Page 84 - Materials Chemistry, Second Edition

Life Cycle Assessment of Beneficial Reuse of Waste Streams 65

project. If the project’s goal is to evaluate waste reduction, the functional
unit should be based on the mass of waste. In contrast, the functional unit
should be based on products such as diesel or electricity if the goal is to
evaluate the wastewater treatment facility as an energy source. Based on
current literature, the majority of LCA projects used input functional units
(Pradel et al., 2016).
3. Waste allocation: LCA modeling can treat waste streams as “zero bur-
den” and charge them with no environmental burden. Arguments may
be raised, because real products are generated from wastes. If the waste
is treated as a resource, it should carry an upstream environmental bur-
den. However, allocating an environmental burden between wastewater
treatment and waste streams is complicated. The study by Pradel et al.
(2016) proposed that allocation should consider the factors between the
sludge production and the water treatment for each step that generates
waste.
4. Reuse benefits: When the LCA aims to assess the waste reduction in treat-
ment facilities, the functional unit will be based on inputs, that is, the waste
flows. The products generated could be treated as credits to replace petro-
leum-based products or fertilizers or energy in markets. The LCA model-
ing could subtract the impacts of producing these products from the final
impacts. Similarly, if the project includes algal biofuel production, it would
be better to account for the removal of pollutants in wastewater as credits to
wastewater treatment.
5. Global warming potential accounting: Wastes for reuse in the treatment
facility are mainly biological wastes. During bioenergy production and
consumption, CO is emitted to the atmosphere, with other gases such
2
as methane (CH ), carbon monoxide (CO), and nitrous oxide (N O). The
2
4
CO is usually accounted for as biological CO , which is not included in
2
2
the global warming potential calculation. However, the CH , N O, and
2
4
other GHGs emitted from the production and consumption processes
should be accounted for, because they have much higher warming poten-
tial than CO .
2
6. Impact analysis: The LCA could use existing analysis methods, such as
TRACI 2 or Impacts 2000+, and so on. The LCA could also focus on sev-
eral key impacts. Based on the project’s goal and scope, the LCA of waste
reuse should include impact categories for both waste reduction and energy
production. For example, impacts of GHG emissions and fossil fuel use
should be included, because they are key to evaluating the energy produc-
tion. When the biosolids are disposed as land nutrients, human health and
ecotoxicity should be included. If algae cultivation includes treating wastes,
as well as these impacts, acidification and eutrophication should be included
in the impact analysis, because the wastewater will be discharged from the
algae cultivation stage.