Italy is one of the leading nations in the biogas sector. Agricultural, landfill, sewage and manure substrates are converted into biogas using anaerobic digestion and, then, into electricity and heat by means of properly arranged internal combustion engines. In this study, after an overview of the European context, the authors present the Italian biogas sector status in terms of development trends and factors that favour/block biogas spread. Despite the fact that biogas is a renewable fuel and a consolidate technology, it is mandatory to examine its real costs, biogas composition and engine combustion products. For this purpose, in the present work, the authors selected six in-operation biogas plants fed by different substrates, investigate plants construction and operation costs and measure both biogas and engine emissions compositions. Biogas status analysis shows a high growth rate until the end of 2012 due to generous Government subsidies while, after supports reduction, a continuous depletion of biogas installations is observed. Alongside the development, established supports overlook also the plant size as well as the cost. In fact, the most widespread plant nameplate electric power is 1 MW while its construction cost ranges between 4.2–4.8 millions of Euros. Real on-site measurements show variable biogas composition while engine emissions are comparable with the natural gas ones.

Italy is a leading country in the biogas sector. Energy crops and manure are converted into biogas using anaerobic digestion and, then, into electricity using internal combustion engines (ICEs). Therefore, there is an urgent need for improving the efficiency of these engines taking the real operation into account. To this purpose, in the present work, the organic Rankine cycle (ORC) technology is used to recover the waste heat contained in the exhaust gases of a 1 MW_el biogas engine. The ICE behavior being affected by the biogas characteristics, the ORC unit is designed, firstly, using the ICE nameplate data and, then, with data measured during a one-year monitoring activity. The optimum fluid and the plant configuration are selected in both cases using an “in-house” optimization tool. The optimization goal is the maximization of the net electric power while the working fluid is selected among 115 pure fluids and their mixtures. Results show that a recuperative ORC designed using real data guarantees a 30% higher net electric power than the one designed with ICE nameplate conditions.

In the agricultural and work machine sectors, hydromechanical transmission competes with traditional mechanical transmission. However, the double energy conversion taking place in hydrostatic transmission lowers the efficiency of the entire transmission. Thus, the dimensioning of hydromechanical transmission must not only meet the functional requirements of speed and power to be transmitted, but must also identify the particular combination of layout and the components that leads to the maximum efficiency. In this study, a general answer to this problem will be given. The design is transformed into a mathematical programming problem, whose goal is the optimisation of both the configuration and internal components of the transmission. The structure of the transmissions is described by means of graph theory, and the resolution of the optimisation problem is obtained by means of a ‘direct search’ algorithm based on the swarm method.

Despite biogas renewability, it is mandatory to experimentally assess its combustion products in order to measure their pollutants content. To this purpose, the Authors selected six in-operation biogas plants fed by different substrates and perform an on-site experimental campaign for measuring both biogas and engines exhausts composition. Firstly, biogas measured compositions are compared among them and with data available in literature. Then, biogas engines’ exhaust compositions are compared among them, with data available in literature and with measurements obtained from an engine characterised by the same design power but fuelled with natural gas. Finally, the Health Impact Assessment analysis is used to estimate the damage on human health caused by both biogas and natural gas engines emissions. Results show that biogas causes a damage on human health three times higher than the natural gas one. But, this approach does not consider biogas renewability. So, to include this important aspect, also an analysis which considers Global Warming categories is carried out. Results highlight that natural gas is twice harmful than biogas.

The aim of the work is to evaluate the damage to human health arising from emissions of in-operation internal combustion engines fed by biogas. The need of including also unregulated emissions like polycyclic aromatic hydrocarbons (PAHs), aldehydes and dioxins and furans is twofold: (i) to cover the lack in biogas engine emissions measurements and (ii) to complete the picture on biogas harmfulness to human health by identifying the substances with the highest impact. To this purpose, an experimental campaign is conducted on six biogas engines and one fed by natural gas all characterised by an electric power of 999 kW_el. Collected data are used to perform an impact analysis on human health combining the Health Impact Assessment and the Risk Assessment. Measurements show that PAHs, aldehydes and diossin and furans are almost always below the detection limit, in both biogas and natural gas exhausts. The carcinogenic risk analysis of PAHs for the two fuels established their substantial equivalence. The analysis of equivalent toxicity of dioxins and furans reveals that biogas is, on average, 10 times more toxic than natural gas. Among regulated emissions, NO_x in the biogas engines exhausts are three times higher than those of natural gas. They are the main contributors to human health damage, with approximately 90% of the total. SO_x ranks second and accounts for about 6% of the total damage. Therefore, (i) the contribution to human health damage of unregulated emissions is limited compared to the damage from unregulated emissions, (ii) the damage per unit of electricity of biogas engines exhausts is about three times higher than that of natural gas and it is directly linked to NO_x, (iii) obtaining a good estimation of the human health damage from both biogas and natural gas engines emissions is enough of a reason to consider NO_x and SO_x.

The anaerobic digestion of biodegradable substrates and waste is a well-known process that can be used worldwide to produce a renewable fuel called biogas. At the time of writing, the most widespread way of using biogas is its direct usage in combined heat and power internal combustion engines (CHP-ICEs) to generate electricity and heat. However, the combustion process generates emissions, which in turn have an impact on human health. Therefore, there is a need to: (i) measure the ICE emissions (both regulated and unregulated), (ii) compute the impact on human health, (iii) identify the substances with the highest impact and (iv) calculate the avoided damage to human health per Euro of investment in technology able to abate the specific type of pollutant. To this end, the authors conducted an experimental campaign and selected as a test case a 999 kW_el biogas internal combustion engine. Then, the collected data, which included both regulated and unregulated emissions, were used to calculate the harmfulness to human health and identify the more impactful compounds. Thus, combining the results of the impact analysis on human health and the outcomes of a market analysis, the avoided damage to human health per Euro of investment in an abatement technology was computed. In this manner, a single parameter, expressed in DALY €⁻¹, provided clear information on the costs to reduce each disability-adjusted life year (DALY). The impact analysis on human health, which was performed using the Health Impact Assessment, showed that NO_x was the main contributor to damage to human health (approximately 91% of the total), followed by SO_x (6.5%), volatile organic compounds (1.4%) and CO (0.7%). Starting from these outcomes, the performed investigation showed that the technology that guarantees the maximum damage reduction per unit of cost is the denitrification system or the oxidizing converter, depending on whether the considered plant is already in-operation or newly built. This is an unexpected conclusion considering that the most impacting emission is the NO_x.