with the collaboration of Iranian Society of Mechanical Engineers (ISME)

Document Type : Research Article


1 Department of Biosystems Engineering, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran

2 Ferdowsi University of Mashhad

3 Department of Chemical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

4 .Department of Biosystems Engineering, Faculty of Agriculture, Ferdowsi University of Mashhad, Mashhad, Iran


Anaerobic bacteria break down organic materials like animal manure, household trash, plant wastes, and sewage sludge during the anaerobic digestion process of biological materials to produce biogas. One of the main issues in using biogas is hydrogen sulfide (H2S), which, in concentrations between 50 and 10,000 ppm, can corrode pipelines and engines. One method for removing H2S from biogas that has minimal operating costs and investment requirements is biofiltration. Whether organic or inorganic, the biofilter's bed filling materials must adhere to certain standards, including having a high contact surface, high permeability, and high absorption. In this study, biochar and compost were used as the biofilter bed particles to study the removal of H2S from the biogas flow in the lab initially. Next, kinetic modeling was used to provide a numerical description of the removal process.

Material and Methods
To remove H2S from the biogas in this study, a biofilter was constructed on a lab size. As materials of the biofilter bed, biochar and compost were employed seperately. Due to its high absorption capacity and porosity, biochar becomes a good choice for substrate and packed bed in biofilters. The biochar was broken into 10 mm long, 5 mm wide, cylindrical pieces that were then used. Compost was also used as substrate particles in addition to biochar because it contains nutrients for microorganisms. Compost granules with average dimensions of 3 mm in diameter and 7.5 mm in length were used. As a biofilter reactor, these substrates were put inside a cylinder with a diameter of 6 cm and a height of 60 cm. The biofilter's bottom is where biogas enters, and its top is where it exits. Biogas was flowing at a rate of 72 liters per hour. Mathematical modeling was also used to conduct kinetic studies of the process in order to better comprehend and generalize the results. This method involves feeding the biofilter column with biogas that contains H2S while the biofilm is present on the surface of the biofilter bed particles. The bacteria in the biofilm change the gaseous H2S into the harmless substance sulfur and store it in their cells. These assumptions form the foundation of mathematical models. The H2S concentration is uniform throughout the gas flow, the gas flow is constant, and the column's temperature is the same at a specific height.

Results and Discussion
In the beginning, biochar was used as a substrate in the biofilter to test its effectiveness, and good results were obtained in removing H2S from the biogas. H2S concentration in biogas has been significantly reduced using biochar beds. It has dropped from 300 ppm and 200 ppm to 50 ppm in the state of greatest H2S concentration reduction. Methane levels in the biogas were not significantly impacted by the biofilter. This issue is regarded as a good and significant outcome when taking into account the goal of producing biogas, which has a high concentration of methane. The elimination effectiveness was 94% in the biochar bed at 185 ppm input H2S concentration. The removal efficiency also reached 76% in the compost bed and at an input concentration of 70 ppm. Using mathematical models, the simulation was carried out by modifying the model's parameters until the predicted results closely matched the actual experimental data. It may be concluded that the suggested mathematical model is sufficient for the quantitative description of H2S removal from biogas utilizing biofilm in light of how closely the calculation results matched the experimental data. The only model parameter that was changed to make the model results nearly identical to the experimental data was the value of the parameter μmax. Besides, μmax has the greatest influence on the model results. The value of μmax for the biochar bed was calculated as 0.0000650 s-1 and for the compost bed at 70 ppm and 35 ppm concentrations as 0.0000071 s-1 and 0.0000035 s-1, respectively.
The primary objective of this study is to examine the removal of H2S from biogas using readily available and natural substrates. According to the findings, at a height of 60 cm, H2S concentration in biochar and compost beds decreased from 185 ppm to 11 ppm (removal efficiency: 94%) and from 70 ppm to 17 ppm (removal efficiency: 76%). The mathematical models that were created may quantify the H2S elimination process, and the μmax values in biochar and compost were calculated as 0.0000650 s-1 and 0.0000052 s-1, respectively.
The authors would also like to thank UNESCO for providing some of the instruments used in this study under the grant number No. 18-419 RG, which was funded by the World Academy of Sciences (twas).


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