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Water and wastewater treatment processes. ENV H 452/ENV H 542. John Scott Meschke Office: Suite 2249, 4225 Roosevelt Phone: 206-221-5470 Email: jmeschke@u.washington.edu. Gwy-Am Shin Office: Suite 2339, 4225 Roosevelt Phone: 206-543-9026 Email: gwyam@u.washington.edu.

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water and wastewater treatment processes

Water and wastewater treatment processes

ENV H 452/ENV H 542

John Scott Meschke

Office: Suite 2249,

4225 Roosevelt

Phone: 206-221-5470

Email: jmeschke@u.washington.edu

Gwy-Am Shin

Office: Suite 2339,

4225 Roosevelt

Phone: 206-543-9026

Email: gwyam@u.washington.edu

key points
Key points
  • Purpose of the individual unit processes
  • The typical operating conditions
  • The outcome of the processes
  • Microbial reduction in the processes
how much wastewater do we produce each day
How much wastewater do we produce each day?

These values are rough estimates only and vary greatly by locale.

Wastewater Characteristics

wastewater treatment systems
Wastewater treatment systems
  • Decentralized
    • Septic tank
    • Waste stabilization ponds
      • Facultative lagoon
      • Maturation lagoon
    • Land treatment
  • Centralized
minimum goals of wastewater treatment processes
(Minimum) Goals of wastewater treatment processes
  • <30 mg/L BOD5
  • <30 mg/L of suspended solids
  • <200 CFU/100ml fecal coliforms
conventional community centralized sewage treatment
Conventional Community (Centralized) Sewage Treatment

Secondary Treatment Using Activated Sludge Process

Sludge drying bed or mechanical dewatering process

Pathogen Reductions Vary from: low (<90%) to Very High (>99.99+%)

slide11

Typical Municipal Wastewater Treatment System

Preliminary or Pre-Treatment

SecondaryTreatment

PrimaryTreatment

Disinfection

Sludge Treatment& Disposal

slide12

Preliminary Wastewater Treatment System

Preliminary or Pre-Treatment

Solids to Landfill

slide13

Preliminary Treatment - Bar Racks

Bar Racks: are used to remove large objects that could potentially damage downstream treatment/pumping facilities.

Preliminary Treatment Facilities

Ref: Metcalf & Eddy, 1991

preliminary treatment grit chamber
Preliminary Treatment - Grit chamber

Grit chamber: used to remove small to medium sized, dense objects such as sand, broken glass, bone fragments, pebbles, etc.

primary sedimentation
Primary sedimentation
  • To remove settleable solids from wastewater
slide17

Primary Clarification

Scum: Oil, Grease, Floatable Solids

PrimaryEffluent

PrimarySludge

Influent from Preliminary Treatment

Section through a Circular Primary Clarifier

Primary Treatment

primary sedimentation1
Primary sedimentation
  • To remove settleable solids from wastewater
  • Maximum flow: 30 - 40 m3 per day
  • Retention period: 1.5 - 2.0 hours (at maximum flow)
  • 50 - 70 % removal of suspended solids
  • 25 - 35 % removal of BOD5
  • ~20 % removal of phosphate
  • ~50 % removal of viruses, bacteria, and protozoa
  • 90 % removal of helminth ova
secondary treatment processes
Secondary treatment processes
  • To remove suspended solids, nitrogen, and phosphate
  • 90 % removal of SS and BOD5
  • Various technologies
    • Activated sludge process
    • Tricking filter
    • Aerated lagoons
    • Rotating biological contractors
secondary treatment using activated sludge process
Secondary Treatment Using Activated Sludge Process

SecondaryTreatment

Sludge drying bed or mechanical dewatering process

Secondary Treatment

the activated sludge process
Aerobic microbes utilities carbon and other nutrients to form a healthy activated sludge (AS) biomass (floc)

The biomass floc is allowed to settle out in the next reactor;

some of the AS is recycled

Simplified Activated Sludge Description

The Activated Sludge Process

Secondary Treatment

activated sludge process
Activated sludge process
  • To remove suspended solids, nitrogen, and phosphate
  • Food to microorganism ratio (F:M ratio): 0.25 kg BOD5 per kg MLSS (mixed liquor suspended solids) per day at 10 oC or 0.4 kg BOD5 per kg MLSS per day at 20 oC
  • Residence time: 2 days for high F:M ratio, 10 days or more for low F:M ratio
  • Optimum nutrient ratio: BOD5:N:P =>100:5:1
  • 90 % removal of BOD5 and SS
  • ~20 % removal of phosphate
  • >90 % removal of viruses and protozoa and 45 - 95 % removal of bacteria
secondary treatment using trickling filter process
Secondary Treatment Using Trickling Filter Process

SecondaryTreatment

TricklingFilter

Secondary Treatment

trickling filter
Trickling Filter

Rotating arm todistribute water evenly over filter

Primary effluent drips onto rock orman-made media

Rock-bed with slimy (biofilm) bacterial growth

Treated waste to secondary clarifier

Primary effluent pumped in

http://www.rpi.edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/streem/trickfil.jpg

trickling filter1
Trickling Filter

http://www.eng.uc.edu/friendsalumni/research/labsresearch/biofilmreslab/Tricklingfilter_big.jpg

tricking filter process
Tricking filter process
  • To remove suspended solids, nitrogen, and phosphate
  • Organic loading (BOD5 X flow/volume of filter): 0.1 kg BOD5 per m3 per day
  • Hydraulic loading: 0.4 m3 per day per m3 of plan area
  • 90 % removal of BOD5 and SS
  • ~20 % removal of phosphate
  • Variable removal levels of viruses, 20-80 % removal of bacteria and >90 % removal of protozoa
wastewater disinfection
Wastewater disinfection
  • To inactivate pathogens in wastewater
  • Several choices
    • Free chlorine and combined chlorine
    • UV
    • Ozone
    • Chlorine dioxide
water contaminants
Water contaminants
  • Chemicals
    • Inorganics
    • Organics
      • Synthetic organic compounds
      • Volatile organic compounds
  • Microbes
    • Viruses
    • Bacteria
    • Protozoa parasites
    • Algae
    • Helminths
barrier approach to protect public health in drinking water
Barrier Approach to Protect Public Health in Drinking Water
  • Source Water Protection
  • Treatment Technology
  • Disinfection
  • Disinfectant residual in distribution system
oxidation
Oxidation
  • To remove inorganics (Fe++, Mn++) and some synthetic organics
    • Cause unaesthetic conditions (brown color)
    • Promote the growth of autotrophic bacteria (iron bacteria): taste and order problem
  • Free chlorine, chlorine dioxide, ozone, potassium permanganate
    • Fe++ + Mn ++ + oxygen + free chlorine → FeOx ↓(ferric oxides) + MnO2 ↓ (manganese dioxide)
    • Fe (HCO3)2 (Ferrous bicarbonate) + KMnO4 (Potassium permanganase) → Fe (OH)3 ↓(Ferric hydroxide) + MnO2 ↓(manganese dioxide)
    • Mn (HCO3)2 (Manganese bicarbonate) + KMnO4 (Potassuim permanganase) → MnO2 ↓(manganese dioxide)
physico chemical processes
Physico-chemical processes
  • To remove particles in water
  • Coagulation/flocculation/sedimentation
  • Filtration
rapid mix

Chemical Coagulant

Rapid Mix
  • Intense mixing of coagulant and other chemicals with the water
  • Generally performed with mechanical mixers
major coagulants
Major Coagulants
  • Hydrolyzing metal salts
    • Alum (Al2(SO4)3)
    • Ferric chloride (FeCl3)
  • Organic polymers (polyelectrolytes)
coagulation with metal salts

Al(OH)3

Al(OH)3

Al(OH)3

Al(OH)3

Al(OH)3

Al(OH)3

Al(OH)3

Al(OH)3

Al(OH)3

Colloid

Colloid

Colloid

Coagulation with Metal Salts

Soluble Hydrolysis Species

+

+

(Low Alum Dose)

(High Alum Dose)

Colloid

Colloid

Alx(OH)y

Colloid

Floc

Al(OH)

Charge Neutralization

Sweep Coagulation

flocculation example
Flocculation Example

Water coming from

rapid mix.

Water goes to sedimentation

basin.

sedimentation basin example
Sedimentation Basin Example

Water coming from

flocculation basin.

Water goes to

filter.

Floc (sludge) collectedin hopper

Sludge to solidstreatment

coagulation flocculation and sedimentation
Coagulation/flocculation/and sedimentation
  • To remove particulates and natural organic materials in water
  • Coagulation
    • 20 -50 mg/L of Alumat pH 5.5-6.5 (sweep coagulation)
    • rapid mixing: G values = 300-800/second
  • Flocculation:
    • Slow mixing: G values = 30-70/second
    • Residence time:10 -30 minutes
  • Sedimentation
    • Surface loading: 0.3 -1.0 gpm/ft2
    • Residence time: 1 – 2 hours
  • Removal of suspended solids and turbidity: 60-80 %
  • Reduction of microbes
    • 74-97 % Total coliform
    • 76-83 % of fecal coliform
    • 88-95 % of Enteric viruses
    • 58-99 % of Giardia
    • 90 % of Cryptosporidium
filtration
Filtration
  • To remove particles and floc that do not settle by gravity in sedimentation process
  • Types of granular media
    • Sand
    • Sand + anthracite
    • Granular activated carbon
  • Media depth ranges from 24 to 72 inches
filter example
Filter Example

Water coming from sedimentation

basin.

Anthracite

Sand

Gravel (supportmedia)

Water going to disinfection

mechanisms involved in filtration
Mechanisms Involved in Filtration

Floc particles

Interception: hits & sticks

Flocculation: Floc gets larger within filter

Sedimentation: quiescent, settles, & attaches

Granular media, e.g., grain of sand

Entrapment: large floc gets trapped in space between particles

Removal of bacteria, viruses and protozoa by a granular media filter requires water to be coagulated

rapid filtration
Rapid filtration
  • To remove particulates in water
  • Flow rate: 2-4 gpm/ft2
  • Turbidity: < 0.5 NTU (often times < 0.1 NTU)
  • Reduction of microbes
    • 50-98 % Total coliform
    • 50-98 % of fecal coliform
    • 10-99 % of enteric viruses
    • 97-99.9 % of Giardia
    • 99 % of Cryptosporidium
disinfection in water
Disinfection in water
  • To inactivate pathogens in water
  • Various types
    • Free chlorine
    • Chloramines
    • Chlorine dioxide
    • Ozone
    • UV