Co-digestão anaeróbia entre dejeto bovino e bagaço de cana-de-açúcar pré-tratado com solução de NAOH em regime semi-contínuo

Abstract

Sugarcane production stands out in the world, and Brazil’s sugarcane production in 2021/22 is estimated to be628.1 million tons. However, after processing, 28% of waste is generated in the form of sugarcane bagasse (SB), which is a lignocellulosic waste with low degradability, which limits its use by biologicaltreatment processes. Another type of waste produced in large quantities is cow manure(CM), which comes from cattle farms. Brazil has about 213 million cattle. CMis a suitable waste that is conducive to its use in biological treatment.This study aimed to evaluate the impact of the combination of CMand SBpretreated with 5% NaOH as substrates in anaerobic co-digestion to balance operational parameters (C/N ratio, pH, alkalinity, and solids content) in a semi-continuous reactor. CMand SBsamples were collected, with a fraction of SBpretreated with 5% NaOH (SBP). The batchassay to determinethemethanogenic potential was performed in 125 mL glass vials and a 2:1 inoculum/substrate ratio. The anaerobic co-digestion took place in a reactor with a volume of 5 L in a semi-continuous regime and different volumetric organic loads (VOC), being 0.40 (phase 1), 1.00 (phase 2), and 2.00 g VS Lreactor-1 d-1(phase 3). The hydraulic retention time (HRT) was 20 days in phase 1 and 40 days in phases 2 and 3. The methanogenic potential obtained was 5.86, 9.44, and 13.63 LCH4kg VS-1for CM, SB, and SBP, respectively. Biogas productivity during mono-digestion with CM (phase 1) was 0.17 LbiogasLreactor-1d-1, while co-digestion with SBand SBP (phase 2) resulted in productivity of 0.45 and 0.49 LbiogasLreactor-1d-1. The productivity during the co-digestion of CMwith SBand SBP (phase 3) was 0.75 and 0.64 LbiogasLreactor-1d-1. The volume of methane generated during mono-digestion with CM (phase 1) was 284 LCH4kg VS-1, while co-digestion with SBand SBP (phase 2) resulted in productivity of 245 and 266 LCH4kg VS-1. The volume of methane generated during the co-digestion of CMwith SBand SBP (phase 3) was 198 and 173 LCH4kg VS-1. The CH4concentrations during phases 1, 2 and 3 were 64.11%, 54.59% and 53.26% without pretreatment and 63.83%, 54.32% and 54.20% with pretreatment, respectively. Comparing phases 2 and 3, there is an increase of 67% in biogas productivity in co-digestion with CMand SBwithout pretreatment and an increase of only 31% using pretreated SBin phase 3. Thus, defining as the best workingcondition was co-digestion with CMand SBP during phase 2 when the VOC was 1.00 g VS Lreactor-1 d-1, with an increase of 8.9% in biogas productivity and 8.6% by volume of methane when compared to co-digestion of CMand SBwithout pretreatment.