Abstract
Marine algae offer a vast renewable energy resource for countries throughout the world that have available coastline. Along the Romanian shore of the Black Sea, the phenomenon of seaweed development took great proportions in 2008. Thus, the National Administration “Romanian Waters” reported a quantity of 25.040 m3 of collected algae that were washed up on beaches in the sector Cap Midia – Vama Veche. Huge masses of algae are accumulated on the beaches by winds and currents movements. Accordingly, the quality of beaches is declined, affecting tourism and environment.
Marine algae consist of polysaccharides with zero lignin and low cellulose content. Considering this, anaerobic digestion of marine algae biomass to obtain renewable energy (methane) appears as an attractive possibility. The resulting co-product is rich in N, P, K and S and other nutrients, and can be used by local farmers as a fertilizer to improve soil quality. The CO2 resulting from the process is used in a small scale photobioreactor to cultivate microalgae, that provides the biomass for biodiesel production.
This paper discusses the possibilities of combining the depollution of unwanted algae with biogas production and biogas and natural gas fueled engine tests. Biogas can be used to replace natural gas, to replace petrol or to produce electricity and heat. The microorganisms used in the process of anaerobic digestion can decompose almost any organic material, and this makes possible the production of energy from different types of waste materials such as algae, manure from local chicken farms, and even the glycerin resulting from the biodiesel production from microalgae.
The biogas that comes out of the reactor is a mixture of several gases, from which we mention: approximately 40 to 75 % methane, 25-55% carbon dioxide, and approximately 2% other gases. The gas is combustible and can be used to produce heat or electricity without advanced cleaning. Moreover, it can be upgraded to 97-100 percent methane, making it an excellent replacement for fossil natural gas as a vehicle. Biogas can be used for fuelling Diesel engines that function with dual fuel combustion procedure or for spark ignition engines with compression ratio of 13÷14. The inferior calorific power of biogas is lower than 30 MJ/m3, therefore, in order to increase the specific energy is necessary to supercharge the engine.
Keywords: algae, biogas, natural gas, anaerobic digestion