Optimization of biogas production from coffee production waste

•The ligno-cellulosic materials in coffee wastes inhibits the biogas production.•NaOH permits the hydrolysis of coffee wastes and a high biogas production.•A scaled-up of the basic pretreatment in continuous mode was realized.•The continuous test reached a good yield of the process: 82%.•The daily biogas production was of 1.14NL/Ld with a methane content of 65%. 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.