Environmental Engineering Reference
In-Depth Information
of cells from the irst 30 min and a complete mortality after 1 h. In static condition, 2 h was
required for a 100% mortality.
The results described above established the bactericidal effect of ZZ on each bacterial
strain. The next step was to study the bactericidal effect using a designed puriication sys-
tem such as a pitcher containing a cartridge with a column of 140 g of ZZ and 2 L of water
iltration capacity (Figure 30.8b). The results were similar for every bacterial strain: the
time required to effectively eliminate the bacteria with ZZ was 30 min to 3 h.
The next experiment used the pitcher with ZZ and 2 L of water contaminated with a
pool of bacteria—
V. cholerae, P. aeruginosa
,
S.
typhi
,
and
S.
sonnei
—with a high number of
cells (10
7
-10
8
CFU), evaluated at two different temperatures: at 4°C, usual temperature of
water consumed in tropical and subtropical countries, and at room temperature, 25°C.
The full bactericidal effect was observed after 3 h at room temperature. The experiment
was reproduced with another pool of bacteria—
P. shigelloides
,
A. hydrophila
,
and
E. coli
(10
6
CFU)—with identical results after 3 h at room temperature.
Giardiasis is an infection of the small intestine produced by the protozoan
G. lamblia
(
Giardia intestinalis
,
Giardia duodenalis
). This parasitosis occurs worldwide, with a major
prevalence in tropical and subtropical regions [25,26]. The cyst is the infection form of this
protozoan released in feces, but it also infects humans through contaminated food and
water. The cysts survive in the environment, although they can be destroyed by drying
and heat; however, they can survive in cold water for 16 days and resist chlorination in the
municipal water treatment plants. When the cysts are released in feces, they can live in wet
soil and water for a few months. Mindful of this, we tested the effect of ZZ in the viability
of
G. lamblia
cysts in drinking water.
The results in Table 30.14 show a 100% elimination of
G. lamblia
cysts counted after
30 min, an effect that remained after 3 h when the drinking water and ZZ were stirred.
On the other hand, although with water and ZZ in static a signiicant reduction of cysts
was also observed, a good exposure to Zn
2+
ions is required to achieve a full microbicidal
effect.
The studies of the microbicidal effect of ZZ show that this material renders abso-
lutely inactive the following microorganisms ordinarily transmitted in drinking water:
A. hydrophila
ATCC 7614,
P. shigelloides
CNCTC 5132,
E. coli
O:149 K8 8 Lt(+),
E. coli
O:101 K99
St(+)
, E. coli
ATTC 25922,
V. c h o l e r a e
C7258 (Ogawa),
V. cholerae
C6706 (Inaba),
P. aeruginosa
5FQ,
P. aeruginosa
O11,
L. interrogans
M20,
S. sonnei
,
S. typhi
,
and
G. lamblia
cysts.
It has been established that to ensure proper disinfection, water with added ZZ should
be left in static for at least 30 min at room temperature before drinking it or putting it in
the refrigerator. The time should be 3 h when the contamination of microorganisms is >10
5
CFU [27-30].
TABLE 30.14
ZZ Effect on
Giardia lamblia
Cysts in Drinking Water
Time/Cysts/mL (%)
Sample
0
30 min
1 h
3 h
Control stirred
20,000
15,000 (25%)
12,500 (37.5%)
12,500 (37.5%)
ZZ stirred
20,000
0 (100%)
0 (100%)
0 (100)
Control static
20,000
15,000 (25%)
15,000 (25%)
7500 (62.5%)
ZZ static
20,000
7500 (62.5%)
5000 (75%)
5000 (75%)
