Case Studies and Evaluation

#### **Chapter 6**

## A Case Study for Economic Viability of Biogas Production from Municipal Solid Waste in the South of Chile

*Jean Pierre Doussoulin and Cristina Salazar Molina*

### **Abstract**

This research evaluated the technical and economic feasibility of a biogas plant in the south of Chile to generate energy (WtE) for the plant's own consumption, energy for sale to the country's electricity grid and produce biofertilizer from municipal solid waste (MSW). In the town of Panguipulli, 26 tons of solid waste are produced daily, of which 12 tons correspond to household organic waste. These arrive directly to a landfill, wasting their potential to generate products and energy. To study the economic feasibility, an analysis was carried out on the investment, costs and income that make up the cash flow of the project evaluated at 15 years. The results gave an NPV of 214.099.637 CLP and an IRR of 15% at a real discount rate of 10%, with a payback period of 6 years. The research concluded that it is feasible to design a biogas plant that works from household organic waste in Panguipulli. This will contribute to the mitigation of climate change and will promote circular economy actions and the sustainable management of MSW in the south of Chile.

**Keywords:** economic viability, biogas, municipal solid waste, Chile, waste to energy

#### **1. Introduction**

This chapter points out the problems present in cities as a result of the excessive growth of waste production. This negative externality must be managed through a management system, which not only accumulates it in a sanitary landfill, but also generates social and economic benefits. From this angle, Doussoulin highlights the important role of the state in supporting the transition from a linear production system to a circular one, urban waste is reused, extending its useful life and reducing negative externalities on the biosphere [1]. One of the key sectors in the generation of urban waste and its recycling is the construction sector in Latin American cities [2, 3].

Currently, there are several options to reuse urban waste. For example, composting, recycling and biomass that can be transformed into biogas, the latter topic will be addressed in the next investigation [2]. It will be necessary to

understand some concepts about biogas. Rivas defines biogas production from household organic waste as a natural process, without oxygen carried out by microorganisms, this involves the fermentation of organic materials to obtain the biogas [3]. Furthermore, biodigesters are systems designed to optimize the production of biogas, obtaining clean and low-cost energy [4]. As some authors have stated; gas extraction from waste, responds to the need to close the circle, returning natural resources to their origin [5]. The technological, legal and economic challenges and the opportunities for improvement in the well-being of developing countries have been studied and pointed out by various authors [6, 7]. The demonstration issues in major countries can be illustrated as follows (see **Table 1**).

**Table 1** shows that the extraction of biogas from garbage is a relevant issue in South American countries. This is also emphasized by various Chilean authors on issues such as: the design of networks of biogas [26], environmental sustainability [27] and municipal waste management [28]. Therefore, this chapter continues and deepens these works taking advantage of the challenges and opportunities of biogas production. Thus, this study aims to study the feasibility of profitably investing in a biogas generating plant in the commune of Panguipulli from household organic waste. This will mean a crucial advance towards the reduction of the waste that reaches the landfill, therefore less environmental pollution, promotion of unconventional energies and direct solutions to citizens' problems by having a low-cost, good-quality product available. This research is mainly related to the search to alleviate energy poverty that currently exists, reducing economic barriers and in this way making a product as essential as gas more accessible to the public, whether it is used directly as fuel or electricity is generated from it [29]. This is why it is intended in the following research, to discover if it is feasible to invest in a generating plant of biogas in the Panguipulli commune by calculating the costs of the installation of a large-scale plant that meets the needs of the commune, as well as a calculation of the costs of the materials involved in the entire generation process of biogas, and finally to discover if the investment is recovered and if so, in how long a time.

The importance of this study concerns: first, the results will provide an important economic and time saving, since they will be of great help in upcoming projects related to landfill waste management policies and the generation of renewable energies in Chile. An attractive investment project in the medium and long term for


#### **Table 1.** *Main demonstration issues related to biogas.*

#### *A Case Study for Economic Viability of Biogas Production from Municipal Solid Waste… DOI: http://dx.doi.org/10.5772/intechopen.104558*

the entity that has the financial resources to carry it out. Second, this research will also carry out a study of the composition and volume of a substrate to be used in this specific case, investment analysis, costs and income that will make up a cash flow of a project evaluated at 15 years. In addition, some economic indicators are calculated to evaluate the viability of the project, these are: net present value (NPV), Internal rate of return (IRR) and Payback. Third, there is not much research on biogas plants in southern Chile. These biogas plants operate on a very small scale, the result of which is that there is no literature related to this geographical area.

This study explores the gap in the literature by answering whether the construction of a biogas plant in the commune of Panguipulli is economically profitable? The added value of this proposal is that it proposes an alternative use of the biogas applicable to the national reality and specifically to the Panguipulli commune, reducing negative environmental externalities as a result of their mismanagement emissions. Indeed, there is a lack of knowledge of the energetic potentiality of the biogas, for which an energetic waste arises and economical from the biogas emanating from the landfill. All of the above allow biogas generated in the sanitary landfill to not be managed correctly, causing the release of greenhouse gases such as *CH*<sup>4</sup> and *CO*<sup>2</sup> to a greater extent, which contribute to global warming, in addition to the contamination of the land and underground water.

Next, a compilation of information related to the biogas generation, similar studies, history of waste management and other data that the author considered relevant, all this was consulted in materials of authors with track records.

The chapter is structured as follows: Section 2 outlines a background of biogas production. Section 3 identifies the main results. Section 4 concludes and proposes future research direction.

#### **2. Background**

A large amount of waste is generated uncontrollably every day. From an environmental perspective, it is good to reduce the amount of waste that ends up to landfills, a part of this garbage being household organic waste that is usually thrown away along with everything else. In some parts of the world, the great potential that these projects have has been understood and projects have been created to reduce pollution, promote non-conventional renewable energies and generate a good quality product that allows an economic profit to be obtained. In other words, Parra refers to the fact that food residues (RA) have a high potential for reuse through biological processes such as anaerobic digestion (AD), especially due to their high content of biodegradable organic matter [30].

As a result of the decomposition of this organic material carried out by microorganisms, biogas is produced. A study by Gamma engineers defines it as a combustible gas that is generated in natural environments or specific devices, by the biodegradation reactions of organic matter, through the action of microorganisms in the absence of oxygen, that is, under anaerobic conditions [31]. Therefore, to optimize biogas production, this process is carried out in biodigesters in order to provide the right conditions for biogas extraction. In addition, as a by-product of this process, you can obtain bio-fertilizer [32].

The need to manage urban waste dates back to the time of the Roman Empire. They already had an environmental conscience, they worried about where their vessels and ceramics would go, and from there comes recycling. They recovered them to make other containers, used as fertilizer in agriculture or even as material for construction.

Some of the first authors to refer to biogas production were Sanghi and colleagues in 1977 [33]. This chapter pointed out the benefits of an anaerobic digester, and its generating potential for energy, where they saw it as an alternative to reduce the money invested in oil imports.

In Chile, there is great potential to generate energy with biogas from waste, not only in landfills but also in agriculture, forestry, the food industry and salmon farming. According to Ortiz, until 2017, there were 25 biodigesters nationwide, of which 10 are in the operating phase located in the Los Lagos region, the other biodigesters were in the project and start-up phase. This shows that the power generation potential has not been fully exploited [34].

When collecting information on business models applied in different parts of the world, we can find that there are five producing countries that have been able to make this product, these are Germany, Spain, Brazil, Canada and Sweden. A report from the ministry of energy of Chile mentions factors that they have in common, that is, they receive a state boost in the form of investment subsidies. In Germany, Spain and Canada the projects of biogas that generate energy for sale to the grid have a guaranteed rate. In Sweden, the use of biogas as a vehicle fuel has also been given impetus. Setting it as tax-free fuel and subsidizing the purchase of vehicles that work with biomethane [31].

It is important to mention that the process of obtaining gas from garbage is commercially viable [35]. Regarding the Chilean national regulation, there are minimum requirements for the sale of energy to the central interconnected network, which suggests that generating electricity from biogas may be a possibility of business. Jaramillo & Matthews mention that in addition to an economic benefit there is a social benefit for this type of project [36]. This allows for meeting the needs of the community, it is friendly to the environment since it does not increase the amount of carbon dioxide in the atmosphere and it constitutes a great sustainable alternative by promoting greater awareness about a more balanced relationship with nature.

A case study in Mexico makes an estimate of waste per capita of Michoacán of waste with its specific percentages for each type of material, estimation of the biogas production through the Mexican biogas model version 2.0, developed by SCS Engineers under agreement with the LMOP program of the Environmental Protection Agency of the United States (US EPA) [37]. The model generates biogas production and capture projections depending on waste management and arrangement of the sanitary landfill, in order to carry out short-term feasibility studies, medium and long term of this type of project. The description of the scenarios of this study will guide the modeling of biogas generation to be done in a larger proportion [38].

This project proved to be technically and economically feasible, the data that were required are very similar to those that will be needed in this investigation, for example, the costs of the entire project, amount of tons available at the end of the project, benefits of each ton of organic waste. The results summarized by Vera indicate that the benefit obtained from saving electricity is compared with the cost of a study that includes three important aspects: the investment cost, operation and maintenance [39]. This study shows that the scenarios studied are above the cost of a sanitary landfill, which indicates that a project with these characteristics is prefeasibility even if the biogas capture efficiency is the lowest (40%) [38].

#### **3. Methods**

As mentioned in the preceding sections, this research analyses an investment project for the creation of a biogas plant, from household organic waste in the commune of Panguipulli. This research arises from identifying a waste of the energy potential of waste in the commune. The general aspects of the project include the following stages.

*A Case Study for Economic Viability of Biogas Production from Municipal Solid Waste… DOI: http://dx.doi.org/10.5772/intechopen.104558*

It is important to mention that the use of the previously exposed methodology allows an analysis of the technical requirements of a biogas plant, in addition, projected income will be considered and expenses to measure its potential returns.

#### **3.1 Stage 1**

#### *3.1.1 Legal framework*

All projects must comply with a minimum regulatory framework for their legal operation:


#### *3.1.2 End products of anaerobic digestion*

From anaerobic digestion, final products are obtained such as biogas with energy-generating potential, as well as a stable biosolid that is used to improve the soil (biofertilizer or biofertilizers). This is an organic product with a high quantity of nutrients, it is not polluting and does not have pathogenic microorganisms, and

finally a mixture of water and solids, the latter are obtained from the anaerobic decomposition of the substratum.

#### **3.2 Stage 2**

#### *3.2.1 Biomass availability*

In 2019 a characterization of the composition of the MSW was carried out, this showed that the total waste generated in Panguipulli is 9361 tons per year. **Figure 1** shows the MSW generated each month in 2019.

A total of 46% of the 9361 tons of household solid waste generated in Panguipulli, corresponds to household organic waste. A graph showing the composition of MSWs is shown below. According to this information, we can conclude that 4,306,060 kilograms per year of organic waste are generated domiciliary, which is equivalent to 11,961 kilograms per day.

It is suggested that organic waste be separated in homes, at the moment in which they are generated, for this the cooperation of the population of Panguipulli is needed. In this process, conscious education on the separation of waste is of vital importance in order to have biogas according to expectations. In addition, this will drive a culture towards the sustainable management of household organic waste in the commune.

Given the current pandemic situation caused by COVID-19, it will be necessary to have safeguards in the handling of organic waste [45]. This is why some authors recommend taking measures for the adequate extraction of organic waste to seek the protection of workers who are part of the collection and transport of the substrate, reducing the possibility of being infected during their workday.

#### *3.2.1.1 Plant*

Plants can produce different amounts of biogas depending on the substrate used. In this study, for all calculations, it is taken into account that the substrate is waste of organic household products, which has a biogas production capacity of 50 m<sup>3</sup> per ton, this substrate is among the most profitable.

#### **Figure 1.**

*Solid waste generated in 2019 in Panguipulli, Chile. Source: Department of Cleaning and Decoration of Panguipulli.*

*A Case Study for Economic Viability of Biogas Production from Municipal Solid Waste… DOI: http://dx.doi.org/10.5772/intechopen.104558*

#### *3.2.1.2 Plant operation*

The biodigester generates methane from household organic waste. When methane begins to be generated, it will flow naturally to the capture point from the biodigester, from there, the electricity generator is fed, which is an engine optimized for the generation of electricity, using methane as fuel. The motor is powered by a gas pump and has a gas meter to monitor consumption.

#### *3.2.1.3 Climatic factors*

In order to implement this project, it will be important to consider climatic factors of the sector where the plant will operate, because the average climate in Panguipulli during the course of the year is between 3°C and 23°C. It may be necessary to implement a heated bioreactor and have proper insulation, this can increase some costs, since as the temperature of the biodigester increases, the speed of the growth of microorganisms increases, therefore, accelerating the digestion process obtaining a high content of methane in the biogas and conclusion obtaining profitable results.

#### *3.2.1.4 Holding time*

To generate the degradation process of organic waste or substrates time must pass, which depends directly on the temperature of the sector. For the calculations, the retention time used in biogas plants in the Los Rios Region will be taken as a reference where its substrate is also household organic waste.

Assuming its load is daily, the retention time will determine when the volume of charge needed to feed the digester is required. It is proposed to work with retention times of between 40 and 50 days and with daily loads of 10 kg per cubic meter of the digester.

#### *3.2.1.5 Biogas generation potential estimate*

The yield can be estimated according to the capacity of the biogas plant, these yield can be affected by factors such as retention time, temperature and agitation of the substrate, among others.

**Table 2** shows total returns; the information used in its generation was: 1 ton is equivalent to 50 m<sup>3</sup> of biogas per day, 1 m<sup>3</sup> of biogas can generate 1.8 kilowatt-hour (kWh) per day, which delivers electrical power to the generator of 50 kW.

In addition, it is necessary to clarify that by the multiplication of the total biogas of each cubic meter per unit of KWh, the total kw per day of electrical energy production is obtained. **Table 2** with its data is shown below.


#### **Table 2.** *Total yields from the listed biogas plant.*

#### *3.2.1.6 Ground*

The land should be a flat surface, ideally, it has a sewer, to facilitate maintenance and be able to channel liquid elimination, if not, it will require trucks, and clean pits, which would increase maintenance costs. Furthermore, it is necessary that there is the availability of water. It is very important that the plant is exposed to the sun, there should not be a mound nearby to shade it. There must be good access for the trucks that will carry the raw material to enter without a problem.

#### *3.2.1.7 Generating potential of biofertilizer*

Among the by-products generated by the biogas plant, is the solid bio stable (soil improver) mentioned above in the scheme of the process of anaerobic digestion, this product can be used as a biofertilizer for soils, as it has nutrients such as potassium, phosphorus, nitrogen among others, which help to recover minerals lost in crops [46].

#### **3.3 Stage 3: economic valuation**

This section describes the aspects of the cash flow elaborated, in detail. Using the cash flow, economic indicators were obtained that allow evaluation of the profitability of the project. The calculations are presented in Appendix 1, with their respective NPV, IRR and Payback. These tools are the most suitable in this investigation as it allows the calculation of the time in which the initial investment will be recovered to be made more precise.

#### *3.3.1 Income from the sale of electricity*

It is one of the main incomes, which corresponds to 60% of the energy produced, it will be injected into the distribution network that under Law 20,571 has entered into force since 2014. For the calculations, we express prices and costs in CLP, 830 CLP is equivalent to 1 US dollar. A price of 385 CLP/kW was estimated, in addition the plant has an electric power of the generator of 50 kW, which generates 31,200 kW-month, the plant will produce electricity 24 hours a day for 6 days a week, taking a total of 4 days a month for maintenance. The income per sale will be constant over time. The above delivers a total annual income of 86.486.400 CLP. This information was collected from the data historical prices of the node near Panguipulli [47].

#### *3.3.2 Income from energy savings in self-consumption*

Energy generated by the biogas plant allows it to pay for the monthly energy supply which corresponds to 40% of all electrical energy produced. For this, the amount of kWh saved annually was valued by installing the biogas plant and the economic savings incurred were estimated. Therefore, an annual saving in electrical energy of 57.657.600 CLP is obtained.

#### *3.3.3 Income from sale of biofertilizer*

It was neither possible to find the value of the fertilizers that are used in the market nor the sale value of biofertilizers generated by biogas plants, since these depend on the chemical compositions. Therefore, to determine in some way the income of the biofertilizer, the price for sale at 44.8 CLP per kg was used and the percentage of recovery of organic matter for the generation of biofertilizer of 30% with respect to the initial organic matter. These data were recovered from a study of a biogas plant using grape marc as substrate [46]. Income from the sale of biofertilizer is equal to 58.060.800 CLP annually and will remain constant over time. The costs associated with this project are investment costs, operating and maintenance costs and costs for investments in intangibles.

#### *3.3.4 Investment costs*

It can be seen in the following table that the total cost of the investment required by the biogas plant amounts to 540.000.000 CLP (810 CLP are approximately 1 US dollar). The estimation percentages of the factors influencing the project were taken from Garay García thesis (see **Table 3**) [48].

#### *3.3.5 Operation and maintenance costs*

These costs are associated with the substrate (since currently the substrate is not used in anything, it does not have a cost or price), maintenance, waste disposal, costs of operating inputs and personnel costs. Total operating costs amount to 53.824.457 CLP yearly.

Regarding the personnel requirements, it is considered for the calculations that it is necessary to work with five people for the operation of the plant, where two people are technicians and work full-time and the others are full-time assistants. Estimates of personnel cost are 27.720.000 CLP per year.

Regarding the costs of inputs, water for the tributary of the digester is necessary, for the calculations of water used for loads of the tributaries, it is estimated 714.457 CLP yearly [49].

Another cost to consider is the maintenance and repairs of the equipment, this will be calculated based on percentages of the total investment cost. Total maintenance costs are equivalent to 25.390.000 CLP per year (see **Table 4**) [48].

#### *3.3.6 Cost of investment in intangibles*

This cost includes patents to function in a legal form, contracts, insurance for damage to equipment or motors, pumps, agitators, among others. In addition, it is recommended to take out insurance in case of earthquakes or other situations that may damage the investment. The cost associated with intangibles varies between 0.8% and 1% of total investments [46]. The total investment amounts to 540.000.000 CLP and must be considered in year 0.


#### **Table 3.** *Net investment cost in CLP.*


#### **Table 4.**

*Total cost of maintenance in CLP.*

#### *3.3.7 Land rental*

Considering that this project could be executed by a municipality, as well as a private company, an estimated market rental value for urbanized land in the surroundings of the city of Panguipulli is equivalent to 3.600.000 CLP per year. The value is constant over time and is exempt from tax in accordance with the provisions of Exempt Resolution No. 300, of 1970, revalidated in accordance with instructions contained in Decree No. 111 of 1975 of Chile [50].


#### **Table 5.** *Depreciation per asset individually in CLP.*

*A Case Study for Economic Viability of Biogas Production from Municipal Solid Waste… DOI: http://dx.doi.org/10.5772/intechopen.104558*

#### *3.3.8 Working capital*

The project will generate income from its start-up by the sale of electrical energy and biofertilizer, a working capital will be estimated that allows it to cover the first 3 months of operation, this includes rent, and operating cost and maintenance. The working capital is equivalent to 163.456.113 CLP annually.

#### *3.3.9 Depreciation*

Depreciation corresponds to the decrease in the value of assets due to their use or deterioration. Depreciation in this project was estimated with a normal useful life. Below is the depreciation of each asset individually, the number of years of useful life was extracted from the SII website (see **Table 5**) [50].

#### **4. Discussion**

The technical evaluation of the biogas project from household organic waste for the production of electrical energy, self-consumption and sale of bio fertilizers, projects that the process is technically feasible mainly due to the fact of the substrate nowadays. It is a problem with high costs for the municipality, and for this project, it is free raw material.

For the start-up of the project, it is important to consider that the costs of the investment evaluated are mainly concentrated in the biodigester and the cogeneration, being 50% of the investment. This indicates that it is very important to know the real cost of this equipment. It is recommended to obtain quotes from several companies, in addition to calculating the dimensions, since this could affect the cost of the investment which would affect the profitability of the project.

For the execution of the project, the variability in time of electricity prices is a consideration. In this study, it was considered that energy production would be sold to the central interconnected system, but there is also another option that was not estimated since it is currently not very feasible. The sale of energy directly to companies, could generate contracts for long periods, but the investment of the installation of wiring and other costs, in the city of Panguipulli there does not currently exist a large company that could be a potential client.

It is important to recognize that a weakness of the project is its high investment cost, which means an entry barrier to the energy and fertilizer market. As was commented previously, the waste for another entity means an expense, but seeing it from this perspective that it is a potential income generator, in addition to being an environmentally friendly process, it provokes an acceptance by the surrounding communities and could be considered in the municipality plan.

The cash flow indicates that the project under the conditions defined in the technical and economic evaluation is profitable according to the economic indicator of net present value. It amounts to 214.099.637 CLP, an IRR of 15% and a recovery period of 6 years.

This is because the sale price of bio fertilizer is high, capable of absorbing almost all annual expenses, a high percentage of sales can be estimated, since the market for fertilizers in this area is great. The information previously presented allows us to answer the hypotheses; where the first two are accepted, the construction of a biogas plant in the Panguipulli commune is economically profitable and the volume of household organic waste in the Panguipulli commune makes it possible to construct a biogas plant, while the third hypothesis is refuted. The investment in the


#### **Table 6.**

*Results of economic indicators in CLP.*

construction and implementation of a biogas plant in the commune of Panguipulli is recovered in 4 years.

The evidence of the results of the indicators economic showed that investment in the construction and implementation of a plant of biogas in the commune of Panguipulli is recovered in 6 years (see **Table 6**).

It is recommended that to reduce the risk of the project, the given climatic factor be considered, which is the greatest limitation for the development of biodigestion projects. This inconvenience can be reduced by implementing complementary heating to the biodigester and implementing proper insolation. In this way, by increasing biogas production, consequently, the generation power of kW will increase the profitability of the system. It is also suggested to include information on the location of the project, this will allow knowledge of environmental conditions, wind speed and direction.

The technical and economic evaluation of a biogas plant from household organic waste allowed a visualization of the economic profitability, points to consider and difficulties that will allow clarification of the situation to potential investors.

#### **5. Conclusion**

Currently, there is excessive growth in waste production at a worldwide level that leads to the search for new solutions that allow the reuse of waste in a sustainable way over time and friendly to the environment, within these options is biogas, that by means of a biodigester offers advantages for the waste treatment which generates a gaseous fuel, which can be used to generate electrical energy. It also generates a quality biofertilizer and with this, it is possible to reduce the environmental damage caused by accumulating this substrate in a sanitary landfill.

When analyzing the composition of the waste, it was calculated that 12 tons of household organic waste per day is generated in the Panguipulli commune. This allowed the size of an appropriate biodigester to store 40 days of retention, and thus generate 600 m3 of biogas per day, which provides electrical power of the generator of 50 kW that allows a generation per year of 374,400 kW-year. Thanks to this, it can self-consume energy electricity and sell the rest to the central interconnected system.

This research has several characteristics that position it with a potential for biogas production, these are; availability of substrate use, geographic availability of the substrate, stable prices and costs and projected in time and finally to create a project that minimizes environmental impact.

Finally, the economic evaluation obtained a net present value (NPV) of the project evaluated to 15 years of 214,099,637 and an internal rate of return (IRR) of 15% to a real discount rate of 10%. The investment payback period is 6 years.

#### **Acknowledgements**

This chapter was written based on Cristina Salazar's commercial engineering thesis at the Universidad Austral de Chile, supervised by Professor Jean Pierre Doussoulin.


*A Case Study for Economic Viability of Biogas Production from Municipal Solid Waste … DOI: http://dx.doi.org/10.5772/intechopen.104558*

**Appendix**

 **1: Cash flow in** 

**millions**

 **of Chilean**

 **pesos (CLP).**

#### **Author details**

Jean Pierre Doussoulin1,2\* and Cristina Salazar Molina3

1 Universidad Austral de Chile, Economic Institute, Chile

2 Université Gustave Eiffel, Research Team on the Use of Panel Data in Economics, France

3 Universidad Austral de Chile, Faculty of Economics and Administrative Sciences, Chile

\*Address all correspondence to: jean.doussoulin@uach.cl; jean-pierre.doussoulin@u-pem.fr

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*A Case Study for Economic Viability of Biogas Production from Municipal Solid Waste… DOI: http://dx.doi.org/10.5772/intechopen.104558*

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[31] Gamma Engineers SA. Modelos de negocio que rentabilicen aplicaciones de biogás en Chile y su fomento. Ministerio de energía. 2011. Available at https:// www.aproval.cl/manejador/resources/ informefinalmodelosbiogasabril2011. pdf

[32] Grass Puga BD. Evaluación y diseño para la implementación de una planta de biogas a partir de residuos orgánicos agroindustriales en la Región Metropolitana. 2013

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#### **Chapter 7**

## Case Studies in Biogas Production from Different Substrates

*Adrian Eugen Cioabla and Francisc Popescu*

#### **Abstract**

The present paper involves applicative research in the field of biogas production with the accent on small laboratory scale installations built for biogas production, preliminary testing of substrate for biogas production and combustion applications for biogas-like mixtures. The interconnected aspect of the presented material involves cumulative expertise in multidisciplinary fields of interest and continuous development of possibilities to determine the energetic potential of substrates subjected to biodegradable fermentation conversion for further applications. The research analyzed the combustion behavior of biogas with different methane/ carbon dioxide ratio without and in the presence of specific catalysts. Also, laboratory analysis on biomass substrates for determining their physical and chemical potential for different applications was performed. The main conclusions are drawn revolve around the untapped potential of the different types of biomasses that are not commonly used in the production of renewable energy carriers, like biogas, and also the potential use of residual biomass in combustion processes for an enclosed life cycle from cradle to the grave. The study involving the use of catalysts in biogas combustion processes present possible solutions which can be developed and implemented for increasing the combustion quality by using relatively cost-effective materials for the production of catalytic materials.

**Keywords:** biomass, biogas, anaerobic digestion, renewable energy, combustion

#### **1. Introduction**

Renewable energy sources have become a milestone of the next decades for European Union member states, due to tough deadline targets to reduce their energy production dependency on fossil fuels. In June 2021, thru its new European Climate Law, the EU targets a reduction of greenhouse gases emission of at least 55% by 2030, compared to the 1990 level, and a net-zero greenhouse gas emissions in the EU by 2015. On top of this ambitious target, the EU is pushing its member states to complete climate neutrality by 2050. In this frame, the new 2030 greenhouse gases emission reduction target for Romania is 12.5% (in respect to 2005 inventory), a target that Romania has already passed in several chapters, with a total reduction in 2019 of 65% compared to 1990 emissions inventory, being the member state that achieved the highest greenhouse gases emissions reduction in the EU, along with Lithuania. However, for a specific chapter, the "transportation, buildings and agricultures sector" Romania has a new reduction target of 12.7% by 2030 (compared to 2005 national GHG inventory) [1].

Having in mind that for Romania most of the industrial sectors have or are close to reach their targets for 2030 and the main 2 sectors that still must reduce with 12.7% of their greenhouse gases emissions by 2030 are transportation and agriculture are clear that the focus should be on developing the renewable sources that can have a significant impact on both sectors. The renewable energy sector had a fast development in the past 2 decades, however, the energy production from biomass/biogas did not increase as other sources. For example, in 2019 in Romania the installed renewable energy installed capacities from biomass/biogas was of 124.16 MW while the photovoltaic installed capacities were 1358.43 MW and wind farms at 2960.64 MW. With this data on mind it becomes quite clear that Romania's focus in the next period should be on biomass/biogas production facilities development as not only will reduce dependency on methane imports but will contribute to reaching greenhouse gasses emissions from the agriculture sector.

The production of biogas from biomass substrates thru anaerobic digestion is well known since antiquity, the technology being constantly developed but due to environmental impact thru pollutants developed (solid, gas and liquids) faces continuous challenges, with continuous scientific efforts in research for innovative materials to be used in biogas production from biomass and urban waste waters [2].

In the Romanian case and any other country with significant agricultural areas and also a large number of urban agglomerations, the potential sources for biogas production thru anaerobe digestion can be classified in four main groups:


In terms of biogas production from any of the sources classified above, the most critical parameter in obtaining the best CH4/CO2 ratio after anaerobic digestion is the substrate composition, as today's substrates are mostly formed for co-digestion of a minimum two waste materials. Depending on the substrate composition the anaerobic reaction temperature will have a different effect on variation of pH, volatile fatty acids, total solid degradation and ammonia/nitrogen ratio that would affect the stability of the digestion process [4].

In the EU country, all biofuels (solid, liquid or gaseous) have a subsidy from EU public budges and accordingly the production of biofuels is subject to sustainability criteria under the Renewable Energy Directive [5]. The Directive introduces significant restrains in the production of raw agricultural materials for energy use, mainly to protect primary forests and biodiversity. In respect of the Directive, the Romanian focus for developing a sustainable biofuel (with emphasis on biogas production for energy purposes) industry should be on agricultural and urban wastes.

#### **2. Applied research on case study**

Currently, the focus is to work on small-scale installations for testing in a controlled environment the potential for different materials and the possibility to develop new bioreactors for further use in anaerobic fermentation processes.

The present chapter will highlight a part of the research conducted so far, covering three main parts:


#### **2.1 Testing in combustion processes of biogas: like mixtures**

Biogas like mixtures represent, in our case, mixtures containing 70–75% methane and around 25–30% carbon dioxide, concentrations by volume, to assess the energetic potential for this type of materials, by comparison with real biogas testing, which contains also other elements, like hydrogen sulfide (the main corrosive and toxic component in biogas), ammonia, water and other impurities from the process of anaerobic digestion.

First, we will present in short, some determinations relative to biogas determinations. Those determinations were made for determining the biogas potential in firing processes and were carried out in situ, by using pilot patented installations, but for our discussions, the test rigs will not be presented, only the part needed for the firing testing.

The tests were carried out at a location for an industrial partner for Politehnica University, and the produced biogas came from anaerobic digestion of municipal residues.

The figure below presents the test rig developed for firing tests (**Figure 1**).

As it can be observed above, from left to right there are the following components: biogas pipe, connected with the system for pressure control and measuring, the burner (in yellow) and the entrance to the firing chamber, where the tests were carried out. At the end of the chamber, there were measured the flue gas and the temperatures were determined at specific points on the outside wall of the testing chamber. The next images will present some results for the measurements of the flue gas. The equipment used in this regard was TESTO 350XL and DELTA 1600 S IV gas analyzers.

**Figure 1.** *Elements of the test rig.*

**Figure 2.** *NO, NOx concentration evolution in time.*

**Figure 2** presents the time variation of NO and NOx during the combustion process of biogas containing around 75% methane and 24% carbon dioxide. The produced biogas was without a filtering system. From the presented graphic, it can be determined that the nitrogen oxides concentration is very low (ppm values), at around 40–43 ppm, which represents very good results in this context.

The used burner had a constructive air-cooled system of the flue gas and by this method, combined with a relatively high rate of combustion, the resulting NOx emission was very low, which represents a positive aspect in this context (**Figure 3**).

Carbon monoxide is one of the most dangerous flue gasses in high quantities and it needs relatively high temperatures and safe firing conditions to be present in low concentrations. The maximum values for CO concentration during the process are also very low, at around 35 ppm, a very good indicator for a relatively complete

*Case Studies in Biogas Production from Different Substrates DOI: http://dx.doi.org/10.5772/intechopen.101622*

**Figure 3.** *CO concentration evolution in time.*

**Figure 4.** *CO2 concentration evolution in time.*

firing process. The obtained values used by parallel measurement with all the other existent flue gas, indicated the low volume presence of CO which is a positive argument for a very safe firing process.

As observed in **Figure 4**, CO2 concentration maximum values were at around 9–10%. It is important to have in mind the fact that those values started at around 25–30% by volume before the firing process, which indicates also that the firing parameters were efficient, even if the overall CO2 did not burn (because of its inert nature to firing reaction). Next, there are going to be presented tests made together with collaborators from Serbia, the Mechanical Engineering Faculty in Belgrade.

The tests were carried out in the presence and absence of catalysts to observe their influence over the firing parameters and also the flue gas was analyzed with the help of a Horiba gas analyzer coupled with a special developed system used for data collection and registration, containing temperature and pressure sensors, and data control and storage equipment (**Figure 5**).

The used catalysts were ZnAl2O4, CoAl2O4 andZnCr2O4. The obtained pellets were inserted in a metal matrix for protection purposes and the firing chamber was prepared for preliminary tests.

#### **Figure 5.**

*Preparation of ZnAl2O4 catalysts: A – Weighting; B – Insertion in the metal matrix; C – Initial testing with and without catalysts.*

#### **Figure 6.**

Before recorded measurements, there were made some preliminary trials to calibrate all the necessary equipment and sensors on the used firing chamber. The next part will present in summary just a small part of the determinations performed inside the firing chamber, with and without the existence of catalysts (**Figure 6** and **Table 1**).

From the gathered data, it was determined that at the base of the reactor, the maximum temperature reached was around 1058°C, with very low gaseous emissions (**Figure 7** and **Table 2**).

By comparison with the first scenario, it can be observed that the maximum temperature reached at the solid phase (the base of the reactor) is around 1097°C, slightly higher than for the process without catalyst, but it was observed an increase of CO concentration, which indicated an incomplete combustion process. The main indicator of an increased CO is usually the area with high temperatures. This aspect combined with an ineffective air/fuel ratio can have as a main result the higher CO concentration, at least this is the author's present explication to this phenomenon.

The only catalyst presented in this study was ZnCr2O4, because for the other used catalysts, there was no visible influence over the firing parameters overall, this meaning they had a very limited impact in this testing scenario. Of course, further testing is to be made available to determine possible applications for the used catalysts and to test new ones for better results over impact during combustion processes.

*Temperature values inside the combustion chamber, without catalyst presence.*

#### *Case Studies in Biogas Production from Different Substrates DOI: http://dx.doi.org/10.5772/intechopen.101622*


**Table 1.** *Testing without catalyst.*

#### *Biogas - Basics, Integrated Approaches, and Case Studies*

#### **Figure 7.**

*Temperature values inside the combustion chamber, with ZnCr2O4 catalyst presence.*

Overall, the started research is to be continued and further tests need to be done for simulating more different regimes, as well as to investigate the influence of catalysts at higher working temperatures.

#### **2.2 Laboratory analysis on biomass substrates for determining their physical and chemical potential for different applications**

This part of the present material will underline a part of the experimental determinations for different types of biomasses to determine their potential for anaerobic digestion or firing (co-firing) processes.

The used standards for laboratory determinations were:


The next table presents a small part of the determinations made for different types of biomasses (**Table 3**).

The chosen materials came from a very large selection, which stands as a base material for a database created by the first author of this chapter, database that is continuously under development and contains materials from agricultural, forestry,

#### *Case Studies in Biogas Production from Different Substrates DOI: http://dx.doi.org/10.5772/intechopen.101622*


**Table 2.** *Testing ZnCr*

*O2*

*4 catalyst.*


#### **Table 3.**

*Types of analyzed biomass.*

household, municipal, and industrial fields of application for all that involves biodegradable or partially degradable materials.

The next tables are going to present some general aspects concerning the properties of the studied materials and the potential application for energetic conversion (**Table 4**).

The moisture of the presented materials is considered for already pre-dried materials. From an ash content, the white poplar and sunroot have the largest values, making them not the first choice for firing processes, due to their high residue and ash content.

The calorific value is high for all the studied materials, and a very interesting aspect is the fact that the arborescent samples have net calorific values close to plant biomass, making them suitable for both energy conversion processes.

The carbon content and nitrogen are very specific for biomass, while the hydrogen content is close in value from one species to another, except hemp. There are no exceptional or different values than the ones expected for this type of material. Relative to C/N ratio, the best suitable biomass would be Sunroot, with a ratio of around 31. According to existing literature, the optimum domain for C/N ratio should be between 20 and 30, but from experience some materials do not meet these criteria and can be used for anaerobic digestion (**Table 5**).

The four specific points are very important to determine the specific temperatures at which the materials are starting to transform and reach a flowing point.


#### **Table 4.**

*Material energy properties, analysis on a dry basis.*



#### **Table 5.**

*Material chemical properties, analysis on dry basis.*

In this regard, combined with the energetic values and the ash content, it can be determined a good behavior of materials from a firing process point of view.

The sunroot material presented an unexpected high value for flowing temperature, while the rest of the materials presented expected values. The bark in white poplar made that the specific flowing point to be of a high value, as estimated.

In the context of the presented materials, the bark is to be excluded from analyzed samples, and the high ash content is a parameter that determines if the materials are suitable for combustion, co-combustion or other processes.

Of course, there are other parameters to be considered, like chlorine, sulfur or heavy metals, when taking into consideration all the variables to the energetic conversion, but this is just a partial analysis and the conclusions are traced accordingly.

The main applications for the study was to determine the energetic potential of biomass types not usually applied for firing or anaerobe digestion processes and to study their potential application in those two directions. The materials were chosen because there is not enough literature to discuss different potential applications for Elephant grass, hemp or sunroot in anaerobic digestion or combustion, while Paulovnia and White poplar were chosen as comparative used materials, especially for firing applications. Present studies are made for anaerobic digestion of a part of the studied materials, but the work is still in progress.

#### **2.3 Laboratory studies for biogas production and system development in terms of parameter monitoring and initial inputs for new different materials used for anaerobic digestion processes**

This last part represents the focus of the research developed so far by the chapter authors. First, there will be depicted some of the small-scale test rigs developed so far, starting with commercial ideas, but less expensive and with good capability in terms of process control and results.

The next two figures present small-scale test rigs designed for preliminary testing of biogas production from different substrates (**Figure 8**).

The components found in the figure are:

1.Thermostatic bath with 6–8 places for heating the used materials for the anaerobic fermentation process (the temperature is controlled with the help of a thermostat and can be checked with the help of a thermometer inserted into the bath);

**Figure 8.** *Small scale test bench.*


6.gas bag for biogas storage.

The second small-scale test rig is dedicated to processes at ~4 L and allows better control for substrate agitation, while offering different levels for temperature (**Figures 9** and **10**).

Each part is a separate module composed of the reactor with lid, syringe for sampling and ph control and control panel for controlling temperature and agitation inside each reactor. In **Figure 11** there can be observed 4 modules that work independently from one to another. Both test rigs were used to determine biogas potential in terms of quantity and methane, carbon dioxide, hydrogen sulfide and dissolved oxygen for different recipes/substrates. The next part presents preliminary results for different experiments.

#### **2.4 Laboratory production of biogas from waste waters, on 2 L scale test bench**

The experiments were conducted in two batches. For the first batch, the used substrate materials were: waste water from urban treatment plant (M1), waste water from brew factory (M2), 95% waste water from treatment plant and 5% beet molasses (MM1), 95% waste water from brew factory and 5% beet molasses (MM2), 95% waste water from treatment plant and 5% cow whey (ZM1) and 95% *Case Studies in Biogas Production from Different Substrates DOI: http://dx.doi.org/10.5772/intechopen.101622*

**Figure 9.** *Small scale modules.*

**Figure 10.** *Substrate pH variation in time, first batch.*

**Figure 11.**

*Substrate pH variation in time, second batch.*

waste water from brew factory and 5% cow whey (ZM2). The temperature regime was held at 36–37°C and the process parameters which were controlled consisted in pH, biogas partial composition and obtained quantities. The pH time variation for the material batches is presented in **Figure 12**.

**Figure 12.** *Substrate pH variation in time, first batch on 4 L reactors.*

From the pH variation, it can be observed that the co-fermented batches containing molasses for both residual sludges had the lowest pH, which increased after many corrections, which inhibited the fermentation process.

The pH for M1 and M2 was in the correct range and needed small interventions in terms of correction, the batch failed to produce a cumulative quantity of biogas that could be properly analyzed.

The most notable biogas quantities were produced by the MM1 (6 L) and ZM1 (4.5 L) batches. The maximum composition obtained after analyzing the produced biogas was for MM1, with 75% CH4 and 10% CO2.

On the second batch, the experiments were conducted in parallel, the second batch material used was formed as follows: 91% residual water from the treatment plant, 4% dehydrated sludge from the treatment plant and 5% cow whey for the first vessel and 91% residual water from the beer factory, 4% dehydrated sludge from treatment plant and 5% cow whey for the second glass vessel. The pH of the suspension was corrected with a solution of NH3 20% concentration and the temperature regime was held inside the domain of 36–37°C.

It can be observed that during the process, the batches presented a relatively high pH value which made the use of the NH3 suspension to be made just at the beginning of the process when the starting pH wasn't neutral.

Even if both batches produced biogas, the main composition of the produced gas until the end of the process was about 60 ÷ 61% CH4 and 38 ÷ 40% CO2 for both batches of material.

The produced quantities were about 4 L of gas for the mixture with residual water from the treatment plant, 4% dehydrated sludge from the treatment plant and 5% cow whey and about 5 L for the batch composed by residual water from the beer factory, and 4% dehydrated sludge from treatment plant and 5% cow whey.

#### **2.5 Laboratory production of biogas from waste waters, on 4 L scale reactors**

These experiments were also conducted in two batches. For the first batch, two reactors were used which had a total volume of 5 L each, of which 4 L was the useful volume. The temperature of reactor 1 (TR1) was 37°C and the temperature of reactor 2 (TR2) was 42°C. Reactor 1 (R1) had a 3.5 L suspension consisting of a specific mixture of biogas with corn silage and wet fraction plus 100 g of degraded maize grains. Reactor 2 (R2) had a 3.5 L suspension consisting of a specific mixture of biogas with corn silage and wet fraction plus 100 g of potato peel.

The figure above shows the pH levels for the two reactors used within 20 days of the experiments. It can be observed that in the first phase (the first 7 days the

*Case Studies in Biogas Production from Different Substrates DOI: http://dx.doi.org/10.5772/intechopen.101622*

**Figure 13.**

*Substrate pH variation in time, second batch on 4 L reactors.*

pH has a slightly decreasing tendency varying between 7.8 and 8.3, in this sense, it is observed that the substrate used is very stable over time even in the initial phase which has as specific a relatively acidic pH (below 6).

Throughout the process, the pH remains slightly alkaline for both reactors, being a good indicator for optimal development of the anaerobic fermentation process.

The first reactor was heated in mesophilic mode, and reactor number 2 in thermophilic mode (in its lower range), and in correlation with the pH identified during the experiment the elements of influence are favorable to produce a quantity optimal biogas with a relatively high methane concentration.

The cumulative amounts of biogas for the two reactors identify a value of about 14 L of biogas for reactor number 1 and about 8 L of biogas for reactor number 2. The difference in quantity between the two reactors can be explained by the temperature regime applied to each reactor in part (the thermophilic regime has as specific a higher production in the time of biogas) and the slightly different composition because the potato peel has a high starch content, an aspect that can be beneficial but also inhibitory, by the appearance of the foaming phenomenon, depending on the behavior of each load separately.

On the second batch, two reactors were used which had a total volume of 5 L each, of which 3.5 L was the useful volume. The temperature of reactor 1 (TR1) was 37°C and the temperature of reactor 2 (TR2) was 42°C. Reactor 1 (R1) had a 3.5 L suspension consisting of a specific mixture of biogas with maize silage and wet fraction of animal biomass plus 100 g of degraded maize grains. Reactor 2 (R2) had a 3.5 L suspension consisting of a specific mixture of biogas with corn silage and the wet fraction of animal biomass plus 100 g of potato peel (**Figure 13**).

For batch number 2, a similar pH behavior is observed for the two reactors with maximum values of about 8.3 for R1 and 7.9 for R2. Under certain conditions, pH values above 8 can slightly inhibit the biogas production process, but some substrates react positively to slightly higher pH values (between 7.5 and 8).

The temperature regime chosen is similar to that of the first batch, again noting that the heating system ensures a relatively constant temperature throughout the process for both reactors, with a difference of up to one degree compared to the desired operating temperature. Reactor number 1 produced about 14 L of biogas while reactor number 2 produced about 8 L of biogas, in this case, both the higher pH values and the slightly higher temperature range high being a negative influencing factor on the anaerobic fermentation process.

The concentration of methane for reactor number 1 is about 49% while for reactor number 2 it is about 51%, values which again are an indicator of a low potential for the use of independent in combustion processes.

### **3. Conclusion**

Relative to the presented material, the further conclusions can be traced:


All the presented elements, even if presented separately, are interconnected to add plus value to a known conversion process to further bring new perspectives in terms of used substrates, increased quality for the produced biogas in terms of methane concentration and further applications in firing processes to maximize the energetic output conversion to heat or electric energy.

### **Acknowledgements**

The authors of this material wish to recognize the support of the following entities and colleagues to the presented results. The catalytic firing process was made together with collaborators from Mechanical Engineering Faculty in Belgrade, and the authors want to address special acknowledgement to Prof. Srba Genic and Ass. Prof. Mirjana Stamenic for all the support in this regard. The laboratory determinations for biomass were conducted with the team from BEA Institute for Bioenergy, Vienna, Austria.

### **Conflict of interest**

The authors declare no conflict of interest.

*Case Studies in Biogas Production from Different Substrates DOI: http://dx.doi.org/10.5772/intechopen.101622*

#### **Author details**

Adrian Eugen Cioabla and Francisc Popescu\* University Politehnica Timisoara, Timisoara, Romania

\*Address all correspondence to: francisc.popescu@upt.ro

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **References**

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### *Edited by Abd El-Fatah Abomohra and El-Sayed Salama*

Anaerobic digestion is by far the most important technology for providing clean renewable energy to millions of people in rural areas around the world. It produces biomethane with anaerobic-digestate as a byproduct that can be used as a biofertilizer. In the context of energy consumption, more than 85% of the total energy consumed currently comes from non-renewable fossil resources. A wide variety of biowastes can be used as feedstocks for biogas production. Biogas technology can provide sustainable, affordable, and eco-friendly green energy along with useful byproducts. This book discusses the basics of biogas production and aims to address the needs of graduate and postgraduate students as well as other professionals through further evaluation of biogas production via case studies.

Published in London, UK © 2022 IntechOpen © kontrast-fotodesign / iStock

Biogas - Basics, Integrated Approaches, and Case Studies

Biogas

Basics, Integrated Approaches,

and Case Studies

*Edited by Abd El-Fatah Abomohra* 

*and El-Sayed Salama*