Environmental Engineering Reference
In-Depth Information
equilibrium with the ammonium ion. Ammonia also forms complexes with several
metal ions and may be adsorbed onto colloidal particles, suspended sediments and bed
sediments. It may also be exchanged between sediments and the overlying water.
Substantial losses of ammonia can occur via volatilization with increasing pH.
Unpolluted waters contain small amounts of ammonia and its compounds, usually less
than 0.20 mg/l expressed as nitrogen (Chapman 1998). A higher concentration could
be an indication of organic pollution such as domestic sewage, industrial waste and
fertilizer runoff. Ammonia at levels in excess of 1 mg/l contributes to the corrosion of
copper pipes and brass plumbing fixtures adding copper salts to the water (Dean &
Lund 1981). Ammonia also interferes with chlorine during the water treatment
process, although low levels of monochloramine are considered desirable in water
distribution systems.
• Nitrate - it is a readily available source of food for algae and higher plants, whereas
nitrite is toxic to most animals and plants. Fortunately, the rate of oxidation of nitrite is
faster than the rate of formation and concentrations of nitrite rarely exceed 1-2 mg/l in
polluted water (Focht & Chang 1976). Nitrate, in contrast, is physiologically inert in
adults at concentrations of 20 mg/l or more. It is well recognized as a curing agent for
meats and leafy vegetables. However, some infants do not have sufficient acidity in
their stomachs to inhibit the growth of bacteria, which can reduce nitrate to nitrites.
Nitrites are objectionable, not only because they combine with hemoglobin, reducing
its oxygen carrying capacity, but also, because they are believed to combine with
organic amines in the body to produce carcinogenic nitro-amines (WHO 1996). The
first effect can cause “blue babies” disease, if the nitrate concentration in water, which
is used to prepare infant formulas, is in excess of 10 mg/l as nitrogen, equivalent to 45
mg/l as nitrate (Dean & Lund 1981). WHO recommended that the maximum limit for
drinking water is 10 mg/l NO
3
-
-N, waters with higher concentrations represent a
significant health risk (Chapman 1998). In lakes, nitrate levels of 0.2 mg/l nitrate
nitrogen tend to stimulate algal growth and indicate eutrophic conditions (Chapman
1998).
• Organic nitrogen - it consists of protein substances (e.g., amino acids, nucleic and
urine) and the products of their biochemical transformations (e.g. humic acids and
fulvic acids). It is formed in natural water principally by phytoplankton and bacteria
and cycled within the food chain. Organic nitrogen is usually determined using the
Kjeldahl method, which gives a combined result of the total ammonia nitrogen plus
total organic nitrogen (TKN).
2.2.2.2 Phosphorous compounds
There is a general agreement that the degree of phosphorus loading to water bodies, in
terms of both dissolved and particulate species, determines the level of algal production
or eutrophication. The relationship between phosphorus loading and algal biomass was
assessed by Vollenweider (1968), and has resulted in remedial measures being taken to
reduce external phosphorus inputs to many lakes suffering the severe effects of
eutrophication.
