In the renewable energy landscape, biogas represents a powerful, sustainable solution that is independent of climatic factors (solar radiation and wind). In Italy, about three-quarters of the total national biogas power generation is provided by four regions: Lombardy, Veneto, Emilia-Romagna and Piedmont. There are about 2,400 biogas production plants in Italy (to be precise, 95% biogas and 5% biomethane) of which about 80% are in agriculture. In this article we will analyze the technical-economic characteristics of biogas production plants. In the next article, however, we will examine how the integration of digital technologies with such plants can significantly increase productivity and efficiency. Through the use of IoT sensors for data collection, AI and ML algorithms, automation and control dashboards, operators can optimize performance, reduce downtime and maximize energy production, laying the foundation for a smarter and more sustainable energy future.
What is biogas
Biogas is the result of anaerobic digestion of organic matter by microorganisms. This gas represents a versatile renewable energy source that can be used for heating, electricity generation, and fuel production. It can be integrated into systems originally designed for natural gas, such as direct combustion systems for heating, cooking, water heating or powering gas turbines. It also finds application in cogeneration plants, where it enables the combined production of heat and electricity with high efficiency.
The biogas can be further purified and converted to biomethane, a refined form that can fuel internal combustion engines for automobiles, natural gas fuel cells or be fed into natural gas distribution networks.
An additional benefit of the biogas production process is digestate, a nutrient-rich by-product that can be used as a natural fertilizer, promoting sustainable agriculture and closing the nutrient loop.
What is a biogas production plant
A biogas plant is a facility that, under anaerobic conditions, converts organic waste into biogas. Through anaerobic digestion, microorganisms decompose organic matter in the absence of oxygen, producing mainly methane (CH₄) and carbon dioxide (CO₂).
The main chemical and physical factors that influence biogas formation are temperature, pH, carbon and nitrogen percentages, solid organic matter content (the particles of biological origin, such as plant remains, food or sludge, that do not dissolve in water) the water, the retention time (the length of time the organic material stays in the digester to allow for complete anaerobic digestion) and the volumetric organic load (the amount of organic matter introduced each day into one cubic meter of useful volume of the anaerobic digester).
The main raw materials are manure, agricultural residues, sewage sludge and food waste. Anaerobic digestion takes place in a sealed digester, where anaerobic bacteria decompose organic matter. Biogas upgrading is a process of purifying the raw biogas produced by the anaerobic digester into high-purity biomethane. This process removes impurities and unwanted gases present in the raw biogas (carbon dioxide (CO₂), hydrogen sulfide (H₂S), moisture and particulate matter, other minor gases). Biogas can be converted into biomethane, equivalent to natural gas, or used directly. Biogas plants capture methane that would otherwise be released into the atmosphere, reducing greenhouse gas emissions.
Raw materials for biogas production
Food waste is widely used in biogas plants, especially those derived from municipal waste. According to UNEP, about 74 kilograms of food is discarded per person each year. One kilogram of volatile solids can produce up to 0.6 m³ of methane, and with 1,000 tons of food waste per day, enough methane can be produced to power 800-1,400 homes.
Volatile solids are the fractions of organic matter in a material that can be decomposed or converted to gas by biological processes, such as anaerobic digestion, or chemical processes, such as combustion. They are called “volatile” because, when subjected to heating in the absence of oxygen (e.g., to about 550°C in the laboratory), they volatilize or are converted to gas.
Volatile solids thus represent the biodegradable part of the material and are a key indicator for assessing biogas production potential in an anaerobic digester. In the case of manure, volatile solids include plant residues, bacterial cells, fats, proteins and carbohydrates. In the case of food waste, they include oils, sugars and starches. Measuring volatile solids helps to estimate the amount of organic material that can be turned into biogas.
Turning to waste from livestock farming, a 500 kg dairy cow produces an average of 40 kg of manure per day. One kilogram of volatile solids from cattle manure generates 0.2-0.3 m³ of methane.
In the context of agricultural residues, straw and corn stalks have moderate methane yields (0.15-0.3 m³ per kg of volatile solids) and often require pretreatment to increase the yield.
Sewage sludge, municipal solid waste and organic fractions of municipal waste produce 0.2-0.4 m³ of methane per kg of volatile solids.
Within industrial waste, sectors such as the food, dairy and pharmaceutical industries provide ideal organic matter for biogas production.
This article does not consider the choice of dedicating agricultural land specifically for the cultivation of biomass for biogas plants.
Why organic waste is a sustainable resource
Organic waste generation grows with increasing population and economic development. Adopting a circular economy and aiming for net zero emissions are crucial approaches to energy security and sustainable waste management. In Europe, installed biomethane plants have a capacity of 6.4 billion cubic meters per year, helping to reduce CO₂ emissions by about 29 million tons compared to the use of fossil fuels. They also produce 830,000 tons of organic fertilizer per year (Source: EBA Report – European Biogas Association, 2023).
The benefits of biogas
Biogas decreases greenhouse gas emissions and dependence on fossil fuels, with a 91 percent reduction in emissions compared to gasoline.
Anaerobic digestion neutralizes germs and parasites, improving water quality.
Digestate, a by-product of anaerobic digestion, is a nutrient-rich fertilizer.
Cost of a biogas production plant
The cost of a biogas plant can vary widely depending on a number of factors, including the size of the plant, the type of feedstock to be processed, the complexity of the technologies used (such as digital monitoring or automation systems), and location.
However, estimates can be given for a small-scale plant (up to 500 kW):
- construction cost: 500 k€ – 1,500 K€
- Construction cost per kW of capacity: 1 k€ – 3 k€/kW
- annual management cost: 50 k€ – 100 k€
The annual operating costs are:
- maintenance and operations weigh about 2-5% per year of the initial cost of the plant
- The energy cost of transporting and processing materials depends on local availability and collection logistics
The main factors influencing cost are:
- If the plant involves purification of the biogas to produce biomethane, costs can increase significantly
- Digital installations using advanced technologies for real-time monitoring and management (sensors, artificial intelligence, automation) may have an upfront surcharge, but bring significant operational savings
Typically, a biogas plant has a payback time (payback period) of 5-10 years, but this can vary depending on operating costs, revenues from energy production (sale of electricity or biomethane), and government incentives.
Italy and Europe offer various subsidies and tax incentives to support the development of biogas plants, thus reducing the initial investment cost. For Italy: Conto Energia for biogas (CVE), Incentives for biomethane production (Certificati Verdi), National Energy Transition Fund, etc. For Europe: Horizon Europe Program, Innovation Fund, Next Generation EU, Common Agricultural Policy (CAP), etc. Local authorities and development agencies also offer regional incentives for the establishment of biogas plants.