Environmental Engineering Reference
In-Depth Information
Quality
[13] and Cuban standard NC 827: 2010 [14]. The resulting product is denominated
ZZ. The characterization of ZZ was conducted by chemical analysis and x-ray diffraction;
microbiological tests were also carried out to determine (i) a possible contamination and
(ii) the bactericidal effect.
As part of the project, domestic and collective water delivery systems have also been
designed. The former are 1.5-L pitchers and lasks with a funnel in the upper part contain-
ing a ZZ cartridge or a load of the product. The collective systems are more complex since
they are connected to the water supply pipes and their capacity can be of either 2 or 4 kg of
ZZ. The ZZ systems have been certiied by the Pedro Kouri Tropical Medicine Institute,
the Finlay Institute, the National Water Resources Institute, the Food and Pharmacy
Institute, and the Havana University Science and Technology of Materials Institute. These
are all prestigious Cuban scientiic institutions recognized for their world-class research.
In 1999, ZZ was certiied by the Registro Sanitario of Cuba [8].
The chemical and microbiological studies of ZZ were conducted in two phases: (i)
in vitro
and (ii) using a pitcher as domestic puriication system.
30.2.1 Chemical Studies
The performance of the exchange of ZZ and the main cations present in drinking water
was studied in kinetic and static conditions. Three samples of ZZ (20 g) were placed in
three glass columns, 10.7 cm length and 2.5 cm diameter, creating a 6-cm-thick bed. The
drinking water was moved through the columns at low rates of 100, 25, and 15 mL/min
during 10 h. Static experiments were designed to evaluate the behavior of the chemical
composition of drinking water when in contact with ZZ for a long time. Ten experiments
with different ZZ/water ratios from 1:1 to 1:10 were conducted for 48 h. The chemical com-
position of drinking water was determined every hour.
An experiment was designed to approach the use of ZZ in a domestic water treatment
system. In a pitcher, a column was assembled with 140 g of ZZ, whose particle size was
1-1.6 mm, and placed in ion-exchange columns of 5-cm in diameter creating an 8.5-cm
bed. The pitcher's volume was 2.2 L and the drinking water was moved through the col-
umn at a low rate of 0.2 mL/min but the column remained inside the drinking water,
allowing it contact with ZZ. The experiment was conducted for 45 days. Zinc content was
determined every day; however, during the irst 8 days, it was monitored hourly.
The content of the cations involved in the ion-exchange process was determined at dif-
ferent times taking drinking water samples and submitting them to chemical analysis
of Ca, Mg, Na, K, and Zn, and the heavy metals Cd, Cr, Mn, Ni, and Pb, using a PYE
UNICAM SP9 atomic absorption spectrophotometer.
30.2.2 Microbicidal Effect
The bactericidal effect of ZZ on bacteria that can be live in drinking water was studied
using strains of reference. The minimum bactericidal dose of 10% of ZZ (10 mg of ZZ/100
mL of culture medium) was established in a study using 33 strains of gram-positive and
gram-negative bacteria, and yeast strains as presented in Table 30.1.
A new series of microbiological tests was conducted using the bacterial strains that
can contaminate drinking water. For each bacterial strain, a preculture in Luria-Bertani
(LB) media was prepared and then incubated for 18 h at 37°C. It was checked for purity
by Gram stain and 1 mL of this preculture was inoculated in a 250 mL Erlenmeyer with
