This document provides information on various stages of municipal wastewater treatment processes. It discusses preliminary treatment including bar racks and grit chambers. Primary treatment includes primary sedimentation to remove settleable solids. Secondary treatment processes like activated sludge and trickling filters are used to further remove suspended solids and nutrients. Final treatment includes disinfection using chlorine or UV to inactivate pathogens before discharge or reuse of treated effluent. The overall goal of wastewater treatment is to reduce BOD, suspended solids and fecal coliforms to levels safe for discharge.

1. Niaz Ahmed
Office: PCSIR
Phone: 92-021-34641841
Email:
niazmemon2000@yahoo.com

2. Key points
 Purpose of the individual unit processes
 The typical operating conditions
 The outcome of the processes
 Microbial reduction in the processes

4. 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 floor
area
Hospitals 240-480 gal/bed
Schools 18-36 gal/student
Travel trailer parks
Without individual
hookups
90 gal/site
With individual
hookups
210 gal/site
Campgrounds 60-150 gal/campsite
Mobile home parks 265 gal/unit
Motels 40-53 gal/bed
Hotels 60 gal/bed
Industrial areas
Light industrial area 3750 gal/acre
Heavy industrial 5350 gal/acre
Source: Droste, R.L., 1997. Theory and Practice of
Water and Wastewater Treatment
These values are
rough estimates only
and vary greatly by
locale.

5. Wastewater treatment systems
 Decentralized
 Septic tank
 Waste stabilization ponds
 Facultative lagoon
 Maturation lagoon
 Land treatment
 Centralized

6. Sewer systems

7. Typical composition of untreated domestic wastewater

8. Microorganism concentrations in untreated wastewater

9. (Minimum) Goals of wastewater
treatment processes
 <30 mg/L BOD5
 <30 mg/L of suspended solids
 <200 CFU/100ml fecal coliforms

10. 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

11. Typical Municipal Wastewater Treatment System
Preliminary or Pre-
Treatment
Primary
Treatment
Secondary
Treatment
Disinfection
Sludge Treatment
& Disposal

12. Preliminary Wastewater Treatment System
Preliminary or Pre-
Treatment
Solids to Landfill

13. 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

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

15. Primary Wastewater Treatment
Primary
Treatment

16. Primary sedimentation
 To remove settleable solids from wastewater

17. Primary Clarification
Primary
Sludge
Primary
Effluent
Influent from Preliminary
Treatment
Section through a Circular Primary Clarifier
Primary Treatment
Scum: Oil, Grease,
Floatable Solids

18. 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

19. Secondary Wastewater Treatment
Secondary
Treatment

20. 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

21. Secondary
Treatment
Secondary Treatment
Sludge drying bed or
mechanical dewatering
process
Secondary Treatment Using Activated Sludge Process

22. 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

23. 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

24. Secondary Treatment Using Trickling Filter Process
Secondary
Treatment
Secondary Treatment
Trickling
Filter

25. Trickling Filter
http://www.rpi.edu/dept/chem-eng/Biotech-Environ/FUNDAMNT/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

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

27. 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

28. Wastewater Disinfection
Disinfection

29. Wastewater disinfection
 To inactivate pathogens in wastewater
 Several choices
 Free chlorine and combined chlorine
 UV
 Ozone
 Chlorine dioxide

30. Overall pathogen reduction in wastewater treatment

32. Water contaminants
 Chemicals
 Inorganics
 Organics
 Synthetic organic compounds
 Volatile organic compounds
 Microbes
 Viruses
 Bacteria
 Protozoa parasites
 Algae
 Helminths

33. Water contaminants (I)

34. Water contaminants (II)

35. Water contaminants (III)

36. Water contaminants (IV)

37. Water contaminants (V)

38. Multiple barrier concept
for public health protection

39. Barrier Approach to Protect Public
Health in Drinking Water
 Source Water Protection
 Treatment Technology
 Disinfection
 Disinfectant residual in distribution system

40. Water treatment processes

41. 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)

42. Physico-chemical processes
 To remove particles in water
 Coagulation/flocculation/sedimentation
 Filtration

43. Rapid Mix
 Intense mixing of
coagulant and other
chemicals with the
water
 Generally performed
with mechanical
mixers
Chemical Coagulant

44. Major Coagulants
 Hydrolyzing metal salts
 Alum (Al2(SO4)3)
 Ferric chloride (FeCl3)
 Organic polymers (polyelectrolytes)

45. 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)3
Al(OH)3
Al(OH)3
Al(OH)3
Al(OH)3
(High Alum Dose)
Floc
Sweep CoagulationCharge Neutralization

46. Horizontal Paddle Flocculator

47. Flocculation Example
Water coming from
rapid mix.
Water goes to sedimentation
basin.

48. Sedimentation Basin

49. Sedimentation Basin ExampleWater coming from
flocculation basin.
Water goes to
filter.
Floc (sludge) collected
in hopperSludge to solids
treatment

50. 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

51. 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

52. Filter Example
Water coming from
sedimentation
basin.
Anthracite
Sand
Gravel (support
media)
Water going to disinfection

53. Mechanisms Involved in Filtration
Interception: 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

54. 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

55. Disinfection in water
 To inactivate pathogens in water
 Various types
 Free chlorine
 Chloramines
 Chlorine dioxide
 Ozone
 UV

56. 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

57. 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