He [Osama bin Laden] came to thank me for my efforts to bring the Americans, our friends, to help us against the atheists. First, the United States began a troop surge in Afghanistan designed to deliver the final blow to the Taliban insurgency. Not one media institution connected the dots that the United States was actively funding the harm that its armed forces were simultaneously fighting. Perhaps such mistakes are the inevitability of a bloated war bureaucracy, or that U.
Goals[ edit ] The goals of the treatment are to remove unwanted constituents in the water and to make it safe to drink or fit for a specific purpose in industry or medical applications. Widely varied techniques are available to remove contaminants like fine solids, micro-organisms and some dissolved inorganic and organic materials, or environmental persistent pharmaceutical pollutants.
The choice of method will depend on the quality of the water being treated, the cost of the treatment process and the quality standards expected of the processed water.
The processes below are the ones commonly used in water purification plants. Some or most may not be used depending on the scale of the plant and quality of the raw source water. Pretreatment[ edit ] Pumping and containment — The majority of water must be pumped from its source or directed into pipes or holding tanks.
To avoid adding contaminants to the water, this physical infrastructure must be made from appropriate materials and constructed so that accidental contamination does not occur. Screening see also screen filter — The first step in purifying surface water is to remove large debris such as sticks, leaves, rubbish and other large particles which may interfere with subsequent purification steps.
Most deep groundwater does not need screening before other purification steps. Storage — Water from rivers may also be stored in bankside reservoirs for periods between a few days and many months to allow natural biological purification to take place.
This is especially important if treatment is by slow sand filters. Storage reservoirs also provide a buffer against short periods of drought or to allow water supply to be maintained during transitory pollution incidents in the source river.
Pre-chlorination — In many plants the incoming water was chlorinated to minimize the growth of fouling organisms on the pipe-work and tanks. Because of the potential adverse quality effects see chlorine belowthis has largely been discontinued.
Sea water can have pH values that range from 7. Fresh water can have widely ranging pH values depending on the geology of the drainage basin or aquifer and the influence of contaminant inputs acid rain.
If the water is acidic lower than 7limesoda ashor sodium hydroxide can be added to raise the pH during water purification processes.
Lime addition increases the calcium ion concentration, thus raising the water hardness. For highly acidic waters, forced draft degasifiers can be an effective way to raise the pH, by stripping dissolved carbon dioxide from the water. Sufficient alkalinity also reduces the corrosiveness of water to iron pipes.
Acid carbonic acidhydrochloric acid or sulfuric acid may be added to alkaline waters in some circumstances to lower the pH. Alkaline water above pH 7. The ability of water to precipitate calcium carbonate to protect metal surfaces and reduce the likelihood of toxic metals being dissolved in water is a function of pH, mineral content, temperature, alkalinity and calcium concentration.
Particles can be inorganic such as clay and silt or organic such as algaebacteriavirusesprotozoa and natural organic matter. Inorganic and organic particles contribute to the turbidity and color of water.
The addition of inorganic coagulants such as aluminum sulfate or alum or iron III salts such as iron III chloride cause several simultaneous chemical and physical interactions on and among the particles.
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Within seconds, negative charges on the particles are neutralized by inorganic coagulants. Also within seconds, metal hydroxide precipitates of the iron and aluminium ions begin to form. These precipitates combine into larger particles under natural processes such as Brownian motion and through induced mixing which is sometimes referred to as flocculation.
The term most often used for the amorphous metal hydroxides is "floc. Iron III hydroxides can form over a larger pH range including pH levels lower than are effective for alum, typically: Where does coagulation end and flocculation begin?
In water purification plants, there is usually a high energy, rapid mix unit process detention time in seconds whereby the coagulant chemicals are added followed by flocculation basins detention times range from 15 to 45 minutes where low energy inputs turn large paddles or other gentle mixing devices to enhance the formation of floc.
In fact, coagulation and flocculation processes are ongoing once the metal salt coagulants are added. Synthetic organic polymers are high molecular weight compounds that carry negative, positive or neutral charges.The papers in this section consider trends in entrepreneurial activity, both in the United States and internationally.
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