Environmental Engineering Reference
In-Depth Information
The greatest challenge that mankind faces today is to solve the problem of scarcity of
clean water by tapping various sustainable and nonsustainable resources and to devise
cost-effective technologies for water treatment to provide healthy drinking water. These
include microiltration, ultrailtration, reverse osmosis, and nanoiltration. The materi-
als include polyvinylidene luoride, polysulfones, polyacrylonitriles, and polyvinyl chlo-
ride compounds. Nanomembranes are made from cellulose acetate and cellulose nitrate
blends [3,4].
1.2 Some Facts and Figures Related to Pollution
It has been reported that at least 50,000 people die daily worldwide because of waterborne
diseases. In South Africa, 12 million people do not have access to adequate water sup-
ply [5]. Contaminated water may contain viruses, bacteria, and pathogens that may cause
diarrhea, dysentery, typhoid, and hepatitis. Millions are exposed each year to unsafe level
during storms, loods, and natural and man-made disasters. Open sewers increase the
risk of contamination of various pathogenic agents. The major sources of contamination
include industrial waste; agriculture and domestic wastes; and discharge of waste from
the industries of manufacturing, power generation, mining, textiles, and construction
sites. Most of the mortality and morbidity in developing countries is associated with infec-
tion agents, causing cholera, dysentery, typhoid, paratyphoid, scabies, yaws, skin ulcers,
and trachoma. Many insects breed in water and cause malaria, dengue, yellow fever, and
onchocerciasis (river blindness). Several techniques have been used for water treatment
since the Egyptians discovered the principles of coagulation in 1871. They applied chemi-
cal alum for suspended particle settlement. The processes of coagulation and locculation
have been employed to separate suspended solids from water. Unit operations such as
coagulation, locculation, precipitation, ion exchange, membrane separation, aeration, and
adsorption have been employed to clarify water [5]. In recent years, various types of mem-
branes have been developed. They increase production, reduce energy costs, reduce yield
costs, and are emission compliant.
Nanotechnology has shown considerable potential for remediation of contaminated
waste. This technology enhances reactivity because of the increasing ratio of the aggregate
reactive surface area to the aggregate particle volume as the particle size decreases. A vari-
ety of materials, such as zeolites, carbon nanotubes, biopolymers, and zero valence nanopar-
ticles, are the focus of attention of engineers and scientists [6]. Considerable improvements
in the water treatment methods during the last decades have been reported [7-9].
HaloPure
®
(HaloSource) is an example of technical advancement in the development of
an entirely new biocidal medium in the form of chlorine rechargeable polystyrene beads.
Polystyrene beads are chemically modiied to enable them to bind chlorine and bromine
reversibly in oxidative form. Almost no free chlorine is released when the beads are placed
in water [10]. A solid form is obtained that is biocidal and rechargeable on exposure to free
halogens. A powerful antibacterial component is introduced that does not need recharging.
Microorganisms making contact with the surface are killed or inactivated. Advanced meth-
ods have always remained in demand for the removal of persistent organic pollutants from
wastewater and groundwater. Photocatalytic methods have proven very effective. These
methods are based on the generation of highly reactive hydroxyl radicals (OH
∙
) and
O
2
−
using ultraviolet (UV)/titanium dioxide (TiO
2
) combination leading to degradation [11-13].
