potential of mass algae production in kuwait

Potential of Mass Algae Production in Kuwait*

Ales Prokopt and Mansoor Fekri Biotechnology Department, Kuwait Institute for Scientific Research (KISR), P.O. Box 24885 Safat, Kuwait

Accepted for Publication March 7, 1984

The rationale for efficient light absorption by algae at a production unit is given and design details of an intensive thin-layer technology outdoor (2.1 1 m2) unit are presented. Data on productivity under extreme conditions were collected. Maximum productivity data are close to those reported in the literature for similar geographic areas.

INTRODUCTION

Once the radiant flux enters an algae system (suspension in a reactor), it is exponentially attenuated as described by Lambert-Beer’s law, which includes variables such as incident irradiance, culture depth, and culture density. The light absorption for most of algae is typically very high and can be easily manipulated by both culture depth and density. A satisfactory complete absorption of the incident radiation can be obtained with various combinations of the absorbing layer depth and algae concentration. It has been demonstrated that the maximum photosynthetic efficiency is achieved at low radiant flux densities and if the density of transmitted flux at the depth of algae unit corresponds to the compensation flux density (usually a very low value of irradiance which is required to maintain basic metabolism of cells). Nevertheless, relatively elevated values of photosynthetic efficiency can be maintained even if the radiant flux density is high (as levels of global radiation in nature). This is possible on the condition that the rate of radiant absorption by the photosynthetic element does not surpass the maximum rate of dark reactions possible at the given temperature. To reduce the limiting effects of dark reactions, a radiant flux of high density strikes the photosyn thetic element for very short intervals, with dark periods of appropriate length between, using intermittent radiation. In a dense culture of algae, the specific time constants of the light and dark intervals can be controlled by the depth of the culture, its density and intensity of agitation. A dis- persion of light flux in time is thus achieved avoiding satu- ration losses.

*This is publication number KISR 1 1 13, Kuwait Institute for Scien-

tPresent address: Biotechnology Research Center, Lehigh University, tific Research, Kuwait.

Bethlehem, Pennsylvania 18015.

Biotechnology and Bioengineering, Vol. XXVI, Pp. 1282-1287 (1984) 0 1984John Wiley&Sons,Inc.

Several circumstances, however, do not allow a straight- forward exploitation of the above effects. As may be seen from experimental observations of some authors, 1-4 intermittent light in relatively short flashes (10-70 ms), sepa- rated by dark period about 100 times as long (0.1-10 s ) , would optimally match the time constants of the photosynthetic reactions involved. Other data5 suggest that relatively longer periods of intensive intermittent light with equal length of light and dark periods (0.2-1 s ) can achieve up to 60% of the value of relatively low continuous irradiation. Marra6 has reported on increases up to 87% by mod- ulating the light on a time scale ranging from minutes to hours. Another difficulty in using intermittent irradiation to increase the efficiency of algal culture is the random nature of turbulent flow. This makes it impossible to subject all the cells in the suspension to the same time pattern of movement in and out of the irradiated layer at the optimal frequency. Some gain in efficiency can be obtained with turbulent mixing even if this is apparently less than with a nonrandom mixing pattern. It has been demonstrated’ that a vortex pattern superimposed on turbulency could be one way to achieve nonrandom mixing using thin-layer (shallow) and dense culture. Besides that, in a reactor composed of two regions, illuminated and nonilluminated (that of the auxiliary reactor space), the exposure pattern (dark/light exposure volumes) and turbulence are controlled by the liquid recirculation rate (linear velocity) between the main reactor and auxiliary space. The viability of this concept under Kuwaiti climatic conditions has been tested and some results are reported in this article. An- other nonrandom mixing was recently described by Laws et aL3 using foils similar in design to airplane wings, immersed in dense, shallow-depth algae culture. The system features low energy consumption.

MATERIALS AND METHODS

Algae Culture

Chlorella sorokiniana ATCC 22521, a high-temperature train,^.^ was used throughout. This strain was selected because of its relative thermo and salt tolerance. Algae were

CCC 0006-3592/84/111282-06$04.00

maintained on agar slopes with a mineral medium (below) and 2% agar. Modified Knop’s medium with a chelating agent (EDTAP was used in laboratory cultures. For outdoor cultivations, the medium consisted of (g/L): MgS04 *

FeS04-7H20, 0.015; CaCI2-6H2O, 0.011; MnSO4-4H20,

ZnS04.7H20, 0.0014; and (NH)2M07024.4H20, 0.0018. The pH of the media was kept at ca. 6.5 by periodic ad- justments by NaOH.

7H@, 0.99; KN03, 2.02; KH2P04, 0.34; EDTA, 0.016;

0.0012; CoS04.7H20, 0.0014; CuS04.5H20, 0.0012;

Outdoor Cultivation

The outdoor cultivation unit was designed and con- structed as a hydraulically closed system (recirculation) consisting of a growth inclined surface with regularly spaced baffles inserted across the stream of algae suspension of about 5 cm in height providing a turbulence pattern and of an auxiliary The suspension of algae, recirculated by a low head axial pump, flows down on a moderately inclined surface and overcomes a resistance presented by narrow barriers (baffles), which in turn gen- erated the desired level of turbulence. During the night, suspension was kept in the auxiliary tank being aerated. The growth surface was made of acrylic polymer. The overall scheme is shown in Figure 1 with standard drawing symbols for each piece of equipment: inclined surface with baffles (slope of the surface, 0.03; height of the baffles, 35 mm; inclination of the baffles, 30”; width of the slot under the baffles, 5 mm; distance between baffles in the direc- tion of flow, 150 mm; liquid discharge rate, 250-340 L/min/m in length across the flow); collecting tank with aeration via solenoid valve (during the night) and level control device (solenoid valve for water supply, level sen- sor); distributing channel with discharge slot and bypass for complete draining; suction piping with C02 introduction via solenoid valve; and axial pump. Technical design details can be found in refs. 7 and 11. The inclined surface was fixed on a supporting frame. An electronic control

n

d... Figure 1. Layout of outdoor cultivation unit.

with a timer provided for COz introduction, pump func- tioning, and water supply during daytime (light) and air supply during the nighttime ( C 0 2 and pump off).

The working volume of the outdoor unit was 160 L; ca. 100 L was on the growth surface, the rest in the collecting and distributing tanks and in pipings. Thus, the “light” fraction of algae suspension was 0.62 and the “dark” fraction was 0.38, according to volumes exposed to light and dark. The C02 supply rate was 0.3-0.4 L/min. The active exposure area of the growth surface was 2.11 m2 (includ- ing a portion of the distributing channel). A continuous record of air temperature, algae suspension on the growth unit, and suspension in the collecting tank were provided. A timer activated a pump and the C02 and air (at night) supply at sunrise and sunset. (The aim of the aeration in the collecting tank during the night was to reduce respiration of cells.) An automatic control of water supply and daily monitoring of evaporated water was also established.

Cultivation Method and Productivity

The mode of outdoor cultivation was semicontinuous with a daily harvest (in the morning) of 10-50 L and re- placement by a growth medium. The growth in both laboratory (inoculum) and outdoor units was followed via optical density and dry weight of cells. Optical density was measured by a Spectronic 20 (Bauch & Lomb) at 560 nm wavelength following culture dilution to optical densities 0.1-0.5. The growth was also measured directly by dry weight of algal suspension. Aliquots were taken, centrifuged, washed and dried at 105°C to a constant weight.

A major parameter of interest in relation to environmental conditions is algal productivity. Using the volu- metric productivity, P,, (in g/L/day, this parameter can easily be calculated from daily increments in dry weight), areal productivity equals:

PA = P,( V / A ) (in g/m2/day),

where V is the culture volume and A is the exposed area. The productivity is of net value as it involves a mainte- nance term (endogeneous metabolism, dark respiration, photorespiration, cell death, etc.). The productivity is density-dependent, and the maximum is located in the range 0.5-2 g/L biomass dry weight, depending on the type of cultivation unit and on irradiation conditions. l2

As an inoculum for the outdoor unit, several laboratory 500 mL glass units in a semicontinuous arrangement with a continuous artificial light were used to collect cells over two weeks. Cells were centrifuged and stored in a refriger- ator before use.

Product Analysis

Algae produced in an outdoor unit were collected, centrifuged, and either vacuum- or freeze-dried for further analysis. The content of C, H, and N was analyzed using a CHN rapid analyzer (HERAEUF), while the content of metals were examined by atomic absorption spectrometry

PROKOP AND FEKRI: KUWAIT MASS ALGAE PRODUCTION 1283

(OPTRON FMD4) and the phosphorus content was checked by colorimetry (based on formation of a diazo- nium salt). The supernatant (unspent medium) was analyzed in terms of metals and nitrate by colorimetry (phos- phoammonium molybdate).

Dust Analysis

The elemental content of dust was analyzed by conven- tional methods (atomic absorption). The leaching of elements into water was estimated after the dust was exposed to water and by analysis of the supernatant.

Physical Analysis

During outdoor experiments, the air temperature (in shade) and algae suspension temperatures on the growth surface and in the reservoir were measured every hour and provided information on the mean air temperature, the absolute minimum and maximum air temperatures, the absolute minimum and maximum algae temperatures, and the mean algae temperature during the daylight. The data on relative air humidity, wind velocity, precipitation, and solar radiation were provided by the Energy Depart- ment of KISR; global and diffuse radiation was measured by an Eppley Radiometer (pyranometer) in the range 280- 2800 nm. The water evaporation from the algae outdoor unit was a daily reading of the water reservoir level as the volume of algae suspension was kept constant automati- cally.

RESULTS AND DISCUSSION

Table I presents averages of outdoor cultivation data during different periods. Data are grouped either on the

Table I. Summary of growth data of Chiorella sorokiniana in outdoor unit.

monthly basis or for shorter periods with an emphasis on the stability of climatic and culture conditions. During summer, when the shade air temperature approached 48"C, the algae suspension temperature was not higher than 41OC (the maximum tolerated temperature for this alga is 42-43OC). This difference between air and algae temperature is due to water evaporation, which kept the water temperature down. The maximum evaporation took place usually between 1-3 p.m. January/February had the lowest temperatures (lowest sunlight global radiation); even under those conditions, some productivity was noted because of reasonable algae suspension temperatures. The temperature is obviously a limiting factor in winter.

Water evaporation from the cultivation unit was corre- lated with mean air temperature (Fig. 2) and with a product of global radiation and mean air temperature, following the Jensen formula13 (not shown). It is of interest that the former plot yielded a better fit than the highly recom- mended Jensen's equation, which incorporates more climatic factors. Thus, evaporation can be predicted using one of the plots. Some typical data relating evaporation to climatic conditions are in ref 14. A summary of meteorological data relevant to both algae production and evaporation is presented in Table 11. Some of the values are reported only from sunrise to sunset, others for the entire day. Water evaporation from the algae unit imposes a certain limitation on algae production in arid areas, since water is a precious commodity there, This problem can be allevi- ated by using an alga fully or partially resistant to seawater or brackish water. Marine algae, although salt-resistant, are usually not thermotolerant. Chiorella sorokiniana can tolerate (without growth reduction) up to 15 g/L NaCl in the presence of calcium ions according to Chimiklis and Karlander.

~

Temperature Average Average Average

Period Mean Areal global density dilution (days) Air rnax Algae max Algae min algae productivity radiation Evaporation (range) rate

(day/month/year) ("C) ("C) ("(3 ("C) (g/m2/day) (Wh/m2) (L/day) ( g m Up' )

14/4/82-26/4/82 35.4 34.9 20.9 28.1 (29. 6)a 585 1 27.6 (0.3-0.9) 0.0094 (11)

(23)

(43)

(43)

(28)

(31)

(19)

(22)

1/5/82-23/5/82 37.8 35.4 24.9 30.3 11.80 6065 31.1 0.78(0.4-1.0) 0.0089

24/5/82-5/7/82 41.6 37.5 25.2 32.3 25.70 6664 41.6 1.21 (0.9-1.5) 0.0124

20/ 12/82-31 / 1 /83 16.9 21.8 9.3 16.6 8.05 3345 11.9 1.63 (1.3-1.8) 0.0024

1/2/83-28/2/83 20.6 25.2 10.0 19.1 8.05 43 78 15.8 1.62 (1.5-1.85) 0.0027

1/3/83-31/3/83 24.8 29.2 12.8 28.2 10.49 5685 21.3 1.33(1.15-1.6) 0.0043

1 /4/83- 19/4/83 30.6 33.0 17.7 26.6 17.82 6152 23.1 1.3 (1.15-1.46) 0.0075

26/4/83-17/5/83 38.4 35.7 22.9 29.7 22.50 6312 33.9 1.09 (0.88-1.3) 0.011

aThis was not considered since only peak values were measured.

1284 BIOTECHNOLOGY AND BIOENGINEERING, VOL. 26, NOVEMBER 1984

50 - - - 1 0

= 40- 0

@ 3 0 -

z

9 w

20 -

10 -

0 ; I 1 I I

0 10 20 30 40

MEAN AIR TEMPERATURE ( ' C )

Figure 2. Water evaporation versus mean air temperature.

A summary of production data with corresponding average culture densities and dilution rates is also presented in Table I. The densities in wintertime were intentionally kept higher to protect the culture from a relative excess of radiation (during that period growth was not light-limited but temperature-limited). Surface densities were in the range 50-80 g dry weight/m2, except for the two first periods. De Zarlo et a1.16 reported 55-70 g/m2 for Tetraselmis sp. culture in southern Italy in summer. The average dilution rates in our case varied between 0.02 and 0.012 h-l,

Table II. Summary of meteorological data.

depending on climatic conditions. The maximum value corresponds to the average residence time of three days.

Average productivities were between 8 and 26 g/m2/day with peak values up to 50 g/m2/day. During July-August, the unit was not operated and perhaps one could expect somewhat higher productivities during that time. Ike- nouye and co-workersl' in Kuwait reported on Spirulina yields with peak values of 23 g/m2/day (for an algae culture depth of 25 cm). In general, data on productivities should be considered preliminary, even when obtained

Period 16/4/82- 115182- 24/5/82- 20/13/82- 1/2/83- 1/3/83- 1/4/83- 26/4/83- (day/month/year) 26/4/82 23/5/82 5/7/82 31/1/83 28/2/83 31/3/83 19/4/83 17/5/83

Daily totals of global incident radiant energy at 280-2800 nm (Wh/mz)

("C) Air temperature

Relative air humidity ( 7 0 )

Wind velocity W s )

Precipitation (mm)d

Average value Minimum value Maximum value

Mean value" Absolute minimumb Absolute maximumb Mean value" Absolute minimumb Absolute maximumb Mean value' Absolute maximum'

585 1 3084 7198

29.5 20.0 38.0 33.5 2.0

87.0 4.9

14.3 0.6

6065 3342 8008

32.8 23.0 43.0 29.2

1 .o 74.0

7.9' 21.9' 3.3

6664 1317 8565

36.2 25.0 47.0 20.6 0

59 7.2

21.4 1.5

3345 689

5038

14.3 3.0

25.0 73.4 32.0 99.0 3.7 9.8

24.3

4378 1887 5894

16.9 5.0

26.0 47.Y 25. Oe 99.0' 5.2

11.2 6.0

5685 3477 6764

20.5 7.0

31.0 39.2 21 .o 99.0 6.8

13.0 12.6

6152 3181 7706

26.1 14.0 35.0 36.7 15.0 99.0

7.6 22.3 17.4

6312 291 I 8706

34.2 18.0 43.0 37.6 15.0 99.0

7.0 22.8 0.7

aMean daily values of temperature and air humidity were calculated from measurements from sunrise to sunset. bAbsolute minimum and maximum values include night measurements. CWind velocity measured from sunrise to sunset. dMeasured at Kuwait International Airport. eData on 15/2/83-26/2/83 not available. 'Data on 15/5/82-23/5/82 not available.


over quite a long period of time and at different seasons. The main drawback is the size of the cultivation surface (2.11 m2). The edge effects together with a relatively high dark zone in the collecting tank represent the main problem. The size of the unit, however, is representative for projection to a larger unit and the optimal ratio of the dark/light period is open for further exploration. Obvi- ously, with growth surface enlargement, the dark volume will be reduced. Lee and Pirt18 reported on an optimal light fraction of 0.77 as deduced from loop reactor studies.

The thin-layer intensive algae concept, originally developed some years ago7 (cultivation area 1000 m2) is gain- ing interest in other parts of the world. Thus, Vendlovt~'~ and ProkeS and co-workers2* reported on a 550 m2 cultivation area very similar to the design in Bulgaria. Anthony2' patented an enclosed apparatus with a thin-layer surface with an adjustable ratio of illuminated and dark zones, and Piron-Fraipont22 reported on the use of a thin-layer cultivation apparatus in Belgium provided with a heat ex- changer to control temperature in winter. The concept is almost equivalent to that of Destordeur and co- workersU installed a similar 32-m2 system in Belgium. Another similar project was developed in Peru with a 111-m2 sloped cultivation area with recirculation by a pump,24 and in Hawaii with a 49-m2 sloped area with air- lift recir~ulation.~

Productivity data obtained in this project are in accor- dance with published data collected under similar climatic condition^.^^ A further interesting comparison is possible for units of similar design. Thus, Vendl~vii '~ in Bulgaria reported on Scenedesmus obliquus average productivities of 25 g/m2/day for summer (maximum 45 g/ m2/day) with average culture densities of 1.3-1.65 g (dry wt)/L for a 10-cm layer. In Peru, with a yearly precipitation of 15 mm, Heussler and co-workers26 obtained average summer productivities of 25 g/m2/day (peak 53 g/m2/ day, winter 15 g/m2/day) with Scenedesmus acutus var. altemans for a 9-13-cm culture layer. The average yearly evaporation was 6 L/m2/day (our average. for Kuwait is 11.8 L/m2/day for December-July).

The suspension turbulence is far from being optimized. The turbulence is mainly controlled by the liquid discharge rate from a pump; as the flow rate varied from 250 to 340 L/min, linear velocity from 8 to 11 cm/s (for a 5-cm algae layer). Heussler et al.,24 in Peru, in a similarly designed unit (except without baffles across the liquid stream) used higher linear velocities (31-41 cm/s for 10-cm algae layer; for a 5-cm layer, velocities are double). Laws et al.,3 in Hawaii, used a velocity of 30 cm/s for a 7.7-cm algae layer provided with immersed foils to create defined hydrodynamic pattern.

Similarly, the C02 supply rate was only empirically ad- justed and will require direct verification by a pC02 mea- surement to eliminate C02-limited operation.

During the outdoor operation of algae, some parasitic infections are usually e n c o ~ n t e r e d . ~ ~ Our experience is more encouraging because a nonidentified flagellates in-

fection caused a loss of culture only once, although occa- sionally minor count of protozoa was noted.

The heat balance around the culture unit was very satisfactory. In winter the culture temperature was higher than air by several degrees than in summer, when it is usually the other way around because of evaporation. It would not be too complicated to insulate a storage tank (in the earth or with a plastic material) to retain algae temperatures overnight to encourage algae growth immediately after sunrise. In winter, another possibility is solar heating of the algae suspension during the day (suggested by Piron-Fraipont and co-workers22).

During the operation of the unit, some product was se- cured and analysis established. Results showed that the medium was properly balanced and that the crude protein content of the product was in the range 57-6670 (based on the total nitrogen content).

One of the environmental problems encountered in Ku- wait is dust fallout .28 Dust can contaminate the product and can also change, to some extent, the medium compo- sition. As may be deduced from the results of dust, water, and supernatant analysis (after resuspending dust in water), some elements can leach from dust (water soluble fraction represents up to 13% of total solids) and contrib- ute to the mineral algae nutrition (calcium, ferrous, po- tassium, phosphorus, and nitrogen) and, as appears from other analyses,28 anions such as chlorides and sulphates are most probably also leaching out. From the production viewpoint, dust does not represent a major problem. Dur- ing dusty days, the culture can stay out of the production surface in a reservoir minimizing direct dust fallout. Dust contamination of algae suspension can be eliminated by regular cleaning of the surface as dust tends to sediment in front of baffles. No harm to the culture was noted during the entire growth period, except that dust considerably reduced the amount of global radiation and thus also productivity.

The presence of dust in the air may alter sunlight quality and amount of direct radiation. It is probable that the blue light is considerably reduced and only red light penetrates through the dust layer. H a n ~ e l m a n n ~ ~ reported on a model experiment using broken quartz sand of 0.1-0.25 mm size. Red light of 750 nm was 40 times more transmitted than that of 450 nm. The sunlight spectrum modi- fication from dust (haze) is not known. In any case, even a slight haze considerably reduces the amount of direct radiation and diffuse radiation is enhanced.

CONCLUSIONS

The semi-pilot-scale outdoor cultivation unit served for algae optimization with respect to light, depth, culture density, and mineral nutrition. Results on productivities are convincing enough to consider the application of thin- layer intensive technology for mass algae production in the arid climatic conditions of Kuwait.

Outdoor cultivation featured remarkable culture sta-

1286 BIOTECHNOLOGY AND BIOENGINEERING, VOL. 26, NOVEMBER 1984

bility and low area and manpower consumption compared with less intensive (rural) algae technologies. It is pro- posed that this intensive algae technology be used for mass cultivation of marine algae as a live feed for rotifers of the fish chain.

The authors appreciate the financial support of the Kuwait Founda- tion for the Advancement of Sciences. Global and diffuse radiation data were kindly provided by the Energy Department of KISR. The excellent technical help of Mr. S. Abu-Zant is very much appreciated.

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potential of mass algae production in kuwait

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