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Fresh water microbiology. Microorganisms in different aquatic zones.
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Fresh water microbiology C.Fortelius 2008 Biochemistry& Microbiology
Microorganisms in different aquatic zones • A variety of microorganisms live in fresh water. The region of a water body near the shoreline (the littoral zone) is well lighted, shallow, and warmer than other regions of the water. Photosynthetic algae and bacteria that use light as energy thrive in this zone. • Further away from the shore is the limnitic zone. Photosynthetic microbes also live here. • As the water deepens, temperatures become colder and the oxygen concentration and light in the water decrease. Now, microbes that require oxygen do not thrive. Instead, purple and green sulfur bacteria, which can grow without oxygen, dominate. • Finally, at the bottom of fresh waters (the benthic zone), few microbes survive. Bacteria that can survive in the absence of oxygen and sunlight, such as methane producing bacteria, thrive. C.Fortelius 2008 Biochemistry& Microbiology
Saltwater presents a different environment to microorganisms. The higher salt concentration, higher pH, and lower nutrients, relative to freshwater, are lethal to many microorganisms. But, salt loving (halophilic) bacteria abound near the surface, and some bacteria that also live in freshwater are plentiful (i.e., Pseudomonas and Vibrio). Also, in 2001, researchers demonstrated that the ancient form of microbial life, known as archaea, is one of the dominant forms of life in the ocean. The role of archaebacteria in the ocean food chain is not yet known, but must be of vital importance. C.Fortelius 2008 Biochemistry& Microbiology
Water can also be an ideal means of transporting microorganisms from one place to another. For example, the water that is carried in the hulls of ships to stabilize the vessels during their ocean voyages is now known to be a means of transporting microorganisms around the globe. One of these organisms, a bacterium called Vibrio cholerae, causes life threatening diarrhea in humans. C.Fortelius 2008 Biochemistry& Microbiology
Which microrganisms in water cause diseases? Sometimes microrganisms that cause health effects can be found in drinking water. However, as drinking water is thoroughly disinfected today, disease caused by microrganisms is rarely caused by drinking water. People that swim in swimming pools will find that the water they swim in is disinfected with either chlorine, ozone, UV or chlorine dioxide. But there are people that swim outside in surface water every year. There are various bacteria and protozoa that can cause disease when they are present in surface water. Bacteria are not only known to cause disease when they enter a human body through food, surface water may also be an important source of bacterial infection. In table 1 you can see various bacteria that can be found in surface water, and the diseases they cause when swallowed in large amounts, along with the symptoms. C.Fortelius 2008 Biochemistry& Microbiology
Protozoa can accumulate in certain body parts, after they have penetrated a human body. The accumulations are called cysts. Because of their parasitic nature, protozoa can cause various diseases. In table 2 you can see various protozoa that can be found in surface water, and the diseases they cause when swallowed in large amounts, along with the symptoms. C.Fortelius 2008 Biochemistry& Microbiology
Drinking water is usually treated to minimize the risk of microbial contamination. The importance of drinking water treatment has been known for centuries. For example, in pre-Christian times the storage of drinking water in jugs made of metal was practiced. Now, the anti-bacterial effect of some metals is known. Similarly, the boiling of drinking water, as a means of protection of water has long been known. An important aspect of water microbiology, particularly for drinking water, is the testing of the water to ensure that it is safe to drink. Turbidity gives an indication of the amount of suspended material in the water. Typically, if material such as soil is present in the water then microorganisms will also be present. The presence of particles even as small as bacteria and viruses can decrease the clarity of the water. Turbidity is a quick way of indicating if water quality is deteriorating, and so if action should be taken to correct the water problem. C.Fortelius 2008 Biochemistry& Microbiology
Ancient Water Treatment Because nothing was known about microorganisms or chemical contaminants, the motive for treating water was to make it smell and taste better. The first documented attempts to treat drinking water are recorded in ancient Greek and Sanskrit writings that date back to 2000 B.C. At this time, people were aware that boiling water helped to purify it and that filtration and straining methods helped to reduce visible particles and turbidity in water. C.Fortelius 2008 Biochemistry& Microbiology
The Greek scientist Hippocrates, who invented the first cloth bag filter around 500 B.C, also believed that if water tasted and smelled clean, it must be healthful for the body. His invention, called the “Hippocratic sleeve,” was one of the first domestic water filters (Baker & Taras 1981). Hippocrates Sleeve: a conical strainer, made by stitching together two adjacent sides of a square piece of cloth, esp. flannel of linen.; a woollen bag of a square piece of flannel, having the opposite corners joined, so as to make it triangular. Used by chemists for straining syrups, decoctions, etc. Baker, M.N. and Taras, Michael J. 1981. The Quest for Pure Water: A History of the Twentieth Century, Volume 1 and 2. Denver: AWWA C.Fortelius 2008 Biochemistry& Microbiology
Disinfection of Drinking Water Disinfection is the final process to which water is subjected prior to distribution. All other treatment processes such as sedimentation, flocculation, coagulation, filtration cannot give guarantee for safe water. Only the disinfection process can assure that the water is safe. In the absence of all other processes disinfection alone can be employed as a single effective treatment process. C.Fortelius 2008 Biochemistry& Microbiology
Disinfection is different from sterilization in which complete destruction of all living organisms occurs and the effect is permanent. Whereas disinfection primarily inactivates infectious microorganisms and is effective for a limited period. Complete sterilization of a water supply is extremely difficult to achieve and would not be necessary. Both chemical and physical methods are used for the disinfection of water. C.Fortelius 2008 Biochemistry& Microbiology
1. Chemical Disinfection Various chemical agents have been used for the disinfection of drinking waters. Each agent has its own advantages and limitations. The commonly used agents are chlorine, chlorine compounds like chlorinated lime, oxidants like ozone and potassium permanganate and halogens. C.Fortelius 2008 Biochemistry& Microbiology
1.1 Chemical Disinfection by Chlorine Chlorine and its compounds are the common chemical disinfectants. Comparatively they are less harmful and more effective. They are quick in action. In the presence of moisture chlorine is highly corrosive to all metals except silver and lead. The chlorination process may be of two types. In pre-chlorination method chlorine is applied prior to any other treatment, usually for controlling algae, taste and odor. In post-chlorination method chlorine is applied after other treatment processes, especially after filtration. C.Fortelius 2008 Biochemistry& Microbiology
The chlorine dosage must be sufficient to leave a residual of 0.2 to 2.0 mg/l free chlorine. Two common methods used to measure the residual chlorine in water are diethyl para-phenylene diamine method and ortho toluidine method. Chlorinated limeIt is commonly known as bleaching powder. Before the discovery of liquid chlorine, chlorinated lime was widely used for chlorination. It is a loose combination of slaked lime and chlorine gas.When added to water it decomposes to give hypochlorous acid. Chlorinated lime is unstable and on exposure to air, light and moisture reduces the chlorine content rapidly. C.Fortelius 2008 Biochemistry& Microbiology
1.2 Chemical Disinfection by Ozone It is a powerful oxidising agent and highly unstable. It must be manufactured on site by passing dry air through a high voltage high frequency electrical discharge. It has a more rapid effect than chlorine in destroying viruses and bacteria including spores. It is also effective in eliminating compounds that give objectionable taste and color to water. C.Fortelius 2008 Biochemistry& Microbiology
The treatment with ozone should leave 1-2 mg/l of residual ozone. But ozone usually leaves very low level of residuals and thus there is no protection against new contamination of the water after disinfection. The high installation and operation costs further reduce its use as a disinfectant. C.Fortelius 2008 Biochemistry& Microbiology
1.3 Chemical Disinfection by Potassium Permanganate It is also a powerful oxidising agent. It has been found to be effective against cholera pathogen but not other pathogens. Since it leaves stains in the container it is not a satisfactory disinfectant. C.Fortelius 2008 Biochemistry& Microbiology
1.4 Chemical Disinfection by Halogens Bromine is used as a disinfectant for swimming pool water because of its less irritability to the eyes than chlorine. Fluorine and iodine are also at times used as disinfectants. C.Fortelius 2008 Biochemistry& Microbiology
http://www.nhmrc.gov.au/publications/synopses/eh19syn.htm C.Fortelius 2008 Biochemistry& Microbiology
2. Physical Disinfection by UV Radiation Two important physical disinfection methods are ultraviolet (UV) radiation and boiling of water. UV radiation Electromagnetic radiation of ultraviolet range can be used to destroy microorganisms. This process is effective in certain small water supplies where the water is highly polished i.e., filtered and demineralised. The process is also used in industries. For example in breweries, pharmaceutical manufactures, fish hatcheries and aquariums. C.Fortelius 2008 Biochemistry& Microbiology
Actually irradiation must strike the organism to kill it. In this process some of the radiation energy is absorbed by the organism and other' constituents in the medium surrounding the organisms. So if sufficient dosage of UV reach the organisms water can be disinfected.The germicidal effect of ultraviolet energy is thought to be associated with its absorption by certain organic components essential for the functioning of cells. Dissipation of energy by excitation causes disruption of unsaturated, bonds, particularly of the purines and pyrimidines. And this leads to lethal biochemical changes. C.Fortelius 2008 Biochemistry& Microbiology
UV treatment does not alter the water chemically. Only energy is added, which produces heat, resulting in a temperature rise in the treated water. UV rays can penetrate the cell walls of micro-organisms. So the only requirement in disinfection by UV radiation is it must reach the organisms since the UV radiation absorbed by the organisms alone can kill them. This is, one of the main disadvantage of the UV process. Other disadvantages are lack of a field test to readily establish the efficiency of the process inability of UV irradiation to provide a residual disinfecting power high cost of the system. C.Fortelius 2008 Biochemistry& Microbiology
2.1 Germicidal Efficiency It has been found out that the germicidal action of ultraviolet rays is maximal at the wave length of 250-260nm. There is an abrupt decrease in the efficiency at 290-300nm and continues upto the visible range. C.Fortelius 2008 Biochemistry& Microbiology
At a fixed UV intensity, the contact time required to achieve a 99.9% kill for certain organisms is given below.E.coli - 60 sec Shigella - 47 secStreptococcus faecalis - 165 secBacillus subtilis - 240 sec Bacillus spores - 369 sec B.subtilis spores UV radiation has also been found to be effective in the inactivation of viruses. There is no reference to the ability of UV radiation to destroy cysts. It is the consensus that UV radiation will not kill any organism which can be seen with naked eye. C.Fortelius 2008 Biochemistry& Microbiology
Monitoring of water quality In many countries, water microbiology is also the subject of legislation. Regulations specify how often water sources are sampled, how the sampling is done, how the analysis will be performed, what microbes are detected, and the acceptable limits for the target microorganisms in the water sample. Testing for microbes that cause disease (i.e., Salmonella typhymurium and Vibrio cholerae) can be expensive and, if the bacteria are present in low numbers, they may escape detection. Instead, other more numerous bacteria provide an indication of fecal pollution of the water. C.Fortelius 2008 Biochemistry& Microbiology
Escherichia coli has been used as an indicator of fecal pollution for decades. The bacterium is present in the intestinal tract in huge numbers, and is more numerous than the disease-causing bacteria and viruses. The chances of detecting E. coli is better than detecting the actual disease causing microorganisms. E.coli also had the advantage of not being capable of growing and reproducing in the water (except in the warm and food-laden waters of tropical countries). Thus, the presence of the bacterium in water is indicative of recent fecal pollution. Finally, it can be detected easily and inexpensively. C.Fortelius 2008 Biochemistry& Microbiology
EPA Microbiological Methods/Online Publications: http://www.epa.gov/nerlcwww/online.htm Australian goverment National Health and Medical Research Council http://www.nhmrc.gov.au/publications/ FINNISH STANDARDS ASSOCIATION SFS 07.100.20 Vesimikrobiologiahttp://www.sfs.fi/luettelo/ C.Fortelius 2008 Biochemistry& Microbiology
SURVIVAL OF EXCRETED PATHOGENS Health risks associated with wastewater use: http://www.fao.org/docrep/w5367e/w5367e04.htm C.Fortelius 2008 Biochemistry& Microbiology
