called
pyruvate–ferredoxin–oxidoreductase
pathway
which
suppresses
Fe-hydrogenase activity (Gong et al. 2008; Kumar and Das 2000; Lee et al. 2002).
Lee et al. (2007) explained that pH affects the activity of hydrogenase and nitrogenase. He observed that at a pH of 5.0, the enzyme gets inactivated. Kosourov et al.
(2007) reported higher rates of hydrogen gas at pH 7.7 which decreased at pH 6.5
during cultivation of sulfur-deprived cultures of the green algae Chlamydomonas
reinhardtii. Goldman et al. (1982) reported that marine algae requirements for pH
are different from those of fresh algae and the levels of nitrate are major factors
affecting pH. Antal et al. (2003) observed the optimal pH of 6.0–7.5 was required for
hydrogen generation in Gloeocapsa alpicola. Biosurfactant and microwave were
used for sludge treatment at basic pH by Banu et al. (2018b). Kumar et al. (2019)
used microwave for pretreatment of biofuel production. Ionizing radiation under
acidic conditions was used as a pretreatment method for enhancing biohydrogen
(Yang and Wang 2018). Temperature is a key factor that is responsible for the
growth of microalgae, as it influences rate of photosynthesis. Bechet et al. (2017)
reported that optimum temperature enhances algal growth, but beyond this algal
growth is retarded. Temperature causes a downturn in the action of ribulose-1,5bisphosphate (Rubisco) affecting photosynthesis, and its activity increases with a
rise in temperature up to an acceptable level and then reduces (Salvucci and CraftsBrandner 2004). At lower temperatures, algal enzymatic reactions become slower
causing oxidative stress. Algae may produce more of a given enzyme, or optimal
enzymatic activity may be shifted toward lower temperature to compensate for
slower enzymatic reactions (Morgan-Kiss et al. 2006). Singh and Singh (2015)
observed that the favorable temperature range required for the growth of most
algal species is 20–30
C. The importance of temperature in growth and survival
of algal systems was described by Ras et al. (2011). Banu et al. (2018a) have
investigated the use of microwave for disintegration of waste. Ultrasonics and
microwave were combinedly also used for biomass disintegration (Kavitha et al.
2018). Temperature range of 20–32
C was found to be optimum for the growth of
Chlamydomonas reinhardtii (Schroda 2004). Ibrahim et al. (2020) have conducted
hydrothermal liquefaction (HTL) experiments on microalgae Galdieria sulphuraria
in a membrane reactor using Pd 77 Ag 23 hydrogen-selective membrane. This membrane was reported to recover hydrogen and aid in the conversion of biochar to fuels.
Zhang et al. (2020) have studied the alkaline and thermal treatment of brown
seaweed for production of pure biohydrogen with reduced carbon dioxide formation.
They have observed that Ni/ZrO 2 catalyst improved the secondary hydrogen generation through steam methane reforming and water-gas shift reactions. Muñoz-Páez
et al. (2020) have studied acid agave bagasse hydrolyzates as substrate for hydrogen
production. The effect of increasing concentrations of acid hydrolyzates from Agave
on hydrogen production and stability of granular biomass in an expanded granular
sludge bed (EGSB) reactor and suspended biomass in an anaerobic sequencing batch
reactor (AnSBR) fed with acid hydrolyzates were investigated. The hydrogen
production from acid agave hydrolyzates was higher for EGSB reactor than for the
AnSBR, but was less stable. Rebello et al. (2020) have performed life cycle analysis
of various pretreatment strategies used in anaerobic digestion process for biofuel
198
R. Kumar et al.
pyruvate–ferredoxin–oxidoreductase
pathway
which
suppresses
Fe-hydrogenase activity (Gong et al. 2008; Kumar and Das 2000; Lee et al. 2002).
Lee et al. (2007) explained that pH affects the activity of hydrogenase and nitrogenase. He observed that at a pH of 5.0, the enzyme gets inactivated. Kosourov et al.
(2007) reported higher rates of hydrogen gas at pH 7.7 which decreased at pH 6.5
during cultivation of sulfur-deprived cultures of the green algae Chlamydomonas
reinhardtii. Goldman et al. (1982) reported that marine algae requirements for pH
are different from those of fresh algae and the levels of nitrate are major factors
affecting pH. Antal et al. (2003) observed the optimal pH of 6.0–7.5 was required for
hydrogen generation in Gloeocapsa alpicola. Biosurfactant and microwave were
used for sludge treatment at basic pH by Banu et al. (2018b). Kumar et al. (2019)
used microwave for pretreatment of biofuel production. Ionizing radiation under
acidic conditions was used as a pretreatment method for enhancing biohydrogen
(Yang and Wang 2018). Temperature is a key factor that is responsible for the
growth of microalgae, as it influences rate of photosynthesis. Bechet et al. (2017)
reported that optimum temperature enhances algal growth, but beyond this algal
growth is retarded. Temperature causes a downturn in the action of ribulose-1,5bisphosphate (Rubisco) affecting photosynthesis, and its activity increases with a
rise in temperature up to an acceptable level and then reduces (Salvucci and CraftsBrandner 2004). At lower temperatures, algal enzymatic reactions become slower
causing oxidative stress. Algae may produce more of a given enzyme, or optimal
enzymatic activity may be shifted toward lower temperature to compensate for
slower enzymatic reactions (Morgan-Kiss et al. 2006). Singh and Singh (2015)
observed that the favorable temperature range required for the growth of most
algal species is 20–30
C. The importance of temperature in growth and survival
of algal systems was described by Ras et al. (2011). Banu et al. (2018a) have
investigated the use of microwave for disintegration of waste. Ultrasonics and
microwave were combinedly also used for biomass disintegration (Kavitha et al.
2018). Temperature range of 20–32
C was found to be optimum for the growth of
Chlamydomonas reinhardtii (Schroda 2004). Ibrahim et al. (2020) have conducted
hydrothermal liquefaction (HTL) experiments on microalgae Galdieria sulphuraria
in a membrane reactor using Pd 77 Ag 23 hydrogen-selective membrane. This membrane was reported to recover hydrogen and aid in the conversion of biochar to fuels.
Zhang et al. (2020) have studied the alkaline and thermal treatment of brown
seaweed for production of pure biohydrogen with reduced carbon dioxide formation.
They have observed that Ni/ZrO 2 catalyst improved the secondary hydrogen generation through steam methane reforming and water-gas shift reactions. Muñoz-Páez
et al. (2020) have studied acid agave bagasse hydrolyzates as substrate for hydrogen
production. The effect of increasing concentrations of acid hydrolyzates from Agave
on hydrogen production and stability of granular biomass in an expanded granular
sludge bed (EGSB) reactor and suspended biomass in an anaerobic sequencing batch
reactor (AnSBR) fed with acid hydrolyzates were investigated. The hydrogen
production from acid agave hydrolyzates was higher for EGSB reactor than for the
AnSBR, but was less stable. Rebello et al. (2020) have performed life cycle analysis
of various pretreatment strategies used in anaerobic digestion process for biofuel
198
R. Kumar et al.