There are a number of infectious, enteric (that is, intestinal) diseases of man which are transmitted through fecal wastes. Pathogens (disease-producing agents) include bacteria, viruses, protozoa, and parasitic worms. Widespread diseases generally occur in regions where sanitary disposal of human feces is not practiced. The most common waterborne bacterial diseases are typhoid fever (Salmonella typhosa), Asiatic cholera (vibrio comma), and bacillary dysentery (Shigella dysenteriae). The first of these is an acute infectious disease. Symptoms of typhoid fever are high fever and infection of the spleen, gastrointestinal tract, and blood. For cholera, symptoms include diarrhea, vomiting, and severe dehydration. Dysentery produces diarrhea, bloody stools, and high fever. These diseases can cause death and are still prevalent in many underdeveloped nations. However, in this country, proper environmental control has virtually eliminated these problems. Waterborne outbreaks of infectious hepatitis have occurred. However, the main transmission mechanism is by person-to-person contact. The probability of outbreaks from municipally treated water supplies is low. Symptoms include loss of appetite, nausea, fatigue, and pain. Also, a yellowish color appears in the white of eyes and skin (yellow jaundice is an older term for the disease). It is generally not fatal except to individuals with weaker or older metabolisms. Amoebic dysentery is the most common enteric protozoal infection. It is caused by Endamoeba histolytica and is transmitted by direct contact, food, and through the water in tropical climates. It is not transmittable via water in temperate climates. Disinfection, as with all these diseases, is the safest means of prevention. Bilharziasis (or Schistosomiasis) is a parasitic disease generated by a small, flat worm that can infest the internal organs, such as the heart, lungs, and liver, and even the veins. Eggs of these worms existing in human abdominal organs can be transmitted to water via fecal discharges. Once in water, they hatch into miracida and enter into snails. They then develop into sporocysts that produce fork-tailed cercariae which eventually abandon their shells and attach onto humans. They bore through the skin, enter the bloodstream, and eventually find their way to the internal organs to establish their homes. There is no immunization for this disease. Many feel it is one of the world's worst health problems, particularly in agricultural regions of Africa and South America. Fortunately, this disease does not occur in the United States (the intermediate snail host just happens to be one of several specific species not found on the continental United States).
Bacteria consists of simple, colorless, one-celled plants that utilize soluble food. They are capable of self-reproduction without the aid of sunlight. As decomposers, they represent decaying organic matter in nature. They typically range in size from 0.5-5 and as such are only visible through a microscope. Individual bacteria cells take on various geometries. Typical configurations include spheres, rods, or spirals. They may be single, in pairs, packets, or chains. Reproduction is by binary fission, meaning a cell divides into two new cells, each of which matures and divides again. Fission takes place every 1,530 mill under ideal conditions. Ideal conditions mean that the growth environment has abundant food, oxygen, and essential nutrients.
Bacteria are named according to a binomial system. The first word is the genus and the second is the species name. The most frequently referred to bacterium in the sanitary field is Escherichia coli. E. coli is a common coliform that can be used as an indicator of water's bacteriological quality. Under a microscope and magnified 1,000 times, cells appear as individual short rods.
There are two major classifications of bacteria called heterotrophic and autotrophic. Heterotrophs, also called saprohytes, utilize organic substances both as a source of energy and carbon. Heterotrophs are further subclassified into three groups. Subclassifications are based on the bacteria's action toward free oxygen. Aerobes need free dissolved oxygen to decompose organics to derive energy for growth and reproduction. This can be described by:
The second subgroup are anaerobes, which oxidize organics in the absence of dissolved oxygen. This is accomplished by using the oxygen which is found in other compounds (such as nitrate and sulfate). Anaerobic behavior can be described by the following reactions:
Organics + N03 — C02 + N2 + Energy Organics + S04= — C02 + H2S + Energy
458 WATER AND WASTEWATER TREATMENT TECHNOLOGIES Note also that:
Organics ■*■ Organic + S + C02 + H20 + Energy and that the organic acids undergo further reaction: Organic Acids ->- CH4 + C02 + Energy
Facultative bacteria comprise the last group and use free dissolved oxygen when available. However, they can also survive in its absence (that is, they also gain energy from the anaerobic reaction). Heterotrophic bacteria decompose organics to obtain energy for the synthesis of new cells, respiration, and motility. Some energy is lost in the process as heat. Autotrophic bacteria oxidize inorganic constituents for energy and utilize carbon dioxide as a source of carbon. The major bacteria types in this class are nitrifying, sulfur, and iron bacteria. Nitrifying bacteria will oxidize ammonium nitrogen to nitrate. Sulfur bacteria perform a reaction given which causes crown corrosion in sewers. Water in sewers quite frequently turns septic and generates hydrogen sulfide gas by generating hydrogen sulfide. The H2S generated absorbs in the condensation moisture on the sewer side walls and the crown of the pipe. Those sulfur bacteria able to survive at very low pH (pH < 1) oxidize weak H2S acid to strong sulfuric acid. This oxidation reaction depletes the oxygen from the sewer air. Crown corrosion of concrete-lined systems can greatly reduce the structural integrity of piping and eventually cause walls to collapse. Iron bacteria oxidize soluble inorganic ferrous iron to insoluble ferric. Certain types of filamentous bacteria (Leptothrix and Crenothrix) deposit oxidized iron in the form of Fe(OH)3 in their sheath. This produces yellow or reddish-colored slimes. Water pipes are ideal environments for these type bacteria as they have an abundance of highly dissolved iron content to provide energy and bicarbonates to serve as a carbon source. As these microorganisms mature and die, they decompose, generating obnoxious odors and foul tastes.
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