The use of microalgae culture to convert CO2 from power plant flue gases into
biomass that are readily converted into biofuels offers a new frame of
opportunities to enhance, compliment or replace fossil-fuel-use. Apart from
being renewable, microalgae also have the capacity to utilise materials from a
variety of wastewater and the ability to yield both liquid and gaseous biofuels.
However, the processes of cultivation, incorporation of a production system for
power plant waste flue gas use, algae harvesting, and oil extraction from the
biomass have many challenges. Using SimaPro software, Life cycle
Assessment (LCA) of the challenges limiting the microalgae (Chlorella vulgaris)
biofuel production process was performed to study algae-based pathway for
producing biofuels. Attention was paid to material use, energy consumed and
the environmental burdens associated with the production processes. The goal
was to determine the weak spots within the production system and identify
changes in particular data-set that can lead to and lower material use, energy
consumption and lower environmental impacts than the baseline microalgae
biofuel production system. The analysis considered a hypothetical
transesterification and Anaerobic Digestion (AD) transformation of algae-to-
biofuel process. Life cycle Inventory (LCI) characterisation results of the
baseline biodiesel (BD) transesterification scenario indicates that heating to get
the biomass to 90% DWB accounts for 64% of the total input energy, while
electrical energy and fertilizer obligations represents 19% and 16% respectively.
Also, Life Cycle Impact Assessment (LCIA) results of the baseline BD
production scenario show high proportional contribution of electricity and heat
energy obligations for most impact categories considered relative to other
resources. This is attributed to the concentration/drying requirement of algae
biomass in order to ease downstream processes of lipid extraction and
subsequent transesterification of extracted lipids into BD. Thus, four prospective
alternative production scenarios were successfully characterised to evaluate the
extent of their impact scenarios on the production system with regards to
lowering material use, lower energy consumption and lower environmental
burdens than the standard algae biofuel production system. A 55.3% reduction
in mineral use obligation was evaluated as the most significant impact reduction
due to the integration of 100% recycling of production harvest water for the AD
production system. Recycling also saw water demand reduced from 3726 kg
(freshwater).kgBD-
1
to 591kg (freshwater).kgBD-
1
after accounting for
evaporative losses/biomass drying for the BD transesterification production
process. Also, the use of wastewater/sea water as alternative growth media for
the BD production system, indicated potential savings of: 4.2 MJ (11.8%) in
electricity/heat obligation, 10.7% reductions for climate change impact, and 87%
offset in mineral use requirement relative to the baseline production system.
Likewise, LCIA characterisation comparison results comparing the baseline
production scenarios with that of a set-up with co-product economic allocation
consideration show very interesting outcomes. Indicating -12 MJ surplus (-33%)
reductions for fossil fuels resource use impact category, 52.7% impact
reductions for mineral use impact and 56.6% reductions for land use impact
categories relative to the baseline BD production process model. These results
show the importance of allocation consideration to LCA as a decision support
tool. Overall, process improvements that are needed to optimise economic
viability also improve the life cycle environmental impacts or sustainability of the
production systems. Results obtained have been observed to agree reasonably
with Monte Carlo sensitivity analysis, with the production scenario proposing the
exploitation of wastewater/sea water to culture algae biomass offering the best
result outcome. This study may have implications for additional resources such
as production facility and its construction process, feedstock processing
logistics and transport infrastructure which are excluded. Future LCA study will
require extensive consideration of these additional resources such as: facility
size and its construction, better engineering data for water transfer, combined
heat and power plant efficiency estimates and the fate of long-term emissions
such as organic nitrogen in the AD digestate. Conclusions were drawn and
suggestions proffered for further study.
| Identifer | oai:union.ndltd.org:CRANFIELD1/oai:dspace.lib.cranfield.ac.uk:1826/9304 |
| Date | 07 1900 |
| Creators | Mathew, Domoyi Castro |
| Contributors | Di Lorenzo, Giuseppina, Pilidis, Pericles |
| Publisher | Cranfield University |
| Source Sets | CRANFIELD1 |
| Language | English |
| Detected Language | English |
| Type | Thesis or dissertation, Doctoral, PhD |
| Rights | © Cranfield University 2014. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner. |
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