Biomedical Engineering Reference
In-Depth Information
of the algae to biogas without prior recovery of the lipid fraction for biodiesel. This
approach allowed avoidance of the concentration and cell disruption steps, thereby
reducing the energy and economic costs. The digestate following methane produc-
tion has potential to provide a source of N and P for further algal growth. Partial
recycle has been demonstrated in the
Spirulina
system.
9.4
ECONOMIC CONSIDERATIONS OF
MICROALGAL PRODUCTION
9.4.1 C
ost
oF
a
lGal
b
ioMass
and
a
lGal
o
il
Currently, commercial processes for the production of microalgae only exist for the
production of specialty products such as health supplements, carotenoids, and specific
aquaculture feeds. Furthermore, most of the algal species used in these processes are
extremophilic
algae. Data on the cost of large-scale algal processes are largely based on
pre-implementation costing of these. Typical costs estimated are presented in Table 9.4.
From Table 9.4, the disparity in costing that arises from an immature technology
position is clear. This was also noted in a comparison of environmental analyses.
As a general trend, the algal biomass cost from the raceway system lies in the range
of US$0.23 to $0.60 kg
−1
DW, with the exception of the estimate of Norsker et al.
(2011), for which the biomass was recovered by centrifugation, noted as a major
capital and energy cost. The production of algal biomass from photobioreactors
was characterized by a greater variation from US$0.42 to $3.04 kg
−1
DW. Here it
is evident that the two lowest values are based on the same calculations (Chisti,
2007), while the majority of the values (four of the eight available) lie in the range
US$3.18 to $9.54. Refinement in this costing is required. Factors impacting the cost-
ing are discussed in Section 9.4.2.
These costs are not competitive with the cost of crude oil (US$0.48 to $0.71 L
−1
;
US$76 to $113 bbl
−1
). Van Harmelen and Oonk (2006) estimated that cost of pro-
duction with current technology exceeded potential earnings from algal oil as sole
product by 1.7- to 3.9-fold, depending on the assumptions and process decisions
made. In costing a production facility for algal oil in South Colorado, Richardson
et al. (2012b) indicated that a 60% reduction in CAPEX (capital expenditure) and
90% reduction in OPEX (operating expenditure) are required for a cost-effective
pond system with algal oil as the sole product. These reductions increase to 80% on
CAPEX and 90% on OPEX using a photobioreactor system. Norsker et al. (2011)
translated their costs based on algal biomass to an energy-based cost, yielding val-
ues in the range of US$32.60 to $295.50 GJ
−1
. It is noted that the lower value of
US$32 GJ
−1
estimated for a high light intensity environment is similar to the cost of
delivered electricity.
These costings raise clearly two key considerations:
1. The necessity to operate the algal oil process as a biorefinery, achieving
value from multiple products for the same growth costs
2. The need to interrogate component process costs to identify key targets
for cost savings and technology development
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