Environmental Engineering Reference
In-Depth Information
Problems with tastes and odors are usually associated with surface rather
than groundwater. Surface water taste and odor problems are normally
caused by algae and other microorganisms, whereas groundwater taste and
odor problems are generally the result of human interference or influence
(e.g., landfill leachate).
Note:
The human ability to detect odor thresholds of various substances
in water ranges from a low of about 1 µg/L for methylisoborneol to a
high of about 20 mg/L for chloroform.
For testing performed in laboratories, consult
Standard Methods for the
Examination of Water and Wastewater
(Appendix A-VIII, “General References”).
The qualitative terms used to describe taste and odor are often classified
as grassy, swampy, septic, musty, fishy, phenolic, and sweet. In water treat-
ment, one of the common methods used to remove taste and odor is to use
oxidants, including potassium permanganate and chlorine, to oxidize the
materials causing the problem. Another common treatment method is to
feed powdered activated carbon prior to the filter. The activated carbon has
numerous small openings that adsorb the components that cause the odor
and tastes. Taste and odor problems are also often controlled by watershed
management, algicides, aeration, and pretreatment. Properly functioning
water filtration systems help to minimize taste and odor problems, as well.
Odor is typically measured and expressed in terms of a
threshold odor num-
ber
(TON), which represents the dilution required to make the odor become
virtually unnoticeable. In 1989, the USEPA issued a secondary maximum
contaminant level (SMCL) of 3 TON for odor. (Remember that secondary
standards apply to parameters not related to health.) When a dilution is
used, a number can be devised to describe clarifying odor:
VV
V
ThresholdOdorNumber =
T
D
( 7.1)
T
where
V
T
= volume tested, and
V
D
= volume of dilution with odor-free dis-
tilled water. For
V
D
= 0, TON = 1 (lowest value possible); for
V
D
=
V
T
, TON =
2; for
V
D
= 2
V
T
, TON = 3, etc.
Note:
Although taste and odor (along with color) are seldom connected
to toxicological effects, the drinking water practitioner should never be
fooled into assuming that a water supply with a “bit” of taste and odor
will not offend the consumer. It will.
DID YoU KNoW?
1 liter = 0.2642 gallons = 1.0568 quarts = 61.02 cubic inches
