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Use of Engineered Chitosan Materials to Treat Wastewater for Reuse and Material Recovery

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Organic and inorganic substances which were released into the environment as a result of domestic, agricultural and industrial water activities lead to organic and inorganic pollution

The normal primary and secondary treatment processes of these wastewaters have been introduced in a growing number of places, in order to eliminate the easily settled materials and to oxidize the organic material present in wastewater.

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Nanomaterials can also be activated, either by an external source of light or by using oxidizing agents such as hydrogen peroxide (non-irradiated), as a new insight for the application of nanomaterials to deal with emerging environmental pollutants (Wiedmer et al., 2016). In addition, providing an external source of energy is of high importance for reactors which are dependent on the light illumination (Xu et al., 2018a)

Effective penetration of the light into the system to provide enough reactive zone in the media is a barrier that needs to be addressed in such reactors. In this regard, solar light mediated processes have attracted recently a significant attention. Hence, the development of visible-light active materials can considerably help to overcome this barrier. It can be stated that the methods for the synthesis of visible light active nanomaterials (such as nitrogen doped TiO2 NMs (Ansari et al., 2016)) have been sufficiently developed and are ready to be used in such reactors (Pelaez et al., 2012; Ponraj & Danie, 2017; Mohapatra & Parida, 2017) but still need scaling-up to be more economic. Recovery of the nanomaterials after being used is another issue which demands further efforts. For instance, the application of ceramic membranes to recover the nanomaterials (Westerhoff et al., 2016), incorporation of the nanomaterials on the surface of the membranes (Paul & Jons, 2016), and also the application of magnetic nanomaterials easily collected after use can be considered as attractive solutions (Kamali et al., 2018). However, no magnetic separation reactor has been yet commercialized for the treatment of polluted water and wastewater, so far. An ideal configuration has to ensure the possibility to provide (i) the necessary light (ultraviolet, visible, or both) in case of advanced oxidation processes with nano photocatalysts, (ii) enough contact time between the materials and the pollutants, and (iii) to recover the nanomaterials after being used.

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To meet the water requirements of a growing population, and with escalating efforts to deliver clean drinking water to the estimated 29% of the global population that do not currently have access to it (WHO 2017), there is an ever-increasing demand for clean and safe drinking water. In order to supply this increasing demand, raw water must be treated to remove any waterborne microorganisms, excess mineral content and suspended sediment. One of the most common methods employed to remove suspended particles and colloids from raw water is the addition of metal salts to initiate a coagulation–flocculation process. However, this process results in the generation of vast quantities (generally between 10 and 30 mL of WTRs for every litre of water clarified) of a sludge-like waste (or by-product) known as water treatment residuals (WTRs), which require an outlet for their disposal or end use (Dassanayake et al. 2015). Previous reviews have described some of the potential beneficial uses for WTRs considered up to that time, the most recent of which being in 2011, along with the research that had been conducted into their uses (e.g

Babatunde and Zhao (2007); Ippolito et al. (2011)). However, considerable advancements in the testing and application of WTRs have been made in the past 10 years. To illustrate, a search on the Web of Science Core Collection for ‘water treatment residual*’ OR ‘water treatment sludge’ for the period 2008–2018 returned > 400 articles. Recent reviews have focussed on various aspects of the WTR reuse, ranging from use as a sorbent (Ippolito et al. 2011), coagulant recovery (Keeley et al. 2014) and the broader scope of WTR utilisation at international levels (Ahmad et al. 2016; Zhao et al. 2018).

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In essence, to guarantee water safety, the indirect potable reuse process requires understanding environmental and health standards. As such, the employment of recent technologies needs thorough risk assessments and health and safety evaluations performed to mitigate potential risks of the technology itself. While no legislation pertaining to EPC maximum allowable concentrations in water has been established, legislations regulating drinking water processes tend to be very strict to ensure human health and environmental safety. For instance, in an ongoing effort to maintain the safety of drinking water and lessen the effect of EPCs, the European Union has added additional requirements for pharmaceuticals whereby more extensive environmental risk assessments need to be conducted for each pharmaceutical’s use to be allowed.

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Yusuff, S., Ong, K., Yunus, W. Z. W., Fitrianto, A., & Ahmad, M. (2017). Removal of methylene blue from aqueous solutions using alum sludge: sorption optimization by response surface methodology. Journal of Fundamental and Applied Sciences, 9, 532–545.

Zhao, Y., & Yang, Y. (2010). Extending the use of dewatered alum sludge as a P-trapping material in effluent purification: study on two separate water treatment sludges. Journal of Environmental Science and Health, Part A, 45, 1234–1239.

Zhao, Y., Zhao, X., & Babatunde, A. (2009). Use of dewatered alum sludge as main substrate in treatment reed bed receiving agricultural wastewater: long-term trial. Bioresource Technology, 100, 644–648.

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