Potential of New Strains of Marine and Inland Saline-Adapted Microalgae for Aquaculture

JOURNAL OF THE WORLD AQUACULTURE SOCIETY

Vol. 18, No. 4 December, 1987

Potential of New Strains of Marine and Inland Saline-Adapted Microalgae for Aquaculture

W. R. BARCLAY,' K. L. TERRY,~ AND N. J. NAGLE Solar Energy Research Instilute. Golden. Colorado 8040 I USA

J. c. WEISMAN AND R. P. GOEBEL Microbial Products Inc.. Fairfield, Calqornia 94533 USA

Abstract Several problems currently limit the relibility of algal cultivation systems for the production of

aquaculture feeds. Many of these problems may be eventually solved through research in culture system design and operation. However, research into the isolation and development of new strains of microalgae may also directly lead to improved system performance.

Through a collection and screening program aimed at isolating microalgae tolerant to high light, high salinity, and high temperatures, we have been able to isolate several new strains with enhanced production potential (30-35 g/m*/d). The overall range of environmental tolerance exhibited by these strains may result in enhanced culture stability, leading to the high production rates.

The estimated costs of producing strains with these high production rates range from $1.18 to $1.71 per kg (unharvested), depending on the size of the production system. Total production costs for harvested algae (15% solids algal cell paste) range from $1.63 to $2.45 per kg. The major costs for producing harvested algae include the cost of CO,, as well as capital and operating costs for the harvesting systems.

Of the over forty different microalgal species currently cultivated as aquaculture feeds (De Pauw et al. 1984), nearly all have been isolated from marine habitats. Marine strains of Chlorella and small flagellates from genera such as Dunaliella, Tetraselmis, Monochrysis, and Zsochrysis have been cultivated as food for oyster spat (Langdon and Waldock 198 1; Rornberger and Epifanio 1981; Epifanio 198l), larval fish (Specto- rova and Doroshev 1976; Scott and Mid- dleton 1979; Spectorova et al. 1982), and larval marine shrimp (Simon 1978; Mock et al. 1980). Several marine diatoms, such a5 Chaetoceros gracilis, Thalassiosira pseudonana, Phaeodactylum tricornutum, and Skeletonema costatum, have also been demonstrated to be suitable algal diets for cultured bivalve molluscs and larval shrimp (Wilson 1978; Roels et al. 1979; Scura et al.

I Corresponding author. Current address: Ocean Genetics, 140 Dubois St..

Santa Cruz, California. 95060 USA.

1979; Mock et al. 1980; Rodhouse et al. 1983; Webb and Chu 1981).

Despite the recognized suitability of microalgae as aquaculture feeds, several problems currently limit the reliability of algal production systems for aquaculture pur- poses. These constraints include: variations in the nutritional value of microalgae due to varying culture conditions (Enright et al. 1986); lack of culture stability and species control (Pruder and Bolton 1980); and the high costs of microalgal production and harvesting (De Pauw et al. 1984). De Pauw et al. (1984) have suggested that efforts di- rected at improving the production of microalgae should focus on reducing the costs of production largely through culture system improvements. They suggested research in areas including: design of inexpensive culture systems; automation of culture systems; use of energy efficient mixing systems; use of covered production systems; and the identification of inexpensive sources of nutrients.

Q Copyright by the World Aquaculture Society 1987

218

219 NEW STRAINS OF ALGAE FOR AQUACULTURE

While research in these areas will almost certainly improve the overall economic fea- sibility of algal culture systems (Terry and Raymond 1985), research into the isolation and development of new strains of microalgae may also directly address several of the constraints outlined above which inhibit the development of reliable algal culture systems. Many of the marine strains of microalgae now utilized for aquaculture foods exhibit relatively narrow ranges of temperature and salinity tolerances, possibly as a result of their adaptation to the relatively stable, and well-buffered marine environ- ment. However, strains with wider ranges of temperature, salinity and light intensity tolerances may result in more stable cultures, and ultimately may better resist in- vasion by other species. Additionally, strains with faster growth rates, and with the ability to grow in dense cultures, may also result in higher productivities and reduced production costs.

This study presents some initial results of research into the isolation and characterization of new microalgal strains for biomass production. Some of the physiological characteristics of these new strains are summarized with respect to their potential for mass cultivation. Based on these data and the most recent developments concerning the mass culture of microalgae, an economic evaluation of the cost of producing these strains is presented.

Materials and Methods Collection and Screening

Water samples containing microalgae were collected from shallow inland saline habitats in Colorado, Utah, New Mexico, and Florida. Strains were enriched for and screened under conditions of high irradiance (400-1,000 pE/m2/s) and temperature (30-35 C). The dominant strains were isolated as unialgal cultures on agar or in liquid cultures. The growth responses of the selected strains to 30 combinations of temperature and salinity were evaluated for three

water types: 1) artificial seawater (Rila Ma- rine Mix); 2) Type I inland saline water, a class of water with a high divalent cation concentration; and 3) Type I1 inland saline water, a sodium bicarbonate class of water. Procedures for preparing the water types have been previously described by Barclay et al. (In press).

The growth experiments were conducted on a temperature gradient table which was a modified version of the design described by Siver (1 983). Irradiance from a bank of twelve 40 W fluorescent cool white lamps suspended over the table was adjusted to 200 pE/m2/s. The growth responses of the algae to 30 combinations of temperature and salinity were evaluated in each of three water types (Type I, Type 11, and artificial seawater). Cultures (25 ml) were grown in 50 ml Erlenmeyer flasks over a matrix of 5 salinities (10, 25, 40, 55 and 70 mmho/cm) by 6 temperatures (10, 15, 20, 25, 30 and 35 C), a total of 30 experimental cultures for each water type. Each treatment was enriched to 600 pM urea, 60 pM phosphate, 1.8 mM silicate, 3 pM iron, and contained 1 mVL of a vitamin stock (1 pg/L Biz, 2 pg/ ml biotin and 1 mg/L thiamine-HC1) and 5 rnl of a trace element stock containing the following dissolved in one liter: 6.0 g Na2EDTA, 0.29 g FeC13-6H20, 6.84 g H3B03, 0.86 MnCI2.4H20, 0.06 g ZnC12, 0.026 gCoCl2.6H2O, 0.052 gNiS04.6H20, 0.002 g CuS04.5H20, and 0.005 g Na2MoO4-2HZO. Prior to initiation of the experiments, stock cultures were precon- ditioned on the gradient table at 17 and 27 C in the appropriate water type at each of the 5 experimental salinities, and these cultures were used to inoculate the experimental cultures. The experimental cultures were grown in semicontinuous mode. They were inoculated at an initial absorbance at 750 nm ('4750) of 0.03 ( 1 cm path length). A750 was measured daily and the culture diluted to 0.03 with fresh medium when an A750 greater than 0.06 was reached. Exponential growth rates were calculated daily from the A750 after dilution (if necessary) and from

220 BARCLAY ET AL.

TABLE 1. Specified and calculated parameters for the portion of the spreadsheet model calculating design parameters for a 0.4 ha production pond.

Specified parameters Calculated parameters

Pond area 0.4 ha Channel width 9.7 m No. of channels 2 Paddle length 7.3 m LengtWwidth ratio 20 Centerwell length 193.7 m Depth 15 cm Single channel length ~ 208.9 m Channel velocity 20 Cdsec Total channel length 417.8 m Mannings 'n' 0.016 sec/m3 Total wall height 0.4 m

Drive efficiency 0.40 Total head loss 5.8 cm PWa IengtWChan width 0.75 Total efficiency 24% Detention time 2.50 days Hydraulic power 153 W Wall ht. (above grade) 30 cm Total power 637 W Wall ht. (below grade) 10 cm Total unit power 0.16 w/m2 Sump depth 1.5 m Channel velocityb 26.7 cm/s Pond volume 607 m3 Harvest flowrate 243 Urnin

Paddle efficiency 0.60 Slope 1.28 x 10-4

a Paddle wheel length per channel width. At paddle.

the before a dilution the following day; these values were averaged overa minimum of 5 days duration.

All microalgal strains evaluated in this study have been deposited in the Solar En- ergy Research Institute Microalgal Culture Collection, funded by the U.S. Department of Energy.

Outdoor Production For evaluation of outdoor production po-

tential, the algae were cultivated in 1.4 m2 outdoor ponds located in Vacaville, Cali- fornia (38"21'N, 121"58'W). The ponds were operated continuously (continuous dilution during daylight hours) and semi-continuously (sequential batches diluted every three to seven days). Culture mixing was provid- ed by paddlewheels and averaged 15 c d s . The ponds were kept nutrient saturated, and cell densities ranged between 20G700 mg/L depending on the species.

Estimation of Production Costs The design of both a 0.4 ha and a 4.0 ha

production system was camed out with the aid of a computer spreadsheet model. The model first calculated pond geometry, flows, power consumption, etc. based on a given

set of assumptions. Table 1 shows the specified and calculated parameters for the 0.4 ha pond model. The second part of the model, used for multiple pond systems, calculated the same quantities for a 4.0 ha system, taking into account shared walls for adjacent ponds. This information was then used to calculate the costs of production ponds in detail. The spreadsheet format al- lowed unit prices to be easily adjusted for scale or new cost data. Separate worksheets were used to calculate the mixing and harvesting system designs and costs. These were then combined in a system capital cost table, which included system-wide costs (e.g., electrical supply and distribution, buildings, etc.), as well as engineering, contingency, and land costs. The model was run for several different harvesting options, since harvesting most strongly affected the overall capital cost. A similar approach was used to calculate operating costs, which included nutrients, power, maintenance, and labor. The capital costs were amortized at the rate of 20% per year, The cost per kg of dry algae was calculated for several different productivity levels. All costs were expressed as 1985 U.S. dollars.

The costs used in the model were based

22 1 NEW STRAINS OF ALGAE FOR AQUACULTURE

TABLE 2. Summarized growth performance parameters of several strains isokued by the collection and screening protocol.

Species (strain)

Temperatureb SalinityC Avg. Growth outdoor

rate Min Max Opt Min Max Oet - . Amphora coseiformis Ag. (AMPHOI) 5.1 20 >35 30 < l o >70 -C 30

Boekelovia hooglandii Nic. & B. Becking Amphora sp. (AMPHO2) 2.5 16 >35 32 <I0 >70 -' 35

Chaeroceros muelleri Lemm. (CHAET14) 4.0 13 >35 2-35 <10 >70 -c 35 (BOEKEI) 3.4 <I0 33 23 < I 0 >70 25 ndf

Chaetoceros muelleri Lemm. (CHAET6) 3.4 < 10 >35 30 <10 >70 25 35 Monoraphidium minwum Nag. (MONORI) 3. I 12 33 29 <I0 55 25 25 Monoraphidium minutum Nag. (MONOR2) 2.8 1 1 33 28 < I 0 55 25 30 Navicula saprophila Lange-Bert. & Bon.

(NAVICi) 4.0 13 >35 30 < l o >70 -e nd

a Maximum observed growth rate, in doublingdday. Temperatures in degrees Celsius. Minima and maxima reflect levels above or below which growth rates fell

below 1 doubling/d. Some optima are the midpoints of reported optimum ranges. Salinity in mmho/cm. Minima, maxima, and optima are as for temperature. Outdoor productivity expressed as g/m2/d. Growth rate was independent of salinity over the range examined. nd = not determined.

on information gathered from published sources (current building cost manuals), contractors, consultants and actual vendor quotes. For high cost items, such as centrifuges, costs were obtained for the actual units specified in the design. Carbon dioxide, the major nutrient, was assumed to cost $100 per metric ton. Electricity was priced at $0.10 per kWh. A different approach was taken for the 0.4 and 4.0 ha systems as far as utilities were concerned. For the 0.4 ha system, it was assumed that utilities would be available on site, whereas for the 4.0 ha system, they would need to be developed. The authors envision the 0.4 ha system as attached to an existing venture, whereas the 4.0 ha system would be a stand-alone production facility.

Results and Discussion Strain Characteristics

The growth performance characteristics of several strains isolated by the collection and screening protocol are summarized in Table 2. Five of the eight strains exhibited high productivities (25-35 g/m2/d) under outdoor conditions. The most outstanding physiological characteristic of these strains

was their wide range of temperature and salinity tolerance. Most of the strains grew at the rate of at least one doubling per day over a temperature range of 15-33 C, and a salinity range from Y3 to 2 times the concentration of seawater. The maximum growth rates of several strains were also close to the highest growth rates (4.5-6.0 dou- blingsld) reported for marine species of microalgae such as Chaetoceros sp. and Nan- nochloris sp. (Thomas 1966).

d I 1 I I 0 10 20 30 40

Temperature

FIGURE 1 . Contours of exponential growth rate (dou- blings/d) of Chaetoceros muelleri (CHAETI4) in semicontinuous culture in at-tificial sea water. Each point represents the mean of at least five separate dailv growth rate determinations.

222 BARCLAY ET AL.

80-

= M- $ g 40- E - 2 30-

; 20-

.- C .- -

10

0.F (0.3 ( 1 . t 1.?4\ 2;24 2.?4

1.0 1.5 2 0

70-b

-

01 I I I 1 0 10 20 30 40

Tempanlure

Contours of exponential growth rate (dou- blings/dl of Amphora sp. (AibfPHO2) in semicontin- uotts ctrlttrrc in Type I inland saline water. Each point represenrs the mean of at least Jive separate daily growth rate determinations.

FIGURE 2 .

Growth responses of some of the strains are illustrated further in Figs. 1-3. The growth of Chaeroceros muelleri (CHAET 14) and Amphora sp. (AMPHOZ) was independent of salinity over a range of salinity from 10-70 mmho/cm, Y3 to 2 times that of seawater (Figs. 1-2). Additionally, many of the strains were very tolerant of large changes in the elemental composition of the culture media. For example, Monoraphidium minutum (MONOR2) exhibited very similar growth profiles in both seawater and Type 11 inland saline medium (Figs. 3a, b). These saline water types have very different major ion compositions, as illustrated in Table 3.

The wide salinity tolerance of the isolated strains was probably an outcome of the collection protocol rather than the screening process. By focusing on shallow, temporal saline habitats, the collection protocol was predisposed to selecting strains with a wide range of salinity tolerance. From this group of strains, the screening process selected for the most rapidly growing strains and for strains with elevated temperature tolerance. The salinity tolerance of the strains isolated to date is much wider than that reported for most marine forms. A few marine diatoms are known to tolerate broad-ranging salinities (540%) including Chaetoceros afinis (Bonin 1969), Chaetoceros radians. Cera-

0.17 O.?l 0.?8 041 0..38 0.38 * 0.5

1.18 1.42 1.63 1.74 1.98 1.25

01 I 0 10 20 30 40

Tmpwature (‘C)

d I I I I 0 10 20 30 40

Contours of e.rponential growth rate (dou- biingdd) of Monoraphidium sp. (S/iMONORZJ in semicontinuous culture in a) atlificiol seawater; and b) Type I I inland saline water. Each point represents the mean of at least Jive separate daily growth rate determinations.

Temperature

FIGURE 3.

taulina pelagica, Leptocylindrus danicus, and Thalassiosira decipiens (Takano 1963). The chrysophyte Olisthodiscus luteus also tolerates salinities from 2-509i0 (Tomas 1978). The processes which microalgae em- ploy to adapt to osmotic stress vary widely and have been reviewed by Bonin et al. (1 98 1). A unique feature of the strains isolated by protocol in this study is that they exhibit broad-ranging tolerance in three very different types of saline water (based on ion- ic composition). Thus, they appear to exhibit a much wider range of environmental tolerance than has been demonstrated in microalgae to date.

The collection and screening protocol developed to isolate these strains was designed to isolate strains tolerant of high temperatures and high irradiance for use in inland

NEW STRAINS OF ALGAE FOR AQUACULTURE 223

TABLE 3. Comparison of the major ion concentrations (mM) of the three saline water types 01 25 mmho/cm conductivity.

~~ ~

Ion

Water type Na' K' Ca2+ Mg2 + a- S042- HCO3- WIT

I 109 5 35 58 20 258 2 0.6 I1 256 13 0.25 14 41 101 27 9.4 ASWb 250 5 7 28 15 296 2 3.6

a Monovalent : divalent cation ratio. Artificial seawater.

biomass production applications. By de- veloping a protocol for selecting strains that exhibit increased tolerance to a combina- tion of high light, salinity and temperature, we have been able to isolate strains with enhanced outdoor production capabilities. Simple modifications of this protocol would allow its use for isolating cool water-adapted strains, further extending the temperature range over which microalgal cultures could exhibit stable production rates. Re- search in modifying the protocol for this purpose is currently underway.

Ofthe algal species evaluated in this study, the best overall strains for potential aquaculture applications appear to be the strains of Chaetoceros muelleri (CHAET6 and CHAET 14) and Monoraphidium minutum (MONORI and MONOR2). Both of these strains grew well outdoors and easily re- mained suspended as unicells in culture. With regard to the other strains, Boekelovia hooglandii grew well in the laboratory but would not grow at all outdoors. Addition- ally, cells of the strains of Amphora and Navicula tended to be sticky. This led to clumping, with the cells readily falling out of suspension, reducing overall productivity. Clumping also presents problems if there is a need to present a u n i f m size cell suspension to a filter feeding organism.

Production Costs Without Harvesting Algal cultivation systems without cell

harvesting capabilities are envisioned for the on-site use of microalgae for feeding warm- water shellfish to market size. Since there is no requirement for harvesting moderately

dense (e.g., 500 ppm) microalgal suspensions, algal pond effluents are diluted into shellfish systems as needed. Algal productivity is controlled by standing density, i.e., dilution rate or interval. Such a system, of 0.4 ha size, is capable of producing from 22 mt/yr ( I 5 g/m'/d) using previously available marine microalgal strains, to a projected 37 mt/yr (25 g/m2/d), utilizing strains such as those described in this paper. Table 4 lists the cost figures for both 0.4 and 4.0 ha microalgal production facilities without cell harvesting capabilities. Economies of scale were minimal in both cases, since large scale capital items for harvesting contribute the most towards scale-related cost reductions. Labor, the other major scalable item, did cost less for the larger system on a product output basis. Also, as the 4.0 ha facility was stand-alone whereas the 0.4 ha pond was assumed to be an addition to an existing facility, significant cost savings were incor- porated into the latter.

At the 4.0 ha scale, the cost of production (breakeven price) ranged from $1.204 1.70 per kg dry algae, depending on the productivity assumed. As shown in Table 4, the major operating cost centers, in terms of operating costs, are carbon dioxide (20-259'0 of the production cost), silica (lo%), and labor (&lo%). Carbon cost can be quite variable depending on location and amount purchased, but a cost of $100-$200 per metric ton is usual. Cost of silica vanes with the nutritive requirement of each algal species. Labor was already assumed to be minimal in the estimate due to the lack of heavy machinery required for harvesting the

224 BARCLAY ET AL.

TABLE 4. A comparison of the cost of live unharvesled algaekom 0.4 and 4.0 ha production systems. Assumes average productivity of currently available marine strains = I5 g d / d and that of improved strains = 25 g/m-'/d.

Scale (ha) Production parameters 0.4 4.0

Total installed cost. 0 1,000 126 1,010 Productivity, muyr 22 37 220 370 Operating cost, S/kg 1.42 1.04 0.75 0.64 Total production cost (TPC), $/kg 2.54 1.71 1.67 1.18 Annualized capital cost, % of TPC

Total 44 39 55 46 Linear 10 9 14 12 Land 9 8 6 5 A&E, contingency 7 6 10 8

Total 56 61 45 54 co2 12 18 18 25 Si 5 7 7 10 Labor 31 27 10 8

Operating cost. % of TPC

algal biomass. The total annualized capital cost (depreciable and non-depreciable) was the overall major cost factor, contributing about 50% of the total production cost. The cost centers for capital costs were the high grade membrane pond liner (10940), A&€ (architectural and engineering) and contingency ( 1 O%), and land (6%). Alternative open pond designs and less expensive land costs ($4,000-$8,000/ha) would only reduce overall costs about 10-15940. Only a large increase in scale (which is not practical for aquaculture applications) would significantly lower the impact of high construction costs in particular, and overall costs in general. At the 0.4 ha scale, the cost of labor becomes more significant. Otherwise, the critical cost centers remain the same.

In order to produce algal biomass at a cost approaching $1 .OO per kg dry mass utilizing a non-harvest strategy, the scale of the system must be on the order of 4.0 ha and the productivity must be near 350 mtlyr. This size system, with such an output, could sup- port the production of 4-5 million bivalves per year, assuming a 109'0 dry weight to dry weight conversion efficiency. In order to significantly reduce feed costs further (to $0.6& $0.70 per kg), the system size would need to be increased five-fold. This cost estima-

tion includes an annualization of the capital and operating costs. How this annualization was done, including the assumed cost of capital, had significant impact on the final production cost. A simplified method was used here: 209'0 of the installed system cost was added to the annual operating costs to amve at the final cost. This was approxi- mately equivalent to a 10% per annum cost of capital. The actual annual operating cost, excluding interest charges and return on investment, was $0.65 per kg at the 4.0 ha scale.

Production Costs with Cell Harvesting

If it is assumed that use of frozen algal biomass is feasible, an algal production facility remote from shellfish production systems becomes feasible. Due to the consid- erable added expense of cell harvesting, secondary concentration, freezing, and transport, the scale of the algal production system must be increased to a minimum of 4.0 hectares. The large production capacity of such a system would require that the major use of the algal product be for the growth of shellfish beyond the seed stage. In this study, several algal harvesting processes were analyzed, resulting in different cost projec-

225 NEW STRAINS OF ALGAE FOR AQUACULTURE

tions. Centrifugation, employing automat- ed, solids ejecting or continuous solid-bowl decanter centrifuges, is feasible for concentrating from 0.05% to 15.0% solids. Despite the high cost of multi-shift labor, efficient utilization of this capital intensive machinery dictates a continuous (24 h) harvesting operation. Tangential, or cross-flow filtration (CFF) is an alternative to centrifugation. In most cases, the 10- to 20-fold con- centrated output from the filtration system would still require secondary concentration by further filtration or centrifugation. Both centrifugation and filtration produce cell suspensions which are free of additives. A third alternative is to use organic polymers to coagulate the algal biomass, followed by sedimentation to collect the flocculated algae. Research at Microbial Products, Inc. (unpublished data) has demonstrated that costs of food grade chemical coagulants are less than $0.05 per kg of dry algal biomass harvested. Although the tenacity of the flocculated algae is controllable within wide limits, reliable redispersion into single cells may not be feasible, thereby limiting their use as an aquaculture feed for filter feeding organisms.

All cell harvesting techniques add significant capital investment and operating costs to an algal production system. This im- mediately renders a small scale system less economical. The two mechanical harvesting processes considered in the model, centrifugation and CFF, both have inherent un- certainties. Although centrifugation is a well-known process, the sedimentation properties of different algal cells vanes con- siderably. In the current analysis, all algal cells were assumed to centrifuge like bakers’ yeast, but at 67% of the throughput. The other harvesting technique, CFF, is a relatively new approach to recover cells from fermentations on an industrial scale, and little published data exists for its use in concentrating algal cells. The throughput rates decrease when any significant amount of ex- opolymer or cell debris is present. Rates are highly dependent on the viscous properties

of the concentrating cells. Thus, the flux rates attainable with algae may be expected to depend on cell type, culture conditions, and harvesting conditions. Two sets of conditions were assumed for the use of CFF. To be conservative, it was assumed that primary concentration of the algal suspensions (0.05% to 0.5%) could be achieved by CFF at a flux rate of 2.5 L/min/mz of membrane. A centrifuge was specified to further con- centrate the slurry by a factor of 30. In a more liberal analysis, CFF was used for both primary concentration (at a flux rate of 25 L/min/m’) and secondary concentration (at 2.5 Umidm’). In short, centrifugation costs could be estimated at the study level ac- curacy of 30%, but CFF estimates are probably not very reliable, due to the lack of available data.

Centrifuging algd pond effluents is expensive due to the low standing biomass concentrations. Economies of scale for industrial centrifuges render them very costly (per ha) for small scale systems. In addition, the power consumption is large and maintenance cost high. This was reflected at the 0.4 ha scale in an operating cost increase of about 1 OOYo for centrifuged algal biomass versus unharvested biomass. Capital costs for a 0.4 ha system increase more than threefold, with annualized installed system costs becoming more than 55% of the production cost. Thus, the total cost of product is very high ($4-$7 per kg). At the 0.4 ha scale, the conservative assumptions concerning cross-flow filtration lead to product costs similar to those of centrifugation. When a pure CFF operation is assumed, product costs are still high, ranging from $2.50-$4.00 per kg depending on the algal productivity. CFF constitutes 35% of the installed cost of a 0.4 ha system, and 18% of the total production cost. These production costs, however, compare favorably with published production costs of algae for aquaculture foods, which range from $4- $200 per kg depending on the type of algae and cultivation system employed (De Pauw et al. 1984).

226 BARCLAY ET AL.

TALK€ 5. Estimatedcost ofharvestedalgd biomass ( m e w marine aquaculture foodstrains vs. improvedstrains) from a 4 ha scale production system. Assumes final product is an algal cell paste containing 15% solids.

costs Centrihgation' CFFb PolymerC

Total installed system cost (S 1 ,OOO) 2,250 1,400 1,600

Operating cost (Wkg) 220 mVyr 370 mVyr

Total production cost (S/kg) 220 mVyr 370 mVyr

1.73 1.16 0.80 1.23 0.89 0.75

3.80 2.40 2.37 2.45 1.65 1.63

Major cost centers (96 of TPCd 370 mUyr) co2 12 Harvesting system 22 Harvesting operating cost I 1 Labor 14

18 10 12 7

18 16 2 6

a Harvest 24 hr/d. Harvest 8 hr/d flux rate = 25 Ym2/min. Harvest 8 hr/d. Total production cost.

Table 5 presents a cost comparison using centrifugation, CFF, or polymer coagula- tion for harvesting algae from a 4.0 ha production system. At this larger scale, algal biomass harvested by centrifugation costs $2.50-$4.00 per kg to produce. This is still quite high, especially considering that freezing, storage, and transport charges have not been included in the estimate. In general, use of capital intensive centrifuges for harvesting is very expensive, adding $1-$2 per kg of product at a 4.0 ha scale and twice that at a 0.4 ha scale. CFF harvested algae can be produced for $1.65-$2.40 per kg given the high flux rate assumptions. At lower flux rates, and using centrifugation for secondary concentration, the production cost is $2.10-$3.10 per kg, or 30% higher. As the system increases further in scale, secondary concentration by centrifugation becomes more competitive with CFF. Poly- mer flocculation, followed by sedimentation and secondary concentration of the flocculated algae by centrifugation, is the least expensive harvesting method.

In all cases, installed system costs are high even for 4.0 ha systems. Due to the high capital investment, centrifuges must be operated at as close to a 100% duty cycle as

possible. This requires multi-shift labor which markedly increases operating costs. Whenever centrifuges are not specified, multi-shift labor was avoided in the estimation process. It can be appreciated that even for secondary concentration, substi- tution of CFF for centrifugation (if it is feasible technically) leads to substantial cost reductions in small scale systems. CFF adds significantly to the production cost, but the modular nature of the installation renders it more cost-effective than centrifugation. Total production costs of CFF harvested algal biomass can only be projected to be below $2 per kg if algal productivity is high (averaging 25 g/m2/d or better) and if flux rates are also high. Polymer harvesting of algae is less expensive than CFF at the small scale (and even more so as scale increases), but it does not produce a product suitable for filter feeders.

In summary, it is now possible to produce many new unialgal strains of marine and inland saline-adapted microalgae at high rates. The best strategy for producing inexpensive algd biomass for aquaculture feed is one that does not involve harvesting. This approach would require an aquaculture operation in a semi-tropical or tropical region

NEW STRAINS OF ALGAE FOR AQUACULTURE 227

in order to attain high productivities year round and to maintain stable algal popu- lations. The projected cost of this unharvested biomass was estimated to be $1 per kg. Assuming a 10% food chain conversion efficiency of live phytoplankton to shellfish meat (dry wt. to dry wt.), 6-1 2 month grow- out to market size, a density of 500 bivalves per square meter, and an algal productivity of 15-25 g/m2/day, a 4.0 ha phytoplankton production facility could feed 4 million bivalves per year.

Acknowledgments

This work was supported by the Biomass Energy and Waste Technology Division of the U.S. Department of Energy under WPA 5 13.

Literature Cited

Barclay, W., N. Nagle, K. Terry, S. Ellingston and M. Sommerfeld. (In press). Characterization of saline groundwater resource quality for aquatic biomass production: a statistically-based approach. (Journal of Water Research).

Bonin, D. J. 1969. Influence de diffkrents facteurs kcologiques sur la croissance de la diatom& Chae- toreros a&is Lauder en culture. Tethys 1:173- 238.

Bonin, D. J, S. Y. hlaestrini and J. W. Leftley. 198 1 . Some processes and physical factors that affect the ability of individual species of algae to compete for nutrient partition. Pages 292-30 in T. Platt, editor. Physiological bases of phytoplankton ecology. Canadian Bulletin of Fisheries and Aquatic Science, volume 210.

De Pauw, N, J. Morals and G. Persoone. 1984. Mass culture of microalgae in aquaculture: progress and constraints. Hydrobiologia I 16/ I 17338-342.

Enright. C. T, G. F. Newkirk, J. S. Cragie and J. D. Castell. 1986. Growth of juvenile Ostrea edulis fed Chaeroceros gracilis of varied chemical composition. Journal of Experimental Marine Biology and Ecology 96( 1): 15-26.

Epifanio, C. E. 198 I . Phytoplankton and yeast as food for juvenile bivalves: a review of research at the University of Delaware. Pages 292-304 in G. D. Pruder, C. Landgon, and D. Conklin, editors. Proceedings of the second international conference on aquaculture nutrition: biochemical and physiological approaches to shellfish nutrition. Louisiana State University, Baton Rouge, Loui- siana, USA.

Langdon, C. J. and M. J. Waldock. I98 1. The effect of algal and artificial diets on the growth and fatty acid composition of Crassostrea gigas spat. Jour- nal of the Marine Biological Association of the United Kingdom 6 1 :43 1-448.

Mock, C. R, C. T. Fontaine and D. B. Revera. 1980. Improvements in rearing larval penaeid shrimp by the Galveston Laboratory method. Pages 33 1- 342 in G. Persoone, P. Sorgeloos, 0. Roels, and E. Jaspers, editors. The brine shrimp Artemia. volume 3. Ecology, culturing, and use in aquaculture. Universa Press, Wetteren, Belgium.

Pruder. C. D. and E. T. Bolton. 1980. Differences between cell division and carbon dioxide fixation rates associated with light intensity and oxygen concentration: implications in the culture of an estuarine diatom, Thalassiosira pseudonana. Ma- rine Biology 59( 1):1-6.

Rodhouse. C. R. and M. E. SomrnervilleJacklin. 1983. Nutritional value of microalgal mass cultures to the oyster Ostrea edulis L. Aquaculture 32: I 1-18.

Roels, 0. A, J. B. Sunderlin and S. Laurence. 1979. Bivalve molluscan culture in an artificial upwell- ing system. Proceedings of the World Mariculture Society 10:122-138.

Romberger. H. P. and C. E. Epifanio. 198 I . Com- parative effects of diets consisting of one or two algal species upon assimilation efficiencies and growth of juvenile oysters, Crassostrea vrrginica (Gmelin). Aquaculture 25:77-87.

Scott. A. P. and C. Middleton. 1979. Unicellular algae for turbot (Scophthalmus marimus L.) larvae-the importance of dietary long-chain poly- unsaturated fatty acids. Aquaculture 18:227-240.

Scura. E. D., A. M. Kulgiq R. H. York and R. S. LeCoff. 1979. The commercial production of oysters in an intensive raceway system. Proceed- ings ofthe World Mariculture Society 10:624430.

Simon, C. M. 1978. The culture of the diatom Chae- toceros gracilis and its use as a food for penaeid protozoeal larvae. Aquaculture 14: 105- I 13.

Siver, P. 1983. A new thermal gradient device for culturing algae. British Journal of Phycology 18:

Spectorova, L. V. and S. 1. Doroshev. 1976. Experi- ments on the artificial rearing of the Black Sea turbot (Scophthalmus maeoticus maeoticus). Aquaculture 9:275-286.

Spectorova, L. V, 0. I. Goronkova, L. P. Nosova and 0. N. Albitskaya. 1982. High density culture of marine microalgae-promising items for mariculture. I. Mineral feeding regime and installations for culturing Dunaliella tertiolecta Butch. Aqua- culture 26:289-302.

Takano, H. 1963. Diatom culture in artificial seawater. I. Experiments on five pelagic species. Bul- letin of the Tokai Regional Fisheries Research Laboratory 37:17-25.

Terry, K. L. and L. P. Raymond. 1985. System design

159-163.

228 BARCLAY

for the autotrophic production of microalgae. En- zyme and Microbial Technology 7:474-487.

Thomas, W. H. 1966. Effects of temperature and il- luminance on cell division rates of three species of tropical oceanic phytoplankton. Journal of Phy-

Tomns, C. R. 1978. Olisthodiscus luteus (Chryso- phyceae). I. Effects of salinity and temperature on growth, motility and survival. Journal of Phycol- ogy 14:309-313.

Webb, K. L. and Chu, F. E. 1981. Phytoplankton as

C O I O ~ Y 2: 17-22.

ET AL.

a food source for bivalve larvae. Pages 272-290 . in G. D. Pruder, C. Landgon, and D. Conklin,

editors. Proceedings of the second international conference on aquaculture nutrition: biochemical and physiological approaches to shellfish nutrition. Louisiana State University, Baton Rouge, Louisiana, USA.

Wilson, J. H. 1978. The food value of Phueoductv- Ium tricornutum Bohlin to the larvae of Ostreu edulis L. and Crassostreu gigas Thunberg. Aqua- culture 13:3 13-323.

Documents

Potential of New Strains of Marine and Inland Saline-Adapted Microalgae for Aquaculture