Next Article in Journal
Characteristics of Accelerations and Pressure Gradient during Run-Down of Solitary Wave over Very Steep Beach: A Case Study
Previous Article in Journal
Assessing Temporal and Spatial Inequality of Water Footprint Based on Socioeconomic and Environmental Factors in Jilin Province, China
Previous Article in Special Issue
Fe0/H2O Filtration Systems for Decentralized Safe Drinking Water: Where to from Here?
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Editorial

Editorial for the Special Issue: Filters in Drinking Water Treatment

Department of Applied Geology, Universität Göttingen, Goldschmidtstraße 3, D-37077 Göttingen, Germany
Water 2019, 11(3), 522; https://doi.org/10.3390/w11030522
Submission received: 1 March 2019 / Revised: 11 March 2019 / Accepted: 12 March 2019 / Published: 13 March 2019
(This article belongs to the Special Issue Filters in Drinking Water Treatment)

Abstract

:
Slow sand filters were first used for safe drinking water provision during the 19th century. The technology has been gradually improved and utilized at several scales. Based on their intrinsic limitations other filtration systems have been developed, including membrane technologies. The universal applicability of filtration in drinking water supply makes filters a device of choice to facilitate the achievement of the UN Sustainable Development Goals (‘drinking water for all by 2030’). Available strategies to rationally design efficient and sustainable water filters are scattered in the literature and are difficult to access and evaluate by starting researchers. The present Special Issue summarizes knowledge on two key filtration systems for drinking water supply: (i) membrane technology and (ii) metallic iron based filters. The five (5) accepted articles are being briefly presented herein.

This Special Issue was conceived to accelerate the achievement of the United Nations Sustainable Development Goals (SDGs) for universal access to safe drinking water [1]. The intention was to critically review the available literature on all relevant aspects of water filtration as applicable in a decentralized manner. The key idea was that the century-old slow sand filtration is universally applicable, but its efficiency can be optimized by several approaches. This optimization effort is equally not new, but available data have been mostly gathered on a pragmatic basis, making any scientific progress challenging. The Special Issue seeks to provide a foundation for further investigations which could enable the achievement of the UN SDG on universal access to clean drinking water within the remaining decade up to 2030. Accordingly, the goal was not to provide any new data but to systematically review available information and present a roadmap for the design of the next-generation water filters for decentralized safe drinking water provision.
From the five received papers, four deal with using metallic iron (Fe0) in filters, and provided a current state-of-the-art on the existing knowledge. During the preparation of the Special Issue, it was realized that a critical review focused on using Fe0 for water treatment in a decentralized manner is lacking. Existing literature mostly compare Fe0-based systems to other systems, for example, in the context of arsenic removal [2] or compare the efficiency of Fe0 filters constructed with various materials [3]. The major shortcoming of this approach is that the most intrinsic property of iron corrosion is not really addressed: The volumetric expansion of iron on corrosion, which is key to contaminant removal and loss of porosity in the long-term. On the other hand, the long-term kinetics of the generation of contaminant scavengers (iron corrosion products) is yet to be properly addressed. This knowledge gap will soon be filled, and a roadmap to achieve this was presented in Nanseu-Njiki et al. [4].
A paper on “Functional channel membranes for drinking water production” was gratefully accepted, wherein Gonzalez-Perez and colleagues [5] addressed the pivotal role of new bioinspired materials in the development of more efficient and environmentally friendly membrane solutions for safe drinking water (and clean environment). The global market for polymer-based membrane separation technologies for water treatment is discussed. The key role of new strategies for embedding ion-channels or water-channels into the next generation of membrane filters, as functional motifs to purify water, is comprehensively presented. The core idea of this contribution is a summary of the different strategies for developing new, advanced membranes with a wide variety of functional motifs and their possible impact on drinking water applications.
It was very gratifying to receive a paper on “Progress in understanding the mechanism of CrVI removal in Fe0-based filtration systems” [6], wherein the author presented an extensive and useful review on the technology of using metallic iron (Fe0) for water treatment and environmental remediation. The contribution is focused on Cr removal, but the state-of-the-art mechanistic discussion recalls that Fe0 is a generator of contaminant scavengers in the form of iron corrosion products, whose formation is accompanied by volumetric expansion. Dr. Gheju recalled that systems designed for single contaminants underestimate the huge potential of Fe0 for water treatment. Based on this demonstration, new routes to investigate Fe0/H2O systems are suggested while insisting on long-lasting column experiments and extending the admixing materials to include manganese oxides (MnOx). MnOx has the potential to sustain iron corrosion and overcome the commonly claimed ‘reactivity loss’ for Fe0 filters widely reported in the literature [7,8,9].
Hu et al. [10] draws attention to the scientific history of the Fe0/H2O system and demonstrate that regarding Fe0 as a reducing agent under environmental conditions in the 1990s was an avoidable mistake. A review of existing literature at that time could have addressed some of the perpetuated flaws in the literature on Fe0 [11,12,13]: (i) Misconception that Fe0 is directly involved in the reductive transformation of contaminants, and (ii) failure to account for the volumetric expansive nature of Fe0 in the design process. The incidence of this thinking mistake on the Fe0 technology is discussed together with some consequences for its further development. The key role of characterizing the intrinsic reactivity of Fe0 materials in future research is emphasized.
Nanseu-Njiki et al. [4] is a timely paper focusing on decentralized safe drinking water provision using Fe0-based systems. The authors excellently resolved the prevailing confusion that has strongly hampered the design of efficient and sustainable Fe0 filters for drinking water. The rationale for the success of two existing designs is given: (i) The SONO arsenic filter used at household scale [14], and (ii) the IITB arsenic filter (community scale) [15]. Particularly, ways are given to optimize the IITB arsenic filter. The same tools should be used to optimize amended biosand filters [3]. A time-line for systematic investigations is given, which application would surely enable universal safe drinking water within one decade.
The last paper by Ndé-Tchoupé and colleagues [16] is an extensive piece of work that has involved an impressive range of collaborators from various backgrounds and countries. Ndé-Tchoupé et al. [16] presented a roadmap for the implementation of the newly discussed Kilimanjaro Concept [17] in Tanzania. Specifically, the authors highlight how affordable water filters based on Fe0/biochar can be integrated into rainwater harvesting (RWH) systems to provide fluoride-free drinking water to Tanzanians and the population of the whole great East African Rift Valley. It is, thus, about defeating fluorosis on a long-term, self-reliant basis. The authors are expecting African engineers and scientists to take the lead in translating this concept into reality for the benefit of public health. Although the paper focuses on Africa, the concept may also be applicable in other regions with problems of high fluoride (and even arsenic) in groundwater sources.
Managing to secure more papers on well-known available, affordable technologies (including conventional slow sand filters) for safe drinking water production was not possible within the time frame of the call. Even for the Fe0 based technology, there remains a requirement for a critical systematic review. Nevertheless, the excellent paper of Nanseu-Njiki et al. [4] has largely considered the main cause of failures. The needed up-to-date review in this area would benefit from available three-decades-field experience on the vertical flow multi-soil-layering technology (MSL) for domestic wastewater treatment [18,19,20]. MSL systems use reactive beds containing 10 % Fe0 and have never experienced clogging. To sum up, this Special Issue is clearly filling a gap in knowledge on the Fe0/H2O system, but no papers were received for other important affordable technologies largely reported in the literature. There is, thus, scope for at least another Special Issue on these decentralized technologies in the near future.
Finally, special thanks are due to all the authors for accepting the call and to the publishers for their professional assistance at all stages.

Funding

This research received no external funding.

Acknowledgments

The manuscript was improved thanks to the insightful comments of anonymous reviewers from Water. The author acknowledges the support by the German Research Foundation and the Open Access Publication Funds of the Göttingen University.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. UN SDGs. Transforming Our World: The 2030 Agenda for Sustainable Development. Resolution Adopted by the UN General Assembly. 25 September 2015. Available online: https://sustainabledevelopment.un.org/post2015/transformingourworld 2015 (accessed on 5 December 2018).
  2. Banerji, T.; Kalawapudi, K.; Salana, S.; Vijay, R. Review of processes controlling Arsenic retention and release in soils and sediments of Bengal basin and suitable iron based technologies for its removal. Groundw. Sustain. Dev. 2018, 8, 358–367. [Google Scholar] [CrossRef]
  3. George, D.; Ahammed, M.M. Effect of zero-valent iron amendment on the performance of biosand filters. Water Supply 2019, 19. [Google Scholar] [CrossRef]
  4. Nanseu-Njiki, C.P.; Gwenzi, W.; Pengou, M.; Rahman, M.A.; Noubactep, C. Fe0/H2O filtration systems for decentralized safe drinking water: Where to from here? Water 2019, 11, 429. [Google Scholar] [CrossRef]
  5. Gonzalez-Perez, A.; Persson, K.M.; Lipnizki, F. Functional channel membranes for drinking water production. Water 2018, 10, 859. [Google Scholar] [CrossRef]
  6. Gheju, M. Progress in understanding the mechanism of CrVI removal in Fe0-based filtration systems. Water 2018, 10, 651. [Google Scholar] [CrossRef]
  7. Henderson, A.D.; Demond, A.H. Long-term performance of zero-valent iron permeable reactive barriers: A critical review. Environ. Eng. Sci. 2007, 24, 401–423. [Google Scholar] [CrossRef]
  8. Li, L.; Benson, C.H. Evaluation of five strategies to limit the impact of fouling in permeable reactive barriers. J. Hazard. Mater. 2010, 181, 170–180. [Google Scholar] [CrossRef] [PubMed]
  9. Guan, X.; Sun, Y.; Qin, H.; Li, J.; Lo, I.M.C.; He, D.; Dong, H. The limitations of applying zero-valent iron technology in contaminants sequestration and the corresponding countermeasures: The development in zero-valent iron technology in the last two decades (1994–2014). Water Res. 2015, 75, 224–248. [Google Scholar] [CrossRef] [PubMed]
  10. Hu, R.; Cui, X.; Gwenzi, W.; Wu, S.; Noubactep, C. Fe0/H2O systems for environmental remediation: The scientific history and future research directions. Water 2018, 10, 1739. [Google Scholar] [CrossRef]
  11. Noubactep, C. Aqueous contaminant removal by metallic iron: Is the paradigm shifting? Water SA 2011, 37, 419–426. [Google Scholar] [CrossRef]
  12. Noubactep, C. Flaws in the design of Fe(0)-based filtration systems? Chemosphere 2014, 117, 104–107. [Google Scholar] [CrossRef] [PubMed]
  13. Noubactep, C. Research on metallic iron for environmental remediation: Stopping growing sloppy science. Chemosphere 2016, 153, 528–530. [Google Scholar] [CrossRef] [PubMed]
  14. Hussam, A. Contending with a development disaster: SONO filters remove arsenic from well water in Bangladesh. Innovations 2009, 4, 89–102. [Google Scholar] [CrossRef]
  15. Banerji, T.; Chaudhari, S. A cost-effective technology for arsenic removal: Case study of zerovalent iron-based IIT Bombay arsenic filter in West Bengal. In Water and Sanitation in the New Millennium; Nath, K., Sharma, V., Eds.; Springer: New Delhi, India, 2017. [Google Scholar] [CrossRef]
  16. Ndé-Tchoupé, A.I.; Tepong-Tsindé, R.; Lufingo, M.; Pembe-Ali, Z.; Lugodisha, I.; Mureth, R.I.; Nkinda, M.; Marwa, J.; Gwenzi, W.; Mwamila, T.B.; et al. White teeth and healthy skeletons for all: The path to universal fluoride-free drinking water in Tanzania. Water 2019, 11, 131. [Google Scholar] [CrossRef]
  17. Marwa, J.; Lufingo, M.; Noubactep, C.; Machunda, R. Defeating fluorosis in the East African Rift Valley: Transforming the Kilimanjaro into a rainwater harvesting park. Sustainability 2018, 10, 4194. [Google Scholar] [CrossRef]
  18. Wakatsuki, T.; Esumi, H.; Omura, S. High performance and N, P removable on-site domestic wastewater treatment system by multi-soil-layering method. Water Sci. Technol. 1993, 27, 31–40. [Google Scholar] [CrossRef]
  19. Masunaga, T.; Sato, K.; Zennami, T.; Fujii, S.; Wakatsuki, T. Direct treatment of polluted river water by the multi-soil-layering method. J. Water Environ. Technol. 2003, 1, 97–104. [Google Scholar] [CrossRef]
  20. Latrach, L.; Ouazzani, N.; Hejjaj, A.; Mahi, M.; Masunaga, T.; Mandi, L. Two-stage vertical flow multi-soil-layering (MSL) technology for efficient removal of coliforms and human pathogens from domestic wastewater in rural areas under arid climate. Int. J. Hyg. Environ. Health 2018, 22, 64–80. [Google Scholar] [CrossRef] [PubMed]

Share and Cite

MDPI and ACS Style

Noubactep, C. Editorial for the Special Issue: Filters in Drinking Water Treatment. Water 2019, 11, 522. https://doi.org/10.3390/w11030522

AMA Style

Noubactep C. Editorial for the Special Issue: Filters in Drinking Water Treatment. Water. 2019; 11(3):522. https://doi.org/10.3390/w11030522

Chicago/Turabian Style

Noubactep, Chicgoua. 2019. "Editorial for the Special Issue: Filters in Drinking Water Treatment" Water 11, no. 3: 522. https://doi.org/10.3390/w11030522

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop