Mass cultivation of Nannochloropsis
sp. in annular reactors
G.C. Zittelli, L. Rodolfi, M.R. Tredici-2003
Journal of Applied Phycology, 15(2):
107-114
Abstract:
A study was made on the mass cultivation of Nannochloropsis
sp. in newly designed annular reactors operated under natural, artificial or
combined illumination. The annular reactor consists of two 2-m-high
Plexiglas cylinders of different diameter placed vertically one inside the
other so as to form an annular culture chamber. Artificial illumination is
supplied by lamps placed inside the inner cylinder. Two annular reactors of
different diameter (50 and 91 cm), light path (4.5 and 3.0 cm) and
illuminated surface area (5.3 and 9.3 m2) were experimented with.
The effect of two different artificial light sources (fluorescent tubes and
metal halide lamps) on culture productivity was investigated in both
systems. The highest productivity on a per reactor basis (about 34 g (d. wt)
reactor-1 24 h-1) was achieved with the larger reactor
illuminated by a 400-W metal halide lamp. From February to May a 91-cm
reactor illuminated only with natural light was operated in parallel with a
91-cm reactor subjected to combined illumination. Under natural illumination
productivity increased from 16.6 g (d. wt) reactor-1 d-1
in February to 34.1 g (d. wt) reactor-1 d-1 in May.
Under combined illumination productivity was 41.3 g (d. wt) reactor-1
d-1 in February and increased up to 48.3 g (d. wt) reactor-1
d-1 in May. Although the culture exposed to combined illumination
always attained higher yields, the productivity gap between the two cultures
decreased gradually along the season as solar radiation and minimum night
temperatures increased. A 1200-L plant made of ten 50-cm annular reactors
was set up and operated for two years with combined illumination yielding an
average of 270 g of dry Nannochloropsis sp. biomass per day. More
than 2000 L of concentrate suspension (50 g (d. wt) L-1) of Nannochloropsis
sp. were produced and successfully used by fish hatcheries as live feed for
rotifers and for rearing seabream larvae with the green-water technique.
This study indicates that the annular reactor can be profitably used for
long-term cultivation of Nannochloropsis in temperate climates.
Besides reliability and ease of operation, the main advantage of the system
is that it can be used under natural illumination, yet artificial light can
be also supplied to maintain high productivity levels in winter or on cloudy
days.
(Istituto per lo Studio degli
Ecosistemi, CNR, Sezione di Firenze, P.le delle Cascine 28, Firenze, 50144,
Italy, e-mail of M.R. Tredici: mario.tredici@unifi.it)