Viability of production of biodiesel and biogas from microalgae: A net energy analysis

Recently, there has been a growing interest in finding alternative forms of energy. This is mostly driven by increasing prices of oil, concerns over greenhouse gases emission from fossil fuels, and some form of government subsidies. One of the alternatives which has been gaining much public and scientific attention is biofuel, a type of fuel which is derived in some way from biological materials of living or recently living organisms. This includes biodiesel, made from vegetable oil, animal fats, or recycled greases that have been chemically modified so that its physical properties resemble those of diesel fuel. It is usually used as diesel additives to reduce levels of particulates, carbon monoxide emission, and hydrocarbons from diesel-powered vehicles.

Although environmentally friendly, the use of these alternative forms of energy has not been without criticism. One of the issues is the associated consumption of water and land resources which could have been used for the production of food. Thus, to help policy makers decide on which is more advantageous, it is necessary to have a quantitative assessment of the viability of various potential systems for producing biofuels. One of the simplest, and oldest, approaches is net energy analysis. In simple terms, the analysis looks at the net energy produced by the system and compares it to the energy inputs required to produce the fuel.

In a recent paper entitled “Net energy analysis of the production of biodiesel and biogas from the microalgae: Haematococcus pluvialis and Nannochloropsis” (Applied Energy, vol. 88, 2011), Drs. Luis Razon and Raymond Tan from De La Salle University performed a net energy analysis of production systems based on two types of oil-bearing algae, the Haematococcus pluvialis and Nannochloropsis. Their calculations showed that the energy ratios, based on the technology being proposed for commercial operation of such systems, fall short of thermodynamic break-even, even if highly optimistic assumptions about the operations were made (i.e., assuming that the residual algal biomass is used to produce biogas, which later can be used to produce eletricity and process steam). The problem mainly stems from the large energy demand of separating the valuable oil from water and from the rest of the algal biomass.

For the analyzed algal system to be commercially viable, the authors noted that significant innovations in developing less energy-intensive technique in separating oil from algal biomass is needed. Alternatively, they suggested that multiple products from the algae could also be considered to spread the energy usage allocations over a wider range of useful products. For instance, the remaining algal biomass after oil extraction could be used to make a co-saleable product or recycled back into the process to offset other costs for the entire process.

Although the production of algal biodiesel has been demonstrated in the lab, much work still needs to be done to make it thermodynamically viable. It may still take some time and more effort before biodiesel can be put to actual production – grown outdoors, under real climate conditions that can be used on a much larger scale, and compete with the fuels derived from petroleum supplies.

Details of the study can be read in “Net energy analysis of the production of biodiesel and biogas from the microalgae: Haematococcus pluvialis and Nannochloropsis” by Luis Razon and Raymond Tan, Applied Energy 88 (2011).