Page 164 - Materials Chemistry, Second Edition

152 A. Singh and S. I. Olsen

2.2.5 Sensitivity Analysis
The sensitivity analysis was conducted with higher oil content of algal biomass
(i.e., 60 %), reported by Rodolfi et al. (2009), and this oil content can be obtained
in Nannochloropsis sp. by creating N stress at the adequate time of biomass
cultivation.

3 Results and Discussion

Impact assessment of all scenarios was made using Impact 2002+ method in
SimaPro 7.3.2. The impact categories considered in the present study include
human health, ecosystem quality, climate change, and resources. These impact
categories are further subdivided into carcinogens, non-carcinogens, respiratory
inorganics, ionizing radiation, ozone layer depletion, aquatic ecotoxicity, terres-
trial ecotoxicity, respiratory organics, terrestrial acid/nutrient, land occupation,
global warming, non-renewable energy, and mineral extraction. The network of all
scenarios is presented in Figs. 1, 2, 3, 4, 5, and 6. The scenarios considering the
press and co-solvent oil extraction perform better than sCO 2 for oil extraction.
Among the harvesting techniques, lime flocculation showed best results, followed
by centrifugation and aluminum flocculent techniques. The press and co-solvent
method might be better than sCO 2 due to lesser requirement of electricity in
comparison with sCO 2 technique. Centrifugation technique required about 10
times higher electricity demand than the flocculation techniques. Aluminum pro-
duction might involve higher energy input than the lime production, which
resulted in a higher impact harvesting technique.
The comparison results of passenger car running with algal biodiesel produced
in different scenarios and fossil diesel are presented in Figs. 7, 8, 9, 10, and 11.
The characterization results depicted that algal biodiesel provides very high sav-
ings of GHG in comparison with diesel, while other impacts (carcinogens, non-
carcinogens, respiratory inorganics and organics, ionizing radiation, mineral
extraction, etc.) were higher in algal biodiesel produced in all scenarios in com-
parison with fossil diesel (Fig. 7). The higher reduction in global warming caused
by the uptake of CO 2 during growth of algae makes algal biodiesel superior to the
fossil diesel. Impact on mineral extraction was very high in the scenarios of
aluminum flocculent used for harvesting (Fig. 7), because of the use of aluminum
in the scenarios that require mineral extraction. Impact on non-renewable energy
and aquatic eutrophication was also high in algal biodiesel scenarios than in fossil
diesel ones (Fig. 7) and this might be due to higher chemical, electricity and heat
demand during cultivation and conversion steps of algal biodiesel production.
Damage assessment of the study showed savings in climate change impact with
the algal biodiesel in comparison with the fossil diesel. Human health, ecosystem
quality, and resources get higher impacts with the use of algal biodiesel in