Measuring energy embodied in New Zealand's
organic waste stream
Simon Love, Haylon Smith, Alison Slade, Daniel Gapes
1. Scion’s ‘Waste to Gold’ Project
2. NZ Organic Waste Audit
3. Energy Potential of Organic Waste
4. Case Study: Rotorua District Council
Part One: The Waste to Gold Project
!
Feedstock: Organic Waste
Process: Thermochemical Deconstruction
(complex inputs
simpler outputs)
Outputs: Organic Intermediates
""
Compelling value propositions:
− Reduce costs
− Generate income
− Mitigate impacts
• Energy production and beyond
Photo / Daily Post
High Carbon
Solid Wastes
Biodegradable
Intermediates
Biomass
Deconstruction
Energy Recovery
Bioenergy
Bioconversion
Liquid biofuels
Biopolymers
Part Two: New Zealand Organic Waste Audit
#
# $
%
%
• Undertaken by Haylon Smith in 2008
• An audit – real data used, no estimations
• Survey respondents:
− 57 of the 72 territorial local authorities (TLAs)
− 4 of the 12 regional councils
• Builds on:
− MfE 2006 Waste Strategy target review1
− Sinclair Knight Merz (SKM) ‘Waste Facilities Survey’2
1.
Ministry for the Environment (MfE) (2007): Targets in the New Zealand Waste Strategy – 2006
Review of Progress
2.
SKM (2008) Waste Facilities Survey
$
%
% &
• Putrescibles
− Kitchen & food wastes
• Green Waste
− Household garden waste
− Commercial green waste
• Biosolids
− Residual solid organic waste from
wastewater treatment processes
• Other
− All waste that does not fall into above
three categories (e.g. mixed green and
putrescible waste, primary industry
waste, paper & timber)
'
%
$
%
% (
)%
%
'
*
• Why is the ‘other’ category so high?
− Waikato
Dairy/Meat processing
Boiler fuel (pulp & paper)
− Bay of Plenty
Tasman Mill
− Hawke’s Bay
Food processing (fruit)
New Zealand Organic Waste Audit
Average Makeup of Organic Waste
Other
27%
Putrescible
34%
Biosolid
12%
Greenwaste
27%
+%
Points to note:
• Some waste streams are still excluded as data is
poor (e.g. paunch grass from meat processing)
• Data missing from some important regions (e.g.
Auckland)
• Still an underestimate
• Figures from MfE Waste Levy are coming in now
Part Three: Energy Potential of Organic Waste
#
%,
%
)
*
%
Step 1: Literature review
Step 2: Estimation of methane potentials
Step 3: Calculation of energy potentials
%
-% #
Recent research papers gathered on:
• Properties of organic wastes
(e.g. % content volatile solids)
• Methane potentials of organic wastes
• Methane yields from experimental data
• Energy yields from current waste-toenergy technologies
.
%
• Methane potentials of crop waste & grass clippings
were used to get an average for ‘green waste’
• Food waste potentials were used for putrescibles
• ‘Organic fraction of municipal solid waste’ was
used for ‘other’
• Biosolids figures were used for biosolids
.
Method 1: Energy calculations using methane potentials
% Volatile Solids (VS)
Deliverable
Energy
Methane Potential
(m3 per kg VS)
Methane Density
(kg per m3)
Generator Efficiency
(%)
Calorific Value
(MJ per kg)
Putrescibles Green Biosolids
Waste
Estimate of Actual
Deliverable Energy
(GJ/t Total Waste)
1.37
1.41
0.67
Other
1.70
* Deliverable energy is assumed to be from a combined cycle gas power
plant, with an efficiency of 50%
.
Method 2: Energy calculations using energy data
% Volatile Solids (VS)
Energy Data
(kWh per kg VS)
Deliverable
Energy
Putrescibles* Green Biosolids* Other
Waste
Estimate of Actual
Deliverable Energy
(GJ/t Total Waste)
2.2
2.6
0.9
2.4
* No energy data was found for putrescibles or biosolids so their figures are
an average of existing data for other wastes
* +%
Total potential energy from each waste stream (GJ)
Method Putrescibles Green
Waste
Biosolids Other
Total
1
852,000
693,000
171,000
1,955,000
3,670,000
2
1,367,000
1,291,000
238,000
2,776,000
5,672,000
So a total energy potential of 3.7 – 5. 7 Petajoules
To put this in context……
# $
Source
% %*
%
/001
% of total
Energy
(PJ)
Hydro
52.3%
79.50
Gas
23.7%
36.02
Coal
10.5%
15.96
Geothermal
9.4%
14.29
Wind
2.5%
3.80
Wood
0.8%
1.22
Biogas
0.5%
0.76
Oil
0.3%
0.46
Waste Heat
0.1%
0.15
Source: MED (2009) New Zealand Energy Data File
5.7
3.7
*
%
• Maximum generation potential of ~4% of New
Zealand’s electricity needs
• This assumes all waste recorded in the organic
waste audit is used for energy!
• Figures based on many assumptions, but show
potential
• Economic potential yet to be evaluated
, %
%
)%
• Reduction in solid waste to landfill, resulting in
increased landfill life
• Reduction of emissions from solid waste
decomposition
• Can produce a range of useful outputs (organic
intermediates or energy)
RDC Case Study
2' '
*
• Rotorua District Council looking at diverting
biosolids from landfill
• W2G process:
− Biosolids
acetic acid
− Used for denitrification in WWTP
2'
'
• Scion in partnership with RDC
• Initial focus: biosolids
• Life cycle assessment in progress
• Experimental work in progress
Conclusions
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•
•
•
•
•
%
Organic waste stream estimate: 2.7 million tonnes
Best estimate currently – uncertainties remain
Potential energy from this: 3.7 – 5.7 PJ
= approximately 4% of NZ’s electricity needs
Scion’s Waste to Gold project under way
− Lab scale stage currently
− Pilot plant for biosolids in 2010