Water Quality
Ambient Water Quality Criteria for Dissolved
Oxygen
5.0 Other Water Uses
5.1 Drinking Water
There are both positive and negative attributes
of having dissolved oxygen in domestic drinking water. While
corrosion within older cast iron water supply systems is a result
of oxidative processes, the effects of oxygen are mostly beneficial.
Dissolved oxygen prevents the chemical reaction and leaching
of iron and manganese from the sediments in source water, which
otherwise would stain plumbing fixtures and cause taste problems.
It facilitates the biochemical oxidation of ammonia to nitrate,
reduces the chlorine demand of waters and increases the disinfection
efficiency of chlorination (NAS/NAE, 1972). Also, a high level
of dissolved oxygen is generally considered more palatable in
water, as opposed to there being a 'flat' taste.
Dissolved oxygen criteria for drinking water which exist in
adjacent jurisdictions include: 5 mg/L minimum-same as for aquatic
life (Alberta Environment, 1977), >8.0->9.5 mg/L-same as
for aquatic life (State of Washington, 1982) and 4 mg/L (Alaska,
1979). Public drinking water supplies in British Columbia are
generally well-oxygenated and an additional criterion for this
category is not considered necessary at this time.
5.2 Recreation and Aesthetics
Most agencies, including the CCREM (1987)
and US EPA (1986), have not developed dissolved oxygen criteria
for recreational uses or the aesthetic quality of natural waters.
Where such criteria do exist, they are typically within an all-encompassing
limit to be applied to the most sensitive water use category.
A separate criterion for recreation/aesthetics could be intended
as an indirect safeguard to preserve the natural vitality of
a waterbody for people's enjoyment, rather than be directly related
to recreation / aesthetic use per se. A possible application
might be where aquatic life was negligible or absent and an aquatic
life criterion could not be used. If such waters were characterized
by excessive decomposition of natural organic material or discharged
wastes, in an anaerobic reducing environment for example, odorous
byproducts such as hydrogen sulphide and unsightly surface films
could be a problem.
Criteria for recreation and aesthetics which exist in neighbouring
jurisdictions are listed in Table 14.
Table 14. Dissolved Oxygen Criteria for Recreation
/ Aesthetics from Various Sources
|
|
Criteria
Value
(mg O2/L)
|
|
|
(i) Freshwater
A minimum of
5 mg/L at any time
|
5
|
Alberta Env.,
1977
|
Dissolved
oxygen (D.O.) shall be 4 mg/L
|
4
|
Alaska,
1979
|
Primary
contact recreation: (dependent upon State classification
of water value)
|
>8.0
- >9.5
|
State
of Wash., 1982
|
For
lakes, no decrease from natural conditions
|
|
|
Secondary
contact recreation:
|
6.5
|
|
(ii) Marine
Surface D.O.
in coastal water shall not be <6.0 mg/L for a depth
of 1 m except when natural condition cause this value
to be depressed. D.O. shall not be reduced below
4 mg/L
at any point beneath the surface. D.O. in estuaries
and tidal tributaries shall not be <5.0 mg/L except
where natural conditions cause this value to be depressed.
In no case shall D.O. levels above 17 mg/L be permitted.
|
5-6
<17
|
Alaska, 1979
|
Primary
contact recreation:
D.O. shall
exceed 6.0 or
7.0 mg/L depending
upon the classification. When natural conditions such
as upwelling occur, causing the D.O. to be depressed
near or below these levels, natural D.O. levels can
be degraded up to 0.2 mg/L by man-caused activities.
|
>6.0
- >7.0
|
State
of Wash., 1982
|
Secondary
contact recreation:
D.O. shall
exceed 4.0 or
5.0 mg/L depending
upon the classification (and as above).
|
>4.0->5.0
|
|
Dissolved oxygen criteria for recreation and aesthetics
are not deemed necessary for British Columbia, as the criteria
for aquatic life can be protective of virtually all waters implicated
in these use categories.
5.3 Industry
5.3.1 Effects
With the exception of the food and beverage
industries (using production water) and aquaculture, the presence
of natural levels of dissolved oxygen in water for industrial
operations generally is undesirable for the following reasons:
- Oxygen increases corrosion in metal
pipes and related equipment, particularly in heating (boilers)
and cooling systems. In a packaged power reactor, dissolved
oxygen
can cause stress corrosion of stainless steel (McKee and
Wolfe, 1963). These corrosive effects increase substantially
in the
presence of low pH.
- Oxygen promotes slime-forming organisms
and deposits, and interferes with paper fibre retention in
pulp
and paper processing (CCREM, 1987). Dissolved oxygen reduces
hydrogen
bonding between fibres, which can cause imbalance of clays
and fines in pulping stock (Schmok, 1992).
5.3.2 Criteria from the Literature
Water quality requirements of industries are as varied as the products
they produce and it is not within the scope of this report to identify
specific dissolved oxygen criteria except those generally quoted for generic
uses. It is accepted that industries incorporate conditioning processes
to provide the quality levels necessary. Common additives to remove oxygen
are sulphites and hydrazine.
The pulp and paper industry is the largest industrial process water user
in British Columbia. On an industry-wide basis in Canada, the major use
categories are cooling, condensing and steam generation (CCREM, 1987).
Table 15 contains a listing of the more common guidelines for dissolved
oxygen in major industries. Since the low concentrations of dissolved
oxygen necessary for industry have little relation to natural levels and
must be attained by internal scavenging processes, no criteria for intake
water are proposed. In the specific case of food processing water, which
typically has some minimum dissolved oxygen requirement, the aquatic life
criteria established in Section 4 would be adequate for this use. Similarly,
oxygen requirements for the aquaculture industry (marine and freshwater)
should be adequately met by the aquatic life criteria herein. As the level
of survival success under natural conditions is not acceptable to fish
hatchery operators, incubation systems attempt to optimize physical variables
such as oxygen and temperature throughout development. These requirements
do not fall within the scope of ambient criteria. Models such as that
of Rombough (1986) have been prepared on the oxygen requirements of hatchery
fish, and some of the references cited earlier cover this subject (e.g.,
SIGMA, 1983 and Rombough, 1988).
Table 15. Dissolved Oxygen Criteria for Industry from
Various Sources
|
Criteria statement
|
Criteria
Value
(mg o2/L)
|
Reference
|
(i)
Freshwater
Levels should
not exceed 0.03 mg O2/L to prevent stress
corrosion of stainless steel in packaged power reactors
|
0.03
|
McKee and Wolfe,
1963
|
Levels
for boiler feed water not to exceed:
2 mg O2/L
for 0-1.03 M Pa; 0.2 mg O2/L for 1.03-1.72
M Pa; and 0.0 mg O2/L for >1.72 M Pa
|
2.0
0.2
0.0
(depending
on pressure)
|
McKee
and Wolfe, 1963
|
Some
industrial uses
|
4.0
|
DOE,
1972
|
Maximum
levels for feedwater at the following operating pressures:low
(0-1.03 M Pa) 2.5 mg O2/L, moderate (1.03-4.83
M Pa) 0.007 mg O2/L and high (4.83-10.34)
0.007 mg O2/L. For electrical utilities (pressure
between 10.34-34.48 M Pa) 0.007 mg O2/L
|
2.5
(boiler)
0.007
(depending
on pressure)
|
NAS/NAE,
1972
|
Minimum
to maintain aerobic conditions at point of use for the
iron and steel industry
|
aerobic
|
NAS/NAE,1972
CCME, 1987
|
Industrial
uses (other than food processing)
-no detrimental
effects on established water supply treatment levels
|
|
Alaska,
1979
|
Industrial
uses (other than food processing)
|
3.0
|
Montana,
1980
|
Industrial
water
|
4.0
|
State
of Wash., 1982
|
Levels
to be less than the following for feedwater incurrent
design industrial steam generators-assumes the pressure
of a deaerator but measured before chemical oxygen scavenging:
Industrial
Watertube
0-3.1 M Pa:
0.04 mg O2/L
3.11-13.7 M
Pa: 0.007 mg O2/L
Industrial
Firetube w/o Superheater
0-2.07 M Pa:
0.04 mg O2/L
Industrial
Coil-Type Watertube
0-4.14 M Pa:
0.2 mgO2/L
>4.14 M
Pa: 0.007 mg O2/L
|
0.2
0.04
0.007
(depending
on pressure)
|
CCME,
1987
|
(ii)
Marine
Seafood processing
|
>5
|
Alaska, 1979
|
