Although biogas is clean and environmentally friendly, its existence is often unsustainable, especially in rural area. Consumption of fossil fuel energy still dominates because cheaper, higher in energy efficiency and ready to use than biogas. One of the efforts to make biogas can compete with fossil fuel energy is by increasing calorific value. Reduction of carbon dioxide by adsorption enhances the calorific value that evidenced by methane enrichment. In this study, we investigated the effect three types of combined adsorbent: pure natural zeolite (Z-Z), zeolite-biochar from chicken manure (Z-B1) and zeolite-modified biochar (Z-B2) on methane content. The result showed that adsorption of biogas using Z-Z, Z-B1 and Z-B2 increased methane level with enhancement of 1,36; 28,92; and 11,27% respectively compared before adsorption. To confirm whether these results were influenced by adsorbent’s character or not as consequence adsorbent characterization have been done in this study.

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Rice husk-based biochar has been prepared by pyrolysis process for carbon dioxide adsorption in biogas. Biochar is considered as porous material for carbon dioxide adsorption. In this study, the adsorption of carbon dioxide, the largest impurity in biogas, was evaluated. The adsorptions were conducted in five treatments (mass variation): 80 grams of biochar (RB1), 60 grams of biochar and 20 grams of zeolite (RB2), 40 grams of biochar and 40 grams of zeolite (RB3), 20 grams of biochar and 60 grams of zeolite (RB4), 80 grams of zeolite (RB5). The best performance of carbon dioxide adsorption showed by RB1 with the decrease in carbon dioxide up to 31.59%. Characterization of adsorbents were also investigated by surface area analyzer to know relation between surface area and adsorption capability. It was found that the larger surface areas are favorable to adsorb carbon dioxide.

The energy needs in Indonesia are mainly fulfilled by fossil fuels based energy. Since there is the rise of fuel price, Indonesia government considers seeking alternative energies from renewable resources. Biogas becomes one of the alternative energy that supplies energy needs and manages cow manure waste in Indonesia. To increase adoption of biogas technology, biogas production through methane enrichment is required. The experiment was conducted with return sludge system. These instruments consist of a series portable bio-digester, gas holder and return sludge unit. There were three treatments on biogas production without and with sludge addition or re-use bio-digester sludge that produced after biogas production as raw material for next biogas production. Biogas that produced was observed every two days during 40 days. The results showed that the addition of bio-digester sludge increased biogas production and methane concentration. The optimum retention time of biogas production with sludge addition was 20 days with accumulation biogas volume of 156.38 liters or increased of 38.75 from biogas production without bio-digester sludge). The optimum retention time to increase methane level was 15 days with methane enrichment from 0.8% to 29.41%.

Biogas become one of many alternative energies that are claimed to contribute to greenhouse gas mitigation. The improved technology to gain good quality biogas has been developed over many years such as carbon dioxide adsorption and methane enrichment. Implementing biochar-based renewable sources can replace activated carbon-based fossil fuels. This study is developing activated biochar-based rice husk by chemical activation to replace 25% volume of natural zeolite to adsorb carbon dioxide in biogas purification. Three treatments of adsorption time variation were used in this study: 10, 20, and 30 minutes. The results showed that activation of biochar repaired the capability of biochar to adsorb carbon dioxide and methane levels in biogas. The best result was shown by biogas purification for 30 minutes with a methane enrichment of 24% compared to biogas before purification. Our results highlight the activated biochar based-rice husk becomes a candidate for an adsorbent in biogas purification and the chemical activation process as a strategy to improve the capability of the adsorbent.

We evaluated the adsorption of CO 2 in biogas mixtures using the combination of adsorbents: natural zeolite-natural zeolite (Z-Z), natural zeolite-chicken manure based biochar (Z-CM) and natural zeolite-biogas sludge based biochar (Z-BS). The amount of CO 2 adsorption was controlled at room temperature and under a gas pressure range of 5-7 bar. Samples of biogas before and after adsorption were analyzed by gas chromatography (GC) to determine the percentage of CH 4. The relationship between the percentage of CH 4 composition and calorific value of biogas was investigated. The results of data from GC showed that the highest CH 4 enrichment was performed by Z-CM (28.92%). The highest CH 4 enrichment increased the calorific value of biogas in comparison to biogas before adsorption. The result suggested that CO 2 adsorption using natural zeolite and chicken manure based biochar successfully increased the calorific value of biogas.

The increase in intensive using of production elements has been reflected on the increasing of organic waste. Without appropriate treatment, waste leads to the contamination of environment. The conversion of organic waste into material with economic value will contribute to increasing productivity, for example in biogas system. Today, the utilization of waste, biogas sludge, as bio-fertilizer has been developed. However, the utilization of biogas sludge from cow manure as biochar is still rare. The aims of this study were to investigate the recycling of biogas sludge from cow manure as biochar in biogas purification. Biochar made of biogas sludge from cow manure as adsorbent in biogas purification leads to the cycle loop of biogas system. We also investigated the effect of mass variation of biochar made of biogas sludge from cow manure on biogas purification performance. The variation of zeolite and biochar made of biogas sludge with mass ratio of 0:80; 20:60; 40:40; 60:20; and 80:0 had been put inthe adsorption column of biogas purification. The results showed that the increase in biochar mass affected on methane enrichment of biogas. The highest methane enrichment was performed by biochar with ratio 40:40. The utilization of biochar mass above 50% of the total mass per each column decreased methane enrichment. From this study, we concluded that biogas sludge has potential to be used as adsorbent in biogas purification. Biochar from biogas sludge leads to organic cycle system in biogas system that provides option in sustainable energy and additional benefits for farmers.

The utilization of the recycling of biomass waste for carbon dioxide (CO2) adsorption in biogas is still rare. Even though the experiments on the biogas purification still using synthetic biogas. This paper investigated the recycling of biomass waste, sugarcane bagasse for biogas purification. The conversion of biomass into biochar was claimed to expand the surface area of its pores for capturing CO2 in biogas. Five treatments of adsorbents used in this study, 100% volume of zeolite or biochar, 75% volume of zeolite and 25% biochar, 50% volume of zeolite and biochar, 25% volume of zeolite and 25% volume of zeolite, and 25% volume of biochar. The difference of volume treatment in adsorbents affected methane (CH4) and CO2 composition of biogas. Biogas purification by adsorption was conducted at 5-7 bar pressure range and room temperature. Biogas before and after purification were tested of CH4 and CO2 composition by gas chromatography. A significant reduction in CO2 was shown when 50% volume of zeolite was replaced by biochar. The highest in CO2 reduction showed by the composition of 50% sugarcane bagasse-based biochar and 50% natural zeolite. The CO2 decreases did not accompany by the CH4 increases because mesopore-sized still dominated the adsorbents’ pore size.