Environmental Engineering Reference
In-Depth Information
TABLE 1.3
Physiochemical Analysis
Crumb Rubber and
UV Radiation
Tests
Crumb Rubber
WHO Standard
pH
6.8
7.8
6.0
Color (CU, color units)
8
6
6.0
Odor
None
None
None
Turbidity (NTU)
3
3
6
Total suspended solids (mg/l)
None
None
None
Total dissolved solids (mg/l)
250
250
500
Total hardness (mg/l)
180
78
500
Ca
2+
hardness (mg/l)
67
67
75
Mg
2+
hardness (mg/l)
65
60
50
Chloride (mg/l)
170
170
200
Iron (mg/l)
6.1
0.1
0.3
Arsenic (mg/l)
None
None
None
may be the future choice if the transmission of UV radiation is assured, such as in Corning
glass. UV radiation penetrates Pyrex and Corning glasses. The presence of iron oxide pre-
vents transmission of UV radiation. The results of physiochemical analysis of the bimodal
water treatment are given in Table 1.3.
The composition shown in Table 1.3 demonstrates that the quality of water obtained by
combined crumb rubber and UV radiation process complies with the WHO standards.
The water produced is healthy and free of pathogens.
1.4.2
Photocatalytic Treatment
In the processes mentioned above, trace metals such as mercury (Hg), chromium (Cr), lead
(Pb), and several heavy metals such as cadmium (Cd) and arsenic (As) may go undetected.
Also, several organic compounds such as alcohol, carboxylic acid, phenolic derivatives, or
mineral acids may be encountered. Dyes may be released in water by textile industries.
In addition, organochlorine pesticides such as lindane,
p
,
p
′-DDT (dichlorodiphenyltrichlo-
roethane), and methoxychlor are present in the environment. In cases where true metals,
heavy metals, and agricultural pesticides may be present, the bimodal treatment (crumb
rubber + solar radiation) may be extended to photocatalytic treatment by using nanopar-
ticles of TiO
2
, ZnO, and Ce
2
O
3
. TiO
2
solution was prepared by controlled hydrolysis, using
a sol-gel technique. Tetrabutyl titanate was slowly poured into 20 ml of anhydrous ethanol
with stirring in a magnetic stirrer with a speed of 850 rpm. Another solution containing
1.5 ml of acetic acid, 20 ml of anhydrous ethanol, and 1.5 ml of water was prepared. The
reaction mixture was heated for 24 h. On completion of hydrolysis, a transparent solution
was obtained. The bottle was rolled in a way that the lower half was coated with an
n
-TiO
2
sol coating and the other remained uncoated. The bottle was heated at 105°C in an oven
until a thin layer of TiO
2
dried out. In another commercial practice, bottles of coated Pyrex
glass for TiO
2
coatings were used to ensure immobilization of TiO
2
nanoparticles was com-
plete. Finally, the bottle was annealed at 250°C for 15 h. Heating at 250°C is a prerequisite
for gelation and polymerization of the
n
-TiO
2
coatings.
The sol-gel reaction proceeds in two steps, hydrolysis and polycondensation, and leads
to the formation of polymers with a metal-oxide-based skeleton.
