Biogas from anaerobic digestion of organic materials is a renewable energy resource that consists mainly of CH4 and CO2. Trace components that are often present in biogas are water vapor, hydrogen sulfide, siloxanes, hydrocarbons, ammonia, oxygen, carbon monoxide, and nitrogen. Considering the biogas is a clean and renewable form of energy that could well substitute the conventional source of energy (fossil fuels), the optimization of this type of energy becomes substantial. Various optimization techniques in biogas production process had been developed, including pretreatment, biotechnological approaches, co-digestion as well as the use of serial digester. For some application, the certain purity degree of biogas is needed. The presence of CO2 and other trace components in biogas could affect engine performance adversely. Reducing CO2 content will significantly upgrade the quality of biogas and enhancing the calorific value. Upgrading is generally performed in order to meet the standards for use as vehicle fuel or for injection in the natural gas grid. Different methods for biogas upgrading are used. They differ in functioning, the necessary quality conditions of the incoming gas, and the efficiency. Biogas can be purified from CO2 using pressure swing adsorption, membrane separation, physical or chemical CO2 absorption. This paper reviews the various techniques, which could be used to optimize the biogas production as well as to upgrade the biogas quality.

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The use of waste to produce biogas not only limited to the waste from nature such as agricultural waste, food waste, or cattle manure; but can also use human waste hereinafter called human excreta. The use of human excreta for biogas generation considered beneficial either in the term of process or environment. It is at the same time produce energy and reducing environmental problem that caused by unmanaged human excreta disposal. In Indonesia, the main use of biogas itself is for cooking and generating electricity. The huge population and inequality deployment of electricity supply in Indonesia becomes a strong reason in developing biogas system from human excreta. This review paper will discuss utilization of human excreta to produce biogas as alternative energy source and the prospect of this technology in Indonesia.

Biogas has been recognized as a clean and renewable form of energy that is produced from biodegradable organic materials via an anaerobic digestion. In fact, biogas has been well expected to substitute current conventional sources of energy. The main composition of biogas includes methane (CH4) and carbon dioxide (CO2), which is accompanied by different contaminants in varied quantities such as ammonia (NH3), water vapour (H2O), hydrogen sulphide (H2S), methyl siloxanes, nitrogen (N2), oxygen (O2), halogenated volatile organic compounds (VOCs), carbon monoxide (CO) and hydrocarbons. Biogas has been widely utilized as either engine fuel or starting material for chemicals, hydrogen and/or synthesis gas productions. For certain applications, a certain purity degree of biogas is required. Technically, the presence of trace components in biogas has been known to negatively affect engine performance. Therefore, a removal of contaminants, particularly H2S and CO2, is expected to significantly improve biogas quality, thus enhancing its performance in various applications. Besides, the removal is performed to meet standardized gas specifications for its usage as vehicle fuel or being injected into a natural gas grid. In practices, different methods for biogas cleaning and upgrading have been recognized, in which differ in terms of functions, efficiency, and required quality of input gas. This study, therefore, aims at reviewing various H2S removal-based biogas cleaning techniques during and after digestion process.

Anaerobic digestion plays an important role in the gastrointestinal tract and in organic waste treatment. Thermodynamic analysis based on the reaction Gibbs free energy can be used to predict the favorability of some reactions occurring during anaerobic digestion. In this study, we used a thermodynamic approach to evaluating reactions and stoichiometric coefficients of the anaerobic process of in vitro rumen microbiota. The favorability of glucose, butyrate, propionate, and hydrogen utilizations was analyzed by calculating the Gibbs free energy change of each reaction. A previously published Gibbs free energy dissipation method was also used to calculate stoichiometric coefficients of the total metabolism reaction of glucose and hydrogen utilization. For glucose utilization in which the metabolism follows several different pathways, the fraction of glucose following each pathway is estimated by considering the number of electron transfer attributed throughout the catabolism reaction. Glucose utilization always occurs in the system, and the syntrophic correlation among butyrate, propionate, and hydrogen utilizations run well with propionate utilization following the alternative pathway that yields lower hydrogen. The approach applied in this research significantly reduces the stoichiometric coefficients that must be predicted in kinetic modeling. To verify the calculation result, the yield coefficients obtained were then applied in the previous mechanistic model of in vitro rumen microbiota, and the results were compared to the experimental data from literature.