11

CTC 450 ReviewCTC 450 Review Preliminary & Primary TreatmentPreliminary & Primary Treatment

Measure flowMeasure flow ScreenScreen Grit chamberGrit chamber Primary SettlingPrimary Settling

22

ObjectivesObjectives Understand basic processes of Understand basic processes of

biological treatmentbiological treatment

33

Stone Media Trickling FilterStone Media Trickling Filter

http://www.centervilleut.net/img/Public%20Works/2TricklingFilter.jpg

44

Stone-Media Trickling FiltersStone-Media Trickling Filters Major componentsMajor components

Rotary distributorRotary distributor Underdrain systemUnderdrain system Filter media (5-7’ depth)Filter media (5-7’ depth)

Most common media is crushed rock, Most common media is crushed rock, slag or field stone (3-5” in dia.)slag or field stone (3-5” in dia.)

Media must be durable, insoluble and Media must be durable, insoluble and resistant to spallingresistant to spalling

55

Stone-Media Trickling FiltersStone-Media Trickling Filters Some ww is recycled to the filterSome ww is recycled to the filter Two-stage consists of 2 filters in Two-stage consists of 2 filters in

series (with or w/o an intermediate series (with or w/o an intermediate clarifier)clarifier)

Second filter is less efficient since Second filter is less efficient since food concentration is lessfood concentration is less

BOD removal is influenced by temp.BOD removal is influenced by temp.

RecirculationRecirculation

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Recirculation Ratio (R)Recirculation Ratio (R) R = Qr divided by QR = Qr divided by Q Where:Where:

Qr=recirculation flowQr=recirculation flowQ=incoming wastewater flowQ=incoming wastewater flow

R can be less than 1 or greater than R can be less than 1 or greater than 11

77

88

Biological TowersBiological Towers Plastic media is usedPlastic media is used

High percentage of voidsHigh percentage of voids High surface area per unit of volumeHigh surface area per unit of volume Uniform media (random or modular)Uniform media (random or modular) Light weightLight weight Chemical resistanceChemical resistance Can treat high-strength wastewatersCan treat high-strength wastewaters

99

Biological TowerBiological Tower

Plastic media - Trickling filter at Madras Refineries Ltd, Chennai -http://www.paramountlimited.com/wwtpfotoct15a.htm

1010

Biological Tower MediaBiological Tower Media

www.aquacare.de/produkte/ filtermat/e_riesel.htm

http://www.engr.psu.edu/ce/enve/images/XF-media.JPG

1111

Biological TowerBiological Tower Theoretical removal rates get Theoretical removal rates get

complex and are based on soluble complex and are based on soluble BOD BOD

Packing configuration impacts Packing configuration impacts residence time, which is related to residence time, which is related to hydraulic loading and filter depthhydraulic loading and filter depth

Another complication is that effluent Another complication is that effluent from the tower is recirculated from the tower is recirculated

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Biological TowerBiological TowerRecirculationRecirculation

Sp is soluble BOD of primary effluentSp is soluble BOD of primary effluent So is soluble BOD of tower influent So is soluble BOD of tower influent Se is soluble BOD of tower effluentSe is soluble BOD of tower effluent Equation 11-13 (pg 311) can be used Equation 11-13 (pg 311) can be used

to calculate the efficiency of a to calculate the efficiency of a biological tower (w/ random packing). biological tower (w/ random packing). Efficiency =Se/Sp Efficiency =Se/Sp

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Example 11-3Example 11-3Biological Tower Biological Tower

Flow is 1.6 mgdFlow is 1.6 mgd Primary Clarifier/Biological Tower/Secondary Clarifier Primary Clarifier/Biological Tower/Secondary Clarifier Single Stage Biological Tower:Single Stage Biological Tower:

Diameter = 70’Diameter = 70’ Media Depth = 7’Media Depth = 7’ Primary Effluent has a soluble BOD of 100 mg/lPrimary Effluent has a soluble BOD of 100 mg/l Water temp is 15C (59F)Water temp is 15C (59F) Constants for random plastic media are:Constants for random plastic media are:

n=0.44n=0.44 kk2020=0.0023 =0.0023 AAss=35 square ft per cubic foot=35 square ft per cubic foot

Calculate the effluent soluble BOD assuming indirect Calculate the effluent soluble BOD assuming indirect recirculation to the wet well of 560 gpmrecirculation to the wet well of 560 gpm

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Example 11-3Example 11-3Biological Tower Biological Tower

Handout in ClassHandout in Class

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Combine filters/activated Combine filters/activated sludgesludge

Biological tower can be used before Biological tower can be used before activated sludgeactivated sludge

Analyzing the process is difficultAnalyzing the process is difficult

Read discussion on page 312-313Read discussion on page 312-313

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Filter/Tower ProblemsFilter/Tower Problems OdorOdor Effluent qualityEffluent quality Cold weatherCold weather FliesFlies SnailsSnails

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CoversCovers Odor ControlOdor Control Limits heat lossLimits heat loss

http://www.cityoflaporte.com/wwtp/secondary.htm

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Activated Sludge Activated Sludge Liquid suspension of microorganisms Liquid suspension of microorganisms

(mixed liquor)(mixed liquor) MLSS-mixed liquor suspended solidsMLSS-mixed liquor suspended solids Aerobic processAerobic process

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Activated Sludge Activated Sludge Settleability Settleability

Depends on food-to-microorganism Depends on food-to-microorganism ratio and sludge ageratio and sludge age

High MLSS concentrations and High MLSS concentrations and extended times encourage extended times encourage endogenous growthendogenous growth

Endogenous growth-microorganisms Endogenous growth-microorganisms are starved and rapidly utilize the are starved and rapidly utilize the food sourcefood source

2020

Activated SludgeActivated SludgeExample 11-5Example 11-5

Rework example to understand Rework example to understand calculationscalculations

2121

RBC RBC

40% submerged40% submerged Four stages often Four stages often

used (each with used (each with separate tanks)separate tanks)

Plug flowPlug flow

http://nett21.gec.jp/JSIM_DATA/WATER/WATER_1/html/Doc_204.html

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Stabilization Ponds Stabilization Ponds (lagoons)(lagoons)

Used in rural areas Used in rural areas (7% of population)(7% of population)

Used as polishing Used as polishing ponds (tertiary ponds (tertiary treatment)treatment)

Can be facultative, Can be facultative, aerated or aerated or anaerobicanaerobic www.sequencertech.com

2323

DisinfectionDisinfection Chlorine added by rapid initial mixing Chlorine added by rapid initial mixing

in a contacting basinin a contacting basin UV (hypochlorite used as standby)UV (hypochlorite used as standby)

Outfall-Railroad InterceptorOutfall-Railroad Interceptor

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Outfall-Grace CreekOutfall-Grace Creek

2525

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Private SystemsPrivate Systems 25% of homes not connected to a 25% of homes not connected to a

municipal systemmunicipal system Septic tank and drainfield (absorption Septic tank and drainfield (absorption

field)field)

2727http://www.thenaturalhome.com/septic.html