Chicgoua Noubactep

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SCIEPublish is an international open-access journal publishing service provider run by SCIE Publishing Limited, dedicated to supporting and inspiring scientists or institutions/societies who aspire to publish high-quality journals.

Published results on rainwater management systems revealed a lack of holistic science-based design principles. A new approach to rainwater management is proposed. Its necessity and feasibility are discussed. It is demonstrated that quantitatively harvesting rainfall and infiltrating a fraction should be mandatory. Thus, the primary site-specific parameter is the intensity of rainfall. Clearly, rainwater should be harvested and used everywhere as a valuable resource. Under arid semi-arid conditions large tanks maximize water storage for the long dry season while under humid conditions the same helps to minimize the frequency of emptying to avoid flooding. The new approach separates rainwater (and stormwater) from sewage and has the potential to maintain the natural hydrological cycle in urban areas despite urbanization. In already crowded slums, rainwater harvesting (RWH) can also be used to restore the hydrological cycle. The new approach advocates for decentralized RWH infrastructures to harvest, infiltrate, and store rainwater in individual residences, while piping overflows to semi-centralized cluster-scale tanks. Rooting integrated water resource management on RWH appears to be the missing puzzle in: (i) restoring the natural hydrological cycle where it has been disturbed (landscape restoration), (ii) avoiding flooding, and (i) mitigating soil erosion. This is essential for sustainable development.

Water pollution is calling for a sustainable remediation method such as the use of metallic iron (Fe⁰) to reduce and filter some pollutants, yet the reactivity and hydraulic conductivity of iron filters decline over time under field conditions. Here we review iron filters with focus on metallic corrosion in porous media, flaws in designing iron filters, next-generation filters and perspectives such as safe drinking water supply, iron for anaemia control and coping with a reactive material. We argue that assumptions sustaining the design of current Fe⁰filters are not valid because proposed solutions address the issues of declining iron reactivity and hydraulic conductivity separately. Alternatively, a recent approach suggest that each individual Fe⁰atom corroding within a filter contributes to both reactivity and permeability loss. This approach applies well to alternative iron materials such as bimetallics, composites, hybrid aggregates, e.g. Fe⁰/sand, and nano-Fe⁰. Characterizing the intrinsic reactivity of individual Fe⁰materials is a prerequisite to designing sustainable filters. Indeed, Fe⁰ratio, Fe⁰type, Fe⁰shape, initial porosity, e.g. pore size and pore size distribution, and nature and size of admixing aggregates, e.g. pumice, pyrite and sand, are interrelated parameters which all influence the generation and accumulation of iron corrosion products. Fe⁰should be characterized in long-term experiments, e.g. 12 months or longer, for Fe dissolution, H₂generation and removal of contaminants in three media, i.e., tap water, spring water and saline water, to allow reactivity comparison and designing field-scale filters.

Rainwater harvesting (RWH) is principally based on collecting, storing, and using rainfall which would otherwise be lost as surface runoff. Runoff threatens in several ways: accelerating erosion, intensifying flooding, and reducing groundwater recharge. Therefore, purposely retaining rainfall in the urban water cycle rather than draining has several positive impacts on designing sustainable cities. This work presents a proposal on how to avoid flooding in cities by systematically harvesting, storing rainwater, and using it for multiple purposes. The concept of RWH presented here has the potential to be a radical innovation to solve the social, economic, and environmental challenges associated with flash flooding. Each residence is regarded as a water production unit. Depending on the climatic conditions, people can meet their water needs on a local household basis, or alternatively use piped water as a complement. By infiltrating rainwater, groundwater is locally recharged and downstream wells are more productive. The implementation of this idea involves entrepreneurial agency that challenges existing structures, rather than adapting to them. Clearly, social entrepreneurship and social innovation are expected to catalyse the realization of this social innovation, also in rural areas. It is about mobilizing ideas, capacities, and resources to create a sustainable social transformation.

Permeable reactive barriers (PRBs) containing metallic iron (Fe⁰) as reactive materials are currently considered as an established technology for groundwater remediation. Fe⁰ PRBs have been introduced by a field demonstration based on the fortuitous observation that aqueous trichloroethylenes are eliminated in Fe⁰-based sampling vessels. Since then, Fe⁰ has been tested and used for treating various biological (e.g. bacteria, viruses) and chemical (organic and inorganic) contaminants from polluted waters. There is a broad consensus on the view that “reactivity loss” and “permeability loss” are the two main problems hampering the design of sustainable Fe⁰ systems. However, the view that Fe⁰ is a reducing agent (electron donor) under environmental conditions should be regarded as a distortion of Corrosion Science. This is because it has been long established that aqueous iron corrosion is a spontaneous process and results in the Fe⁰ surface being shielded by an oxide scale. The multi-layered oxide scale acts as a conduction barrier for electrons from Fe⁰. Accordingly, “reactivity loss”, defined as reduced electron transfer to contaminants, must be revisited. On the other hand, because “stoichiometric” ratios were considered while designing the first generation of Fe⁰ PRBs (Fe⁰ as reductant), “permeability loss” should also be revisited. The aim of this communication is to clarify this issue and reconcile a proven efficient technology with its scientific roots (i.e. corrosion science).