Biodigestion of Mixed Substrates of Cow Manure-Delignified Spent Coffee Ground (DSCG) using Microorganism Enhancer for Biogas Production and Its Kinetic Study

Abstract

Environmentally benign energy strategies have been implemented to cope with the rapidly increased global energy needs. Indonesia’s coffee consumption has triggered an increase in the generation of spent coffee ground (SCG) that can be used as a biogas raw material. The novelty that we offer in this research effort is to reduce the premature formation of biogas, so that we can extend the biogas production period during the digestion of spent coffee ground by adjusting the right pH and digestion time. This study aimed to produce biogas from an organic substrate mixture containing cow manure and SCG with a 25:1 C/N ratio by employing effective microorganisms-4 (EM-4). The process began with delignification of SCG using sodium hydroxide solution to obtain delignified SCG (DSCG). The biodegradation of the substrate was performed in an anaerobic batch digestion (AD) system at ambient temperature by varying pH (5, 7, and 9) and EM-4 concentration (6%, 9%, and 12%). The biogas product and chemical oxygen demand measurements were carried out every two days for 60 days of digestion. The results showed that the increase in EM-4 concentration induced earlier initial biogas production enhanced the volume, and extended the production time. The pH 7 level and 9% EM-4 loading gave the ideal digestion substrate condition containing cow manure and SCG with a 25:1 C/N ratio to obtain 11.28 mL of biogas/g COD with 100.2% production enhancement. The modified Gompertz equation fitted the experimental data very well as indicated by a high value of the coefficient of determination (R2 > 0.95).

Anaerobic Fermentation of Slaughterhouse Waste—Codigestion with Wheat Straw to Determine Methane Biochemical Potential and Kinetic Analysis

“…Ref. [31] Reported the reactor pH influences both the AD process and efficiency in the digestion process. Methanogens perform their roles more effectively between pH ranges of 6.5-8.2, with an optimum 7.0 pH.…”

“…Table 2 indicates that the optimal initial pH maximizing CMY is 7.34, a lower amount of inoculum caused the pH to rise, leading the digester to a medium that tends to reach (7.76) alkalinity affecting CMY. Indeed, pH variation can be due to some influential digestion parameters, such as VFA, bicarbonate concentration, system alkalinity and by CO 2 fraction produced during the process [31]. The initial and final pH levels belonging to the experiment I:S-2:1 is adequate to increase CMY.…”