The Influence of Straw Treatment by Acid Hydrolysis on Methane Production Efficiency of Agricultural Biogas Plant

Abstract

Straw is largely produce raw material which can have many different uses. One of the most promising applications is the straw usage as substrate for biogas plant feeding. However, it has to be underlined that straw is not easily degradable material because of higher content of lignocellulose compounds. That is why in order to make straw more susceptible for anaerobic digestion process, it has to pass by some pre-treatments (mechanical, thermal, biological etc.). The aim of this study was to estimate the influence of straw treatment by acid hydrolysis (AH) on methane production efficiency in the anaerobic digestion process. In order to increase the digestibility of straw, whole material was also pre-treated by extrusion process. The methane productivity was tested under standard German methodology DIN 38 414/S8 in Ecotechnologies Laboratory (ET) at Institute of Biosystems Engineering. ET, with 250 different fermenters, is the biggest Polish biogas laboratory. The results have shown that acid hydrolysis (happened in pH<4.5 for 48 hours) strongly influenced on methane productivity growth. Extruded straw without acid hydrolysis produced 186.09 m³/Mg of Fresh Mass (224.23 m³/Mg of Volatile Solids) while straw after treatment with acid hydrolysis reached 248.17 Mg of FM (279.43 m³/Mg of VS). Result obtained after acid hydrolysis has showed the growth by 33.4% comparing to treatment without AH. We found also the growth of methane content in produced biogas. The biogas obtained from straw fermented without acid hydrolysis had 49.07% of CH₄ while after AH the CH₄ content reached 52% (almost 6% more). This result shows clearly that application of acid hydrolysis to real scale biogas plant can clearly decrease the annual consumption of straw reaching by app. 1500 Mg for the installation class 500 kW of electric power.