What are the major reasons for drinking water treatment of water and what are the major principles and processes of water treatment?
Provision of safe, palatable water is the primary goal of drinking water treatment. Water quality varies greatly depending on the source. The major constituents of concern that are addressed by water treatment are pathogenic microorganisms and chemicals that are either harmful to human health or that make the water unpalatable or appear unclean (some organic matter and inorganic compounds). The microbial quality of water is paramount because the presence of pathogens in water can lead to acute infectious illness and death. Untreated water has been the source of countless epidemics of infectious disease around the world. The current dominant water treatment paradigm for most surface waters follows the multiple barrier principle, which maintains that multiple treatment processes should be used so that any breakdown in one of the processes will not lead to complete failure. The processes involved in treatment include protection of the water source, and physical and chemical treatment to remove physical particles, chemicals, and microorganisms, followed by addition of a chemical disinfectant to inhibit any organisms reintroduced during storage and distribution. Removal mechanisms include prefiltration to remove large particles. Sedimentation, with or without a chemical coagulant, removes smaller particulates prior to a media (often sand) filtration unit which also relies on physical removal to further cleanse the water of small particulates. Addition of a chemical disinfectant (usually chlorine) kills or inhibits any remaining potential pathogenic microorganisms and a residual is maintained to ensure that any microorganisms introduced during storage or distribution will be inactivated. Although chlorine is highly reactive oxidizing agents that also react with organic and inorganic chemical species in the water to form harmful byproducts which have been shown to cause health effects, the risk of microbially contaminated water causing infectious disease outbreaks warrants the use of these chemicals judiciously to maintain adequate disinfection of water. Water treatment facilities, therefore, maintain a delicate balance between treating the water to render it safe from infectious disease causing organisms while forming the lowest quantity of harmful chemical byproducts which could cause chemical-induced diseases in the future. Additional and advanced processes are often added to the treatment process to achieve certain goals, such as removal of pesticides or other organic contaminants (granular activated carbon [GAC}), metals such as iron (ion exchange, GAC) , or provide additional disinfection capability (ozone, UV light).
Explain the significance of hemolysis in classification of Streptococcal species.
In clinical microbiology, species of Streptococcus are classified with respect to their ability to rupture, or hemolyze, red blood cells. Alpha-hemolytic species oxidize hemoglobin-iron within red blood cells, causing a greenish sheen surrounding microbial growth on blood agar. Beta-hemolytic species completely rupture blood cells, resulting in a clear zone forming around microbial colonies grown on blood agar. Gamma-hemolytic species are not able to hemolyze red blood cells. Certain alpha-hemolytic and beta-hemolytic species of Streptococcus are important human pathogens. If an isolate is found to be capable of hemolysis, further specific tests are run to more fully determine the identity of the isolate so that proper treatment can begin.
Explain ecological succession and give a detailed example of succession from the natural world.
Ecological succession refers to the change in the species composition of a community in a particular habitat over time. Succession can be primary colonization of habitat that hasn't been colonized before, or secondary succession in a disturbed habitat. A classic example of secondary ecological succession is the reintroduction of vegetation after a forest fire. A fire destroys above-ground vegetation. Grasses and small, non-woody plants grow back first. Pioneer species of shrubs and fast-growing trees (such as pines) colonize the habitat. As the pioneer species grow they shade the area, allowing slower growing, shade-tolerant species to establish. The slower growing species grow toward maturity and overtake the fast growers, and the fast-growing trees die off due to age and limited light availability. Typical under-story vegetation takes the place of the pioneer species, leading to a robust climax community similar in composition to the original community inhabiting the area before the fire.