Page 683 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

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

Hypochlorite: Hypochlorite ion is OCl . Common forms are span is about 7500–8800 h (based on one restart

sodium hypochlorite, NaOCl, solution, called every 8 h. The operating intensity declines with
‘‘bleach’’ and calcium hypochlorite, Ca(OCl) 2 .As time, for example, to 0.75 fraction of its output at
household bleach, the NaOCl solution strength var- 0 h by the end of its life span, for example, t(life
ies 3%–6%. In water treatment, 12%–15% NaOCl span) 8000 h.
solutions are used; NaOCl occurs only in the solu- Low-pressure high output (LPHO) lamp: The lamp has the
tion form. More commonly, however, Ca(OCl) 2 , that same monochromatic output of l ¼ 253.7 nm as the
is, ‘‘bleaching powder,’’ is used for larger scale uses low-pressure lamp, but the output power per unit
since it is cheaper than NaOCl solution and is pro- length is about 2–3 times that of the low-pressure
duced in a solid form. Bleaching powder is actually a lamp (Bolton, 2001, p. 17).
mixture of calcium hypochlorite Ca(ClO) 2 and the MCL: Maximum contaminant level (Federal Register,
basic chloride CaCl 2 , Ca(OH) 2 ,H 2 O with some December 16, 1998).
slaked lime, Ca(OH) 2 . Medium-pressure UV lamps: The medium-pressure mer-
Inactivation: (1) The rendering of an organism not capable cury lamps operate at pressure, 1 p(Hg) 10
for reproduction. (2) Killing of an organism, that is, atm, and temperature 5008C–8008C. Because of its
rendering the organism not capable of metabolism higher emission output, a medium-pressure lamp
(or of reproduction). [See also, disinfection.] may replace 6–16 low-pressure lamps. The spectrum
Iodine: A nonmetallic halogen element obtained usually of light energy emitted is more broadband than low-
as heavy shining blackish gray crystals and used pressure lamps. The lamp can carry up to 30,000 W.
especially in medicine, photography, and analysis. At maximum output, the bulb life ranges, 2000
Discovered in 1814 and named from the Greek t(life-span) 5000 h. Although the power required
‘‘ioeides.’’ MW ¼ 126.90447 g=mol. Iodine is as to deliver a given UV dose is higher than for a low-
effective as chlorine as a germicide and does not pressure lamp, the present value analysis shows that
react with ammonia and is effective at pH ¼ 7as the cost is less than low-pressure lamps (because
about 50% I 2 and 50% HOI. there are fewer lamps, the cost of lamps, lamp
Irradiance: (1) Radiance. (2) The density of radiation inci- replacement, and cleaning are less). The emission
dent on a given surface usually expressed in spectra cover 200 < l < 400 nm with several broad
watts per square centimeter or square meter (http:== peaks, most of which are outside the germicidal
www.merriam-webster.com). range. Those within the germicidal range seem to
Log removal: Log removal, that is, log R, as used in disin- have appreciably more energy than the low-pressure
fection, is the same as that used in filtration; it is a lamps (see Bolton, 2001, p. 18).
means to compare the influent concentration (of a MRDL: Maximum residual disinfectant level (Federal
microorganism in the case of disinfection) entering Register, December 16, 1998).
a reactor to the effluent concentration leaving the MRDLG: Maximum residual disinfectant level goal (Federal
reactor, that is, Register, December 16, 1998).
Log removal, log R: Defined: log R log N in log N out in
log R log C o log C which N in is the concentration in the influent and
N out is the concentration in the effluent of whatever
C o constituent species is being measured. Conversion to
¼ log
C %R is: %R ¼ 1 10 log R .
Monochromatic: (1) Radiation of a single wavelength. (2)
where log R is the common log of the removal ratio. From the Greek, ‘‘one color’’ (Silberberg, 1996,
The relationship between the %R and log R is, p. 258).
NPDES: National Pollution Discharge Elimination System
log R
%R ¼ 100 10
(an acronym introduced with PL-500).
The definition for log R and the associated relations Ozone: A highly reactive gas, produced by passing a stream
may be used for any reactor, for example, for adsorp- of dry air or oxygen between the electrodes. To be
tion, oxidation, filtration, etc. effective as a water disinfectant the ozone gas must
Low-Pressure UV Lamps: The most common lamps used be dissolved, usually by a diffuser located in the
for disinfection are ‘‘low-pressure’’ having a mercury reactor. MW ¼ 3 15.9994 ¼ 47.9982 g=mol. H(O 3 ,
vapor pressure, 10 3 p(Hg) 10 2 mm Hg with 208C) ¼ 482 mg=L=atm.
surface operating temperature 408C–508C; as noted pC: Negative logarithm of the concentration of an ion or
by DeMers and Renner in 1992, they mimic the molecule. For example, for a Clorox solution as
behavior of conventional fluorescent lamps (Snicer packaged, the label reads, ‘‘6% sodium hypochlor-
et al., 2000, p. 18). About 0.85 fraction of the energy ite,’’ which is 60 g NaOCl=L solution, or 60=74.5 or
emitted is at l ¼ 253.7 nm; the conversion of electric 0.80 mol NaOCl=L solution. pC ¼ log(0.80) ¼
energy applied to light is about 0.35–0.40. The life ( 0.097) 0.10. If the dilution is ten times,