**4.2 Seasonal challenges for biomass yield**

Microalgal outdoor cultivation is subjected to diurnal and seasonal variations in temperature, solar irradiance, photoperiod and humidity, which in turn affect physiological responses and biomass yield. For instance, light is essential for photosynthesis, but excess light leads to photoinhibition, oxidative stress, damage of proteins

**463**

*Recent Advances in Algal Biomass Production DOI: http://dx.doi.org/10.5772/intechopen.94218*

irradiance (2035 μmol/m<sup>2</sup>

ranged from 4 ± 0 g/m<sup>2</sup>

irradiance was 15.9 MJ/m2

**4.3 Recycling nutrients**

recycling post biomass conversion process.

m2

irradiance was 300 ± 157 w/m<sup>2</sup>

was 23°C and irradiance was 468 ± 292 w/m2

Nov, when both temperature and irradiance were low [75].

involved in electron transfer and in turn affects CO2 fixation in photosynthesis and biomass yield. Similarly, low light also reduces photosynthetic efficiency and thus biomass yield [70]. O2 buildup in culture, which increases from morning till noon also can inhibit growth if O2 concentration is more than 20 mg/L [71]. Temperature is another important factor, which is affected by light intensity, photoperiod and season. Optimal growth temperature for majority of algal strains lies between 20 and 25°C. However, temperatures above 35°C increases photorespiration, affects nutrient availability, increases the concentration of NH3 in the medium, decreases CO2 solubility and increases evaporation losses leading to salinity variations [71, 72]. The impact of these environmental variations is significant on biomass productivity but there are very few reports on quantification of effects of seasonal variations on algae biomass productivities in large scale production systems. For instance, growth performance of *Scenedesmus obtusiusculus* was studied in airlift extended loop photobioreactor operated in outdoor conditions. Yearlong study revealed that biomass productivity was maximum during spring (0.29 g/L/d) where

by autumn (0.22 g/L/d), summer (0.21 g/L/d) and winter (0.19 g/L/d). However, biomass productivity was much higher (0.97 g/L/d)under optimum laboratory conditions [73]. In another study, *Scenedesmus* sp. cultivated in outdoor pilot scale raceway ponds for waste water treatment resulted in biomass productivities, which

and 17 ± 1 g/m<sup>2</sup>

sp. namely, *Chlorella vulgaris*, *Botryococcus braunii*, *Chlamydomonas reinhardtii*, *Euglena gracilis* and *Nannochloropsis oculata* were evaluated in open bioreactors with 30 L capacity in green house conditions. Experiments were conducted from March to April, June to July and Oct to Nov to evaluate growth response of these microalgae with seasonal variations. *C. vulgaris, B. braunii* resulted in highest growth during month of March and April when average temperature was 28.5°C and

the month of June when average temperature was 36.1°C and irradiance was 6.6 MJ/

It is clear from these studies that seasonal variations play significant role in microalgal biomass production and it is important to note that the effect of the environmental changes is strain specific. As complete control of abiotic factors is not possible at large scale outdoor cultivation complete, careful strains selection and adoption of right cultivation practices ensuring effective light and nutrient

Optimal microalgal growth relies on continuous and adequate supply of nutrients (nitrogen, phosphorous, carbon, potassium, trace elements and water) and sunlight. Nutrient input can be in the form of fertilizer and waste-water streams. Nutrient supply in the form of fertilizers can incur significant cost to the cultivation and is also a competition to fertilizer for agriculture [65]. Therefore, it is important to minimize nutrient losses during cultivation. One way is through stoichiometrically balanced nutrient management to minimize nutrient losses during cultivation [76] and other ways are by recycling of spent medium (water recycle) and nutrient

utilization can help in tackling the seasonal variability to some extent.

/d. while, *E. gracilis* grew comparably during March and June months. In general growth response was low for all five microalgae tested during the month of Oct and

/s) and temperature (11–47°C) were highest, followed

/d in December when average temperature was 13°C and

/d. Whereas, *C. reinhardtii* and *N. oculata* grew best in

/d in July when average temperature

[74]. In another study, five microalgal

**Figure 3.** *Factors affecting algae biomass production.*

#### *Recent Advances in Algal Biomass Production DOI: http://dx.doi.org/10.5772/intechopen.94218*

*Biotechnological Applications of Biomass*

**4.1 Criteria for siting production facilities**

Cultivation is a vital starting point in algae biomass production and hence choice of production site, strain and cultivation system are very crucial in attaining high biomass productivity. In addition, seasonal influence, crop losses, harvesting processes and nutrient and water recycling are some of the primary governing factors influencing biomass yield and production economics (**Figure 3**). The following section will cover the recent advances in some of the key areas mentioned above.

First and critical aspect in establishing successful algae cultivation facility is selection of suitable cultivation site. Site selection is quite a complex task and involves considerable attention on terrain, land costs, sunlight availability, seasonal temperatures, proximity to CO2 and water sources, well-connected transport system, power supply etc. Economical, non-arable flat land with constructible soil is needed for raceway pond installation. Availability of adequate acreage is also an important criterion, as algal cultivation facility should be of scale where production of algae meets economics [64]. Another very important aspect in algal cultivation is availability of enough sunlight. Therefore, it is important to select a geographic location, which is less prone to seasonal variations, receives less rainfall and is climatically suitable to the strain being cultivated. For example, low altitude regions having warm climate and average solar radiation availability for 250 h/ month are considered as good sites climatically [65]. CO2 is regarded as free of cost, but its transportation can add substantial cost to the algae production if the CO2 generation facility is far from the cultivation site [66]. Water availability is another important criterion. Proximity to sea in case of marine microalgae cultivation and assessment of water scarcity footprint in the region in case of fresh water algae cultivation is essential while selecting a site [67]. Various site selection models that consider parameters, such as soil properties, water availability, growth rate, infrastructure proximity etc. have been reported for identification of a suitable site for algae cultivation [68, 69]. These models can serve as useful tools for algae produc-

Microalgal outdoor cultivation is subjected to diurnal and seasonal variations in temperature, solar irradiance, photoperiod and humidity, which in turn affect physiological responses and biomass yield. For instance, light is essential for photosynthesis, but excess light leads to photoinhibition, oxidative stress, damage of proteins

**4. Cultivation**

tion site selection.

**4.2 Seasonal challenges for biomass yield**

**462**

**Figure 3.**

*Factors affecting algae biomass production.*

involved in electron transfer and in turn affects CO2 fixation in photosynthesis and biomass yield. Similarly, low light also reduces photosynthetic efficiency and thus biomass yield [70]. O2 buildup in culture, which increases from morning till noon also can inhibit growth if O2 concentration is more than 20 mg/L [71]. Temperature is another important factor, which is affected by light intensity, photoperiod and season. Optimal growth temperature for majority of algal strains lies between 20 and 25°C. However, temperatures above 35°C increases photorespiration, affects nutrient availability, increases the concentration of NH3 in the medium, decreases CO2 solubility and increases evaporation losses leading to salinity variations [71, 72]. The impact of these environmental variations is significant on biomass productivity but there are very few reports on quantification of effects of seasonal variations on algae biomass productivities in large scale production systems. For instance, growth performance of *Scenedesmus obtusiusculus* was studied in airlift extended loop photobioreactor operated in outdoor conditions. Yearlong study revealed that biomass productivity was maximum during spring (0.29 g/L/d) where irradiance (2035 μmol/m<sup>2</sup> /s) and temperature (11–47°C) were highest, followed by autumn (0.22 g/L/d), summer (0.21 g/L/d) and winter (0.19 g/L/d). However, biomass productivity was much higher (0.97 g/L/d)under optimum laboratory conditions [73]. In another study, *Scenedesmus* sp. cultivated in outdoor pilot scale raceway ponds for waste water treatment resulted in biomass productivities, which ranged from 4 ± 0 g/m<sup>2</sup> /d in December when average temperature was 13°C and irradiance was 300 ± 157 w/m<sup>2</sup> and 17 ± 1 g/m<sup>2</sup> /d in July when average temperature was 23°C and irradiance was 468 ± 292 w/m2 [74]. In another study, five microalgal sp. namely, *Chlorella vulgaris*, *Botryococcus braunii*, *Chlamydomonas reinhardtii*, *Euglena gracilis* and *Nannochloropsis oculata* were evaluated in open bioreactors with 30 L capacity in green house conditions. Experiments were conducted from March to April, June to July and Oct to Nov to evaluate growth response of these microalgae with seasonal variations. *C. vulgaris, B. braunii* resulted in highest growth during month of March and April when average temperature was 28.5°C and irradiance was 15.9 MJ/m2 /d. Whereas, *C. reinhardtii* and *N. oculata* grew best in the month of June when average temperature was 36.1°C and irradiance was 6.6 MJ/ m2 /d. while, *E. gracilis* grew comparably during March and June months. In general growth response was low for all five microalgae tested during the month of Oct and Nov, when both temperature and irradiance were low [75].

It is clear from these studies that seasonal variations play significant role in microalgal biomass production and it is important to note that the effect of the environmental changes is strain specific. As complete control of abiotic factors is not possible at large scale outdoor cultivation complete, careful strains selection and adoption of right cultivation practices ensuring effective light and nutrient utilization can help in tackling the seasonal variability to some extent.
