Water Technology and Sciences - page 23

21
Water
Technology and Sciences.
Vol. VI, No. 3, May-June, 2015
Haro & Perales,
Kinetics of Nutrient Uptake and Growth of a Bloom of Microalgae in a High Rate Algae Pond (HRAP) Photobioreactor
S
µ
X
:
concentration of substrate obtained by
substituting
µ
x
(Table 1) in equation (6).
S
µ
S
:
concentration of substrate obtained by
substituting
µ
S
(Table 2) in equation (6).
Results and Discussion
Light and Temperature
Solar radiation and temperature were moni-
tored throughout the entire experiment. The
mean solar radiation obtained was 562.87 ±
145.94
μ
mol m
-2
d
-1
(
p
= 95%,
n
= 107), and
the mean temperature inside and outside the
HRAP was 20 ± 0.71 ºC and 21 ± 0.99 ºC (
p
=
95%,
n
= 107), respectively.
pH
At the beginning of the experiment the pH
was 8.2, which increased until approximately
72 h when it stabilized at a mean pH of 10.27
± 0.08 (
p
= 95%,
n
= 24). This is higher than
that obtained by Arbib
et al
(2012) (pH = 9.32
± 0.30) for the same HRAP photobioreactor
but using wastewater instead of synthetic
media, and higher than the 8.5 obtained
by Ketheesan and Nirmalakhandan (2012)
which used
Scenedesmus
sp. in a Bold’s basal
medium with a 23 liter raceway and artificial
lighting in the laboratory. These differences
may be due to the time at which the pH was
measured.
The pH value recorded is highly depen-
dent on the time at which the measurement
is taken. In our case, it was measured every
day at approximately the same time (9:00 –
11:00), but the pH evolves throughout the day,
as indicated by some authors (Ketheesan &
Nirmalakhandan, 2012; Putt, Singh, Chinna-
samy, & Das, 2011). To verify this evolution,
a complete registry of pH was taken over 24
hours (Figure 2).
Figure 2 clearly shows the increase in pH
over the day, reaching a maximum at sunset
and decreasing gradually during the night.
These changes in pH are due to biological
photosynthesis processes (uptake of CO
2
)
and respiration (generation of CO
2
) by the
microalgae (Margalef, 1983).
Figure 2. Evolution of pH over 24 hours, from 05/30 at 7:00 to 05/31 at 7:00. On 05/30,
the sun rose at 7:09 and set at 21:37.
1...,13,14,15,16,17,18,19,20,21,22 24,25,26,27,28,29,30,31,32,33,...169
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