Integrated Waste Treatment System Combining Biogas Technology and Pyrolysis

Abstract

Anaerobic digestion allows combining waste treatment and energy production from biomass, but lignin and lignocellulosic fractions, which typically make up 10-25 wt. % of biomass can’t be converted efficiently. Another treatment pathway for bio-waste (including lignocellulosic biomass) are thermochemical processes such as gasification and pyrolysis which prevent technical and environmental issues related to solid biomass combustion and generate gas as an energy carrier. In this paper the method of low-temperature pyrolysis (torrefaction) of sewage sludge which is formed during anaerobic digestion is investigated. The torrefaction temperature is 220 °C and 300 °C. The data on mass balances of torrefaction process, specific volume yield, composition and calorific value of gas mixture formed in torrefaction, characteristics of torrefied material (mass loss, proximate and ultimate composition, calorific value, hygroscopicity limit) are presented. The effect of the initial sludge ash content on the calorific value of the torrefied material is calculated. Based on the obtained data the torrefaction process conditions of sewage sludge after anaerobic digestion are determined.