Pré-tratamento alcalino da cama de bovinocultura leiteira para produção de biogás

Abstract

Energy sustainability is a strategic priority for many developed and developing countries, especially with investments in renewable energy. In this scenario, biogas has been standing out, as it promotes the growth and strengthening of the agricultural production chain. However, some biomasses, despite their potential for biogas production, require pretreatment, which is the process to convert more complex organic compounds into simpler organic compounds. This process can break the lignocellulosic structure of substrates such as corn straw, rice husks, grasses, poultry, cattle litter, among others, so that cellulose and hemicellulose can be degraded via anaerobic digestion. Thus, this work sought to solve a market challenge declared by CIBiogás, which is to enable the use of beef cattle bed (litter) as biomass for biogas production in anaerobic reactors. Therefore, this study aimed to enable the production of biogas from the dairy cattle (CB) litter using combined physical and alkaline chemical pretreatments. The CB was collected in a screening system from one of the CIBiogás Demonstration Units at Starmilk Farm. The samples were dried at 50 °C and part of it was ground using a knife mill to reduce its grain size and, consequently, the fiber length. Then, the CB was subjected to alkaline hydrolysis, in which the NaOH dose ranged from 2 to 7% and the exposure time was 24 h at room temperature. To characterize the pretreatment efficiency regarding fiber degradation and biogas production, the following parameters were evaluated: biogas production; methane content; lignin, cellulose and hemicellulose content; total carbon (C); macro and micro nutrients; chemical oxygen demand (COD); total solids (ST); volatile solids (SV); fixed solids (SF). Data analysis was performed using the following statistical methods: principal component analysis, ANOVA, and Tukey test. The treatment that received 3% NaOH (CBH3%) yielded the highest biogas production (771 mL.biogas / kg.SV) and demonstrated economic viability, with a Payback of 1.4 years. When the NaOH dose reached 7% there was a significant increase in lignin degradation (7.6%); however, doses above 3% NaOH showed unsatisfactory biogas production, ranging from 342 to 502 mL.biogas / kg.SV. It can be concluded from this work that the combined physical and chemical alkaline pretreatment with 3% of NaOH could be a viable option for full scale CB biogas production, meeting market needs.