Techno-economic analysis of glucosamine and lipid fuels production from autotrophic diatom algae
Algae exhibit high versatility in production of food, feed, fertilizers, and high-value products (e.g. fatty acids and coloring substances). In addition, the high lipid content can potentially serve as a sustainable feedstock for biodiesel. Several different types of fuels can be produced from algae, including methane, hydrogen, alcohols, and biodiesel from oil (Ferrell and Sarisky-Reed, 2010). Compared to conventional crop-derived feedstock, algae grow rapidly and have significantly higher potential oil yield per area than terrestrial plants (Chisti, 2007). Currently the production of biofuel from algae is not economically competitive with petroleum fuel. However, co-production of a high-value product may be able to justify the cost of large-scale algae cultivation. This article describe the techno-economics of the production of glucosamine and algal lipid from diatom algae.
Many high-value products have been derived from algae, including human and animal food and nutrients, poly-unsaturated fatty acids (mainly omega-3), anti-oxidants (mainly β-carotene), coloring substances (carotenoids & astaxanthin), fertilizers, and specialty compounds for cosmetics and pharmaceuticals (Ferrell and Sarisky-Reed, 2010). Glucosamine is an amino-monosaccharide dietary supplement that is commercially derived from chitin. It is believed that glucosamine molecules simulate cartilage to generate proteoglycans and collagen that hold joint tissue together (Cao et al., 2007). Glucosamine is widely used as a base ingredient in joint health supplements worldwide. Industrially it is produced through chitin hydrolysis using acid. The raw material, chitin, is commonly derived from crustacean shells, insect exoskeletons, and fungal and algae cell walls (Zhu et al., 2007). Most commercial glucosamine is derived from the exoskeletons of shellfish. However, this production method has some limitations for people who are allergic to shellfish and those who follow Jewish dietary laws may refuse to consume shellfish-derived glucosamine (Cao et al., 2007). Algal and fungal biomass is the primary sources for the glucosamine supplement to avoid these limitations.
Techno-economic analysis (TEA) is conducted to determine the economic viability of process by combining the technology design and process modeling with economic evaluations. This study evaluates the technology and economics the production of glucosamine and co-production of lipid biofuel from diatom algae. The base process is designed to produce 500 metric ton of glucosamine per year and co-product biofuel by Cyclotella sp. diatom. Both open pond and photobioreactor (PBR) are evaluated for algae cultivation.
2. Approach and Methodology
The production of glucosamine and lipid from diatom algae has several steps, including algae cultivation, algae harvesting, chitin separation and hydrolysis, and lipid extraction. Algae can be grown in open ponds and PBRs which depend on the type of algae. Most chitin separation and lipid extraction processes require high concentration of algae cells so dewatering processes are utilized to harvest algae. Several dewatering processes can concentrate low concentration algae into slurries, including flocculation, sedimentation, dissolved air flotation (DAF), filtration, and centrifugation. Then the chitin and lipid can be separated from algae can be converted to glucosamine or biodiesel respectively.
In this scenario, the objective is to produce 500 metric ton of glucosamine per year. The algal lipid production and processing pathway is based on the model created by NREL (Davis et al., 2011). The algae grow through the input of water, CO2 and nutrients. Cyclotella has a low grow rate of 0.1 g/m2/day in PBR based on the results from experiments at Oregon State University. The algae harvesting process includes settling, DAF and centrifugation which are proposed by Benemann and Oswald (1996) and Davis et al. (2012). It is assumed that 95% of water is recycled after dewatering process. Concentrated algae are used for chitin separation and lipid extraction. The chitin content is 12% and the efficiency for chitin separation and harvest efficiency are 80% during centrifugation. Then the chitin solution will be aggressively treated by 20% acid at a high temperature (90℃) and maintained at 3 hours. It is predicted that 0.8 mol of glucosamine can be produced from 1 mol of chitin from experimental results. The remaining concentrated diatom is sent to hexane lipid extraction process. Lipid content for Cyclotella is 20%. A 5% carryover loss of oil into the water phase is assumed which results in a 95% overall extraction efficiency. Finally, the hexane solvent is recycled via a stripping column. The spent diatom and wastewater are sent to anaerobic digestion to provide heat and electricity for other equipment. 75% of the nitrogen, 50% of the phosphorus, and 75% of water from the debris medium are assumed to be recycled from anaerobic digestion to the algal cultivation system. The flue gas from the biogas turbine is also recycled to deliver CO2 for diatom growth.
This study aims to establish a baseline economic model of selling price by taking account of capital cost, manufacturing cost, deprecation, tax, present value discount, and internal rate of return. Total capital investment is the sum of equipment costs and fixed capital costs. By taking account of equipment installation, piping, control and services, fixed capital cost is estimated to be certain ratio of equipment purchase cost. Manufacturing costs consist of raw materials, manufacturing labor, power for operations, and insurance and maintenance. The internal rate of return is 10% and tax rate is 35%. Finally, the selling price of glucosamine will be estimated by the capital cost, manufacturing cost, deprecation, tax, present value discount, and internal rate of return.
3. Results and Discussion
The glucosamine cost for the open pond system is estimated to be $42/kg, while PBR system was found to be $237/kg. One main reason for high price of diatom derived glucosamine is due to low productivity of Cyctolella which is ten times smaller than about 1 g/m2/day for most studied freshwater algae (e.g. Cholorella). By economic analysis, the costs of glucosamine are highly sensitive to the algae productivity, especially for PBR system. Low diatom productivity would require large amount of open pond and PBR cultivation system for diatom growth.
The major capital costs includes the cost of open pond or PBR tubular system, settling, DAF, centrifuge, reactor, evaporator, homogenizer, stripping, anaerobic digestion reactors and etc. The PBR systems are dominated by the capital costs of tubular PBR system which contribute about 90% of costs. For open pond, diatom cultivation system contribute about 50% of total capital costs. With low productivity, diatom cultivation system is the major capital costs for the production of glucosamine and biofuel from Cyclotella. Manufacturing cost is the sum of raw material, labor, power and maintenance and operating overhead. Labor and power costs are major parts for PBR system because labor use and electricity consumption for large number of tubular PBRs. Paddle wheel systems and pump systems for water cycle consume most of power in both open pond and PBR systems.
In this study, lipid is a byproduct for diatom derived glucosamine production process. For the production of 1 kg of glucosamine, it determined that 3.7 kg of lipid are produced, and 1800 kg of freshwater, 0.16 kg of phosphorus, 0.54 kg of nitrogen, 1.4 kg of silicon nutrient, and 46 kg of CO2 are used for algae cultivation. Water recycle after harvesting process and nutrient recycle by anaerobic digestion are two processes to reduce the demand of nutrient and freshwater for the production of glucosamine and lipid from diatoms.
The glucosamine product from Cyclotella was found to be $42/kg for open pond system and $237/kg for PBR system. The economics of diatom derived glucosamine are still not be competitive with shellfish derived glucosamine. However, algae growth rate, glucosamine content and material used for tubular PBR are appear to show high sensitivity for the costs of diatom derived glucosamine. It is promising that glucosamine and biofuel from diatom become economically viable with those improvement to the technology.