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Fundamentals of Wastewater Treatment. 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

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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 Treatment

Wastewater Treatment
wastewater contaminants
3

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 agriculture

Wastewater contaminants
slide4
4

What does wastewater look like?

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

routine bacterial testing consists of measuring indicator organisms
5Routine bacterial testing consists of measuring indicator organisms
  • 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)
initial steps in satellite and centralized wastewater treatment
6

Fixed film process

Screens

Primary settling

Grit removal

Digester

Sludge drying

Initial steps in satellite and centralized wastewater treatment

Suspended growth process

slide7
7

Biofilm

Waste Water

Facultative/Anaerobic

Bed Media

Aerobic

~1 mm

100µm

Fixed film biological processes

Treated Water

rotating biological contactor 40 submerged rotates at 1 1 5 rpm
8Rotating biological contactor(40% submerged rotates at 1-1.5 rpm)

Fixed film biological processes

Trickling filter

Uses biofilm to treat water to remove BOD

slide9
9

Trickling filter effectiveness

BOD5 removal rates for trickling filters

Source: Environmental Engineers Handbook, 1997.

slide10
10

Waste Water

Activated Sludge

Anoxic

Aerobic

Coagulation

Clarifier

sludge

Treated Water

Return activated sludge

Suspended growth biological processes

Anoxic – no dissolved oxygen

slide11
11

Aerobic Conditions

Anaerobic/Aerobic Conditions

Aerobic Conditions

Anoxic Conditions

BOD + O2

P

Organic N

NO3

CO2 + increased cell mass

NH4

increased cell mass

Alum

N2

NO2

inorganic sludge

organic sludge

NO3

BOD and nutrient

(nitrogen and phosphorous) removal

slide12
12

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 required
slide13
13

Activated sludge process stages

Aerobic Basin

Anoxic Basin

Sedimentation

Final Clarification

slide14
14

Anaerobic sludge digestion reduces solids - makes methane

Anaerobic sludge digestors produce methane

(65% CH4 - 35% CO2)

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

liquid process train
15Liquid process train

Sedimentation

C6H14 Biomass + CO2

NH3+ NO2

Norg NH3+

Mixing

Aeration

NO2N2

Solids Handling

Sedimentation

slide16
16

Modified Ludzack-Ettinger (MLE Process)

A2O

Bardenpho

Exemplary process stages

RAS = Return Activated Sludge

WAS = Waste Activated Sludge

solids handling involves anaerobic conditions
17Solids handling involves anaerobic conditions

PNM

Diesel Generators

Anaerobic Fermentation (30 days)

C6H14 + H2O

CH4 + CO2

6.6 MW

Biosolids

Disposal or Reuse (150 t/day)

Aeration Blowers

Centrifuges

a typical process
18A Typical Process

CO2

H2S

N2

HOCl-

SO2

Sewers

River

H2O+C+N+S

Settling & Aeration

H2O

Heat

Microbes

CO2

O2

(Biosolids)

NH3+

Power

Fermentation

Composting

CH4

CO2

Humus

slide19
19

Water reuse often uses membrane bioreactor with submerged membranes

Conventional activated sludge plant

MBR membrane cassette

  • Uses submerged hollow fiber membranes
  • High Solids Retention Time membrane bioreactor
slide20
20

Screens

Anoxic

Aerobic

Submerged Membrane

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

slide21
21

Membrane separation spectrum

Source: Zenon Membranes

slide22
22

Screen before membrane bio reactor

slide23
23

Kubota MBR pilot plant

slide24
24

Raw feed and MBR product

slide25
25

Reverse osmosis after MBR makes water suitable for groundwater recharge

RO treated water is better than most surface water sources

slide26
26

Hyperion Wastewater Plant

Los Angeles 450 mgd

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

slide27
27

West Basin Microfiltration Plant

(35 mgd from Hyperion)

Submerged microfiltration for treated wastewater effluent

slide28
28

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

  • Chlorination to kill the remaining pathogens
    • Cl2HOCl
  • Dechlorination to remove chlorine
    • SO2 + HOCl + H2O  HCl + H2SO4
    • SO2 + NH2Cl + 2H2O  NH4Cl + H2SO4
  • UV radiation reduces chemical needs and chlorinated products
slide29
29

Effect of wastewater on disinfection

Source: Wastewater Engineering- Metcalf & Eddy

slide30
30

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)
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