water & wastewater treatment

57
Water and wastewater treatment processes Niaz Ahmed Office: PCSIR Phone: 92-021-34641841 Email: [email protected]

Upload: niaz-memon

Post on 08-Aug-2015

83 views

Category:

Documents


1 download

TRANSCRIPT

Page 1: WATER & WASTEWATER TREATMENT

Water and wastewater treatment processes

Niaz Ahmed

Office: PCSIR

Phone: 92-021-34641841

Email: [email protected]

Page 2: WATER & WASTEWATER TREATMENT

Key points

Purpose of the individual unit processesThe typical operating conditionsThe outcome of the processesMicrobial reduction in the processes

Page 3: WATER & WASTEWATER TREATMENT

Wastewater treatment processes

Page 4: WATER & WASTEWATER TREATMENT

How much wastewater do we produce each day?

Wastewater Characteristics

Source Average Daily FlowDomestic sewage 60-120 gal/capitaShopping centers 60-120 gal/1000 ft2 total floor

areaHospitals 240-480 gal/bedSchools 18-36 gal/studentTravel trailer parks

Without individualhookups

90 gal/site

With individualhookups

210 gal/site

Campgrounds 60-150 gal/campsiteMobile home parks 265 gal/unitMotels 40-53 gal/bedHotels 60 gal/bedIndustrial areas

Light industrial area 3750 gal/acreHeavy 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.

Page 5: WATER & WASTEWATER TREATMENT

Wastewater treatment systemsDecentralized

Septic tankWaste stabilization ponds

Facultative lagoon Maturation lagoon

Land treatmentCentralized

Page 6: WATER & WASTEWATER TREATMENT

Sewer systems

Page 7: WATER & WASTEWATER TREATMENT

Typical composition of untreated domestic wastewater

Page 8: WATER & WASTEWATER TREATMENT

Microorganism concentrations in untreated wastewater

Page 9: WATER & WASTEWATER TREATMENT

(Minimum) Goals of wastewater treatment processes<30 mg/L BOD5

<30 mg/L of suspended solids<200 CFU/100ml fecal coliforms

Page 10: WATER & WASTEWATER TREATMENT

Conventional Community (Centralized) Sewage Treatment

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

Secondary Treatment Using Activated Sludge Process

Sludge drying bed or mechanical dewatering process

Page 11: WATER & WASTEWATER TREATMENT

Typical Municipal Wastewater Treatment System

Preliminary or Pre-Treatment

PrimaryTreatment

SecondaryTreatment

Disinfection

Sludge Treatment& Disposal

Page 12: WATER & WASTEWATER TREATMENT

Preliminary Wastewater Treatment System

Preliminary or Pre-Treatment

Solids to Landfill

Page 13: WATER & WASTEWATER TREATMENT

Preliminary Treatment Facilities

Preliminary Treatment - Bar Racks

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

Ref: Metcalf & Eddy, 1991

Page 14: WATER & WASTEWATER TREATMENT

Preliminary Treatment - Grit chamberGrit chamber: used to remove small to medium

sized, dense objects such as sand, broken glass, bone fragments, pebbles, etc.

Page 15: WATER & WASTEWATER TREATMENT

Primary Wastewater Treatment

PrimaryTreatmentPrimary

Treatment

Page 16: WATER & WASTEWATER TREATMENT

Primary sedimentation To remove settleable solids from

wastewater

Page 17: WATER & WASTEWATER TREATMENT

Primary Clarification

PrimarySludge

PrimaryEffluent

Influent from Preliminary Treatment

Section through a Circular Primary Clarifier

Primary Treatment

Scum: Oil, Grease, Floatable Solids

Page 18: WATER & WASTEWATER TREATMENT

Primary sedimentationTo remove settleable solids from wastewaterMaximum flow: 30 - 40 m3 per dayRetention period: 1.5 - 2.0 hours (at maximum

flow)50 - 70 % removal of suspended solids25 - 35 % removal of BOD5

~20 % removal of phosphate ~50 % removal of viruses, bacteria, and protozoa90 % removal of helminth ova

Page 19: WATER & WASTEWATER TREATMENT

Secondary Wastewater Treatment

SecondaryTreatment

SecondaryTreatment

Page 20: WATER & WASTEWATER TREATMENT

Secondary treatment processesTo remove suspended solids, nitrogen, and

phosphate90 % removal of SS and BOD5

Various technologiesActivated sludge processTricking filterAerated lagoonsRotating biological contractors

Page 21: WATER & WASTEWATER TREATMENT

SecondaryTreatment

Secondary Treatment

Sludge drying bed or mechanical dewatering process

Secondary Treatment Using Activated Sludge Process

Page 22: WATER & WASTEWATER 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

Secondary Treatment

Simplified Activated Sludge Description

Page 23: WATER & WASTEWATER TREATMENT

Activated sludge processTo remove suspended solids, nitrogen, and

phosphateFood 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 =>100:5:190 % removal of BOD5 and SS~20 % removal of phosphate>90 % removal of viruses and protozoa and 45 -

95 % removal of bacteria

Page 24: WATER & WASTEWATER TREATMENT

Secondary Treatment Using Trickling Filter Process

SecondaryTreatment

Secondary Treatment

TricklingFilter

Page 25: WATER & WASTEWATER TREATMENT

Trickling Filter

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

Primary effluent drips onto rock orman-made media

Rotating arm todistribute water evenly over filter

Rock-bed with slimy (biofilm) bacterial growth

Primary effluent pumped inTreated waste to secondary clarifier

Page 26: WATER & WASTEWATER TREATMENT

Trickling Filter

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

Page 27: WATER & WASTEWATER TREATMENT

Tricking filter processTo remove suspended solids, nitrogen,

and phosphateOrganic 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 area90 % removal of BOD5 and SS~20 % removal of phosphateVariable removal levels of viruses, 20-80

% removal of bacteria and >90 % removal of protozoa

Page 28: WATER & WASTEWATER TREATMENT

Wastewater Disinfection

Disinfection

Page 29: WATER & WASTEWATER TREATMENT

Wastewater disinfectionTo inactivate pathogens in wastewaterSeveral choices

Free chlorine and combined chlorineUVOzoneChlorine dioxide

Page 30: WATER & WASTEWATER TREATMENT

Overall pathogen reduction in wastewater treatment

Page 31: WATER & WASTEWATER TREATMENT

Water treatment processes

Page 32: WATER & WASTEWATER TREATMENT

Water contaminants Chemicals

InorganicsOrganics

Synthetic organic compounds Volatile organic compounds

MicrobesVirusesBacteriaProtozoa parasitesAlgaeHelminths

Page 33: WATER & WASTEWATER TREATMENT

Water contaminants (I)

Page 34: WATER & WASTEWATER TREATMENT

Water contaminants (II)

Page 35: WATER & WASTEWATER TREATMENT

Water contaminants (III)

Page 36: WATER & WASTEWATER TREATMENT

Water contaminants (IV)

Page 37: WATER & WASTEWATER TREATMENT

Water contaminants (V)

Page 38: WATER & WASTEWATER TREATMENT

Multiple barrier concept for public health protection

Page 39: WATER & WASTEWATER TREATMENT

Barrier Approach to Protect Public Health in Drinking Water

Source Water ProtectionTreatment TechnologyDisinfectionDisinfectant residual in distribution system

Page 40: WATER & WASTEWATER TREATMENT

Water treatment processes

Page 41: WATER & WASTEWATER TREATMENT

OxidationTo remove inorganics (Fe++, Mn++) and some

synthetic organicsCause unaesthetic conditions (brown color)Promote the growth of autotrophic bacteria (iron

bacteria): taste and order problemFree chlorine, chlorine dioxide, ozone, potassium

permanganateFe++ + 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)

Page 42: WATER & WASTEWATER TREATMENT

Physico-chemical processesTo remove particles in water Coagulation/flocculation/sedimentationFiltration

Page 43: WATER & WASTEWATER TREATMENT

Rapid MixIntense mixing of

coagulant and other chemicals with the water

Generally performed with mechanical mixers

Chemical Coagulant

Page 44: WATER & WASTEWATER TREATMENT

Major CoagulantsHydrolyzing metal salts

Alum (Al2(SO4)3)Ferric chloride (FeCl3)

Organic polymers (polyelectrolytes)

Page 45: WATER & WASTEWATER TREATMENT

Coagulation with Metal Salts

Al(OH)

Alx(OH)y

Colloid

Al(OH)3

Al(OH)3 Colloid

Al(OH)3

Al(OH)3

Colloid

+ +Soluble Hydrolysis Species

(Low Alum Dose)

Colloid

Colloid

Colloid

Al(OH)3Al(OH)3

Al(OH)3

Al(OH)3

Al(OH)3

(High Alum Dose)

Floc

Sweep CoagulationCharge Neutralization

Page 46: WATER & WASTEWATER TREATMENT

Horizontal Paddle Flocculator

Page 47: WATER & WASTEWATER TREATMENT

Flocculation ExampleFlocculation ExampleWater coming from rapid mix. Water goes to sedimentation

basin.

Page 48: WATER & WASTEWATER TREATMENT

Sedimentation Basin

Page 49: WATER & WASTEWATER TREATMENT

Sedimentation Basin ExampleSedimentation Basin ExampleWater coming from flocculation basin.

Water goes to filter.

Floc (sludge) collectedin hopperSludge to solids

treatment

Page 50: WATER & WASTEWATER TREATMENT

Coagulation/flocculation/and sedimentation To remove particulates and natural organic materials in water Coagulation

20 -50 mg/L of Alum at 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

Page 51: WATER & WASTEWATER TREATMENT

FiltrationTo remove particles and floc that do not

settle by gravity in sedimentation processTypes of granular media

SandSand + anthraciteGranular activated carbon

Media depth ranges from 24 to 72 inches

Page 52: WATER & WASTEWATER TREATMENT

Filter ExampleFilter ExampleWater coming from sedimentation basin.

Anthracite

Sand

Gravel (support

media)

Water going to disinfection

Page 53: WATER & WASTEWATER TREATMENT

Mechanisms Involved in FiltrationInterception: hits & sticks

Sedimentation: quiescent, settles, & attaches

Flocculation: Floc gets larger within filter

Entrapment: large floc gets trapped in space between particles

Floc particles

Granular media, e.g., grain of sand

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

Page 54: WATER & WASTEWATER TREATMENT

Rapid filtrationTo remove particulates in waterFlow rate: 2-4 gpm/ft2

Turbidity: < 0.5 NTU (often times < 0.1 NTU)

Reduction of microbes50-98 % Total coliform 50-98 % of fecal coliform 10-99 % of enteric viruses97-99.9 % of Giardia99 % of Cryptosporidium

Page 55: WATER & WASTEWATER TREATMENT

Disinfection in waterTo inactivate pathogens in waterVarious types

Free chlorineChloraminesChlorine dioxideOzoneUV

Page 56: WATER & WASTEWATER TREATMENT

Trend in disinfectant use (USA, % values)

Disinfectant 1978 1989 1999

Chlorine gas 91 87 83.8

NaClO2 (bulk) 6 7.1 18.3

NaClO2 (on-site)

0 0 2

Chlorine dioxide

0 4.5 8.1

Ozone 0 0.4 6.6

Chloramines 0 20 28.4

Page 57: WATER & WASTEWATER TREATMENT

Comparison of major disinfectants

Consideration Disinfect ants

Cl2 ClO2 O3 NH2Cl

Oxidation potential

Strong Stronger? Strongest Weak

Residuals Yes No No Yes

Mode of action

Proteins/NA

Proteins/NA

Proteins/NA

Proteins

Disinfecting efficacy

Good Very good Excellent Moderate

By-products Yes Yes Yes? No