industrial water treatment process ppt

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RyanCanon,United Arab Emirates,Teacher
Published Date:21-07-2017
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Lecture 8: Water treatment processes th (Jan 27 2015) by Dr. Arun Kumar ( Objective: Understand functioning of different unit processes for water treatment Courtesy: Dr. Irene Xagoraraki (Michigan State University, East Lansing, USA) January 28, 2015 Arun Kumar 1 ( lecture re-cap • Introduction of water treatment schematic concepts • Discussion on production of water of different final usages • Discussion on checks – Remove solids before removing bacteria – Remove solids using sedimentation process before using filtration – Remove organic compounds and ammonia-based compounds before disinfection • Discussion on need for calculating solids waste produced from every unit processes and solid waste managementExample 2: River Water Drinking water January 28, 2015 3Example 2 schematic contd. January 28, 2015 4Treatment schematic (SW Potable drinking water) • Sequence of unit processes: pre-sedimentation mixing, flocculation, settlingfiltrationadsorptiondisinfection • Function of unit processes: solids removal  removal of ions, and solids using chemical additionremoval of smaller particlesremoval of organic compounds and ionsoxidation of oxygen- demanding wastes and chemical killing of pathogens in water January 28, 2015 5(SW Potable drinking water) contd.. • Chlorine is added in sedimentation and filtration tank to avoid microbial growth • Chorine is used as a oxidizing agent as well as a disinfection solution. January 28, 2015 6Surface Water TreatmentConventional Surface Water Treatment • Screening (remove relatively large floating and suspended debris) • Rapid-mix (mixing water with chemicals that encourage suspended solids to coagulate into larger particles that will settle easily) • Flocculation (gently mixing water and coagulant allowing the formation of large particles of floc)Conventional Surface Water Treatment • Sedimentation (flow is slowed enough so that gravity will cause flocs to settle) • Sludge processing (mixture of solids and liquids collected from settling tank are dewatered and disposed of) • Disinfection (ensure that water is free of harmful pathogens) • Distribution system protection (residual disinfection)Solids removal January 28, 2015 10Method 1.SedimentationMethod1. Sedimentation • Solids settle based on their gravitational force (with and without externally added chemicals). • Settling depend on solid physical characteristics (diameter, density) and medium temperature, viscosity, density, etc. • Some solids do not interact with each other during settling (i.e., discrete particles) (no change in their size and shape). The settling is called discrete settling (Type 1 settling). Ex: settling of sand. January 28, 2015 12Method1. Sedimentation • Some solids interact during their settling and change their size and shape (i.e., flocculent particles) (Type 2 settling). Ex: settling of clay; bacteria. January 28, 2015 13Sedimentation • Time for settling = column depth/settling velocity at steady state • Some particle take less time and some particles take longer time to settling. • if t_designt_settling, particles remove 100%. All patcies now constitute to solid waste. • if t_designt_settling, particles do not remove 100%. Remaining particles go to next unit in treatment plant scheme. January 28, 2015 14Method 2. Coagulation-Flocculation- Sedimentation Some coagulants: Some coagulant aids: aluminum sulfate, activated silica ferric sulfate clay ferric chloride polymersCoagulation-Flocculation-Sedimentation Full-scale Pilot-scale Bench-scaleSizes of Particles in WaterMethod2. Coagulation-flocculation (sedimentation after chemical addition) • Some solids take very long time to settle (size in submicron range or in nanometer range). • Chemicals (ex: alum; ferric chloride) are added in solution to (1) increase size of particles, (2) capture them in hydroxide flocs and then precipitate them. January 28, 2015 18Coagulation - Flocculation + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Colloidal particles (0.001 - 10 μm) floc (1 - 100 μm)Method2. Coagulation-flocculation (sedimentation after chemical addition) • Coagulation methods: (i) ionic layer compressions, (2) charge neutralization and surface complexation, (3) sweep coagulation(iv) polymeric bridging • Ex: ferric chloride gives ferric ions (acidic pH) and ferric hydroxide (basic pH). These species work in 2 different ways to improve particle settling. January 28, 2015 20

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