Nature-based solutions (NBS) can protect, manage and restore natural or modified ecosystems. They are a multidisciplinary, integrated approach to address societal challenges and some natural hazards effectively and adaptively, simultaneously providing human well-being and biodiversity benefits. NBS applications can be easily noticed in circular cities, establishing an urban system that is regenerative and accessible. This paper aims to offer a review on NBS for urban water management from the literature and some relevant projects running within the COST Action ‘Implementing nature-based solutions for creating a resourceful circular city’. The method used in the study is based on a detailed tracking of specific keywords in the literature using Google Scholar, ResearchGate, Academia.edu, ScienceDirect and Scopus. Based on this review, three main applications were identified: (i) flood and drought protection; (ii) the water-food-energy nexus; and (iii) water purification. The paper shows that NBS provide additional benefits, such as improving water quality, increasing biodiversity, obtaining social co-benefits, improving urban microclimate, and the reduction of energy consumption by improving indoor climate. The paper concludes that a systemic change to NBS should be given a higher priority and be preferred over conventional water infrastructure.

The occurrence, fate and removal of microplastics (MPs) in a wastewater treatment plant (WWTP) in Central Italy were investigated together with their potential adverse effects on anaerobic processes. In the influent of the WWTP, 3.6 MPs . L -1 were detected that mostly comprised polyester fibers and particles in the shape of films, ranging 0.1-0.5 mm and made of polyethylene and polypropylene (PP). The full-scale conventional activated sludge scheme removed 86% of MPs, with the main reduction in the primary and secondary settling. MPs particles bigger than 1 mm were not detected in the final effluent and some loss of polymers types were observed. In comparison, the pilot-scale upflow granular anaerobic sludge blanket (UASB) + anaerobic membrane bioreactor (AnMBR) configuration achieved 94% MPs removal with the abatement of 87% of fibers and 100% of particles. The results highlighted an accumulation phenomenon of MPs in the sludge and suggested the need to further investigate the effects of MPs on anaerobic processes. Accordingly, PP-MPs at concentrations from 5 PP-MPs . gTS -1 to 50 PP-MPs . gTS -1 were spiked in the pilot-scale UASB reactor that was fed with real municipal wastewater, where up to 58% decrease in methanogenic activity was observed at the exposure of 50 PP-MPs . gTS -1 . To the best of our knowledge, the presented results will be the first to report of PP-MPs inhibition on anaerobic processes.

Italy is among the top biowaste-generating countries in Europe, and has a well-structured waste management framework with quite a number of centralized composting facilities. In recent years, there has also been huge interest from local communities in decentralized composting. Although decentralized community composting is common in some countries, there is still a lack of information on the operative environment together with its potential logistical, environmental, economic, and social impacts. Considering the national Italian legislation on community composting as well as successfully implemented projects at EU level, Italy can set a model especially for Mediterranean countries that intend to build decentralized composting programs. Therefore, in the context of this review paper, a brief overview of the composting process was presented together with main applications in centralized and especially in decentralized composting, while the main focus was kept on the operative and legislative information gathered from Italian community composting. There is a huge difference in the number of composting plants between the regions, and the lack of centralized facilities in the central and southern regions can be supported by decentralized solutions. Decentralizing waste treatment facilities and thus creating local solutions to urban waste management strategies will help to achieve the resource recovery and valorization targets in line with the circular economy.

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