Adoption of water reuse technologies: An assessment under different regulatory and operational scenarios

Influence of policymakers and civil society stakeholders on sewage sludge management strategies: Empirical results from European utilities

Sewage sludge management is crucial for water utilities to move towards a circular valorisation of resources. The current literature focuses mainly on the technological aspects of sludge management strategies. However, the current discussion of these strategies does not consider possible pressures arising from the utilities' civil society stakeholders and from policymakers. To fill this gap, this paper develops a conceptual framework, based on the current literature, that identifies the utility's key decisions on sludge management strategies (valorisation route, overperformance and vertical integration), and links them to possible pressures arising from civil society and existing regulations. Subsequently, the study validates the framework through a multiple explanatory case study, investigating the empirical relevance of such pressures in six water utilities across Europe. The influence of citizens and municipalities is found to be crucial in the choice of sludge valorisation routes. Economic instruments, command and control instruments and, new to the literature, regulatory uncertainty are found to be key policy features influencing utilities' decisions on sludge management. The paper provides a first-of-its-kind investigation that highlights the mechanisms through which policymakers and civil society stakeholders shape utilities' sewage sludge management strategies. The results complement and extend existing theoretical knowledge on the role of institutional pressures in the implementation of sustainable environmental systems.

Combined recovery of polyhydroxyalkanoates and reclaimed water in the mainstream of a WWTP for agro-food industrial wastewater valorisation by membrane bioreactor technology

The present study investigated the combined production of reclaimed water for reuse purposes and polyhydroxyalkanoates (PHA) from an agro-food industrial wastewater. A pilot plant implementing a two-stage process for PHA production was studied. It consisted of a mainstream sequencing batch membrane bioreactor (SBMBR) in which selection of PHA-accumulating organisms and wastewater treatment were carried out in, and a side-stream fed-batch reactor (FBR) where the excess sludge from the SBMBR was used for PHA accumulation. The performance of the SBMBR was compared with that of a conventional sequencing batch reactor (SBR) treating the same wastewater under different food to microorganisms' ratios (F/M) ranging between 0.125 and 0.650 kgCOD kgTSS-3 d-1. The SBMBR enabled to obtain very high-quality effluent in compliance with the relevant national (Italy) and European regulations (Italian DM 185/03 and EU, 2020/741) in the field of wastewater reclamation, whereas the performances in the SBR collapsed at F/M higher than 0.50 kgCOD kgTSS-1d-1. A maximum intracellular storage of 45% (w/w) and a production yield of 0.63 gPHA L-1h-1 were achieved when the SBMBR system was operated with a F/M ratio close to 0.50 kgCOD kgTSS-1d-1. This resulted approximately 35% higher than those observed in the SBR, since the ultrafiltration membrane avoided the washout of dispersed and filamentous bacteria capable of storing PHA. Furthermore, while maximizing PHA productivity in conventional SBR systems led to process dysfunctions, in the SBMBR system it helped mitigate these issues by reducing membrane fouling behaviour. The results of this study supported the possibility to achieve combined recovery of reclaimed water and high-value added bioproducts using membrane technology, leading the way for agro-food industrial wastewater valorization in the frame of a circular economy model.

Influence of the Deposition Parameters on the Properties of TiO2 Thin Films on Spherical Substrates

Wastewater treatment targeting reuse may limit water scarcity. Photocatalysis is an advanced oxidation process that may be employed in the removal of traces of organic pollutants, where the material choice is important. Titanium dioxide (TiO₂) is a highly efficient photocatalyst with good aqueous stability. TiO₂ powder has a high surface area, thus allowing good pollutant adsorption, but it is difficult to filter for reuse. Thin films have a significantly lower surface area but are easier to regenerate and reuse. In this paper, we report on obtaining sol-gel TiO₂ thin films on spherical beads (2 mm diameter) with high surface area and easy recovery from wastewater. The complex influence of the substrate morphology (etched up to 48 h in concentrated H₂SO₄), of the sol dilution with ethanol (1:0 or 1:1), and the number of layers (1 or 2) on the structure, morphology, chemical composition, and photocatalytic performance of the TiO₂ thin films is investigated. Etching the substrate for 2 h in H₂SO₄ leads to uniform, smooth surfaces on which crystalline, homogeneous TiO₂ thin films are grown. Films deposited using an undiluted sol are stable in water, with some surface reorganization of the TiO₂ aggregates occurring, while the films obtained using diluted sol are partially washed out. By increasing the film thickness through the deposition of a second layer, the roughness increases (from ~50 nm to ~100 nm), but this increase is not high enough to promote higher adsorption or overall photocatalytic efficiency in methylene blue photodegradation (both about 40% after 8 h of UV-Vis irradiation at 55 W/m²). The most promising thin film, deposited on spherical bead substrates (etched for 2 h in H₂SO₄) using the undiluted sol, with one layer, is highly crystalline, uniform, water-stable, and proves to have good photocatalytic activity.

Climate crisis and recent developments in bio-based restoration of ecosystems

Over the years, due to the climate crisis, sustainable economic growth and biodiversity protection have been increasingly promoted. Scientists, researchers, and experts in the field of sustainable development highlighted that bio-based restoration of ecosystems and responsible management of existing resources are needed to meet the needs of future generations. This paper discusses some of the latest developments in three main areas of sustainability, i.e., energy, water and environment, that emerged from the "16th Sustainable Development of Energy, Water and Environment Systems Conference - SDEWES 2021". The purpose of this introduction article is to briefly review the articles included in this Virtual Special Issue. As such, it acts as an editorial paper for the virtual special issue of the Journal of Environmental Management, dedicated to the SDEWES 2021 conference.

Integrating water science, economics, and policy for future climate adaptation

Water science, water economics, and water policy issues continue to rise in importance internationally as elevated population, income growth, and climate change magnify scarcity, shortages, and injustices in water access. Based on the unique physical, institutional, and economic characteristics of water, this work's first contribution is to characterize a road forward for research innovations that enable better integration of water science, water economics, and water policy. Meeting water's sustainable development and justice goals calls for several research innovations that humanity awaits. The advances called for in this work include deep uncertainty management, red team reviews, innovative water rights design, accelerating SDG achievement, valuing water infrastructure, valuing natural water retention, incentivizing water conservation, improving financial performance of rural water systems, water network modularization, non-price scarcity signals, optimization model calibration, remote sensing, transboundary benefit sharing, optimal growth, and water valuation. The work's second contribution is to present a prototype scalable basin scale hydroeconomic analysis (HEA) as a framework for integrating these above innovations when they occur. Results of the HEA show that losses from a 50% shortage in the basin's surface water supply can continue to protect 93% of total economic benefits across economic sectors if an efficient water trading system is established to move water from lower to higher valued uses when shortages occur. The work concludes by noting that great advances remain needed for better and longer lives.