Metallic iron filters for universal access to safe drinking water 1 
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(for CLEAN - Soil, Air, Water – Accepted 04-Sep-2009) 
Noubactep Chicgoua*(1), Schöner Angelika(2), Woafo Paul(3)
(1) Angewandte Geologie, Universität Göttingen, Goldschmidtstraße 3, D - 37077 Göttingen, Germany.  
(2) Institut für Geowissenschaften, Ingenieurgeologie, Martin-Luther-Universität Halle; Von-Seckendorff-Platz 3, 
D - 06120 Halle, Germany. 
(3) Laboratory of Modelling and Simulation in Engineering and Biological Physics, Faculty of Science, 
University of Yaounde I, Box 812 Yaounde, Cameroon 
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(*) corresponding author: cnoubac@gwdg.de; Tel. +49 551 39 3191, Fax: +49 551 399379. 
Abstract 
The availability of sustainable safe drinking water is one of Millennium Development Goals 
(MDGs). The world is on schedule to meet the MDG to “halve by 2015 the proportion of 
people without sustainable access to safe drinking water in 2000”. However, present 
technologies may still leave leaves more than 600 million people without access to safe water 
in 2015. The objective of the present article is to present a concept for universal water filters 
primarily made of metallic iron (Fe0) and sand. The concept of Fe0/sand filters is based on the 
combination of: (i) recent development of slow sand filtration and (ii) recent progress in 
understanding the process of contaminant removal in Fe0/H2O systems. The filters should be 
made up of more than 60 % of sand and up to 40 % of Fe0. The actual Fe0 proportion will 
depend on its intrinsic reactivity. The most important question to be answered regards the 
selection of the material to be used. The design of the filter can be derived from existing 
filters. It appears that Fe0/H2O based filters could be a technology for the whole world. 
Keywords: Contaminant removal, Point of use, Safe water, Water filtration, Zerovalent iron. 
Acronym List 
AMD   Acid mine drainage 
BSF  Biosand filter 
CIM  Composite iron matrix 
EDTA  Ethylenediaminetetraacetate 
KAF  Kanchan™ arsenic filters 
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MDG   Millennium Development Goal 
NGO  Non-governmental organization 
POU   Point-of-use 
ZVI   Zerovalent Iron 
Introduction 
Naturally readily available waters (shallow groundwater; surface water, water from boreholes 
and springs) are the main sources for drinking water production. These waters may become 
contaminated with organic/inorganic chemical pollutants and pathogenic microorganisms 
(bacteria, fungi, protozoa, viruses) from various origins: (i) natural (geogenic) 
hydrogeochemical processes, (ii) artificial recharge with wastewater or water from septic 
tanks or leaking sewage pipes, (iii) discharges of wastewater and/or manure run-off from 
agricultural land.  
To produce safe drinking water from natural waters, chemical pollutants and pathogens need 
to be removed. One effective natural way is the passage of surface water through soil, as is 
the case in bank filtration [1-4]. The effectiveness of bank filtration to produce safe drinking 
water from natural waters depends on four major factors: (i) the extent of water pollution, (ii) 
the nature of the soil, (iii) the thickness of the soil or the travel distance within the soil, and 
(iv) the water flow rate or travel time. One can learn from nature and produce drinking water 
at small scale. For this purpose, it can be assumed that for a sufficient amount of any relevant 
treatment material in a filter, an adequate water flow rate will yield satisfactory contaminant 
mitigation. The reactive material can be (i) a natural material, (ii) a synthetic material or 
composites, or (iii) a mixture of materials. The material amount determines the thickness of 
reactive layer in the filter. The water flow rate determines travel time. 
During the past three decades, treating water at the household level has been shown to be one 
of the most efficient means of preventing waterborne diseases world wide [5-10]. Here are six 
examples for illustration: the use of (i) commercial filtration devices (e.g. Brita) mostly in 
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developed countries [11-13], (ii) ceramic pot filters or Kosim filters in Ghana [14], (iii) 3-
Kolshi filters and SONO filters in Bangladesh [6, 15, 16], (iv) Kanchan™ arsenic filters in 
Nepal [17, 18], (v) Danvor plastic biosand filter [19], and (vi) Potters for Peace Filtron 
ceramic filter [19,20]. Promoting household water treatment and safe storage helps 
populations to actively take charge of their own water security. Therefore, providing people 
with the knowledge and affordable tools to treat their own drinking water at the point of use is 
a noble objective. 
The present study aims at presenting a concept using metallic iron (Fe0) as universal filter 
material for water treatment at the point of use (POU) in general and at household level in 
particular. The secondary objective is to demonstrate the suitability of Fe0 for water treatment 
in remote locations of developing countries. In these regions, available water could be 
chemically safe (no geogenic or anthropogenic contamination). In this case, microbial 
contamination due to lack of sanitation and improper hygiene is the sole source of water 
contamination. Table 1 summarises some relevant water pathogens and related diseases [21]. 
The presentation is based on the state-of-the-art knowledge on the mechanism of contaminant 
removal in the presence of Fe0 (Fe0/H2O systems) which will be presented first.  
Mechanisms of contaminant removal in Fe0/H2O systems 
Passive remediation of water pollution by using Fe0/H2O systems has been developed for 
about 20 years [22-24]. Applications of these innovative systems included (i) groundwater 
remediation, (ii) drinking water treatment, and (iii) wastewater treatment. Successful 
quantitative removal of metals (e.g. Cd, Co, Cr, Cu, Pb, U, Zn), non-metals (e.g. As, Mo, Se, 
Sn), anions (e.g. AsO43-, F-, MoO42-, NO3-, PO43-, SeO42-, SO42-), organic dyes, organic 
compounds (e.g. benzene, chlorinated solvents, phenol, pesticides, toluene), bacteria, 
suspended solids, and viruses has been reported [16, 25-30]. Almost all studies dealing with 
pollutant removal were limited to proving the viability of Fe0/H2O systems for a few target 
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pollutants and were not incorporated within a broad-based understanding of Fe0 remediation 
technology. 
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It is interesting to note that another technology, electrocoagulation [31-33], using Fe0, could 
exhibit similar efficiency for a large spectrum of contaminants. Iron electrocoagulation can be 
considered as an electrochemically driven accelerated corrosion process. In both cases 
(passive Fe0/H2O and iron electrocoagulation), pollutants are removed from water by a 
multitude of mechanisms operating synergistically. 
Likely removal mechanisms include: (i) adsorption onto Fe0 and Fe oxides/hydroxides, (ii) 
co-precipitation with Fe oxides (or co-precipitation on the substrate), (iii) direct reduction by 
Fe0, (iv) indirect reduction by FeII or H/H2, (v) indirect oxidation by in situ generated radicals 
HO.. The exact sequence of these reactions depend on the system. Because redox-insensitive 
pollutants have been quantitatively removed in passive Fe0/H2O systems, any individual redox 
process could not be the fundamental removal mechanism as originally assumed [23, 34]. 
Therefore, the fundamental mechanisms of contaminant removal in Fe0/H2O systems are 
adsorption (including surface complexation) and co-precipitation [35, 36]. 
Certainly, for some contaminants, such as CrVI which are reducible even in the aqueous phase 
by FeII (under local anoxic conditions), quantitative reduction may precede adsorption and co-
precipitation. However, considering the nature of the Fe0/H2O system, there is no reason to 
consider quantitative reductive transformation a priori for some species. Moreover, a Fe0/H2O 
system should be considered as zone of precipitating iron oxides/hydroxides [37]. During this 
process expansive amorphous iron hydroxides are generated and further transformed by 
dehydration to more crystalline oxides (Tab. 2) [38, 39]. 
Diversity in the reactivity of iron oxides in Fe0/H2O systems 
In order to better understand the role of metallic iron in Fe0/sand filters, the dynamic nature of 
iron corrosion in Fe0/H2O systems will be discussed. For this purpose, synthetic bulk oxides 
and oxide-films on Fe0 should be compared in terms of reactivity towards contaminant 
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removal. Synthetic oxides and in situ formed oxide-films are fundamentally different in that 
the latter are reactive systems (“reactive oxides”) by virtue of the continual generation and 
annihilation of point defects at the interfaces. Furthermore, oxide-films (passive layers), 
unlike synthetic oxides, continually grow into the metal at the Fe
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0/layer interface while being 
simultaneously destroyed by dissolution or restructuring at the layer/H2O interface [40, 41]. 
Accordingly, synthetic oxides are strictly “coatings” and hence, with respect to the processes 
that influence Fe0 reactivity, they are “dead” [40]. Synthetic oxides can only act as 
contaminant adsorbents. Although synthetic oxides may be capable of simulating the 
properties of the deposited outer layers (at the layer/H2O interface), it is difficult to see how 
they can simulate the barrier layer (at the Fe0/layer interface – “reactive oxides”), whose 
defect concentration is normally far in excess of that which can be obtained in bulk oxides. 
“Reactive oxides” are better adsorbents and may co-precipitate contaminants during their 
formation and transformation to “dead oxides” [25, 35, 36, 42, 43]. “Dead oxides” are good 
adsorbents of limited and selective affinity to some contaminants. The consequence of this 
analysis is that Fe0 can be regarded as a permanent source of highly reactive hydroxides 
(“reactive oxides”) in a treatment system (statement 1). Statement 1 is the major argument on 
which the concept of Fe0/sand filters for universal access to safe drinking water is built. 
A schematic illustration of the time-dependant evolution of iron corrosion products is given in 
Figure 1. The cross-section of a spherical Fe0 material experiencing uniform corrosion is 
represented. It is assumed that the initial material (Fe0 in Fig. 2) is progressively covered by 
concentric layers of iron oxides from which the three most internal layers (d1, d2, d3, Fig. 2) 
are “reactive” (see above) and all the external layers (d4) are comparative in their reactivity to 
synthetic bulk oxides (“coatings”). While this assumption is somewhat arbitrarily, d1 can be 
regarded as a layer of amorphous ferrous iron hydroxides (Fe(OH)2), d2 a layer of mixed 
amorphous iron hydroxides (Fe(OH)2 and Fe(OH)3), d3 a layer of mixed amorphous iron 
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hydroxides/oxides (green rust, magnetite) and d4 a layer of aged corrosion products 
(crystallized iron oxides). 
The schematic representations in Fig. 1 and 2 have intentionally neglected the expansive 
nature of the process of iron oxide/hydroxide production form metallic iron [39, 44]. In fact, 
the theoretical ratio (α1 = Voxide/VFe) between the volume of corrosion products and the 
volume of iron in the metallic structure varies between 2.0 for Fe3O4 and 6.4 for 
Fe(OH)3.3H2O (Tab. 2). This volume increase is the principal cause of the expansion and 
ultimately the loss of hydraulic conductivity (permeability loss) for remediation Fe0/H2O 
systems. Clearly, Fe0/sand filters end of service is not (or should not be) dictated by Fe0 
depletion but rather by loss of hydraulic conductivity. The practical expansion of corrosion 
products can be discussed from a proper kinetic law which correlates the radius loss of Fe0 
and the corresponding volume of accumulated iron oxides [39]. In this work, mixing inert 
sand and Fe0 is a practical tool to extent filter service life. It is expected that for any 
appropriate Fe0 material, an optimal weight ratio sand/Fe0 should exist for satisfactorily water 
treatment in the medium or long term (e.g. ≥ 12 months).  
Water treatment by sand filtration
Promising strategies for providing people with access to safe water are available, but may not 
be suitable/affordable for areas of low population density with little perspective for economic 
growth (e.g. rural areas, [45, 46]). It may further prove challenging to guarantee the quality of 
drinking water in these populations. Methods that allow the treatment of the water at the place 
where it is consumed (POU methods) may provide a low-cost, promising, easy and flexible 
solution for increasing drinking water quality in much of the population in need. Slow sand 
filtration is one of these methods. 
Basic sand filtration 
The earliest form of water treatment was slow sand filtration. Slow sand filters were 
developed in the 1820’s in Scotland by Robert Thom and in England by James Simpson. They 
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became successfully established in Europe by the end of the 19th century [47-50]. This 
technology used sand filter beds through which water is slowly trickled. The natural 
formation of a biological layer (biofilm, widely termed as Schmutzdecke) and the filtering 
action of sand removes bacteria, silt and chemical pollutants. The treatment efficiency is 
affected partly by physical straining but more importantly by biological action within the 
biofilm that formed on top of the sand [51]. A household-scale intermittent slow sand filter 
(the Davnor Biosand filter or Davnor BSF) developed by Manz has been successfully tested 
by several governments, research and health institutions and NGOs in Bangladesh, Brazil, 
Canada, Haiti, Nicaragua, Vietnam and other countries [52, 53]. Lantagne et al. [5] 
summarized the drawbacks of the BSF as follows: (i) low rate of virus inactivation, (ii) lack 
of residual protection and removal of less than 100 percent of the bacteria, which leads to 
recontamination, (iii) current lack of studies proving health impact, and (iv) difficulty in 
transport and high initial cost, which make scalability more challenging. Accordingly the 
major problem with BSF is that complete pathogen removal can not be guaranteed. Therefore, 
if water can be successfully freed from pathogens within a sand filter, this technology can be 
used with more confidence for safe drinking water at a household level. The presentation on 
the mechanisms of contaminant removal in Fe
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0/H2O systems suggests that coupling reactive 
Fe0 to sand could solve the problem (statement 1). This work has already been done but Fe0 
aimed at eliminating arsenic as presented below. 
Improved sand filtration 
Recently, the Arsenic Biosand Filter (KanchanTM Arsenic Filter - KAF) was developed and 
distributed in Nepal by Ngai et al. [17, 18]. The KAF is built on the platform of a slow sand 
filter, modified to include/increase arsenic removal capability. The KAF combines the 
concepts of slow sand filtration and an intermittent household-scale system with the 
innovation of a diffuser basin containing iron nails for arsenic removal. In the KAF, arsenic is 
certainly quantitatively removed by adsorption onto or by co-precipitation with iron 
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oxyhydroxides from rusting iron nails. Pathogens (e.g. bacteria) have been reported to be 
removed mostly by physical straining provided by the fine sand layer, by attachment to 
previously removed particles and, to a lesser degree, by biological predation occurring in the 
top few centimeters of the sand. The KAF was demonstrated successful for simultaneous 
arsenic and pathogen removal and is considered as the best among all household arsenic 
filters available in Nepal [18]. Chiew et al. [54] have recently published primary results on 
attempts to extent the concept of KAF filtration in Cambodia (Fig. 3). 
Recent developments in the understanding of the process of contaminant removal in Fe0/H2O 
systems demonstrates that pathogens are certainly removed/inactivated by co-precipitation 
with iron oxyhydroxides from a rusting Fe0. Therefore, a further development of the 
KanchanTM Arsenic Filter is to disseminate Fe0 in of the “pathogen removal unit” of the filter 
(BioSand filter – Fig. 2) or to replace the “arsenic removal unit” by a water saturated Fe0/sand 
layer. The second possibility is discussed below. Such a filter will remove all possible 
contaminants (including arsenic and bacteria) from the aqueous solution. 
Fe0/sand filters 
The works of Dr. Manz yielded an efficient intermittent household-scale slow sand filtration 
system for “safe” drinking water [50]. Ngai et al. [18] further developed this system by 
adding small amount of metallic iron to optimize arsenic (and pathogen) removal. As a rule 
the nature and extent of water contamination in rural areas of developing countries is 
unknown [46]. However, despite the variability of the influents the system outputs have to be 
satisfactory. Based on the state-of-the-art knowledge on the mechanism of contaminant 
removal by Fe0/H2O systems, the used of metallic iron as universal material for safe drinking 
water has been suggested [55, 56]. The works of Ngai et al. [18] suggested that the amount of 
Fe0 in the filter is not necessarily high (e.g. 10 % weight). Furthermore, since chemical 
contaminants and pathogens are certainly co-precipitated with precipitating iron corrosion 
products, the flow rate of contaminated waters through the Fe0/sand filter can be enhanced to 
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reach the daily demand of individual families within a few tens of minutes. That is the idea 
behind Fe
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0/sand filters. 
The innovation in Fe0/sand filters 
People familiar with the problematic of arsenic contamination in Bangladesh and Nepal are 
aware that an effective Fe0/sand filtration system (3-Kolshi system) was abandoned because 
of loss of porosity of the system. A close look of the 3-Kolshi filtration system reveals that the 
top Kolshi was filled with 3 kg of cast iron and 2 kg of sand on top of the iron turnings [15]. 
In other words the Kolshi with Fe0 (here cast iron) contains a zone of 100 % Fe0 overlying the 
sand layer. The 3-Kolshi filtration system was replaced by the SONO filter. Here, the primary 
active material is a porous composite iron matrix (CIM), a mass made of cast iron turnings 
through a proprietary process to maintain active CIM integrity for years [6, 16]. Again a 100 
% layer of composite is sandwiched between two layers of (coarse) sand. The reported loss of 
porosity is necessarily coupled to the too high proportion of Fe0 in the reactive zone (actually 
100 %). Given the relative low concentration of arsenic in contaminated waters, this huge 
amount of Fe0 (and possibly composite) is obviously unnecessary. As discussed above Fe0 
depletion should not occur. However, even the KAF of Ngai et al. [18] contains a 100 % layer 
of iron nails at the top of fine sand, coarse sand and gravel. The relative amount of iron nails 
in KAF was small compared to that of reactive materials in 3-Kolshi and SONO filtration 
systems and the KAF are efficient for several years [17]. Therefore, reducing the proportion 
of Fe0 in the system is a sensible modification to maintain filter permeability for a long time. 
The real novelty with the proposed Fe0/sand filters is that no 100 % Fe0 will be available. 
Rather, the Fe0 reactive layer will be a mixture of at least 60 % sand, gravel or porous 
volcanic rocks and up to 40 % Fe0. The actual proportion of the Fe0 will depend on its 
intrinsic reactivity and particle size. The advantage of porous volcanic rocks [57-59] is that 
generated iron hydroxides may fill their porous structure extending service life (or retarding 
loss of hydraulic conductivity). On the other hand, Fe0 materials could be produced locally 
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[60-63] or selected from available iron products (including production wastes and by-
products) such as nails rivets, nuts, bolts, barbed wire, packing wire, chicken wire mess, 
fencing wire, steel wool, construction materials and other Fe
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0 products. Using available Fe0 
materials will protect filter users from the market law as increased demand is only indirectly 
coupled to the original use of the material. For example, it can not be expected that the price 
of packing wire increases just because it is used for water treatment. Another approach will 
consist of testing potential Fe0 materials in industrialised countries (including China), that are 
likely exported to developing countries and built a database for suitable materials.  
Potential beneficiaries of Fe0/sand filters 
It is certain that Fe0/sand filters will accelerate the health gains associated with improved 
drinking water until the goal of universal access to piped, treated water is achieved [5]. Even 
after this hypothetical goal is achieved, the world will still have to face critical situations (e.g. 
accidental contamination, earthquakes, epidemic plagues, wars, tsunamis), in which available 
water should be rapidly treated. These critical situations are managed worldwide mostly by 
armies and NGOs (including the Red Cross). Therefore, the Fe0/sand filters are not only 
suitable for developing countries but for the whole world. Recently, an uranium 
contamination was discovered in drinking water production wells in Barlissen in Lower 
Saxony/Germany and the wells were precautionary put out of service [64]. Barlissen is a 
typical situation where Fe0/sand filters could help in industrialized countries. 
On the other hand, working on Fe0/sand filters will give researchers from developing 
countries the opportunity to solve a crucial problem with local solutions. The technology is 
low cost and good results can be achieved with simple equipment. Furthermore, experiments 
do not involve any stringent reaction conditions nor expensive devices, as the major 
experiments are to be conducted under atmospheric conditions. It is expected that research 
groups working on Fe0/sand filters will achieve results which are helpful for the further 
development of iron reactive walls. In fact, Fe0/sand filters can be regarded as a sort of “rapid 
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small scale column test” which could help to bridge the gap between short-term studies in the 
lab (few weeks) and field Fe
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0 reactive barriers (some two decades). In fact, testing Fe0/sand 
filters offers a unique opportunity to test the reactivity of the same Fe0 material at several sites 
with natural waters of various characteristics. Clearly, a South/North symbiosis can be 
expected: a technology developed in the North tested and used in a modified version in the 
South could contribute to the further development of the original technology (not only for the 
North). 
Ways to affordable Fe0/sand filters 
The concept of Fe0/sand filters is based on scientific understanding of the complex chemical 
and physical processes involved in an evolving technology (iron remediation technology) that 
has being successfully applied for almost 20 years. Provided that a relevant reactive Fe0 is 
used, the effectiveness of Fe0/sand filters is not to be demonstrated, except some technology 
verification in the field (monitoring). The sole tasks are: (i) selecting and processing the 
appropriate Fe0 materials, (ii) designing the filters, and (iii) avoiding the use of Fe0/sand 
filters for waters of pH ≤ 5. In fact, Fe0/sand filters are based on the anodic dissolution of iron 
in neutral and close-to-neutral aqueous systems. In this pH range, primary iron dissolution is 
followed by a continuous build up and transformation of a corrosion product layer in the 
vicinity of Fe0 [41, 65, 66]. 
Material selection 
Practically any available Fe0 material (mainly low alloyed steel and cast iron) is theoretically 
applicable for water treatment. Ideally, any newly obtained Fe0 material should be 
characterized and tested for water treatment capacity by a standard method. In using activated 
carbon for wastewater treatment for example, it is generally accepted that a good decolorizing 
carbon should fulfil at least 200 mg/g removal capacity for methylene blue in batch 
experiments [67]. Until recently, there was no experimental parameter to characterize the 
intrinsic reactivity of Fe0 materials [68-70]. Noubactep [69, 70] has introduced a parameter, 
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kEDTA, which could enable purposeful material selection. Per definition, kEDTA is the slope of 
the line of the time-dependent oxidative dissolution of ion from a given Fe
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0 material in a 2 
mM EDTA solution. kEDTA is determined in batch experiments and characterized material 
intrinsic reactivity under any given experimental conditions [70]. For example, materials used 
in Fe0/sand filters should exhibit a kEDTA value above a critical value. This critical value is yet 
to be determined. The kEDTA value of the iron nails used by Ngai et al. [18] could be used as 
guide to select the Fe0 loading of the filter. For a less reactive material a larger Fe0 loading 
than in the KanchanTM Arsenic Filter will be applied and lesser Fe0 loadings are needed for 
more reactive materials. The long term reactivity of available Fe0 materials has to be tested as 
well. Initially, iron nails from the KAF filters or iron composites from the SONO filters can 
be used as starting point. 
Filter designs 
Basically, Fe0/sand filters are slow sand filters for intermittent use [49, 50]. Almost 130 years 
of experience is available for this type of system. The most recent developments are those of 
KanchanTM Arsenic Filter [18], SONO filters [6, 16] and Kosim filters [14]. These devices 
can be modified to use a Fe0/sand reactive layer as described above. Alternatively, new 
designs may be conceived based on local specifications [71]. Fig. 3 shows a cross-section of 
the filter design used by Chiew et al. [54]. Arsenic removal and bacterial removal units are 
illustrated. A potential shortcoming of this design is that the "arsenic removal unit" 
experiences wet and dry periods. In an improved design, the high of the outlet pipe should 
enable immersion of the Fe0 layer.  
In all cases the filters should be constructed from local materials and the reactive layer should 
be embedded in sand layers. Available Fe0 materials (e.g. iron nails, steel wool) should be 
tested and approved at least in the early stage of technology implementation. The Fe0/sand 
filter should be manufactured locally by trained workers regardless of their scholar education. 
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To sustain the Fe0 reactivity, intermittent additions (e.g. once a month) of boiled water [16] or 
lemon juice [72] could be envisaged.  
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While Hussam and Munir [16] used boiled water to eventually kill pathogens, the present 
review demonstrated that upon purposeful dimensioning, pathogens will be sequestrated by 
iron corrosion products. Therefore, boiled water should increase/sustain Fe0 reactivity by 
elevating the temperature. Intermittent temperature elevation certainly disturb the process of 
iron passivation, and thus sustain Fe0 reactivity as reported by Hussam and Munir [16]. 
The rational for the use of citric acid is the well-known increase iron corrosion with 
decreasing pH value [65, 66]. Cornejo et al. [72] tested three commercially available lemon 
species as citric sources. Commercial lemon species may content undesirable preservatives 
and little parts of fruit. Even though these undesirable contents are non toxic, these additives 
should be regarded as contaminants and will be removed in the filtering system as well. In 
rural areas natural lemon juice should be at least seasonally available at low cost or cheaper 
than commercial lemon juices. While testing the ability of citric acid (pKa1 = 3.15, pKa2 = 
4.77, pKa3 = 6.40) to sustain reactivity, care will be taken to keep the pH > 4.5 to avoid 
dissolved Fe in filtered water. Again, this technology is not applicable for the treatment of 
waters of initial pH < 5. Such waters, known as from acid mine drainage (AMD) are world 
wide available at abandoned and active mining sites [73]. 
Conclusions 
The fact that field Fe0/H2O systems have successfully removed various contaminants from 
polluted water is a testament to their potential, which is yet to be fully realized. This paper 
presents a concept to realize this potential at a household level by a simple water filtration on 
a Fe0/sand column. The Fe0/sand filter is an innovation combining two proven water treatment 
techniques: (i) adsorption and co-precipitation in Fe0/H2O systems, and (ii) size exclusion by 
slow sand filtration. There is no doubt that a proper material selection and design of the 
filtration system will contribute to achieve and even exceed the Millennium Development 
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Goal. The original merit of this concept is that it allows researchers from developing countries 
to actively work on a crucial problem while results will be useful for the developed world as 
well. Intensive laboratory and field research is needed to develop Fe
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0/sand filters. The efforts 
should be accompanied by numerical modeling. This aspect is under investigation in the 
research group of one of the authors (P. Woafo) using mathematical equations describing the 
spatio-temporal evolution of pollutants concentration and porosity in the filters complemented 
by experiments. On the other hand, reportedly efficient filters (e.g. Danvor BSF, Filtron 
ceramic filter, Kosim filter) can be amended with Fe0 to enhanced pathogen inactivation. 
Acknowledgments 
Thoughtful comments provided by Prof. Abul Hussam (Center for Clean Water and 
Sustainable Technologies, George Mason University - USA) on the draft manuscript are 
gratefully acknowledged. Sven Hellbach (student research assistant) is acknowledged for 
technical assistance. The manuscript was improved by the insightful comments of anonymous 
reviewers from CLEAN Soil, Air, Water. 
Conflict of Interest 
The authors have declared no conflict of interest. 
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 21
545 
546 
547 
548 
549 
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 22
Table 1: Some relevant water pathogens and related diseases. Compiled after ref. [21]. 549 
Microbes Examples Diseases 
Bacteria Vibrio cholerae Cholera  
 Shigella sonnei Bloody diarrhea 
 Salmonella enterica Gastrointestinal illness 
 Helicobacter pylori Chronic ulcers and cancer 
 Escherichia coli Bloody diarrhea, kidney failure 
 Arcobacter butzleri Acute gastrointestinal illness 
Viruses 
Astro- and Caliciviruses Gastrointestinal illness 
 
Hepatitis A/E virus Acute liver disease (hepatitis) 
 Rotavirus Severe diarrhea 
Protozoa 
Blastocystis hominis Diarrhea and abdominal pain 
 Entamoeba histolytica Gastrointestinal illness 
 Naegleria fowleri Amebic meningoencephalitis 
Fungi Aspergillus fumigatus  Respiratory illness 
 Fusarium solani Skin-related infections 
550 
551 
 
 23
Table 2: Some relevant characteristics of metallic iron and its main corrosion products. α is 
the molecular weight of iron to the molecular weight of the corrosion products. α
551 
552 
553 
554 
555 
1 is 
the ratio of volume of expansive corrosion products to the volume of iron in the 
metallic structure. Compiled from refs. [38] and [39]. 
 
Name Formula Structure Density α α1
   (kg/m3)   
Iron a-Fe bcc 7800 - - 
Hematite 1/2 Fe2O3 Trigonal 5260 0.699 2.12 
Magnetite 1/3 Fe3O4 Cubic 5180 0.724 2.08 
Goethite α-FeOOH Orthorhombic 4260 0.629 2.91 
Akageneite β-FeOOH Tetragonal 3560 0.629 3.48 
Lepidocrite γ-FeOOH Orthorhombic 4090 0.629 3.03 
 Fe(OH)2 Trigonal 3400 0.622 3.75 
 Fe(OH)3 n.a. n.a. 0.523 4.20 
 Fe(OH)3.3H2O n.a. n.a. 0.347 6.40 
556 
557 
558 
n.a. = not available 
 
 24
558 
559 
Figure 1 
 
 560 
561 
562 
 
 25
562 
563 
Figure 2: 
 
 564 
565 
 26
565 
566 
Figure 3 
 
 567 
568 
569 
570 
571 
 
 
 
 27
Figure captions 571 
572 
573 
574 
575 
576 
577 
578 
579 
580 
581 
582 
583 
584 
585 
586 
587 
 
Figure 1: Time dependence evolution of Fe0 and Fe corrosion products from a spherical 
material assuming uniform corrosion. Fe0 corrosion continuously produces 
concentric layers of iron hydroxides which are transformed to iron oxides. It is 
assumed (see text) that the three layers next to Fe0 surface are reactive (d1, d2, d3) 
while the outer layers are non reactive (d4). 
 
Figure 2: Cross-sectional diagram of a uniformly corroding Fe0 particle at t > t2 (Fig. 1). d1, 
d2 and d3 are supposedly the reactive or transforming layers in which contaminants 
may be adsorbed, co-precipitated or chemically transformed. d4 is the growing 
layer of aged corrosion products on which contaminants could adsorb. d4 is less 
porous than the inner layers but may be fissured. 
 
Figure 3: Design of the filter tested for arsenic and pathogen removal in Cambodia by Chiew 
et al. [54]. Rigorously the pathogen removal unit is a conventional BioSand filter 
in which suspended solid are removed. 
 28