In natural blooms of microalgae occurring in lakes or
rivers, flocculation sometimes occurs spontaneously. This
spontaneous flocculation is assumed to be caused by extracellular
polymer substances in the medium and is called
bioflocculation [10]. Bioflocculation is often successfully
used for harvesting microalgae in facilities where microalgae
are used in wastewater treatment [44]. The underlying
mechanism, however, is poorly understood and
deserves further research because it may lead to a chemical-
free method for flocculating microalgae. Some microalgal
species flocculate more readily than others and such
naturally bioflocculating microalgae can be mixed with
other species to induce flocculation [45,46]. There are
indications that bioflocculation may be initiated by infochemicals
[47]. Recently, an infochemical isolated from a
senescent and flocculating culture of a Skeletonema species
was found to be capable of inducing flocculation in a culture
of another species of microalgae [48].
Bacteria or fungi can also induce bioflocculation of
microalgae. Some fungi, for instance, have positively
charged hyphae that can interact with the negatively
charged microalgal cell surface and cause flocculation
[49,50]. Specific consortia of bacteria can also induce flocculation
of microalgae [51,52]. These flocculating fungi or
bacteria can be cultivated separately or in combination
with the microalgae. Cultivating bacteria or fungi in combination
with microalgae requires a carbon source in the
medium. In wastewater, a carbon source is usually present
and this allows cocultivation of microalgae and bacteria.
This results in a culture of mixed algal–bacterial flocs that
can be easily harvested [53,54]. The use of bacteria or fungi
as a flocculating agent avoids chemical contamination of
the biomass but results in microbiological contamination,
which may also interfere with food or feed applications of
the microalgal biomass.
In natural blooms of microalgae occurring in lakes orrivers, flocculation sometimes occurs spontaneously. Thisspontaneous flocculation is assumed to be caused by extracellularpolymer substances in the medium and is calledbioflocculation [10]. Bioflocculation is often successfullyused for harvesting microalgae in facilities where microalgaeare used in wastewater treatment [44]. The underlyingmechanism, however, is poorly understood anddeserves further research because it may lead to a chemical-free method for flocculating microalgae. Some microalgalspecies flocculate more readily than others and suchnaturally bioflocculating microalgae can be mixed withother species to induce flocculation [45,46]. There areindications that bioflocculation may be initiated by infochemicals[47]. Recently, an infochemical isolated from asenescent and flocculating culture of a Skeletonema specieswas found to be capable of inducing flocculation in a cultureof another species of microalgae [48].Bacteria or fungi can also induce bioflocculation ofmicroalgae. Some fungi, for instance, have positivelycharged hyphae that can interact with the negativelycharged microalgal cell surface and cause flocculation[49,50]. Specific consortia of bacteria can also induce flocculationof microalgae [51,52]. These flocculating fungi orbacteria can be cultivated separately or in combinationwith the microalgae. Cultivating bacteria or fungi in combinationwith microalgae requires a carbon source in themedium. In wastewater, a carbon source is usually presentand this allows cocultivation of microalgae and bacteria.This results in a culture of mixed algal–bacterial flocs thatcan be easily harvested [53,54]. The use of bacteria or fungias a flocculating agent avoids chemical contamination ofthe biomass but results in microbiological contamination,which may also interfere with food or feed applications ofthe microalgal biomass.
การแปล กรุณารอสักครู่..
