• Energy Research

This article examines the potential benefits of using Data Envelopment Analysis (DEA) for conducting energy-efficiency assessment of wastewater treatment plants (WWTPs). WWTPs are characteristically heterogeneous (in size, technology, climate, function …) which limits the correct application of DEA. This paper proposes and describes the Robust Energy Efficiency DEA (REED) in its various stages, a systematic state-of-the-art methodology aimed at including exogenous variables in nonparametric frontier models and especially designed for WWTP operation. In particular, the methodology systematizes the modelling process by presenting an integrated framework for selecting the correct variables and appropriate models, possibly tackling the effect of exogenous factors. As a result, the application of REED improves the quality of the efficiency estimates and hence the significance of benchmarking. For the reader's convenience, this article is presented as a step-by-step guideline to guide the user in the determination of WWTPs energy efficiency from beginning to end. The application and benefits of the developed methodology are demonstrated by a case study related to the comparison of the energy efficiency of a set of 399 WWTPs operating in different countries and under heterogeneous environmental conditions.

Abstract Thailand as one of the global food exporting countries shares the worldwide concerns on climate change and initiated carbon footprinting and labeling in 2008. Individual quick frozen fried chicken meat and canned tuna in sunflower oil were selected as the pioneering case studies for carbon footprinting using the PAS 2050:2008 standard. It was revealed that broiler farm and tuna fisheries are the key stages contributing significantly to the total carbon footprint of the two products considered. The study also revealed the need for using representative data of raw materials according to the local context requiring the urgent development of agricultural and food databases. The rules of using substitute data must also be clearly defined. The industry argued for using a mass instead of the economic basis required by PAS 2050:2008 in allocating the carbon footprint to chicken parts and tuna white and red meat. The commitment of producers to reduce the size of carbon footprint is suggested to be emphasized for carbon labeling rather than displaying a carbon footprint value to avoid the comparison between products. Product Category Rules (PCRs) should be developed with stakeholder consultations and harmonized at the global scale.

Given the increasing importance of the wastewater sector in terms of energy usage, the understanding of the level of energy efficiency of wastewater treatment plants (WWTPs) is useful to both the industry itself as well as policy makers. Here, based on economic foundations, we apply a Stochastic Frontier Analysis (SFA) approach for energy demand modelling to estimate energy efficiency in the wastewater sector. Using specific SFA models and panel data from 183 Swiss WWTPs over the period 2001 to 2015, the paper illustrates that distinguishing between persistent and transient inefficiency is essential to deduce appropriate energy efficiency diagnosis in WWTPs. In this respect, persistent energy inefficiency is found to be more severe than transient energy inefficiency. Furthermore, it is shown that the age of the equipment influences the demand for energy and the energy savings due to technological innovation are quantified. Finally, economies of output density and scale are estimated demonstrating that for plants operating below optimal scale significant energy savings can be achieved if plants would be operated at higher size. Moreover, our analysis reveals also that for plants larger than 100,000 Population Equivalent, at least from an energy efficiency point of view, it would be no more beneficial to increase their scale.

Purpose Biofuels have received special research interest, driven by concerns over high fuel prices, security of energy supplies, global climate change as well as the search of opportunities for rural economic development. This work examines the production of biodiesel derived from the transesterification of crude rapeseed oil, one of the most important sources of biodiesel in Europe, paying special attention to the environmental profile-associated to the manufacture life cycle (i.e., cradle-to-gate perspective).

Milk, an example of staple food, has an outstanding demand by consumers as it is considered a prescription for good health. Life cycle assessment (LCA) is an excellent tool of environmental management and it provides a widespread knowledge on the environmental burdens associated to a product or to a human activity. In this study, a simplified methodology of LCA has been applied to analyse a representative scheme of milk production in Galicia (Spain), where a reliable inventory is still lacking. High quality data for the inventory was obtained in different representative fodder factories, farms and dairies for time periods over two years. The analysis of these data by LCA has permitted to quantify the potential impact associated to milk production and also to determine the reductions attained by the application of different improvement actions, such as the most adequate formulation of cattle feed and the implementation of treatment systems for water and air emissions. The consideration of these actions can lead to a maximum reduction of almost 22% of the global normalised impact.

Many studies have shown the effectiveness of pretreatments prior to anaerobic digestion of solid wastes, but to our knowledge, none analyzes their environmental consequences/costs. In this work, seven different pretreatments applied to two types of waste (kitchen waste and sewage sludge) have been environmentally evaluated by using life cycle assessment (LCA) methodology. The results show that the environmental burdens associated to the application of pretreatments prior to anaerobic digestion cannot be excluded. Among the options tested, the pressurize-depressurize and chemical (acid or alkaline) pretreatments could be recommended on the basis of their beneficial net environmental performance, while thermal and ozonation alternatives require energy efficiency optimization to reduce their environmental burdens. Reconciling operational, economic and environmental aspects in a holistic approach for the selection of the most sustainable option, mechanical (e.g., pressurize-depressurize) and chemical methods appear to be the most appropriate alternatives at this stage.

Galicia is an Autonomous Community located in the north-west of Spain. As a starting point to implement mitigation and adaptation measures to climate change, a regional greenhouse gas (GHG) inventory is needed. So far, the only regional GHG inventories available are limited to the territorial emissions of those production activities which are expected to cause major environmental degradation. An alternative approach has been followed here to quantify all the on-site (direct) and embodied (indirect) GHG emissions related to all Galician production and consumption activities. The carbon footprint (CF) was calculated following the territorial life cycle assessment (LCA) methodology for data collection, that combines bottom-up and top-down approaches. The most up-to-date statistical data and life cycle inventories available were used to compute all GHG emissions. This case study represents a leap of scale when compared to existing studies, thus addressing the issue of double counting, which arises when considering all the production activities of a large region. The CF of the consumption activities in Galicia is 17.8 ktCO2e/year, with 88% allocated to Galician inhabitants and 12% to tourist consumption. The proposed methodology also identifies the main important contributors to GHG emissions and shows where regional reduction efforts should be made. The major contributor to the CF of inhabitants is housing (32%), followed by food consumption (29%). Within the CF of tourist consumption, the share of transport is highest (59%), followed by housing (26%). The CF of Galician production reaches 34.9 MtCO2e/y, and its major contributor is electricity production (21%), followed by food manufacturing (19%). Our results have been compared to those reported for other regions, actions aimed at reducing GHG emissions have been proposed, and data gaps and limitations identified.

Sewage sludge handling is becoming a concern in Europe due to its increasing amount and the presence of contaminants, such as heavy metals and pharmaceutical and personal care products (PPCPs). Currently, over 70% of sludge in Europe is treated thermally by incineration or used as fertilizer in agriculture. New thermochemical methods are under development and are expected to be implemented in the near future. This paper considers the life cycle environmental impacts of the following five alternatives for sludge handling, taking into account the presence of heavy metals and PPCPs: i) agricultural application of anaerobically digested sludge; ii) agricultural application of composted sludge; iii) incineration; iv) pyrolysis; and v) wet air oxidation. The results suggest that anaerobic digestion with recovery of nutrients and electricity has the lowest environmental impacts in 11 out of 18 categories considered. For the mean to maximum resource recovery, composting is the worst alternative, followed by pyrolysis with lower recovery rates. Agricultural application of anaerobically digested sludge has the highest freshwater ecotoxicity due to heavy metals, unless their concentration is in the lowest range, as found in some European sewage sludge applied on land. Therefore, stricter control of heavy metals in the sludge is needed for this option to limit freshwater ecotoxicity to the levels comparable with the thermal processes. The results also indicate that PPCPs have a negligible contribution to freshwater ecotoxicity when compared to heavy metals in the anaerobically digested sludge. Since thermal processes are currently drawing attention due to their potential benefits, the findings of this work suggest that their adoption is environmentally beneficial only if high resource recovery rates can be achieved.