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Anaerobic process for the biogas production


An opportunity for nanotechnology

Christian  Rojas  Ph.D.

Universidad Santo Tomás, Villavicencio

Environmental Engineering Faculty

E-mail: christian.rojas@usantotomas.edu.co

One of the most challenging problems of the XXI century is the global climate change, a problem of great complexity that must be confronted from every aspect of the actual development state of the humanity.

The industrialization of the last century has created an increase in the greenhouse gases (CO2, CH4, etc) that makes inevitable the increase of the global temperature. However that can be mitigated in several ways, one of the most relevant is the change of the actual energy mix based on fossils fuels. Although in Latin-American a great proportion of the energy mix is provided by hydroelectric energy, the climate changes is also affecting negatively this source of power due to the change in the dry-wet season patterns.  Also there are regions where the net power (electrical and others) does not reach the total of the population, especially in rural zones. The renewable energies play here an important role as alternative source of energy as an action to mitigate the global warming. Colombia with an important agricultural sector produces important amounts of residues that can be converted in energy through the anaerobic process to produce biogas. In this way these residues (biomass) are as the same time producing an energy product (biogas) as bio-fertilizer (manure) from the transformation of the organic waste.

The biogas production actually

The transformation of waste to produce biogas is known since XIX century, however it was from the late XX Century and begins of XXI that the technology of the anaerobic process took impulse due to the renewable energy politics to mitigate the climate change [1]. The process reproduces what in nature occurs under specific conditions: absence of oxygen, warm temperatures, neutral pH and anaerobic bacteria in swamps and wetlands, that transform the biodegradable organic waste into biogas, a mixture of methane (CH4) and carbon dioxide (CO2) plus traces of others compounds such as H2O, H2S, N2, H2 [2]. To replicate the anaerobic process are use different types of bioreactors according to the environmental, technological and financial conditions of the location where the biogas will be produce.

Nowadays the technology has a great development especially in Europe and Asia[3], as it is represented in the total amount of biogas production worldwide (Figure 1).  Many countries in Europe with important agricultural sectors as Germany, Denmark, The Netherlands, Spain to mention a few, take advantage of the biomass produce in agriculture and food industry to produce energy as biogas. The biogas production is carried out usually in  big volume reactors 1000 – 3000 m3 (Figure 2(A)), constructed of steel with flexible dome cover and constant agitation, highly automated to keep the feed constant and the critical parameters, specially the temperature, controlled. 

Figure 1.  Biogas production presented by continents (2016). Source: WBA, 2018.

The anaerobic process was introduced in Latin-American in the 70´s with mixed results. Some Countries as Chile and Mexico have reached a technological development similar to European countries while others have not reached the real potential. The technology had advantages for rural isolated zones, where the lack of electricity and burn fuels make the production of biogas attractive [4]. In this zones prevailed a less sophisticated type of reactor, without technical, mechanical or electrical devices within, known as tubular biodigester (Figure 2(B)). In Colombia, most of the reactors for the production of biogas (biodigester) found in rural areas use this kind of technology for the production of biogas. The body of the reactor is a PCV tubular bag, where the input waste gets in one side of the reactor and the liquid effluent exits the opposite side.

Figure  2. a) Typical biogas plant in Europe: Lower Saxony-Germany.  b) Typical biodigestor in Latin -America: Meta-Colombia

An opportunity for  nanotechnology

Inside the reactor multiple reactions are carried out by a diverse population of anaerobic bacteria, which will depend of the substrate and environmental conditions of the anaerobic process. The more established model to describe this is divided in four stages: Hydrolysis, Acidogenesis, Acetogenesis, and Methanogenesis.  The complexity of reaction sequenceand bacteria population related makes difficult the manipulation of a single step of the process [2].

Therefore a part of the latest advances in the area of biodigestion consist of large-scale process automation, due to the great influence of the substrate on anaerobic digestion, much of the current research also focuses on improving the biodegradability of substrates, to maximize their biogas potential and avoid the use of fossil fuels in view of the consequences of climate change.In agricultural regions the majority of the organic waste available, can be classified as particulate material. This kind of substrate needs to be transform in more simple components at the first stage of the anaerobic process to accelerate the biogas yield. Therefore to optimize the process is necessary the speed up of anaerobic process through the pretreatment of the substrate, such as thermal processes [5], using microwave [6] or other procedures that allow better efficiency in biomass transformation [7]. Among those is the use of catalytic substances [8] as nanoparticles, which can optimize the enzymatic reactions that occurs during the anaerobic process.  That is particularly relevant in the actual panorama in Colombia were the absence of technological devices and small size of the rural biodigester makes very difficult the implementation of other alternatives. Additionally the amount and diversity of agricultural waste (Figure 3) shows the huge potential that the country has in biomass available for the production of this kind of energy. 

There are waste residues from corn, sugar cane, rice, banana, palm, etc. that with the residues from the animal sector (pig and cow manure) offer the possibility of a stable operation for the anaerobic process [9].   

The state of the anaerobic process in Colombia has not reached a mature development in comparison with other countries with similar characteristic; production of great amount of biomass residues form agricultural activities. However subsists hide potential that can be exploited in the in rural and isolated regions where the standard sources of energy are out of the range. The lack of technological devices in the rural biodigestors usually implemented in the rural regions of Colombia, makes the use of nanotechnology an attractive option to increase the  performance in the biogas production.Figure 3. Atlas of agricultural residues expressed in TJ/year in the different districts of Colombia (2018). Source: UPME, 2018.

REFERENCES

[1] EBA. Statistical Report of the European Biogas Association 2018. Brussels, Belgium. European Biogas Association – EBA. Available in: https://www.europeanbiogas.eu/eba-statistical-report-2018/

[2] Bischofsberger W., Dichtl N., Rosenwinkel K.-H., Seyfried C.F., Böhnke, B. (Hrsg.). (2005): Anaerobtechnik. Springer Verlag, Berlin-Heidelberg.

[3]WBA. Global Bioenergy Statistics 2018. Summary Report. World Bioenergy Association, Stockholm, Sweden(2018).  Available in: https://www.reportlinker.com/report-summary/Bioenergy/25586/Global-Biogas-Industry.html

[4] Ferre I., Garfi M. & Ferrer-Marti L. UPS: Una década investigando los biodigestores familiares en los países andinos. Revista RedBioLAC, 1(2017)9-10. 

[5] Sage M., Daufin G. & Gesan-Guiziou G. Effect of Prehydrolysis of Milk Fat on its Conversion to Biogas. Journal of Dairy Science, 91(2008)4062-4074.

[6] Nowicka A., Zielinski M., Debowski M., Dudek M. & Rusanowska P. Progress in the production of biogas from Virginia mallow after alkaline-heat pretreatment. Biomass and Bioenergy, 126(2019)174-180.

[7] Scarlat N., Dallemand J.F. & Fahl F.  Biogas: Developments and perspectives in Europe. Renewable Energy, 119 (A)(2018)457-472.

[8] Zaidi A.A., RuiZhe F., Malik A., Khan S.Z., Bhutta A.J., Shi Y. & Mushtaq K. Conjoint effect of microwave irradiation and metal nanoparticles on biogas augmentation from anaerobic digestion of green algae. International Journal of Hydrogen Energy, 44(2019)14661-14670.

[9] UPME, Atlas biomasa residual (2018) [on line]. Available in: http://upmeonline.maps.arcgis.com/apps/webappviewer/index.html?

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