Page 52 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Water Treatment 7

TABLE 1.1 (continued)
Unit Processes and Associated Technologies
No. Unit Process Principle Treatment Technologies
12 Oxidation Electrons are removed from outer shell of substance being oxidized Chlorine
Chlorine dioxide
Ozone
Ozone-hydrogen peroxide
Potassium permanganate
Ultraviolet radiation
13 Supercritical oxidation Pressure and temperature are raised to create supercritical conditions Wet air oxidation
High pressure high temperature
oxidation
14 Aerobic biological treatment Bacterial enzymes permit metabolism of organic molecules with products Activated sludge
new bacteria, carbon dioxide, and water Complete mix
Plug flow
Aerated lagoon
Facultative pond
Fixed film reactor
Trickling filters (traditional)
Bio-filters (forced air)
Rotating biological contactor
15 Anaerobic biological treatment Two stage reaction: acid formers metabolize organic molecules with organic Anaerobic biological reactor
acids as products and methane formers metabolized organic acids to Digester
produce methane and carbon dioxide Anaerobic pond
Anaerobic filter

treatment of wastewaters became an issue after 1860 in England
TABLE CD1.2 where chemical precipitation became one of the first unit pro-
Treatment Technology Matrix (Excerpt from cesses, but did not develop into widespread use. In 1880, the
Table CD1.2b) Lawrence Experiment Station was established (Massachusetts,
1953) that later led in the development of several technologies,
CAS Contaminant Empirical
including trickling filters, and where experimentation inspired
No. Water Contaminant Numbers Type Formula
Ardern and Lockett to develop activated sludge in England in
1 Acenaphthene 83-32-9 PAH C 12 H 10
1914. Settling, called ‘‘subsidence,’’ was well established by
2 Acenaphthylene 208-96-8 PAH C 12 H 8
1900; the technology was cheap and was an obvious alternative.
3 Acetaldehyde 75-07-0 Aldehyde C 2 H 4 O
By 1885, deep-bed filtration was an innovation that by 1900 had
4 Acetamide 60-35-5 Not found
become established in America. In Europe, Klaus Imhoff devel-
5 Acetamide, 2832-40-8 Not found
oped the Imhoff Tank about 1905 and Cameron in England
N[4-[(2-hydroxy-5-
developed the septic tank. How the stage was set for the devel-
methyl . . . )]]
opment of environmental engineering as a field from Ancient
6 Acetone 67-64-1 Ketone C 3 H 6 O
times to 1900 was reviewed by Symons (2001).
7 Acetone cyanohydrin 75-86-5 Nitrile C 4 H 7 NO
Ion exchange had been known scientifically by early 1800,
and became an established technology for softening by 1924
using zeolites. The use of chlorine, ozone, and ultraviolet radi-
ation as disinfectants were established by 1900. Ozone was
1.3.5 STATUS OF UNIT PROCESSES
adopted widely in Europe, while chlorine became established
The treatment of water became an issue in the first decades of the in America. By the third decade of the twentieth century, gas-
nineteenth century with drinking water. In this context, James eous chlorine became the technology of choice (in the United
Simpson developed the slow sand filtration technology for Lon- States). Advances in the application of technologies have con-
don, enumerating design guidelines and support components to tinued over the following decades. The point is that water
have a workable process. Slow sand became an accepted tech- treatment technologies have been developing and expanding
nology for drinking water by the 1870s and was in widespread starting only since 1829 with slow sand. The impetus has been
use, particularly in Europe, by 1890, where it was credited societal issues that were recognized as government responsibil-
with saving Altoona, Germany, from a cholera epidemic. The ities with advances through research and practice.