Page 553 - Industrial Wastewater Treatment, Recycling and Reuse

Industrial Wastewater Treatment, Recycling, and Reuse—Past, Present and Future 523

20in%20the%20US.pdf; http://www.activatedsludgeconference.com/
downloads/OneHundredYearsofActivatedSludge-Abriefhistory.pdf). In
the following years, increased understanding of wastewaters led to the
evolution of various treatment methods, especially for the removal of
odor, color, and solids. The main methods included adsorption, ion
exchange, coagulation, and chemical treatment. The application of
the ASP created a secondary treatment problem in the form of sludge gen-
eration, and methods were researched to minimize sludge production,
compacting, and other undesired results. The importance of dissolved
oxygen was also realized during this period.
After 1950, waste water treatment scenario changed dramatically. Global
industrial development also increased in speed and scale, largely due to the
emergence of technologies in the form of novel materials, processes, and
equipment configurations and devices. During this period, communities also
developed new regulations for the release and treatment of wastewaters,
fuelling further advances in water management. An increased understanding
of biological oxygen demand and chemical oxygen demand propelled the
development of methodologies for reducing the organic load in waste-
waters, as well as the classification of pollutants in different forms. The mem-
brane separation process also started in this period, with simple symmetric
membranes acting merely as filtration medium. Asymmetric membranes fol-
lowed, allowing for increased flux, as did membranes with diverse materials,
better characteristics, and improved mechanical and chemical properties.
Eventually, more complex hybrid membranes systems emerged, providing
facilitated transport and reactive membranes for highly specific applications.
This development, needless to say, widened the scope of application tre-
mendously for industrial wastewater treatment (Microfiltration, Ultrafiltra-
tion, Nanofiltration, Reverse Osmosis, emulsion liquid membranes,
membrane distillation) and also altered biological treatments in the form
of membrane bioreactors. Aside from the developments in technology
and instrumentation, overall awareness about environmental pollution
and more particularly water pollution increased tremendously in the late
twentieth century.

14.3 THE PRESENT

Present day industrial wastewater treatment involves primary, secondary,
and tertiary treatment stages. It also tends to employ a combination of chem-
ical and biological treatment methods in order to meet the discharge norms