Environmental Engineering Reference
In-Depth Information
mainly carbonate, bicarbonate, chloride, sulfate, nitrate, potassium, sodium,
magnesium, and calcium. Organic material such as plant fibers and biological
solids (e.g., bacteria) are also common constituents of surface waters. Inorganics
include clay, silt, and other soil constituents common in surface waters. These
materials are often natural contaminants resulting from the erosive action of
water flowing over surfaces. The filtering properties of soil generally mean
that suspended solids are seldom a constituent of groundwater.
Other suspended material may result from human use of the water; for
example, domestic wastewater usually contains large quantities of suspended
solids that are mostly organic in nature. Industrial use of water may result
in a wide variety of organic or inorganic suspended impurities. Immiscible
liquids such as oils and greases are often constituents of wastewater.
The solids parameter is used to evaluate and measure all suspended and
dissolved matters in water. Solids are classified (in spite of their chemical
composition) among the physical parameters of water quality. In water, sus-
pended material is objectionable because it provides adsorption sites for
biological and chemical agents. These adsorption sites provide a protective
barrier for attached microorganisms against the chemical action of chlo-
rine disinfectants. Suspended solids in water may be degraded biologically,
resulting in objectionable byproducts. These factors make the removal of
these solids of great concern in the production of clean, safe drinking water
and wastewater effluent. In water treatment, the most effective means of
removing solids from water is by filtration; however, some solids, (including
colloids and other dissolved solids) cannot be removed by filtration.
Several different tests may be performed on raw and treated waters in rela-
tion to solids:
•
Total dissolved solids (TDS)
—Total dissolved solids in water samples
are limited to the solids in solution. The recommended TDS upper
limit is 500 mg/L.
•
Settleable solids
—Settleable solids are solids in suspension that can
be expected to settle by gravity only in a quiescent state, such as
is found in an oversized settling tank. The period of time must be
defined. Commonly used in the analysis of sewage, this test may
provide data useful to evaluate the sedimentation process, but only
when dealing with very high turbidity.
•
Suspended solids (SS or TSS)
—Also called suspended matter, these
are solids that are not dissolved. They have little or no significance
for domestic water consumption where turbidity provides a propor-
tional if not equivalent value but with easier determination.
•
Total solids
—Total solids are all solids contained in the water sam-
pled, as determined by evaporation and drying.
•
Volatile solids
—Volatile solids are made up of organic chemicals.
