Environmental science

Summary

Environmental science is an interdisciplinary academic field that integrates physics, biology, and geography (including ecology, chemistry, plant science, zoology, mineralogy, oceanography, limnology, soil science, geology and physical geography, and atmospheric science) to the study of the environment, and the solution of environmental problems. Environmental science emerged from the fields of natural history and medicine during the Enlightenment. Today it provides an integrated, quantitative, and interdisciplinary approach to the study of environmental systems. Environmental studies incorporates more of the social sciences for understanding human relationships, perceptions and policies towards the environment. Environmental engineering focuses on design and technology for improving environmental quality in every aspect. Environmental scientists seek to understand the earth's physical, chemical, biological, and geological processes, and to use that knowledge to understand how issues such as alternative energy systems, pollution control and mitigation, natural resource management, and the effects of global warming and climate change influence and affect the natural systems and processes of earth. Environmental issues almost always include an interaction of physical, chemical, and biological processes. Environmental scientists bring a systems approach to the analysis of environmental problems. Key elements of an effective environmental scientist include the ability to relate space, and time relationships as well as quantitative analysis. Environmental science came alive as a substantive, active field of scientific investigation in the 1960s and 1970s driven by (a) the need for a multi-disciplinary approach to analyze complex environmental problems, (b) the arrival of substantive environmental laws requiring specific environmental protocols of investigation and (c) the growing public awareness of a need for action in addressing environmental problems.

Reducing Greenhouse Gas emissions is not the only solution

Justine Brun

With the increasing strength and frequency of climate change events, the urgency to mitigate climate change impact is ever so important. Canada reported his Nationally Determined Contribution (NDC) and submitted its ambition to reduce his Greenhouse Gas (GHG) emissions by 40-45% by 2030 compared to 2005 and reach net-zero emissions by 2050. Interest for energy system modelling has been increasing for planning future energy systems, as a result of growing concern for sustainable development and transition towards renewable energies. Nevertheless, planning a decarbonization of energy system can potentially lead to environmental burden shifting, and can increase impacts on other environmental impacts such as ecosystem quality or human health. Thus, this project aims towards integrating Life Cycle Analysis (LCA) and more specifically Life Cycle Impact Assessment (LCIA) within Energy Systems Modelling, in order to minimize not only climate change impacts, but human health and ecosystem quality. In addition, a dual spatial resolution was integrated in the model in order to increase data precision and computational efficiency. The results show that a low-carbon energy system, based on the optimization of GHG emissions allows to greatly reduce all the environmental impacts under analysis, compared to an all economic- based energy system, but a multi-objective optimization allows to simultaneously reduce impacts on ecosystem quality and human health, while reducing GHG emissions and keeping good economical and technical performances. The results also show that it is theoretically possible for Canada to keep on track with their emission reduction ambition by 2030, by deploying more renewable energies. This project does not allow assessing Canada’s potential to reach net-zero emissions, as environmental impacts from carbon capture technologies are still to be characterized and integrated in the model.

2022

Micropollutants (MP) such as residues of pharmaceuticals, industrial chemicals or pesticides can be detected in almost all water resources. Various processes can be used to abate them in drinking water treatment, e.g., ozonation, advanced oxidation processes (AOP), adsorption on activated carbon or membrane filtration. The selection of a suitable process combination is a complex task for water suppliers.This thesis compares two process chains in the context of a multi-barrier system including managed aquifer recharge (MAR). To protect soils and aquifers from MP in the future, an additional barrier against MP upstream of the MAR was investigated: (1) a full-stream treatment using the AOP UV/H2O2, and (2) a side-stream treatment with low-pressure reverse osmosis (LPRO) or nanofiltration (NF) and ozonation of the retentate to treat the concentrated MPs.Pilot-scale experiments were conducted to determine the relative abatements of MP by UV/H2O2 treatment and by a subsequent soil column treatment. Compared to a soil column fed with water without UV/H2O2 pretreatment, the performance of the combined process (UV/H2O2 + soil column) was more efficient. However, this could be explained by an additive effect of the individual processes.Relative abatements in the UV/H2O2 process are mainly based on the introduced UV fluence and hydroxyl radical exposure. These parameters could be calculated with a model based on the measured relative abatements of two MPs (probe compounds) and their kinetic data (second-order rate constants for the reactions with hydroxyl radical, absorbance and quantum yield).With this information, the relative abatements of other MPs could be predicted with an accuracy of ±20%. A sensitivity analysis of the model showed that the relative abatements of the selected probe compounds should be >50%. In this case, the accuracy of the calculated parameters depends mainly on the precision of the kinetic data.In the case of membrane-based treatment of water by LPRO or NF, a concentrate is produced. Ozonation to treat MP in the concentrate is accompanied by a formation of the possibly carcinogenic bromate by oxidation of bromide. To achieve the highest possible MP abatement with simultaneously low bromate formation, both membrane selection and subsequent concentrate ozonation were investigated. In laboratory tests with standardized concentrates, neither the water source nor the membrane type caused a change in bromate yield for similar relative MP abatements. However, NF membranes have lower relative retentions of bromide and MP than LPRO membranes, making NF concentrates more suitable for ozonation with limited bromate formation.A comparison of UV/H2O2 with membrane treatment showed that full-stream treatment with UV/H2O2 has about four times lower costs and an about five times lower environmental impact. In addition it achieves significantly higher disinfection. In contrast, side-stream treatment with LPRO causes up to two times lower impacts for the environment when the electrical energy source is wind or hydropower. This study thus contributes technical, economic, and environmental aspects to a holistic evaluation of the two process options.

EPFL2022

Biogas-based power-to-X technology allows storing renewable electricity, while producing CO2-neutral products.This work investigates the conversion and upgrading of digestion-derived gas mixtures with focus on increasing the operational flexibility of the overall process. Compensation of fluctuations in the feed gases enable a better economic predictability of the processes and increase the product gas output.A techno-economic evaluation was performed on bubbling fluidised bed (BFB) methanation and biological methanation for CO2 conversion in all-year operation. Each considered process was modelled and optimised to obtain grid-ready biomethane. Rate-based models were used for the main units (BFB reactor, H2-separation membrane). For the biological methanation, simulated performance data from literature were included. The analysis revealed a 17 - 19% lower production cost for BFB methanation, mainly due to lower investment cost for the main reactor vessel. Instead of using PEM electrolysis, high temperature electrolysis (SOE) would allow for heat integration with the BFB reactor, which increases the plant efficiency from 54% to 73% (LHV). A further production cost reduction can be achieved by direct methanation of biogas, omitting prior separation of CO2.Based on gas separation experiments with a commercial biogas upgrading module (Evonik Sepuran) performed in a TRL 5 plant, a flexible upgrading concept using a permeation model was developed. It allows to swiftly switch between conventional membrane-based CO2 separation by a 2-stage membrane unit and direct methanation of biogas and subsequent H2 recycling.A techno-economic analysis was performed on the flexible upgrading concept. The operation hours of the electrolyser were determined by applying a threshold to the electricity price distribution of the past years. The sensitivity on electricity cost (i.e. PtG operation hours) is clearly reduced with the flexible processes, resulting in a better economic predictability of the overall process, compared to a pure PtG installation. System analysis shows the need to allow part load operation of the methanation.Symmetric part load operation (reduced availability of CO2 and H2) was tested in a field experiment by direct methanation of biogas with subsequent H2 recycling in the TRL 5 methanation pilot plant. Stable operation of the methanation plant could be achieved at part load levels from 45% to 100% with closed recycle loop. The BFB reactor alone was tested in a load range of 20 to 100%. A dynamic experiment demonstrated fast, successive load changes while still producing grid-ready biomethane.Asymmetric part load (only H2 limiting) operation was investigated by process simulations and field experiments. Since CO2 is present in the system in an over-stoichiometric amount, H2 recycle and CO2 separation have to be performed simultaneously. Process simulations showed that selecting a most ideal PtG configuration based on technical feasibility is difficult, as further constraints, such as overall economics and operation scheduling have to be considered in process design and evaluation. In all cases, the CO2 separation from the integrated processes leads to a loss of H2 and CH4 from the process. The introduction of an additional membrane stage with a sweep stream is proposed to reduce the loss of reactive gases via the off gas stream.

EPFL2022