Effect of thermal and acid pre-treatment on increasing organic loading rate of anaerobic digestion of coffee pulp for biogas production

The coffee pulp is the solid waste most generated during the coffee humid pulping. It contains an elevated concentration of organic matter and lignocellulosic materials. In addition, the low rate of biodegradability of the coffee pulp waste may cause severe environmental damage. Therefore, the aim of this study was to evaluate the effect of acid and thermal pre-treatments in the biodegradability rate, followed by an anaerobic digestion of the coffee pulp and collect biogas production. Thermal and acid pre-treatments (50, 70, and 90 °C, and concentration of 2.5, 5, and 10% V·V−1 of acetic acid, respectively) were applied, both during 1 h, evaluating the organic matter solubilization. Posteriorly, the biodegradability and biogas production using anaerobic digestion for 35 days were evaluated. Finally, during 90 days in semicontinuous, the increase of applied organic load of 1 kg VS m−3 day−1 with Δ 1 kg VS m−3 day−1 every 30 days until reaching 3 kg m−3 day−1 was evaluated. The thermal pretreatment to 90 °C and 1 h improved the solubility and hydrolysis considered limiting of the anaerobic process, reducing the hydraulic retention time from 21 to 15 days, and increasing the biogas yields (0.92 L g VSrem−1 year 79.8% CH4).