Page 259 - Algae Anatomy, Biochemistry, and Biotechnology
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242                                   Algae: Anatomy, Biochemistry, and Biotechnology

                  are the numerous temporary or permanent lakes along the northeast border of Lake Chad, where
                  Arthrospira sp. grows almost as monoculture, and is collected for human consumption by the
                  Kanembou people inhabiting those areas. Arthrospira sp. naturally blooms also in old volcanic
                  craters filled with alkaline waters in the Myanmar region. Production began at Twin Taung Lake
                  in 1988, and by 1999 increased to 100 tons per year. About 60% is harvested from boats on the
                  surface of the lake, and about 40% is grown in outdoor ponds alongside the lake. During the blooming
                  season in the summer, when the cyanobacterium forms thick mats on the lake, people in boats
                  collect a dense concentration of spirulina in buckets. Arthrospira is harvested on parallel inclined
                  filters, washed with fresh water, dewatered, and pressed again. This paste is extruded into noodle
                  like filaments which are dried in the sun on transparent plastic sheets. Dried chips are taken to a
                  pharmaceutical factory in Yangon, pasteurized, pressed into tablets ready to be sold. Another cya-
                  nobacterium to be used as a food supplement is Aphanizomenon flos-aquae, which since the early
                  1980s has been harvested from Upper Klamath Lake, Oregon, and sold as a food and health food
                  supplement. In 1998 the market for A. flos-aquae as a health food supplement was about $100
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                  million with an annual production greater than 10 kg (dry weight). A. flos-aquae blooms are
                  often biphasic, with a first peak in late June to early July, and a second peak late in September
                  to mid-October. The harvested biomass is screened and centrifuged to remove small extraneous
                  material. The algal concentrate is then gravity-fed into a vertical centrifuge that applies high cen-
                  trifugal force to separate cells and colonies, removing about 90% of the remaining water. At this
                  stage the algal product is 6–7% solids. Once concentrated, the product is chilled to 28C and
                  stored before being pumped to the freezers. The frozen algae is then put into storage boxes and
                  shipped to the freezer facility for storage. When needed, the frozen product is shipped to an external
                  commercial freeze drying facility to be freeze dried into a powder containing 3–5% water content.
                  This final product is processed into consumable products such as capsules or tablets.
                     Natural ponds that do not necessitate mixing, and need only minimal environmental control,
                  represent other extensive cultivation systems.
                     The largest natural ponds used for commercial production of microalgae are Dunaliella salina
                  lagoons in Australia. Western Biotechnology Ltd. operates 250 ha. of ponds (semi-intensive culti-
                  vation) at Hutt Lagoon (Western Australia); Betatene Ltd., a division of Henkel Co. (Germany),
                  operates 460 ha. unmixed ponds (extensive cultivation) at Whyalla (South Australia). Both facili-
                  ties produce biomass for b-carotene extraction. Other facilities use raceway culture ponds, such as
                  those operated by Cyanotech Co. in Hawaii and Earthrise farms in California for the production of
                  Haematococcus and Artrosphira biomass. In both cases large raceway ponds from 1000 to 5000 m 2
                  are adopted, with stirring accomplished by one large paddle wheel per pond. Raceway pond are also
                  used for intensive cultivation of D. salina by Nature Beta Technologies Ltd. in Israel.
                     The nutrient medium for outdoor cultures is based on that used indoors, but agricultural-grade
                  fertilizers are used instead of laboratory-grade reagents. However, fertilization of mass algal cul-
                  tures in estuarine ponds and closed lagoons used for bivalve nurseries was not found to be desirable
                  as fertilizers were expensive and it induced fluctuating algal blooms, consisting of production peaks
                  followed by total algal crashes. In contrast, natural blooms are maintained at a reasonable cell
                  density throughout the year and the ponds are flushed with oceanic water whenever necessary.
                  Culture depths are typically 0.25–1 m. Cultures from indoor production may serve as inoculum
                  for monospecific cultures. Alternatively, a phytoplankton bloom may be induced in seawater
                  from which all zooplankton has been removed by sand filtration. Algal production in outdoor
                  ponds is relatively inexpensive, but it cannot be maintained for prolonged period and is only suit-
                  able for a few, fast-growing species due to problems with contamination by predators, parasites,
                  and more opportunistic algae that tend to dominate regardless of the species used as inoculum. Fur-
                  thermore, outdoor production is often characterized by a poor batch to batch consistency and unpre-
                  dictable culture crashes caused by changes in weather, sunlight, or water quality. As stated earlier,
                  at present, large-scale commercial production of microalgae biomass is limited to Dunaliella, Hae-
                  matococcus, Arthrospira, and Chlorella, which are cultivated in open ponds at farms located
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