Page 595 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

550 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

17.2.1.1 Beginnings American Membrane Technology Association (AMTA)
Asymmetry of pores in animal membranes was reported in ‘‘Hall-of-Fame’’ in 2009, honouring his many decades of
1845. Also, in 1845, nitrocellulose, a generic name for the innovation and leadership in the field. By 1968, there was
nitration products of cellulose, was synthesized accidentally, hope of desalination by RO, but the technology was expensive
which paved the way for synthetic membranes. Collodion, a (Anon., 1968, pp. 60–64). By about 1975, however, mem-
term for such cellulosic polymers, is a solution of nitrocellulose branes were operational for the Orange County Water District
in an ether–alcohol mixture or an acetic acid–acetone mixture, Plant (Water Factory 21) as the final unit process in a treatment
which when poured over a flat surface was found to form a thin train for treating the wastewaters for recharging groundwater.
film. Pore structure was controlled by the time allowed for the
evaporation of solvents. By 1872, collodion membranes were 17.3 THEORY
formed in sheets. At this time, membranes were viewed as
objects of curiosity but with little practical value. Issues of theory relate to solute or particle rejection and
permeate flux density. These are the ‘‘dependent’’ variables.
17.2.1.2 The Development Period The independent variables depend, in general, on the kind of
In 1918, Zsigmondy and Bachmann at the University of membrane, operating factors, and feed-flow water quality.
Göttingen patented a graded series of membranes and used
cellulose and esters of cellulose in a method proposed for
17.3.1 PERFORMANCE VARIABLES
commercial production of membrane filters. The membranes
had conical pores, as with Brown’s membranes. The Zsig- The key variables of performance are effluent concentrations
mondy method led to the developmental period of membrane (of constituents of interest), flux density vs. time (and thus
technology. ‘‘run-length’’), transmembrane pressure, and costs (capital and
Before World War II, membranes were used mostly to operating). Table 17.5 lists these as ‘‘dependent’’ variables
remove microorganisms and particles from liquids, in diffusion and shows in the right-hand column the associated ‘‘independ-
studies, and for sizing macromolecules. The art of using the ent’’ variables.
membrane filters for growing bacterial colonies on the surface
was to come later. This idea was developed by the Germans in
17.3.2 SOLUTE=PARTICLE REJECTION
World War II as a means to determine more rapidly the bacter-
ial quality of their drinking water. Mueller and others devel- Membranes are, technically speaking, ‘‘screen’’ filters (as
oped the membrane filtering and culturing process, the one that opposed to ‘‘depth’’ filters). Screen filters, by definition, retain
is commonly used today, to quickly assess drinking water material that is smaller than the opening of the screen. Screen
quality. This was developed further in 1951 by Goetz at the filters have defined pore sizes and can therefore be given a
California Institute of Technology, which led to the widespread
adoption of the membrane filter method for enumeration of
bacteria, that is, by the Millipore Corporation. TABLE 17.5
Variables in Membrane Process
17.2.1.3 Modern Period
Dependent Variables Independent Variables
RO membranes were invented independently by Reid and
Brenton at University of Florida and by Sourirajan at UCLA Concentrations in effluent Concentrations in influent
in 1958. Later Leob working with Sourirajan invented a film Membrane pore size
casting technique for the production of asymmetric CA mem- Product flow, Q P Feed flow, Q F , Q C
branes that serves as the basis for modern membrane manu- Flux density, j P ¼ Q P =A Concentrate flow, Q C
(membrane) R ¼ Q P =Q F
facturing (Saurirajan, 1981; Loeb, 1981). Following this, that
Pressure differential, Dp, across
is, during the 1960s and 1970s, a sequence of materials were
membrane
used and included cellulose triacetate, polyvinyl chloride,
Solute chemical composition
nylon, polycarbonate, polyamide, and polysulfone (see also,
Solute MW
Turbak, 1981a,b).
pH
Membrane used
17.2.2 MEMBRANES IN WATER TREATMENT PRACTICE Run length Particle kind and composition
SDI
The major breakthrough that led to modern membrane water
Scaling potential
treatment practice was the work of Sourirajan and Leob who
Biological fouling potential
discovered how to make anisotropic membranes and then Disposal cost Site
learned how to cast a membrane sheet. So it was about 1962 Cost Pretreatment
when several companies were borne from embryo start-ups Membrane used
along the Los Angeles–San Diego axis (from discussion with Reject disposal
D. Furukawa, c. 1996) with the goal of seawater desalination. Source water
As a note, David H. Furukawa was inducted into the