Page 421 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

single treatment train by a sequential set of experiments,
which increases the time for an experimental program. Con-
ducting the experiments in parallel reduces the time, but
requires more manpower.

12.6.1 EQUIPMENT
The pilot plant schematic of Figure 12.43 shows some of the
equipment required and its configuration to investigate chem-
ical factors, for example, rapid-mix conditions may vary or
chemicals may vary in dosages, polymers, sequence, etc. If
physical conditions, for example, in filter design, are to be
investigated, a common pretreated water header would feed
one to four filters. The functions of a pilot plant which are the
same as a full-scale plant, for example, metering flow, meas-
uring selected influent and effluent characteristics, providing
for chemical additions, sampling taps, backwash, etc., are also
indicated in Figure 12.43. If the pilot plant set-up is dupli-
cated, for example, two, three, or even four trains, the experi-
mental program may progress faster. Too many treatment
trains, on the other hand, could load the laboratory and per-
haps the ability to process and assimilate data.
FIGURE 12.42 One of three pilot plant filters at Bellingham WTP;
rapid-mix precedes filters. (City of Bellingham, WA.) 12.6.1.1 Contaminant Injection
Quite often in pilot plant work, there is interest in testing
removals of specific contaminants, for example, MS-2
would cause a reduction in water quality and to determine virus, total coliform bacteria, certain algae, Giardia lamblia
the effect on length of run. Other questions were whether cysts, Cryptosporidium parvum oocysts, etc. (Hendricks et al.,
chemical dosages could be reduced as an economic question 2005; Al-Ani et al., 1986). Such tests provide a confirmation
and to confirm the capability of the system to remove various of the log removals of such organisms, which may be import-
organisms. ant for various reasons, and may be done by injecting a flow
The theoretical theme of a pilot plant, as in a full-scale of contaminants by a metering pump.
plant, is that chemical factors determine the attachment
efficiency and that physical factors determine the transport
efficiency. The former is related to operation and the latter
to design, for example, coagulant dosage, polymer selec-
tion, pH, etc., and media depth, media size, HLR, etc.,
respectively. In addition, the pilot plant study may determine P P P
the rate of headloss increase, which is affected by the size of
floc and the pore sizes, that is, both chemical and physical P T PC FM ~
factors.
In experiment design, all independent variables, for Sample tap
example, source water, pH, coagulant dosage, HLR, media ~
design, etc., are maintained constant. The selected dependent
variables, for example, effluent turbidity, headloss, are then
measured during the course of the run. For the next several
runs, one independent variable is changed, for example, HLR,
~
and its effect on turbidity and headloss is determined. The ~-Valve P FM ~
single treatment train may be split, if desired, to two or three P-Pump T PC ~
filters each with a different media; this permits comparing the T-Turbidimeter ~
effluent turbidity versus HLR relation for three media designs PC-Particle counter FM Sample tap
(i.e., physical variables). On the other hand, if two treatment P
FM-Flow meter
trains are used, that is, each with its own rapid-mix, identical
filtration columns, etc., then the effect of chemical variables FIGURE 12.43 Pilot plant set-up to investigate chemical factors of
may be explored. The same thing may be done with only a design.