Fundamentals of Wastewater Treatment - PowerPoint Presentation

Slide1

Fundamentals of Wastewater Treatment

1Slide2

Wastewater Treatment

2

Activated sludge processes

Fixed film and suspended processes

Aerobic/anoxic/anaerobic processes modifications.

Nutrient removal

nitrification / denitrification, phosphorous removal

Water reuse and reclamation

membrane bioreactors

Disinfection

Satellite and On-site Wastewater TreatmentSlide3

Wastewater contaminants

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Bacteriological,

Vibrio Cholerae, Campylobacter, Salmonella , Shigella,

Viruses

Hepatitis A, Norovirus

Protozoan

Giardia, Cryptosporidium, Entamoeba

Biological oxygen demand

Organic matter causes algae to thrive and deplete dissolved oxygen

Nutrient removal to prevent eutrophication

Nitrogen and phosphorus from waste, and agricultureSlide4

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What does wastewater look like?

Source: Wastewater Engineering, Metcalf and Eddy- medium strength WW

Measurement

Value

Units

Total Suspended Solids (TSS)

210

mg/L

BOD

190

mg/L

TOC

430

mg/LCOD 140mg/LOrganic Nitrogen15mg/LFree Ammonia25 mg/LNitrite/Nitrate0/0 mg/LPhosphorous7mg/LTotal coliform107-109 colonies/100mLFecal coliform104-106 colonies/100mLCryptospiridium oocysts0.1-10 no./100mLGiardia Lamblia0.1-100no./100mLSlide5

Routine bacterial testing consists of measuring indicator organisms

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Testing for pathogens directly is expensive and hazardous

Indicators from the family

Enterobacteriacae

are used

(E. Coli, Citrobacter,Enterobacter, Klebsiella)

Grow bacteria on a specified medai and count the number of colonies after incubation

Other assays are used and are approved by the US EPA (Colilert shown)Slide6

Initial steps in satellite and centralized wastewater treatment

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Suspended growth process

Fixed film process

Primary settling

Screens

Sludge drying

Grit removal

DigesterSlide7

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Treated Water

Waste Water

Facultative/Anaerobic

Bed Media

Aerobic



100µm

~

1 mm

Biofilm

Fixed film biological processesSlide8

Rotating biological contactor

(40% submerged rotates at 1-1.5 rpm)

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Trickling filter

Fixed film biological processes

Uses biofilm to treat water to remove BODSlide9

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Trickling filter effectiveness

BOD

5

removal rates for trickling filters

Filter Type

Hydraulic loading m

3

/m

2

day

BOD5 Removal (%)

Low Rate

1-4

80 - 90Intermediate 4-1050 - 70High Rate10-4065 - 85Roughing Filter 40 - 65Source: Environmental Engineers Handbook, 1997.Slide10

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Suspended growth biological processes

Anoxic – no dissolved oxygen

Waste Water

Aerobic

Treated Water

Activated Sludge

Anoxic

sludge

Return activated sludge

Coagulation

ClarifierSlide11

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BOD and nutrient

(nitrogen and phosphorous) removal

Aerobic Conditions

Anoxic Conditions

BOD + O

2

CO

2

+ increased cell mass

NO

3

Organic N

NH4NO2 NO3 N2 Aerobic ConditionsPincreased cell massAnaerobic/Aerobic ConditionsAlumorganic sludgeinorganic sludgeSlide12

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Suspended growth activated sludge processes requires energy

Use forced air suspension of biological sludge to reduce BOD

Largest expense for this process is the electrical energy requiredSlide13

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Activated sludge process stages

Anoxic Basin

Sedimentation

Final Clarification

Aerobic BasinSlide14

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Anaerobic sludge digestion reduces

solids - makes methane

Anaerobic sludge digestors produce methane

(65% CH

4

- 35% CO

2

)

On-site electricity is produced with the methane 50% of plant power (2.2MW)Slide15

Liquid process train

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Aeration

Sedimentation

Sedimentation

Solids Handling

N

org



NH

3

+

NH

3+  NO2NO2  N2MixingC6H14  Biomass + CO2Slide16

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Modified Ludzack-Ettinger (MLE Process)

A

2

O

Bardenpho

RAS = Return Activated Sludge

WAS = Waste Activated Sludge

Exemplary process stagesSlide17

Solids handling involves anaerobic conditions

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CH

4

+ CO

2

C

6

H

14

+ H

2

O

Anaerobic Fermentation (30 days)

Aeration Blowers6.6 MWDisposal or Reuse (150 t/day)Diesel GeneratorsBiosolidsCentrifugesPNMSlide18

A Typical Process

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NH

3

+

Settling & Aeration

Fermentation

River

Sewers

CO

2

N

2

CH

4MicrobesCompostingCO2H2OH2O+C+N+SO2HumusHeatPowerH2SCO2HOCl-SO2(Biosolids)Slide19

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Water reuse often uses membrane bioreactor with submerged membranes

Uses submerged hollow fiber membranes

High Solids Retention Time membrane bioreactor

Conventional activated sludge plant

MBR membrane cassetteSlide20

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Membrane bioreactors offer small size, high rate of reaction for satellite WW

Screens

Anoxic

Aerobic

Submerged MembraneSlide21

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Membrane separation spectrum

Source: Zenon MembranesSlide22

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Screen before membrane bio reactorSlide23

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Kubota MBR pilot plantSlide24

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Raw feed and MBR productSlide25

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Reverse osmosis after MBR makes water suitable for groundwater recharge

RO treated water is better than most surface water sourcesSlide26

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Hyperion Wastewater Plant

Los Angeles 450 mgd

10% of discharge from this plant is sent to microfiltration plant to purify for groundwater injectionSlide27

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West Basin Microfiltration Plant

(35 mgd from Hyperion)

Submerged microfiltration for treated wastewater effluentSlide28

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The final step is disinfection and discharge (no residual free chlorine)

Chlorination to kill the remaining pathogens

Cl

2

HOCl

Dechlorination to remove chlorine

SO

2

+ HOCl + H

2

O  HCl + H

2

SO4SO2 + NH2Cl + 2H2O  NH4Cl + H2SO4UV radiation reduces chemical needs and chlorinated productsSlide29

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Effect of wastewater on disinfection

Chlorine

Ozone

UV

BOD,COD,TOC

Chlorine demand

Ozone demand

Little effect

Oil and grease

Chlorine demand

Ozone demand

May block light

Nitrite

Forms NDMAOxidized No effectNitrateForms chloraminesReduce O3effectivenessNo effectIron and ManganeseOxidizedOxidizedMay block lightForms disinfection byproductsYesYes, but nonchlorinatedNoSource: Wastewater Engineering- Metcalf & EddySlide30

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Satellite and on-site waste disposal

Satellite facilities are mid scale sewage treatment plants that treat waste near the point of generation

Lagoons

Aeration ditches

Trickling filters

Membrane bioreactor

On-site waste disposal is

septic tank

system with drain field

Provides low cost alternative

Can be very effective

Need little maintenance (but maintenance is important)