Daniela Zingaretti

This review presents a process-based decision-making framework for chlorinated vapor intrusion (CVI) mitigation. CVI mitigation refers to the set of engineered strategies aimed at interrupting, attenuating or transforming vapor fluxes before they reach indoor environments. Existing literature and technical guidelines typically classify mitigation strategies according to technological configuration (active versus passive), rather than physical and chemical processes governing vapor transport and attenuation, which may lead to suboptimal design choices and reduced system resilience. To address this limitation, this framework proposes a process-based classification of CVI mitigation strategies based on the dominant mechanisms controlling vapor migration in subsurface. Five mechanistic categories are identified: driving-force control through pressure manipulation, dilution via air exchange, diffusive flux control through physical barriers, density-driven attenuation in permeable sub-slab layers, and in situ transformation based on sorption or degradation. By explicitly linking mitigation technologies to transport and transformation processes, the proposed framework provides a structured basis for mechanism-oriented selection, integrating performance, longevity, climate resilience, and lifecycle energy demand. In addition to established mitigation approaches, such as sub-slab depressurization, this work highlights emerging passive strategies, including high permeable granular layers and horizontal reactive or adsorbing barriers, as potential low-energy alternatives for durable management. Overall, the proposed framework supports site-specific, sustainability-oriented decision-making on CVI mitigation.

Ferrate(VI) has increasingly been proposed as an environmentally friendly oxidant due to its high reactivity and the relatively low toxicity of its by-products. However, its performance in degrading emerging pollutants (EPs) has not been systematically compared with conventional systems. This study presents a novel comparative assessment of three oxidation systems for the degradation of acetaminophen (APAP): (i) Fe⁰-activated hydrogen peroxide (HP), (ii) Fe⁰-activated persulfate (PS), and (iii) a commercial ferrate(VI)-based product, Envifer^® (Fe(VI)). Optimal conditions were determined based on degradation kinetics, pH dependence, and oxidant stability. Oxidant systems were then evaluated in realistic matrices, including tap water and synthetic wastewater. When UP water was used, the HP/Fe⁰ system achieved the highest APAP mineralization (i.e., 66%) with 1 mM of oxidant dosage, and PS/Fe⁰ was shown to be effective without pH adjustment. Nevertheless, these heterogeneous systems presented serious limitations when applied in more complex matrices. Fe(VI) instead achieved a rapid APAP degradation even in the presence of carbonates and natural organic matter without pH adjustment. This represents a key advantage over HP- and PS-based systems, enabling simpler implementation and lower chemical demand. Furthermore, Fe(VI) resulted in lower dissolved iron concentrations, potentially enabling less intensive post-treatment requirements. Overall, the results identify Fe(VI)-based AOPs as a potentially green alternative to conventional systems for wastewater treatment.

In this study, zero-valent iron-copper (Fe-Cu) and iron-nickel (Fe-Ni) bimetals were prepared by disc milling for the dehalogenation of trichloroethylene vapors. For both Fe-Ni and Fe-Cu, three combinations in terms of percentage of secondary metal added were produced (1%, 5%, 20% by weight) and the formation of the bimetallic phase by milling was evaluated by X-ray diffraction (XRD) analysis. The disc milled bimetals were characterized by a homogenous distribution of Ni or Cu in the Fe phase and micrometric size visible from scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) analysis and by a relatively low specific surface area (0.2–0.7 m²/g) quantified by the Brunauer–Emmett–Teller (BET) method. The reactivity of the produced bimetals was evaluated by batch degradation tests of TCE in the gas phase with 1 day of reaction time. Fe-Ni bimetals have shown better performance in terms of TCE removal (57–75%) than Fe-Cu bimetals (41–55%). The similar specific surface area values found for the produced bimetals indicated that the enhancement in the dehalogenation achieved using bimetals is closely related to the induced catalysis. The obtained results suggest that ZVI-based bimetals produced by disc milling are effective in the dehalogenation of TCE vapors in partially saturated conditions.

In this paper, we present a case study on the optimization of the biostabilization process of an Italian mechanical–biological treatment (MBT) plant to account for changes in feed waste composition related to a progressive increase in separate collection of MSW fractions, biowaste in particular. After ten years of operation (2009–2019), a decrease of the stabilization degree of the output material of the plant was detected, with Dynamic Respiration Index (DRI) values above the established limit of 1,000 mgO₂/kg_VS/h (average values of 4,000 mgO₂/kg_VS/h determined weekly for eight weeks). The investigations carried out in 2019 on the waste samples feeding the MBT plant showed that paper and plastic materials constitute around 75% of the input waste to the two aerobic bioreactors of the MBT plant, against 55% at the start-up (2009). Furthermore, the airflow rates and the moisture content analyzed weekly for eight weeks in the bioreactors resulted below the optimal values suggested in the literature. To improve the performances of the biostabilization process, a series of modifications were implemented in the plant. The main modification involved the primary mechanical treatment by varying the mesh size of the screens to 50 mm circular holes mesh. Furthermore, the configuration of the aerobic bioreactors was changed by placing the two bioreactors in series (instead of the previous configuration in parallel) and using a screening unit (25 mm) between the two bioreactors instead of at the end of the process. In this way, the residence time of the materials in the aerobic treatment was enhanced from 16 days with the previous configuration to 27 days. Together with an increase of the airflow rates of around 40% and a water supply of approximately 10% in the bioreactors, these modifications allowed to achieve the desired stability of the output waste, with DRI values below 1000 mgO₂/kg_VS/h. Graphical Abstract