips.

Materials & methods

Schematic Design of Composters

10

23.5 L

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Composter

Loading weights

Material & Methods

Biological Load Cells

Results

Relative Heat Generation (RHG) Over Time

12

0

50

100

150

200

250

300

350

400

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

RH

G (

°Cd

)

Time (day)

C0

C10

C20

C30

C40

C50

C75

C100

247

334

294

354

Results

Stability - Specific Oxygen Uptake Rate

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200

300

400

500

600

700

800

900

1000

1100

1200

0 20 40 60 80 100

SO

UR

(m

g O

2.k

g O

M-1

. h

-1)

Time (day)

C0

C40

C100

Stabilityend point

Results

ROR, RHG, & Stability

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0

5

10

15

20

25

30

35

40

200

250

300

350

400

450

500

550

600

650

700

0 10 20 30 40 50 60 70 80 90 100

Stab

ility

tim

e (d

ay)

RO

R (

g O

M re

mo

ved. k

g-1 O

Mad

de

d)

RH

G (

°C d

)

Digestate (%)

RHG ROR Stability time

Best performance at 20 to 40 % digestate. Why?

Results

Total Biodegradable Carbon

Calculated versus Observed

15

5

7

9

11

13

15

17

19

21

23

25

0 20 40 60 80 100

CalculatedObserved

• Total biodegradable C

determined in each

reactor.

• Biodegradable C for

each reactor calculated

from controls, i.e. C0 &

C100 (blue line).

• Calculated is what was

expected.

• Observed significantly

higher that expected.

Tota

l C

bio

(% D

M)

Digestate Added (% DM)

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y = -2E-09x3 + 1E-05x2 - 0.0018x + 175.25R² = 0.96

50

100

150

200

250

0 2000 4000 6000 8000

Discussion

Chemical Characteristics

Inorganic Nitrogen Effect

• Up to 5,000 mg TAN

kg-1 DM may have

stimulated C removal.

• >5,000 mg TAN kg-1

DM may have inhibited

C removal. Tota

l C

bio

(g k

g-1

M)

Initial TAN (mg kg-1 DM)

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Digestate Co-composting

Summary & conclusion

Effects of co-composting of digestate (inoculation amount)

Best performance with about 20-40% digestate (wet weight)

Digestate prepared in AD, mixed with fresh OFMSW, added to composters

Next steps: molecular biology analysis & practical significance . . . ?

Enhanced C removal may be attributed to high TAN

Acknowledgments

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19Kibale National Park, Uganda

McCartney 2016

Questions?Daryl.McCartney@ualberta.ca

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Flow meter

Material & Methods

Experimental Setup

Dryer unit

Cooler

Flow meter

Gas sensor

Materials & methods

Experimental set-up

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Analyses UnitsStable/matur

eTest method

Monitoring

BD Kg.m-3 NA1 TMECC 03.01A

TS %, ww NA TMECC03.09

OM %, dw NA TMECC05.07

pH - NA TMECC 04.11

EC μs. cm-1 NA TMECC 04.10

Temperature °C <82 NA

O2 concentration % NA NA

Microbial

population% NA Pyrosequencing

Stability

C/N - <25 -

SOUR mg O2.g–1 OM. d–1 3-10 TMECC 05.08-A

Solvita® CO2 Solvita color code for CO2 5-6 TMECC 05.08-E

Maturity

Solvita® NH4 Solvita color code for NH4 4 TMECC 05.08-E

NH4 mg NH4. kg–1 dw 75-500 NRAL-105

NH4/NO3 - 0.5-3 NRAL-105

Materials & methods (Analytical method)

1 Not applicable2 Temperature changes.

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Discussion

• Changes of total Cbio at varying initial

TAN, fitted 3rd order polynomial function.

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y = -2E-09x3 + 1E-05x2 - 0.0018x + 175.25R² = 0.96

50

70

90

110

130

150

170

190

210

230

250

0 2000 4000 6000 8000

To

tal C

bio

(g. k

g-1

DM

)

Initial TAN (mg. kg-1 DM)

1. Inoculation within ranges 20-40%

• Increase the process performance

• Provides enough microorganisms

that could survive in the presence

of the indigenous microorganisms

2. Inoculation <20%

• No considerable impacts

• Possibly due to insufficient sources

of microorganisms

3. Inoculation >40%

• Reduction in process performance

(OM removal)

• Possibly because substrates

became the limiting factor

Biological effects (digestate inoculation)chemical characteristics effects (inorganic

nitrogen)