Pre-treatment techniques used for anaerobic digestion of algae

Biogas is one essential renewable energy source which can replace natural gas after its purification. Biogas is produced from different biomass materials though the anaerobic digestion process. Algae are considered as a feedstock for biogas production, which does not compete with food production and does not need large areas of arable land and fresh water resources. In order to improve the biogas production, pre-treatment techniques have been investigated to disrupt the structure of algae increasing the availability of substrates. In this paper, a review of these pre-treatment methods is presented. Pre-treatment methods are categorised into mechanical, ultrasound and micro-wave, thermal, chemical, biological and combined groups. The effect of the application of each of the studied techniques on the biogas yield and the energy balance is discussed. A comparison of the used techniques is carried out, and discussed.