lecture 15 2009 revised

8/6/2019 Lecture 15 2009 Revised

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Wastewater treatment

processes (I)

ENV H 440/ENV H 541

John Scott Meschke

Office: Suite 2249,

4225 Roosevelt

Phone: 206-221-5470

Email:

[email protected]

Gwy-Am Shin

Office: Suite 2339,

4225 Roosevelt

Phone: 206-543-9026

Email:

[email protected]


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Key points

Purpose of the individual unit processes

The typical operating conditions

The outcome of the processes Microbial reduction of the processes


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How much wastewater do we

produce each day?

Wastewater Characteristics

Source Average Daily Flow

Domestic sewage 60-120 gal/capita

Shopping centers 60-120 gal/1000 ft2 total floorarea

Hospitals 240-480 gal/bed

Schools 18-36 gal/student

Travel trailer parks

Without individualhookups

90 gal/site

With individualhookups

210 gal/site

Campgrounds 60-150 gal/campsite

Mobile home parks 265 gal/unit

Motels 40-53 gal/bedHotels 60 gal/bed

Industrial areas

Light industrial area 3750 gal/acre

Heavy industrial 5350 gal/acre

Source: Droste, R.L., 1997. Theory and Practice ofWater and Wastewater Treatment

These values are

rough estimates only

and vary greatly by

locale.


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Wastewater treatment systems

Decentralized

Septic tank

Waste stabilization ponds Facultative lagoon

Maturation lagoon

Land treatment

Constructed wetland

Centralized


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Sewer systems


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Typical composition of untreated domestic wastewater


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Microorganism concentrations in untreated wastewater


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(Minimum) Goals of wastewater

treatment plants


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Conventional Community (Centralized) Sewage

Treatment

Pathogen Reductions Vary from:

low (99.99+%)

Secondary Treatment Using Activated Sludge Process

Sludge drying bed ormechanical dewatering

process


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Typical Municipal Wastewater Treatment System

Preliminary or PrePreliminary or Pre--

TreatmentTreatmentPrimary

Treatment

Secondary

TreatmentDisinfection

Sludge Treatment& Disposal


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Preliminary Wastewater Treatment System


TreatmentTreatment

Solids to Landfill


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Preliminary Treatment Facilities

Preliminary Treatment - Bar Racks

Bar Racks: are used to remove large objects that

could potentially damage downstreamtreatment/pumping facilities.

Ref: Metcalf & Eddy, 1991


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Preliminary Treatment - Grit chamber

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

fragments, pebbles, etc.


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Primary Wastewater Treatment

Primary

Treatment

Primary

Treatment


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Primary sedimentation

To remove settleable solids from wastewater


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Primary Clarification

PrimarySludge

Primary

Effluent

Influent from Preliminary

Treatment

Section through a Circular Primary Clarifier

Primary Treatment

Scum: Oil, Grease,

Floatable Solids


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Primary sedimentation

To remove settleable solids from wastewater

Average flow: 800-1200 gpd/ft2

Retention time: 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


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Secondary Wastewater Treatment

Secondary

Treatment

Secondary

Treatment


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Secondary treatment processes

To remove suspended solids, nitrogen,

and phosphate

90 % removal of SS and BOD

5

Various technologies

Activated sludge process

Tricking filter

Stabilization ponds


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Secondary Treatment Using Activated Sludge Process

Secondary

Treatment

Secondary Treatment

Sludge drying bed ormechanical dewatering

process


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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

Secondary Treatment

Simplified Activated Sludge Description


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General Microbial Growth

Carbon Source: Dissolved organic matter

Energy Source: Dissolved organic matter

Terminal Electron Acceptor: Oxygen

Nutrients: Nitrogen, Phosphorus, Trace

Metals

Microorganisms: Indigenous in

wastewater, recycledfrom secondary clarifier

Secondary Treatment


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Activated Sludge Aeration Basins

Empty basin, air

diffusers on bottom

Same basin,in operation

Secondary Treatment


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The Oxidation Ditch

Ref: Reynolds & Richards,1996, Unit Operations and Processes inEnvironmental Engineering Secondary Treatment


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The Oxidation Ditch

Ref: Reynolds & Richards,1996, Unit Operations and Processes inEnvironmental Engineering Secondary Treatment


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Circular Secondary Clarifier

Secondary

Effluent

Influent from ActivatedSludge Aeration Basin

or Trickling Filter

Section through a Circular Secondary Clarifier

Return (Secondary)

Sludge Line

Secondary Treatment


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Activated sludge process

To remove suspended solids, nitrogen, and phosphate

Food to microorganism ratio (F:M ratio): 0.25 kg BOD5per kg MLSS (mixed liquor suspended solids) per day at10 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 ormore for low F:M ratio

Optimum nutrient ratio: BOD5:N:P =>100:5:1

90 % removal of SS and BOD5 ~20 % removal of phosphate

> 90 % removal of viruses and protozoa and 45 - 95 %removal of bacteria


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Secondary Treatment Using Trickling Filter Process

Secondary

Treatment

Secondary Treatment

Trickling

Filter


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Trickling Filter

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

Primary effluent

drips onto rock or

man-made media

Rotating arm to

distribute water

evenly over filter

Rock-bed with slimy(biofilm) bacterial growth

Primary effluent pumped in

Treated waste to

secondary clarifier


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Trickling Filter

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


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Tricking filter process

To remove suspended solids, nitrogen, andphosphate

Organic loading (BOD5 X flow/volume of filter):0.1 kg BOD

5

per m3 per day

Hydraulic loading: 0.4 m3 per day per m3 of planarea

90 % removal of SS and BOD5 ~20 % removal of phosphate

Variable removal levels of viruses, 20-80 %removal of bacteria and > 90 % removal ofprotozoa


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Stabilization Ponds

The oldest wastewater treatment systems Requires a minimum of technology

Relatively low in cost

Popular in developing countries and smallcommunities in the US (90 % communities with

population


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Facultative Pond

Ponds and Lagoons


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Facultative ponds

3 zones: upper photic (aerobic) zone, facultative (aerobicand anaerobic) zone and lower anaerobic zone. Upper aerobic zone: algae use CO2, sunlight and inorganic

nutrients (photosynthesis) to produce oxygen and algal biomass.

Facultative zone: bacteria and other heterotrophs convert organicmatter to carbon dioxide, inorganic nutrients, water and microbial

biomass. Lower anaerobic zone: anaerobic bacteria degrade the biomass

from upper zones

Influence by many factors Sunlight

Temperature pH

Biological activities

Characteristics of wastewater

Ponds and Lagoons


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Facultative ponds

To remove suspended solids, nitrogen, phosphate, andpathogens

Operating water depth: 1-2.5 meters

(maximum) BOD loading: 2.2-5.6 g/m3 /day

Retention time: 3-6 months

>90 % SS and BOD removal (warm and sunny climates)

Microbe removal may be quite variable dependingupon pond design, operating conditions and climate. 90-99% removal of indicator and pathogenic bacteria

99 % removal of PV1

99.9 reduction ofGiardia and Cryptosporidium


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Aerated Lagoons

http://www.lagoonsonline.com/marshill.htm

Ponds and Lagoons

Stabilization Lagoon

Aerated Lagoons


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Aerated lagoons

Biological activity is provided by mainly

aerobic bacteria

Influence by many factors Aeration time

Temperature

pH

Biological activity

Characteristics of wastewater


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Aerated lagoons

To remove suspended solids, nitrogen, phosphate,and pathogens

Operating water depth: 1-2 meters

Retention time:


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Wastewater Disinfection

Disinfection


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Typical Municipal Wastewater Treatment System


TreatmentTreatmentPrimary

Treatment

Secondary

TreatmentDisinfection

Sludge Treatment& Disposal


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Sludge processing

Thickening

Digestion

Dewatering Disposal


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Sludge thickening

To reduce the volume of sludge to increase sludge solids at least 4 %

Gravity thickening and mechanical thickening

Gravity thickening Used for primary and tricking filter solids

Without chemical flocculants loading rate: 30-60 kg/m2 per day

Mechanical thickening Used for activated sludge solids

With chemical flocculants

dissolved air flotation, gravity belt thickeners, and centrifuge thickening

loading rate: 10-20 kg/m2 per day (dissolved air flotation), 400-1000 L/m(gravity belt thickeners), 1500-2300 L/m (centrifuge thickening)

The concentration of pathogens increased during this process


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Gravity belt thickener


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Regulatory requirement for

disposal of sewage sludge

Class B biosolids (agriculture land) < 2 million MPN/g of fecal coliforms

Seven samples over 2-weeks period

~2 log removal Class A biosolids (home lawn and garden)

< 1000 MPN/g of fecal coliforms

< 3 MPN/4g ofSalmonella sp.

< 1 PFU/4g of enteric viruses < 1/4g of Helminth ova

~ 5 log removal


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Processes to significantly reduce pathogens

(PSRP) for a Class B biosolids

Aerobic digestion

Anaerobic digestion

Air drying

Composting

Lime stabilization


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Digestion

To stabilize organic matter, control orders,and destroy pathogens

Aerobic digestion and anaerobic digestion

Aerobic digestion

Sludge is agitated with air/oxygen

loading rate (maximum): 640 g/m2 per day

Temperature and retention time: 68 oF for 40days or 58 oF for 60 days

Solids and BOD reduction: 30-50 %


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Anaerobic digestion

Sludge is treated in the absence of air

Operation conditions (optimum) Temperature: 85-99 oF (98 oF)

pH: 6.7-7.4 (7.0-7.1)

Alkalinity: 2000-3500 mg/L

Solid loading: 0.02-0.05 lb/ft3/day

Retention time: 30-90 days

Treatment outcome

Solid reduction: 50-70 % Significant reduction of most pathogens

Gas production: methane and carbon dioxide


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Anaerobic digester


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Air drying, composting, and lime

stabilization Air drying

Sludge is dried on sand beds/(un)paved basins

Retention time: minimum of 3 months

Composting

Various methods: in-vessel, static aerated file, and periodicallymixed windrows

File temperature should be raised > 40 oC for 5 days

For 4 hours during the 5 days, the file temperature should be >55 oC

Lime stabilization

Sufficient lime should be added to raise the pH 12 after 2 hourcontact

4 log inactivation of enteric viruses, 2-7 log inactivation ofindicator bacteria, no inactivation of Acaris ova


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Processes to further reduce pathogens

(PFRP) for a Class A biosolids

Heat drying Sludge is dried by contact with hot gases

The temperature of gas is >80 oC

Thermophilic aerobic digestion Sludge is agitated with air/oxygen

132-149 oF for 4-20 hours

Pasteurization

158

o

F for 30 minutes Beta- or gamma ray irradiation Sludge is irradiated with either beta- or gamma ray

> 1.0 Mrad at room temperature


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Dewatering

To concentrate sludge by removing water

Pressure filtration, centrifugation, and screw

press

Pressure filtration (belt filter press and plate-and-frame filter)

Usually with polymer flocculation

Loading rate: 40-60 gpm/m (hydraulic) and 500-1000

lb/m/h (solid)

Feed solid: 1-6 %

Cake solids: 15-30 %


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Belt filter press


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Disposal

Land application

Landfill

Incineration Ocean dumping (no longer allowed in US)

lecture 15 2009 revised

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