The major objective of this research was to produce biogas, primarily biohythane, from organic waste. The organic waste used in this study was food waste, which included fruits, leaves, paper, and sawdust. To facilitate the experiment, four plastic drums were specially constructed and used. City-generated organic waste was utilized to estimate the generation of various bio gases such as methane (CH₄), hydrogen (H₂), hydrogen sulphide (H₂S), and carbon monoxide (CO).
Measurement of biogas
The biogases were measured after two days. This experiment lasted about nine weeks. The biogases from each plastic drum were analyzed with a portable gas analyzer.
Methane production (%) from organic waste
During the process of decomposition, the generation of CH4 is very important as it is the main ingredient for bio energy. The methane emission was measured through a digital portable gas analyzer. Figure 1 display that the highest value of CH4 was 74.2% in T4 Organicwaste + Acidithiobacillus thioxidans)/Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense, 69% in T3 Organic waste + Methanosarcina thermophila / Methanobacterium beijingense, 64% in T2 Organic waste + Acidithiobacillus thioxidans/Acidithiobacillus ferroxidans, and 57.6% in T1 (Control) on week 8th. While the lowest value of CH4 was 32% in T1 Control, 38.6% in T2 Organic waste + Acidithiobacillus thioxidans/Acidithiobacillus ferroxidans, 35% in T3 Organic waste + Methanosarcina thermophila / Methanobacterium beijingense, and 37.6% in T4 Organic waste + Acidithiobacillusthioxidans)/Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense at week 2nd. The application of iron and sulfur-oxidizing bacteria in biohythane generation, especially in the context of methane production, absorb their distinctive metabolic pathways to enhance the anaerobic digestion process. The mechanism of iron and sulphur oxidizing bacteria includes Iron oxidizing bacteria oxidizing ferrous iron (Fe²⁺) to ferric iron (Fe³⁺), which has multiple benefits, including the oxidation process can help break down complex organic materials, making it more accessible to methanogens. IOB precipitates sulfides as iron sulfides, which reduces sulfide inhibition of methanogenic bacteria. Iron Oxidizing Bacteria oxidative activity can boost hydrogen-producing bacteria, resulting in increased hydrogen yields .Sulfur oxidizing bacteria oxidizes sulphur molecules like hydrogen sulfide (H₂S) to sulfate (SO₄²⁻). Sulfide control involves converting harmful H₂S to sulphate, which decreases sulphide toxicity and inhibits methanogenesis. By eliminating hydrogen sulfide, Sulphur Oxidizing Bacteria creates a more approving environment for methanogens, increasing methane production. Sulphur Oxidizing Bacteria and methanogens can develop syntrophic partnerships, which boosts overall process efficiency. Iron Oxidizing Bacteria and Sulphur Oxidizing Bacteria activities reduce sulfide toxicity and increase substrate availability, resulting in more stable anaerobic digestion. The presence of these bacteria may result in greater hydrogen and methane yields. Reducing hydrogen sulfide content enhances biogas quality, making it more acceptable for energy uses.By converting hydrogen and carbon monoxide into methane, Methanobacterium beijingense contribute to the ultimate methane yield in the biohythane mixture [29, 30]. Methanosarcina thermophila can convert many metabolites produced during the fermentation stage into methane, making them incredibly beneficial for use in mixed-substrate anaerobic digesters. The presence of both Methanobacterium beijingense and Methanosarcina thermophila can improve anaerobic digestion stability by assuring efficient hydrogen and substrate consumption.These methanogens complementary metabolic pathways help maximize methane synthesis from a wide range of substrates.The combined activity of these methanogens increases biogas quality, resulting in increased methane content and lower hydrogen sulfide levels, especially when paired with iron and sulfur-oxidizing bacteria [31, 32].
Hydrogen production (%) from organic waste
Figure 2 showed that the highest value of H2 was 14.96% in Organic waste + Acidithiobacillus thioxidans)/Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense in the 5th week, 10.53% in T3 Organic waste + Methanosarcina thermophila / Methanobacterium beijingense in the 5th week, 8.8% in T2 Organic waste + Acidithiobacillus thioxidans/Acidithiobacillus ferroxidans in 6th week, and 7.4% in T1 (Control) on 5th week. While the lowest value of H2 was 3.2% in T1(Control) on 1st week, 2.8% in T2 Organic waste + Acidithiobacillus thioxidans/Acidithiobacillus ferroxidans on 9th week, 3.6% in T3 Organic waste + Methanosarcina thermophila / Methanobacterium beijingense on 9th week, and 3.5% in T4 Organic waste + Acidithiobacillusthioxidans /Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense on 9th week.In terms of its potential to reduce global carbon dioxide (CO2) emissions, hydrogen gas is a clean energy source and a promising substitute for fossil fuels. It is less energy-intensive and more environmental friendly.Research indicated that pure cultures were preferable to mixed cultures, particularly in terms of substrate selectivity and relatively simple growth manipulation. Iron-oxidizing bacteria oxidize ferrous iron, generating electrons that hydrogen-producing bacteria can use to convert protons (H+) to hydrogen gas (H2).Sulfur oxidizing bacteria can oxidize organic molecules and create hydrogen sulphide. Hydrogen-producing bacteria can then use hydrogen sulphide to make hydrogen gas [12, 33] .
Hydrogen Sulfide (ppm) from organic waste
The amount of hydrogen sulfide generated during the breakdown of city waste is entirely dependent on the waste's composition. Anaerobic digestion was found to generate more hydrogen sulfide than aerobic digestion. Figure 3 revealed that the maximum value of H2S was 63.3ppm in T4 Organic waste + Acidithiobacillus thioxidans)/Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense, 54.66ppm in T2 Organic waste + Acidithiobacillus thioxidans/Acidithiobacillus ferroxidans, and 45.33ppm in T3 Organic waste + Methanosarcina thermophila / Methanobacterium beijingense, and 28.66ppm in T1 Control at 3rd week. While the minimum value of H2S was 13.6ppm in T1 Control, 24ppm in T3 Organic waste + Methanosarcina thermophila / Methanobacterium beijingense, 27.33ppm in T2 Organic waste + Acidithiobacillus thioxidans/Acidithiobacillus ferroxidans, and 31.66ppm in T4 Organic waste + Acidithiobacillusthioxidans)/Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense in the 1st week.The combination of IOB and SOB can effectively regulate hydrogen sulphide levels through precipitation and oxidation mechanisms.Iron Oxidizing Bacteria can provide ferrous iron for sulphide precipitation, whereas SOB can oxidize the remaining hydrogen sulphide, resulting in complete sulphide control. Lower hydrogen sulphide levels decrease corrosion and toxicity, leading to a more stable and effective anaerobic digestion process [29, 34].
Carbon monoxide (ppm) from organic waste
Figure 4 indicated that the mean maximum value of carbon monooxide was 855 ppm in T3 Organic waste + Methanosarcina thermophila / Methanobacterium beijingense, 680 ppm in T2 Organic waste + Acidithiobacillus thioxidans/Acidithiobacillus ferroxidans 561.6 ppm in T4 Organic waste + Acidithiobacillusthioxidans)/Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense, and 460 ppm in T1 Control at 4th week. While the mean minimum value of CO was 461.6ppm in T3 Organic waste + Methanosarcina thermophila / Methanobacterium beijingense, 562.3ppm in T1 Control, 681.6ppm in T2 Organic waste + Acidithiobacillus thioxidans/Acidithiobacillus ferroxidans, and 565ppm in T4 Organic waste + Acidithiobacillusthioxidans)/Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense on the 7th week.Iron and sulfur-oxidizing bacteria can help produce biohythane, a combination of hydrogen and methane from organic materials. These bacteria can help manage and reduce carbon monoxide (CO) levels, which can be toxic to many microorganisms involved in biogas production. These bacteria play an important role in iron oxidation and can influence the cycling of metals and other element cycles in various situations. Their metabolic activities can be leveraged in biohydrogen and biogas generation processes due to their propensity to oxidize iron compounds, which can ultimately impact microbial populations participating in biohythane production. Acidithiobacillus ferrooxidans are sulfur-oxidizing bacteria that contribute to the generation of sulfate and protons. These metabolic processes can be integrated into biohythane synthesis, where the oxidation of sulphur compounds may contribute to maintaining the redox balance and providing substrates for other microorganisms involved in biogas production .Carbon monoxide dehydrogenase (CODH) enzymes enable certain bacteria and archaea to use CO as both a carbon and an energy source. These enzymes aid in the oxidation of CO to CO2, which can subsequently be used in a variety of biosynthetic pathways, including methane and hydrogen synthesis.These microbes' metabolic plasticity makes them beneficial in biohythane production, as carbon monoxide can be a by-product of organic matter decomposition [35, 36].
Measurements of Temperature (⁰C)
Figure 5 illustrated the outcomes of the temperature were recorded in T4 Organic waste + Acidithiobacillus thioxidans)/Acidithiobacillus ferroxidans) + Methanosarcina thermophila / Methanobacterium beijingense, which revealed that the maximum peak of the temperature was 50.2 ⁰C on day 36th, while treatment (control) showed the lowest temperature of 27 ⁰C on the 62nd day. Temperature effects on biogas generation were discovered at 20°C, 35°C, and 45°C. According to studies, thermophilic bacteria Methanosarcina thermophila are more efficient in terms of loading rate, gas yield, and hydraulic retention period, but require a larger temperature input. Furthermore, thermophilic bacteria are more sensitive to temperature variations and environmental factors than mesophilic bacteria.Several microbial communities increased and became more prevalent as the temperature increased, whereas others were carried away by anaerobic digestion [20, 24].Methanogens are categorized as mesophilic (37°C) and thermophilic (55°C) due to their capacity to function well over a variety of temperatures [37, 38] .
Challenges and Future consideration
Biohythane production facilitates the recovery of valuable resources from organic waste, reducing landfill use and associated environmental impacts. By converting organic waste into biohythane, methane emissions from landfills are reduced, contributing to lower overall greenhouse gas emissions. Advances in microbial strains, enzymes, and reactor designs can enhance the efficiency and yield of biohythane production. Integrating biohythane production with other renewable energy technologies can create more resilient and efficient waste management systems. By addressing these challenges and focusing on future considerations, biohythane can offer significant benefits for waste management, contributing to a more sustainable and efficient system for handling organic waste.The use of methanogens microorganisms, specifically Methanosarcina thermophila and Methanobacterium beijingense, in the combined application for city waste decomposition and biohythane synthesis, provides substantial advantages. Iron- and sulfur-oxidizing bacteria facilitate the breakdown of complex organic compounds, thus promoting methanogenesis. Methanosarcina thermophila and Methanobacterium beijingense, both essential methanogenic bacteria, efficiently convert the resulting simpler substances into methane, which is the main component of biohythane.This integrated microbial strategy accelerates the waste breakdown and increases biohythane yield, helping to promote sustainable waste management and renewable energy production. The improved decomposition process minimizes odorous emissions while limiting the production of persistent and toxic organic compounds, addressing environmental and public health issues. Furthermore, this technology promotes the circular economy by converting city waste into valuable bio-energy. Future research should focus on optimizing the microbial consortia ratios, researching the capacity for growth of this technique, and assessing the financial potential of large-scale deployment. By improving these processes, combining iron and sulphur oxidizing microorganisms with Methanosarcina thermophila and Methanobacterium beijingense can completely transform urban waste management and biohythane production, leading the way for more sustainable and efficient waste-to-energy solutions.