Environmental Engineering Reference
In-Depth Information
30.1 Introduction
The World Health Organization (WHO)
Guidelines for Drinking Water Quality
provide in its
preface:
“Access to safe drinking water is essential to health, a basic human right and a component
of effective policy for health protection.”
The quality of drinking water is not a simple issue
but one with a major inluence in a myriad of problems.
“The great majority of evident water-
related health problems are the result of microbial (bacteriological, viral, protozoan or other biologi-
cal) contamination. Nevertheless, an appreciable number of serious health concerns may occur as a
result of the chemical contamination of drinking water.”
The protection of drinking water is based on the establishment of many barriers from
the source to the consumer, aimed at preventing or reducing contamination to harmless
levels for human consumption. This protection includes the selection of adequate water
treatment procedures as well as the best possible management and operation of distribu-
tion systems. The inal manipulation of drinking water at home before human consump-
tion is also relevant to its preservation from contamination. The storage of drinking water
in poorly or seldom cleaned cisterns and tanks is the main source of microbiological con-
tamination at homes. The most recurrent solution for the inal treatment of drinking water
is the home iltration system.
A great variety of more or less eficient systems have been created to remove contami-
nants. They are all based on the physical and chemical properties of one or various materi-
als; thus, their useful life is limited to the effectiveness of such materials. Not one water
puriication system exists that can remove
every
water contaminant [1,2], although the
water treatment plans that combine different processes to remove impurities and achieve
microbiological puriication can be rather eficient. However, the combination of all the
processes involved in a water treatment plant in a compact and easy-working domestic
system has until now eluded scientists.
Disinfection is of unquestionable importance in the supply of safe drinking water.
The destruction of microbial pathogens is essential and usually involves the use of
reactive chemical agents such as chlorine. In the past 10 years, several articles have
reported the potential of silver and zinc oxide nanoparticles in drinking water treat-
ment to eliminate mostly microbiological contamination [3]. KDF ilters release small
quantities of Cu and Zn [4]. Some articles have related the use of Ag/Zn zeolite for the
same purpose [5].
In 1990, a new material was obtained at the Zeolites Engineering Laboratory of the
University of Havana. This material with microbicidal and ion-exchange properties was
given the name “ZZ
®
”—zinc in zeolite or a Zn
2+
form of the puriied natural clinoptilolite
NZ [ZZ
®
: Registro de Marca No. 130531, Resolución: 4876/99, OCPI (Oicina Cubana de la
Propiedad Industrial)]. ZZ was designed and developed as a controlled releaser of zinc
ions to enhance their microbicidal effect against bacteria, yeast, and protozoans. The Zn
ions are exchanged in the crystalline nanostructure of the clinoptilolite zeolite without
modiication of the unit cell. The lattice parameters of the clinoptilolite are as follows:
a
=
1 7. 7 1,
b
= 1 7. 8 4 ,
c
= 7. 4 1,
and β
=
116.30°, space group
C2/m
. This zeolite has three channels
interconnected {channel A [001] 10 members 3.1 × 7.5 Å, channel B 8 members 3.6 × 4.6 Å,
and channel C [100] 8 members 2.8 × 4.7 Å}. The dimensions of the channels vary owing to
the considerable lexibility of the framework. The representation of a unit cell of the Zn-
clinoptilolite is shown in Figure 30.1. The clinoptilolite crystals have the tabular and lath
morphology observed in the micrograph of Figure 30.1.
