Benefits in the valorization of sewage sludge and wine vinasse via a two-stage acidogenic-thermophilic and methanogenic-mesophilic system based on the Circular Economy concept.

Abstract

Anaerobic digestion can be considered as a promising solution to solve the problems, increase of energy demand and waste generation, caused by the increasing population growth. The main objective of this work was to study anaerobic codigestion of sewage sludge and wine vinasse in a two-stage acidogenic-thermophilic and methanogenic-mesophilic system within the framework of the circular economy. This system was compared with anaerobic codigestion in single-stage reactors (thermophilic and mesophilic conditions) in order to assess the potential benefits of a two-stage system in terms of energy production and pathogenic microorganisms removal. Hydrogen was only produced in the first stage of the two-stage system (22.90 mL H2/gVSadded). Both the highest specific methane production (212.56 mL CH4/gVSadded) and electricity generation were obtained in the second stage of the two-stage system. The electrical energy generated was estimated at 14.03 kWh/tonne fed, which represents 5 % of the total energy used by Guadalete wastewater treatment plant (SW Spain). All the systems achieved lower values of E. coli and Salmonella than those stipulated by legislation regarding Class A biosolids quality, therefore digestate can be used as fertilizer