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The European Union is currently in the process of transformation toward a circular economy model in which different areas of activity should be integrated for more efficient management of raw materials and waste. The wastewater sector has a great potential in this regard and therefore is an important element of the transformation process to the circular economy model. The targets of the circular economy policy framework such as resource recovery are tightly connected with the wastewater treatment processes and sewage sludge management. With this in view, the present study aims to review existing indicators on resource recovery that can enable efficient monitoring of the sustainable and circular solutions implemented in the wastewater sector. Within the reviewed indicators, most of them were focused on technological aspects of resource recovery processes such as nutrient removal efficiency, sewage sludge processing methods and environmental aspects as the pollutant share in the sewage sludge or its ashes. Moreover, other wide-scope indicators such as the wastewater service coverage or the production of bio-based fertilizers and hydrochar within the wastewater sector were analyzed. The results were used for the development of recommendations for improving the resources recovery monitoring framework in the wastewater sector and a proposal of a circularity indicator for a wastewater treatment plant highlighting new challenges for further researches and wastewater professionals.

The steel industry is the largest consumer of energy in the world among industrial sectors. It is generally acknowledged that energy and environment are intimately related. Steel production is an energy intensive process that has a significant environmental impact. This paper reviews the progress made on energy consumption, carbon dioxide emissions and water consumption in the steel industry worldwide. The reduction in the availability of fresh water resources combined with the effects of global warming and climate change have increased pressure on industries, especially steel, to reduce its overall pollution, and specifically its water and carbon footprint. The implications of these effects on the value chain is discussed in this review. The contribution of new emerging technologies of iron and steelmaking is also reviewed. Finally, the important issues that contribute to define a sustainable industrial activity such as the recycling of steel and of by-products of steel production are studied. The history of steel industry is full of lessons, one of which is the need to keep the dreams alive. There are indeed expectations to solve problems created by technical progress.

Abstract In addition to CO2 released by the combustion of fossil fuel and leading to climate change, large steelworks emit pollutants that have other environmental impacts. ArcelorMittal Gent, an integrated steelwork producing ca. 5 × 106 tons of steel per year, not only decreased its specific energy consumption and CO2-emissions, but also reduced the environmental impact of its other emissions. This is illustrated by means of the evolution of 6 partial eco-efficiency indicators for the impact categories acidification, photo-oxidant formation, human toxicity, freshwater aquatic ecotoxicity, eutrophication and water use. The partial eco-efficiency indicators are eco-intensities, defined as the environmental impact in the respective impact category, divided by the amount of liquid steel produced. In the period 1995 – 2005 these indicators decreased by 45, 4, 52, 9, 11 and 33% respectively, whereas the steel production increased by 17%. The net impact of discharges of wastewater is negligible for human toxicity and is negative (concentrations lower than in the canal water used) for freshwater aquatic toxicity and eutrophication. For acidification, human toxicity (only emissions to air) and water use, the decoupling between environmental impact and production was absolute; for photo-oxidant formation, freshwater aquatic ecotoxicity (only emissions to air) and eutrophication, it was relative.

The impact of urban water fluxes on the river system outflow of the Grote Nete catchment (Belgium) was studied. First the impact of the Waste Water Treatment Plant (WWTP) and the Combined Sewer Overflow (CSO) outflows on the river system for the current climatic conditions was determined by simulating the urban fluxes as point sources in a detailed, hydrodynamic river model. Comparison was made of the simulation results on peak flow extremes with and without the urban point sources. In a second step, the impact of climate change scenarios on the urban fluxes and the consequent impacts on the river flow extremes were studied. It is shown that the change in the 10-year return period hourly peak flow discharge due to climate change (−14% to +45%) was in the same order of magnitude as the change due to the urban fluxes (+5%) in current climate conditions. Different climate change scenarios do not change the impact of the urban fluxes much except for the climate scenario that involves a strong increase in rainfall extremes in summer. This scenario leads to a strong increase of the impact of the urban fluxes on the river system.

Anaerobic digestion is generally considered to be an economic and environmentally friendly technology for treating waste activated sludge, but has some limitations, such as the time it takes for the sludge to be digested and also the ineffectiveness of degrading the solids. Various pre-treatment technologies have been suggested to overcome these limitations and to improve the biogas production rate by enhancing the hydrolysis of organic matter. This paper studies the use of peracetic acid for disintegrating sludge as a pre-treatment of anaerobic digestion. It has been proved that this treatment effectively leads to a solubilisation of organic material. A maximum increase in biogas production by 21% is achieved. High dosages of PAA lead to a decrease in biogas production. This is due to the inhibition of the anaerobic micro-organisms by the high VFA-concentrations. The evolution of the various VFAs during digestion is studied and the observed trends support this hypothesis.

Drought can have a significant impact on both society and the economy, resulting in issues such as scarcity of water and shortages of food and energy, as well as elevated health risks. However, as global temperatures continue to rise, the impact of drought events is increasingly exacerbated, manifested by an increase in the frequency, intensity, duration, and spatial extent of their effects. Therefore, studying the changing characteristics of drought events with the background of climate change is of great significance. Based on the high-precision and high-resolution CN05.1 dataset, this study obtained the monthly Standardized Precipitation Evapotranspiration Index (SPEI) dataset from 1961 to 2020, and then identified regional drought events in China using the Intensity–Area–Duration (IAD) method, which considers both temporal continuity and spatial dynamics. On this basis, the spatiotemporal variations in frequency, intensity, duration, and affected area of drought events in China and its seven subregions were analyzed. The results showed that the subregions located in the northern region of China generally have lower mean, maximum, and minimum temperatures than those located in the southern region, but the associated interannual change rate of the subregions in the north is higher than that in the south. As for the annual total precipitation, results show a clear pattern of decreasing southeast–northwest gradient, with an increasing trend in the northern subregions and a decreasing trend in the southern subregions except for the subregion south China (SC). The northeast of China (NE), SC, the southwest of China (SW) and north China (NC) are the regions with a high frequency of drought events in China, while the frequency of drought events in NW and Qinghai–Tibetan Plateau (QTP), although lower, is on a significantly increasing trend, and the increasing rate is higher than for the other regions. For drought intensity, Xinjiang (XJ) and QTP had greater drought intensity, and the change rate of these regions with greater drought intensity was also greater. The drought impact area in China showed a significant increasing trend, mainly concentrated in QTP, NW and NE. Particular attention needs to be focused on the southwest of QTP, where drought events in this region show a significant increase in frequency, intensity, duration and impact area.

We used CMIP6 GCMs to quantify climate change impacts on precipitation and potential evapotranspiration (PET) across water management zones (WMZs) in Uganda. Future changes are assessed based on four Shared Socioeconomic Pathways (SSP) scenarios including SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 over the periods 2021–2040, 2041–2060, 2061–2080, and 2081–2100. Both precipitation and PET are generally projected to increase across all the WMZs. Annual PET in the 2030s, 2050s, 2070s, 2090s will increase in the ranges 1.1–4.0%, 4.8–7.9%, 5.1–11.8%, and 5.3–17.1%, respectively. For the respective periods, annual precipitation will increase in the ranges 4.0–7.8%, 7.8–12.5%, 7.9–19.9%, and 6.9–26.3%. The lower and upper limits of these change ranges for both precipitation and PET are, respectively, derived under SSP1-2.6 and SSP5-8.5 scenarios. Climate change will impact on PET or precipitation disproportionately across the WMZs. While the eastern WMZ (Kyoga) will experience the largest projected precipitation increase especially towards the end of the century, the southern WMZ (Victoria) exhibited the largest PET increase. Our findings are relevant for understanding hydrological impacts of climate change across Uganda, in the background of global warming. Thus, the water sector should devise and implement adaptation measures to impede future socioeconomic and environmental crises in the country.

Anaerobic digestion is widely applied for the recovery of energy from waste activated sludge. Pre-treatment methods are of high interest to increase the biodegradability of the sludge and to enhance the digestion efficiency. This paper studies the application of a microwave pre-treatment. An experimental set-up of two pilot scale semi-continuous digesters was used. During a long term experiment, one of the reactors was fed with untreated sludge, while microwave pre-treated sludge (336 kJ/kg sludge) was introduced in the second one. A solid retention time of 20 days was kept during the experiments. (Organic) dry solids, carbohydrates, proteins and volatile fatty acids were monitored during digestion. It was seen that the microwave pre-treatment resulted in an effective solubilization of the organic matter in the sludge. The changes to the sludge composition resulted in an increase in biogas production by 50%, while the methane concentration in both reactors remained stable.