Page 332 - Industrial Wastewater Treatment, Recycling and Reuse

304 Industrial Wastewater Treatment, Recycling, and Reuse

expected with both primary treatment and chemical precipitation.
Newer technologies offering significantly higher removal rates need to
be designed and implemented, e.g., membrane technologies are now
increasingly used for the production of high-quality water for indirect
potable reuse and are expected to lead current treatment technologies
in the near future, either in isolation or in combination in the form of
process integration.
In view of the continued development in the area of sewage treatment
and also in view of the fact that sewage wastewaters are relatively easy to
treat, especially using biological methods, it is recommended that most
appropriate technologies be used for proper treatment such that the water
can be treated reused. The concept of wastewater treatment, recycling,
and reuse is most appropriate in this case, and it is believed that it can sub-
stantially alleviate the pains of water scarcity by reducing water requirements
significantly—be it for public consumption or for agricultural application.
The benefits go beyond water treatment, recycling, and reuse. The successful
operation in this regard would relieve the rivers from pollution, reduce health
hazards to the surrounding population, and thereby increase sustainability. It
will be most appropriate that some industries in the adjoining area also be
involved in this scheme so that if the industrial wastewater is not severely pol-
luted, it can also be included in the treatment. Alternatively, industries can also
be assigned part of the wastewater treatment, if they can treat wastewater bet-
ter than the conventional approach for enhanced reuse. This type of cooper-
ation at local and governmental level can certainly help.

7.3.1 Urban Sewage: Primary and Secondary Treatment
Options
7.3.1.1 Primary Treatment
The first step in wastewater treatment involves separating large pieces of
debris when the wastewater first enters the treatment plant. Debris may
include wood, cloth, plastics, glass, metal, sand, and gravel. This is referred
to as pretreatment.
The wastewater is held in a large sedimentation tank for several hours.
This allows heavier solids to settle to the bottom and form a sludge layer.
Lighter solids, fats, oil, and grease float to the top, creating a scum layer.
The solids and scum are removed to receive further treatment as sludge.
The clarified wastewater flows on to the next stage of wastewater treatment
if there is to be further treatment of the effluent. If primary treatment is the