further decrease the BOD and COD of the wastewater, achieving the desired
objective of wastewater treatment as well.
Several studies have been reported for reduction in nitrogen and phosphorous
containing compounds coupled with biomass growth. Removal of nitrogen and
phosphorus was reported using C. vulgaris with a removal efficiency of 72 and
28%, respectively (Aslan and Kapdan 2006). Chlamydomonas polypyrenoideum
was used in a study of dairy wastewater treatment, and it was reported that nitrate
level could be reduced by 90%, ammonia by 90%, phosphorus by 70%, and COD
by 60% in 10 days (Lu et al. 2015). Chlorella sorokiniana when used for treatment
of alcohol distillery wastewater in a 50 L PBR could decrease the nitrate content by
95%, phosphate by 77%, and sulfate by 35% in a time period of 3 days
(Solovchenko et al. 2014). In a study performed by Li et al. (2011a), it has been
reported that using bench scale continuous cultures, 0.92 g/L/d productivity of
Chlorella strain was achieved using wastewater rich in ammonium, phosphorus, and
organic matter with a COD of 1300 mg/L. Emerging contaminants (EC) can also be
treated by microalgae to some extent as compared to other commonly available
biological treatment. Microalgae can treat emerging contaminants in sequence of
pharmaceuticals > PCPs (personal care products) > EDCs (endocrine disruption
chemicals) > pesticides (Ahmed et al. 2017). Microalgae can also be used in the
removal of heavy metals and can be employed based on the detoxification and
biosorption techniques (Suresh Kumar et al. 2015). It can be clearly concluded from
the studies mentioned above that cultivation of microalgae from wastewater not
only reduces the pollution caused but also provides a rich sustainable feedstock in
the form of algal growth which can be further utilized in biofuel production.
3 Harvesting
Process of harvesting consists of separation of biomass from the medium used for
cultivation of microalgae. It is basically a separation process which separates
microalgae biomass from cultivation medium. It is important that the process is a
cost-effective one as it makes to about 20–30% of the total cost required for the
whole process. Filtration, centrifugation, flocculation and floatation, gravity sedimentation, etc., are the techniques mostly used for this operation. The exact method
is selected based on the cell size, cell density, and total quantity of the product to be
separated. New techniques of harvesting and application of process intensification
have also been reported based on techniques like flocculation assisted by the use of
magnetic microparticles (Vergini et al. 2016), magnetic membrane filtration (Bilad
et al. 2013), sedimentation assisted by the use of polymers (Zheng et al. 2015),
electrical methods like electro-coagulation-filtration (ECF) (Gao et al. 2010) and
electrochemical harvesting (ECH) (Misra et al. 2015). Low-frequency ultrasound
can also be applied to the grown microalgal cells which results in decrease in the
buoyancy and increases the sedimentation of the cells resulting in 90–92% as the
harvesting efficiency (Kim et al. 2013).
64
S. Joshi and P. Gogate
objective of wastewater treatment as well.
Several studies have been reported for reduction in nitrogen and phosphorous
containing compounds coupled with biomass growth. Removal of nitrogen and
phosphorus was reported using C. vulgaris with a removal efficiency of 72 and
28%, respectively (Aslan and Kapdan 2006). Chlamydomonas polypyrenoideum
was used in a study of dairy wastewater treatment, and it was reported that nitrate
level could be reduced by 90%, ammonia by 90%, phosphorus by 70%, and COD
by 60% in 10 days (Lu et al. 2015). Chlorella sorokiniana when used for treatment
of alcohol distillery wastewater in a 50 L PBR could decrease the nitrate content by
95%, phosphate by 77%, and sulfate by 35% in a time period of 3 days
(Solovchenko et al. 2014). In a study performed by Li et al. (2011a), it has been
reported that using bench scale continuous cultures, 0.92 g/L/d productivity of
Chlorella strain was achieved using wastewater rich in ammonium, phosphorus, and
organic matter with a COD of 1300 mg/L. Emerging contaminants (EC) can also be
treated by microalgae to some extent as compared to other commonly available
biological treatment. Microalgae can treat emerging contaminants in sequence of
pharmaceuticals > PCPs (personal care products) > EDCs (endocrine disruption
chemicals) > pesticides (Ahmed et al. 2017). Microalgae can also be used in the
removal of heavy metals and can be employed based on the detoxification and
biosorption techniques (Suresh Kumar et al. 2015). It can be clearly concluded from
the studies mentioned above that cultivation of microalgae from wastewater not
only reduces the pollution caused but also provides a rich sustainable feedstock in
the form of algal growth which can be further utilized in biofuel production.
3 Harvesting
Process of harvesting consists of separation of biomass from the medium used for
cultivation of microalgae. It is basically a separation process which separates
microalgae biomass from cultivation medium. It is important that the process is a
cost-effective one as it makes to about 20–30% of the total cost required for the
whole process. Filtration, centrifugation, flocculation and floatation, gravity sedimentation, etc., are the techniques mostly used for this operation. The exact method
is selected based on the cell size, cell density, and total quantity of the product to be
separated. New techniques of harvesting and application of process intensification
have also been reported based on techniques like flocculation assisted by the use of
magnetic microparticles (Vergini et al. 2016), magnetic membrane filtration (Bilad
et al. 2013), sedimentation assisted by the use of polymers (Zheng et al. 2015),
electrical methods like electro-coagulation-filtration (ECF) (Gao et al. 2010) and
electrochemical harvesting (ECH) (Misra et al. 2015). Low-frequency ultrasound
can also be applied to the grown microalgal cells which results in decrease in the
buoyancy and increases the sedimentation of the cells resulting in 90–92% as the
harvesting efficiency (Kim et al. 2013).
64
S. Joshi and P. Gogate