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epc_fa2011_lecture_6

epc_fa2011_lecture_6 - Introduction to Water Treatment...

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1 Introduction to Water Treatment Processes -- Purpose of Water treatment; a) Protect users from pathogens and other "unhealthy" substances b) Insure a certain quality before industrial or commercial use (degree of water quality depends on Intended Use ) The Source Æ the Users (Water treatment) The Users Æ Receiving waterbody (Wastewater treatment) -- Source characteristics (river, reservoir, groundwater, snowmelt) -- Receiving waterbody characteristics (river, reservoir, estuary, ocean) 2 Water Supply Sources -- Public water supplies are consist of lakes and reservoirs, rivers and groundwater -- Large municipalities/utilities prefer lakes/reservoirs for their main water supply sources, because a) Seasonal variation in supply is far less than rivers b) More economical than the groundwater c) Quantity of the available source is generally larger than the groundwater d) Easier to manage/protect/control the water quality due to their enclosures e) Source Isolation
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3 Main Objectives of Water Treatment -- With given source characteristics (water or wastewater) and required water quality objectives, objectives of water treatment are to design, build, and operate a cost-effective treatment plant . -- However, the science time to time lags behind practice, and as a result, proven treatment plant designs are normally used with very conservative safety factors built into the design, i.e., to ensure its 'life- supporting' infrastructure grid capacity. 4 Treatment Process Categories (Unit processes) -- Unit processes (or Unit operations) used in environmental engineering can be classified as physical, chemical, or biological treatments according to their functional principles. -- (In a strict sense,) an Unit process = a chemical or biological treatment an Unit operation = a physical treatment However, the terms unit processes and unit operations are frequently used interchangeably.
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5 Common Treatment Processes in Water Treatment Physical process Separation using physical properties Æ Unit Operation screening flocculation settling sedimentation gas transfer Chemical process Chemical reactions Æ Unit Process coagulation softening oxidation precipitation disinfection Biological process Micro-organisms enhance chemical reactions Æ Unit Process activated sludge trickling filters anaerobic digestion 6 Municipal Water Treatment -- Traditional basic layout of municipal water treatment processes
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7 Common types of treatment plant -- 1 -- Depending on type of the source water to be treated: Surface water source (lake/reservoir/river) a) Rapid Sand Filtration plants (RSF) b) Lime-Soda Softening plants (LSS) Groundwater source a) Gas stripping (to remove supersaturated CO 2 from groundwater) and Chlorination plants b) Softening plants (lime-soda or ion exchange) 8 Common types of treatment plant – 2 Rapid Sand Filtration (RSF) plants Raw water Bar Rack Traveling Screen Coagulant Mixing Flocculation Settling Granular Filtration (Rapid Sand Filter) Clear Well Distribution System (High pressure Pumps) Disinfection
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