Optimization of Biogas Production Efficiency from Anaerobic Digestion of Organic Fraction of Municipal Solid Waste under Thermal Pretreatment at Different Concentrations

Document Type : Research Article

Authors

• M. Kamali ¹
• R. Abdi ²
• A. Rohani ³
• Sh. Abdollahpour ²
• S. Ebrahimi ⁴

¹ Ph.D. in Agricultural Mechanization Engineering, University of Tabriz, Iran

² Department of Biosystems Engineering, University of Tabriz, Iran

³ Department of Biosystems Engineering, University of Mashhad, Iran

⁴ Faculty of Chemical Engineering, Sahand University of Technology, Iran

https://doi.org/10.22067/jam.2021.68771.1018

Abstract

Introduction
Since anaerobic digestion leads to the recovery of energy and nutrients from waste, it is considered the most sustainable method for treating the organic fraction of municipal solid wastes.
However, due to the long solid retention time in the anaerobic digestion process, the low performance of the process in biogas production as well as the uncertainty related to the safety of digested materials for utilizing in agriculture, applying different pretreatments is recommended.
Thermal pretreatment is one of the most common pretreatment methods and has been used successfully on an industrial scale. Very little research, nevertheless, has been done on the effects of different temperatures and durations of thermal pretreatment on the enhancement of anaerobic digestion of the organic fraction of municipal solid wastes (OFMSW). 
The main effect of thermal pretreatment is the rapturing cell membrane and dissolving organic components. Thermal pretreatment at temperatures above 170 ^°C may result in the formation of chemical bonds that lead to particle agglomeration and can cause the loss of volatile organic components and thus reduce the potential for methane production from highly biodegradable organic waste. Therefore, since thermal pretreatment at temperatures above 100 ^°C and high pressure requires more energy and more sophisticated equipment, thermal pretreatment of organic materials at low temperatures has recently attracted more attention. According to the researchers, thermal pretreatment at temperatures below 100 ^°C did not lead to the decomposition of complex molecules but the destruction of large molecule clots.
The main purpose of this study was to find the optimal levels of pretreatment temperature and time and the most appropriate concentration of digestible materials to achieve maximum biogas production using a combination of the Box Behnken Response Surface Method to find the objective function followed by optimizing these variables by Genetic Algorithm.
Materials and Methods
In this study, the synthetic organic fraction of municipal solid waste was prepared similar to the organic waste composition of Karaj compost plant. The digestate from the anaerobic digester available in the Material and Energy Research Institute was used as an inoculum for the digestion process. Some characteristics of the raw materials that are effective in anaerobic digestion including the moisture content, total solids, volatile solids of organic waste, and the inoculum were measured. Experimental digesters were set up according to the model used by MC Leod. After size reduction and homogenization, the synthetic organic wastes were subjected to thermal pretreatment (70, 90, 110 ^°C) at specific times (30, 90, 150 min).
The Response Surface methodology has been used in the design of experiments and process optimization. In this study, three operational parameters including pretreatment temperature, pretreatment time, and concentration of organic material (8, 12, and 16%) were analyzed. After extracting the model for biogas efficiency based on the relevant variables, the levels of these variables that maximize biogas production were determined using a Genetic Algorithm.
Results and Discussion
The Reduced Quadratic model, was used to predict the amount of biogas production. The value of the correlation coefficient between the two sets of real and predicted data was more than 0.95. The results suggested that pretreatment time followed by the pretreatment temperature had the greatest contribution (50.86% and 44.81%, respectively) to biogas production. Changes in the organic matter concentration, on the other hand, did not have a significant effect (p ˂ 0.01) on digestion enhancement (1.63%) but were statistically significant at p ˂ 0.10.
The response surface diagram showed that the increase in pretreatment time first led to a rise and then a fall in biogas production. The decline in biogas production seemed set to continue with pretreatment time. Meanwhile, the increase in pretreatment temperature from 70 ^°C to 110 ^°C first contributed to higher biogas production and then the decrease in gas production occurred.  
The reason for this fall was probably the browning and Maillard reaction.
The regression model was applied as the objective function for variables optimization using the Genetic Algorithm method. Based on the results of this algorithm, the optimal thermal pretreatment for biogas production was determined at 95 ^°C for 104 minutes and at the concentration of 12%. The expected amount of biogas production by applying the optimal pretreatment conditions was 445 mL-g^-1 VS.
Conclusion
In this study, the variables including thermal treatment temperature and time as well as the concentration of organic waste to be anaerobically digested were optimized to achieve the highest biogas production from anaerobic digestion.
Statistical analysis of the results revealed that the application of thermal pretreatment increased biogas production considerably. According to the regression model, the contribution of pretreatment time and temperature to biogas production was significant (50.86% and 44.81% respectively). In stark contrast, varying substrate concentrations in the range of 8 to 16% had a smaller effect (1.63%) on biogas production. The results of this study also showed that the best pretreatment temperature and time were 95 ^°C and 104 minutes, respectively, at a concentration of 12% by generating 445 mL-g^-1 VS biogas which is 31.17% higher than the biogas yield from anaerobic digestion of untreated organic wastes at this concentration.

Keywords

• Anaerobic digestion
• Genetic algorithm
• Optimization
• Thermal pretreatment

20.1001.1.22286829.1401.12.3.11.5

Main Subjects

• Bioenergy

Open Access

©2021 The author(s). This article is licensed under Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source.

References

1. Aboudi, K., C. J. Alvarez-Gallego, and L. I. Romero-García. 2017. Influence of total solids concentration on the anaerobic co-digestion of sugar beet by-products and livestock manures. Science of the Total Environment 586: 438-445. DOI: 1016/j.scitotenv.2017.01.178.
2. American Public Health Association (APHA). Standard methods for the examination of water and wastewater. 22. Washington DC (USA): American Public Health Association/American Water Works Association/Water Environment Federation.
3. Angelidaki, I., M. Alves, D. Bolzonella, L. Borzacconi, J. L. Campos, A. J. Guwy, and J. B. Van Lier. 2009. Defining the biomethane potential (BMP) of solid organic wastes and energy crops: A proposed protocol for batch assays. Water Science and Technology 59 (5): 927-934. DOI: 2166/wst.2009.040.
4. Appels, L., J. Degreve, B. Van der Bruggen, J. Van Impe, and R. Dewil. 2010. Influence of low temperature thermal pre-treatment on sludge solubilisation, heavy metal release and anaerobic digestion. Bioresource Technology 101 (15): 5743-5748. https://doi.org/10.1016/j.biortech.2010.02.068.
5. Ariunbaatar, J., A. Panico, G. Esposito, F. Pirozzi, and P. N. Lens. 2014. Pretreatment methods to enhance anaerobic digestion of organic solid waste. Applied Energy 123: 143-156. https://doi.org/10.1016/j.apenergy.2014.02.035.
6. Barjenbruch, M., and O. Kopplow. 2003. Enzymatic, mechanical and thermal pre-treatment of surplus sludge. Advances in Environmental Research 7 (3): 715-720. https://doi.org/10.1016/S1093-0191(02)00032-1.
7. Bien, J. B., G. Malina, J. D. Bien, and L. Wolny. 2004. Enhancing anaerobic fermentation of sewage sludge for increasing biogas generation. Journal of Environmental Science and Health Part A 39 (4): 939-949. DOI: 1081/ese-120028404.
8. Bougrier, C., C. Albasi, J. P. Delgenès, and H. Carrere. 2006. Effect of ultrasonic, thermal and ozone pre-treatments on waste activated sludge solubilisation and anaerobic biodegradability. Chemical Engineering and Processing: Process Intensification 45 (8): 711-718. https://doi.org/10.1016/j.cep.2006.02.005.
9. Bougrier, C., J. P. Delgenes, and H. Carrere. 2008. Effects of thermal treatments on five different waste activated sludge samples solubilisation, physical properties and anaerobic digestion. Chemical Engineering Journal 139 (2): 236-244. https://doi.org/10.1016/j.cej.2007.07.099.
10. Carlsson, M., A. Lagerkvist, and F. Morgan-Sagastume. 2012. The effects of substrate pre-treatment on anaerobic digestion systems: A review. Waste Management 32 (9): 1634-1650. https://doi.org/10.1016/j.wasman.2012.04.016.
11. Carrere, H., C. Dumas, A. Battimelli, D. J. Batstone, J. P. Delgenes, J. P. Steyer, and I. Ferrer. 2010. Pretreatment methods to improve sludge anaerobic degradability: A review. Journal of Hazardous Materials 183 (1-3): 1-15. https://doi.org/10.1016/j.jhazmat.2010.06.129.
12. Chamchoi, N., H. Garcia, and I. Angelidaki. 2011. Methane potential of household waste; Batch assays determination. Applied Environmental Research 33 (1): 13-26.
13. Climent, M., I. Ferrer, M. del Mar Baeza, A. Artola, F. Vazquez, and X. Font. 2007. Effects of thermal and mechanical pretreatments of secondary sludge on biogas production under thermophilic conditions. Chemical Engineering Journal 133 (1-3): 335-342. https://doi.org/10.1016/j.cej.2007.02.020.
14. Edelmann, W., U. Baier, and H. Engeli, 2005. Environmental aspects of the anaerobic digestion of the organic fraction of municipal solid wastes and of solid agricultural wastes. Water Science and Technology 52 (1-2): 203-208.
15. Elliot, A., and T. Mahmood. 2012. Comparison of mechanical pretreatment methods for the enhancement of anaerobic digestion of pulp and paper waste. Water Science Technology 84: 497-505. DOI: 2175/106143012x13347678384602.
16. Fernandez, J., M. Perez, and L. I. Romero. 2008. Effect of substrate concentration on dry mesophilic anaerobic digestion of organic fraction of municipal solid waste (OFMSW). Bioresource Technology 99 (14): 6075-6080. DOI: 1016/j.biortech.2007.12.048.
17. Ferrer, I., S. Ponsa, F. Vazquez, and X. Font. 2008. Increasing biogas production by thermal (70 ) sludge pre-treatment prior to thermophilic anaerobic digestion. Biochemical Engineering Journal 42 (2): 186-192. DOI: 1016/j.bej.2008.06.020.
18. Ge, X., F. Xu, and Y. Li. 2016. Solid-state anaerobic digestion of lignocellulosic biomass: Recent progress and perspectives. Bioresource Technology 205: 239-249. https://doi.org/10.1016/j.biortech.2016.01.050.
19. Li, C., P. Champagne, and B. C. Anderson. 2011. Evaluating and modeling biogas production from municipal fat, oil, and grease and synthetic kitchen waste in anaerobic co-digestions. Bioresource Technology 102 (20): 9471-9480. https://doi.org/10.1016/j.biortech.2011.07.103.
20. Li, Y., S. Y. Park, and J. Zhu. 2011. Solid-state anaerobic digestion for methane production from organic waste. Renewable and Sustainable Energy Reviews 15 (1): 821-826. https://doi.org/10.1016/j.rser.2010.07.042.
21. Li, Y., Y. Jin, J. Li, H. Li, and Z. Yu. 2016. Effects of thermal pretreatment on the biomethane yield and hydrolysis rate of kitchen waste. Applied Energy 172: 47-58. https://doi.org/10.1016/j.apenergy.2016.03.080.
22. Liu, G., R. Zhang, H. M. El-Mashad, and R. Dong. 2009. Effect of feed to inoculum ratios on biogas yields of food and green wastes. Bioresource Technology 100 (21): 5103-5108. https://doi.org/10.1016/j.biortech.2009.03.081.
23. Liu, X., W. Wang, X. Gao, Y. Zhou, and R. Shen. 2012. Effect of thermal pretreatment on the physical and chemical properties of municipal biomass waste. Waste Management 32 (2): 249-255. DOI: 1016/j.wasman.2011.09.027.
24. Maghanaki, M. M., B. Ghobadian, G. Najafi, and R. J. Galogah. 2013. Potential of biogas production in Iran. Renewable and Sustainable Energy Reviews 28: 702-714. https://doi.org/10.1016/j.rser.2013.08.021.
25. Marin, J., K. J. Kennedy, and C. Eskicioglu. 2010. Effect of microwave irradiation on anaerobic degradability of model kitchen waste. Waste Management 30 (10): 1772-1779. https://doi.org/10.1016/j.wasman.2010.01.033.
26. McLeod, J. D., M. Z. Othman, D. J. Beale, and D. Joshi. 2015. The use of laboratory scale reactors to predict sensitivity to changes in operating conditions for full-scale anaerobic digestion treating municipal sewage sludge. Bioresource Technology 189: 384-390. https://doi.org/10.1016/j.biortech.2015.04.049.
27. Mirmasoumi, S., R. K. Saray, and S. Ebrahimi. 2018. Evaluation of thermal pretreatment and digestion temperature rise in a biogas fueled combined cooling, heat, and power system using exergo-economic analysis. Energy Conversion and Management 163: 219-238. https://doi.org/10.1016/j.enconman.2018.02.069.
28. Mottet, A., J. P. Steyer, S. Deleris, F. Vedrenne, J. Chauzy, and H. Carrere. 2009. Kinetics of thermophilic batch anaerobic digestion of thermal hydrolysed waste activated sludge. Biochemical Engineering Journal 46 (2): 169-175. https://doi.org/10.1016/j.bej.2009.05.003.
29. Neyens, E., and J. Baeyens. 2003. A review of thermal sludge pre-treatment processes to improve dewaterability. Journal of Hazardous Materials 98 (1-3): 51-67. https://doi.org/10.1016/S0304-3894(02)00320-5.
30. Panda, S., and N. P. Padhy. 2008. Comparison of particle swarm optimization and genetic algorithm for FACTS_based controller design. Applied Soft Computing 8 (4): 1418-1427. https://doi.org/10.1016/j.asoc.2007.10.009.
31. Pavan, P., P. Battistoni, J. Mata-Alvarez, and F. Cecchi. 2000. Performance of thermophilic semi-dry anaerobic digestion process changing the feed biodegradability. Water Science and Technology 41 (3): 75-81.
32. Penaud, V., J. P. Delgenes, and R. Moletta. 1999. Thermo-chemical pretreatment of a microbial biomass: Influence of sodium hydroxide addition on solubilization and anaerobic biodegradability. Enzyme and Microbial Technology 25 (3-5): 258-263. https://doi.org/10.1016/S0141-0229(99)00037-X.
33. Prorot, A., L. Julien, D. Christophe, and L. Patrick. 2011. Sludge disintegration during heat treatment at low temperature: A better understanding of involved mechanisms with a multiparametric approach. Biochemical Engineering Journal 54 (3): 178-184. https://doi.org/10.1016/j.bej.2011.02.016.
34. Rafique, R., T. G. Poulsen, A. S. Nizami, J. D. Murphy, and G. Kiely. 2010. Effect of thermal, chemical and thermo-chemical pre-treatments to enhance methane production. Energy 35 (12): 4556-4561. https://doi.org/10.1016/j.energy.2010.07.011.
35. Raposo, F., M. A. De la Rubia, V. Fernandez-Cegri, and R. Borja. 2012. Anaerobic digestion of solid organic substrates in batch mode: An overview relating to methane yields and experimental procedures. Renewable and Sustainable Energy Reviews 16 (1): 861-877. https://doi.org/10.1016/j.rser.2011.09.008.
36. Skiadas, I. V., H. N. Gavala, J. Lu, and B. K. Ahring. 2005. Thermal pre-treatment of primary and secondary sludge at 70 prior to anaerobic digestion. Water Science and Technology 52 (1-2): 161-166.