- Currently the production of biofuel from algae is not economically competitive with petroleum fuel. However, co-production of high-value products may be able to justify the cost of large-scale algae cultivation. The basic goal of this study is to develop a techno-economic analysis (TEA) and Life-cycle assessment (LCA) for the production of glucosamine, a high value product, and lipid from the diatom Cyclotella. This analysis considers two algal growth pathways, e.g. raceway open pond (RWP) and photobioreactor (PBR) cultivation. It demonstrated that large-scale PBR
costs are much more than open pond systems for the production of glucosamine and lipid from diatoms. The selling price of glucosamine is highly sensitive to Cyclotella productivity and chitin content. In order to generate 1 kg of glucosamine, 9700 kg (RWP HL) /1050 kg (PBR HL) freshwater, 40 kg CO2, 0.70 kg nitrogen, 0.18 kg phosphorus, and 1.2 kg silicon nutrients are required for algae cultivation with water recovery. With a price of $1.50 for lipid as coproduct, the projected selling price of glucosamine is $35/kg, $106/kg and $82/kg for RWP, PBR high lipid cultivation conditions, and PBR high chitin cultivation condition systems, respectively.
Currently, these prices are not competitive with industrial shellfish-derived glucosamine, but can be reduced by technology improvements such as producing food grade lipid, increasing algal productivity or chitin content.
Life-cycle assessment (LCA) was used to investigate the resource consumption and environmental impacts of production of glucosamine and lipid co-product from the marine diatom Cyclotella sp. A well-to-product (WTP) LCA was performed that included algae cultivation, algae harvesting, glucosamine production, and lipid extraction. With 95% recycle during the dewatering process, water consumption for algae cultivation for production of 1 kg glucosamine and 4.7 kg lipid was estimated to be 9730 and 1050 kg for raceway open pond (RWP) and photobioreator (PBR) cultivation, respectively. The global warming potentials (GWP) were -0.37 kg CO2 eq/kg-glucosamine for RWP and 69 kg CO2 eq/kg-glucosamine for the PBR system. The analysis of net energy ratio (NER) showed low energy return with 2.7 and 8.5 MJ/MJ-lipid for the RWP and PBR cultivation systems, respectively. Results from sensitivity analysis demonstrate that the environmental impacts in the operation are strongly sensitive to the algal productivity and chitin content.
Anaerobic digestion (AD) is a potential process to treat large quantities of residual biomass after lipid extraction from the algal biomass. The objective for the experimental study
was to investigate AD strategies that enable biogas utilization and nutrient recovery from oil-extracted algal biomass (Chlorella and Cyclotella). The AD of lipid-extracted Chlorella had a biogas yield 0.37±0.02 L-biogas/g-algaeVS (volatile solid in algae) and a methane yield of 0.21±0.01 L-CH4/g-algaeVS of methane. The AD of lipid-extracted Cyclotella had a biogas yield of 0.38±0.02 L-biogas/g-algaeVS and a methane yield 0.25±0.03 L-CH4/g-algaeVS. Thus, the high inorganic content of Cyclotella did not have a negative impact on AD. For both algae species, the majority of methane was produced during the first 10 days of digestions (62-66% for lipid-extracted Chlorella and 73-83% for lipid-extracted Cyclotella). An average of 47±9% of the nitrogen from the lipid-extracted Cyclotella was converted to soluble ammonium. With the low phosphorus content (0.9-1.1%) in the biomass from both lipid-extracted Chlorella and Cyclotella, recovery of phosphorus from algae was not evident.
The TEA model for lipid and glucosamine production was implemented in Matlab with a convenient user interface to change input parameters, and illustrative output on the cost categories and selling price of glucosamine. This model was used in a senior bioengineering process design class project to provide students an opportunity to practice and become comfortable with decision making with multiple concerns and types of evidence, promote student understanding of how a process design (techno-economic model) can be used, and enable students’ ability to navigate uncertainty. Evidence from the student-produced work (recommendation memos for investment, post-project survey) indicated that the project accomplished these goals.