Page 76 - Materials Chemistry, Second Edition

Table 6.3 Configurations in waste management options Life cycle assessment and waste management 63
Source Residual waste treatment
separated Paper and
organics Land- Aerobic Anaerobic Gasification/ Incinera- container
treatment fill stabilisation digestion pyrolysis tion recycling
None A1 A2 Mixed with
residual
A
waste
None B1 B2 B3 B4 B5 Separate
collection
Aerobic C1 C2 C3 C4
composting of rigid
green waste containers
in crate and
Aerobic D1 D3 D4 paper via
composting kerbside
green and bundle
food waste
Anaerobic D2
digestion
A Upfront sorting (metal, plastic and paper) is assumed to take place at the treatment process. Scenario A models
one-stream collection, Scenario B models two-stream collection, and Scenarios C and D model three-stream collection.

s human toxicity
s eco-toxicity in freshwater, marine and terrestrial environments.
The characterisation factors for these indicators were also taken from CML with the excep-
tion of the toxicity indicators, which were taken from Huijbregts and Lundie (2002) and spe-
cifically modelled using Australian environmental conditions. Characterisation factors are
used to calculate the contribution of individual substance flows in the inventory to the indica-
tor result (i.e. for global warming, characterisation factors for carbon dioxide = 1, methane =
21 and nitrous oxide = 310).
As an illustration, Figure 6.10 presents greenhouse gas savings by gas and net savings across
the 15 waste management configurations. Significant savings are achieved when green waste is
diverted from landfill to composting (from scenario B1 to C1) and also food waste (scenario
C1 to D1). Methane from degradation of organic waste in an anaerobic landfill environment is
avoided when these waste fractions are sent to aerobic composting instead.
The key conclusions from this study were:
s Kerbside recycling delivers significant environmental benefits through avoided virgin
materials and reduced energy use and can be further improved.
s Production and application of compost delivers additional benefits, including increased
water-holding capacity, carbon sequestration, and reduced pesticide and fertiliser use.
This study was the first to incorporate such benefits from compost applications in
Australia.
s Organic residual waste treatment delivers substantial environmental benefits through
avoided or reduced emissions from landfill and recovery of additional recyclable
materials, particularly metals. Energy recovery from anaerobic digestion of residual
waste is relatively small, after accounting for energy use in processing.
s Thermal residual waste treatments deliver greater benefits in most environmental
categories. This result is based on the assumption that energy recovered from waste will
replace electricity generated from south-east Australia’s electricity supply system, which is
largely based on black and brown coal. The issue of benefits from replacing ‘dirty’ electricity

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