Environmental Engineering Reference
In-Depth Information
general change of river morphology. However, it should be pointed out that a
considerable portion of the diffuse pollution load with respect to different constituents
are attached to insoluble mineral particles, which serve as a transportation vehicle of
these pollutants to surface water bodies.
• Oil pollution - oil spreading as a thin film on water has the effect of interfering with gas
exchange and hence preventing or severely reducing the rate at which the atmospheric
oxygen can be adsorbed into deoxygenated water. Most oils will rapidly spread to
achieve a thickness of about 1 mm in a matter of minutes. Although the direct organic
load exerted by oil may be limited, the effect of a spill is potentially catastrophic
because it retards the natural self-purification process, as well as, enhances the oxygen
depletion of the water body, which has an adverse effect on the struggling aquatic life.
In addition, many oils have direct toxic effects on humans and aquatic life.
2 POLLUTANT CONSTITUENTS
2.1
Physical characteristics
• Solids - this characteristic represents the sum of all constituents in a water sample, in
particulate or dissolved form, expressed as solids content or TS, which is determined
by evaporating a sample and weighting the dry residue. In the practice of pollution
control and water/wastewater treatment it is often important to know the form in
which the solids are present. Thus, we could differentiate between the suspended
fraction (TSS) and the dissolve fraction (TDS) of TS. TSS is determined by filtering a
sample of water through a standard glass-fiber filter, followed by drying and weighing
of the residue. TDS could be determined either by evaporating and weighing the
filtrate residue, or as the difference between TS and TDS. TS and TDS concentrations
in conjunction with a detailed chemical analysis, is used to assess the pollution status
of water samples and their suitability for various water uses - public, industrial or
agricultural. Additional characterization of the solids content, in terms of organic or
inorganic components, is shown in Figure 1.1. Actually, only TSS is considered to be
a physical component, as it represents all impurities in particulate or colloidal (large
colloids) form, while TDS should be considered a chemical characteristic as it presents
constituents in ionic or molecular form. Based on the size of the particles and their
ability to separate from suspension by means of gravity, TSS fractions could be
characterized as settable and non-settable. This parameter is measured in Imhoff
cones, where the water sample is left at rest, and the volume of the sediment is
recorded after a specified period of time.
• Turbidity - it is a parameter closely related to TSS. It reflects the presence of suspended
and colloidal particles, which are too small to settle and stay in suspension, thus
causing specific opalescence and decreasing the clarity of water. It is measured by
turbidimeters - instruments, which measure the deflection of a beam of light due to the
opalescence of the water sample, and compare it to the deflection of a standard
solution. Clay, silt, soil particles and other colloidal impurities usually cause turbidity
in natural water and the level of turbidity would depend on the fineness of the particles
and their concentration.
