This report (Weissman and Goebel 1987) originated from a competition held by the ASP for the development of a pilot plant (“test facility”) for microalgae production. As mentioned in Section III. A.4., two companies were selected to develop competing processes: Aquasearch, Inc., of San Diego, California, and Microbial Products, Inc., which had carried out the ASP pond project in California. The objectives were to arrive at cost projections for such a test facility, and also for scale-up costs of a future full-scale facility based on the selected process. Aquasearch, Inc., developed a concept for a closed system microalgae production process, using large plastic bag tubular reactors contained in a greenhouse. This system was not selected for further development, and no final report is available. Aquasearch, Inc. recently established in Hawaii a closed photobioreactor process for cultivating Haematococcus pluvialis, an alga high in astaxanthin.

This study further developed the concept of the HRP system for large-scale microalgae production, providing considerable additional detail, and performing extensive sensitivity analysis of various design options. A site was identified near Brawley, California, in the Imperial Valley, for locating a pilot plant and a full-scale system. Ample groundwater resources were available at this site. There was also significant water supply available from the Salton Sea, which is as saline as ocean water, although of different ionic composition. As discussed in Benemann et al. (1978), the Salton Sea is a potential source of saline water and land for more than 10,000 ha of algal ponds, as such ponds could help manage the salinity of this inland sea, a major problem. The report proposed building two 0.4-ha ponds to validate the process, as well as several smaller ponds for process development and inoculum production. A covered anaerobic lagoon was to be included to test the digestion of the algae and the recycling of nutrients to the algal ponds.

The design of these experimental and pilot plant-scale ponds was provided in great detail. A larger-scale, 400-ha, pond system was also designed and costed. This report presents the most detailed, comprehensive, and realistic cost estimates currently available for large-scale, low-cost microalgae biomass and fuels production.

Several significant advances were made in this design and analysis. Perhaps most importantly, the report presented a fundamental analysis of CO2 supply and in-pond transfer issues, in combination with water chemistry and transit times between carbonation issues. The analysis concluded that CO2 utilization efficiencies can overall be very high, more than 95%, within parameters that would allow high microalgae productivity. Another innovation was the use of small amounts of high molecular weight polymers to improve the flocculation, settling characteristics and harvesting efficiency of the basic bioflocculation process. The polymers can be used in very small amounts, without contributing a major cost to the overall process.

The base case (30 g/m2/d) capital costs were estimated at almost $72,000/ha, without working capital, or almost twice as high as the prior effort (Benemann et al. 1982). This was due to higher costs for many components, such as earthworks, which were several-fold higher. Among other

things, higher costs were assumed for rough and fine (laser) grading, which depends on the type of site assumed to be available. Also the 1987study estimated about $5,000/ha to provide a 3-5 cm crushed rock layer, specified to reduce the suspension of silt from the pond bottom. There is, however, little evidence for a need for such erosion prevention, except perhaps for some areas around the paddle wheel and perhaps the turns. Further, the Weissman and Goebel (1987) study selected slipform poured concrete walls and dividers (baffles) as the design choice. For the curved portions of the walls and berms, the authors specified corrugated walls, with an average cost of about $25/m. This resulted in a cost of over $8,000/ha for the walls (perimeter central, etc.). Clearly, such design options and engineering specifications can result in very large differences in capital costs. For another example, in the present design, a power generation system was specified to produce electricity from the methane generated from the algal residues (at about 10% of total costs). This had not been included in the earlier study. Despite these higher costs, and perhaps because of them, this engineering design and cost analysis effort may be considered the most detailed and realistic one available.

Table III. D.5. summarizes two design cases (from more than a dozen presented in the report), with 30 and 60 g/m2/d average productivities. By using an annual capital charge of 25% (depreciation, return on investment, insurance, taxes), biomass costs of some $273/mt and $185/mt were estimated for the two productivity cases (Table III. D.5.). These costs were more than twice the cost derived from the “conservative” case in the earlier study (Benemann et al.1982), which used only the lower productivity. Note that this even included a significant credit for power production from the methane produced (most of which was used internally). Although this report is the most detailed and complete analysis of microalgae biomass production for fuels available, it can also be criticized for not attempting to examine cost reduction possibilities in the various design options, which would be required to make microalgae fuels production viable. Possible strategies for cost reduction were the objective of the study discussed in the following section.

I Publications:

Weissman, J. C.; Goebel, R. P. (1987) “Design and analysis of pond systems for the purpose of producing fuels.” Report, Solar Energy Research Institute, Golden, Colorado, SERI/STR-231-2840.

Table III. D.5. Capital and Operating Costs for an Open Pond System*

(Source: Weissman and Goebel, 1987.)

Table III. D.5. Capital and Operating Costs for an Open Pond System*

(Source: Weissman and Goebel, 1987.)