• Energy Research

AbstractThe updated Bioeconomy Strategy document “A sustainable bioeconomy for Europe: strengthening the connection between economy, society and the environment”, which was issued by the European Commission in October 2018, encourages the exploitation of organic wastes according to a pyramidal hierarchy in which the extraction of valuable biomolecules, which will be used as they are or as precursors of high‐added‐value compounds, is a priority in biofuel production. This review considers a biorefinery platform in which food waste and sewage sludge are adopted to produce volatile fatty acids (VFAs) through a dark fermentation process. VFA fermentation is optimized by slightly acid pH (6–7), short hydraulic retention time (1–7 days) and high organic load rate (more than 10 gTS L−1 d−1). Attention has been focused on VFA exploitation for polyhydroxyalkanoate (PHA) production via a ‘feast and famine’ strategy performed in sequencing batch reactors. The obtained PHA yields are around 0.4–0.5 gPHA gCOD−1. Moreover, VFAs allow for the production of biofuels, such as hydrogen and methane, through single‐ or double‐staged anaerobic digestion. Innovative bioelectrochemical upgrade strategies for biogas helps producers to obtain biomethane for the automotive sector. Moreover, biogas has recently been tested for the production of polyhydroxybutyrate, a biodegradable and biocompatible thermoplastic made by microorganisms from C1 carbon sources (CO2 and CH4). Digestates from anaerobic bioreactors are still rich in nitrogen and phosphorus compounds. These latter compounds have been identified as critical raw materials due to their low availability in the European Union and to increasing demand from the growing global population. Thus, nutrient recovery from digestate allows users to close the loop of the ‘circular economy’ approach. © 2019 Society of Chemical Industry

Abstract The present paper discusses issues, scenarios, new ideas and processes with the specific purpose of quantitatively evaluating the feasibility of applying industrial symbiosis (IS) to regions where Waste-to-Energy (WtE) processes are not fully utilised (e.g. many Mediterranean regions), in order to exploit the potential synergies between 1) wastewater treatment (WWT), 2) WtE and 3) Anaerobic Digestion (AD) processes in a new, holistic approach that is able to maximise the efficient use of resources, while reducing the current environmental impacts. The enormous energy that can be obtained from residual waste is partially used, through an IS-based biorefinery approach, to thermally support the AD and drying processes of organic waste and sludge, thereby allowing 100% of the increased biogas production to be upgraded to biomethane. The need to landfill can be reduced to less than 5–10%, which allows the 2035 EU target to be achieved, with relevant economic and environmental benefits. Electricity from the WtE plant is exploited to supply the utilities of the 3 main processes and in particular to lower the costs of the required tertiary WWT and wastewater pumping phases in order to make the reclaimed water cost competitive with that of conventional water resources and thus to make this marginal water resource fully sustainable. The proposed approach can be applied in numerous countries, where landfilling is still predominant, to help stakeholders favouring a cultural shift towards a more sustainable, integrated waste/wastewater management while lowering the sterile “Not In Anyone's BackYard” (NIABY) opposition to WtE plants.

Municipal solid waste (MSW) production in the world has increased by 60 % in recent years. Incineration of MSW reduces their volume in conjunction with energy recovery. Incineration produces two residues, namely bottom ash (BA) and fly ash (FA), with high concentration of heavy metals and organic pollutants, especially for FA, making them an environmental concern. Vitrification is a costly, highly safe high temperature treatment, ensuring encapsulation of heavy metals. FA vitrification requires a source of silica to be able to get vitrified. In this study, we have proposed valorizing treated (vitrified) FA through the production of porous glass-ceramics, subsequently to MSWI. The entire process, from incineration to glass-ceramics production, was evaluated for several scenarios by Life Cycle Assessment (LCA) using Sima Pro 9.0. Three main scenarios were analysed; each one considering a different silica source: bottom ash (BA), glass cullet (G) and silica sand (S), and for each scenario, three thermal recovery subscenarios were assumed: no thermal recovery used to heat FA prior to vitrification (N), heating FA prior to vitrification using incineration gases thermal recovery (T) and methane-combustion-aided thermal recovery, which exploits methane combustion to further increase the gases temperature (M). Results proved that vitrification was a technically feasible and environmentally-energetically sustainable technology. The result indicates that the most eco-sustainable scenario was using bottom ashes as a silica source together with methane-combustion-aided recovery: 0.467 kgCO2,eq, 5.83 × 10-8 carcinogenic-CTUh and 9.26 MJ required per kg of glass-ceramics produced.

The loading of a diesel particulate filters (DPFs) entails the need of trap regeneration by particulate combustion, whose efficiency and frequency are somehow affected by the way soot is deposited along the channels. Great efforts are thus spent to improve the understanding of the filtration process of DPFs, aimed at obtaining a deeper insight into the relationship between engine performance and filter loading so as to take advantage of this insight for DPF design and optimization purposes. Small lab-scale 300 cpsi DPF samples were loaded downstream the Diesel oxidation catalyst (DOC) in an ad hoc designed reactor capable of hosting five samples with part of the entire flow produced by an automotive diesel engine at the 2500 × 8 BMEP operating condition, selected to be representative as one of the critical engine points of the New European Driving Cycle (NEDC). Soot layer thickness was estimated by means of Field emission scanning electron microscope (FESEM) observations after sample sectioning at progressive locations, obtained through a procedure defined not to affect the distribution of the soot inside the filter and to enable estimation of the actual soot thickness along the channel length. This is a pre-requisite to get suitable data for the validation of the DPF models required for trap design and optimisation.

AbstractThe present investigation concerns the phenomena that occur during the non‐catalytic regeneration of Diesel Particulate Filters (DPFs). The temperature evolution in the filter has been correlated to the emissions of CO, HC, NO, and NO2 during the loading and regeneration process. The emissions were assessed over both the diesel oxidation catalyst (DOC) and the DPF, in order to characterise the chemical species evolution inside the after‐treatment line. Different regeneration temperatures, which have been found to have a strong impact on the evolution of the soot oxidation rate, have been assessed. Finally, the particulate emissions during regeneration have been measured on a number and size basis.

Abstract The effects of using a 30% by volume blend of a renewable fuel, called Farnesane, and fossil diesel in a small Euro 5 displacement passenger car diesel engine have been evaluated in this paper. Farnesane is a 15-carbon long molecule that can be obtained from the fermentation of biomass-derived sugars (such as sugar cane, amidaceous and cellulosic crops), which are first fermented to Farnesene and then hydrogenated to Farnesane. Farnesane has similar chemical and physical properties to diesel fuel, as far as its viscosity and density are concerned. Its higher Lower Heating Value (LHV) and cetane number mean that the biofuel has better combustion properties, and the lack of aromatics and sulfur could contribute to a decrease in smoke and particulate matter emissions. Tests were carried out on a small displacement Euro5 automotive diesel engine for passenger car applications. The impact that the Farnesane blend could have on engine performance was first evaluated at full load. The effects of the use of the Farnesane blend on engine emissions and fuel consumption were then evaluated at seven different part load operating points, considered representative of the New European Driving Cycle. Other experimental investigations have been carried out to fully exploit the benefits that could be obtained by adjusting the Exhaust Gas Recirculation (EGR) rates in order to take into account the different Soot–NOx and CO–NOx biofuel blend trade-offs. When the engine was fueled with the Farnesane blend in diesel at full load operating conditions, without any modifications of the ECU calibration, brake torque output levels that were comparable with the reference diesel could be observed over almost the entire speed range. At part load operating conditions, which are representative of the New European Driving Cycle, no significant variations in fuel consumption were found on a mass basis, for the same fuel conversion efficiency and CO2 emissions for the Farnesane blend compared to the diesel. The specific CO and HC emissions were reduced significantly for the biofuel blend at low and medium loads, while only modest or even insignificant variations were registered at higher loads. The NOx emissions with the biofuel blend were generally comparable with those of the reference diesel fuel, while a noticeable reduction in smoke level was generally observed for medium and high load operating conditions. Finally, the Soot–NOx and CO–NOx trade-off, obtained from EGR sweeps, has highlighted the possibility of obtaining some further emission benefits through a better exploitation of the biofuel characteristics by means of a more extensive ECU recalibration.

In order to obtain 85% recycling, several procedures on Automotive Shredder Residue (ASR) could be implemented, such as advanced metal and polymer recovery, mechanical recycling, pyrolysis, the direct use of ASR in the cement industry, and/or the direct use of ASR as a secondary raw material. However, many of these recovery options appear to be limited, due to the possible low acceptability of ASR based products on the market. The recovery of bottom ash and slag after an ASR thermal treatment is an option that is not usually considered in most countries (e.g. Italy) due to the excessive amount of contaminants, especially metals. The purpose of this paper is to provide information on the characteristics of ASR and its full-scale incineration residues. Experiments have been carried out, in two different experimental campaigns, in a full-scale tyre incineration plant specifically modified to treat ASR waste. Detailed analysis of ASR samples and combustion residues were carried out and compared with literature data. On the basis of the analytical results, the slag and bottom ash from the combustion process have been classified as non-hazardous wastes, according to the EU waste acceptance criteria (WAC), and therefore after further tests could be used in future in the construction industry. It has also been concluded that ASR bottom ash (EWC - European Waste Catalogue - code 19 01 12) could be landfilled in SNRHW (stabilized non-reactive hazardous waste) cells or used as raw material for road construction, with or without further treatment for the removal of heavy metals. In the case of fly ash from boiler or Air Pollution Control (APC) residues, it has been found that the Cd, Pb and Zn concentrations exceeded regulatory leaching test limits therefore their removal, or a stabilization process, would be essential prior to landfilling the use of these residues as construction material.

Recently, we have introduced a new bioeconomic indicator in order to avoid the difficulties in evaluating the process and technologies for sustainability. In this paper, we wish to improve this new indicator for the analysis of sustainability. Indeed, the indicator has been based on the exergy analysis of dissipation and irreversibility, and it was proven in some social and technical application. In this work, a more general definition has been introduced in order to use it in any evaluation of sustainability. In particular, it has been applied to improve the biofuel production obtained by microorganisms, starting from the biophysical behaviour of the microorganisms themselves. Indeed, in industrialised countries, the management of CO2emissions represents one of the present compelling issues. In this context, the improvement of the energy efficiency, and its rational use, can be considered a fundamental economic strategy for the sustainable development of the industrialised countries. Our indicator takes into account all these requests for the development and sustainability, resulting a very interesting thermoeconomic quantity to be used by decision makers. Moreover, it is used to prove that mutualism can represent a new approach for the optimisation of biofuels production.