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Unit 3-8/18/2015

YEAR 3 SEMESTER 2

2015

SHIROMI KARUNARATNE

EMAIL-SHIROMI.K@SLIIT.LK

MOBILE- 0776368620

CE3610 Environmental

Engineering:Week 3

mailto:Email-shiromi.k@sliit.lkmailto:Email-shiromi.k@sliit.lkmailto:Email-shiromi.k@sliit.lk

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8/18/2015Also refer-http://www.epa.gov/ogwdw/watertreatmentplant/flash/index.html

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Sedimentation

• Removal of suspended particles whether such particles already exis

in water or are produced by the action of coagulation-flocculation.Principle: Solid liquid separation by gravitational force Applicationsin Water Treatment:

• •Settling of coagulated and flocculated waters prior to filtration

• •Settling of treated waters in an iron and manganese removal plantApplications in Wastewater Treatment:

• •Grit removal

• •Suspended solids removal in primary clarifier

• •Biological flocs removal in activated sludge

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Sedimentation tank

• Elements of sedimentation tank: Four zones namely inletzone, settling zone, sludge zone, and outlet zone.

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Sedimentation tank• Proper inlet and outlet design is important to achieve the best

efficiency Inlet structures are designed to uniformly distribute theinfluent suspension across the cross section of the settling zone.

• Inlet zone:

• •Should dissipate influent energy

• •Distribute the flow

• •Minimize sludge blanket disturbance

• Outlet zone:

• •Outlet zone should be placed as far from the inlet as possible

• •At the outlet water should not be rushed to avoid scouring(washing out of the flocs)

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Sedimentation Tank

• Settling Zone:

Where the actual settling takes ofparticles

takes place.

• •Settling characteristics of the suspendedmatter

• •Surface loading (over flow rate)

• •Width/length ratio or diameter• •Detention time

• Sludge zone: A storage space for sludgeneed to be provided

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Sedimentation Tank

• Sedimentation Tank To better design the sedimentation tank, V> Vo

• Vo = overflow rate = surface loading rate=(Volume/Time)/(Surface area) = Depth/Time

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Ideal Sedimentation

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Determination of VS

• Determination of particle-settling velocity (Vs) is different fotypes of particles. Settling properties are categorized into onthree classes:

• •Type I Sedimentation: settling of grit, sand, gravel• •Type II Sedimentation: settling of chemically coagulated wa

• •Type III or Zone Sedimentation: settling of highly concentraparticles (> 1000 mg/L)

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Type I Sedimentation

• •Discrete settling

• •Settle as individual particles

• •Examples are sand, gavel or other particles settling

• •Easily described by analysing the settling velocity

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Determination of Vs for Type I

• •Vs – particle settling velocity (m/s)

• •By equating gravitational, buoyancy, and drag forces the Vsterminal velocity of particle) can be determined.

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Example

• The town of San Jose has an existing horizontalflow sedimentation tank with and overflow rate of17 m3/d m2 and it wishes to remove particles thathave settling velocities of 0.1 mm/s, 0.2 mm/s, and1 mm/s. What percentage of removal should beexpected for each particle in an idealsedimentation tank?

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Upflow solids-contact Sedimentation Tan

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Coagulation, flocculation andsedimentation in a single unit.

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Retention Time

• •Retention time (age of water or detention time) is

defined as the average time water spends in the tank.

• • t = V/Q

• 1.Using your knowledge of required retention times,

calculate the size of the tank required for rapid mixing,flocculation basin and sedimentation tank for a water flowof 2.5 m3/s.

• 2.Water is flowing with velocity of 0.5 m/s in a pipelinehaving uniform cross sectional area and length of 100km,calculate the water retention time in the pipeline?

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Dissolved Air Flotation

• Flotation is a unit operation in which solids are made tofloat to the surface by applying air

• •On account of the solids adhering to the rising airbubbles, they are separated out from the water.

• Dissolved Air Flotation

• •Alternative to sedimentation• •Higher energy need

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Dissolved Air Flotation

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Filtration

• Settling does not remove all flocs – further treatment isrequired

• Filtration provides the additional opportunity for separation ofsmall flocs or particles

• Types of Filtration

• Granular media filters• •Slow sand filters• •Rapid sand filters

• •High rate filters

• Membrane filters• •Microfiltration membrane• •Ultrafiltration membrane• •Nano filtration membrane

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Filtration

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Slow Sand Filter Membrane Filter

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Typical multimedia filter

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Filtration Mechanisms

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Filter Operation

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Sand Filters

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Disinfection

• To inactivate pathogens so that they are notinfectious to humans and animals

• •Achieved by altering or destroying structures orfunctions of essential components within thepathogens

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Detection of pathogen presence

• •Difficult to enumerate one by one

• •Mostly from faecal origin

• •Need to select some indicators which are easy tocount and monitor

• •Most widely used test involves measurement ofcoliform group

• –Coliforms outnumber the pathogens

• –They inhabit the intestinal tract of people, but are alsfound in most domestic animals and birds, as well as icertain wild species.

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Microbial quality measurement• •What we are interested in is how many are there in a given

volume.

• •Measured as number of microbes per mL or per 100 mL or pe40L depending on the necessity!!!

• •More specifically we are interested in what it would do?

• •When considering the health impacts, we are concernedabout pathogenic organisms

• •Pathogens could be discharged by an infected person or by aperson simply carrying the disease without showing symptoms(See Table 3-12 of Metcalf and Eddy)

• •Measuring pathogens is difficult

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Types of disinfectants

• –Chlorine

• –Chloramine

• –Ozone

• –Chlorine dioxide

• –Ultraviolet radiation

• –Advance oxidation process. (Photocatalytic oxidation etc.

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Disinfection kinetics

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Disinfection

kinetics in a

given water is

given by

Usually, water

authorities

work on CT

requirement.

• CT = (concentration, mg

(h or min)

• CT is defined for a perce

kill or log reduction.

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  inactivation & log removal

• •After 99% inactivation, 100,000 -> 1000

• •This is equivalent to 2 log removal

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CT values for Giardia (which is difficult to

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CT values for Giardia(which is difficult tokill)

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h d f ( l f

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Other disinfectants (CT values for 99.99Giardiacyst inactivation

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Lecture 3: Practice Questions

• Q1: You have two different suspended particles with settling

velocities of 0.1 and 0.2 mm/s. The particles are present at 60:40ratio. What will be the removal efficiency for an overflow rate of 17m/d.

• •For particle with removal efficiency of 0.1 mm/s

• •For particle with removal efficiency of 0.2 mm/s

• •All particles

• Q2. Why should coliforms and E.coli be monitored?

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Lecture 3: Practice Questions

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Lecture 3: Practice Questions

• Q6) Equilibrium molar concentrations of OCl- and HOCl as a functioof pH are given in the chart of lecture notes. Two samples were

taken from a distribution system where chlorination is practiced.Distribution system sample’s pH was 7.5. One portion of the samplewas adjusted to pH of 8.5.

•Calculate the comparative disinfection ability.

•Which one has the higher disinfection ability, higher pH orlower pH?

• Q7) Answer the following questions regarding disinfection ofmicroorganisms.

•If you have 105 organisms per mL and if you achieve 3 logremoval, how many organisms will remain in water?

•If the CT requirement is 85 mg/L.min, what do youunderstand by this? If 2 mg/L chlorine is dosed how long do you haveto wait to achieve CT of 184 mg/L. min?

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