Water Treatment Processes- Processes Physical Chemical Biological

1. TRAETMENT OF DOMESTIC &
INDUSTREIAL WASTE WATER
Lecture by-
Dr. Rajendra Singh Thakur

2. Classification of Treatment
Processes
Wastewater treatment is usually characterized as consisting of
four sequential processes:
• Preliminary treatment ,
• Primary treatment ,
• Secondary treatment and
• Tertiary (sometimes called “advanced”) treatment.

5. 1.Preliminary Treatment
• Preliminary treatment to screen out, grind up, or
separate debris is the first step in wastewater
treatment.
• Sticks, rags, large food particles, sand, gravel, toys,
etc., are removed at this stage to protect the pumping
and other equipment in the treatment plant.
• Treatment equipment such as bar screens, a large
version of a garbage disposal, and grit chambers are
used as the wastewater first enters a treatment plant.
• The collected debris is usually disposed of in a landfill.

6. Bar Screen
Vendor-Provided Equipment
• Purpose: to remove large objects (sticks, cans,
etc) which may cause flow obstructions.
• Depending on the size of the plant, bar screens
are either hand or mechanically cleaned.
• Hand cleaned: used primarily at small plants.

7. Screen Type

8. Bars for screen
Figure : Fixed Bar-Screen (course or medium)
Effluent
Effluent

9. (i) Screening
Waster Water Treatment Animationbarscr1.gif
Barscreen Room, Barscreens in blue

10. Bar Screen
Mechanically Cleaned
• More frequently used because labor and
overflowing are greatly reduced.
• A by-pass channel with a hand cleaned bar
screen must also be provided.
• A second mechanically cleaned bar screen can
also be provided.
• Screens are either front or back cleaned.

11. 11
Bar Screen

12. Mechanical Bar Screen
General Design Criteria
• Bar Width: 1/4 to 5/8 in
• Spacing: 5/8 to 3 in
• Depth: 1 to 1.5 inches
• Slope: 30 – 60o from the vertical.

13. Screens
• Bar Screens
• Bar Racks

14. (ii) Grit chambers
• Purpose: remove inert dense material, such as sand,
broken glass, silt and pebbles
• Avoid abrasion of pumps and other mechanical
devices
• Material is called “grit”

15. Types of Grit Chambers
• Grit chambers are of two types: mechanically cleaned
and manually cleaned.
• In mechanically cleaned grit chamber, scraper blades
collect the grit settled on the floor of the grit chamber. The
grit washing mechanisms are also of several designs
most of which are agitation devices using either water or
air to produce washing action.
• Manually cleaned grit chambers should be cleaned at
least once a week. The simplest method of cleaning is
by means of shovel.

16. Principle of Working of
Grit Chamber
• Grit chambers are nothing but like sedimentation tanks,
designed to separate the intended heavier inorganic
materials (specific gravity about 2.65) and to pass
forward the lighter organic materials.
• Hence, the flow velocity should neither be too low as to
cause the settling of lighter organic matter, nor should
it be too high as not to cause the settlement of the silt and
grit present in the sewage.
• This velocity is called "differential sedimentation and
differential scouring velocity". The scouring velocity
determines the optimum flow through velocity.

17. Grit removal

18. Grit Chamber
General Design Criteria
• Specific gravity of grit: 2.4 - 2.65
• Diameter of grit: 0.22 mm
• Settling velocity: 0.075 fps
• Equivalent overflow rate: 48,400 gpd/ft2
• Disposal of Grit: land fill or incineration (Grit must be washed before
disposal)
• Grit chamber storage:
– Small Plant: provide storage below the design invert depending on
the quantity and frequency of removal.
– Large Plant: continuous removal, the conveyor hopper is designed
based on the size of the equipment.

19. Grit Chambers
Types
• Square Clarifier (Detritus Tank)
• Aerated Tanks

20. Grit Chamber
Square Clarifier (Detritus Tank)
• Detritus tanks are continuous flow settling tank, where both
grit and fine sand particles are removed from sewage.
• Detritus tanks are designed Slightly longer detention time
about 3-4 min. so that the horizontal velocity is 0.09
m/sec.
• This means that at low flow, the velocity is less than 0.09
m/sec and therefore, organic material will settle down.
• Organics are removed by counter current washing as the
grit moves up an incline for disposal.

21. Grit Chamber
Aerated Grit Chamber
• Upon discovering that grit accumulated in the bottom
of activated sludge aeration basins, it has became
common practice to use aerated grit chambers.
• Aeration also provides pretreatment of the waste by
removing odors and inducing flocculation of the
organic material making primary clarification more
effective.

22. Aerated Grit Chamber
Benefits of Pre-aeration
• By providing preaeration, primary treatment is
improved through:
– Grit removal
– Flocculation
– Odor Control
– Grease Separation
• Design the detention time and aeration rate to
control all four

24. (iii) Skimming Tank
• Grease, oil in sewage includes fats, fatty acids, mineral oils, waxes,
soaps etc. from kitchens of houses and restaurants, garage, oil
refineries, soap and candle factories etc.

25. Parallel Plate Separators

26. 2. Primary Treatment
• Primary treatment is often called clarification, sedimentation
or settling.
• The benefits of primary treatment include:
– Reduction in suspended solids
– Reduction in BODs
– Reduction in the amount of waste activated sludge (WAS)
in the activated sludge plant .
– Removal of floating material .
– Partial equalization of flow rates and organic load.

27. (i) Primary Sedimentation Tank
– Remove grease, oil
– Fecal solid settle,
floating material rise
to the surface
– Produce a
homologous liquid for
later biological
treatment
– Fecal sludge are
pumped to sludge
treatment plant

28. Primary Treatment Parameters

29. Primary Sedimentation Tank
• Clarifier is used for reducing turbidity by reducing smaller suspended
solids (colloids) in the water.
• A clarifier contains 3 type of processes, i.e. mixing, flocculation of
smaller solids and settling.
• To settle down, colloids matters need to be coagulated to form larger
particles by chemical (coagulant).
• Addition of coagulant is usually done in the rapid mixing tank (pre-mix
tank) that work under fast and intensive agitation.
• Clump of larger solids are then settled down in a clarifier and is blown-down
from the bottom of the clarifier.

30. Important Parts of a
Sedimentation Tanks
• (a) Inlet zone – at the central well, which has a round baffle plate, the
flow is established in a uniform radial direction so that short-circuiting
does not take place.
• (b) Settling zone – where settling is assumed to occur as the water
flows towards the outlet.
• (c) Outlet zone – in which the flow converges up and over the
decanting weirs.
• (d) Sludge zone – where settled material collects and is pumped out.

31. Types of Sedimentation Tank
• Typical sedimentation tanks:
• (a) rectangular horizontal flow tank;
• (b) circular, radial-flow tank;
• (c) hopper-bottomed, upward flow tank

35. An Empty Primary Clarifier

36. An Operating Primary Clarifier

37. Oil Skimmer in a Primary Clarifier

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40. Coagulation-CCllaarriiffiiccaattiioonn UUnniittss
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MMiixxiinngg TTaannkk
((rraappiidd mmiixx))
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sseettttlliinngg
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41. Coagulation Mechanism

42. Coagulation
• Rachel Casiday, Greg Noelken, and Regina Frey, Washington University (
http://wunmr.wustl.edu/EduDev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html)
isis.csuhayward.edu/alss/Geography/ mlee/geog4350/4350c4f01.ppt

43. Flocculation
• This process is used when the small suspended solids
having low specific gravity and low settling velocity
cannot be separated by sedimentation easily.
• In wastewater treatment, this usually occurs particularly
with particles of less than 50 micrometer in size.

44. 3. Secondary or
Biological Treatment
• Secondary treatment is a biological treatment process to remove
dissolved organic matter from wastewater.
• Sewage microorganisms are cultivated and added to the wastewater.
• The microorganisms absorb organic matter from sewage as their
food supply.
• Three approaches are used to accomplish secondary treatment; fixed
film, suspended film and lagoon systems.

45. (i) Fixed Film Systems
• Fixed film systems grow microorganisms on substrates
such as rocks, sand or plastic.
• The wastewater is spread over the substrate, allowing
the wastewater to flow past the film of microorganisms
fixed to the substrate.
• As organic matter and nutrients are absorbed from the
wastewater, the film of microorganisms grows and
thickens.
• Trickling filters, rotating biological contactors, and
sand filters are examples of fixed film systems.

46. (ii) Suspended Film Systems
• Suspended film systems stir and suspend microorganisms in
wastewater. As the microorganisms absorb organic matter and
nutrients from the wastewater they grow in size and number.
•
• After the microorganisms have been suspended in the wastewater for
several hours, they are settled out as a sludge.
• Some of the sludge is pumped back into the incoming wastewater to
provide "seed" microorganisms.
• The remainder is wasted and sent on to a sludge treatment process.
• Activated sludge, extended aeration, oxidation ditch, and
sequential batch reactor systems are all examples of suspended film
systems

47. Lagoon Systems
• Lagoon systems are shallow basins which hold the waste-water for
several months to allow for the natural degradation of sewage.
• These systems take advantage of natural aeration and microorganisms
in the wastewater to renovate sewage

48. Filtration

51. Secondary treatment:
Aerobic
• Activated sludge process
• Trickling filters
• Rotating discs
• Rotating drums
• Oxidation Ponds

52. Activated Sludge process
• Oxidation of organic waste by aerobic bacteria
encouraged by aeration

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((aaeerroobbiicc mmiiccrroobbiiaall mmeettaabboolliissmm))
• Mixed Liquor Suspended Solids (MLSS)
• Air is pumped through the wastewater
• Sludge is removed from the bottom and sent to the
anaerobic sludge digestor
• Some of the sludge is used to inoculate the fresh,
incoming wastewater entering the aeration tank
Food/Microbes
Q x BOD
Ratio = _____________
MLSS x V
Q = flow rate of sewage in millions of
gallons per day (MGD)
MLSS is in mg/l
V is volume of aeration tank (gallons)

54. Trickling Filters
• Trickling filter beds: rotating pipes sprinkle waste water over
stones which have bacteria and algae growing on them
which consume the waste and some nitrates.
• Not a true filtering or sieving process
• Material only provides surface on which bacteria to grow
• Can use plastic media
 Lighter - can get deeper beds (up to 12 m)
 Reduced space requirement
 Larger surface area for growth
 Greater void ratios (better air flow)
 Less prone to plugging by accumulating slime

55. Trickling Filters Plan

56. Trickling Filters

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58. Important Operating Parameters
• Organic loading rate
• Oxygen supply
• Control and operation of the final settling tank
Final settling tank
Functions:
Clarification
Thickening
Sludge settleability is determined
sludge by sludge volume index (SVI)
V x 1000 where V is volume of
SVI (ml/g) = ___________
MLSS
settled sludge after 30 min

59. Rotating Biological Contactors
• Called RBCs
• Consists of series of closely spaced discs mounted on a horizontal
shaft and rotated while ~40% of each disc is submerged in wastewater
• Discs: light-weight plastic
• Slime is 1-3 mm in thickness on disc

61. Rotating Biological Contactors

63. Rotating Biological Contactors
Primary
Settling
Sludge
Treatment
Secondary
Settling
Sludge Treatment

64. Low-Tech Solutions
• Aerobic ponds
• Facultative ponds
• Anaerobic ponds

65. Aerobic Ponds
• Shallow ponds (<1 m
deep)
• Light penetrates to
bottom
• Active algal
photosynthesis
• Organic matter con-verted
to CO2, NO3
-,
HSO4
-, HPO4
2-, etc.

67. Secondary Sedimentation
Secondary treatment:
Anaerobic
• Anaerobic digestion
• Anaerobic Up flow filters (AUF)
• Anaerobic filters

68. AAnnaaeerroobbiicc SSlluuddggee DDiiggeesstteerr
• Maintain temp at
37C
• 30-day retention
time
• Kills pathogens
• Produces methane
used to run facility
CH4
Energy to run plant
sludge
from settling
tanks
Gravity thickener plant
1% 6% solids content

69. Anaerobic Sludge Digester

70. ANAEROBIC DIGESTION
HASBAYA
MCI

71. Upflow Anaerobic Sludge Blanket
• Wastewater flows upward through
a sludge blanket composed of
biological granules that
decompose organic matter
• Some of the generated gas
attaches to granules that rise and
strike degassing baffles releasing
the gas
• Free gas is collected by special
domes
• The effluent passes into a settling
chamber

72. Anaerobic filters
• Saucer shaped filter:
Made with polypropylene
• Granular filter :
A porous filter media of aluminous-silicate filled inside the
anaerobic tank.

73. 4. Tertiary Treatment
• Process used when water is to be used for
irrigation, recreation, drinking water
• Involves
– Filtration
• Very effective in removing Crytosporidium and
Giardia
• 90% removal of enteric bacteria and viruses
– Coagulation (iron and aluminum salts, pH>11
• 99% removal of enteric viruses
– Activated carbon adsorption
– Additional disinfection

74. • Involves a series of steps to further reduce
organic concentration, turbidity, N, P, metals,
and pathogens
Sand or mixed Settling tank
media filter
Disinfection
tank
Discharge
to
environment
Sludge
digestor
filters out
protozoans
& pathogenic
bacteria

75. Tertiary Treatment: Precipitation
• Chemical precipitation- is the method of addition of chemicals to the
wastewater, converting undesired soluble substances into an insoluble
precipitate which can be removed easily and rapidly.
• Ions like cadmium, lead, mercury and phosphate ions can be precipitated
by adding ions which form insoluble compounds with the heavy metal or
phosphate ions
• To precipitate phosphates, aluminium or calcium ions are added which
form insoluble phosphates; these phosphates then precipitate out
3Ca2+ (aq) + 2PO4
3- (aq) ® Ca3(PO4)2 (s)
2Al3+ (aq) + PO4
3- (aq) ® AlPO4 (s)
• To precipitate heavy metal ions, hydrogen sulphide gas is added; the heavy
metal ions form their sulphide salts which have very low solubilities:
Pb2+ (aq) + H2S (g) ® PbS (s) + 2 H+ (aq)

76. Reverse osmosis
• Is the process in which water is separated from
dissolved salts in the solution by filtering through
semi permeable membrane at a pressure than
the osmotic pressure caused by the dissolved
salts in wastewater.

78. Sorption
• Conventional alum treatment for removal of phosphate
increases the concentration of sulphate ions in the
solution.
• To avoid this, sorption is developed.
• Sorption is a process of removing various forms of
phosphate without increasing the concentration of
sulphates.

79. Advanced chemical processes
• Ion exchange- although both natural and synthetic ion
exchange resins are available, synthetic resins are used
more widely because of their durability.
• Some natural zeolites (resins) are also used for the
removal of ammonia from wastewater.

80. Electrochemical treatment
• Wastewater is mixed with seawater and is
passed into a single cell containing carbon
electrodes.

81. Oxidation
• Oxidation - Chemical oxidation is used to remove
ammonia, to reduce the concentration of residual
organics and to reduce bacterial and viral contents of
wastewater.
• At present on of the few process for the removal of
ammonical nitrogen, found operationally dependable, is
chlorination.

82. Reduction
• Nitrates present in wastewater can be reduced
electrolytically or by using strong reducing
agents( e.g. ferrous oxide).
• The reaction must usually catalyzed while using
reducing agents.
• The two step processes using different reducing
agents and catalysts are limited by the
availability of chemicals at low cost, and the fact
that the treated effluent and waste sludge may
contain toxic compounds derived from the
chemicals used for catalyzing various reactions.

83. SSuummmmaarryy
• Municipal wastewater treatment plant is engineered
to reduce area/volume normally required in nature to
remove nutrients and pathogens from wastewater
– Primary treatment
• Physical removal of large debris
– Secondary treatment
• Microbiological conversion of organic-C to CO2 and H2O
– Tertiary treatment
• Inactivate pathogens, remove, N, P, toxins from water before
release to environment

84. Sludge Processing
• Thickening
– Settling or centrifugation
• Digestion
– Microbial process
• Stabilization of solids, removal of pathogens, production of methane
• Takes 2-3 weeks in large covered tanks
• Conditioning
– Addition of alum, ferric chloride, lime to aggregate solids
• Dewatering to remove water
– Air drying, spreading basins, centrifugation, vacuum filtration
• All of above results in reduction of pathogens in solids

85. Sludge
Processing
Steps

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87. LLaanndd ddiissppoossaall ooff bbiioossoolliiddss
• Application of biosolids on agricultural land