Characterization of Coffee-Pulp Biochar as an Additive to Enhance Biogas Production from Coffee Mucilage

Abstract

Biogas has been effectively produced from solid as well as liquid biomass waste through anaerobic digestion (AD). It has been proved that AD is the most efficient technology and less environmental effect in converting biomass to biogas. However, it is challenging that the rate of biogas production might slow down by many factors. It requires continues research in order to overcome the problem, such as by adding an additive. The use of several additives for AD has received great attention due to the positive influence in improving the production performance of biogas in terms of process stability and efficiency, and production capacity. Among all types of additives, carbon material in the form of bio-char has been considered as the most profitable due to low cost and easy to produce from various carbon source materials. This study aimed to determine the characteristics of coffee pulp bio-char which will be used as an additive in biogas production from coffee mucilage by the AD method. Coffee pulp biomass and coffee mucilage were obtained from Aceh Tengah, Indonesia. Preparation of bio-char was carried out by washing and soaking of the coffee pulp with tap water for 24 hours, then drying under the sun for three days. Carbonization of dried coffee pulp was then performed using a pilot plant-scale pyrolysis reactor at temperature of 400 °C for 60 minutes. Resulting biochar was then ground and sieved to 60 mesh size. Based on to proximate analysis result, it was found that the moisture, ash, volatile matter, and fixed carbon contents were respectively 1.98%, 11.93%, 42.36%, and 43.72%. N2-physisorption analysis of coffee-pulp bio-char suggested pore volume of 0.21 cm3/g. From BET calculation method it was found that the surface area was 224.1 m²/g. This high surface area is beneficial for providing sheltered spaces for microbes to attach and hindering them against metabolic inhibitors. The effect of adding biochar additives from coffee skin waste in the anaerobic digestion process of coffee mucilage waste provides significant results on the yield of biogas products. The yield of biogas products increased by 225% with the addition of 15 gr/L of biochar coffee pulp.