Page 91 - Materials Chemistry, Second Edition

72 Life Cycle Assessment of Wastewater Treatment

4.6 CONCLUSION AND DISCUSSION
The study proposed a waste reuse system that reuses centrate and sludge created from
sludge thickening to bioenergy and land nutrients. The results showed that the inte-
grated system could bring environmental benefits as well as impacts. When compared
with digestion followed by land application, the integrated system improved the envi-
ronmental performance on fossil fuel use, GHG emissions, eutrophication, and acidifi-
cation, but increased impacts on ecotoxicity and carcinogens. Decision makers should
pay more attention to this trade-off when adding treatment facilities to MWTPs.
The study was just a primary analysis for the integrated waste management of the
waste streams in an MWTP. A sensitivity analysis should be conducted to identify
key factors for environmental performance where a strategy for improvement can be
figured out. As the major benefits were created from the generation of bioenergy, and
impacts stemmed from land application of digestate, the environmental performance
can be improved by generating more bioenergy and reducing biosolids for disposal.
Some feasible technologies that can be considered to further improve the integrated
system are

1. Cycling CO from digestion and injecting it into algae cultivation, which
2
could improve algae yields and remove more nutrients from centrate.
2. Adding Scum-to-Biodiesel production into the integrated waste manage-
ment system. More biodiesel could be produced.
3. Further treating digestate with pyrolysis or gasification or liquefaction
technology, which could produce more biofuels and reduce biosolids for
disposal.
4. Considering other algal biofuel production technologies, such as pyrolysis
or liquefaction, to increase biofuel yields and therefore improve environ-
mental performance.

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