Environmental Engineering Reference
In-Depth Information
seaweed using the fi sh waste material as fertilizer
and the fi sh eating the epiphytes, such as
Enteromorpha species, that would otherwise
become serious pests for the seaweeds. Control
with tilapia ( Oreochromis mossambicus ) and
milkfi sh ( Chanos chanos ) was satisfactory as
long as the fi sh were removed before they started
to eat the Gracilaria ; larger fi sh were periodi-
cally removed and replaced by small fi sh. This
concept of polyculture, or integrated aquaculture
to use the more recent terminology, has since
been utilized in many situations where the effl uent
from the aquaculture of one species, potentially
threatening environmental damage, can be utilized
by another species to its advantage, with a reduc-
tion in pollution. Various strategies have been
tried. Seaweed cultivation around the outside of
fi sh cages has led to signifi cantly better growth
of seaweed but was only partly successful in
removing the large amount of nutrients coming
from the fi sh cages. Unattached Gracilaria has
been grown in the effl uent from shrimp ponds.
Semi-enclosed or land-based systems have been
suggested, but the higher capital investment has
been a deterrent (McHugh 2003 ).
Integrated aquaculture is developing as solutions
are sought to problems of environmental sustain-
ability, including the management of coastal
areas and the disposal of effl uents from large-scale
aquaculture activities. Animal aquaculture tech-
niques affect adversely the environment in one
way or another (Ackefors and Enell 1990 ). They
generate increased sedimentation, biochemical
oxygen demand, nutrient loadings, etc., inherent
to highly intensive stocking and feeding.
Wastewater contains a large amount of nitrogen
excreted by the animals as particulate or in the
dissolved state (del Rio et al. 1996 ). The worldwide
increase during the last few years on mono-species
aquaculture has generated severe environmental
problems and is a matter of great concern. Haglund
and Pedersén ( 1993 ) investigated the potential of
the red seaweed Gracilaria tenuistipitata when
cocultivated with Oncorhynchus mykiss (rainbow
trout) for the removal of nitrogen and phosphorus
from the pond. Integrated management of seaweed
in shrimp aquaculture ponds is a common prac-
tice in China and Taiwan since it attributes the
following: (1) the seaweeds could be a suitable
shelter for the animals especially during the day;
(2) the oxygen evolved during photosynthesis by
seaweed helps the aerobic bacteria to accelerate
the degradation of complex organic substances to
simple elements; (3) ammonia, urea, and other
nutrients present in the excreta of the animals are
being utilized by the seaweed for its productivity
thereby reducing the nutrient loading; (4) the
polysaccharides and other products obtained
from the seaweed while grown in aquaculture
farms exhibit good quality since the ambient
water is enriched with nutrients; (5) the shrimp
farmers benefi ted not only from the animals but
also from the seaweeds; and (6) the level of oxygen
during the day is increased due to photosynthesis.
However, both animals and plants compete for
oxygen during night. Therefore, maintenance
of stocking density of seaweed in the pond is a
prerequisite for integrated aquaculture practice
(Kavitha and Rengasamy 2002 ).
10
Utilization of Seaweed
Biomass for Fuel
Continued use of petroleum sourced fuels is now
widely recognized as unsustainable because of
depleting supplies and the contribution of these
fuels to the accumulation of CO 2 in the environ-
ment. Renewable, carbon-neutral transport fuels
are necessary for environmental and economic
sustainability (Chisti 2007 ). Biodiesel can be car-
bon neutral and produced intensively on relatively
small areas of marginal land. The quality of the
fuel product is comparable to petroleum diesel
and can be incorporated with minimal change into
the existing fuel infrastructure. Innovative tech-
niques, including the use of industrial and domes-
tic waste as fertilizer, could be applied to further
increase biodiesel productivity (Campbell 2008 ).
Similar to higher plants like corn, soybeans, sugar
cane, wood, and other plants, algae also used pho-
tosynthesis to convert solar energy into chemical
energy. They store this energy in the form of
oils, carbohydrates, and proteins. The plant oil
can be converted into biodiesel; hence, biodiesel
is a form of solar energy.
 
Search WWH ::




Custom Search