Page 50 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Water Treatment 5

The membrane processes are different in pore size and in 1.3.3 BREADTH OF UNIT PROCESSES AND TECHNOLOGIES
pressures required; defined pores may be lacking, in fact, for
To illustrate the idea further, Table 1.1 lists some 15 unit
the latter two membrane processes:
processes with samples of associated treatment technologies.
The list of associated technologies is not complete, nor does it
. Biological treatment. A reaction between an organic
show the range of variation. The technologies are listed gen-
molecule and a microorganism
erically. If proprietary technologies were listed, Table 1.1
. Disinfection. The inactivation of microorganisms
might be several pages long. All of this is mentioned so that
. Oxidation. The gain of electrons by chemical
one may gain an appreciation for the breadth of the number of
reaction
. Precipitation. The formation of a solid substance technologies that have been developed.
Table CD1.2 is an excerpt from a matrix with some 700
from ions in solution
contaminants listed in rows and 11 basic unit processes listed
in columns with selected technologies under each unit process
To the extent possible, these unit processes are described
(Champlin and Hendricks, 1993). Columns further to the right
in terms of principles. As a rule, however, scientific
list variations. Looking down the columns, the contaminants
principles alone do not provide for a ‘‘complete’’ engineering
that may be subject to treatment by a given technology are
solution.
designated by a code in the intersecting cell based upon the
Engineering has the characteristic that a solution to a
expected percent removal. The matrix expands on what is
problem is the important thing. A problem to be solved
shown in Table 1.1 but includes a listing of contaminants.
cannot wait for a rational explanation. So while the scientific
Table CD1.2a shows an overall layout of the matrix, i.e.,
explanation is sought, it is often necessary to make do with
how to navigate, while Table CD1.2b is the large matrix
some means to make a decision about design. Such methods
with some 700 rows and 100 columns. The idea of the large
may involve judgment, a knowledge of scientific principles,
matrix is to give an appreciation for the scope of water
modeling, laboratory testing, lore concerning how things
treatment as a field of practice.
have been done in the past, rules of thumb, the use of some
kind of calculation method such as a loading rate, associated
criteria, etc. Thus, while the book describes what is known
1.3.4 PROPRIETARY TECHNOLOGIES
as the rationale for a process design, methods used in
practice are reviewed also. (The view taken here is that Proprietary innovation plays a large part in technologies.
the foregoing provides a means for decision-making. Several manufacturers offer their own ‘‘packages’’ of tech-
Scientific certainty and accuracy are sought, but the main nology for the deep-bed filtration process, for example. To
thingistoprovide a basis forachievingadefined level of illustrate, the Parkson Dynasandt filter is a moving bed filter
system performance and doing so economically and with that takes off the floc-saturated media at the bottom, replen-
asocial ‘‘fit.’’) ishes the filter bed at the top, and so backwash is not
A ‘‘state’’ is defined here as the water quality character- required. The Culligan Multi-Techt filter is a complete pack-
istics of a given parcel of water and may include concentra- age plant that provides the means for flocculation within a
tions of suspended solids (including organisms), ions, and coarse media preceding the main filter and is designed for
molecules; temperature; pH; etc. A treatment ‘‘process’’ is the complete automation of the filtration process. The Infilco-
intended to cause a desired change of the state of a volume Dregemont ABWt (automatic backwash) filtration system is
of water. The idea of a water quality ‘‘state’’ was taken from a shallow-bed filter comprised of a series of transverse cells
the field of physical chemistry in which the state of a gas is 305 mm (1.0 ft) wide. A traveling bridge with a hood to
defined by its temperature, pressure, and volume. collect the backwash flow and a backwash pump with ‘‘shoe’’
that places the backwash plumbing over the under-drain open-
ing in the finished water channel provides for a short
1.3.2 TECHNOLOGIES
duration backwash of a single cell. The bridge moves then
For a given unit process, a technology is a means for imple- to the next cell and the filter as a whole is never taken out
mentation. For example, a rapid filter is a means to imple- of operation.
ment a ‘‘deep-bed’’ filtration process. The rapid filter The filtration example illustrates the role of proprietary
includes the array of appurtenances to make it work, e.g., companies in making successful a given process. Essentially,
the filter box depth and area, under-drain system, and back- an array of proprietary technologies have been developed for
wash system. Rules of thumb, tradition, and manufacturer’s each unit process either to provide support for a generic
standards govern the sizing and characteristics of each design such as ancillary equipment or to provide a full oper-
component. ational package technology. Two or three of the unit pro-
In short, a technology is a ‘‘package’’ of design guide- cesses have been developed largely under the impetus of
lines and components that result in a system that supports proprietary research. An example is the membrane processes
a workable process. The manufacturer may provide a that have evolved commercially since the 1960s and have
complete package or some of all of the supporting components. reached the status of widespread use.