excessive contamination would lead to lower growth and lesser productivity of
the algal systems (Hom-Diaz et al. 2015). During cultivation of algae, open ponds
are more contaminated rather than closed systems (Carney and Lane 2014).
Although the association may be beneficial in some cases where waste can be
remediated (Cavaliere et al. 2017). Algae can be infected by bacteria, viruses, and
fungi (Carney and Lane 2014). The most contaminating species which are
encountered during the biohydrogen process are the bacteria belonging to these
families, namely, Proteobacteria, Alphaproteobacteria, Bacteroidetes,
Betaproteobacteria, and Gammaproteobacteria (Carney et al. 2016; Sambles
et al. 2017; Fulbright et al. 2018). Some bacteria belonging to the genus
Alteromonas, Vibrio, Flavobacterium, Saprospira, Pseudomonas, Cytophaga,
and Pseudoalteromonas are reported to cause rot symptoms in algae (Ashen
and Goff 2000). Some bacteria are reported to be involved in the bleaching of
the Delisea pulchra (Zozaya-Valdés et al. 2017). Microbacterium sp. LB1 was
reported to cause Choricistis minor algal cell lysis (Ivanova et al. 2014). Fungal
contamination was also observed which is generally lethal to algal growth
(Hoffman et al. 2008). Contamination can be prevented by using physical
filtration (Carney and Lane 2014), change in pH and temperatures (Ras et al.
2011), and using different kinds of chemicals (Lee et al. 2002).
2. Provision of carbon dioxide and light: The minimum requirements apart from the
nutrients are the requirement of carbon dioxide and light which needs to be
provided to the system. The light entrapment efficiency and levels of carbon
dioxide in the cultivating vessel need to be increased so that proper growth and
biomass generation take place. Algae present in the outermost layers in a bioreactor are more illuminated compared to algae growing in the inner most layer.
Sometimes due to excess light the growth of the outermost layer of algae can be
inhibited due to excessive illumination causing photoinhibition. Secondly, the
effect of self-shading also reduces the light reaching the inner most layers of the
reactor. Apart from this, sulfur deprivation to the cultivating cultures is the major
factor which needs to be looked into as it induces the generation of hydrogen.
Hence, illuminating the inner and outermost layer of algae at required intensities
is a major limitation which needs to be controlled for scaling up and making the
process more economically viable. Once the cells are grown, they should be
shifted to a mode of diverting electrons for the generation of hydrogen. For this to
be achieved, a gene encoding the PSI-hydrogenase proteins needs to be manipulated so that electrons are diverted for generation of hydrogen instead of carbon
dioxide fixation to form carbohydrates.
3. Minimizing space requirements: The amount of land available is the major
constraint for the establishment of a refinery for the production of bioenergy,
and secondly, even if the land is available, it should be supported with good
transportation infrastructure (Cai et al. 2011). The major issues which need to be
addressed would be the location of the land, transportation services, topography
of the land, the presence of water resources, availability of nutrient sources, and
suitable climatic conditions (Cai et al. 2011). Pate et al. (2011) also concluded
that among all other demands for generation of algal hydrogen, land requirements
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R. Kumar et al.
the algal systems (Hom-Diaz et al. 2015). During cultivation of algae, open ponds
are more contaminated rather than closed systems (Carney and Lane 2014).
Although the association may be beneficial in some cases where waste can be
remediated (Cavaliere et al. 2017). Algae can be infected by bacteria, viruses, and
fungi (Carney and Lane 2014). The most contaminating species which are
encountered during the biohydrogen process are the bacteria belonging to these
families, namely, Proteobacteria, Alphaproteobacteria, Bacteroidetes,
Betaproteobacteria, and Gammaproteobacteria (Carney et al. 2016; Sambles
et al. 2017; Fulbright et al. 2018). Some bacteria belonging to the genus
Alteromonas, Vibrio, Flavobacterium, Saprospira, Pseudomonas, Cytophaga,
and Pseudoalteromonas are reported to cause rot symptoms in algae (Ashen
and Goff 2000). Some bacteria are reported to be involved in the bleaching of
the Delisea pulchra (Zozaya-Valdés et al. 2017). Microbacterium sp. LB1 was
reported to cause Choricistis minor algal cell lysis (Ivanova et al. 2014). Fungal
contamination was also observed which is generally lethal to algal growth
(Hoffman et al. 2008). Contamination can be prevented by using physical
filtration (Carney and Lane 2014), change in pH and temperatures (Ras et al.
2011), and using different kinds of chemicals (Lee et al. 2002).
2. Provision of carbon dioxide and light: The minimum requirements apart from the
nutrients are the requirement of carbon dioxide and light which needs to be
provided to the system. The light entrapment efficiency and levels of carbon
dioxide in the cultivating vessel need to be increased so that proper growth and
biomass generation take place. Algae present in the outermost layers in a bioreactor are more illuminated compared to algae growing in the inner most layer.
Sometimes due to excess light the growth of the outermost layer of algae can be
inhibited due to excessive illumination causing photoinhibition. Secondly, the
effect of self-shading also reduces the light reaching the inner most layers of the
reactor. Apart from this, sulfur deprivation to the cultivating cultures is the major
factor which needs to be looked into as it induces the generation of hydrogen.
Hence, illuminating the inner and outermost layer of algae at required intensities
is a major limitation which needs to be controlled for scaling up and making the
process more economically viable. Once the cells are grown, they should be
shifted to a mode of diverting electrons for the generation of hydrogen. For this to
be achieved, a gene encoding the PSI-hydrogenase proteins needs to be manipulated so that electrons are diverted for generation of hydrogen instead of carbon
dioxide fixation to form carbohydrates.
3. Minimizing space requirements: The amount of land available is the major
constraint for the establishment of a refinery for the production of bioenergy,
and secondly, even if the land is available, it should be supported with good
transportation infrastructure (Cai et al. 2011). The major issues which need to be
addressed would be the location of the land, transportation services, topography
of the land, the presence of water resources, availability of nutrient sources, and
suitable climatic conditions (Cai et al. 2011). Pate et al. (2011) also concluded
that among all other demands for generation of algal hydrogen, land requirements
206
R. Kumar et al.