thereby helping in the process of flocculation (Shuba and Kifle 2018). Synthetic
polymers are used which are highly efficient and produce stable flocs but are
associated with various disadvantages such as hazardous nature that result in the
production of a low-quality harvest product. The alternative to the synthetic
polymers is the natural polymer (i.e., chitosan), which is a product of chitin
deacetylation and can also be produced from fungi under anaerobic conditions
(Rinaudo 2006; Rashid et al. 2013, 2014). Flocculation can be of two types:
bio-flocculation and auto-flocculation. Bio-flocculants employ the activities of a
single flocculating microalga which further lead to concentration of the desired
non-flocculating microalgal biomass (Shuba and Kifle 2018; Salim et al. 2010).
The availability of nutrient (mainly nitrogen and phosphorous) and physical
parameters is mainly responsible for bio-flocculation. Exopolysaccharide (EPS) is
produced by the microalgal cells in conditions of nutrition deficiency, and the EPS
further helps in the process of bio-flocculation (Rashid et al. 2014). In case of autoflocculation, the mature microalgae are exposed to sunlight for a longer period with
low concentrations of carbon dioxide. This process is beneficial for large-scale
harvesting as it leads to substantial reductions in the production costs and is
governed by the presence of light (Gouveia 2011; Milano et al. 2016).
8.3.2 Harvesting of Microalgae Using Centrifugation
Centrifugation involves separation of the particles on the basis of size and density.
The microalgae are subjected to higher centripetal acceleration which results in the
separation of the cells into a greater density and low-density area (Milano et al.
2016). For the size and type of the particles, centrifugation techniques can be of
various types such as imperforate basket, decanter, tubular, nozzle type,
multichamber, solid-ejecting type disk, and solid-retaining disk (Shelef et al. 1984;
Shuba and Kifle 2018). The size of the desired algal species determines the efficiency of the process. This method of algal separation cannot be employed on a large
scale as it is a relatively expensive (Uduman et al. 2010) and energy-consuming
technique (Heasman et al. 2000; Shuba and Kifle 2018).
8.3.3 Harvesting of Microalgae Using Filtration
Filtration is the process in which the solution containing the microalgal cells is
passed through a filter, thereby trapping the cells and allowing only the medium to
pass through. Filtration techniques can be divided into four types (i.e., macrofiltration (>10 μm), microfiltration (size of the pores ranges from 0.1 to 10 μm),
ultrafiltration (0.02–2 μm), and reverse osmosis (<0.001 μm) (Harun et al. 2010;
Shuba and Kifle 2018). Filtration techniques are limited by the high operational costs
involved and longer duration of processing (Shuba and Kifle 2018). Microalgae
production mainly employs rotary filters and micro-strainers as these are cost
effective and easy to operate owing to the fine mesh containing micro-strainers
8 Algal Biomass: Potential Renewable Feedstock for Biofuels Production – Part I
213
polymers are used which are highly efficient and produce stable flocs but are
associated with various disadvantages such as hazardous nature that result in the
production of a low-quality harvest product. The alternative to the synthetic
polymers is the natural polymer (i.e., chitosan), which is a product of chitin
deacetylation and can also be produced from fungi under anaerobic conditions
(Rinaudo 2006; Rashid et al. 2013, 2014). Flocculation can be of two types:
bio-flocculation and auto-flocculation. Bio-flocculants employ the activities of a
single flocculating microalga which further lead to concentration of the desired
non-flocculating microalgal biomass (Shuba and Kifle 2018; Salim et al. 2010).
The availability of nutrient (mainly nitrogen and phosphorous) and physical
parameters is mainly responsible for bio-flocculation. Exopolysaccharide (EPS) is
produced by the microalgal cells in conditions of nutrition deficiency, and the EPS
further helps in the process of bio-flocculation (Rashid et al. 2014). In case of autoflocculation, the mature microalgae are exposed to sunlight for a longer period with
low concentrations of carbon dioxide. This process is beneficial for large-scale
harvesting as it leads to substantial reductions in the production costs and is
governed by the presence of light (Gouveia 2011; Milano et al. 2016).
8.3.2 Harvesting of Microalgae Using Centrifugation
Centrifugation involves separation of the particles on the basis of size and density.
The microalgae are subjected to higher centripetal acceleration which results in the
separation of the cells into a greater density and low-density area (Milano et al.
2016). For the size and type of the particles, centrifugation techniques can be of
various types such as imperforate basket, decanter, tubular, nozzle type,
multichamber, solid-ejecting type disk, and solid-retaining disk (Shelef et al. 1984;
Shuba and Kifle 2018). The size of the desired algal species determines the efficiency of the process. This method of algal separation cannot be employed on a large
scale as it is a relatively expensive (Uduman et al. 2010) and energy-consuming
technique (Heasman et al. 2000; Shuba and Kifle 2018).
8.3.3 Harvesting of Microalgae Using Filtration
Filtration is the process in which the solution containing the microalgal cells is
passed through a filter, thereby trapping the cells and allowing only the medium to
pass through. Filtration techniques can be divided into four types (i.e., macrofiltration (>10 μm), microfiltration (size of the pores ranges from 0.1 to 10 μm),
ultrafiltration (0.02–2 μm), and reverse osmosis (<0.001 μm) (Harun et al. 2010;
Shuba and Kifle 2018). Filtration techniques are limited by the high operational costs
involved and longer duration of processing (Shuba and Kifle 2018). Microalgae
production mainly employs rotary filters and micro-strainers as these are cost
effective and easy to operate owing to the fine mesh containing micro-strainers
8 Algal Biomass: Potential Renewable Feedstock for Biofuels Production – Part I
213