The Effect of Anaerobic Granulobacter Microorganisms on the Process of Biogas Production from Urban Organic Waste (A Bench- Scale Study)

Introduction
Organic waste is a significant problem in most countries around the world, including Iran, and every year large sums of public money expenditure are spent on its transportation, burial, and processing to mitigate in order to prevent environmental pollution and health issues risks. There are various methods for collecting and managing the management of organic waste, including waste incineration, as well as aerobic and anaerobic digestion incinerators, aerobic and anaerobic digesters. Biogas is one of the most promising bioenergy options among for non-fossil fuel-based energies, and it is noteworthy that a wide range of many biodegradable organic wastes, such as plant and animal matter organic matter, can serve as substrates for biogas production to urban waste water and some industrial waters, can be used as substrates for biogas production, provided that the necessary chemical and physical conditions for the growth of methane-producing bacteria archaea are established provided. The efficiency quality of the anaerobic sludge decomposition process under anaerobic conditions depends on environmental conditions and the microbial community mechanism of bacteria, so changes in operating conditions that lead to changes in the dominant bacterial species can significantly impact affect the performance of the digester. In this bench-scale study, anaerobic digestion was evaluated with different ratios amounts of feedstock feed, water, and Granulobacter inoculum Granobacteria was investigated with the aim of evaluating its potential using this type of bacteria as an bioaugmentation agent inoculant to increase the efficiency of the anaerobic digestion process on a laboratory bench scale.
Materials and Methods
The raw materials used in the experiment included urban waste (e.g., bread, orange peels, vegetables, egg cartons, fruit peels, rice, meat, eggshells, pasta, tea, and onion peels), Granulobacter, and sodium hydrogen carbonate (NaHCO₃). The treatments consisted of 3033.20 g household waste + 3033.20 g water + 709.30 g Granulobacter (T1), 3972.70 g household waste + 3972.70 g water + 400 g Granulobacter (T2), 2415.30 g household waste + 2415.30 g water + 209.10 g Granulobacter (T3), and 2000 g household waste + 2000 g water + 200 g Granulobacter (T4).  In each treatment, the primary feed sample (urban waste) was crushed into smaller pieces (less than 1 cm) and thoroughly mixed. An equal amount of water was then added, followed by adding Granulobacter to the feed. The pH of the feed was measured using a pH meter. Then, each treatment was poured into the digester tank, and the system was initiated. At the end of the digestion process, the biogas tank was separated from the system, and the gas contents were analyzed using gas chromatography (GC). Then, following the complete discharge of the biogas, the digester door was opened, and the remaining contents were subjected to elemental analysis, similar to the initial feed, as well as physicochemical tests (including dry matter, ash, and organic matter). Changes in pH, temperature, and pressure were measured throughout the process and compared across treatments. Data were analyzed using a factorial experiment in a completely randomized design with three replications. Mean comparisons were performed using Duncan's multiple range test at a probability level of α = 5 % using SPSS software (version 18).
Results and Discussion
The findings revealed that the moisture content of the digested samples increased compared to that of the initial feedstock. Moreover, in all treatments except T4, the ash content of the transformed feedstock during digestion was higher than that of the digested material. The largest reduction in carbon relative to the feedstock (1.80 %) was observed in T1, while the maximum methane content (43 %) was obtained in T2. Additionally, the pH reached approximately 6.75 in T1 after 90 days. However, it reached 7.45, 7.00, and 5.10 in T2, T3, and T4 after 49, 54, and 47 days, respectively. During the anaerobic digestion period, T1 showed low temperature fluctuations, maintaining a steady temperature of around 48 °C until the end of the period. In T2, the temperature declined from 50 °C on day 5 to 37 °C at the end of the period, whereas in T3, it rose by about 10 °C from day 5 to the end of the period. Notably, T4 showed temperature fluctuations within the range of 40–45 °C. Furthermore, reactor pressure fluctuations in T1 varied between 0.12 and 0.50 bar. In T2, the pressure varied between 0.15 and 0.25 bar from day 4 to the end of the period, while in T3, it ranged from 0.20 to 0.25 bar. In T4, the pressure remained almost constant (0.15 bar) throughout the entire period.
Conclusion
Anaerobic digestion is a biological process in which the organic matter is decomposed in the absence of oxygen through the participation of various bacterial species. In this study, the anaerobic digestion process was examined using different amounts of municipal organic waste, water, and Granulobacter. The results demonstrated that Granulobacter, when used as an inoculant, is a promising bacterium for increasing the efficiency of the anaerobic digestion process on a laboratory scale.