Effect of thermo-alkaline pretreatment and substrate inoculum ratio on methane production from dry and semi-dry anaerobic digestion of swine manure

Abstract

Obtaining biogas from biomass, such as swine manure (SM), through anaerobic digestion (AD) is an alternative renewable energy source. In this context, this work aimed to analyze the influence of thermo-alkaline pretreatment (3 % NaOH at 121 ◦C for 30 min) and the substrate/inoculum ratio (SI) on AD at 10 and 15 % total solids – TS. Moreover, mathematical modeling and molecular biology tools were used to understand better the process and obtain kinetic parameters that assist in the optimization and scaling. The experiments were conducted in batch mode at 37 ◦C with orbital shaking at 150 rpm for 90 days. SM pretreatment increased cumulative methane yield from 30 to 205 mL/gVS. Furthermore, increasing the SI ratio from 1 to 3 gVSsubstrate/gVSinoculum enhanced this yield from 205 to 268 mL/gVS, although the lag phase increased from 0 to 3.5 days. When increasing the TS content to 15 %, the accumulated methane yield decreased to 136 mL/gVS, and the lag phase increased from 0 to 13 days. Regarding the microbiological evaluation, the genera Actinobacteriota and Chloroflexi were linked to higher methane production, and the dominant genus of archaea was Methanobacterium in almost all conditions tested.