Biological purification processes for biogas using algae cultures: A review

Bioenergy is a type of renewable energy made from biological sources including algae, trees, or waste from agriculture, wood processing, food materials, and municipalities. Currently, the uses of renewable fuels (bioethanol, biodiesel, biogas and hydrogen) are increased in the transport sector worldwide. From an environmental and resource-efficiency perspective biogas has several advantages in comparison to other biofuels. The main components of biogas are methane (CH4) and carbon dioxide (CO2), but usually biogas also contains hydrogen sulphide (H2S) and other sulphur compounds, water, other trace gas compounds and other impurities. Purification and upgrading of the gas is necessary because purified biogas provides reductions in green house gas emissions as well as several other environmental benefits when used as a vehicle fuel. Reducing CO2 and H2S content will significantly improve the quality of biogas. Various technologies have been developed and available for biogas impurity removal; these include absorption by chemical solvents, physical absorption, cryogenic separation, membrane separation and biological or chemical methods. Since physiochemical methods of removal are expensive and environmentally hazardous, and biological processes are environmentally friendly and feasible. Furthermore, algae are abundant and omnipresent. Biogas purification using algae involved the use of algae’s photosynthetic ability in the removal of the impurities present in biogas. This review is aimed at presenting the algal characteristics, scientific approach, gather and clearly explain the main methods used to clean and purify biogas, increasing the calorific value of biogas and making this gas with characteristics closest as possible to natural gas through algae biological purification processes.