The last 60 years has seen unprecedented groundwater extraction and overdraft as well as development of new technologies for water treatment that together drive the advance in intentional groundwater replenishment known as managed aquifer recharge (MAR). This paper is the first known attempt to quantify the volume of MAR at global scale, and to illustrate the advancement of all the major types of MAR and relate these to research and regulatory advancements. Faced with changing climate and rising intensity of climate extremes, MAR is an increasingly important water management strategy, alongside demand management, to maintain, enhance and secure stressed groundwater systems and to protect and improve water quality. During this time, scientific research—on hydraulic design of facilities, tracer studies, managing clogging, recovery efficiency and water quality changes in aquifers—has underpinned practical improvements in MAR and has had broader benefits in hydrogeology. Recharge wells have greatly accelerated recharge, particularly in urban areas and for mine water management. In recent years, research into governance, operating practices, reliability, economics, risk assessment and public acceptance of MAR has been undertaken. Since the 1960s, implementation of MAR has accelerated at a rate of 5%/year, but is not keeping pace with increasing groundwater extraction. Currently, MAR has reached an estimated 10 km3/year, ~2.4% of groundwater extraction in countries reporting MAR (or ~1.0% of global groundwater extraction). MAR is likely to exceed 10% of global extraction, based on experience where MAR is more advanced, to sustain quantity, reliability and quality of water supplies.@en

This paper addresses the uncertainty and variability in techno-economic studies of carbon capture technologies, based on a detailed comparison of the results of different studies on postcombustion CO₂ capture with advanced amines, and on an in-depth uncertainty analysis using a combination of sensitivity and pedigree analyses. The results show that despite efforts to harmonize capital cost estimates, the capital cost results of the same PCC carbon capture systems can still show large (65%) differences. This uncertainty may simply be inherent to early stage cost estimates. Amongst the most important causes for the variability shown in this work are differences in equipment sizing methods and purchased equipment cost estimates. This capital cost variability only mildly propagates into the Levelised Cost of Electricity and Cost of CO₂ Avoided, more so in case of low power plant utilisation scenarios. To enhance insight into these uncertainties and enable their communication, the paper argues to use in-depth uncertainty evaluation for early stage techno-economic studies. It suggests to complement current practice of sensitivity analysis with pedigree analysis and to combine the results of both analyses in diagnostic diagrams. This may lead to more informed interpretation of the results of techno-economic studies, and helps focus techno-economic research efforts towards the parameters that most influence final performance indicators.

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Aqueous amino acid salt solutions that precipitate due to CO2 absorption are a relatively novel and promising class of solvents. Although the presence of solids in the process stream requires adequate measures related to slurry handling and crystallization control, precipitation also increases the solvent CO2 capacity and the energy performance of the stripper. By using an additional solid–liquid separation step to concentrate the slurry before it is sent to the stripper, known as the DECAB+ process, the energy performance can be further improved. Most of the current experimental work on these systems focuses on the amino acids taurine, α- and β-alanine, sarcosine, glycine, and proline, neutralized with equimolar amounts of potassium hydroxide. Investigated properties include the CO2 concentration at which precipitation is first observed, which is closely related to the solubility of the amino acid, the composition of the precipitate, and the CO2 absorption rate. The precipitate typically contains pure amino acids and/or bicarbonate, depending on the amino acid solubility. Shortcut process simulations have been used to estimate the energy performance of absorption processes using precipitating amino acids, so far focusing on 4M KOH + taurine (K-tau) and 4M KOH + α-alanine (K-α-ala) solutions. Specific regeneration duties below 2 GJ/ton CO2 seem possible for the DECAB+ process when using K-α-ala and lean vapor compressor (LVC). Compared to a conventional process using 30 wt % monoethanolamine and LVC, this corresponds to a reduction of 35% in the regeneration duty. Future research should focus on more-detailed process simulations, based on a predictive thermodynamic model that consistently describes the vapor–liquid–solid equilibria of the system. Demonstration of the DECAB+ process on a pilot scale is also highly recommended, with a special focus on the crystallization and slurry handling process steps and units@en