Page 110 - Materials Chemistry, Second Edition

Will the well run dry? Developments in water resource planning and impact assessment

Greywater Reticulated 97
supply
treatment
system system

Household
water use

Waste
water
System
system
boundary
Figure 8.2 Systems that need to be considered when considering greywater system impact.

LCA typically commences with characterisation of a ‘typical’ existing system, consisting of
potable supply and conventional treatment. However, supply varies according to terrain and
scale, and treatment utilises a variety of physical, chemical and/or biological processes to remove
the waste products from the wastewater stream. Up to four treatment stages are generally recog-
nised. Primary treatment involves the removal of sand, grit, and other settable solids, oils, grease
and fats from the water stream through the use of screening and sedimentation systems. Sec-
ondary treatment involves the removal of biological content such as human waste, food waste
and detergents through the use of fixed film or suspended growth systems in the stream.
Tertiary treatment involves the removal of residual toxins and nutrients such as phosphorus
and nitrogen through the use of filtration, lagooning or constructed wetlands. If the treated
wastewater is to be used where there is the risk of direct human contact, a disinfection stage is
typically added involving chlorination, ultraviolet (UV) light or ozone (O ) treatment. Hence,
3
LCA characterisation of a ‘base’ system can be involved and is invariably unique to each case.
Alternative systems then require additional options to be considered either in addition to
or in lieu of the existing/base system. The example of a household greywater treatment system
illustrates a broadened system boundary. Upon initial consideration, the life cycle impacts of
adding a greywater treatment system appear to be the production and operation of the greywa-
ter system itself. Unfortunately, limiting system analysis in this way does not address the impli-
cations of reducing reticulated water to the household and (potentially) reducing wastewater
treatment requirements. To fully understand the impact of an alternative water supply system
such as greywater treatment requires the LCA practitioner to think broadly about a group of
interrelated system impacts, not just the system of interest (Fig. 8.2).
Once the system boundary is defined, flows of resources and resultant emissions can be
characterised for both the system construction (i.e. the infrastructure establishment) and
system operation. Using this approach, Yarra Valley Water has commissioned research investi-
gating the life cycle impact and cost implications of different water servicing options. Figure
8.3 illustrates how the proportion of life cycle impacts associated with infrastructure varies for
a series of water options considered for a particular reticulated suburban supply and disposal
application (‘global warming’ indicator shown). However, there are specific and different
issues in characterising assessment of infrastructure and operation, and these are discussed in
the following sections.

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