Thesaurus (provided by InterWATER I R C)
- carbon dioxide
- water
- other mineral products.
The need for water treatment
Many "contaminents" are actually beneficial
Many essential, health giving "contaminents" are actualy benficial to humans and the environment. The purpose of the scientific ongoing study of water and its treatment is to provide the most beneficial result in terms of safety and value for humans and the natural environment.
The treatment methods vary greatly.
Purification of water
What kind of contaminants are In the water?
In untreated water contaminants ranging from chemicals, parasites, and bacterias are measurably present. There are also others including algae, bacteria, viruses, fungus, heavy metals and parasites such as Guardia and Cryptosporidium.
Each of these different substances present the potential to cause ill effects on human health. Some of the contaminants in water are actually proven to be hazardous to your health. When these substances are taken out of the water by the use of water treatment methods of purification, the water will improve in taste, smell, colour in what is known as potability.
Major Contaminents
The major pollutants that can make ther way into water can be the following;
Sewage and other oxygen-demanding wastes (largely carbonaceous organic material, the decomposition of which leads to oxygen depletion).
Infectious agents.
Plant nutrients that can stimulate the growth of aquatic plants, which then interfere with water uses and, when decaying, deplete the dissolved oxygen and produce disagreeable odours.
Exotic organic chemicals, including pesticides, various industrial products, surface-active substances in detergents, and the decomposition products of other organic compounds.
Petroleum, especially from oil spills. Inorganic minerals and chemical compounds.
Sediments consisting of soil and mineral particles washed by storms and floodwater from croplands, unprotected soils, mine workings, roads, and bulldozed urban areas.
Radioactive substances from the wastes of uranium and thorium mining and refining, from nuclear power plants, and from the industrial, medical, and scientific use of radioactive materials.
Heat may also be considered a pollutant when increased temperatures in bodies of water result from the discharge of cooling water by factories and power plants.
Effects of water contamination
Notable effects of water pollution include those involved in human health.
Nitrates (the salts of nitric acid) in drinking water can cause a disease in infants that sometimes results in death.
Cadmium in sludge-derived fertilizer can be absorbed by crops; if ingested in sufficient amounts, the metal can cause an acute diarrhoeal disorder and liver and kidney damage.
The hazardous nature of inorganic substances such as mercury, arsenic, and lead has long been known or strongly suspected.
Lakes are especially vulnerable to pollution. One problem, eutrophication, occurs when lake water becomes artificially enriched with nutrients, causing abnormal plant growth. Run-off of chemical fertilizer from cultivated fields may trigger this. The process of eutrophication can produce aesthetic problems such as bad tastes and odours and unsightly green scums of algae, as well as dense growth of rooted plants, oxygen depletion in the deeper waters and bottom sediments of lakes, and other chemical changes such as precipitation of calcium carbonate in hard waters.
Another problem, of growing concern in recent years, is acid rain, which has left many lakes in northern and eastern Europe and north-eastern North America totally devoid of life.
Sources and control
The major sources of water pollution can be classified as municipal, industrial, and agricultural.
Municipal water pollution consists of wastewater from homes and commercial establishments.
For many years, the main goal of municipal sewage disposal was simply to reduce its content of suspended solids, oxygen-demanding materials, dissolved inorganic compounds (particularly compounds of phosphorus and nitrogen), and harmful bacteria.
In recent years, however, more stress has been placed on improving the means of disposal of the biosolids or sludge from municipal treatment processes.
Biosludge
The handling and disposal of solid residues can account for 25 to 50 per cent of the capital and operational costs of a treatment plant.
The characteristics of industrial wastewaters can differ markedly both within and among industries. The impact of industrial discharges depends not only on their collective characteristics, such as biochemical oxygen demand and the amount of suspended solids, but also on their content of specific inorganic and organic substances. Three options (which are not mutually exclusive) are available in controlling industrial wastewater.
Control can take place at the point of generation within the plant; wastewater can be pretreated for discharge to municipal treatment systems; or wastewater can be treated completely at the plant and either reused or discharged directly into receiving waters.
Agriculture, including commercial livestock and poultry farming, is the source of many organic and inorganic pollutants in surface waters and groundwater. These contaminants include both sediment from the erosion of cropland and compounds of phosphorus and nitrogen that partly originate in animal wastes and commercial fertilizers.
Animal wastes are high in oxygen-demanding material, nitrogen, and phosphorus, and they often harbour pathogenic organisms.
Wastes from commercial feeders are contained and disposed of on land; their main threat to natural waters, therefore, is via run-off and leaching. Control may involve settling basins for liquids, limited biological treatment in aerobic or anaerobic lagoons, and a variety of other methods.
Traditional 3 stage water treatment model
Treatment Stages
Traditionally, three levels of sewage or wastewater treatment are defined. These are;
- Primary
- Secondary
- Tertiary (or advanced)
This traditional model is being expanded especially in developed countries with enlightened levels of awareness and ever improving testing facilities. It follows then that there is an argument for introducing a 4th stage that we might refer to as Tertiary ++ that addresses these advances.
Primary
This level removes the majority of bulk solids, from the waste stream. Where required, systems also trap greases, oils, and other non-soluable solids.. Primary treatment provides a clarified raw sewage but does not remove dissolved organic materials or other pollutants from the wastewater; it is a preliminary treatment stage, truly useful only when followed by subsequent treatment. It includes grit removal, screening, grinding, flocculation (aggregation of the solids).
Secondary
This level of treatment removes dissolved organic materials through either chemical or biological mechanisms, and combined with clarification further removes suspended solids.
Secondary treatment processes are generally considered to remove greater than 85% of the BOD and suspended solids from the wastewater stream, and provide limited removal of the nutrients nitrogen (N) and phosphorus (P). Secondary treatment is considered sufficient in cases where the effluent is to be directed to land use where the N and P are beneficial for irrigation, or where the nutrient levels are low following treatment and subsequent analysis.
Tertiary
Wastewater treatment provides an extra stage for the removal of phosphorous and nitrogen nutrients and even further removal of BOD and suspended solids. Generally, advanced wastewater treatment processes can provide removals of greater than 95% for BOD and suspended solids and high levels of nitrogen and phosphorus elimination in the final effluent. Tertiary treatment is necessary when receiving bodies of water would be adversely affected by the influx of the extra nutrients, and could result in contamination of watercourses.
Tertiary ++
In today's tertiary treatments, advances are being made as the level of trace elements and contaminants is being more clearly understood with the development of more sophisticated testing methods. These advances are examining in detail the presence of pathogens and other undesirable elements even when they are in extremely small concentrations.
Micro filtration, advanced or selective biological systems, Ultra Violet Light and Ozone are technologies that are being utilised along with chemical processes, (albeit with understandably less support for their use).
The recent advances in nanotechnology in laboratories, universities and research organisations around the world promises further innovative processes that are expected to become commercially stable and economically viable in the future.
