European Green Deal: Substantiation of the Rational Configuration of the Bioenergy Production System from Organic Waste

Abstract

A review of the current state of the theory and practice of bioenergy production from waste allowed us to identify the scientific and applied problem of substantiating the rational configuration of a modular anaerobic bioenergy system, taking into account the volume of organic waste generated in settlements. To solve this problem, this paper develops an approach and an algorithm for matching the configuration of a modular anaerobic bioenergy production system with the amount of organic waste generated in residential areas. Unlike the existing tools, this takes into account the peculiarities of residential areas, which is the basis for accurate forecasting of organic waste generation and, accordingly, determining the configuration of the bioenergy production system. In addition, for each of the scenarios, the anaerobic digestion process is modeled, which allows us to determine the functional indicators that underlie the determination of a rational configuration in terms of cost and environmental performance. Based on the use of the developed tools for the production conditions of the Golosko residential area, Lviv (Ukraine), possible scenarios for the installation of modular anaerobic bioenergy production systems are substantiated. It was found that the greatest annual benefits are obtained from the processing of mixed food and yard waste. The payback period of investments in modular anaerobic bioenergy production systems for given conditions of a residential area largely depends on their configuration and ranges from 3.3 to 8.4 years, which differ from each other by 2.5 times. This indicates that the developed toolkit is of practical value, as it allows the coordination of the rational configuration of modular anaerobic bioenergy production systems with real production conditions. In the future, it is recommended to use the proposed decision support system to model the use of biomass as an energy resource in residential areas, which ensures the determination of the rational configuration of a modular anaerobic bioenergy production system for given conditions.

1. Introduction

Today, European Union (EU) countries are faced with the problem of the disposal of organic waste generated at individual, residential and industrial facilities. This problem is becoming more and more acute, which makes it necessary to find effective scenarios for the processing of organic waste, in accordance with the environmental and organizational aspects provided by the various concepts and development programs of European countries, for example, the European Green Deal [1]. According to the European Environmental Protection Agency [2], in 2023, the recycling rate of municipal waste (including organic household waste) in Poland was about 49.6%, while more than 40% of this waste was used for energy production from biogas and other renewables energy sources. It is worth noting that recycling rates vary depending on the EU member state. In particular, the highest usage rates are observed in Austria (64%), Germany (62%), Slovenia (61%) and Croatia (60%). The lowest recycling rates are in Bulgaria (11%) and Romania (28%). It is also important to note that the EU has set ambitious goals for waste recycling. By 2030, the EU’s municipal waste recycling rate should reach 65%, and by 2035—70%. As for Ukraine, the recycling rate of household organic waste is much lower. According to statistics, in 2023, Ukrainian cities recycled only 1.6% of the total amount of municipal waste that went to landfills [3,4]. According to the Ministry of Ecology and Natural Resources of Ukraine, only about 5% of Ukrainian cities have organized organic waste collection and recycling systems.

According to the European Commission, in 2023, the average specific annual volume of organic waste from all types of activities per capita in the EU countries was about 131 kg/person [5]. In particular, the highest rate of specific annual volumes of organic waste from all types of activities per capita is in Cyprus—397 kg/person—which is three times higher than the corresponding average for the European Union (Figure 1). At the same time, in such countries as Slovenia and Croatia, the specific annual volumes of organic waste from all types of activities per capita are 68 kg/person and 71 kg/person, respectively, which are almost two times lower than the average for the European Union. In Poland, the specific annual volume of organic waste from all types of activities per capita in 2023 was about 106 kg/person. Compared to Western European countries, this is a lower level of organic waste generation, but at the same time higher than in some other Western and Central European countries.

According to the World Health Organization (WHO), Ukraine has a per capita waste generation rate of about 135 kg per capita. This figure is slightly higher than the average for the European Union and Poland.

One of the most promising solutions is the introduction of anaerobic bioenergy production systems, which not only reduce waste but also produce a valuable product—bioenergy (biogas, electricity, heat and biocompost)—which can be used as a renewable energy source. In this case, modular anaerobic bioenergy production systems, which are produced and used in different countries of the world, deserve attention [6,7,8,9]. At the same time, an important task is to harmonize the configuration of a modular anaerobic bioenergy production system with the actual volumes of organic waste generated in residential areas. The exact solution of this scientific and applied problem ensures not only the optimal operation of modular anaerobic bioenergy production systems but also the maximum efficiency of the waste-processing process.

In our article, we propose an approach for matching the configuration of modular anaerobic systems with the volume of organic waste generated in residential areas. It is based on modeling the processes of bioenergy production, which provide a forecast of functional and cost indicators for given scenarios and the capacity of residential areas to generate organic waste in individual households. At the same time, the use of modular anaerobic systems allows for the production of the required types of bioenergy without the need for additional facilities. This makes it possible to flexibly adapt them to changes in the amount of organic waste and ensure high processing efficiency. Evaluation and consideration of production conditions for individual residential areas are key aspects for the successful implementation of such modular anaerobic bioenergy production systems. Based on the analysis of data on the generation of organic waste, we propose a rational configuration of modular anaerobic systems that takes into account the specifics of each individual residential area.

2. Literature Reviews

Considering today’s urbanization and population growth in cities around the world, the problem of effective organic waste management is becoming more and more urgent from year to year [10,11,12,13,14,15]. The production of bioenergy from organic waste is an environmentally friendly and cost-effective way to generate energy. Anaerobic systems, in which organic matter is decomposed by microorganisms without oxygen, are one of the most efficient methods of processing organic waste and producing biogas, which can be used to generate electricity, heat and compost.

One of the promising approaches to solving the existing problem of organic waste processing in certain areas of cities is the use of modular anaerobic systems for bioenergy production [16,17,18,19,20]. This approach allows us not only to reduce the amount of waste but also to obtain additional sources of energy, which is important in the context of the growing energy needs of certain residential areas of cities and other settlements.

Modular anaerobic systems (MASs) are used to process organic waste to produce biogas, which is converted into electricity or heat. In recent years, a significant amount of research has been devoted to improvement in these systems, in particular their adaptation to different types of waste and operating conditions [21,22,23,24,25,26].

One of the main aspects of the known studies is the optimization of anaerobic digestion processes to ensure maximum biogas yield. Thus, in [27] it was found that the composition and properties of substrates have a significant impact on the efficiency of anaerobic digestion. Other studies have focused on technological aspects such as reactor design, process parameters and waste pretreatment methods [28,29,30,31].

Bioenergy systems, in particular anaerobic digesters, have the potential to provide a significant share of the energy needs of human settlements. According to studies, in particular [32], the use of organic waste for bioenergy production is not only environmentally friendly but also economically feasible, provided that the system configuration is optimized.

One of the main problems in the implementation of modular anaerobic systems in residential areas is the coordination of the system configuration with the volume of organic waste generated. Waste in different residential areas can vary significantly in quantity and composition; therefore, an individual approach to system design is required. Papers [33,34,35,36,37] investigate the influence of conditions on the efficiency of anaerobic digestion and propose methods for adapting systems to different conditions.

Today, there are a significant number of scientific papers on the use of modular anaerobic bioenergy production systems [38,39,40], as well as on the prediction of organic waste generation in residential areas [14,41,42,43,44]. There are also well-known scientific works [45,46,47] that propose approaches and methods for forecasting in other areas. In some scientific papers, their authors point out that the size of a modular anaerobic system should correspond to the amount of organic waste generated in a residential area [7]. Too small a system will not be able to process all the waste, and too large a system will be uneconomical.

There are several types of modular anaerobic systems, each with their own advantages and disadvantages. At the same time, the type and composition of organic waste generated in a residential area will affect the system configuration [7]. For example, systems that process food waste (FW) will require a different configuration than systems that process yard waste (YW). Also, the type and amount of energy to be produced in the system affect its configuration. For example, a system that produces electricity will require a different configuration than a system that only produces heat.

This analysis of scientific papers shows the high potential of modular anaerobic systems for solving the problems of organic waste disposal and bioenergy production. However, for the successful implementation of these systems in residential areas, it is necessary to solve the scientific and applied problem associated with the coordination of their configuration with the volume of organic waste generated. Further research in this area should be aimed at developing an approach and algorithm that will ensure the effectiveness of the use of MASs in the given conditions of residential areas.

Matching the configuration of a modular anaerobic bioenergy production system with the amount of organic waste generated in residential areas is a complex task that requires careful analysis and planning. Factors such as the type and volume of organic waste generated, the size and type of the system, the type of substrate and the energy needs of residential areas must be taken into account.

Existing research in the design and use of bioenergy systems mainly focuses on general approaches to organic waste processing or on optimizing individual elements of anaerobic processes, such as temperature or substrate composition control [23,43,48]. However, these studies do not take into account the peculiarities of the formation of the changing composition of organic waste in different residential areas and do not provide universal solutions for adapting systems to different conditions and volumes of waste [3]. Moreover, although modular anaerobic digesters are considered an efficient approach to scaling up production, there is a lack of specific algorithms that would allow the justification of the configuration of modular systems in accordance with the specific conditions of a particular community or residential area. Our research fills these gaps by proposing an innovative approach that combines the matching of organic waste volumes and composition with the configuration of modular anaerobic systems, thus providing flexibility and efficiency in organic waste management and bioenergy production in residential areas.

In view of the above, the main research problem can be formulated, which concerns the development of an approach to matching the configuration of a modular anaerobic bioenergy production system with the volume and composition of organic waste generated in residential areas. To solve this problem, the following is necessary:

–

develop an approach and algorithm for matching the configuration of a modular anaerobic bioenergy production system with the volume of organic waste generated in residential areas;

–

based on the proposed algorithm, match the configuration of modular anaerobic bioenergy production systems with the amount of organic waste generated in residential areas for given production conditions.

Solving this problem has a number of advantages, including (1) reducing the amount of organic waste that ends up in landfills and is blackened; (2) the possibility of producing clean energy for the needs of residents of residential areas; (3) reducing greenhouse gas emissions; and (4) creating jobs.

Thus, the research and development of an effective approach and algorithm for matching the configuration of modular anaerobic bioenergy production systems with the volume of organic waste generated in residential areas is of significant environmental, economic and social importance.

3. Materials and Method

It is proposed to coordinate the configuration of a modular anaerobic bioenergy production system with the volume of organic waste generated in residential areas on the basis of an approach that is presented in the form of an algorithm. The developed block diagram of the algorithm involves 15 steps that systematically determine the rational modular anaerobic system for the production of bioenergy from organic waste in residential areas. Let us reveal the features of each of the steps of this algorithm (Figure 2).

1. The first step is to initiate the definition of a rational modular anaerobic bioenergy production system from the organic waste of residential areas. The initiation of the definition of a rational modular anaerobic bioenergy production system from the organic waste of residential areas is a complex and multi-stage process. It requires careful preparation and an assessment of data collection and analysis capabilities, process modeling and optimization, and economic feasibility. The successful implementation of this step significantly affects the implementation of further steps to coordinate the configuration of the modular anaerobic bioenergy production system with the volume of organic waste generated in residential areas.

2. After that, set the characteristics of the design object (residential area). At this step, the parameters and dimensions of the residential area are set. The number of households in a given housing estate is estimated, and information on the structure of the population and their consumption habits is collected:

$$C{h}_{ai}=\langle T_{ri},T_{bi},N_{bi},N_{hi},S_{ti},N_{ri},L_{ri},C_{ci},A_{ri}\rangle ,$$

(1)

where T_ri—type of residential area; T_bi, N_bi—number and type of houses in the residential area; N_hi—number of households in each house; S_ti—area of the residential area; N_ri—number of residents in households; L_ri—income level of household residents; C_ci—natural and climatic conditions; A_ri—awareness of residents regarding organic waste.

3. Analyze and quantify the generation of organic waste by households in a given residential area. This step involves collecting data on the k-th types (T_owk) and volumes (Q_owk) of organic waste generated by households. This involves analyzing the dynamics (D_ow) of organic waste generation during the year. Different types of k-th organic waste have different characteristics (Ch_owk) and composition (S_owk). Therefore, information on the different types of organic waste generated in households should first be collected:

$$T_{owk}=\langle C{h}_{owk},S_{owk}\rangle ,$$

(2)

where Ch_owk—characteristics of organic waste; S_owk—composition of organic waste.

For example, it can be food scraps, grass from a lawn mower, etc. After collecting the information, it is necessary to classify organic waste by type and divide it into groups, depending on its characteristics Ch_owk and composition S_owk. Divide it into food and non-food waste, etc. For each type of organic waste, it is necessary to determine the proportion and quantity generated in the n-th households during a certain period, for example, a month or a year. The factors that may affect the change in the volume of organic waste, such as seasonality, temperature changes, technological changes in the waste collection process, etc., are also considered. Once the specific types of organic waste, their quantity and their characteristics are determined, the data obtained can be further used to analyze and model the bioenergy production process.

4. Set the k-th type (T_owk) of organic waste. This step in the algorithm for determining a rational modular anaerobic bioenergy production system from the organic waste of residential areas includes the identification of specific types of organic waste generated by households in a given residential area. This is important for an accurate assessment of the volume and composition of organic waste that can be used for bioenergy production. This step will help to make a more accurate prediction of the amount of organic waste generated in the residential area and identify options for their effective use for bioenergy production using anaerobic digestion systems.

5. Perform forecasting $\left(Q_{owk}^p\right)$ of organic waste generation volumes of k types. This step involves estimating the future volumes of organic waste that will be generated in households over a certain period of time (e.g., month, year). Forecasting organic waste volumes is an important step in developing an efficient bioenergy recycling and utilization system. The initial step is to collect historical data on the amount of organic waste generated in the residential area for previous periods. These can be data on previous years, months, or other predefined time periods. Based on these historical data, organic waste generation trends are analyzed, helping to identify certain regularities, seasonality or changes in the habits of the population that may affect the volume of organic waste in the future. In order to accurately forecast organic waste volumes, it is necessary to take into account the variable factors that affect the volume of organic waste collection:

$$Q_{owk}^p=f\left(T_{ri},T_{bi},N_{bi},N_{hi},S_{ti},N_{ri},L_{ri},q_{dk}\right),$$

(3)

where $Q_{owk}^p$—the projected volume of the generated k-th types of organic waste; T_ri—the type of residential area; T_bi, N_bi—the number and type of houses in the i-th residential area; N_hi—the number of households in each house of the i-th residential area; S_ti—the area of the i-th residential area; N_ri—the number of residents in the households of the i-th residential area; L_ri—the income level of the residents of the households of the i-th residential area; q_di—the daily volume of the generated k-th types of organic waste per capita in the i-th residential area.

Depending on the characteristics of the data and historical trends, a suitable method for predicting organic waste volumes is selected. Computational intelligence methods (machine learning, neural networks, etc.), statistical methods (e.g., exponential smoothing, regression analysis), expert estimates or a combination of different methods can be used. The selected method is used to forecast the volume of organic waste generated for a certain future period. The output is the predicted values for a given type of organic waste.

After obtaining the forecasted values, it is necessary to check the accuracy of the forecast by comparing it with actual data for the same period if such data are available. Ensuring the accuracy of the forecast will help in avoiding possible errors during the modeling and implementation of a modular bioenergy system.

6. Check whether all options for individual types of organic waste have been considered. This step is to ensure that all possible types of organic waste that may be generated by households in the residential area have been considered. The formula for checking the completeness of the organic waste (C_owk) analysis may look like the following:

$$C_{owk}={\displaystyle \frac{N_{owk}^{\prime }}{N_{owk}}}\cdot 100\%,$$

(4)

where $N_{owk}^{\prime }$—the number of types of organic waste that are considered; $N_{owk}$—the total number of types of organic waste that are considered during the system design.

This step is an important step to ensure the completeness and accuracy of the analysis underlying the full modeling and forecasting of bioenergy production functional indicators.

7. Analyze the characteristics of modular anaerobic digesters available on the market for bioenergy production. This step involves a detailed analysis of the technical characteristics and parameters of modular anaerobic systems available on the market. It helps to select the optimal anaerobic digester for bioenergy production that best meets the needs and requirements of the project.

The first step is to gather information about the different models of anaerobic digesters available on the market. This can be completed by analyzing the literature, Internet sources, and contacting manufacturers and suppliers of anaerobic systems. In this case, the following characteristics (Ch_mi) of the r-th modular anaerobic system are obtained:

$$C{h}_{mr}=\langle T_{hr},P_{rr},R_{sr},A_{pr},E_{nr}\rangle ,$$

(5)

where T_hr—technical characteristics of the r-th modular anaerobic system, namely capacity, efficiency, size, scalability, cost and necessary resources for their operation; P_rr—productivity of the r-th modular anaerobic system, including bioenergy production, organic waste processing and process optimization capabilities; R_sr—compliance of the technical characteristics of the r-th modular anaerobic system with the project requirements, as well as availability of their components and spare parts; A_pr—experience of using the r-th modular anaerobic system; E_nr—environmental impact of the r-th modular anaerobic system on the environment and possible mitigation of the negative impact.

After analyzing the characteristics of each modular anaerobic digester, they should be compared according to the selected criteria to select the best option for the project’s needs. This step helps to select the most suitable modular anaerobic digesters for bioenergy production based on the analysis of options available on the market, which will ensure successful project implementation and the most efficient use of organic waste.

8. Formulate possible scenarios for bioenergy production. At this step, different options for possible bioenergy production using organic waste are chosen from the following set:

$$S{c}_j\in \left\{Sc\_I_j,Sc\_I{I}_j,Sc\_II{I}_j\right\},$$

(6)

where $Sc\_I_j$—a scenario involving the installation of modular anaerobic digestion systems using organic waste for a single building of the j-th residential area; $Sc\_I{I}_j$—a scenario involving the installation of modular anaerobic digestion systems using organic waste for several buildings of the j-th residential area; $Sc\_II{I}_j$—a scenario involving the installation of modular anaerobic digestion systems using organic waste for a separate complex of the j-th residential area.

This makes it possible to assess the capabilities of j residential areas, as well as project development options, taking into account different scenarios of bioenergy production, as well as their impact on the environment and economic indicators. In doing so, it should be possible to form different combinations of key parameters that represent different scenarios of bioenergy production. For example, different variants of modular anaerobic systems, different compositions of organic waste, different volumes of servicing the territory of residential areas, etc.

9. Set the bioenergy production scenario. At this stage, a separate predefined bioenergy production scenario is set. At the same time, detailed characteristics and parameters are set that determine the conditions and modes of bioenergy production, which are the basis for a clear action plan for the implementation of a bioenergy project from organic waste.

10. Set the r-th variant of the modular anaerobic system for bioenergy production. When specifying the r-th variant of the modular anaerobic system, the characteristics of a particular j-th residential area, which are presented in expression (1), should be taken into account. Taking into account these characteristics, it is possible to select such variants of the modular anaerobic system that best meet the conditions and requirements of the project. At this stage, a separate predefined r-th variant of the modular anaerobic system for bioenergy production is set.

11. Perform bioenergy production modeling and determine functional indicators. At this stage, mathematical models are created for each of the given bioenergy production scenarios, and the system efficiency and productivity indicators are analyzed. To perform this stage, we propose the use of the relationships between the functional indicators of the bioenergy production system from the organic waste of residential areas, which are presented in [7].

12. The next step is to make sure that all possible modular anaerobic digesters have been considered and accounted for. If there are modular anaerobic systems that have not been considered, then it is necessary to return to step 10, which involves specifying the next option for a modular anaerobic system for bioenergy production.

13. Subsequently, the condition that all possible bioenergy production scenarios have been considered and taken into account is checked. If there are any unexamined scenarios, then it is necessary to return to step 9, which involves setting the next bioenergy production scenario.

14. Compare the bioenergy production scenarios and determine the most efficient one among them. At this step, different bioenergy production scenarios are compared in terms of cost indicators and a rational scenario is selected that maximizes the efficiency as well as the economic and environmental benefits of the project. During this stage, different bioenergy production scenarios are compared according to various criteria (efficiency (E_i), cost-effectiveness (C_i), environmental friendliness (E_ci)) and a rational option is determined. To determine the rational scenario, the method of hierarchy analysis (AHP) is used. Each of the criteria for individual residential areas has its own weighting factors. Let us denote the weighting factors for each criterion (efficiency (E_i), cost-effectiveness (C_i), environmental friendliness (E_ci)) $w_{E_i}$, $w_{C_i}$ and $w_{E_{ci}}$.

After that, you should normalize the metric values for each criterion so that they can be compared on the same scale. We denote the normalized values as $n{E}_i$, $n{C}_i$ and $n{E}_{ci}$, respectively. The metric values for each criterion are normalized using the formula:

$$n{X}_i={\displaystyle \frac{X_i-\min \left(X\right)}{\max \left(X\right)-\min \left(X\right)}},$$

(7)

where X_i—the criterion selected accordingly; it can be efficiency (E_i), economy (C_i) or environmental friendliness (E_ci).

We calculate the total value indicator for the residential area under each scenario, which takes into account all the above criteria, using the weighting coefficients using the formula:

$$Tota{l}_i=w_{E_i}\cdot n{E}_i+w_{C_i}\cdot n{C}_i+w_{E_{ci}}\cdot n{E}_{ci}$$

(8)

A rational scenario is one that ensures the highest overall value for a given residential area Total_i ⟶ max.

This step allows us to assess the potential of different bioenergy production scenarios and make a reasonable choice of a rational scenario that maximizes the benefits for the residential area from bioenergy production and ensures the achievement of the project goals.

15. At the last step, the results of the calculations are saved, the necessary information is provided to the user and the process of determining a rational modular anaerobic bioenergy production system from the organic waste of residential areas is completed.

4. Results of Matching the Configuration of a Modular Anaerobic Bioenergy Production System with the Volume of Organic Waste Generated in Residential Areas

Based on the approach proposed and described above, we have coordinated the configuration of the modular anaerobic bioenergy production system with the volume of organic waste generated in residential areas. For this purpose, we selected the Golosko district of Lviv (Ukraine) (Figure 3).

The Golosko district is located in the western part of Lviv, one of the largest cities in Ukraine, which is located in the southwestern part of the country. Golosko is a residential neighborhood with multi-storey buildings, private homes, educational institutions, shops and restaurants. It is a densely populated area with an active generation of organic waste, which includes FW, green waste from adjacent territories and waste from various commercial establishments. Lviv, in particular the Golosko district, is characterized by a temperate continental climate with distinct seasons. The climatic conditions of Lviv, in particular the Holosko district, have a significant impact on the generation of organic waste and the efficiency of the modular anaerobic digester. Low winter temperatures (average winter temperatures range from −3 °C to −5 °C, sometimes dropping to −10 °C and below) can slow down anaerobic processes, so the system should be equipped with insulation and possibly heating systems. High summer temperatures (average summer temperature ranges from +18 °C to +25 °C, with maximums of up to +30 °C) can accelerate anaerobic processes, increasing biogas productivity. High humidity (ranging from 75% to 85%) promotes the decomposition of organic waste, but can also lead to an increased level of liquid waste, which requires additional treatment. High rainfall (annual precipitation of about 750–800 mm), especially in summer, can affect the amount of green waste, such as grass and leaves.

Seasonal changes in organic waste volumes require flexibility in the configuration and customization of the modular system to ensure stable operation throughout the year. Peak periods of waste generation (for example, in the fall due to fallen leaves) may require additional tanks to store waste until it is processed. Wind conditions (average wind speeds of 3–4 m/s, with stronger winds in winter and spring) can affect the spread of odors and other possible emissions from the anaerobic digester, so the system should be located with consideration for wind direction and distance from residential buildings.

Considering the climatic conditions of the Holosko area, the research and development of the modular anaerobic system required a detailed analysis of the location of the modular anaerobic bioenergy production system and its configuration to ensure efficient operation. It is proposed to adapt modular anaerobic bioenergy production systems to work in a temperate continental climate with distinct seasons, which will ensure stable bioenergy production and the efficient processing of organic waste from residential areas throughout the year.

We considered four types of organic waste generated in residential areas: (1) FW; (2) YW; (3) mixed food and yard waste (FYW); (4) mixed organic waste (MOW). All of them are analyzed in detail in our previous work [7]. In particular, we obtained quantitative values of the mathematical expectation of the indicators of organic substrate production in modular anaerobic systems during bioenergy production, which are shown in the form of histograms (Figure 4).

Based on the research results, it was found that the largest amount of organic substances (TS) is present in food waste (FW)—783 kg/m³. The lowest value of this indicator is observed in MOW—267.4 kg/m³. The mathematical expectation of volatile organic matter (TVS) content in the organic waste of all categories differs slightly and ranges from 84.8% to 91.05%. The mathematical expectation of biogas yield (SGP), depending on the quantitative value of volatile organic matter (TVS) content, is the highest in food waste (FW)—0.847 m³/kg TVS—and the lowest in YW—0.278 m³/kg TVS. The mathematical expectation of the kinetic constant (k) is in the range from 1.606 to 2.003 for all types of organic waste, which indicates that the kinetic properties of different types of organic waste are similar. For further research, we also used the dependencies of the indicators of electricity and heat production, as well as compost, on organic waste biogas, which are presented in [7]. The dependencies of electricity (E, kWh), heat (Q, kWh) and solid fraction (biofertilizers) (F, kg/m³) production on the specific volume of biogas (V_biogas, m³/kg TS) from the organic waste of residential areas were obtained and described by the following equations. The obtained results indicate the existence of dependencies with close correlations between the volume of bioenergy output and the characteristics of the organic waste generated in residential areas. They were subsequently used to coordinate the configuration of a modular anaerobic bioenergy production system with the volume of organic waste generated in residential areas.

Predicting the volume of organic waste generated in residential areas and assessing the potential for biogas production is an important step in optimizing the configuration of a modular anaerobic bioenergy production system. The use of machine learning methods, in particular the machine learning model developed by us based on the Random Forest Regressor algorithm presented in [3], is effective for obtaining accurate forecasts and making informed decisions regarding the volume of biogas production from organic waste in residential areas. The Random Forest Regressor algorithm belongs to ensemble machine learning methods that use a set of trees to perform regression. The use of the Random Forest Regressor allows to accurately predict the volume of biogas production from different types of organic waste based on historical data and various factors, such as the type of waste, the content of organic matter (TS) in the waste, the content of volatile organic compounds (TVC), etc.

To predict the volume of organic waste generated in the residential area of Holosko, Lviv (Ukraine), and to assess the potential for biogas production, we used our decision support system to model the use of biomass as a circular resource in residential areas (Figure 5 and Figure 6) [49].

As a result of the study on the residential area of Holosko, Lviv (Ukraine), possible scenarios for the installation of modular anaerobic bioenergy production systems were substantiated and the volumes of organic waste generated and biogas produced were predicted for them (

Table 1. Results of determining the scenarios for the installation of modular anaerobic bioenergy production systems and forecasting the volume of organic waste generated.

Scenario of Installation of Modular Anaerobic Systems	Number/Number of Floors of Residential Buildings, Units/Floors	The Area of the House Territory, m2	Number of Residents, Persons	Projected Annual Organic Waste Generation, kg/year
				FW	YW	FYW	MOW
I. One residential building	1/9	500	432	55,186	1310	56,496	71,742
II. Two residential buildings	1 + 1/5 + 9	1100	651	82,452	3250	85,702	105,539
III. Three residential buildings	2 + 1/5 + 9	1620	762	96,245	4620	100,865	126,081
IV. Residential area	3 + 4/5 + 9	3250	1875	232,450	8640	241,090	299,861

).

It was found that with an increase in the number of residents, the projected annual volume of organic waste generated increases proportionally. In particular, Scenario IV (residential area), with 1875 residents, has the highest level of organic waste generation. An increase in the area of the adjacent territory leads to an increase in the volume of green waste generated. In particular, in Scenario IV, the curtilage area is 3250 m², which results in 8640 kg of green waste per year. MOW includes food and green waste and has the highest projected annual volume in each scenario. This indicates the need for the proper management of all types of organic waste for the efficient operation of the anaerobic system. Scenario IV (residential area) is the most suitable for large-scale anaerobic systems due to the largest number of residents and the area of the curtilage, which provides the largest volume of organic waste for processing. At the same time, mixed waste (MOW) requires the most attention due to its significant volume in all scenarios, which emphasizes the importance of the effective management of all types of organic waste.

In our research, we used NetelEco modular anaerobic bioenergy production systems by the Indian company Biomali [50]. They are designed to process various organic wastes (kitchen, livestock and food industry, etc.), which makes it possible to produce natural gas, electricity and organic fertilizers. Anaerobic fermentation (without oxygen) of organic substrates is the scientific basis of biogas technology, which produces biogas (methane—60–70%, carbon dioxide—30–35% and small amounts of H₂S, N₂ and H₂). This biogas can be used as a fuel for space heating or for electricity generation. NetelEco has a number of technical expertise certificates. Currently, NetelEco is implementing biogas plants with the capacities shown in

Table 2. Characteristics of modular anaerobic bioenergy production systems Biomali.

Model	Organic Waste Processing Capacity (kg/day)	Biogas Yield (m3/day)	Methane Yield (m3/day)	Organic Manure (kg/day)	Electricity Generation (kWh/day)	Area Required (m2)	Electricity Consumption (kWh/day)
NetelEco Biogas-100	100	8–10	5.8	5–7	Not Recommended	10	1.5
NetelEco Biogas-250	250	20–22	11.6–12.8	13–18	Not Recommended	25	3
NetelEco Biogas-500	500	40–45	23.2–25.6	25–30	48	50	4
NetelEco Biogas-750	750	60–65	34.9–37.2	40–45	72	70	6
NetelEco Biogas-1000	1000	80–90	51.1–53.5	55–60	96	90	9
NetelEco Biogas-1500	1500	120–130	69.7–72	80–100	144	120	14
NetelEco Biogas-2000	2000	160–180	80–85	110–120	192	150	20
NetelEco Biogas-2500	2500	200–220	100–105	140–160	240	200	24

.

Table 3. Results of determining the volumes of biogas V_biogas/methane V_methane production for the given scenarios of installation of modular anaerobic bioenergy production systems.

Installation Scenario for Modular Anaerobic System/Model	Projected Annual Production of of Biogas Vbiogas/Methane Vmethane, m³/year
	FW	YW	FYW	MOW
I. One residential building	18,504	893	31,652	23,069
NetelEco Biogas-750	11,098	450	19,773	13,841
II. Two residential buildings	27,646	2215	48,015	33,936
NetelEco Biogas-1000	16,581	1116	29,995	20,362
III. Three residential buildings	32,271	3149	56,510	40,542
NetelEco Biogas-1500	19,355	1586	35,302	24,325
IV. Residential area	77,941	5889	135,071	96,421
NetelEco Biogas-2500	46,746	2966	84,379	57,852

shows the performance and technical characteristics of different models of Biomali’s NetelEco modular anaerobic bioenergy production systems. The main characteristics include the volume of organic waste processed, gas yield, LPG equivalent, organic fertilizer production, electricity production, required area and electricity consumption. Regarding the rate of organic waste processing, existing models of NetelEco modular anaerobic bioenergy production systems provide processing in the range from 100 to 3000 kg/day (Figure 7). An increase in the rate of waste processing directly affects all other parameters. Biogas yields range from 8–10 m³/day to 240–280 m³/day. NetelEco’s modular anaerobic bioenergy production systems are capable of processing a significant amount of waste, which reduces the amount of waste accumulated and disposed of in landfills. Biogas production provides an alternative energy source that can replace LPG.

Electricity production from biogas allows for energy autonomy in residential areas. The use of biogas reduces greenhouse gas emissions compared to traditional waste incineration. The organic fertilizer produced as a by-product can be used to grow plants and trees in the adjacent territory, which reduces the use of chemical fertilizers. The use of small NetelEco modular anaerobic bioenergy production systems (up to 250 kg/day) is suitable for one or two residential buildings in a residential area. They have low electricity consumption and a small installation area. Medium-sized NetelEco modular anaerobic bioenergy production systems (up to 1000 kg/day) can serve both several residential buildings and a residential area. They are capable of producing a significant amount of electricity. Large modular anaerobic bioenergy production systems of NetelEco plants (over 1000 kg/day) are suitable for residential areas or individual settlements. They are capable of producing a significant amount of biogas, organic fertilizer and electricity. Thus, the choice of a suitable NetelEco modular anaerobic bioenergy production system model depends on the amount of waste generated, the available space for installation and the energy needs of consumers.

The developed decision support system for modeling the use of biomass as a circular resource in residential areas uses the Random Forest Regressor model to predict biogas production [2], which is appropriate and effective for determining the rational configuration of a modular anaerobic system. This model provides 87% forecast accuracy, resistance to overtraining and the ability to take into account a large number of parameters, which allows for the optimization of the system’s operation, reducing costs and improving the environmental situation in the Holosko district of Lviv.

For each of the scenarios under consideration, we selected the appropriate modular anaerobic system, taking into account the projected volumes of organic waste. As a result of our research, we have forecasted the volumes of biogas and methane production for the Holosko residential area in Lviv (Ukraine) (Table 3).

Based on the results of determining the volume of biogas/methane production for the given scenarios of installing modular anaerobic bioenergy production systems in a given residential area, it can be said that an increase in the number of residential buildings leads to an increase in biogas and methane production. In the first scenario, with one multi-storey residential building, a modular anaerobic bioenergy production system should process about 56 tons of organic waste per year and produce up to 36 thousand m³ of biogas. In the second scenario, using raw materials from two multi-storey residential buildings, a medium-sized system should be created that can process up to 105 tons of organic waste per year and produce up to 82 thousand m³ of biogas. In the third scenario, with the use of raw materials from three multi-storey residential buildings, a more productive system should be created, capable of processing up to 126 tons of waste per year and producing up to 96 thousand m³ of biogas. The most productive modular anaerobic bioenergy production system should be envisaged in the scenario of servicing a residential area. In this case, it should provide processing of up to 300 tons of organic waste per year and produce up to 230 thousand m³ of biogas.

Based on the data in Table 2, Table 3 and

Table 4. Results of determining the volumes of electricity E and solid fraction (biochar) F produced for the given scenarios of the installation of modular anaerobic bioenergy production systems.

Installation Scenario for Modular Anaerobic Systems/Model	Projected Annual Production of Electricity E (kWh/year)/Solid Fraction (Biofertilizer) F, kg/year
	FW	YW	FYW	MOW
I. One residential building	21,280	1027	36,400	26,529
NetelEco Biogas-750	12,583	607	21,523	15,687
II. Two residential buildings	31,793	2548	55,217	39,027
NetelEco Biogas-1000	18,799	1506	32,650	23,077
III. Three residential buildings	37,112	3622	64,986	46,623
NetelEco Biogas-1500	23,235	2267	40,687	29,190
IV. Residential area	89,632	6773	155,332	110,884
NetelEco Biogas-2500	55,338	4181	95,901	68,459

, for a given residential area, we forecasted the volumes of electricity and solid fraction (biofertilizer) produced (Table 4).

Based on the obtained quantitative values of functional indicators under different scenarios of installation of modular anaerobic bioenergy production systems in the territory of a given residential area, we have determined their cost indicators. It is assumed that the green tariff rate for electricity in 2024 in Ukraine is 0.146 EUR/kW (Resolution of the National Commission for State Regulation of Energy and Utilities of Ukraine No. 2653 of 29 December 2023). The cost of solid fraction (biofertilizers) is 0.075 EUR/kg. Based on our calculations, we have determined the benefits for each of the scenarios of bioenergy production in the territory of a given residential area (Figure 8).

It was found that the maximum annual benefits are received by the residents of the residential area from the processing of FYW in Scenario IV (residential area)—29,871 EUR—and the lowest in Scenario I (one residential building). In general, the graph shows that an increase in the number of residential buildings or the scale of the residential area leads to an increase in annual benefits from waste management, especially in the case of using organic waste for bioenergy production. It was found that the use of YW brings the lowest benefits, which do not even cover the electricity consumption of the modular anaerobic systems. Therefore, when determining a rational scenario for the installation of modular anaerobic bioenergy production systems in a given residential area, we will not consider the use of YW.

Based on our calculations, we have built a histogram of the payback period of investments in modular anaerobic systems for individual scenarios of bioenergy production in a given residential area (Figure 9).

It was found that Scenario II (two residential buildings) and Scenario IV (residential area) usually have the shortest payback period for all categories of waste. This is due to the larger amount of waste generated in these scenarios and the possibility of more efficient use or recycling. At the same time, the shortest payback period for investments in modular anaerobic systems in certain scenarios of bioenergy production in a given residential area is observed when using FYW. At the same time, the rational scenario for the development of an anaerobic bioenergy production system on the territory of a given residential area is Scenario IV (residential area), in which the payback period of investments is 3.3 years. At the same time, Scenario II (two residential buildings) using FYW is worthy of attention, with a payback period of 3.8 years.

In general, it can be said that the proposed approach and tools make it possible to determine a rational scenario for the installation of modular anaerobic bioenergy production systems in a given residential area. This is the basis of effective waste management, which takes into account not only the amount of waste but also its composition and possible scenarios for its processing, as well as the benefits for residents. The introduction of such systems in residential areas will significantly reduce the amount of organic waste that goes to landfills, reducing greenhouse gas emissions and improving the environmental condition of the region. It has been proven that there is economic feasibility in investing in bioenergy production systems in residential areas, including possible subsidies or grants for the installation of anaerobic systems.

5. Discussion of Research Results

The anaerobic digestion of organic waste generated in residential areas is now attracting the attention of both scientists and practitioners around the world. It is this approach to organic waste disposal that provides significant environmental and economic benefits. It reduces the amount of local waste through recycling, which preserves natural resources, reduces greenhouse gas emissions, and strengthens the economic and energy sustainability of residential areas through energy production and waste disposal. Efficient use of organic waste through recycling preserves natural resources by reducing the area of landfills, eliminating the need for landfilling and maintenance of landfills after they are closed. The transformation of organic waste from residential areas into renewable energy sources contributes to the decarbonization of the economy by reducing harmful emissions and pollutants, which is strategically in line with the philosophy of the Europe Green Deal [1]. At the same time, the problem of coordinating the configuration of a modular anaerobic bioenergy production system with the volume of organic waste generated in residential areas has not been addressed by scientists.

There are known scientific works in other subject areas in which the authors prove the influence of the configuration of systems for given operating conditions on their efficiency [51,52,53,54]. To solve the problem of matching the configuration of a modular anaerobic bioenergy production system with the volume of organic waste generated in residential areas, a special approach and algorithm were developed. This approach includes 15 stages, including the analysis and forecasting of organic waste generation for a given residential area, the selection of possible scenarios for the installation of modular anaerobic bioenergy production systems in a given residential area, the modeling of the anaerobic digestion process for each of them to determine functional indicators and the determination of a rational configuration in terms of cost and environmental indicators.

The proposed algorithm is based on the analysis of available data on the generation of organic waste [3,7], and also takes into account the real production conditions of residential areas and their seasonal fluctuations in the generation of certain types of waste. This makes it possible to improve the accuracy of determining the rational configuration of the installation of modular anaerobic bioenergy production systems in a given residential area. Well-known scientific studies indicate that the correct configuration of such a system can significantly increase the efficiency of waste processing and bioenergy production [16,55,56,57]. Our approach confirms these results and offers a more detailed consideration of the production conditions for processing organic waste in residential areas.

Based on the proposed algorithm, the configuration of modular anaerobic bioenergy production systems was matched with the volume of organic waste generated for the conditions of the Holosko residential area, Lviv (Ukraine). The study [17] substantiated that one of the main problems in setting up such systems is in ensuring the stability of the anaerobic digestion process due to the uneven supply of organic waste. Our results show that the use of the proposed algorithm makes it possible to take into account the seasonality and types of organic waste generated in residential areas, which ensures the stable operation of anaerobic bioenergy production systems, even with significant volumes of waste generated, due to the correct selection of a modular anaerobic bioenergy production system, taking into account the predicted production conditions in a given residential area.

The results of our study are in line with the findings of other scientists on the effectiveness of anaerobic systems for organic waste processing. Well-known studies [37] emphasize that modular systems can be quite effective if the anaerobic system configuration is chosen correctly. Our results show that the use of the developed algorithm not only fully confirms the known conclusions but also extends them by offering a more accurate approach to matching the configuration of modular anaerobic bioenergy production systems with the volume of organic waste generated for the real conditions of a residential area.

The obtained research results confirm the economic feasibility of using modular anaerobic systems, which is consistent with the results of the analysis of the study presented in [15], which shows a significant economic effect from reducing the cost of waste disposal and renewable energy production. In addition, environmental benefits, such as reduced greenhouse gas emissions, were noted in study [18], which are also confirmed in our results. In particular, we have found that the payback period of investments in modular anaerobic bioenergy production systems for given conditions of a residential area largely depends on their configuration and ranges from 3.3 to 8.4 years, which differ from each other by a factor of 2.5. This indicates that the coordination of the configuration of a modular anaerobic bioenergy production system with the volume of organic waste generated in a residential area is an important scientific and applied task that significantly affects the value of anaerobic systems for residents of residential areas.

Our study has identified some challenges similar to those described in the literature [16,18], in particular the need for the continuous monitoring of production conditions for bioenergy production and process optimization, as well as for ensuring a stable supply of organic feedstocks. However, the proposed algorithm and approach make it possible to substantiate a rational scenario of modular anaerobic bioenergy production systems for the real conditions of a residential area, which significantly reduce their risks and ensure the stable and efficient operation of the anaerobic system.

Our study is based on the analysis and use of data from a given residential area of Holosko, Lviv (Ukraine), which allowed us to accurately assess and justify the configuration of modular anaerobic bioenergy systems to local conditions. However, it is important to note that applying the approach, algorithm and developed decision support system to other regions requires additional model adaptation. In particular, each residential area of a particular region has a different composition of organic waste and peculiarities in its formation, which vary depending on demographic, climatic and socio-economic factors. To increase the versatility and reliability of the models, additional empirical studies should be conducted in different geographical regions to validate the model and ensure its accuracy and efficiency in a broader context. This will ensure the model’s wider applicability and the possibility of its integration into waste management and bioenergy production strategies at the level of regions with different conditions.

Thus, the results of our study confirm the effectiveness of the developed approach and algorithm. The results obtained are consistent with existing scientific achievements in the field of bioenergy production from organic feedstocks. Further research should be carried out in the direction of using the developed approach to match the configuration of modular anaerobic bioenergy production systems with the volume of organic waste generated for different types of residential areas in different countries. In addition, it is necessary to consider different options for modular anaerobic bioenergy production systems and, based on such studies, to substantiate recommendations on the feasibility of their use for different types and volumes of organic waste production in residential areas. Also, our study did not address the issues of the territorial location of modular anaerobic bioenergy production systems in residential areas.

6. Conclusions

As a result of the conducted research, an important scientific and applied problem related to the coordination of the configuration of a modular anaerobic bioenergy production system to the volume of organic waste generated in settlements was solved. To solve this problem, a special approach and algorithm, which includes 15 stages, was developed. These stages involve a detailed analysis of the state of the production conditions of residential buildings, forecasting the volume of organic waste generated and the selection of possible scenarios for the installation of modular systems for the production of anaerobic bioenergy in a residential area by modeling the process of determining the functional indicators of anaerobic fermentation. In turn, such indicators are the basis for determining a rational configuration in economic and ecological aspects, which can be one of the directions of implementation of the European Green Deal.

Based on the use of the developed approach and algorithm for the production conditions of the Holosko residential area, Lviv (Ukraine), possible scenarios for the installation of modular anaerobic bioenergy production systems are substantiated and the volumes of organic waste generated and biogas produced are forecasted for them. It is established that the maximum annual benefits will be received by residents of a residential area from the processing of FYW in Scenario IV (residential area)—29,871 EUR—and the lowest in Scenario I (one residential building). An increase in the number of residential buildings or the scale of the residential area leads to an increase in the annual benefits of waste management, especially in the case of using organic waste for bioenergy production. It has been found that the use of YW brings the least benefits, which do not even cover the actual electricity consumption of modular anaerobic systems.

It has been established that the payback period of investments in modular anaerobic bioenergy production systems for given conditions of a residential area largely depends on their configuration and ranges from 3.3 to 8.4 years, which differ from each other by a factor of 2.5. This indicates that the coordination of the configuration of a modular anaerobic bioenergy production system with the volume of organic waste generated in a residential area is an important scientific and applied task that significantly affects the value of anaerobic systems for residents of residential areas. The rational scenario for the development of an anaerobic bioenergy production system in a given residential area is Scenario IV (residential area), in which the payback period is 3.3 years.

The results of the research and the developed tools are valuable for associations of co-owners of apartment buildings, manufacturers of modular anaerobic digesters, public organizations and environmental activists. The developed decision support system based on the proposed approach and algorithm makes it possible to perform modeling to evaluate different scenarios of biomass use, taking into account the specifics of each residential building and the generation of different types of organic waste. This ensures not only a solution to current waste and energy efficiency problems, but also a contribution to the creation of sustainable and environmentally friendly residential areas.

The main limitation of the research is that the modeling is based on simplified assumptions about the variability of organic waste supply and its composition. Actual conditions may differ significantly, which may affect the effectiveness of the proposed solution. In addition, taking into account only economic and environmental factors may not fully reflect the complexity of the process of implementing bioenergy systems. Therefore, it is recommended to conduct further research that will take into account a wide range of social and technical aspects, as well as real data from different regions.