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).

Among numerous energy storage technologies, redox flow battery is one of the promising technologies that can be used to supply reliable continuation of electricity to electricity grids with a scale up to MW or MWh.  In this paper, the process mechanism and optimization of redox flow battery using organic solution such as Riboflavin-5’-phosphate sodium salt dihydrate (FMN-Na) as anolyte and 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) as catholyte were investigated. Sodium and chloride ions in salt feed were moved respectively to anolyte and catholyte by electrochemical reaction of electrolytes during the charge process and return to the feed during the discharge process. The study was carried out by given electric current with different voltage to graphite electrode range 1,5-10,5 volts and TEMPO concentration 0,02-0,08 M. The result shows that the optimum voltage is 7,5 volts with the concentration of TEMPO 0,06 M. The result also confirms the role of TEMPO solutions in the cathode. In addition to that, the FTIR and SEM analysis to the sedimentation generated during the process also revealed the change of the anolyte and catholyte after charging process.Keywords: Organic; Flow Battery; TEMPO; FMN-Na; energy storage

There have been continuous efforts to find environmentally benign energy to cope steady increase of global energy needs. The spent coffee ground (SCG) is one of agricultural wastes that can be utilized as a raw material to produce biogas. This study aims to produce biogas from mixture of organic substrate containing cow manure and spent coffee ground (SCG) with a C/N ratio of 25:1 with the addition of effective microorganisms-4 (EM-4) to enhance biogas production. The biodegradations were performed in an anaerobic batch digestion (AD) at ambient environment. The variables used of this research were pH (5, 7, and 9) and the loading of EM-4 (6, 9, and 12%). The digestions were run for 60 days and the volumes of biogas produced were measured every two days. The results showed that the addition of EM-4 was able to initiate biogas production earlier, enhance biogas volume, and extend biogas production end time. The best digestion condition for substrate containing cow manure and SCG with a C/N ratio of 25:1 was found to be at pH 9 and EM-4 loading of 9% to obtain 11.28 mL biogas/g COD with enhancement of biogas production of about 100.2 %. The experimental data was fitted really well by the modified Gompertz equation as shown by a high determination coefficient (R2 > 0.95).