Assessment of hyper-thermophilic/mesophilic temperature-phased anaerobic co-digestion of crude glycerine and sewage sludge

Temperature-phased anaerobic digestion is considered to be a valuable alternative to achieve new challenges in Wastewater Treatment Plants (WWTP) and biomethane production. This system makes it possible to remove/separate gas toxicants (mainly H2S) in the first phase reactor gas flow (hydrolysis reactor) and improve the profitability of the upgraded biogas flow obtained in the second phase reactor (methanogenic) (i.e. injection into the natural gas grid, vehicle fuel, biogas fuel cell or solid oxide fuel cell quality). The purpose of this study is to investigate the temperature-phased (hyper-thermophilic/mesophilic) anaerobic co-digestion of crude glycerine (CG) and sewage sludge (SS) in semi-continuous reactors. Specifically, to determine the effect of temperature-phased in: i) the quantity and quality of biogas production and ii) the effect on dewatering properties of the digestate obtained in comparison with conventional mesophilic systems. Results show that with a feed composed of 95% SS and 5% CG, the hyper-thermophilic/mesophilic system presents an increase in VSrem (Volatile solids removed) of 5.6% in comparison to the conventional mesophilic system. In reference to biogas quality, the hyperthermophilic/mesophilic system presents a H2S content decrease of >67% in comparison to the control mesophilic reactor. Moreover, an energy balance shows that the proposed system reaches up to 68% extra heat production in comparison to the conventional mesophilic anaerobic system.