Microalgae cultivation in artificial wastewater for nutrient removal artificial wastewater is defined as a synthetic medium, which contains an inorganic nutrient composition similar to real wastewater, however it lacks toxic components,microbes, etc., whic
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Wastewater is a general term used to represent the water with
poor quality that contains more amounts of pollutants and
microbes. If wastewater is discharged into the nearby water
bodies, it can cause serious environmental and health
problems to human beings. Wastewater treatment is an
important measure to reduce the pollutant and other
contaminants present in wastewater. The first step in
wastewater treatment method is primary treatment which
removes the solids, oil, and grease from wastewater.
Secondary treatment or biological treatment is the second step,
which exploits microorganisms to eliminate the chemicals
present in wastewater. Final step is the tertiary treatment;
which eliminates the microbes from wastewater before
discharging into the river (Rawat et al., 2010).
Effluent produced from the secondary treatment plant contains
more amounts of nutrients (nitrogen and phosphorus) and if
these effluents are discharged into water bodies; it causes
eutrophication and affects the ecosystem. To remove these
nutrients, several processes are used, but the disadvantages of
this type of treatment are high cost and increased sludge
production (Yuan et al., 2011). As an alternative to the
conventional treatment methods, microalgae are suggested to
remove the nutrients from wastewater (Mallick, 2002). The
use of microalgae or macroalgae (seaweeds) to remove
pollutants and nutrients from the wastewater is called
phycoremediation. Microalgae wastewater treatment is eco
friendly and offers the advantage of a cost effective way of
nutrient removal and biomass production (Mulbry et al.,
2008). The microalgae grown in wastewater can be used as
energy source, fertilizer, fine chemicals production and as feed
to animals (Vilchez et al., 1997; Mulbry et al., 2006). The aim
of this paper is to summarize the different types of strategies
currently examined to cultivate the microalgae in wastewater
for nutrient removal.
Processing of wastewater
Wastewater contains different types of materials like soluble
organic, inorganic, insoluble inorganic materials, macro solids,
toxins, etc. By processing, it is ensured that only the soluble
fraction of the waste like carbon, nitrogen and phosphate are
used for the microalgae cultivation. Besides pollutants,
bacteria and protozoa are also present in wastewater. If this
wastewater is used as a culture medium, microbes present in it
will compete for microalgae growth and nutrition. Hence ultra
violet light source, filtration, autoclaving and centrifugation
are the different types of pre-treatment method used to remove
suspended solids and algae feeding organism like protozoa and
bacteria. Filtration of secondary effluent using 0.20 µm pore
filters gave the highest biomass growth (Chlorella sp.) with
the total nitrogen removal of 92% and total phosphorus
removal of 86%. In case of UV radiation (pre-treatment
method), UV- B at the dose of 1620 mJ cm -2 gave the
maximum biomass growth (Chlorella sp.) when compared to
270 mJ cm -2 of UV- B dose (Cho et al., 2011). The Chlorella
sp. cultivated in the autoclaved centrate showed higher growth
rate than the raw centrate (Li et al., 2011). After sterilizing
the wastewater, phosphorus level in it gets reduced and it
might have effect on the algal growth. This nutrient level is
increased by adding the chemicals likes KH2PO4, K2HPO4 and
Na2HPO4. In some pre-treatment process, centrifugation alone
is used to process the wastewater e.g. piggery wastewater, but
in case of wastewater from olive oil mill, both filtration and
centrifugation are used to condition wastewater