JOURNAL OF WATER TECHNOLOGY AND TREATMENT METHODS (ISSN: 2517-7427)

The use of metallic iron (Fe⁰ ) for environmental remediation is applied industrially with a great degree of empiricism. Rules of thumb seem to be the only guide followed by the greater part of the Fe⁰ remediation community. The present communication demonstrates the validity of such a harsh statement and hopes that the research community will now follow the 10-year-old path concealing Fe⁰ remediation and mainstream science. A promising application is safe drinking water provision on a decentralized manner. 

Environmental remediation; Frugal technology; Safe drinking water; Zero-valent iron. 

The use of metallic iron (Fe⁰ ) in water treatment was established in the second half of the nineteenth century [1-4]. Related investigations cleared up the nature of Fe⁰ as coagulant-inducing agent both in the Bischof Process (packed-bed filtration) and in the Anderson Process (fluidized bed-like) [1,4-9]. During the past three decades, sophisticated scientific methods have been used to produce a confused mass of discordant and mostly unfounded individual opinions [10-12] demonstrating that Fe⁰ might be an environmental reducing agent [8,9,13-33]. This fact alone explains the absolute empiricism which thus far has dominated and still dominates research and field application of Fe⁰ for environmental remediation and water treatment. The theory of reducing Fe0 was proven false one decade ago [34-37]. In the meantime, new scientific data from systematic and rigorous studies on the Fe⁰ /H₂ O system have been presented [12,31,32,38-46].

Contaminant removal in Fe⁰ /H₂ O systems was wrongly assumed to be an electrochemical process wherein Fe⁰ is oxidatively dissolved and the contaminant is simultaneously reduced (cathodic reaction) [25,46]. This mechanism has never been scientifically demonstrated nor univocally accepted [34]. The first mistake was the absence of a mass balance of iron coupled to the incomplete mass balance of the contaminants [11,12,47,48]. In fact, nonrecovered original species (contaminants) were considered reductively transformed [12,35,43,44,49]. It was properly considered that aqueous iron corrosion produces Fe hydroxides (and oxides) ‘passivating’ the reactive surface of Fe⁰ (reactivity loss). However, two important facts were overseen: (i) water is the solvent meaning that hydroxide generation is quantitative, and (ii) quantitative hydroxide availability implies coagulation (Anderson Process). Accordingly, a real mass balance of any contaminant should go through reductive dissolution of hydroxides/oxides (e.g. sequential extraction) to liberate the ‘coagulated’ fraction [50,51]. The other aspect of in-situ generation of iron hydroxides (and oxides) is that they are larger in volume than their parent (Fe⁰ ), meaning that the initial porosity of a packed bed containing Fe⁰ will be progressively filled. This is the first cause of permeability loss in porous and permeable media [52-54]. It is essential to recall that all these fundamental aspects were documented in the scientific literature before the advent for Fe0 reactive walls in the 1990s (Tab. 1) [11,12, 33]

Even though recent results [52] have confirmed the reasonableness of the hypothesis of foreign mineral precipitates as major cause of permeability loss [55], yet the opinion continued to exist that mixing granular Fe⁰ and other aggregates including sand is a tool to save Fe⁰ costs. Such an opinion, which has in some respects been confirmed scientifically, gave rise to an immense number of attempts to improve the efficiency of nano-scale Fe⁰ . However, these attempts had as their exclusive object the identification of suitable materials to disperse nano-Fe⁰ for the reductive transformation of contaminants. The research on using nano-Fe⁰ for environmental remediation is still conducted along exclusively empirical lines [56-58]. 

The whole research on Fe⁰ for water remediation is merely a question of obtaining maximum contaminant removal in minimum time [11,12,36,37,59]. This approach has mediated the development of multi-metallic systems and nano-Fe⁰ but is questionable because material selection should be based on site specific conditions. In particular, the solution of each individual problem requires precise knowledge including the flux of contaminants and the solution chemistry [33,60-65]. Based on such knowledge and the intrinsic reactivity of Fe⁰ materials, the most suitable material should be selected for designing the water treatment plant (after pilot testing). Despite three decades of intensive research, there is no unified tool to assess the suitability of available Fe0 materials [66-70].

The complexity of the Fe⁰ /H₂ O system has been used to justify or explain why innumerable attempts made during the past 30 years to improve this remediation technology have not been really successful. Coming to the last decade [11,12,34,35,38-40,43,71], however, it is seen that investigations following a truly scientific direction is possible and even successful (Table 1). The alternative approach furnishes a sure means for determining rapidly a large number of operating parameters, such as the Fe⁰ /sand ratio [72,73] the depth of the reactive zone, the selectivity of the system [74-76], the suitability of other aggregates [67,77,78] which are essential for pilot testing the Fe⁰ remediation technology for (i) safe drinking water provision, (ii) wastewater treatment and (iii) environmental remediation.

The next section recalls the nature of the Fe⁰ /H₂ O system to demonstrate that successful system design is possible despite confusing literature report. 

Iron corrosion produces iron oxides and hydroxides that are larger in size than iron atoms (Fe0 ) in the lattice system (V_oxide > V_iron) [79-81]. This evidence means that the volumetric expansive nature of iron corrosion should be considered wherever Fe⁰ oxidative dissolution is likely to produce iron oxides/hydroxides. This is when the final pH value is larger than 4.5 [44]. This volumetric expansion should be considered before any other source of clogging is discussed. For ex-situ applications of Fe⁰ filters, appropriate pre-treatment can totally eliminate all other sources of pore filling.

In cementation using Fe⁰ , the operations take place at lower pH values (pH < 4.0) and there is less or no oxide accumulation [82]. The excess iron consumption is commonly given to characterize the efficiency of the system (1). Clearly, in the cementation reaction the mass balance of the metal ions to be removed (e.g. Cr^VI, Cu^II, Pb^II) and that of iron are given to assess the system efficiency. For Pb removal for example, it is preferable that the Pb concentration of wastewater is low, to avoid clogging (permeability loss) due to the replacement of Fe by larger Pb in the filters. As discussed is section 1, not considering the iron mass balance has been a brake for the development of Fe0 filters.

Once the mass balance for both iron (Fe⁰ , soluble Fe^II/Fe^III and precipitates) and contaminants is properly considered, the mechanism of decontamination can be addressed. At pH > 4.5, hydroxide precipitation is quantitative and contaminant co-precipitation unavoidable [34,35,83,84]. The Fe⁰ surface is shielded by an oxide scale which is positively charged [85]. Negatively charged species are preferentially adsorbed but all contaminants are accumulated in the porous system by size-exclusion. Adsorption, co-precipitation and size-exclusion are thus the fundamental mechanisms of contaminant removal in Fe⁰ /H₂ O systems [34,35,37,59,86]. The remaining question to answer before designing sustainable is the following: What is the rate of generation of iron hydroxides/oxides? In other words, what is the intrinsic reactivity of the Fe0 material to be used? The time-dependent changes of its dissolution kinetics is implicitly considered [32]. 

Fe⁰ materials relevant for water treatment are a large array of metallic materials having in common a high amount of iron (E⁰ (Fe^II/ Fe⁰ ) = -0.44 V) in their elemental composition: mostly cast iron and low alloyed steel. Fe0 materials differ in their:

i. Crystallinity, bulk density and porosity (granular, foam, filamentous, sponge)

ii. Conventional application (iron foam, iron nails, scrap iron, steel wire, steel wool)

iii. Particle size (mm, μm and nm)

iv. Particle shape (filings, plates, shavings, spheres) [11].

It has been demonstrated that none of the chemical or physical characteristics alone can enable the assessment of the intrinsic reactivity [67,68,70,87-91]. Moreover, experiments for characterizing the Fe⁰ intrinsic reactivity should last for several weeks [92].

A central question that should be scientifically answered before engineers can accurately select appropriate Fe⁰ materials for a specific application is the characterization of the intrinsic reactivity and its time-dependent changes. Again, information on elemental composition, particle morphology and size, and surface area are not really helpful in characterizing the reactivity [67-70,88,90]. In essence, the intrinsic reactivity is a characteristic of each material and cannot be measured, but just assessed by appropriate procedures. In fact, the efficiency of Fe⁰ for any specific application is a complex cause-and-effect relationship between a large number of operational parameters, including

i. Fe⁰ reactivity

ii. Mode of generation and long-term permeability of oxide scales on Fe⁰

iii. Solution chemistry

iv. Proportion of Fe⁰ in the reactive zone

v. Thickness of the reactive zone

There is currently no standard method to characterize the intrinsic reactivity of Fe⁰ and thus facilitate material selection [67,68,70,90] Btatkeu-K and colleagues have summarized the most applicable methods that are additionally frugal in nature [78]. They are contaminant independent as they directly characterize Fe⁰ dissolution (EDTA test) or indirectly the extent of Fe hydroxide generation (MB test). These two tests are regarded as the cornerstone on which the design of Fe⁰ filters for safe drinking water provision will be built. The EDTA test evaluates the chemical reactivity of Fe0 materials as the extent of iron dissolution in a diluted solution of ethylenediaminetetraacetate (e.g. 2 mM). The suitability of methylene blue (MB) to characterize the intrinsic reactivity of Fe⁰ materials arises mainly from the historical observation by [93] that iron oxide coated sand exhibits a very low adsorptive affinity for MB. Accordingly, using MB is a powerful tool to comparatively characterize the extent of iron oxide generation by various Fe⁰ materials or the same material under various operational conditions.

Providing the whole world with safe drinking water is challenging because efficient, affordable and transferable water treatment systems should be developed and made available at the smallest scale and in decentralized manner [94-115]. With the information given herein, designing a sustainable Fe⁰ /sand filter for a household or a small community becomes a simple routine exercise similar to the one used in designing cementation beds (e.g. for lead removal) [116,162]. Here, there is an excess iron consumption but there is no need to quantify it. Rather the dissolved iron in the effluent should be measured to assess/decide whether further units for iron removal are needed [49,117,118]. Experiments should be performed for (i) beds packed with different available materials (including the same in different particle sizes), (ii) beds of different lengths (e.g. identical columns in series), and (iii) at different flow conditions. The experimental data should be compared by means of the efficiency of decontamination, the pH value, electric conductivity, the iron breakthrough and changes in the hydraulic conductivity. Such tests should use well-characterized real world samples or natural-near waters (e.g. tap water) artificially contaminated with relevant species (e.g. As, F, U).

If such systematic experiments are performed in several laboratories across the world, Fe⁰ will soon be the savior of several communities still lacking safe drinking water while waiting for their governments to bring along appropriate solutions. The next section present ways to test Fe0 filters for water defluoridation (F- removal).

The African Great Rift Valley accommodates the world’s most severe fluoride belt [29,119-122]. Here, fluoride mitigation by means of alum (Nalgonda technique) has been used, with limited success since the 1980s [121]. In recent years, packed-bed adsorption of columns filled with bone char have been more successfully implemented for water defluoridation [121,123-125]. This adsorption technique is currently the process of choice for fluoride mitigation in Ethiopia, Kenya and Tanzania [121]. Despite some real progress, none of the countries has approached universal access to safe drinking water. However the good news is that proven designs are made available that could be modified to supply both households and small communities with safe drinking water. Larger communities can be supplied with several small modules operating in series [118].

Figure 1 schematically presents a household bone char filter for defluoridation, as commercially available in the Arusha region in Tanzania. Such filters were disseminated to about 2000 families [121]. Dahi [121] also reported on the development and implementation of about 20 different types of larger bone char filters, mainly for use in schools and other institutions (Fig. 2). The drum type filters [126] are easy to recharge and are recommended for pilot testing Fe⁰ filters. Upon successful testing, field water treatment plants can use more robust cement tanks [121,125]. 

Testing Fe⁰ filters for defluoridation at household (Fig. 1) or at small community (Fig. 2) levels is regarded as a continuation of previous works on the wide field of filtration technology for drinking water and sanitation [49,71,86,89,98-100,114,117,121,125,127,128]. The exceptional stability of fluoride in aqueous solution [129,130] implies that larger depths of Fe0 layers (e.g. several columns in series) will likely be necessary to achieve the treatment goal (e.g. ≤1.5 mg/L for drinking water). The particular properties of Fe⁰ aqueous corrosion imply that sustainable filters operate under anoxic conditions [53,54]. Thus, either a Slow Sand Filter (SSF) is used and the operational flow rate is that of a conventional SSF, or the Fe0 filters are preceded with one or several O₂ scavenging units. Fe⁰ itself is a powerful O2 scavenger [131]. However, while using Fe⁰ as O₂ scavenger, care must be taken to avoid that preferential flow created within the scavenger unit don’t disturb the flow regime in the effective Fe⁰ filters.

In testing Fe⁰ filters for water defluoridation, a special attention is due to the presence of anions, such as Cl- , CO₃ ²-/HCO3 - , NO₃ - , PO₄ ^3- and SO₄ ^2-, as well as natural organic matter [36,59,125]. However, only the concentration range relevant to field situations should be investigated. Ideally, relevant natural waters should be used and artificially contaminated with F- (and other relevant contaminants). As stated in section 3, the Fe⁰ /H₂ O is very complex and no single solute has a unique mode of impact on the system. For example, Cl- is known to enhance corrosion because soluble FeCl₂ /FeCl₃ is generated. Accordingly, if the presence of Cl- is coupled with a relative high flow velocity, generated FeCl₂ /FeCl₃ can be transported out of the system without having time to precipitate. This does not mean that Fe0 filters is not fundamentally efficient or that iron corrosion is not enhanced. It suffices to reduce the flow velocity (increase residence time) to achieve better results.

Another fundamental aspect is the used Fe0 material. Porous Fe⁰ materials have been shown more efficient than compact ones in Fe0 filters [5,89,91,99,132]. In essence, a porous Fe⁰ is a continuous network of metal co-existing with a network of interconnected voids. The metal is less dense and could be depleted under field conditions. The more the metal is compact the more uncertain is it long-term corrosion behavior. Another important tool that has been used to modify the efficiency (not the reactivity) of Fe⁰ / H₂ O systems is alloying [27,41,43,55]. In the context of fluoride removal using electro coagulation, Al-alloyed have shown better efficiency that Fe electrodes [133]. The similitude of both processes [36,37,134-136] suggests that Al-alloyed materials will be better for fluoride mitigation [137,138]. Coincidentally, such materials have already been developed and used for other contaminants including pathogens [134,135,139,140]. It can be postulated, that one efficient group of materials for Fe⁰ filters is an Al-alloyed sponge Fe⁰ . Ideally, such a material is comparable to sand in its bulk density (2.5 to 3.0 cm3 /g) to facilitate homogenous mixture to build the reactive zone. As regarding the pH value, natural waters (6.0 ≥ pH ≤ 8.5) correspond to the range of minimal Fe solubility [44]. This is the major property making Fe⁰ a remediation agent [34,35,43,72]. Wherever necessary, starting water treatment at slightly acidic pH values (e.g. pH 4.0 to 4.5) should be investigated because Fe⁰ has the inherent property to enhance the pH value through aqueous corrosion. For small community treatment plants, further filtration through pH-enhancing units (e.g. CaCO₃ or CaMg(CO₃ )2 ) could be envisaged.

Figure 3 gives the general treatment train involving Fe⁰ filters. A slow sand filter (SSF) would eliminate pathogens and lower the dissolved O₂ level. A second filter (e.g. biochar) would serve as pre-treatment for the Fe⁰ filter. Excess Fe from the Fe⁰ filter can be scavenged by a second SSF or a wood charcoal filter. Where necessary, each type of filter can be made up of several filters in series.

The bone char technology has been adopted in Tanzania, Kenya, and Ethiopia due to its superiority in comparison with the Nalgonda technique [121]. However, the process costs of the bone char technology are still too high to be affordable by the low income population. Moreover, self-reliance in operation and maintenance, essential for the technology sustainability, are yet to be secured. On the other hand, the bone char has an inbuilt limitation in treating waters with high bicarbonate levels [121,125]. These limitations are the key points on which testing Fe⁰ filters will insist.

As clearly discussed elsewhere [49] it is difficult to reliably assess the costs of Fe⁰ filters. There are at least three reasons for this:

i. There is no reference Fe⁰ material to which available or new materials could be compared

ii. The efficiency of Fe⁰ filters is contaminant- and site-specific

iii. The technology is not yet developed to the point where comparison of independent data is possible. Nevertheless, because Fe⁰ filters are using the same construction materials like other filtration techniques, while using sand and readily available (and mostly affordable) Fe⁰ materials like iron nails, steel wire or steel wool, it is expected that efficient Fe⁰ filters will be more affordable than existing filters [79,105,108,141,142]. Two other key points support the likely affordability of Fe⁰ filters:

1. The local availability of the technology of iron making [143]

2. The recyclable nature of filter materials (iron oxides). Iron oxides are the main raw materials of iron making [49].

Despite the lack of a sound comparison basis, the Fe0 filtration technology is generally perceived and presented as an affordable technology for low-income communities [21,22,98,99,144- 149].

Available information about Fe⁰ filter design is insufficient and not organized [9,25,31,32,42,44,46,57,150,151]. A number of previous studies have identified major design flaws [11,25,46] and presented some paths to the next generation efficient and sustainable Fe⁰ filters [31,37,49,52,53,71,73,76,86,89,117,118,152,154,155]. There is no doubt on the fundamental appropriateness of Fe⁰ filters for safe drinking water provision (and sanitation) [49,153]. Here are just four examples to corroborate the evidence that the open issue is a proper design [31,49,71,152]:

1. Fe⁰ filters (containing spongy iron) were efficient at household level before 1881 and were successfully tested at the water works of Antwerpen (Belgium). They were efficient for 18 months without any maintenance [3,8,9].

2. Fe⁰ filters (containing steel wool) were efficient at removing radioactive contaminants from waters. Simple filters were designed for two weeks [144]. This can be used as starting point for further investigations [10,117].

3. Fe⁰ filters (containing iron filings) were very efficient at removing selenium and several other toxic species from agricultural wastewaters [145]. These filters were not sustainable as they contained 100 % Fe0 in their reactive zones [11]. In other words, using hybrid systems (e.g. Fe0 /sand) would have yielded more sustainable systems [10,52-54,72,73,156].

4. Fe⁰ filters (containing iron nails) were very efficient at removing arsenic and other toxic species from drinking water mostly in Nepal [98].

Researchers are encouraged to long-term pilot test Fe⁰ filters. Ideally, the first design and implementation should be supervised by scientists. Fe⁰ materials should be routinely characterized unless a patented own material is used. In all the cases the efficiency of the systems should be analytically documented [117,157]. It would be beneficial, if the results are made available to a broader audience [158]. It is certain, that Fe⁰ alone can solve the long lasting universal crisis of shortage in safe drinking water provision in low-income communities [159,160]. However, combination with other affordable technologies have been recommended [31,144,161,162].

Thanks are due to Mohammad A. Rahman (Leibniz Universität Hannover/Germany) for his valuable advice. Marius Gheju (Politehnica University of Timisoara, Romania) has proof-read the manuscript. The manuscript was improved by the insightful comments of anonymous reviewers on a previous version. We acknowledge support by the German Research Foundation and the Open Access Publication Funds of the Göttingen University.

1. Nichols WR. Water Supply, considered mainly from a chemical and sanitary standpoint. New York (NY): John Wiley & Sons. 1883.
2. Slater JW. Sewage treatment purification and utilization. London/New York: Whittaker & Co.1888;pp:320.
3. Devonshire E. The purification of water by means of metallic iron. J Frankl Inst. 1890 Jul;25(248):449–461.
4. Baker MN. Sketch of the history of water treatment. Journal American Water Works Association.1934 Jul;26(7):902–938.
5. Bischof G. On putrescent organic matter in potable water. Proc R Soc Lond. 1877;26:152-156.
6. Anderson W. On the purification of water by agitation with iron and by sand filtration. Journal of the Society for Arts. 1886 Nov;35(1775):29–38.
7. Van Craenenbroeck W. Easton & Anderson and the water supply of Antwerp (Belgium). Ind Archaeol Revi. 1998 Jul;20(1):105– 116.
8. Mwakabona HT, Nde-Tchoupe AI, Njau KN, Noubactep C, Wydra KD. Metallic iron for safe drinking water provision: Considering a lost knowledge. Water Res. 2017 Jun;117:127–142.
9. Noubactep C. Metallic iron for water treatment: Lost science in the West. Bioenergetics. 2017Mar;6:149.
10. Makota S, Nde-Tchoupe AI, Mwakabona HT, Tepong-Tsinde R, Noubactep C, et al. Metallic iron for water treatment: Leaving the valley of confusion. Appl Water Sci Mehta. 2017 Dec;7(8):4177- 1496.
11. Noubactep C, Makota S, Bandyopadhyay A. Rescuing Fe0 remediation research from its systemic flaws. Res Rev Insights. 2017 Nov;1.
12. Noubactep C. Metallic iron for environmental remediation: How experts maintain a comfortable status quo. Fresenius Environmental Bulletin. 2017.
13. O´Hannesin SF, Gillham RW. Long-term performance of an in situ “iron wall” for remediation of VOCs. Ground Water. 1998 Jan;36(1):164–170.
14. Bigg T, Judd SJ. Zero-valent iron for water treatment. Environ. Technol. 2010 May;21(6):661–670.15. Scherer MM, Richter S, Valentine RL, Alvarez PJJ. Chemistry and Microbiology of Permeable Reactive Barriers for In Situ Groundwater Clean up. Crit Rev Environ Sci Technol. 2000 Jun;30(3):363–411.
15. Tratnyek PG, Scherer MM, Johnson TL, Matheson LJ. Permeable reactive barriers of iron and other zero-valent metals. Environmental Science and Pollution Control Series, 26 (Chemical Degradation Methods for Wastes and Pollutants). 2003 Jan;371-421. 
16. Henderson AD, Demond AH. Long-term performance of zerovalent iron permeable reactive barriers: a critical review. Environ Eng Sci. 2007 Apr;24:401–423.
17. Cundy AB, Hopkinson L, Whitby RLD. Use of iron-based technologies in contaminated land and groundwater remediation: A review. Sci Tot Environ. 2008 Aug;400(1-3):42– 51.
18. Gillham RW. Development of the granular iron permeable reactive barrier technology (good science or good fortune). I: Y. Chen, X. Tang, L. Zhan, editors. Advances in environmental geotechnics: proceedings of the International Symposium on Geoenvironmental Engineering; 2007 September 8-10; Hangzhou, China. Berlin/London, Springer. 2008:p. 5–15.
19. Thiruvenkatachari R, Vigneswaran S, Naidu R. Permeable reactive barrier for groundwater remediation. J Ind Eng Chem. 2008 Mar;14(2):145–156.
20. Thiruvenkatachari R, Vigneswaran S, Naidu R. Permeable reactive barrier for groundwater remediation. J Ind Eng Chem. 2008 Mar;14(2):145–156.
21. Li L, Benson CH. Evaluation of five strategies to limit the impact of fouling in permeable reactive barriers. J Hazard Mater. 2010 Sep;181(1-3):170–180.
22. Comba S, Di Molfetta A, Sethi R. A Comparison between field applications of nano-, micro-, and millimetric zero-valent iron for the remediation of contaminated aquifers. Water Air Soil Pollut. 2011 Feb;215(1-4):595–607.
23. Fu F, Dionysiou DD, Liu H. The use of zero-valent iron for groundwater remediation and wastewater treatment: A review. J Hazard. Mater. 2014 Feb;267:194–205.
24. Noubactep C. Flaws in the design of Fe0 -based filtration systems? Chemosphere. 2014a Dec;117:104–107.
25. Obiri-Nyarko F, Grajales-Mesa SJ, Malina G. An overview of permeable reactive barriers for in situ sustainable groundwater remediation. Chemosphere. 2014 Sep;111:243–259.
26. Guan X, Sun Y, Qin H, Li J, Lo IMC, et al. The limitations of applying zero-valent iron technology in contaminants sequestration and the corresponding countermeasures: The development in zerovalent iron technology in the last two decades (1994–2014). Water Res. 2015 May;75:224–248.
27. Noubactep C. Metallic iron for environmental remediation: A review of reviews. Water Research. 2015Nov; 85:114–123.
28. Santisukkasaem U, Olawuyi F, Oye P, Das DB. Artificial Neural Network (ANN) for evaluating permeability decline in permeable reactive barrier (PRB). Environ Process. 2015 June;2(2):291–307.
29. Warner SD. Two Decades of Application of Permeable Reactive Barriers to Groundwater Remediation. In: R Naidu and V Birke, Editors. Permeable Reactive Barrier Sustainable Groundwater Remediation. CRC Press. 2015:25–39.
30. Noubactep C. Designing metallic iron packed-beds for water treatment: A critical review. CLEAN - Soil, Air, Water. 2016a April; 44(4):411–421.
31. Noubactep C. Predicting the hydraulic conductivity of metallic iron filters: Modeling gone astray. Water. 2016b;8(4):162.
32. Zhang X, Li J, Sun Y, Li L, Pan B, Zhang W, et al. Aging of zerovalent iron in various coexisting solutes: Characteristics, reactivity toward selenite and rejuvenation by weak magnetic field. Sep Purif Technol. 2018 Jan;191:94–100.
33. Noubactep C. Processes of contaminant removal in “Fe⁰ –H₂ O” systems revisited. The importance of co-precipitation. Open Environ Sci. 2007;1: 9–13
34. Noubactep C. A critical review on the mechanism of contaminant removal in Fe⁰ –H₂ O systems. Environ Technol. 2008 Aug;29(8):909-920
35. Noubactep C. Metallic iron for safe drinking water worldwide. Chem Eng J. 2010a Dec;165(2) 740–749
36. Noubactep C. Metallic iron for safe drinking water production. Freiberg Online Geoscience. 2011b;27:38
37. Antia DDJ. Sustainable Zero-Valent Metal (ZVM) water treatment associated with diffusion, infiltration, abstraction and recirculation. Sustainability. 2010 Aug;2(9):2988–3073.
38. Ghauch A, Abou Assi H, Bdeir S. Aqueous removal of diclofenac by plating elemental iron: Bimetallic systems. J Hazard Mater. 2010 Oct;182:64–74.
39. Antia DDJ. Modification of aquifer pore-water by static diffusion using nano-zero-valent metals. Water. 2011 Jan;3:79–112.
40. Ghauch A, Abou Assi H, Baydoun H, Tuqan AM, Bejjani A. Fe0 -based trimetallic systems for the removal of aqueous diclofenac: Mechanism and kinetics. Chem Eng J. 2011 August;172(2-3):1033–1044.
41. Gheju M. Hexavalent chromium reduction with zero-valent iron (ZVI) in aquatic systems. Water Air Soil Pollut. 2011 Apr;222(1- 4):103–148.
42. Gheju M, Balcu I. Removal of chromium from Cr(VI) polluted wastewaters by reduction with scrap iron and subsequent precipitation of resulted cations. J Hazard Mater. 2011 Nov; 196:131–138.
43. Ghauch A. Iron-based metallic systems: An excellent choice for sustainable water treatment. FOG. 2015;38:1-80.
44. Gatcha-Bandjun N, Noubactep C, Loura Mbenguela B. Mitigation of contamination in effluents by metallic iron: The role of iron corrosion products. Environ Technol Innov. 2017 June;8:71–83.
45. Noubactep C. Research on metallic iron for environmental remediation: Stopping growing sloppy science. Chemosphere. 2016c June;153:528-530.
46. Lavine BK, Auslander G, Ritter J. Polarographic studies of zero valent iron as a reductant for remediation of nitroaromatics in the environment. Microchem J. 2001 Nov;70(2):69–83.
47. Lee G, Rho S, Jahng D. Design considerations for groundwater remediation using reduced metals. Korean J Chem Eng. 2003 Dec;219(3):621–628.
48. Naseri E, Nde-Tchoupe AI, Mwakabona HT, Nanseu-Njiki CP, Noubactep C et al. Making Fe0-based filters a universal solution for safe drinking water provision. Sustainability 2017 July;9(7):1224.
49. Noubactep C, Schöner A, Meinrath G. Mechanism of uranium removal from the aqueous solution by elemental iron. J Hazard Mater. 2006a May;132(2-3):202–212
50. Noubactep C, Schöner A, Dienemann H, Sauter M. Investigating the release of co-precipitated uranium from iron oxides. J Radioanal Nucl Chem. 2006b;267(1):21–27
51. Caré S, Crane R, Calabrò PS, Ghauch A, Temgoua E, et al. Modelling the permeability loss of metallic iron filtration systems for water treatment. Clean Soil Air Water. 2013 Mar;41(3):275–282.
52. Domga R, Togue-Kamga F, Noubactep C, Tchatchueng JB. Discussing porosity loss of Fe0 packed water filters at ground level. Chem Eng J. 2015 Mar;263:127–134.
53. Domga R, Togue-Kamga F, Tchatchueng JB. Mathematic analysis of porosity loss in granular metallic iron (Fe0 ) water filter. Int J Emerging Eng Res Technol. 5:28–35.
54. Henderson AD, Demond AH. Impact of solids formation and gas production on the permeability of ZVI PRBs. J Environ Eng. 2011 Mar;137(8):689–696.
55. Gillham RW. Discussion of Papers/Discussion of nano-scale iron for dehalogenation. In: Nyer EK, Vance D, editors. Ground Water Monitoring & Remediation. Wiley; New Jersey (NJ) 2003:p.21– 30.
56. Noubactep C, Caré S. On nanoscale metallic iron for groundwater remediation. J Hazard Mater. 2010a Oct;182(1-3):923–927 
57. Noubactep C, Caré S, Crane RA. Nanoscale metallic iron for environmental remediation: prospects and limitations. Water Air Soil Pollut. 2012a Mar;223(3):1363–1382
58. Noubactep C. Aqueous contaminant removal by metallic iron: Is the paradigm shifting? Water SA. 2011a;37(3):419–426
59. Morrison JS, Tripathi SV, Sprangler RR. Coupled reaction/ transport modeling of a chemical barrier for controlling uranium (VI) contamination in groudwater. Jour Contam Hydrol. 1995 Feb;17(4):347–363.
60. Morrison JS, Metzler RD, Carpenter CE. Uranium precipitation in a permeable reactive barrier by progressive irreversible dissolution of zerovalent iron. Environ Sci Technol. 2001 Nov;35(2):385–390.
61. Morrison S. Performance evaluation of a permeable reactive barrier using reaction products as tracers. Environ SciTechnol. 2003 Apr;37(10):2302–2309.
62. Morrison SJ, Carpenter CE, Metzler DR, Bartlett TR, Morris SA. Design and performance of a permeable reactive barrier for containment of U, As, Se, V, Mo, and NO3 , Monticello, Utah. In Handbook of groundwater remediation using permeable reactive barriers: Applications to radionuclides, trace metals and nutrients. Naftz D, Morrison SJ, Fuller CC, and Davis JA. (eds.), Academic Press, San Diego, Calif. Pp.539
63. Morrison SJ, Metzler DR, Dwyer BP. Removal of As, Mn, Mo, Se, U, V and Zn from groundwater by zero-valent iron in a passive treatment cell: reaction progress modeling. J Contam Hydrol. 2002 May;56(1-2):99–116.
64. Morrison SJ, Mushovic PS, Niesen PL. Early Breakthrough of Molybdenum and Uranium in a Permeable Reactive Barrier. Environ Sci Technol. 2006 Feb;40(6):2018–2024.
65. Noubactep C, Meinrath G, Dietrich P, Sauter M, Merkel B. Testing the suitability of zerovalent iron materials for reactive walls. Environ Chem. 2005;2:71–76
66. Btatkeu KBD, Miyajima K, Noubactep C, Caré S. Testing the suitability of metallic iron for environmental remediation: Discoloration of methylene blue in column studies. Chem Eng J. 2013 Jan;215-216:959–968.
67. Kim H, Yang H, Kim J. Standardization of the reducing power of zero-valent iron using iodine. J Environ Sci Heal. 2014;49(5):514–523.
68. Velimirovic M, Carniatoc L, Simons Q, Schoups G, Seuntjens P, et al. Corrosion rate estimations of microscale zerovalent iron particles via direct hydrogen production measurements. J Hazard Mater. 2014 Apr;270:18–26.
69. Li S, Ding Y, Wang W, Lei H. A facile method for determining the Fe(0) content and reactivity of zero valent iron. Anal Methods. 2016;8(6):1239–1248.
70. Noubactep C, Schöner A, Woafo P (2009a) Metallic iron filters for universal access to safe drinking water. Clean: Soil, Air, Water. 2009a Dec;37(12):930–937
71. Miyajima K. Optimizing the design of metallic iron filters for water treatment. FOG. 2012;32:107.
72. Miyajima K, Noubactep C. Impact of Fe0 amendment on methylene blue discoloration by sand columns. Chem Eng J. 2013 Feb;217:310–319.
73. Phukan M. Characterizing the Fe0 /sand system by the extent of dye discoloration. Freiberg Online Geoscience. 2015;40:70.
74. Phukan M, Noubactep C, Licha T. Characterizing the ion-selective nature of Fe0 -based filters using three azo dyes in batch systems. J Environ Chem Eng. 2016 Nov;4:65–72.
75. Phukan M, Noubactep C, Licha T. Characterizing the ionselective nature of Fe0 -based filters using azo dyes. Chem Eng J. (2015);259:481–491.
76. Btatkeu-K BD, Olvera-Vargas H, Tchatchueng JB, Noubactep C, et al. Characterizing the impact of MnO2 on the efficiency of Fe0 - based filtration systems. Chem Eng J. 2014 Aug;250:416–422.
77. Btatkeu-KBD, Tchatchueng JB, Noubactep C, Care S. Designing metallic iron based water filters: Light from methylene blue discoloration. J Environ Manage. 2016 Jan;166:567–573.
78. Erickson AJ, Gulliver JS, Weiss PT. Enhanced sand filtration for storm water phosphorus removal. J Environ Eng. 2007 May;133(5):485–497.
79. Holmes DR, Meadowcroft DB. Physical methods in corrosion technology. Phys Technol. 1977;8:2–9.
80. Lazzari L. General aspects of corrosion. Italy: 2008. 9.1, Istituto Enciclopedia Italiana. pp:485–505.
81. Noubactep C. Elemental metals for environmental remediation: Learning from cementation process. J Hazard Mater. 2010b Sep;181(1-3):1170–1174
82. Crawford RJ, Harding IH, Mainwaring DE. Adsorption and co precipitation of single heavy metal ions onto the hydrated oxides of iron and chromium. Langmuir. 1993a Nov;9(11):3050–3056.
83. Crawford RJ, Harding IH, Mainwaring DE. Adsorption and co precipitation of multiple heavy metal ions onto the hydrated oxides of iron and chromium. Langmuir. 1993b Nov;9(11):3057– 3062.
84. Sato N. Surface oxides affecting metallic corrosion. Corros Rev. 2001;19(3-4):253–272.
85. Noubactep C, Temgoua E, Rahman MA. Designing iron-amended biosand filters for decentralized safe drinking water provision. Clean: Soil, Air, Water. 2012b Aug;40(8):798–807
86. Reardon JE. Anaerobic corrosion of granular iron: Measurement and interpretation of hydrogen evolution rates. Environ Sci Technol. 1995 Dec;29(12):2936–2945.
87. Miehr R, Tratnyek GP, Bandstra ZJ, Scherer MM, Alowitz JM, et al. Diversity of contaminant reduction reactions by zerovalent iron: Role of the reductate. Environ Sci Technol. 2004;38(1):139–147.
88. Rahman MA, Karmakar S, Salama H, Gactha-Bandjun N, Btatkeu KBD, et al. Optimising the design of Fe0 -based filtration systems for water treatment: The suitability of porous iron composites. J Appl Solution Chem Modeling. 2013;2(3):165–177.
89. Birke V, Schuett C, Burmeier H, Friedrich HJ. Impact of trace elements and impurities in technical zero-valent iron brands on reductive dechlorination of chlorinated ethenes in groundwater. R Naidu and V Birke, editors. In Permeable Reactive Barrier Sustainable Groundwater Remediation. Boca Raton (FL): CRC Press. 2015:87–98.
90. Moraci N, Lelo D, Bilardi S, Calabro PS. Modelling long-term hydraulic conductivity behaviour of zero valent iron column tests for permeable reactive barrier design. Canadian Geotech J. 2016 Dec;53:946–961.
91. Noubactep C. Characterizing the reactivity of metallic iron in Fe0 /EDTA/H2 O systems with column experiments. Chem Eng J. 2010c Aug;162(2):656–661
92. Mitchell G, Poole p, Segrove HD. Adsorption of methylene blue by high-silica sands. Nature. 1955 Nov;176:1025–1026.
93. Khan AH, Rasul SB, Munir AKM, Habibuddowla M, Alauddin M, et al. Appraisal of a simple arsenic removal method for groundwater of bangladesh. J Environ Sci Health A. 2008 Dec;35(7):1021–1041.
94. Leupin OX, Hug SJ. Oxidation and removal of arsenic (III) from aerated groundwater by filtration through sand and zero-valent iron. Wat Res. 2005 May;39(9):1729–740.
95. Westerhoff P, James J. Nitrate removal in zero-valent iron packed columns. Water Res. 2003 Apr;37(8):1818–1830.
96. Leupin OX, Hug SJ, Badruzzaman ABM. Arsenic removal from Bangladesh tube well water with filter columns containing zerovalent iron filings and sand. Environ Sci Technol. 2009 Sep;39(20):8032–8037. 
97. Ngai TKK, Murcott S, Shrestha RR, Dangol B, Maharjan M. Development and dissemination of Kanchan™ Arsenic Filter in rural Nepal. Water Sci Technol Water Supply. 2006;6:137–146.
98. Hussam A, Munir AKM. A simple and effective arsenic filter based on composite iron matrix: Development and deployment studies for groundwater of Bangladesh. J Environ Sci Health A Tox Hazard Subst Environ Eng. 2007 Oct;42(12)1869–1878.
99. Chiew H, Sampson ML, Huch S Ken S, Bostick BC. Effect of groundwater iron and phosphate on the efficacy of arsenic removal by iron-amended biosand filters. Environ Sci Technol. 2009 Aug;43(16):6295–6300.
100. Tuladhar S, Smith LS. SONO filter: An excellent technology for save water in Nepal. SOPHEN. 2009;7:18–24.
101. Giles DE, Mohapatra M, Issa TB, Anand S, Singh P. Iron and aluminium based adsorption strategies for removing arsenic from water. J Environ Manage. 2011 Dec;92(12):3011–3022.
102. Avilés M, Garrido SE, Esteller MV, De La Paz JS, Najera C, et al. Removal of groundwater arsenic using a household filter with iron spikes and stainless steel. J Environ Manage. 2013 Dec;131:103–109.
103. Chiu PC. Applications of zero-valence iron (ZVI) and nanoscale ZVI to municipal and decentralized drinking water systems – A review. ACS Symposium Series. 1123:237-249.
104. Gottinger AM, McMartin DW, Wild DJ, Moldovan B. Integration of zero valent iron sand beds into biological treatment systems for uranium removal from drinking water wells in rural Canada. Can J Civ Eng. 2013 Jul;40(10):945–950.
105. Neumann A, Kaegi R, Voegelin A, Hussam A, Munir AKM et al. Arsenic removal with composite iron matrix filters in Bangladesh: A field and laboratory study. Environ Sci Technol. 2013 Apr;47(9):4544–4554.
106. Chaudhari S, Banerji T, Kumar PR. Domestic-and communityscale arsenic removal technologies suitable for developing countries. Water Reclamation and Sustainability. Elsevier. Boston. 2014;p:155–182.
107. Kowalski K. New method for arsenic compounds elimination from naturally contaminated drinking water systems. [Ph.D. Thesis]. (DK): Aalborg University of Esberg at Denmark. 2014.
108. Kowalski KP, Sogaard EG. Implementation of zero-valent iron (ZVI) into drinking water supply – Role of the ZVI and biological processes. Chemosphere. 2014 Dec;117:108–114.
109. Wenk CB, Kaegi R, Hug SJ. Factors affecting arsenic and uranium removal with zero-valent iron: laboratory tests with Kanchantype iron nail filter columns with different groundwaters. Environ Chem. 2014 Jan;11(5):547–557.
110. Mehta VS, Chaudhari SK. Arsenic removal from simulated groundwater using household filter columns containing iron filings and sand. J Water Process Eng. 2015 June;6:151-157.
111. Nitzsche KS, Lan VM, Trang PTK, Viet PH, Berg M, et al. Arsenic removal from drinking water by a household sand filter in Vietnam – Effect of filter usage practices on arsenic removal efficiency and microbiological water quality. Sci Total Environ. 2015 Jan;502:526–536.
112. Trois C, Cibati A. South African sands as a low cost alternative solution for arsenic removal from industrial effluents in permeable reactive barriers: Column tests. Chem Eng J. 2015 Jan;259:981–989.
113. Feistel U, Otter P, Kunz S, Grischek T, Feller J. Field tests of a small pilot plant for the removal of arsenic ingroundwater using coagulation and filtering. J Water Process Eng. 2016 Dec;14:77– 85.
114. Sharma S, Bhattacharya A. Drinking water contamination and treatment techniques. Appl Water Sci. 2017 Jun;7(3):1043- 1067.
115. Agelidis T, Fytianos K, Vasilikiotis G, Jannakoudakis D. Lead removal from wastewater by cementation utilising a fixed bed of iron spheres. Environ. Pollut. 1988;50(3):243–251.
116. Nde-Tchoupe AI, Crane RA, Hezron T. Mwakabona, Noubactep C et al. Technologies for decentralized fluoride removal: Testing metallic iron based filters. Water 2015;7(12):6750–6774.
117. Tepong-Tsindé R, Crane R, Noubactep C, Nassi A, Ruppert H. Testing metallic iron filtration systems for decentralized water treatment at pilot scale. Water. 2015 Mar;7(3):868–897.
118. Nanyaro JT, Aswathanarayana U, Mungure JS, Lahermo PW. A geochemical model for the abnormal fluoride concentrations in waters in parts of northern Tanzania. J African Earth Sci. 1984;2(2):129–140.
119. Mjengera H, Mkongo G. Appropriate defluorifation technology for use in fluoritic areas in Tanzania. Phys Chem Earth. 2003;28(20-27):1097–1104.
120. Dahi E. Africa’s U-Turn in defluoridation policy: from the Nalgonda technique to bone char. ISFR. 2016 Dec;401-416.
121. Millar GJ, Couperthwaite SJ, Dawes LA, Thompson S, Spencer J, et al. Activated alumina for the removal of fluoride ions from high alkalinity groundwater: New insights from equilibrium and column studies with multicomponent solutions. Sep Purif Technol. 2017 Oct;187:14–24.
122. WHO iris: Fluoride in drinking water [internet] London: IWA Publishing on behalf of the World Health Organization (WHO). 2006. Available from http://apps.who.int/iris/ handle/10665/43514
123. Sorlini S, Pedrazzani R, Palazzini D, Collivignarelli MC. Drinking water quality change from catchment to consumer in the rural community of Patar (Senegal). Water Qual Expo Health. 2013 Mar;5(2):75–83.
124. Wong E. Onsite defluoridation systems for drinking water production. PhD Dissertation, Civil Engineering, University of California. 2017:130.
125. Kearns J. Sustainable decentralized water treatment for rural and developing communities using locally generated biochar adsorbents. Water Conditioning and Purification International. October 24, 2012. Available from: http://www.wcponline. com/2012/10/24/sustainable-decentralized-water-treatmentfor-rural-and-developing-communities-using-locallygenerated-biochar-adsorbents/
126. Shannon MA, Bohn PW, Elimelech M, Georgiadis JG, Marinas BJ, et al. Science and technology for water purification in the coming decades. Nature. 2008 Mar;452(7185):301–310.
127. Ali I. Treatment by adsorption columns: Evaluation at ground level. Sep Purif Rev. 2014 Feb;43(3):175–205.
128. Velizarov S, Crespo J, Reis M. Removal of inorganic anions from drinking water supplies by membrane bio/process. Rev Environ Sci Biotechnol. 2004 Dec;3(4):361–380.
129. Chubar NI, Samanidou VF, Kouts VS, Gallios GG, Kanibolotsky VA, et al. Adsorption of fluoride, chloride, bromide, and bromate ions on a novel ion exchanger. J Colloid Interface Sci. 2005 Nov;291(1):67–74.
130. Xu B, Jia M, Men J. Preparation of modified sponge iron and kinetics of deoxygenization by it. Arab J Sci Eng. 2013 Dec;38(12):3259–3266.
131. Hussam A. Contending with a Development Disaster: SONO Filters Remove Arsenic from Well Water in Bangladesh. Innovations. 2009 Oct;4(3)89–102.
132. Liu S, Ye X, He K, Chen Y, Hu Y. Simultaneous removal of Ni(II) and fluoride from a real flue gas desulfurization wastewater by electrocoagulation using Fe/C/Al electrode. Journal of Water Reuse and Desalination. 2016 June;7(4):288–297. 
133. Bojic ALj, Bojic D, Andjelkovic T. Removal of Cu2+ and Zn2+ from model wastewaters by spontaneous reduction–coagulation process in flow conditions. J Hazard Mater. 2009 May;168(2- 3):813–819.
134. Bojic ALj, Purenovic M, Bojic D, Andjelkovic T. Dehalogenation of trihalomethanes by micro-alloyed aluminium composite under flow conditions. Water SA. 2007 Apr;33(2):297–304.
135. Noubactep C, Schöner A. Metallic iron for environmental remediation: Learning from electrocoagulation. J Hazard Mater. 2010a Mar;175(1-3):1075-1080
136. Twidwell L, Mc Closkey J, Joyce H, Dahlgren E, Hadden A. Removal of selenium oxyanions from mine waters utilizing elemental iron and galvanically coupled metals. In: Cea, Young Editor. Innovations in Natural Resoure Processing — Proceedings of the Jan. D. Miller Symposium, SME;2005/Mar/ ;
137. Twidwell LG, McCloskey JW. Removing arsenic from aqueous solution and long-term product storage. JOM. 2011 Aug;63:94.
138. Bojic A, Purenovic M, Bojic D. Removal of chromium (VI) from water by micro-alloyed aluminium based composite in flow conditions. Water SA. 2004 Jul;30(3):353–359.
139. Bojic A, Purenovic M, Kocic B, Perovic J, Ursic-Jankovic J, et al. The inactivation of Escherichia coli by microalloyed aluminium based composite. Facta Universities. 2001;2(3):115–124.
140. Klas S, Kirk DW. Understanding the positive effects of low pH and limited aeration on selenate removal from water by elemental iron. Sep Purif Technol. 2013 Sep;116:222–229.
141. Erickson AJ, Gulliver JS, Weiss PT. Phosphate removal from agricultural tile drainage with iron enhanced sand. Water. 2017 Jul;9(9):672.
142. Chirikure S. Iron production and its position in Iron Age communities of southern Africa. J Social Arch. 2007 Feb;7(1):72– 100.
143. Lauderdale RA, Emmons AH. A method for decontaminating small volumes of radioactive water. Journal American Water Works Association. 1951;43(5):327–331.
144. Harza Environmental Services. Fundamental aspects of selenium removal by Harza Process. Technical report prepared under contract for the Federal-State San Joaquin Valley Drainage Program, 2800 Cottage Way, Room W-2143 Sacramento, CA 95825-1898.
145. Litter MI, Morgada ME, Bundschuh J. Possible treatments for arsenic removal in Latin American waters for human consumption. Environ Pollut. 2010 May;158(5):1105–1118.
146. Allred BJ, Racharaks R. Laboratory comparison of four ironbased filter materials for drainage water phosphate treatment. Water Environ Res. 2014 Sep;86(9):852–862.
147. Allred BJ, Tost BC. Laboratory comparison of four iron-based filter materials for water treatment of trace element contaminants. Water Environ Res. 2014 Nov;86(11):2221–2232.
148. Casentini B, Falcione FT, Amalfitano S, Fazi S, Rossetti S. Arsenic removal by discontinuous ZVI two steps system for drinking water production at household scale. Water Res. 2016 Dec;106:135–145.
149. Noubactep C, Caré S. Dimensioning metallic iron beds for efficient contaminant removal. Chem Eng J. 2010b Oct;163(3):454–460
150. Noubactep C, Caré S. Enhancing sustainability of household water filters by mixing metallic iron with porous materials. Chem Eng J. 2010c Aug;162(2):635–642
151. Noubactep C, Licha T, Scott TB, Fall M, Sauter M. Exploring the influence of operational parameters on the reactivity of elemental iron materials. J Hazard Mater. 2009 Dec;172(2- 3):943-51
152. Torkelson A. Enhanced granular media filtration of waterborne pathogens: Effect of media amendments for treatment of drinking water and stormwater. PhD Dissertation, Civil and Environmental Engineering UC Berkeley. 2015 Jan.
153. Noubactep C, Schöner A. Metallic iron: dawn of a new era of drinking water treatment research? Fresen Environ Bull. 2010b Feb;19(8a):1661–1668
154. Noubactep C. Metallic iron for water treatment: A critical review. Clean – Soil, Air, Water. 2013 July;41(7):702–710.
155. Noubactep C, Caré S. Designing laboratory metallic iron columns for better result comparability. J Hazard Mater. 2011 May;189(3):809–813
156. Lilje J, Mosler HJ. Continuation of health behaviors: Psychosocial factors sustaining drinking water chlorination in a longitudinal study from Chad. Sustainability. 2016 Nov;8(11):1149.
157. Henheik P, Koester V. Safe drinking water: Solutions and challenges. ChemViews Magazine. Wiley-VCH Verlag GmbH & Co. KGaA, 30 August 2014. Available from: http://www. chemistryviews.org/details/ezine/6473331/Safe_Drinking_ Water_Solutions_and_Challenges.html
158. Noubactep C. Beyond appropriateness and sustainability: Universal self-reliance in water supply. Separation Science & Application 2014b;34:26–27.
159. Noubactep C. Beyond appropriateness and sustainability: Universal self-reliance in water supply. GIT Laboratory (2014c);34:14–16.
160. Gwenzi W, Chaukura N, Noubactep C, Mukome FND. Biocharbased water treatment systems as a potential low-cost and sustainable technology for clean water provision. J. Environ Manage. 2017 Jul;197:732–749.
161. Oldright GL, Keyes HE, Miller V, Sloan WA. Precipitation of lead and copper from solution on sponge iron. Washington D.C. UNT. Digital Library. 1928.
162. Pilling NB, Bedworth RE. The oxidation of metals at high temperatures. J Inst Metals. 1923;29:529–591.