Sorbent-embedded sheets for safe drinking water in developing countries: a case study of lead(II) removal by a zeolite-embedded sheet

Although many kinds of materials for water purification are known, easy-to-use methods that ensure the safety of drinking water for rural populations are not sufficiently available. Sorbent-embedded sheets provide methods for the easy removal of contaminants from drinking water in the home. As an example of such a sorbent-embedded sheet, we prepared a Linde type A (LTA) zeoliteembedded sheet (ZES) and examined its Pb(II) removal behaviour. Different amounts of LTA were added either as powder or as ZES to 0.3 mM Pb(NO3)2 solutions containing 2.5 mM Ca(NO3)2, in which the ratio of the negative charges in LTA to the positive charges in Pb(II) (LTA/Pb ratio) ranged from 1 to 20. After shaking, the mixtures were centrifuged to remove the powder, while the ZES was simply removed from the mixture by hand. The LTA powder removed more than 99% of the Pb(II) from the solution at all LTA/Pb ratios within 1 h, while the ZES removed >99% of the Pb(II) at LTA/Pb ratios of 2 and higher; at the highest LTA/Pb ratio of 20, the ZES removed>99% of the Pb(II) in 30 s. Therefore, the use of appropriate sorbent-embedded sheets enable the facile removal of contaminants from water. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). doi: 10.2166/wh.2017.160 s://iwaponline.com/jwh/article-pdf/16/1/159/240108/jwh0160159.pdf Lester Botoman (corresponding author) Elvis Shukla Satoshi Mitsunobu Naoto Matsue Laboratory of Applied Chemistry for Environmental Industry, Faculty of Agriculture, Ehime University, 3-5-7 Tarumi, Matsuyama 790-8566, Japan E-mail: botomanlester@yahoo.com Lester Botoman Department of Agricultural Research Services, Chitedze Research Station, P.O Box 158, Lilongwe, Malawi Erni Johan Graduate School of Science and Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama 790-8577, Japan


INTRODUCTION
Lack of safe drinking water is one of the most serious global health problems. WHO/UNICEF have reported that nearly 663 million people worldwide do not have access to clean water and 80% of people living in rural areas lack safe drinking water (WHO/UNICEF ). The types and amounts of contaminants in drinking water differ by country and region, and consist mainly of Escherichia coli, heavy metals and arsenic, along with many other kinds of substances and microbes (Amin et al. ). Among these contaminants, heavy metals are natural and become concentrated because of weathering, mining and industries, as well as other factors (Nagajyoti et al. ; Chao & Chen ), and millions of people have been reported to suffer from chronic heavy metal poisoning (Fernández-Luqueño et al. ).
Heavy metals in water are usually removed by a variety of methods that include precipitation, filtration, coagulation, flotation, electrochemical methods and sorption (Fu & Wang  Here, we introduce the use of a sorbent-embedded sheet as a new method for the removal of contaminants on a small scale from, for example, a glass of drinking water. The sorbent-embedded sheet facilitates the addition of the sorbent to water, as well as its removal. As a case study, we prepared a Linde type A (LTA) zeolite-embedded sheet and compared its Pb(II) removal behaviour with that of the LTA powder.
We selected Pb(II) as a universally harmful heavy metal and used LTA because Pb(II) is adsorbed to it with high selectivity (Kabwadza-Corner et al. ).

Materials
All chemical reagents were purchased from Nacalai Tesque, Inc., Japan. LTA was purchased from Wako Pure Chemical Industries, Ltd, Japan, and was washed with 1 M NaCl solution, followed by water, and air-dried prior to use.
Ten non-woven fabrics normally used for filtering kitchen sink waste, each composed of polypropylene and polyethylene (24 × 30 cm; Platec, Ltd, Japan), were sandwiched by 100 g of the LTA powder on an aluminium dish, and gently pressed by hand to loosely attach the LTA powder to the fabric. The dish was placed in an oven at 160 C and removed after 8 min. After cooling, each fabric sample was vigorously washed with water to remove any unattached LTA powder, followed by drying in air. The sheets obtained in this manner were used as LTA zeoliteembedded sheets (ZES). Unembedded LTA powder was also heated prior to use as described for the ZES.

ZES characterisation
The physical appearances of the non-woven fabric sheet and the ZES are shown in Figure 1(a). There was almost no

Removal of Pb(II)
In this study, we added different amounts of LTA in the powder or ZES form to a consistent amount of Pb(II).  Although the accessibility of Pb(II) to the LTA in ZES is lower than that of the LTA powder, the ZES removed >99% of the Pb(II) in solution, except at low LTA/Pb ratios, and the shaking time needed to achieve >99% Pb(II) removal decreased with the increasing LTA/Pb ratio (Figure 2(b)).
Since the Pb(II) concentrations at higher LTA/Pb ratios decreased very rapidly with the reaction time (Figure 2(b)), the results obtained at LTA/Pb ratios of 10 and 20 were re-plotted by restricting the shaking times to 3 min, as shown in Figure 2(c). This figure reveals that the Pb(II) concentrations decrease dramatically over the first minute, and that >99% of the Pb(II) was removed in 30 s at an LTA/Pb ratio of 20. This suggests that Pb(II) in water is easily removed by LTA without the need for any equipment to separate the LTA powder from the water.

CONCLUSION
The use of an appropriate sorbent-embedded sheet provides an easy way of removing contaminants from the drinking water of rural communities in developing countries. Our case study demonstrated that the ZES removes Pb(II) from Pb(II)-polluted drinking water without the need for centrifugation and other separation techniques. Nonetheless, the selection of cheap and effective sorbents, optimisation of the embedding method, and use of sorbent-embedded sheets by rural communities need to be further studied since community cultures, including lifestyle, differ from one country or region to another, which affect the efficacy of any water purification method.