Environmental Engineering Reference
In-Depth Information
Although nitrate electrodes and spectrophotometers can be used in the
field, they have certain disadvantages. These devices are more fragile than
the color comparators and are therefore more at risk of breaking in the field.
They must be carefully maintained and must be calibrated before each
sample run or, if many tests are being run, between samplings. This means
that samples are best tested in the lab. Note that samples to be tested with a
nitrate electrode should be at room temperature, whereas color comparators
can be used in the field with samples at any temperature.
Total Solids
Total solids are dissolved solids plus suspended and settleable solids in
water. In stream water, dissolved solids consist of calcium, chlorides, nitrate,
phosphorus, iron, sulfur, and other ions—particles that will pass through a
filter with pores of around 2 µm (0.002 cm) in size. Suspended solids include
silt and clay particles, plankton, algae, fine organic debris, and other particu-
late matter. These are particles that will not pass through a 2-µm filter. The
concentration of total dissolved solids affects the water balance in the cells
of aquatic organisms. An organism placed in water with a very low level of
solids (distilled water, for example) swells because water tends to move into
its cells, which have a higher concentration of solids. An organism placed
in water with a high concentration of solids shrinks somewhat, because the
water in its cells tends to move out. This in turn affects the ability of the
organism to maintain the proper cell density, which makes keeping its posi-
tion in the water column difficult. It might float up or sink down to a depth
to which it is not adapted, and it might not survive.
Higher concentrations of suspended solids can serve as carriers of toxics,
which readily cling to suspended particles. This is particularly a concern
where pesticides are being used on irrigated crops. Where solids are high,
pesticide concentrations may increase well beyond those of the original
application as the irrigation water travels down irrigation ditches. Higher
levels of solids can also clog irrigation devices and might become so high
that irrigated plant roots will lose water rather than gain it. A high concen-
tration of total solids will make drinking water unpalatable and might have
an adverse effect on people who are not used to drinking such water. Levels
of total solids that are too high or too low can also reduce the efficiency of
wastewater treatment plants, as well as the operation of industrial processes
that use raw water. Total solids affect water clarity. Higher solids decrease the
passage of light through water, thereby slowing photosynthesis by aquatic
plants. Water heats up more rapidly and holds more heat; this, in turn, might
adversely affect aquatic life adapted to a lower temperature regime. Sources
of total solids include industrial discharges, sewage, fertilizers, road runoff,
and soil erosion. Total solids are measured in milligrams per liter (mg/L).
