RESUMO
Spent coffee grounds are rich in high-value compounds, such as saturate and unsaturated fatty acids, and polysaccharides. Therefore, this work investigated a cascade biorefinery to produce: i) biodiesel from coffee oils, ii) cellulose- and hemicellulose-derived fermentable sugars and iii) biomethane from the residual solid fraction after sugars extraction. Transesterification reached the best performances of 86% w/w of fatty acid methyl esters using 1:8 coffee oil/methanol ratio and 2% w/w of KOH as catalyst. The use of glycerol for the pretreatment of spent coffee grounds allowed the internal circulation of a process leftover from transesterification; thus, avoiding the use of clean water. In the best conditions, the total released fermentable sugars were about 40-50% (w/w) on dry weight basis. The low content of easily degradable compounds led to a low methane production of 50 LCH4/kgVS, indicating the need to search for better performing alternatives to close the biorefinery loop.
Assuntos
Biocombustíveis , Café , Esterificação , Metanol , AçúcaresRESUMO
This study was conducted to investigate the effects of chemical pretreatments on biogas production from coffee waste. After the preparation of a mixture of coffee waste with a TS concentration of 10%w/w, basic and acid pretreatments were conducted in batch mode and their performances were compared with the biogas produced from a mixture without any pretreatment stage. The basic pretreatment demonstrated a very good action on the hydrolysis of the lignin and cellulose, and permitted a biogas production of about 18NL/L with a methane content of almost 80%v/v. Thus, the basic pretreatment has been used to scale-up the process. The coffee refuse was has been carried out in a 45L anaerobic reactor working in continuous mode and in a mesophilic condition (35°C) with a Hydraulic Retention Time (HRT) of about 40days. A high biogas production of 1.14NL/Ld, with a methane percentage of 65%v/v was obtained, thus permitting a process yield of about 83% to be obtained.