Water Resources: Management and Industrial Applications
Water Supply
The oceans store 97.6% of natural water (water alone, in solid, liquid, or gas). The water available to organisms of terrestrial life represents only 0.5% of the total, most of it groundwater. While the amount of atmospheric water is relatively small, its rate of recycling in the atmosphere is relatively high, with an average atmospheric residence time of nine days. Therefore, atmospheric water vapor is renewed 40 times a year. The two human activities that consume more water are industrial (32% of the total) and agricultural (57% of the total).
Surface Water Collection
Surface water can be collected in order to avoid the effects of large variations in flow and temperature. The collection itself consists of an opening and a tube that carries the flow to a water trap from which it can be pumped into the treatment plant.
Reservoir Dams
Reservoir dams are subject to great variations in depth. Usually, the water quality is better near the surface. Typically, the lowest levels in depth in reservoirs are cold, and the temperature changes very little during the year. However, the surface temperature varies with air, and during most of the year, it is warmer than the lower levels. During the fall, as the air temperature cools, the surface layers cool and submerge, displacing the lower layers and bringing them to the surface. A similar phenomenon can occur in spring when the ice melts, and the water reaches maximum density (at 4°C) and sinks to the bottom. In general, the water at the bottom of the reservoir is low in dissolved oxygen and high in organic matter. It is not advisable to draw water from this level of abstraction.
Lake Intakes
Intakes in lakes should be located as far away as possible from sources of pollution. It is necessary to consider the wind and current effects on the movement of pollutants. In particular, the winds can remove bottom sediments, which can be brought to the collection if it is located in shallow water or very near the bottom. The formation of ice under the surface of the grids can be a serious drawback, and different types of resources must be used to remove it.
River Intakes
Intakes in rivers should be designed to take water from a level slightly below the surface in order to avoid both suspended sediment at lower levels and floating waste. Grids are particularly suitable in abstraction from rivers, as large amounts of material in suspension might otherwise enter the structure. When the main channel of the river is located on the shore or close to it, one can construct from-shore intakes. For deposits that are located far from the shore of a river or lake, a duct is sent under the bottom. The duct terminates in a well or pool from where the flow is pumped to the treatment plant.
Groundwater
Groundwater represents 0.47% of total resources. It plays an important regulatory role by cushioning the variations in rainfall. The flowing groundwater aquifers contribute 30% of the total flow of the rivers of the world. There are two types:
- Areas covered by permeable materials in which the air occupies the pits and fissures, and water levels can vary, containing the anointing of the recharge capacity, primarily through the surface (free aquifers).
- Other areas covered by almost impermeable materials where the water table is captive or pressurized (captive aquifers).
The exploitation of nonrenewable resources leads to depletion in a more or less long term. It is much more practiced in arid countries, where a significant portion of their supply comes from the exploitation of nonrenewable resources. Possible solutions include:
- Increased conventional supplies (dams)
- Desalination of seawater
- More efficient use (drip irrigation)
Seawater
Seawater represents 97.6% of water resources, although its use for human activities is relatively limited due to its high concentration of salts (35 g/l). It also contains low concentrations of almost all chemical elements. The existing processes to desalinate brackish or seawater are very numerous. They can be classified under different criteria, either based on the energy consumed to achieve its purpose, in which case we must talk about thermal energy, electricity, and mechanical energy, or based on other criteria, such as that of physical or chemical principles on which the process is based. Thus, desalination processes can be divided into four main chapters:
- Processes using distillation
- Processes that use membranes
- Processes which use the principle of crystallization
- Processes based on chemical principles
In all these processes, only a few of them are used on an industrial scale or semi-industrial scale. These processes are multi-effect distillation and flash evaporation, which use thermal energy. Vapor compression, reverse osmosis, and electrodialysis use mechanical energy to electrical energy used.
Treatment of Water for Industrial Use
Characteristics and uses of industrial water – Water used should be large enough to cover the needs of the moment and the near future, taking into account the possible extensions of the industry in question. Secondly, the flow and pressure at which water is available must be suitable for further use. And finally, the water quality should be as close as possible to that which will be needed in subsequent processes in which it will intervene.