Page 87 - Materials Chemistry, Second Edition

68 Life Cycle Assessment of Wastewater Treatment

separately in previous studies. This study used models for unit processes and inte-
grated them into one system model. A summary of the parameters for modeling and
sources of data can be found in Table 4.3. The LCI included all direct inputs and
emissions and also their upstream impacts. All direct and upstream impacts were
either provided by researchers at the University of Minnesota or based on existing
literature and LCA databases such as GREET 2015, EcoInvent 3, and the US-EI
database. Labor, facilities manufacturing, and other impacts were not included in
this analysis.

TABLE 4.3
Process Design Parameters for the Integrated Waste Reuse
System in the MWTP
Unit processes Assumptions References
Algal Biofuel Production
−3
Algae cultivation in Growth rate: 36 g m per day Frank et al. (2011),
PBRs Characteristics of algae: total lipid Murphy et al. (2011),
content = 5 wt.%; ash = 7.8 wt.%; the lower Quinn et al. (2013),
heating value (LHV) = 21.2 MJ kg ; Lardon et al. (2009),
−1
moisture = 80% Alba et al. (2013),
Electricity use: pumps = 0.35 kWh m ; CO 2 Biller et al. (2011),
−3
injection = 22.2 Wh kg CO 2 ; CO 2 Min et al. (2011)
−1
−1
collection = 1.31 MJ kg CO 2
3
Water loss: leak = 0.2 m m per year;
−2
3
evaporation = 0.6 m m per year
−2
Algae harvesting and Flocculation and sedimentation: increase solid
dewatering content by 10 times; algae harvest efficiency is
90 wt.%; flocculant = 2.5 g/m slurry
3
Centrifuge: increase solid content to 20 wt.%;
algae collection efficiency is 95 wt.%; electricity
−3
use = 3.3 kWh m slurry
Algal biofuel Efficiency: homogenization = 94 wt.% algae; Clarens et al. (2011),
production lipid extraction = 90 wt.% lipid; Frank et al. (2011),
transesterification = 99 wt.% bio-oil; Batan et al. (2010),
glycerin = 0.12 kg kg biodiesel Vasudevan et al. (2012)
−1
Chemical inputs: hexane = 45.4 g kg bio-oil;
−1
−1
NaOH = 0.023 kg kg bio-oil; HCl = 0.085 kg
−1
kg biodiesel; KOH = 1.5 wt.% bio-oil;
methanol = 0.117 kg kg biodiesel
−1
Energy use: homogenization = 0.246 kWh elec.
kg dry algae; lipid extraction = 0.51 kWh
−1
elec. + 6.83 MJ heat/kg bio-oil;
transesterification = 0.09 kWh elec. + 1.7 MJ heat
kg diesel
−1
(Continued)