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Large-scale energy storage plants based on power-to-gas-to-power technologies incorporating high temperature electrolysis, catalytic methanation of H₂ and CO₂ and novel, highly efficient methane-fired Allam reconversion cycles allow for a confined and circular use of CO₂ and thus an emission-free storage of intermittent renewable energy. The Allam power cycle is considered as a beneficial power plant concept, which employs supercritical CO₂ as working fluid as well as an oxy-combustion process to reach high efficiencies of up to 66%. The combination of said process chain could reach a maximum roundtrip efficiency of 54.2 % assuming the presence of sufficient storage capacities for all relevant technical gases. In a technically feasible scenario, paired with a separate air separation unit instead of stationary O₂ storages, roundtrip efficiencies of 49.0 % were determined.. The implementation of said energy storage systems into existing national energy systems will pose a major challenge, since they will require far-reaching infrastructural changes to the respective systems itself, such as extensive installations of renewable generation and electrolysis capacities as well as sufficient subsurface storage capacities for both CO₂ and CH₂. Furthermore, an exemplary energy system forecast for Germany for the year of 2050 is presented to show the viability of the energy storage concept. In case of a fully circular use of CO₂, when electricity is solely generated by renewable energy sources (RES), 736 GW of RES, 234 GW of electrolysis and 62 GW of gas-to-power capacities are required. The total storage volume on the national scale of Germany for both CO₂ and CH₄ was determined to be 7.8 billion Nm³, respectively, leading to a CH₄ storage capacity of 54.5 TWh. The present investigation illustrates the feasibility of large-scale energy storage systems for renewable electricity based on high temperature electrolysis, catalytic methanation and Allam power cycles paired with lar

In aerobic wastewater treatment, aeration is the most critical element of the treatment system. It supplies microorganisms with the required amount of dissolved oxygen, maintains solids in suspension and controls membrane fouling, where needed. However, conventional activated sludge, where air is used, is limited to low-strength wastewaters as higher loadings or more intense feeds require both higher biomass and dissolved oxygen concentrations. In membrane bioreactors, despite being able to operate at higher biomass concentrations, their operation at high biomass concentrations and high organic loadings has not been tested. By replacing air with pure oxygen, oxygen transfer rates increase at lower flowrates. In this work, the potential and limitations of pure oxygen systems over conventional ones are reviewed. Also, the effect of the operational parameters or the mixed liquor characteristics on oxygen transfer is determined. Pure oxygen affects bacterial structure, controls foam formation, improves bacterial enzymatic activity and, in membrane bioreactors, leads to a better recovery of permeability after cleanings. It treats much higher loadings without compromising final effluent quality. Fine bubbles are more efficient in oxygen transfer due to their increased contact area. Nevertheless, pure oxygen aeration at times is not essential or it may generate effluent organic matter of a higher refractory character. We then recommend that it be used to applications where conventional aeration is not adequate.

Ammonia is one of the most highly produced chemicals in the world, being the source of all nitrogen-based fertilizers. Its conventional production relies on fossil fuels reforming as its source of hydrogen, cryogenic air separation for nitrogen, and the Haber-Bosch process for the ammonia synthesis itself. This route has made ammonia production responsible for the consumption of 1% of all energy worldwide, and for the emissions of 298 Mt CO2 eq./year. In a future where most energy comes from fluctuating sources, such as the one envisioned in the Energiewende, energy intensive industries like ammonia production would need to adapt its operation to mimic that of energy generation. A potential alternative for ammonia production is to obtain hydrogen and nitrogen from water electrolysis, and pressure swing adsorption (PSA) respectively. In our effort for the flexibilization of the chemical industry, we have designed a small ammonia production plant using these technologies. With it we intend to cover the fertilizing needs of a large German farm (1,000 ha), requiring a minimum production of 100 t NH3/year. As a first step, we purchased the electricity used for the water electrolyzer in the day-ahead market. The rest of the plant relied on a steady industrial supply. Our first results indicated the plant was not profitable. The main reason behind this are the capital investment in the intermediate hydrogen storage unit

This chapter evaluates the economic and environmental implications of MBR using Cost Benefit Analysis (CBA) and Life Cycle Assessment (LCA). A brief introduction to these methodologies and the main developments and achievements when applied to MBR is given before the presentation of two case studies. In the first case study, CBA and LCA were applied for the assessment of seven wastewater treatment plants using MBR and other membrane technologies. The results highlighted the benefits of removal of substances responsible for eutrophication and the relevance of the scale factor regarding electricity use, one of the main environmental and economic costs. In the second case study, LCA alone was applied for the environmental assessment of four novel MBR configurations at pilot-plant scale focusing on the removal of pharmaceutical and personal care products (PPCPs), of which only hormones were found to be relevant in terms of toxicity terms due to their higher concentrations in the influent.

Life Cycle Assessment is a methodology for the evaluation of potential hazards to the environment and to human health. It can be used for decision support when selecting materials for a product. It is a detailed method that can become very labor intensive. As alternatives, we introduce here two methodologies for ranking products and materials according to their safety: Both methods are built on two pieces of European legislation. Hazard Traffic Lights is a qualitative visual way to quickly identify potential hazards. Total Hazard Points is a quantitative method for weighting the different hazards related to a product. It is based on the method developed for the German Environmental Agency (UBA), but its scope includes all materials and hazards, rather than a selection of them. As a case study, we evaluated the 9 batteries described in the UBA study and compared our results with those presented there. In our opinion, batteries are in general terms more hazardous in the UBA study. This is due to more thorough identification of hazards –including some potentially more significant – and the inclusion of all the potential hazards of a material. Since not all the materials present in the battery were quantified, both sets of results should be considered an underestimation of the possible hazard.

Batteries using chloride ions as shuttles have only been under investigation for a few years, but already several publications have dealt with this topic. In this review, we extensively report for the first time the state of the art, along with theoretical screening and calculations and an analysis of safety and toxicity. At the end, possible future approaches are evaluated.