The Maunder minimum (1645-1715) was indeed a grand minimum: a reassessment of multiple datasets

Aims. Although the time of the Maunder minimum (1645–1715) is widely known as a period of extremely low solar activity, it is still being debated whether solar activity during that period might have been moderate or even higher than the current solar cycle (number 24). We have revisited all existing evidence and datasets, both direct and indirect, to assess the level of solar activity during the Maunder minimum. Methods. We discuss the East Asian naked-eye sunspot observations, the telescopic solar observations, the fraction of sunspot active days, the latitudinal extent of sunspot positions, auroral sightings at high latitudes, cosmogenic radionuclide data as well as solar eclipse observations for that period. We also consider peculiar features of the Sun (very strong hemispheric asymmetry of the sunspot location, unusual differential rotation and the lack of the K-corona) that imply a special mode of solar activity during the Maunder minimum. Results. The level of solar activity during the Maunder minimum is reassessed on the basis of all available datasets. Conclusions. We conclude that solar activity was indeed at an exceptionally low level during the Maunder minimum. Although the exact level is still unclear, it was definitely lower than during the Dalton minimum of around 1800 and significantly below that of the current solar cycle #24. Claims of a moderate-to-high level of solar activity during the Maunder minimum are rejected with a high confidence level

Pre-treatment and extraction techniques for recovery of added value compounds from wastes throughout the agri-food chain

The enormous quantity of food wastes discarded annually force to look for alternatives for this interesting feedstock. Thus, food bio-waste valorisation is one of the imperatives of the nowadays society. This review is the most comprehensive overview of currently existing technologies and processes in this field. It tackles classical and innovative physical, physico-chemical and chemical methods of food waste pre-treatment and extraction for recovery of added value compounds and detection by modern technologies and are an outcome of the COST Action EUBIS, TD1203 Food Waste Valorisation for Sustainable Chemicals, Materials and Fuels

Optimising sewage sludge anaerobic digestion for resource recovery in wastewater treatment plants

Recovering resources from sludge generated during wastewater treatment is both an opportunity and a challenge. Thermophilic anaerobic digestion may optimise biogas production and digested sludge properties for further valorisation, in the framework of a circular economy. Thus, this study aimed at evaluating the effect of operational conditions, i.e. temperature, solids concentration in the sludge, and solids retention time (SRT) on the methane production, volatile fatty acids (VFA) concentration, digested sludge hygienisation, and dewaterability, during long-term anaerobic digestion. This is the first time that sludge anaerobic digestion has been evaluated for over 500 days varying control parameters for assessing concomitantly biogas, VFA, and pathogen removal outcomes with focus on resource recovery. Results showed how by shifting from mesophilic (38 °C) to thermophilic (55 °C) conditions, with a short SRT (10 days) in the reactor, the process performance was optimised. Indeed, the methane production reached a maximum of 0.4 m3CH4/m3reactor·d, with a VFA concentration of 4.0 g COD/L and complete pathogen removal in the digestate, for a safe agricultural reuse. Therefore, the transition from mesophilic to thermophilic anaerobic digesters seems beneficial for the valorisation of by-products and promoting the circular economy in wastewater treatment plants.This research was funded by the Spanish Ministry of Science and Innovation (MICINN) and European Regional Development Fund (FEDER). Fabiana Passos acknowledges her Maria Zambrano Fellowship Grant funded by MCIN/AEI/10.13039/501100011033.info:eu-repo/semantics/publishedVersio