• Energy Research

Abstract This study presents an integrated feasibility analysis approach to reduce the carbon footprint in the largest Italian wastewater treatment plant (WWTP). Firstly, a model-based feasibility analysis was carried out to assess the applicability of upgrading scenarios, for an ongoing anaerobic sludge digestion process. Application of dynamic sludge thickener, as well as hybrid thermo-alkali pre-treatment of waste activated sludge, were assessed to enhance the biogas production in the WWTP. Further, an implementation of the selective membranes was proposed and studied to upgrade the produced biogas in sludge treatment units to biomethane with an average efficiency of 98.6%. Model-based sludge pre-treatment and biogas upgrading strategies were developed and evaluated in terms of mass, energy, and greenhouse gas emission balance. The obtained results prove that practicing the proposed upgrading scenario can lead to an 18% improvement in biogas production and a significant reduction of thermal energy auto-consumption and total greenhouse gas emissions. In the second phase, the laboratory-based feasibility analysis was performed about the integration of microalgae technology into the current process of the WWTP. A planar photobioreactor was built to estimate the volumetric mass transfer coefficient (KLa) and CO2 consumption of the reactor. By the use of 44 and 76 μmol/m2/s light intensities, the results show 80% and 70% reductions in total CO2, respectively. The tested configuration guaranteed 11.763 and 27.943 mg/l/h CO2 consumptions, as well as 0.5775 h−1 and 17.7 h−1 KLa values. Overall, the results prove that applications of the technologies proposed in this study can significantly reduce the carbon footprint of the WWTP.

Nowadays, when the energy, industry and transport sectors are adapting to climate change and need to reduce their environmental impact, it is vital that the optimal solutions are found for individual countries and their different circumstances. Territories, which have a hydrocarbon deficit, should use non-conventional energy sources while the countries with substantial resources of hydrocarbons should be focused on the strategy of raising the energy efficiency, i.e. to reduce the specific consumption of fuel consumed. The paper discusses these scenarios and describes some innovative technologies for both cases. Energy production from biomass is encouraged in some European countries by the granting of generous economic subsidies so that renewable energy plants, such as anaerobic digestion plants that produce biogas for use in internal combustion engines, in particular, are receiving much funding. An alternative technology for biogas valorisation could be that of biomethane (so called green gas) production through biogas purification and upgrading processes to remove CO2, H2S and water vapour. Different technologies have been proposed to remove CO2 from gas streams, such as physical absorption, absorption by chemical solvents, cryogenic and membrane separation and CO2 fixation by chemical or biological methods. Production of biomethane and its introduction into the natural gas grid or its use as a fuel for vehicles could increase the energy efficiency and reduce specific emissions (combined cycle gas turbines, district heating of CHP units, methane powered vehicles). A simple and low-cost method of improving energy efficiency and environmental safety of transport by introducing into hydrocarbon fuels micro doses of a universal multifunctional additive is proposed. The method will make a significant contribution towards solving the problems of adapting to global climate change and improving the environment. It is capable of reducing specific fuel consumption by up to 12% and the requirements for a gasoline octane number by 10 points. It significantly reduces emission levels of greenhouse gases and toxic substances and provides complex improvement of the properties of fuels and the condition of engines.

Waste-to-energy (WtE) technologies can offer sustainable solutions for waste that cannot be further reused or recycled, such as the part of municipal solid waste (MSW) that is not suitable for recycling processes. The two main (most widely used) thermal treatment technologies that can be applied to MSW are direct combustion in an incineration plant and gasification. This paper examines in particular the direct combustion in incineration plants, explaining the main process, the main technologies applied, and the resulting environmental aspects. Moreover, this work focuses on analyzing flue gas emissions from thermal treatment in order to better understand the impacts of these kinds of processes. A particular focus on the CO2 parameter is performed. CO2 is a persistent atmospheric gas, and it is one of the greenhouse gases (GHGs) potentially responsible for the climate change phenomenon. In this sense, specific indexes (tCO2/tMSW and tCO2/MWh) are elaborated considering the thermal treatment plants present in six Italian regions. The main aim of this review paper is to try to fill the gap that still exists regarding the emissions environmental compatibility coming from these type of plants, the evaluation of the amount of CO2 emitted, and the possible reduction of the CO2 parameter. One of the main outcome obtained is in fact the evaluation of the amount of CO2 coming from these kinds of plants and some indications about the technological possibilities of reducing this amount.

Domestic hot water heat pumps (DHW HPs) have spread fast in recent years in Europe and they now represent an interesting opportunity for implementing renewable energy sources in buildings with a centralized/district heating system, where DWH is generally produced by a gas boiler or an electric water heater. Replacing these appliances has several environmental benefits, including the removal of air pollution sources and the reduction of Green House Gasses (GHG) emissions. In this work, we present the techno-economic and environmental evaluation of implementing DHW HPs in Turin, where 66% of the DHW demand is covered by dedicated gas boilers. The impact of such boilers was assessed through numerical air dispersion modeling conducted with the software SPRAY (Aria Technologies, Paris, French). Results show that removing these sources would reduce yearly average concentrations of NOx up to 1.4 µg/m3, i.e., about 1% of monitored concentrations of NOx, with a benefit of 1.05 ÷ 15.15 M€/y of avoided health externalities. Replacing boilers with DHW HPs is always financially feasible with current incentives while, in their absence, it would be convenient for residential units with 3 cohabitants or more (51.22% of the total population), thanks to scale economies.

While the demand for energy in Italy continues to increase, the European Union Directive 2009/28/EC has set a goal of obtaining 20 % of all energy from renewable sources by 2020. It is required both for efficient energy utilization and the development of renewable energy plants, including biomass. In this context, we consider the use of residues from forest maintenance, residues from livestock, the use of energy crops, the recovery of food waste, and the residuals from agro-industrial activities. At the same time, it is necessary to consider the consequent environmental impact. In this study, we applied these considerations to two specific areas in Italy, with different characteristics using the tool of environmental balance. This approach presents a substantial innovation for performing a quantitative analysis of the environmental impact. The specific-considered cases can also indicate a general methodology, useful for energy production compatibility planning.

Abstract Energy consumption represents a significant part of the operative costs of a wastewater treatment plant but, with a correct design and a careful management model, there are important possibilities for its limitation. The proposed research presents a multi-step methodology for the evaluation of the energetic aspects of wastewater treatment, which was implemented on the largest facility in Italy (2.7 M population equivalents as organic load), managed by Societa Metropolitana Acque Torino (SMAT). The study initially took into account each phase of the process scheme, in order to obtain specific electricity consumption values for all the electro-mechanic devices. Data from tele-control system and direct measurements in field have both been acquired. The total electric energy demand of the plant was evaluated (66.78 GW h/y, about 50% from aeration in oxidation tanks). In account of large contribution the energy efficiency of the blowers was verified with positive results. Four specific energy consumption indexes were considered to carry out a critical analysis of SMAT wastewater treatment plant with other facilities performing biological oxidation processes and of a different order of magnitude about design capacity, and congruent values were obtained. The considered indexes related the electric energy demand to the equivalent population, to the volume of treated water and to the amount of removed COD and total Nitrogen. Furthermore the thermal energy demand of the plant was estimated (49.15 GW h/y, more than 93% from sludge line). An energy balance for the whole plant was finally evaluated, and some energy optimization solutions to decrease the corresponding costs were suggested.

With the need of limiting pollutants emissions, careful management of energy plants should be considered to reduce the footprint that can be caused by these systems. Advantages of district heating (DH) systems have been linked to a decrease in local and global emissions, centralized heat production located outside urban centres, possible utilization of renewable heat sources. District heating, consisting of the distribution of hot water by means of underground networks for the buildings’ heating and sanitary water, is an ever-expanding technology that allows the optimization of energy resources, with positive consequences in terms of both economic savings and environmental impacts. The aim of this work is to analyse the district heating system from an environmental point of view, in way to realize a general procedure of evaluation. To this end, the Italian city of Turin is taken as case study. Turin has long been subject to high concentration levels of pollutants, especially NOx and particulate. The environmental compatibility of extending the district heating network is evaluated. Two different tools are used: first, the environmental balance is defined to perform an evaluation of the flux modification at the emission sources; secondly, the atmospheric impacts of emissions are estimated using CALPUFF dispersion model. The results show a future reduction in overall NOx emission, as well as a reduction of ground level average NOx concentration ranging between 0.2 and 4 μg/m3. This study provides important information on the effects of a change of the energy configuration on air quality in an urban area. The proposed comprehensive methodology is applicable for other similar cases.

The goal of making the urban environment safer amid increasing human impact adds to the importance of district heating management. The article outlines the results of a study into the problem of improving the urban environment by implementing two innovative solutions. Technological innovations imply the introduction of modern sustainable tools of reducing emissions in district heating networks, one of them being the combination of district heating and combined heat and power plants (a case study of Turin). Organizational innovations are built upon the management of demand for thermal energy that makes it possible to reduce investment in new construction and to optimize the architecture of heat load schedules for the purpose of alleviating energy and environmental pressure on the city. The authors propose formats and areas of demand side management for thermal energy and methods of offering economic incentives to program participants.