Marine seaweeds are attracting great attention all over the world as the main source of 3rd generation biofuels. One of the sources of bioethanol production (the most widely used biofuel in the world - in 2017 its production amounted to 106 billion liters) can be brown seaweeds.
To date, research on the production of bioethanol from brown algae is being carried out in the USA, Norway, the Republic of Korea, Ireland, etc. Russia also has a high potential for the production of biofuel from brown seaweeds. The most common type of brown seaweeds in the Russian seas is kelp, the commercial stock of which can exceed 2 million tons.
The aim of the work is to analyze the possibilities of producing bioethanol from brown seaweeds from the point of view of feedstocks preliminary processing, technological scheme, the use of strains of microorganisms for the fermentation process, identifying the advantages and disadvantages of the obtained bioethanol and assessing the global warming potential.
It was revealed that the technological scheme for the production of bioethanol from brown seaweeds is similar to the production of bioethanol from lignocellulosic biomass with the difference that instead of lignocellulose, seaweeds contain alginate, mannitol, fucoidan and laminarin. Alginates can account for up to 50% of the carbohydrate fraction in brown seaweeds and are considered essential for maximum bioethanol recovery during yeast fermentation.
The most commonly used hydrolysis method is thermal hydrolysis using dilute acids, the most effective is enzymatic. However, each of these methods has serious drawbacks that do not allow the methods to be used together to increase the yield of bioethanol.
For fermentation of sugars of brown seaweeds, it is preferable to use strains of microorganisms Saccharomyces cerevisiae or Escherichia coli. These organisms are widespread, they have a low cost, and the bioethanol yield of kelp is practically the same as for terrestrial biomass. Thus, the mass yield of bioethanol during fermentation of S. cerevisiae was 0.42 g of ethanol per 1 g of reducing sugar, for corn, the yield of bioethanol is 0.48 g, and for waste paper - 0.39 g per 1 g of reducing sugar. The yield of bioethanol with E. coli was 0.4 g per 1 reducing sugar. However, the possibility of using marine microorganisms, as having a common developmental environment with seaweeds, is being considered and, probably, they will allow the release of a larger amount of bioethanol than terrestrial strains of microorganisms.
Potential difficulties for the production of bioethanol from brown seaweeds can be collection of seaweeds (both manual and mechanical), transportation of seaweeds to the processing plant, preliminary seaweeds preparation for the production process (drying, grinding), energy costs and materials to maintain the desired level of the process. Another problem is the uneconomical collection of seaweeds 1-3 months a year (in Russia, the collection occurs from May to October) and the distillation of ethanol from the fermentation broth.
The main advantages derived from the use of seaweed compared to terrestrial lignocellulosic biomass (2nd generation) include the lack of agricultural land use and the lack of resources such as fertilizers, pesticides and water. CO2 between the production and combustion of bioethanol from algae and the absorption of CO2 by algae during photosynthesis. It is known that algae have a much higher photosynthetic efficiency (6–8%) than land biomass (2%).
Bioethanol derived from brown seaweeds and land-based feedstocks can have significantly different global warming potentials (GWPs), since the GWP of bioethanol is significantly influenced by biomass cultivation and bioethanol production. Bioethanol from seaweed has no carbon debt as no crop area is used for its production. At the same time, the GWP of bioethanol from brown seaweeds is 396 kg CO2-eq / year, which is less than the GWP of bioethanol from corn grain (421 kg CO2-eq / year), corn hay (307 kg CO2-eq / year) or millet (236 kg CO2 -eq / year).
Considering all the difficulties and potentials of bioethanol production from brown seaweeds, over time, it is possible to transfer research from laboratories to industry and further construction of the first seaweedы plants producing bioethanol.
|Affiliation of speaker||RUDN University|
|Position of speaker||postgraduate student|
|Publication||Impact Factor journals|