Sustainable Biodegradable Waste Management for Circular Economy: Comparative Assessment of Composting Technologies

Abstract

Waste management is essential for advancing sustainable development and applying circular economy principles. The growing generation of waste—particularly organic municipal waste—combined with limited processing technologies, financial constraints, and overconsumption, intensifies its negative environmental and social impacts. This study examines the conditions necessary for implementing the circular economy concept in the context of organic municipal waste management. The research is based on literature review and an experiment involving the composting of biodegradable waste classified under code 20 02 01, analyzing its transformation into a soil improver commonly known as compost. Two composting approaches—single-stage and two-stage—were compared to evaluate their effectiveness in producing a high-quality end product that complies with national and EU legal standards, as well as the requirements for obtaining decisions (certificates) from the Ministry of Agriculture and Rural Development (MARD). The study is particularly relevant in light of the increasing volume of this waste stream, which exceeds 1.8 million tons annually in Poland, and the ambitious recycling targets set by the European Union, requiring 55% to be achieved by 2025. Results demonstrate that both composting methods contribute to circular resource use but differ in process efficiency and final product quality. These findings provide practical guidance for selecting composting technologies and support progress towards more sustainable, circular waste management. Moreover, they help define the output parameters of the products, which enables proper categorization and facilitates the issuance of relevant decisions from the MARD.

1. Introduction

The Sustainable Development Goals (SDGs), established by the United Nations, were formulated to guide global economic efforts toward solving the most pressing challenges facing society and the natural environment. A central priority of these goals is to achieve economic growth without simultaneously increasing the consumption of natural resources. At the core of most SDGs lies the concept of rational and responsible resource management, aiming to transform current economic structures toward a circular economy. One of the key mechanisms for implementing this objective is sustainable waste management [1]. Within the framework of the circular economy, the focus is on the efficient use of available resources through repeated processing and the regeneration of natural ecosystems. A crucial role is played by the development of policies that support the design of products with extended life cycles, which reduces waste generation while simultaneously fostering economic innovation [2].

Waste is typically associated with the inefficient functioning of communities and the squandering of resources. Waste management has become a particularly important issue in the face of challenges related to sustainable development [3].

Global waste production has increased significantly over the recent decades and continues to rise. According to data from the World Bank, between 7 and 9 billion tons of waste are generated annually worldwide, of which over 2 billion tons are municipal solid waste. Approximately one-third of this waste is not managed in an environmentally safe manner [4,5,6]. The volume of waste generated is anticipated to grow significantly, depending on regional development levels, with increases in several dozen percent expected by 2050 [7].

Waste management constitutes a critical component of environmental governance. Unsustainable practices in this area can result in numerous ecological problems and pose risks to human health. Waste generation depletes natural resources, consumes energy and water, places pressure on land use, pollutes the environment, and incurs additional economic costs associated with disposal and treatment [8]. These costs are particularly burdensome for local governments, which, in most countries, including Poland, bear the primary responsibility for waste management [3]. Waste management operations are costly and complex, and their financing must compete with other priorities such as access to clean water, education, and healthcare. Consequently, waste management is often carried out with limited resources and capabilities [8].

Developing appropriate waste management methods, particularly within the context of the circular economy, remains a challenge and calls for continued research [9,10]. The primary aim of such research is to mitigate the negative environmental impact of waste, which can be achieved through sustainable waste management. Recommended actions include waste minimization, enhanced resource recovery, recycling promotion, and safe disposal [11]. It is essential to implement waste management systems based on waste prevention, material efficiency, and resource recovery [12]. The development of processes for the recovery of nutrients [13] and products from biowaste is particularly important [6]. Substantial waste management solutions are needed that are tailored to local needs but simultaneously deliver global, cumulative benefits. In this context, the present study aims to address the gap in effective processing of solid biodegradable municipal waste, in accordance with the principles of the circular economy.

The paper attempts to analyze the technological approach to the processing of biodegradable municipal waste code 20 02 01 (Waste code 20 02 01 refers to biodegradable waste. In accordance with legal regulations, this waste comes mainly from gardening, park and household activities) and to examine selected factors influencing the management of this process, with the ultimate goal of producing high-quality soil improvers.

An analysis of applied technologies used in biowaste management indicates that improving source separation quality and implementing more advanced recycling technologies are of key importance [14]. The authors assume that a life cycle analysis of the selected biodegradable waste treatment process will support a better balance of technological, economic, social, and environmental dimensions. Given the benefits of transforming waste into usable products, this has a significant impact on shaping the circular economy.

The main objective of this experiment was to assess the effectiveness of a single-stage composting process of biodegradable waste in industrial conditions at the Remondis Bydgoszcz JSC plant. The study was practical and focused on the assessment of the intensive composting phase carried out in closed bioreactors, excluding the maturation phase in the heaps. To this end, a sequence of five technological steps was designed, including shredding, four subsequent composting phases in bioreactors and an additional drying phase followed by screening of the material. The results obtained in the course of the experiment are to provide guidance on the selection of effective organic recycling technologies that can support the implementation of circular economy goals.

2. Literature Review

2.1. Circular Economy

The resources necessary for the functioning of humanity are being depleted at an increasingly rapid pace, necessitating the implementation of multidimensional actions across the domains of economy, politics, and society to meet the objectives of sustainable development. A key solution is the transition from a linear economy to a circular economy (CE), which enables the provision of sustainable access to natural resources, such as food, water, a clean environment, and overall well-being for future generations. The CE represents not only a model for efficient resource management but also a global economic paradigm aimed at achieving ecologically and economically beneficial solutions. The fundamental goal of this model remains the minimization of resource consumption at every stage of the value chain [15,16,17].

The implementation of circular economy principles is currently taking place both at the international and regional levels, within the European Union countries as well as in Poland. The realization of CE goals requires the involvement of multiple stakeholders and coordination of actions throughout the entire product life cycle: from raw material extraction, through design, production, and consumption, to waste management. Businesses play a key role in this process by implementing strategies for product reuse, resource recovery, and reintegration of valuable materials and energy into the economic cycle. An example of the effective application of these principles is the development of industrial symbiosis in Japan, where waste from one industrial sector becomes a resource for another, highlighting the importance of international cooperation in optimizing such solutions [4].

The Polish waste management system is undergoing a transformation in line with the EU waste treatment hierarchy and circular economy strategy, focusing on efficient resource use, reduced landfilling, and the development of biowaste recycling and thermal processing technologies. Significant progress has been made in the area of bio-waste recycling and the development of thermal processing technologies, which has made it possible to reduce the amount of waste deposited in landfills. These changes are in line with the circular economy strategies, the main goal of which remains the efficient management of resources and minimization of the negative impact on the environment [14].

Waste management plays an increasingly significant role in shaping environmental outcomes; therefore, raising public awareness and encouraging behavioral change in terms of waste reduction and generation are essential. Waste management also serves as a form of preventive action against various environmental problems, such as greenhouse gas emissions (CH₄, CO₂) [18], which contribute to further climate deterioration [19].

The circular economy and its associated bioeconomy represent a foundation for addressing global environmental, economic, and social challenges. The evolution of this economic model began with waste management and resource consumption reduction (e.g., energy and water), and has since shifted its focus to the use of waste as input materials. Currently, the CE encompasses a restorative and regenerative system, focused on two material flows: biological and technical. Within this system, the development of biodegradable and fully recyclable products is promoted, enabling efficient management of materials and energy [20]. One example of this approach is organic recycling, which converts waste into products or raw materials for further production, thereby contributing to the reduction in waste generation.

In 2013, the Netherlands recognized the significant potential of the circular economy as a system based on the reuse of materials and products, the aim of which is to protect natural resources and create value for society, the environment and the economy. In international literature, special attention is given to the concept of decoupling, which posits that economic growth can be separated from the increased exploitation of natural resources. Within the CE framework, there is an emphasis on maximizing positive environmental and economic effects through long-term solutions that support product durability, ease of repair, and recyclability. However, achieving decoupling requires the deployment of innovative production technologies and more efficient waste management systems, both of which are crucial to sustainable development and the transformation of global economic processes in the spirit of ecological responsibility [15]. Regardless of its scale, from national implementation to the enterprise level, the CE model is characterized by a holistic approach to the value chain and an extended producer responsibility, while also strengthening the role of the consumer. The European Union’s Circular Economy Action Plan is an integral part of the EU industrial strategy. Its objectives include improving resource use efficiency, reducing waste generation, and developing a well-functioning secondary raw materials market. Measures include reuse, recycling, and resource recovery from waste, particularly from critical raw materials that are not available within the EU. In addition, the multiple use of water and waste heat is considered vital for closing the resource loop [15,21].

Thus, the circular economy is no longer a theoretical concept but an actively implemented system of critical importance for the future of both the environment and the economy, fully integrated within the global sustainable development strategy.

2.2. A New Perspective on Waste and the Consumer’s Role

In the traditional linear economic model, waste is perceived as a burden on the natural environment, resources, and public health. Managing waste involves high costs and numerous organizational challenges. In this approach, part of society treats waste as devoid of economic value, which leads to its disposal. However, there are entities that recognize its potential as a resource capable of generating financial benefits. In developing countries, waste management is primarily regarded as a basic social service, resulting in the need to allocate a significant portion of municipal budgets to its implementation, usually without the expectation of a substantial return on investment. Even when public–private partnership models are employed, the priority typically remains ensuring the efficiency of collection, transportation, and disposal services, while minimizing the financial burden on society [22].

The concept of circular economy (CE) introduces a radically different perspective, promoting an approach in which waste is viewed as a resource that can be reintroduced into the production–consumption cycle. The principle of circularity places particular emphasis on designing products with durability, reparability, and ease of disassembly; features that facilitate recycling and reuse. Through innovative technologies, such as upcycling and downcycling processes, it is possible to increase the added value of waste materials while reducing the use of primary raw materials, thereby decreasing the environmental footprint of human activity [2]. Enhanced sorting systems and innovative material processing methods are key tools that enable the practical implementation of this concept.

The CE model emphasizes the need to repurpose products that have reached the end of their life cycle in one system as raw materials in other production processes. This concept integrates environmental, economic, and social benefits, underlining the necessity of decoupling economic growth from the consumption of finite natural resources by implementing breakthrough technologies and developing business models that support circularity [2,22,23]. These efforts include designing products that are easily recyclable and capable of full biodegradation or reuse of all their components.

Circular economy offers promising prospects for waste management, particularly in developed countries where its principles are reflected in both theory and practice, as well as in public policy. However, in low- and middle-income countries, the implementation of this concept faces challenges stemming from insufficient knowledge, socio-economic constraints, and lack of access to information. These barriers highlight the need for educational initiatives and the promotion of new economic models [1].

Consumers are central to the circular economy, as the quantity and quality of municipal waste generated depend on their lifestyles, consumption patterns, and commitment to waste segregation at the source. Growing environmental awareness is fostering the popularity of deposit-return systems and sharing economy models, which help reduce the demand for primary raw materials. Educational campaigns and the promotion of responsible consumer habits are essential for improving recycling efficiency [14].

In conclusion, the implementation of the circular economy concept is based on the three Rs principle: reduce, recycle, reuse, which aims to limit the use of raw materials, to recycle materials, and to reuse products [15]. This approach supports the creation of closed-loop systems in which waste becomes a resource for subsequent stages of production, thereby minimizing the negative environmental impact [24]. Furthermore, engaging consumers in CE-related processes through education and the promotion of sustainable consumption habits plays a key role in the effective implementation of this model [25].

2.3. The Importance of Sustainable Management in Waste Management

It is difficult to provide a universal classification of waste, as the literature offers various categorizations based on different criteria. The origin-based criterion distinguishes between municipal and industrial waste [26] or presents a broader catalog of common sources of waste, including municipal waste, commercial waste, ash, animal waste, biomedical waste, construction waste, solid industrial waste, biodegradable waste, non-biodegradable waste, and hazardous waste [27]. In Poland, waste classification is governed by the Regulation of the Minister of Climate of 2 January 2020, on the waste catalog, which lists waste types by source across 20 categories and several dozen subcategories [28].

Rising purchasing power, economic growth, and shifting social dynamics are driving increased waste generation and variability, with no clear signs of this upward trend reversing [4,29,30,31].

In recent years, biodegradable waste has become one of the most recognized categories. In 2021, it constituted a significant portion of selectively collected municipal solid waste (MSW), highlighting its growing importance in terms of recycling rates and potential for derivative products. In Poland, biodegradable waste accounted for around 20% of the total mass of MSW, with households responsible for as much as 83% of that volume. While the share of segregated waste is gradually increasing, mixed waste still dominates, representing nearly 60% of total MSW in 2021. Currently, municipal waste management (of MSW) is facing a growing challenge—the amount of waste will increase to over 3.8 billion tons in 2050, and management systems vary significantly between countries. Circular economy policies and technologies supporting higher levels of recycling and recovery, such as advanced sorting using AI (Artificial Intelligence)/IoT (Internet of Things) [32], anaerobic digestion for the organic fraction or innovative thermochemical processes (gasification, pyrolysis), are becoming increasingly important. Research indicates that the implementation of these solutions can reduce negative environmental effects and at the same time improve the economic efficiency of waste management systems [33,34,35]. This analysis clearly points to the need for further improvements in waste management, taking into account the specific characteristics of different waste fractions [36,37]. MSW is generated, collected, transported, and disposed of within municipalities. It typically consists of biodegradable materials (food, paper, organic waste) [26], non-biodegradable materials (plastics, metals, polystyrene), hazardous waste (oil, batteries, paints, electronic waste), and construction waste. It is estimated that the production of such waste doubles annually, with a significant impact on both the environment and public health. Although many countries have implemented strategies for treating municipal and biodegradable waste, continuous improvement in these processes is still necessary.

The composition of MSW is generally dominated by organic waste. Organic waste is biodegradable and can generate greenhouse gases [18]. Proper waste management is expected to reduce the release of these gases into the atmosphere and may serve as one of the methods to support the development of health-conscious and environmentally sustainable communities, such as low-emission communities [4]. Waste management begins at the source through waste sorting, followed by collection and final disposal at final processing site (TPA). The potential for reuse and recycling depends on the quantity, composition, and characteristics of the waste. Biowaste can become a valuable resource not only for energy production but also for the recycling of high-value products. However, converting biowaste into bioproducts remains a challenging issue, with many obstacles yet to be addressed.

Biodegradable waste is primarily processed through aerobic or anaerobic composting. Some of it is also used in fermentation, mostly in the form of food and kitchen waste, with smaller quantities of green waste. Composting is a natural process involving the microbial breakdown of organic matter in an oxygen-rich environment. Microorganisms, such as fungi and bacteria, decompose complex organic substances into simple and usable organic compounds known as compost [38]. The composting process includes four phases: the mesophilic phase, the thermophilic phase, the cooling phase, and the maturation phase. In the mesophilic phase, the growth and activity of mesophilic microorganisms cause a temperature increase, which lasts only a few days. Energy-rich compounds are also broken down by fungi and bacteria. The decomposition of biodegradable waste occurs during the thermophilic phase, which lasts from a few days (in industrial composting) to several months, driven by heat-loving organisms. This stage eliminates parasites and pathogens, ensuring maximum sanitary conditions. In the cooling phase, as the substrate is depleted, the reproduction of thermophilic organisms declines. New mesophilic communities emerge and continue the process over several months. The final product of compost pile stabilization during the maturation phase is a valuable substance used in many applications.

Composting is a preferred method for small-scale biodegradable waste processing, producing compost that can be used as fertilizer in agriculture. However, the process involves several challenges and limitations, such as availability, scalability, and economic sustainability. The methods used in biodegradable waste processing significantly affect the biological and physicochemical purity of the final products. It is also crucial to ensure the quality of the input material, that is, green biodegradable waste, which should be clean and free from heavy metals. If heavy metals accumulate in plants that later become biowaste, no process will reduce the concentration of these elements; on the contrary, their content may increase in the final waste [39].

A precondition for high-quality recycling of biodegradable waste is source separation, which becomes a complex step prior to processing. The raw material for conversion should be located close to the source of generation to address the issue of dispersed waste distribution.

3. Materials and Methods

Contemporary environmental challenges and the implementation of the Sustainable Development Goals (SDGs) require a change in dominant economic models towards a circular economy. Sustainable waste management, especially biodegradable municipal waste, remains a key area of this transition. Despite growing environmental awareness and legislative changes, Poland still lacks modern and comprehensive technological solutions for the effective processing of bio-waste. Low quality of segregation and limited use of innovative technologies mean that a significant part of waste ends up in landfills, causing environmental damage and generating additional costs.

A particular research gap is the lack of local life-cycle analyses (LCAs) of bio-waste treatment processes. This type of research allows for a full environmental, economic and social assessment of the proposed solutions and their impact on sustainable development—including reducing emissions and improving soil quality.

In the face of growing requirements for local governments, practical tools are needed to support rational investment decisions in the area of bio-waste management. Research in this area can significantly support the implementation of more efficient and sustainable systems.

In response to the above challenges, the following research objectives were formulated:

Main objective: Development and evaluation of a technological process for the processing of biodegradable municipal waste (code 20 02 01) in Polish conditions, in accordance with the principles of circular economy, in order to obtain high-quality products improving soil properties.

The specific aims are as follows:

• Analysis of the procedure for obtaining a decision of the Ministry of Agriculture and Rural Development (MARD) on the marketing of a soil conditioner produced from municipal biodegradable waste, with particular emphasis on the technological, quality and formal requirements that must be met by waste processing installations in Polish conditions.
• Evaluation of the effectiveness of the single-stage composting process of biodegradable waste (code 20 02 01) in industrial conditions, taking into account the quality parameters of the final product, technological requirements and comparison with the two-stage method in the context of the possibility of application in the circular economy.

Achieving the above objectives will enable a better understanding of the process of transforming biodegradable waste into a marketable product, in accordance with quality and legal requirements. This will identify the main administrative and technological barriers that hinder this process. An analysis of the factors affecting the quality of the final product will indicate which elements of the process need to be optimized. This will also make it easier to assess whether the product meets the expectations of the market and end users. In the context of the circular economy, the results of the research can contribute to streamlining certification procedures and increasing the availability of high-quality soil conditioners.

4. Results

4.1. Modern Approaches to Processing Municipal Biodegradable Waste in Poland

Upon joining the European Union, Poland committed to reducing the volume of waste deposited in landfills in favor of recycling, which remains one of the key objectives in the area of waste management. Despite numerous initiatives undertaken in this regard, public environmental awareness still requires further education and action, while the rising costs of disposal continue to hinder the implementation of effective waste management solutions. Particular importance is placed on modern methods of processing municipal biodegradable waste, with a focus on composting, which is considered the most sustainable form of organic recycling.

The research highlights a growing interest in biodegradable waste management, stemming from its crucial role in meeting mandatory recycling targets and the need to reduce processing costs. The quality of the input material and the use of advanced technologies are considered essential, as they ensure compliance with both EU and national circular economy (CE) standards. In particular, year 2021 saw an increased emphasis on the necessity of selective biowaste collection and the application of monitoring technologies, which enable the production of high-quality compost. As a result, the volume of such waste could be reduced by as much as 40–50%, while producing nutrient-rich biofertilizers.

The composting process, when carried out on an industrial scale, can follow either a single-stage or two-stage system, where intensive processing takes place in bioreactors, followed by maturation of the material on a composting pad. Proper quality of the input material and the implementation of modern technologies make it possible to produce compost that meets the standards defined by the circular economy framework. Municipal facilities responsible for processing this type of waste may apply for a decision from the Ministry of Agriculture and Rural Development (MARD), allowing them to place the product on the market as a soil improver or organic fertilizer.

The procedure for obtaining an MARD decision is characterized by a high level of complexity and can take from 8 months to 2 years. It requires detailed physicochemical, chemical, and biological analyses conducted by accredited laboratories. In parallel, opinions must be obtained from specialized scientific institutes. Once these stages are completed, producers submit documentation to the Department of Plant Breeding and Protection of the MARD. The decisions are issued with indefinite validity; however, products under such authorization remain under continuous supervision by the State Plant Health and Seed Inspection Service. The inspections include, among others, documentation verification, sampling, and analysis to ensure compliance with the decision requirements. In the event of any irregularities, a ban on placing the product on the market may be issued, or the product may be withdrawn from circulation.

Procedure for Obtaining Approval from the Ministry of Agriculture and Rural Development (MARD) to Introduce a Product to the Market

Recently, biodegradable waste, commonly referred to as “green waste”, has attracted considerable attention. This growing interest stems from the rising costs of managing such waste in the Polish market, the increasing amounts of biodegradable waste generated at source, and its inclusion in the algorithm used to calculate recycling performance levels. A crucial factor in this context is the quality of the feedstock, that is, the biodegradable waste itself, as well as the technology employed for its processing.

In Poland, the growing number of decisions concerning soil-improving agents highlights the dynamic development of biodegradable waste processing technologies. In 2021, particular emphasis was placed on the quality of biowaste destined for compost production, necessitating the implementation of advanced monitoring techniques and selective collection of feedstock at source. This approach ensures compliance with standards set by both national legislation and EU regulations related to the circular economy [14].

According to the Act on Waste of 14 December 2012 [26], biodegradable waste is defined as waste that undergoes aerobic or anaerobic decomposition with the participation of microorganisms. This means that waste subjected to composting under the right conditions: temperature, water content, and oxygen availability, undergoes organic decomposition.

Composting is considered the most sustainable method of recycling organic waste due to the continuously increasing volume of such waste. It is a method for processing organic waste into compost (a usable product), and it offers advantages over other disposal strategies because it reduces the volume of waste by 40–50% and results in a nutrient-rich biofertilizer. In recent years, compost and other organic fertilizers have gained greater prominence over chemical fertilizers, both in terms of supplying adequate nutrients and improving soil conditions, leading to higher crop yields and attractive pricing.

Under industrial conditions, composting may be conducted as a single-stage or two-stage process, where the intensive composting stage is carried out in sealed bioreactors, followed by a maturation phase conducted on a composting pad. With sufficiently high-quality feedstock (free from high levels of heavy metals), modern and proven technologies, and a properly managed process, a valuable product can be obtained from biodegradable waste. This approach represents a transformation of waste into a product, aligning with the circular economy model by reintroducing a product, rather than waste—back into the economy.

Given this context, any municipal facility may apply for a decision from the Ministry of Agriculture and Rural Development (MARD) permitting the placement of a soil-improving agent or organic fertilizer on the market, in accordance with the Fertilizers and Fertilization Act. A few years ago, only a handful of municipal installations (Regional Municipal Waste Processing Facilities, the RIPOKs) held MARD approvals for introducing such products into commercial circulation. Today, there are over 600 such decisions allowing for the marketing of soil-improving agents in Poland. Obtaining this decision is a complex process, taking between 8 months and even up to 2 years. To receive approval from MARD, the following are required:

• Results of tests on physicochemical, chemical, and biological properties performed by the Institute of Soil Science and Plant Cultivation—State Research Institute (IUNG-PIB) in Puławy, or another accredited laboratory;
• Opinions on quality compliance and suitability for use, issued, depending on the product’s intended application, by the Institute of Soil Science and Plant Cultivation—IUNG-PIB in Puławy, the Institute of Technology and Life Sciences in Falenty, the Institute of Horticulture in Skierniewice, or the Forest Research Institute in Warsaw.

While the above documents may appear simple to prepare, they require significant effort and commitment to properly prepare the product for testing, regarding both the process and the cleanliness of the feedstock, as well as the quality of the final product.

Table 1. Minimum content of organic substances and nutrients in soil improvers.

Type of Fertilizer	Composition of Ingredients *
Organic	N [wt%]	P2O5 [wt%]	K2O [wt%]	Organic substance [wt%]
	0.3	0.2	0.2	30

* Source: own elaboration based on [40].

presents the minimum content levels of organic matter and nutrients in soil-improving agents, indicating the threshold values of nutrients required in the product submitted to IUNG-PIB and subsequently to MARD. Naturally, the actual content of these nutrients may be higher, depending on the producer’s declaration.

In addition to nutrient content, soil-improving agents must not contain heavy metals in concentrations exceeding those specified in

Table 2. Maximum content of heavy metals and biological contaminants.

Type of Fertilizer	Content of Heavy Metals in 1 kg DM [mg] *
Organic	Cr	Cd	Ni	Pb	Hg
	100	5	60	140	2

* Source: own elaboration based on [40].

, and they must also be biologically clean. This means that a soil-improving agent must not contain Salmonella, Ascaris, Toxocara, and Trichuris eggs.

After producing a soil-improving agent, the following documents must be submitted to the Institute of Soil Science and Plant Cultivation—State Research Institute (IUNG-PIB) in Puławy: an order form, a manufacturer’s declaration regarding quality parameters, a description of the production technology, a list of raw materials used in the production of the agent, results of quantitative and qualitative tests, and a draft instruction for use and storage. Samples of the agent for testing are collected by Regional Chemical and Agricultural Stations and forwarded to an accredited laboratory.

Once the tests are completed and a positive opinion is issued by IUNG-PIB for agents produced from collected waste, three mandatory opinions from the following must be obtained:

• Institute of Rural Medicine in Lublin confirming no harmful effects on human health;
• National Veterinary Research Institute—State Research Institute in Puławy confirming no harmful effects on animal health;
• Institute of Environmental Protection in Warsaw confirming no harmful effects on the environment.

After obtaining the above opinions, additional, non-mandatory approvals may be sought, allowing the product to be used for specific crops. These include opinions from the Research Institute of Horticulture in Skierniewice, within which opinions are issued by the Vegetable Research Institute, the Institute of Ornamental Plants, and the Fruit Research Institute.

Once the test results and all necessary opinions are collected, the producer of the soil-improving agent submits all documentation to the Department of Plant Breeding and Protection at the Ministry of Agriculture and Rural Development (MARD). The ministry has 30 days to review the application, but in the case of missing documents, the deadline may be extended by another 30 days. After the application is reviewed, the producer receives a positive decision, which allows the soil-improving agent to be placed on the market. The decision is granted for an indefinite period, but it may be revoked if an inspection reveals that the fertilizer does not meet the quality requirements specified in the permit. Until 2019, inspections were rare. However, since 2022, inspections have been carried out by the State Plant Health and Seed Inspection Service (Pol. PIORiN). The procedure and possible sanctions are defined by the Act on Fertilizers and Fertilization. The inspection includes, among other things, verifying documentation and permits, as well as sampling the soil-improving agent. The samples are analyzed for physicochemical and biological properties, and the results must be consistent with the decision issued by MARD. If, during the inspection specified in Article 30(2)(3) of the Act of 10 July 2007 [41], on Fertilizers and Fertilization, the Voivodeship Inspector of Plant Health and Seed Inspection finds that the quality requirements are not met, that permissible levels of contaminants have been exceeded, or that market placement conditions have not been met, they may issue a decision to perform the following:

• Prohibit the marketing of the fertilizer, the fertilizer marked with the “EC Fertilizer” label, or the plant cultivation aid;
• Order the withdrawal from the market of the fertilizer, EC-marked fertilizer, or the plant cultivation aid.

Article 38(1) of the Act on Fertilizers and Fertilization specifies that an entity marketing a fertilizer, fertilizer labeled as “EC Fertilizer,” or a plant cultivation aid must cover the costs of the inspection and laboratory testing performed by the Inspection Service if the fertilizer is found to not meet the quality requirements set by Regulation No. 2003/2003, the provisions issued under Articles 10(5) and (6), 11(5), or 12(5) of the Act, or the permit referred to in Article 4(1), or if it does not meet the requirements set out in Article 5 or the additional requirements declared by the producer, importer, or other marketing entity [41].

From the above, it is clear that obtaining the MARD decision to place a soil-improving agent on the market is only the beginning of the process of turning waste into a product. In the subsequent stages, the quality declared by the producer must be maintained. This quality must be upheld not only in the primary product but also in all repackaged versions produced by other manufacturers selling the same product. Inspections by PIORiN (State Inspectorate) and WIORiN (Voivodeship Inspectorates) cover not only municipal installations but also all other organizations that market the product either in bulk or packaged.

4.2. Assessment of the Efficiency of the Composting Process in Industrial Conditions—A Case Study of the Remondis Bydgoszcz SA Installation

4.2.1. Research Experiment Assumptions

Organic recycling is a technological process that involves the processing of waste, including biodegradable waste. It is carried out under controlled conditions and with the use of microorganisms, which leads to obtaining an organic product in the form of a soil conditioner or fertilizer (aerobic treatment) or methane during anaerobic treatment. The biggest problem with recycling is selective waste collection. Favorable conditions for both processes occur, among others, in the compost environment, i.e., with the participation of high temperature, high humidity and the presence of microorganisms.

The composting process can be carried out in two ways. First, as a single-stage composting process, conducted entirely in bioreactors or in windrows under uncontrolled conditions. The second method is the two-stage composting, which includes an initial intensive composting phase in sealed bioreactors, followed by a maturation phase in windrows.

The experiment aimed to examine the effectiveness of the single-stage composting method at the Remondis Bydgoszcz SA Municipal Facility. The approach involved using only the intensive composting phase of biodegradable waste (originating from the city of Bydgoszcz and neighboring municipalities) in closed bioreactors, according to the following steps:

• Sample of biodegradable waste no. 1392 was pre-shredded.
• The shredded material was loaded into bioreactor no. 1—duration of Phase I: 7 days.
• Transfer from bioreactor no. 1 to bioreactor no. 2—duration of Phase II: 7 days.
• Transfer from bioreactor no. 2 to bioreactor no. 3—duration of Phase III: 4 days.
• Transfer from bioreactor no. 3 to bioreactor no. 4—duration of Phase IV: 4 days. During the experiment, after Phase IV, an additional drying phase (Phase V) was added due to excessive material moisture.
• Material drying in the bioreactor—duration of Phase V: 6 days.
• Screening of the material using a star screen. Screening with the star screen was not possible due to excessive moisture.
• Screening of the material using two drum screens with different mesh sizes—conducted twice (

  Table 3. Detailed data for individual stages of the experiment.

  Specification	Loading	Transfer 1	Transfer 2	Transfer 3	Drying
  Bioreactor number	1	1-6	6-2	2-3	3
  Duration of the process	7 days	7 days	4 days	4 days	6 days
  Selected parameters of the process	T * = 52 °C H * = 70 °C H2O * = 55 m3	T = 52 °C H2O = 15 m3	T = 52 °C H2O = 5 m3	T = 52 °C H2O = 5 m3	T = 52 °C H2O = 0 m3
  Material weight	220.00 t	210.00 t	195.50 t	184.20 t	157.93 t
  Mass loss	-	10.00 t −4.54%	14.50 t −6.90%	11.30 t −5.78%	26.27 t −14.26%

  * Legend: T = temperature; H = higienization; H₂O = water.

  ).

4.2.2. Results of Individual Stages of the Experiment

The research experiment aimed to determine the effectiveness of a single-stage composting method for biodegradable waste with the code 20 02 01 and to compare its effectiveness with the two-stage composting method.

Based on the experiment, the following conclusions can be drawn:

• Advantages of the single-stage method:
  • It is carried out exclusively in bioreactors and does not require additional space in the form of a composting pad for material maturation, as is the case with the two-stage method.
  • The analysis of NPK (nitrogen, phosphorus, and potassium), Ca, and Mg content in the final product is comparable to the two-stage method and meets the requirements for soil improvers in Poland, in line with the manufacturer’s assumptions (

    Table 4. Results of laboratory tests of soil improvement agent (SIA ¹).

    REVITA	Parameters		Results *
    			SIA Two-Stage Method	SIA Single-Stage Method Sample 1	SIA Single-Stage Method Sample 2	Minimum Parameters According to the Regulation
    	pH		8.30	8.50	7.80	-
    	[%]	Organic substance	30.00	25.80	22.60	30.00
    		Total N	2.17	2.19	2.61	0.30
    		K	0.95	0.88	0.86	0.20
    		P	0.24	0.22	0.21	0.1–0.2
    		Ca	2.58	2.40	1.91
    		Mg	0.28	0.27	0.22
    		Hg	0.07	0.07	0.09	2.00
    		Cd	0.45	0.37	0.36	5.00
    		Cr	12.70	29.90	11.30	100.00
    		Ni	8.97	19.90	7.19	60.00
    		Pb	46.90	22.30	24.00	140.00
    			not detected	not detected	not detected	not detected
    			not found	not found	not found	not found

    ¹ Pol. ŚPWG; * Source: own study based on a study carried out by SGS Polska LLC.

    ).
  • The material after processing did not contain Salmonella, Ascaris, Toxocara, or Trichuris, similarly to the two-stage method (Table 4).
• Disadvantages of the single-stage method:
  • The single-stage method requires the involvement of a larger number of bioreactors. The composting time in bioreactors is 28 days, while in the two-stage method it is 14 days in bioreactors plus 30–45 days on composting pads. This results in the bioreactors being occupied for a longer period (Table 3).
  • Multiple transfers of material between bioreactors and pre-drying increase labor demands (Table 3).
  • The moisture content of the resulting material is 40–45%. In the two-stage method, it is 20–30%. Consideration should be given to reducing the amount of water added during the process (

    Table 5. Summary of the single-stage process (without screening).

    Specification	Duration	Water Consumption	Mass Loss	Mass Loss	Comments
    Sample 1392	28 days	80 m3	62.07 t	−28.21%	The moisture content of the final material is 45.94% and 44.04% Difficulties with screening using the star screen

    ).
  • A lower mass loss/reduction compared to the two-stage method (Table 5).
  • A higher proportion of coarse material and waste coded 190503 after screening the final product. The amount is on average 10–15% greater than with the two-stage method (

    Table 6. Screening of material using a drum screen—results.

    Specification	REVITA	191212	190503	Material Returned to the Process	SUM
    Sample 1392	79.78 t	38.00 t	20.15 t	20.00%	157.93 t
    Share	50.51%	24.06%	12.76%	12.66%	100.00%

    ).
  • The final product did not meet the minimum organic matter content required by the Fertilizers and Fertilization Act (<30%) (Table 1 and Table 4).
  • In terms of organoleptic and visual qualities, the final product is significantly inferior to the material obtained using the two-stage method. While the material may be suitable for agricultural use, it will be difficult to offer and sell to individual customers or to clients producing growing media (Figure 1).

The single-stage composting process, although space-efficient, did not meet the minimum regulatory standards for organic matter content, which indicates a risk of non-compliance with the decisions issued by the Ministry of Agriculture and Rural Development. Therefore, it should only be applied as a preliminary or supporting treatment, followed by further processing to ensure compliance with legal and quality requirements, or to obtain an additional certificate for a product with lower parameters, provided that these do not negatively affect the environment, human health, or animal health. These findings highlight the need to strike a balance between operational efficiency and regulatory compliance in the management of biodegradable waste at the municipal level.

Based on the above findings, it was concluded that the single-stage composting method may be considered as an alternative, particularly in conditions where space availability is limited. However, limitations regarding the quality of the final product and higher technological requirements suggest that, in the context of high standards and market expectations, the two-stage method may be more advantageous in most cases.

5. Discussion

Composting municipal organic solid waste has numerous environmental benefits, including reduced waste sent to landfills, lower methane emissions, and the production of valuable products such as soil improvers and bio-fertilizers. This process supports carbon sequestration and contributes to improving soil fertility [39,42].

The results of meta-analytical studies conducted by Liu [43] have shown that key parameters of the composting process, such as C/N ratio, moisture and tipping frequency, significantly affect the level of greenhouse gas emissions. Composting supports the circular economy by recycling nutrients and reducing the demand for synthetic fertilizers. In the effort to increase the efficiency of biological processing of municipal waste, the growing importance of input material quality and the need to implement more advanced processing methods are emphasized. Similar conclusions have been drawn by Manea et al. [44] and Nowak et al. [45]. Reducing humidity reduces methane emissions by up to 31.8% and more frequent tipping by 62.6%. Additionally, the use of biochar reduces N₂O and CH₄ emissions by 44% and 43.6%, respectively [42].

Studies conducted at Danish composting plants reported methane emissions ranging from 8 to 42.5 kg CH₄ per hour, depending on the feedstock, technology, and season, with emissions in spring and summer being about 50% higher than in autumn [44]. The composition and volume of emitted gases may vary depending on the composting method and even the season of the year, although these emissions can be reduced. Key factors in this regard include optimizing composting conditions, adding amendments, and applying advanced technologies [39].

The issue of compost quality is related not only to fertilizing values, but also to the risk of the presence of contaminants. Modern technologies, such as microbiological inoculants and composting in enclosed bioreactors, have significantly improved the efficiency and quality of the resulting compost. Despite technological advancements, challenges remain in managing contaminants such as heavy metals and microplastics, as well as in ensuring compost quality and safety.

Research by Steiner et al. [46] demonstrated that compost and organic fertilizers produced from biodegradable waste are significantly contaminated with microplastics, whose quantity and size vary considerably depending on the technological process and sampling stage. The final product predominantly contains fragments of polypropylene and polyethylene fibers. These particles tend to decrease in size (from 1328 μm to 1093 μm) and develop a rougher surface, which may enhance their interaction with other contaminants [45]. Similar findings were reported by Braun et al. (2021), who emphasized the significance of these pollutants: the plastic content in compost can reach 1.36 g/kg, which, at the farm scale, translates into several dozen kilograms of plastic being introduced into fields annually [47,48].

Problems related to contamination of the composting feedstock indicate the need to implement more advanced sorting methods and legal regulations on the quality of compost.

Research results clearly indicate that the effectiveness of the single-stage method could be further improved through the application of technologies that reduce raw material moisture during the composting stage. Similar technologies are used in other EU countries, contributing to increased process efficiency and reduced greenhouse gas emissions [4].

Socio-economic barriers, such as lack of awareness and public acceptance, hinder the widespread implementation of composting. Dygudaj et al. point out that waste collection fees and environmental education of residents are key factors in the waste management system in Poland [49].

Collaboration among different stakeholders is a key element of effective circular economy implementation, as emphasized by H. Matsuda [4]. The author notes that the involvement of businesses, governments, consumers, and waste management service providers is essential to building effective networks and partnerships. This approach facilitates the sharing of resources, knowledge, and infrastructure, promoting efficient material use and the development of circular business models. Examples of such initiatives include industrial symbiosis, where one company’s waste becomes another’s raw material; and reverse logistics systems, which allow for the collection and recycling of products. Matsuda [4] also emphasizes that political and regulatory support is crucial for creating a favorable environment for such collaborations through the introduction of appropriate legal frameworks, tax incentives, and recycling targets [4].

6. Conclusions and Recommendations for Practice

Composting of biowaste is one of the most sustainable waste treatment methods. This process significantly reduces the amount of waste sent to landfills while producing valuable products, such as compost and organic fertilizers. Ensuring the appropriate quality of feedstock—i.e., source-separated collection in containers rather than plastic bags, low heavy metal contamination in green materials, and the use of modern composting technologies—enables the production of a final product that meets environmental protection standards and fulfills agricultural requirements.

Despite numerous benefits, challenges remain, such as ensuring high compost quality, reducing contamination, and raising public environmental awareness. Achieving EU and national targets requires not only optimization of technological processes, but also active legal support and cooperation between various stakeholders.

The experimental studies carried out made it possible to evaluate the effectiveness of the single-stage composting method for biodegradable waste (code 20 02 01) and compare it with the effectiveness of the two-stage method. The results show that the two-stage approach is superior in terms of the quality of the final product, although the single-stage method does not exclude the possibility of applying for a decision from the Ministry of Agriculture and Rural Development (MARD). However, the producer would need to apply for a new decision with lower nutritional parameters, while ensuring that the product remains free from contaminants such as heavy metals, Salmonella, Toxocara, Trichuris, and Ascaris.

Future research should focus on improving technological processes, optimizing parameters (moisture, C/N ratio, turning frequency), and developing methods for reducing contamination. Social and political engagement, as well as public education, are also crucial in promoting composting as a sustainable waste management strategy.

Compost production remains a key element in the treatment of biodegradable waste, reducing the amount of waste going to landfills and enabling the reuse of resources in agriculture, improving soil structure, and supporting plant growth.

The main conclusions can be summarized as follows:

• Two-stage composting in closed bioreactors ensures higher final product quality compared to the single-stage method.
• Compliance with MARD decisions: Single-stage composting does not meet the minimum legal requirements for organic matter content (<30%), which limits its application as a standalone method; however, obtaining a new decision would allow for marketing of the product with lower nutritional parameters.
• The single-stage method is more space-efficient, easier to operate, less labor-intensive, and less costly.
• The results highlight the importance of aligning composting technology with legal and quality requirements and suggest that the two-stage approach is more suitable for high-quality industrial-scale processing of biodegradable waste.

The results of the analyses conducted so far indicate the need for the following:

• Optimization of process parameters (moisture, carbon-to-nitrogen ratio, turning);
• Research on reducing contaminants in compost;
• Studies on social acceptance and the effectiveness of waste policy.

Only a comprehensive approach that combines technological, environmental, and social aspects will allow the full potential of composting to be realized within a circular economy.