heavily on fashion and changing needs, which complicates the possibility of
forecasting water requirements in this sector, over long periods. The only
comfort is that there are only few industries requiring very large amounts of
water. And, if the country does not have plentiful supplies, the industry will
never be set up.
The guiding principle is that, given water supplies in a region are limited, nothing
more can be provided, except at prohibitive prices (desalination, import, etc).
However, ingenious schemes may be developed to use the water resources more
fully than ever before, and eventually, used several times over (hydropower, domestic use, and then recycled for irrigation). Typically, hotels in tropical climates may
use some 400 cubic metres daily for potable purposes; the effluents are treated and
recycled for irrigation use (at night, to avoid any accidents).
1.2.14 Wastewater
Water is essential for development. Once the water has been used it is essential to
have a good sewerage system to sustain the development.
A small coastal community might discharge untreated sewage directly into the
sea without any ill effects, but if the same population were located besides a small
stream, a high degree of treatment might be required, particularly during the low
flow season. Improved standards of living, urbanisation, and industrial growth have
increased the strength and quantity of municipal sewage in recent decades to the
point that dilution alone is not enough to prevent the undesirable effects of pollution.
The level of treatment required depends on the composition and strength of the
sewage and the disposal facilities.
There are many different ways to treat sewage, while sometimes, more advanced
treatment may be required. Water-quality control has become a new concept in the
field of water-resources management. Recognising the economic value of water
quality has introduced the need to maintain certain minimum flows in rivers.
Treatment processes are often classified as primary, secondary, or tertiary
processes.
Primary treatment separates the suspended solids from the sewage, by screening
and sedimentation in settling basins. The separated solids are then decomposed by
bacterial action in a tank, and the liquid effluent is diluted before disposal or used
irrigation, although some care is needed. Considerable organic material remains in
the liquid effluent resulting from primary treatment, and needs much oxygen to
oxidise it. This is the BOD (Biochemical Oxygen Demand), which is used as an
indicator of organic pollution in the water.
Secondary treatment goes further: effluent from a primary treatment process is
oxidised, generally, through biological processes using filters, aeration, oxidation
ponds, and other means. The ensuing effluent will usually have little oxygen demand
and may even contain several milligrams per litre of dissolved oxygen.
1.2 Examples of Infrastructure
27
forecasting water requirements in this sector, over long periods. The only
comfort is that there are only few industries requiring very large amounts of
water. And, if the country does not have plentiful supplies, the industry will
never be set up.
The guiding principle is that, given water supplies in a region are limited, nothing
more can be provided, except at prohibitive prices (desalination, import, etc).
However, ingenious schemes may be developed to use the water resources more
fully than ever before, and eventually, used several times over (hydropower, domestic use, and then recycled for irrigation). Typically, hotels in tropical climates may
use some 400 cubic metres daily for potable purposes; the effluents are treated and
recycled for irrigation use (at night, to avoid any accidents).
1.2.14 Wastewater
Water is essential for development. Once the water has been used it is essential to
have a good sewerage system to sustain the development.
A small coastal community might discharge untreated sewage directly into the
sea without any ill effects, but if the same population were located besides a small
stream, a high degree of treatment might be required, particularly during the low
flow season. Improved standards of living, urbanisation, and industrial growth have
increased the strength and quantity of municipal sewage in recent decades to the
point that dilution alone is not enough to prevent the undesirable effects of pollution.
The level of treatment required depends on the composition and strength of the
sewage and the disposal facilities.
There are many different ways to treat sewage, while sometimes, more advanced
treatment may be required. Water-quality control has become a new concept in the
field of water-resources management. Recognising the economic value of water
quality has introduced the need to maintain certain minimum flows in rivers.
Treatment processes are often classified as primary, secondary, or tertiary
processes.
Primary treatment separates the suspended solids from the sewage, by screening
and sedimentation in settling basins. The separated solids are then decomposed by
bacterial action in a tank, and the liquid effluent is diluted before disposal or used
irrigation, although some care is needed. Considerable organic material remains in
the liquid effluent resulting from primary treatment, and needs much oxygen to
oxidise it. This is the BOD (Biochemical Oxygen Demand), which is used as an
indicator of organic pollution in the water.
Secondary treatment goes further: effluent from a primary treatment process is
oxidised, generally, through biological processes using filters, aeration, oxidation
ponds, and other means. The ensuing effluent will usually have little oxygen demand
and may even contain several milligrams per litre of dissolved oxygen.
1.2 Examples of Infrastructure
27