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Algal production 239

also influenced by this parameter, making temperature to be not nearly as
important as sunlight in controlling algal productivity. To achieve maximum
algal yield in outdoor HRAP, consideration must be given also to the factors
that affect algal growth as described in section 5.2.1.
Some of the engineering models to predict algal productivity in outdoor mass
culture or HRAP are given below.

Goldman formula

Based on the simple energy balance in photosynthesis and considering the
characteristics of sunlight, Goldman (1979b) derived the following model in
which the effect of algal decay was excluded:

Pa = 0.28 Is [ln 0.45 I 0 /Is + 1] (5.5)

Where

Pa = algal productivity (dry weight), g/ (m^2 -day),

Is = saturation light intensity, gcal/ (cm^2 -day)

Iois as defined in Equation 5.4.

The values Is depends on temperature and is not the same for all cultures of
algal species, but rather is a function of the physiological make-up of the
particular cells in the culture. Goldman (1979b) stated that good values of Is for
different algal species from the literature generally are lacking. The data of Is
given in Table 5.7 only represent the general magnitude of Is for different types
of algae and demonstrate the effect of temperature on the Is values or the
photosynthetic efficiency factor. The range of Is values likely to be experienced
with outdoor HRAP is 29-86 gcal/ (cm^2 -day) (Goldman 1979b). The value of Io
depends on the latitude and local weather conditions such as cloudy or clear sky,
which can range from 0 to 800 gcal/(cm^2 -day).
The effects of Is and Io or Pa values, based on Equation 5.5, are graphically
shown in Figure 5.9. It is apparent from this figure that the algal productivity
can be almost double by culturing the algal species with an Is value of 86
gcal/(cm^2 -day) instead of an Is value of 29 gcal/(cm^2 -day) at the higher light
intensities (or higher Is values). However, Pa values do not linearly increase with
Io at higher Io values because of the light saturation effect on algal growth. The
large data compilation of maximum algal yields attained in outdoor HRAP
systems (Goldman 1979a) falls within the ranges shown in Figure 5.9.