2.4.3. Bioethanol by Photofermentation

Algae can generate bioethanol directly through the photosynthetic process, which is referred to as thephotofermentative or photanol method [105,107]. Photofermentation is a technology whichis gaining popularity, especially after the announcement of industrial operations that will use modified algae to create bioethanol directly [108]. The photofermentative approach is a natural technique to transform sunlight into fermentation products via a highly efficient metabolic pathway [109].

There has been a recent surge in the number of compounds such as ethanol produced by modified cyanobacterias photofermentation metabolism. This has been made possible by the information gained from traditional fermentation which is carried out by *Escherichia coli* and *Sacchromyces cerevisiae*, which have been genetically modified to generate biofuels such as bioethanol. Algae is a varied group of creatures with a lot of unwrapped genetic potential. Although microalgae are morphologically identical single-celled photosynthetic organisms, the functional genetic diversity is relatively high, as evidenced by the number of unique genes found among distinct species. This genetic diversity is being used to create novel algae strains for the production of biofuels [110].

The use of carbon dioxide and sunlight for carbon uptake and conversion into organic molecules is the most fundamental feature of photosynthesis. Thus, it can be understood that carbon dioxide and light are the two most important variables in increasing production of bioethanol. The photosynthetic efficiency of microalgae ranges from 6–10% of the incident light, whereas in higher plants, the efficiency is just 1 or 2 percent [111,112]. The refinement of geometry, the study of optimal growing circumstances, and the capacity of the photosynthetic machinery to absorb light all contribute to the desired result. In general, microalgae are suitable for the generation of third generation biofuels such as ethanol. Similar to biogas from microalgae, the ethanol production is determined by the pretreatment and the algal strain used [113].
