IMPROVING SPECIFIC POWER CONSUMPTION FOR MECHANICAL MIXING OF THE FEEDSTOCK IN A BIOGAS FERMENTER BY MECHANICAL DISINTEGRATION OF LIGNOCELLULOSE BIOMASS

Abstract

Lignocellulosic biomass particles in biogas fermenter batch either sediment towards vessel bottom or rise towards batch surface, where they float and form a compact thick scum. These processes have primarily the negative influence on batch homogeneity, on evenness of batch temperature field, on removal of produced biogas bubbles out of liquid batch and also on mass transfer among microorganisms. These facts result in non-effective usage of biomass energy-potential that entails in low biogas yields. Therefore, good mixing of bioreactor batch is very important in order to stabilize anaerobic digestion process. The aims of the present study were to evaluate the impact of wheat straw disintegration and its hydration on hydrodynamic behaviour and on specific power consumption for mechanical mixing of wheat straw-water suspension. Based on experimental results, it was concluded that both hydration and mechanical disintegration of lignocellulosic biomass significantly improve homogeneity and pump-ability of biomass-water batches. Wheat straw hydration itself decreases specific power consumption for batch mixing by 60 % towards untreated straw. Moreover, mechanical disintegration itself decreases specific power consumption by 50 % at least towards untreated hydrated straw.