Cost Analysis of Microalgae Biomass Systems

This report (Benemann et al. 1978) originated with a Request for Proposals (RFP) by ERDA for a “Cost Analysis of Algal Biomass Systems” which included both micro — and macroalgae. The contract was awarded to the Dyantech R/D Co., who subcontracted for the analysis of the microalgal work with CSO International, Inc. Although the RFP specified a minimum scale for such systems of “100 square miles,” a single large unit was not feasible, and the analysis was carried out for individual modules of 800-ha. This system was to be independent of wastewater treatment and nutrients, which were deemed too small to provide “meaningful” energy supplies.

The first step in the analysis was to list 10 major sets of assumptions on which this process could be based (Table III. D.1.). These included

• essentially effortless species control,

• a yield of about 45 mt/ha/yr (20 t/ac/y),

• 4% N and 0.4% P in the algal biomass,

• 40 ha (100 ac) growth ponds with multiple channels, and

• harvesting by bioflocculation.

Month-by-month variations in biomass density, productivity, water and CO2 utilization, etc. were estimated based on a typical southwestern United States location, with productivities ranging from a minimum of 6 to a maximum of 18 g/m2/d.

Based on these assumptions, designs of the various system components were carried out, and supporting calculations made for the subsystems, including earthworks, pumps to move and lift the water, the supply channels and piping required, transfer structures, settling ponds, ducting for CO2, etc. The algal biomass would be digested to methane gas, but this was not included in the analysis. Based on estimates for various components, total capital costs were estimated (in 1978 dollars) at about $9,000/ha, without contingencies or engineering. Annualized costs, based on a 15% per annum capital charge, plus $700/ha operating costs for labor and nutrients, assuming free CO2, were about $2,000/ha, or about $45/t biomass. As pointed out in the report, “the basis for choosing many of the design features was low cost, or, actually, the highest cost allowable.” Thus, this report was primarily useful in identifying the major design assumptions and cost centers for such a process.

This report was the first truly detailed analysis of such systems, though it still was, in many aspects, highly conceptual. It was used by Regan (1980) for a similar analysis of a large-scale algal (B. braunii) hydrocarbon production process in Australia, and served as the basis for subsequent analysis by DOE and the ASP.

I Publications:

Benemann, J. R.; Persoff, P.; Oswald, W. J. (1978) “Cost analysis of microalgae biomass systems.” Final Report prepared for the U. S. Dept. of Energy, HCP/t1-605-01 Under Contract EX-78-X-01-1 605.

Regan, D. L. (1980) “Marine biotechnology and the use of arid zones.” Search 111:377-381.

Table III. D.1. Design assumptions for a microalgae production system.

(Source: Benemann et al. 1978.)

SUMHAEX LIST OF ASSUMPTIONS

Z ALGAE CULXTVAXION: Bio flocculating type* of microalgaa can

b« cultivated. № aigoificaat: effort at species control need be undertaken. Mixed populations cultivated. Mo pest control.

IX vTPT. n? yield is assuaed to be 20 tons/acre/year (ac 10,000 ВТО/lb higher heating value) corresponding to somewhat less than 22 solar conversion efficiency In southern U. S. Losses resulting as a consequence of predation, disease or excretion of phoeosynthedc products are already subscracted.

Ш CHEMICAL COMPOSХТХ0Н: Algaa contain 42 N, and 0.42 P.

Major nutrient losses are 102 of N and 10 2 of P (and other olcrountrlents) in the algal biomass produced per year (e. g.

160 lbs/acre/year M lose and 16 lbs/acre/year P lost.)

17 атяаі. DEHSiry: Tiald is not significantly affected by operating

ponds from —302 to +202 of algal densities specified by the yield and harvesting rate assumptions.

7 WAXES. USE: Water use is assumed to be 502 higher than

calculated rates from class A pan evaporation minus pre­cipitation data, to account for increased evaporation rates in growth ponds as wall as evaporation In harvesting ponds, conveyance channels and minor percolation. Can use brackish, saline waste or sea water. Surge and equalization basins must be provided.

71 CLIMATE ДМ0 SIZE: Avoid cold and low insolation regions.

Meed cheap level land. Land coecs are not considered.

711 GS0WTH PONDS: Channel width 200 ft?, baffle height IS",

earthwork height 24" with 2:1 sloping sides, growth ponds 100 acres (1,200 x >,630 ft). Assumes self or clay sealing or ponds (no significant percolation).

Till MIXING SYSTSI: Paddlewheels, three sets per 100 acre growth

pond. 0.2 ft/sec to 0.5 ft/sec mixing velocity. Assumes no erosion.

XI САВ20КДХЮН: Meed up to 5 M fc^/day of flue gas per 100

acre growth pond. Carbonatiou in covered paddlevheel stations and of return harvesting water.

2 HARVESTING STSTEM: Use a pond isolation process which operates

on a two day detention time (plus one day for fill and draw process). Assume up to ten-fold concentration and up to three successive stages of isolation.

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