Soil is a non-renewable natural resource. However, the current rates of soil usage and degradation have led to a loss of soil for agriculture, habitats, biodiversity, and to ecosystems problems. Urban and former industrial areas suffer particularly of these problems, and compensation measures to restore environmental quality include the renaturation of dismissed areas, de-sealing of surfaces, or the building of green infrastructures. In this framework, the development of methodologies for the creation of soils designed to mimic natural soil and suitable for vegetation growth, known as constructed soils or technosols, are here reviewed. The possible design choices and the starting materials have been described, using a circular economy approach, i.e., preferring non-contaminated wastes to non-renewable resources. Technosols appear to be a good solution to the problems of land degradation and urban green if using recycled wastes or by-products, as they can be an alternative to the remediation of contaminated sites and to importing fertile agricultural soil. Nevertheless, waste use requires analysis to ensure the salubrity of the starting materials. Moreover, materials produced on site or nearby minimize the cost and the environmental impact of transport, thus the involvement of local stakeholders in the urban land management must be encouraged.

Currently, the pollution of soils by heavy metals is a problem of paramount relevance and requires the development of proper remediation techniques. In particular, lead is a frequently detected soil contaminant that poses adverse effects to the environment and human health. In this review, we provide an overview of the bioremediation treatments promoted by plants (phytoremediation), fungi, or bacteria that could be applied to areas polluted by lead. These restoration processes have the advantage of being environmentally friendly and cost-effective solutions that exploit plants to immobilize and extract contaminants from soil and water, and fungi and bacteria to degrade them. Phytoremediation is an extensively studied and mature practice, with many in-the-field applications where numerous plant species have been employed. In contrast, bioremediation processes promoted by fungi and bacteria are very promising but, up to now, studies have been mostly performed at a laboratory scale with only a few implementations in real-world situations; therefore, further research is needed.

A LaFeO₃ photocatalyst is obtained by solution combustion synthesis from a bio-based substance extracted from urban wastes and tested for its catalytic activity.

Here, the performances of two different catalysts, Ce-ZnO and TiO₂ synthetized in our laboratories, were compared with the commercial TiO₂-P25 for degradation of a mixture of seven emerging pollutants under UV irradiation. The investigation included monitoring pollutants abatement in Milli-Q water and in wastewater effluent and identifying their transformation products by HPLC-HRMS. Structural characterization of intermediates supported by data available from literature allowed elucidation of the transformation pathways occurring in the presence of all investigated catalysts in the wastewater effluent. Preliminary results showed a good removal efficacy for almost all examined contaminants, even in real water matrix (i.e. wastewater effluent). The type of matrix and catalyst affects the number and/or the abundance of transformation products, which suggests differences in their transformation routes.

The exploitation of organic waste as a source of bio-based substances to be used in environmental applications is gaining increasing interest. In the present research, compost-derived bio-based substances (BBS-Cs) were used to prepare hybrid magnetic nanoparticles (HMNPs) to be tested as an auxiliary in advanced oxidation processes. Hybrid magnetic nanoparticles can be indeed recovered at the end of the treatment and re-used in further water purification cycles. The research aimed to give new insights on the photodegradation of caffeine, chosen as marker of anthropogenic pollution in natural waters, and representative of the contaminants of emerging concern (CECs). Hybrid magnetic nanoparticles were synthetized starting from Fe(II) and Fe(III) salts and BBS-C aqueous solution, in alkali medium, via co-precipitation. Hybrid magnetic nanoparticles were characterized via X-ray diffraction (XRD), thermo-gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The effect of pH, added hydrogen peroxide, and dissolved oxygen on caffeine photodegradation in the presence of HMNPs was assessed. The results allow for the hypothesis that caffeine abatement can be obtained in the presence of HMNPs and hydrogen peroxide through a heterogeneous photo-Fenton mechanism. The role of hydroxyl radicals in the process was assessed examining the effect of a selective hydroxyl radical scavenger on the caffeine degradation kinetic.