Water Pollution 165
reported, of fish as well as of domestic animals, caused by using water
containing high concentrations of algae.
• Accumulation of radioactivity and metals: Algae take up and store
toxic metals or radioactive elements that are dissolved in water in very
low concentrations. These elements may be relatively harmless for the
algae, but through biomagnification (Chapters 4 and 7), high concentrations of radioactive elements or metals may reach humans via fish,
agriculture (where water containing algae is used for irrigation), or
animals (whose drinking water contains algae).
• Creation of odours, colour and bad taste: Problems of smell and taste
in drinking water are generally associated with the presence of algae
in sources from which water is taken. The odours and tastes that are
created vary according to local conditions and species of algae. Even
after raw water undergoes proper treatment, certain odours and tastes
remain. High algal growth may also cause colouring of the water.
• Problems during treatment of raw water: When water undergoes filtration in a purification plant, algae (along with other colloidal and
suspended materials) gradually clog the filter medium. Chemically
assisted sedimentation, using suitable flocculants prior to filtration,
may succeed in removing 90–95% of algae. However, the algae that
remain may create clogging problems, making it necessary to flush
out the filter more often. When algae are present it may be necessary
to decrease the amount of time between two successive backflushings
(from 30 to 100 hours to less than 10 hours). In extreme cases, the
amount of water needed for backflushing may be greater than the
amount of water that enters the water supply. Thus the presence of
algae slows down the processes of cleaning raw water and increases
costs substantially.
• Creation of scum: Slime created by algae is most likely due to decomposition of their cell membranes (a similar phenomenon occurs with
bacteria and other organisms). These substances appear in open tanks
and open conduits and may create serious problems when the water
is used by certain industries (e.g. spotting on paper and food industry
products or gelatinous films in liquefaction pipes of industries using
cooling systems).
8.4 PathogEnic MicroorganiSMS —contaMination
The most important waterborne pathogenic microorganisms are typhus,
paratyphus, dysentery and cholera bacteria, as well as various viruses, primarily infectious hepatitis (with which crustaceans may be contaminated
and transmit infection to consumers) and poliomyelitis.
reported, of fish as well as of domestic animals, caused by using water
containing high concentrations of algae.
• Accumulation of radioactivity and metals: Algae take up and store
toxic metals or radioactive elements that are dissolved in water in very
low concentrations. These elements may be relatively harmless for the
algae, but through biomagnification (Chapters 4 and 7), high concentrations of radioactive elements or metals may reach humans via fish,
agriculture (where water containing algae is used for irrigation), or
animals (whose drinking water contains algae).
• Creation of odours, colour and bad taste: Problems of smell and taste
in drinking water are generally associated with the presence of algae
in sources from which water is taken. The odours and tastes that are
created vary according to local conditions and species of algae. Even
after raw water undergoes proper treatment, certain odours and tastes
remain. High algal growth may also cause colouring of the water.
• Problems during treatment of raw water: When water undergoes filtration in a purification plant, algae (along with other colloidal and
suspended materials) gradually clog the filter medium. Chemically
assisted sedimentation, using suitable flocculants prior to filtration,
may succeed in removing 90–95% of algae. However, the algae that
remain may create clogging problems, making it necessary to flush
out the filter more often. When algae are present it may be necessary
to decrease the amount of time between two successive backflushings
(from 30 to 100 hours to less than 10 hours). In extreme cases, the
amount of water needed for backflushing may be greater than the
amount of water that enters the water supply. Thus the presence of
algae slows down the processes of cleaning raw water and increases
costs substantially.
• Creation of scum: Slime created by algae is most likely due to decomposition of their cell membranes (a similar phenomenon occurs with
bacteria and other organisms). These substances appear in open tanks
and open conduits and may create serious problems when the water
is used by certain industries (e.g. spotting on paper and food industry
products or gelatinous films in liquefaction pipes of industries using
cooling systems).
8.4 PathogEnic MicroorganiSMS —contaMination
The most important waterborne pathogenic microorganisms are typhus,
paratyphus, dysentery and cholera bacteria, as well as various viruses, primarily infectious hepatitis (with which crustaceans may be contaminated
and transmit infection to consumers) and poliomyelitis.