Humic Substances
The drop on water
Humic
substances are the end product of decaying organic matter.
Tannin and lignin are organic compounds
similar to humic substances.
Tannin is a complex organic compound found
naturally in soil and in certain tree barks.
Lignin is a natural compound common in woody
plants and trees.
Source
Humic
substances come from the accumulation and natural chemical reaction of by-products
produced by the biodegradation of organic matter.
They are commonly present in soils, surface
water, sewage, compost heaps, marine and lake sediments, peat bogs,
carbonaceous shales and lignites.
There are three types of humic substances,
which differ slightly in acidity and chemical composition. They are:
- humic acid,
- fulvic acid, and
- humin.
Tannin is abundant in the bark, fruit, and
leaves of plant material. Lignin is one of the principal constituents of the
woody structure of seed plants.
Tannin and lignin are part of a natural group
of organic substances in soil, produced by decaying vegetation.
The main source of humic substances, tannin,
and lignin is natural organic material. They may also be present in groundwater
due to:
• the
proximity to areas underlain by coal
• the
dissolution of bark mulch
• buried
organic debris such as tree stumps
• the
wastewaters of leather and wood-working industries (tannin and lignin)
• pulp and
paper mill effluent (lignin)
QUICK FACTS
• Humic
substances are the end product of decaying organic matter.
• Tannin
and lignin are natural organic substances found in plants and soil.
• Humic
substances, tannin, and lignin may be present in well water that is
hydraulically connected to surface water, but may also be found in certain
bedrock types, such as those containing coal.
• No
numerical drinking water quality guidelines exist for humic substances, tannin,
or lignin. Their presence may sometimes be inferred from measurement of color
and dissolved organic carbon.
• Humic
substances, tannin, and lignin may affect the taste, color, or smell of
drinking water.
The presence of humic substances, tannin, or
lignin in well water may indicate a natural benign source or the presence of
other contaminants in the water.
• Several
treatment options can reduce the concentration of humic substances, tannin, and
lignin in drinking water.
Humic substances, tannin, and lignin are most
common in surface water and shallow groundwater hydraulically connected to
surface waters or wetlands.
These organic substances may occasionally be
found in well water, particularly if the well is not properly constructed.
Maximum Acceptable Concentration for Drinking
Water
No
numerical drinking water quality guidelines exist for tannin, lignin, or humic substances.
Humic Substances in Drinking Water
Humic
substances are not believed to be harmful to human health.
At higher concentrations, humic substances
can impart a characteristic yellowish to brownish color in water, and can cause
drinking water to have a bitter taste or unpleasant odor.
The odor is not from the humic substances
themselves.
Humic acid may stimulate the growth of
aquatic micro-organisms, some of which may produce an odor.
The presence of humic substances in drinkingwater may be due to natural organic sources, but may also indicate
contamination from surface water sources.
The presence of pathogens or other
contaminants present in surface water may cause adverse health effects.
Humic substances can adsorb a variety of
organic substances.
Many metals present in drinking water can
also react with humic substances in water, which can increase the concentration
of metals in the water.
Tannin and Lignin in Drinking Water
Tannin and
lignin can impart a yellow or light brown color, bitter taste, and unpleasantodor in drinking water.
The presence of tannin or lignin in drinking
water may be from benign natural sources, but could be cause for concern if
contaminants present in surface water are also present in well water.
Solutions
If humic
substances, tannin, or lignin are suspected or found to be present in well
water, it may be due to natural conditions.
Or may mean that the groundwater in the well
is under the direct influence of surface water.
To determine whether humic substances,
tannin, or lignin are naturally present in the groundwater or if microbial
pathogens are able to travel from nearby surface water to the groundwater
source, you should:
• have a
water quality professional investigate the source of the contamination
• check
the bacterial quality of the water
• inspect
the well construction If bacterial quality and well construction are
acceptable, and there is no evidence of other contamination, treating yourwater is optional.
You may wish to
• Obtain
drinking water from an alternate source, such as bottled water or a nearby well
that has been tested and found to be safe.
• Install
a treatment system to improve the appearance of your water.
Treatment
There are
currently no treatment units certified specifically for the reduction of humic
substances, tannin, or lignin.
Effective treatment methods for reducing
their levels in drinking water include
• anion exchange
The best treatment option may depend on the
source of the humic substance, tannin, or lignin.
Once installed, re-test your water to ensure
the treatment system is working properly.
Maintain the system according to the
manufacturer’s instructions to ensure a continued supply of safe drinking water
Considerations
The characteristics
of iron, iron bacteria, and humic substances can be very similar in drinking
water.
It is important to determine which of these
is causing water problems, because the treatment options are very different.
Chlorine can be used to treat iron and ironbacteria, but chlorine added to water containing humic substances may
contribute to the formation of trihalomethanes (THMs).
Eliminating humic substances, tannin, and
lignin is extremely difficult, especially at higher concentrations.
The presence of humic substances, tannin, and
lignin may also affect the efficiency of several other types of treatment units
for other parameters.
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