OWLS™ Water Education: What Is Water Pollution?
Water pollution is any chemical, physical or biological change in the quality of water that has a harmful effect on any living thing that drinks or uses or lives (in) it. When humans drink polluted water it often has serious effects on their health. Water pollution can also make water unsuited for the desired use.
There are several classes of water pollutants. The first are disease-causing agents. These are bacteria, viruses, protozoa and parasitic worms that enter sewage systems and untreated waste.
A second category of water pollutants is oxygen-demanding wastes; wastes that can be decomposed by oxygen-requiring bacteria. When large populations of decomposing bacteria are converting these wastes it can deplete oxygen levels in the water. This causes other organisms in the water, such as fish, to die.
A third class of water pollutants is water-soluble inorganic pollutants, such as acids, salts and toxic metals. Large quantities of these compounds will make water unfit to drink and will cause the death of aquatic life.
Another class of water pollutants are nutrients; they are water-soluble nitrates and phosphates that cause excessive growth of algae and other water plants, which deplete the water’s oxygen supply. This kills fish and, when found in drinking water, can kill young children.
Water can also be polluted by a number of organic compounds such as oil, plastics and pesticides, which are harmful to humans and all plants and animals in the water. A very dangerous category is suspended sediment, because it causes depletion in the water’s light absorption and the particles spread dangerous compounds such as pesticides through the water.
Finally, water-soluble radioactive compounds can cause cancer, birth defects and genetic damage and are thus very dangerous water pollutants.
Water pollution is usually caused by human activities. Different human sources add to the pollution of water. There are two sorts of sources, point and nonpoint sources. Point sources discharge pollutants at specific locations through pipelines or sewers into the surface water. Nonpoint sources are sources that cannot be traced to a single site of discharge.
Examples of point sources are: factories, sewage treatment plants, underground mines, oil wells, oil tankers and agriculture.
Examples of nonpoint sources are: acid deposition from the air, traffic, pollutants that are spread through rivers and pollutants that enter the water through groundwater. Nonpoint pollution is hard to control because the perpetrators cannot be traced.
Water pollution is detected in laboratories, where small samples of water are analysed for different contaminants. Living organisms such as fish can also be used for the detection of water pollution. Changes in their behavior or growth show us, that the water they live in is polluted. Specific properties of these organisms can give information on the sort of pollution in their environment. Laboratories also use computer models to determine what dangers there can be in certain waters. They import the data they own on the water into the computer, and the computer then determines if the water has any impurities.
In most manufacturing processes a lot of heat originates that must be released into the environment, because it is waste heat. The cheapest way to do this is to withdraw nearby surface water, pass it through the plant, and return the heated water to the body of surface water. The heat that is released in the water has negative effects on all life in the receiving surface water. This is the kind of pollution that is commonly known as heat pollution or thermal pollution.
The warmer water decreases the solubility of oxygen in the water and it also causes water organisms to breathe faster. Many water organisms will then die from oxygen shortages, or they become more susceptible to diseases.
For more information about this, you can take a look at thermal pollution.
Eutrophication means natural nutrient enrichment of streams and lakes. The enrichment is often increased by human activities, such as agriculture (manure addition). Over time, lakes then become eutrophic due to an increase in nutrients.
Eutrophication is mainly caused by an increase in nitrate and phosphate levels and has a negative influence on water life. This is because, due to the enrichment, water plants such as algae will grow extensively. As a result the water will absorb less light and certain aerobic bacteria will become more active. These bacteria deplete oxygen levels even further, so that only anaerobic bacteria can be active. This makes life in the water impossible for fish and other organisms.
Typical rainwater has a pH of about 5 to 6. This means that it is naturally a neutral, slightly acidic liquid. During precipitation rainwater dissolves gasses such as carbon dioxide and oxygen. The industry now emits great amounts of acidifying gasses, such as sulphuric oxides and carbon monoxide. These gasses also dissolve in rainwater. This causes a change in pH of the precipitation – the pH of rain will fall to a value of or below 4. When a substance has a pH of below 6.5, it is acid. The lower the pH, the more acid the substance is. That is why rain with a lower pH, due to dissolved industrial emissions, is called acid rain.
When water is enriched with nutrients, eventually anaerobic bacteria, which do not need oxygen to practice their functions, will become highly active. These bacteria produce certain gasses during their activities. One of these gases is hydrogen sulphide. This compounds smells like rotten eggs. When water smells like rotten eggs we can conclude that there is hydrogen present, due to a shortage of oxygen in the specific water.
Water contains many compounds. A few of these compounds are calcium and carbonate. Carbonate works as a buffer in water and is thus a very important component. When calcium reacts with carbonate a solid substance is formed, that is called lime. This lime is what causes the white deposit on showers and bathroom walls and is commonly known as lime deposit. It can be removed by using a specially suited cleaning agent.
What causes pollutants in freshwater ecosystems?
There have been listed some 1500 substances that are classified as pollutants in freshwater ecosystems, and each of them occurs in the following types of freshwater pollutants. Here is a generalized list of them:
Acids & alkalis
The different pollutants exert different problems to different freshwater waterways. Mostly expressed in the amount of oxygen that is available for fish and other species. This sometimes results in habitat destruction and extinction of local populations.
You can click on the pollutants above to learn more about their characteristic feature and their fate in freshwater ecosystems when they show up in there. Species are often used for toxicity tests, and there responses also may differ.
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Water-borne diseases are any illness caused by drinking water contaminated by human or animal faeces, which contain pathogenic microorganisms. The full picture of water-associated diseases is complex for a number of reasons. Over the past decades, the picture of water-related human health issues has become increasingly comprehensive, with the emergence of new water-related infection diseases and the re-emergence of ones already known.
Data is available for some water-, sanitation- and hygiene-related diseases (which include salmonellosis, cholera, shigellosis), but for others such malaria, schistosomiasis or the most modern infections such legionellosis or SARS CoV the analyses remain to be done. The burden of several disease groups can only partly be attributed to water determinants. Even where water plays an essential role in the ecology of diseases, it may be hard to pinpoint the relative importance of aquatic components of the local ecosystems.
Water related diseases:
Anaemia / Arsenicosis / Ascariasis /Botulism / Campylobacteriosis / Cholera / Cryptosporiodiosis / Cyanobacterial toxins / Dengue / Diarrhoea / Dracunculiasis / Fluorosis / Giardiasis / Hepatitis / Hookworm infection / Japanese encephalitis / Lead poisoning / Legionellosis / Leptospirosis / Lymphatic filariasis / Malaria / Malnutrition / Methaemoglobinemia / Onchocerciasis / Polio / Ring Worm or Tinea / Scabies / Schistomiasis / Trachoma / Trichuriasis /Typhoid Back to Top
Dimension of the problem
In developing countries four-fifths of all the illnesses are caused by water-borne diseases, with diarrhoea being the leading cause of childhood death.
The global picture of water and health has a strong local dimension with some 1.1 billion people still lacking access to improved drinking water sources and some 2.4 billion to adequate sanitation. Today we have strong evidence that water-, sanitation and hygiene-related diseases account for some 2,213,000 deaths annually and an annual loss of 82,196,000 Disability Adjusted Life Years (DALYs) (R. Bos, Dec. 2004).
WHO estimates indicate that worldwide over 2 billion people are infected with schistosomes and soil transmitted helminthes and 300 million of these suffer serious illness as a result. Malaria kills over a million people every year, and a large percentage of them are under five as well, mainly in Africa South of the Sahara. In 2001 the estimated global burden of malaria amounted to 42.3 million DALYs, constituting 10 % of Africa’s overall disease burden. Malaria causes at least 396.8 million cases of acute illness each year. Pregnant women are the main adult risk group.
As one of the major public health problems in tropical countries, it has been claimed that malaria has reduced economic growth in African countries by 1.3 % each year over the past 30 years (*). An estimated 246.7 million people worldwide are infected by schistomiasis, and of these 20 million suffer severe consequences of the infection, while 120 million suffer milder symptoms. An estimated 80% of transmission takes place in Africa south of the Sahara (*). Diarrhoea occurs worldwide and causes 4% of all deaths and 5% of the health loss to disability. In Bangladesh alone, some 35 million people are exposed, on a daily basis, to elevated levels of arsenic in their drinking water, which will ultimately threaten their health and shorten their life expectancy. After the Tsunami attack in Asia on Sunday the 26th of December 2004 people faced the threat of water borne diseases linked to flooding, like Shigellosis, Cholera, Hepatitis A, Leptospirosis, Typhoid Fever, Malaria and Dengue fever.
Source ‘Global Water Supply and Sanitation Assessment 2000 Report’, section 2.2, WHO 2000
Water borne diseases spread by contamination of drinking water systems with the urine and faeces of infected animal or people. This is likely to occur where public and private drinking water systems get their water from surface waters (rain, creeks, rivers, lakes etc.), which can be contaminated by infected animals or people.
Runoff from landfills, septic fields, sewer pipes, residential or industrial developments can also sometimes contaminate surface water. This has been the cause of many dramatic outbreaks of faecal-oral diseases such as cholera and typhoid. However, there are many other ways in which faecal material can reach the mouth, for instance on the hands or on contaminated food. In general, contaminated food is the single most common way in which people become infected.
The germs in the faeces can cause the diseases by even slight contact and transfer. This contamination may occur due to floodwaters, water runoff from landfills, septic fields, and sewer pipes.The following picture shows the faecal-oral routes of diseases transmission.The only way to break the continued transmission is to improve the people’s hygienic behaviour and to provide them with certain basic needs: drinking water, washing and bathing facilities and sanitation.
Malaria transmission is facilitated when large numbers of people sleep outdoors during hot weather, or sleep in houses that have no protection against invading mosquitoes. Malaria mosquitoes, tropical black flies, and bilharzias snails can all be controlled with efficient drainage because they all depend on water to complete their life cycles. Click here for more information about contagion by pathogenic microorganisms.
Clean water is a pre-requisite for reducing the spread of water-borne diseases. It is well recognised that the prevalence of water-borne diseases can be greatly reduced by provision of clean drinking water and safe disposal of faeces. Water is disinfected to kill any pathogens that may be present in the water supply and to prevent them from growing again in the distribution systems.
Disinfection is then used to prevent the growth of pathogenic organisms and to protect public health and the choice of the disinfect depends upon the individual water quality and water supply system. Without disinfection, the risk from waterborne disease is increased. The two most common methods to kill microorganisms in the water supply are: oxidation with chemicals such as chlorine, chlorine dioxide or ozone, and irradiation with Ultra-Violet (UV) radiation. Source: The United Nations World Water Development Report ‘Water for people Water for life’ p.102 and following.
What specific water purification methods are there?
Water that is distributed in cities or communities is treated extensively. Specific water purification steps are taken, in order to make the water meet current water standards. Purification methods can be divided up into settling of suspended matter, physical/ chemical treatment of colloids and biological treatment. All these treatment methods have several different applications.
How do specific water purification methods work?
1 Physical water purification
Physical water purification is primarily concerned with filtration techniques. Filtration is a purification instrument to remove solids from liquids. There are several different filtration techniques. A typical filter consists of a tank, the filter media and a controller to enable backflow. Screens
Filtration through screens is usually done at the beginning of the water purification process. The shape of the screens depends on the particles that have to be removed.
Sand filtration is a frequently used, very robust method to remove suspended solids from water. The filter medium consists of a multiple layer of sand with a variety in size and specific gravity. When water flows through the filter, the suspended solids precipitate in the sand layers as residue and the water, which is reduced in suspended solids, flows out of the filter. When the filters are loaded with particles the flow-direction is reversed, in order to regenerate it. Smaller suspended solids have the ability to pass through a sand filter, so that secondary filtration is often required.
Cross flow filtration
Cross flow membrane filtration removes both salts and dissolved organic matter, using a permeable membrane that only permeates the contaminants. The remaining concentrate flows along across the membrane and out of the system and the permeate is removed as it flows along the other side of the membrane. There are several different membrane filtration techniques, these are: micro filtration, ultra filtration, nano filtration and Reversed Osmosis (RO). Which one of these techniques is implemented depends upon the kind of compounds that needs to be removed and their particle size. Below, the techniques of membrane filtration are clarified.
1) Microfiltration Microfiltration is a membrane separation technique in which very fine particles or other suspended matters, with a particle size in the range of 0.1 to 1.5 microns, are separated from a liquid. It is capable of removing suspended solids, bacteria or other impurities. Microfiltration membranes have a nominal pore size of 0.2 microns.
2) Ultrafiltration Ultrafiltration is a membrane separation technique in which very fine particles or other suspended matters, with a particle size in the range of 0.005 to 0.1 microns, are separated from a liquid. It is capable of removing salts, proteins and other impurities within its range. Ultrafiltration membranes have a nominal pore size of 0.0025 to 0.1 microns. 3) Nanofiltration Nanofiltration is a membrane separation technique in which very fine particles or other suspended matters, with a particle size in the range of approximately 0.0001 to 0.005 microns, are separated from a liquid. It is capable of removing viruses, pesticides and herbicides. 4) Reversed Osmosis (RO) Reversed Osmosis, or RO, is the finest available membrane separation technique. RO separates very fine particles or other suspended matters, with a particle size up to 0.001 microns, from a liquid. It is capable of removing metal ions and fully removing aqueous salts. More on RO Cartridge filtration
Cartridge filtration units consist of fibres. They generally operate most effectively and economically on applications having contamination levels of less than 100 ppm. For heavier contamination applications, cartridges are normally used as final polishing filters.
2 Chemical water purification Chemical water purification is concerned with a lot of different methods. Which methods are applied depends on the kind of contamination in the (waste)water. Below, many of these chemical purification techniques are summed up. Chemical addition There are various situations in which chemicals are added, for instance to prevent the formation of certain reaction products. Below, a few of these additions are summed up: – Chelating agents are often added to water, in order to prevent negative effects of hardness, caused by the deposition of calcium and magnesium. – Oxidizing agents are added to act as a biocide, or to neutralize reducing agents. – Reducing agents are added to neutralize oxidizing agents, such as ozone and chlorine. They also help prevent the degradation of purification membranes. Clarification Clarification is a multi-step process to remove suspended solids.
First, coagulants are added. Coagulants reduce the charges of ions, so that they will accumulate into larger particles called flocs. The flocs then settle by gravity in settling tanks or are removed as the water flows through a gravity filter. Particles larger than 25 microns are effectively removed by clarification. Water that is treated through clarification may still contain some suspended solids and therefore needs further treatment. Deionisation and softening Deionisation is commonly processed through ion exchange. Ion exchange systems consist of a tank with small beds of synthetic resin, which is treated to selectively absorb certain cations or anions and replace them by counter-ions.
The process of ion exchange lasts, until all available spaces are filled up with ions. The ion-exchanging device than has to be regenerated by suitable chemicals. One of the most commonly used ion exchangers is a water softener. This device removes calcium and magnesium ions from hard water, by replacing them with other positively charged ions, such as sodium. For specific information on water softening move to the water softener FAQ Disinfection Disinfection is one of the most important steps in the purification of water from cities and communities. It serves the purpose of killing the present undesired microrganisms in the water; therefore disinfectants are often referred to as biocides.
There are a variety of techniques available to disinfect fluids and surfaces, such as: ozone disinfection, chlorine disinfection and UV disinfection. Chlorine has a downside: it can react to chloramines and chlorinated hydrocarbons, which are dangerous carcinogens.
To prevent this problem chlorine dioxide can be applied. Chlorine dioxide is an effective biocide at concentrations as low as 0.1 ppm and over a wide pH range. ClO2 penetrates the bacteria cell wall and reacts with vital amino acids in the cytoplasm of the cell to kill the organism. The by-product of this reaction is chlorite. Toxicological studies have shown that the chlorine dioxide disinfection by-product, chlorite, poses no significant adverse risk to human health. Ozone has been used for disinfection of drinking water in the municipal water industry in Europe for over a hundred years and is used by a large number of water companies, where ozone generator capacities up to the range of a hundred kilograms per hour are common. When ozone faces odours, bacteria or viruses, the extra atom of oxygen destroys them completely by oxidation.
During this process the extra atom of oxygen is destroyed and there are no odours, bacteria or extra atoms left. Ozone is not only an effective disinfectant, it is also particularly safe to use. UV-radiation is also used for disinfection nowadays. When exposed to sunlight, germs are killed and bacteria and fungi are prevented from spreading.
This natural disinfection process can be utilised most effectively by applying UV radiation in a controlled way. Distillation Distillation is the collection of water vapour, after boiling the wastewater. With a properly designed system removal of organic and inorganic contaminants and biological impurities can be obtained, because most contaminants do not vaporize. Water will than pass to the condensate and the contaminants will remain in the evaporation unit. Electro dialysis Electro dialysis is a technique that employs an electrical current and special membranes, which are semi permeable to ions, based on their charge.
Membranes that permeate cations and membranes that permeate anions are placed alternately, with flow channels between them, and electrodes are placed on each side of the membranes. The electrodes draw their counter ions through the membranes, so that these are removed from the water. pH-adjustment Municipal water is often pH-adjusted, in order to prevent corrosion from pipes and to prevent dissolution of lead into water supplies. The pH is brought up or down through addition of hydrogen chloride, in case of a basic liquid, or natrium hydroxide, in case of an acidic liquid. The pH will be converted to approximately 7 to 7.5, after addition of certain concentrations of these substances. Scavenging Most naturally occurring organics have a slightly negative charge.
Organic scavenging is done by addition of strong-base anion resin. The organics will fill up the resin and when it is loaded it is regenerated with high concentrations of sodium chloride. 3 Biological water purification Biological water purification is performed to lower the organic load of dissolved organic compounds. Microrganisms, mainly bacteria, do the decomposition of these compounds. There are two main categories of biological treatment: aerobic treatment and anaerobic treatment. The Biological Oxygen Demand (BOD) defines the organic load. In aerobic systems the water is aerated with compressed air (in some cases merely oxygen), whereas anaerobic systems run under oxygen free conditions.
Lenntech was founded in 1993 by Alumni from the Technical University of Delft, the Netherlands. Until recently it was still based within the campus of the University. Its main goal is developing, designing, manufacturing and installing environmentally friendly water treatment and air purification systems for the industry – world-wide.
Originally, the organization’s main focus was around water disinfection, oxidation and recycling technologies. During Lenntech’s development the necessary surrounding technologies such as fine filtration, biofiltration and odor control were included in the scope of competence and delivery.
As of the turn of the century Lenntech can deliver full-scale turn-key systems for any industry. Although many solutions and manufactured equipment are proprietary, Lenntech sees a continuous need for co-operation and partner-ship with other specialist companies in order to always offer the best systems.