Environmental Engineering Reference
In-Depth Information
for a few seconds and placed horizontally on a shiny surface of corrugated iron sheets in
the sun, in a speciied location such that no shadows were cast on the bottles. In another set
of experiments, a surface made from shiny aluminum foil was used as a base where bottles
were placed, to obtain maximum heat from the sun. A temperature of 55°C was required
to kill the pathogens in the water. The time to attain the required temperature decreased
with constant exposure, low wind velocity, clear sky, and magnitude of heat adsorption
and relection depending on the type of the surface. It took 10 h to obtain a temperature of
55°C on the aluminum foil compared with corrugated iron sheet, which took 15 h to reach
the same temperature. To keep a stock of clean water, suficient water was stored at a time
when the temperature was favorable. After attaining the maximum temperature, the water
was analyzed for pathogenic
Escherichia coli
,
Salmonella typhi
,
Shigella
spp. bacteria, and
Vibrio cholerae
. Also, analytical studies were made for protozoa (
Entamoeba histolytica
and
Giardia
spp.). The densities of coliform and
Shigella
spp. (colonies/100 ml) were determined
in the iltered water. The results are summarized in Table 1.1. The bacteriological analysis
of water treated by crumb rubber is shown in Table 1.2.
The synergistic effect of infrared and UV radiation above 55°C completely kills the
pathogens in the water obtained from crumb rubber iltration. In one particular locality
near Khafi (Saudi Arabia), a very high count of
Shigella
spp. was determined (300) in the
raw water.
A hybrid technique combining crumb rubber iltration and exposure to solar radiation
(UV + SODIS) results in complete reduction of pathogens. Using the above hybrid tech-
nique, the desired temperature of 60°C was obtained only in 3 h, which shows a great
reduction in time to kill the pathogens. Selection of a heat-absorbent base, the direction
of the bottle holders, the types of bottles, wind speed, moisture, and humidity affect the
attainment of the required temperature. The blowing of wind increases the time to reach
the required temperature of 55°C under the sun. The results of ield studies obtained only
after solar treatment showed a 24% reduction in the number of cases of diarrhea. The
technique has the advantage that it removes turbidity, TDS, and solid suspended parti-
cles (SSP) to levels accepted by the Environmental Protection Agency and World Health
Organization. Although opinion against the use of PTE bottles is increasing, glass bottles
TABLE 1.1
Number of Colonies for
E.
coli
and
Shigella
spp.
Sample
E. coli
Count
Shigella
spp. Count
1
>960
>1800
2
>1000
>7960
3
>700
4000
4
1500
6000
TABLE 1.2
Bacteriological Analysis of Water Treatment by
Crumb Rubber and UV Radiation
Sample
E. coli
Count
Shigella
spp. Count
1
0/100 ml
0/100 ml
2
3/100 ml
2/100 ml
3
0/100 ml
0/100 ml
4
0/100 ml
0/100 ml
