Sorgo gigante boliviano ensilado como cultura energética na codigestão anaeróbia de dejetos bovinos de corte: viabilidade técnico‑econômica

Abstract

Anaerobic digestion (AD) of livestock residues allows for the stabilization of organic matter and the production of biogas and biofertilizer. This study evaluated the anaerobic co-digestion (CoAD) of beef cattle manure (CM) with two varieties of Bolivian giant sorghum, combining batch and semi-continuous experiments. The objective was to analyze the technical and economic feasibility of using ensiled Bolivian giant sorghum, with and without panicles, in anaerobic co-digestion with manure from confined beef cattle. In the batch experiment, five treatments were tested: CM (control treatment) and CM combined with the two sorghum varieties (with and without panicles), both fresh and ensiled, added as 30% of the reactor solids (5% total solids) under controlled temperature, for 360 days. In the semi-continuous experiment, CM was tested as mono-digestion (AMonoD) and compared with CoAD treatments using sorghum silages with and without panicles, maintaining the loading proportion of the batch experiment, but with a daily load of 3% TS and a hydraulic retention time (HRT) of 30 days, also under controlled temperature. Based on the semi-continuous results, an economic feasibility analysis was carried out. In the batch system, AMonoD, fresh sorghum without panicles (DS2), and silage without panicles (DSS2) showed the highest CH₄ yields, while silage with panicles (DSS1) accumulated volatile acids, indicating that the proportion and preparation method of sorghum are critical to avoid process instabilities. In the semi continuous experiment, DSS1 increased the specific production of biogas and CH₄ by 39.5% and 42.3%, respectively, without compromising the agronomic quality of the biofertilizer. The economic analysis, comparing AMonoD and DSS1, revealed that both scenarios are feasible for investment. However, AMonoD showed greater efficiency in capital allocation, while ACoD demonstrated higher financial returns (greater NPV) over 10 years, due to the higher initial investment required. In conclusion, ACoD with DSS1 was favorable for technical and economic feasibility, since in addition to improving the AD process, it proved to be a good investment according to the economic analysis, even though it showed lower investment efficiency compared to AMonoD.