CO2 Absorption by Using a low-cost Solvent: Biogas Slurry Produced by Anaerobic Digestion of Biomass

Abstract

Due to the characteristics of low cost, abundance in nutrients used beneficially as a liquid fertilizer and weak alkalinity of the biogas slurry came from the anaerobic digestion of biomass, an investigation was performed in this study to assess the feasibility of CO2 absorption by using the biogas slurry and the application of CO2-rich biogas slurry into horticultural or agricultural use. Equilibrium CO2 loading of biogas slurry was adopted to assess the CO2 absorption performance and germination index (GI) of Chinese cabbage seeds in CO2-rich biogas slurry was selected to evaluate its phytotoxicity directly related to the application of biogas slurry. Raw biogas slurry can be used to absorb CO2 to reach the maximum CO2 loading with 0.13 molCO2/L. However, the highest equilibrium CO2 loading and lowest phytotoxicity of CO2-rich biogas slurry can not be obtained simultaneously at the same temperature, which means that a compromise on absorption temperature should be made. In addition, effect of additives like potassium glycinate (PG), monoethanolamine (MEA), potassium hydroxide (KOH) and aqueous ammonia (AA) on improvement of CO2 absorption and phytotoxicity of CO2-rich biogas slurry were also experimented. Results showed that organic additives can get the higher CO2 absorption loading but lower GI values compared to inorganic additives. In order to obtain lowest phytotoxicity of CO2-rich biogas slurry, concentration of additives should be limited, and inorganic additives can adopt the higher concentration than organic additives, implying that inorganic additives may probably be more suitable than organic additives to improve the comprehensive CO2 absorption performance of biogas slurry.