## 1 Introduction  
Historically, the management and disposal of manures from small and dispersed livestock farms was not considered a problem [1]. Besides, these wastes, both solid and liquid, were rich in organic matter and nutrients, primarily nitrogen, phosphorus, and potassium, making them valuable for maintaining soil fertility [1, 2]. Until now, they are typically spread on arable land after undergoing long-term stabilization in lagoons and composting piles [3]. Unfortunately, in such cases, the energy content of manure is not utilized, combined with the release of greenhouse gases, notably methane, and odors into the atmosphere [4]. Incidents of surface and groundwater pollution are frequently reported when lagoons and composting pits lack proper insulation [5]. Nowadays, the importance of sustainable livestock waste management, environmental protection, and creating value for farmers is increasingly recognized. Energy recovery from animal waste can be achieved through thermal or biochemical processes [6, 7]. One widely used technology for livestock waste treatment is anaerobic digestion, a biochemical process wherein organic compounds are converted into biogas and digestate. Biogas typically comprises methane (55-65%), carbon dioxide (45-35%) and traces of other gases, like sulfide and ammonia [8]. The residue left after anaerobic digestion, known as digestate, is rich in organics and nutrients and can serve as a soil conditioner to enhance agricultural production [9]. Implementing anaerobic digestion technology offers several advantages, including waste volume reduction, odor control, decrease in manure pathogens (especially during thermophilic processes), recovery of nutrients in digestate, and energy production [10]. Anaerobic digestion facilities represent complex technical systems that demand substantial investments in infrastructure, such as buildings and tanks, mechanical and safety equipment [11; 12]. The setup of such a facility involves meticulous design, construction of infrastructure, acquisition and installation of equipment, operation overseen by trained personnel, and annual maintenance to minimize or address unforeseen breakdowns. Specialized construction firms, known as EPC technology providers, collaborate with waste producers (i.e., livestock farmers) to establish these facilities. Given the variations in livestock farms regarding type and size, leading to the generation of diverse types and quantities of waste, technology providers implement customized solutions tailored to each client's needs. These solutions encompass various aspects, including anaerobic digestion technology (e.g., wet, dry, mesophilic, thermophilic) and waste pretreatment technology, as well as equipment for biogas utilization (e.g., hot water production, electricity, and heat, or biomethane upgrading). According to the European Biogas Association (EBA), as of 2023, Europe hosted \(\sim\)21,000 anaerobic digestion facilities generating approximately 21 billion cubic meters (bcm) of biogas. While biogas was primarily utilized for electricity generation, there was a growing trend of upgrading it to biomethane, which was either injected into the natural gas grid or used as a vehicle fuel. The EBA reported a significant increase in biomethane production from 0.9 to 4.2 bcm between 2013 and 2023. Despite this progress, the Repower EU initiative has set a target of further increasing biomethane production to 35 bcm by 2030. Achieving this objective necessitates the establishment of an additional 14 bcm of biogas production capacity, equivalent to the construction of \(\sim\)14,000 new anaerobic digestion facilities, alongside the conversion of existing facilities into biomethane plants. Many European countries, such as Greece, Ukraine, Latvia, Ireland and Serbia, lag behind in biogas production, each hosting fewer than 60 biogas plants. Consequently, a considerable amount of energy from manure remains untapped.