A slidedeck that Is a few years old now but something I used to use when training people in the basics of wastewater treatment. It takes a fast three hours to deliver the presentation and ideally should be followed by a visit around a wastewater treatment works. Feel free to use but please credit where you got it from alternatively if you are from the UK I'm usually quite amenable to coming out delivering a course

1. Wastewater and Sewage Sludge
A Basic Introduction

2. What I’m going to talk about
Brief introduction to the history of wastewater
What a wastewater treatment plant looks like
The basic wastewater treatment processes
Sewage sludge – a whole new world

3. Why Treat Sewage??
A Potted History of
Sewage Treatment in
the UK

4. 14th
Century - First mention of river pollution in
UK in the River Fleet
Up till 1800 most rivers clean –last Salmon caught
in the River Aire
1820 - Industrial Revolution created large
conurbations discharging untreated sewage to
rivers and unregulated trade discharges to rivers
of organic and toxic pollution – metals and
chemicals
The Early Days

5. 1850’s –
“The great stink “ in London that affected
even the proceedings in parliament.”
Bazalgette built the first large scale public
sewers in the world and created the London
embankment.
But no treatment, he just moved the point of
discharge to further downstream
Cholera rampaged the land throughout the
period 1850 -1870
The Early Days

6. 1860’s -Dr Snow established that Cholera
is waterbourne and spread by
contaminated drinking water.(Koch did
not isolate the bacillus until 1891)
He noticed that a single water pump was
causing a large amounts of deaths..
He removed the pump handle stopping
the outbreak and preventing the spread
of a cholera to a much wider area
Dr Snow in Soho

7. 1865 –Bazalgette’s first pumping stations
completed converting London from an open
sewer to a city with proper sewerage,
transporting sewage to lower down in the
Thames.
Designed with enough capacity that it is still
enough capacity in it to still be in use today
The Thames Tideway is the modern
equivalent and is being constructed now,
almost 150 years later and is going to cost
£3.6 billion taking 15 years (the same as
Bazalgette) to build 22 miles of sewer
(compared to 100 miles for Bazalgette)
Bazalgette’s London

8. Still quite early for wastewater
treatment
1850’s – Typically water abstraction downstream of sewage
discharge points
Water treatment problem resolved by building moorland
catchment reservoirs and distribution system to take the
“clean” water to people’s taps.
1876 - Rivers Pollution Prevention Act – good idea but ahead
of its time because nobody knew how to treat sewage. Get out
clause which meant no improvements

9. 1880’s Sewage farms – First primary
settlement tanks (horizontal flow) with
Ferrous Sulphate/Lime addition which
reduced BOD by 40-50%. Used soil as
a media for secondary treatment but
not possible to aerate soil and soil
went rapidly anaerobic and provided
very little treatment
1892 – Stone- First percolating filters
at Salford
1914 – Arden and Lockett first
activated sludge plant at Davyhulme
Early beginnings in Manchester

10. Sewage gets the Royal Treatment
Royal commission set up in 1898 to review methods of sewage
treatment
Took 17 years and ten reports to complete their findings
Trade waste should be treated in admixture with sewage
Consent standard 30:SS 20 BOD proposed where a minimum
of 1 in 8 dilution in clean water is available
Set river water classification based on BOD

11. Things can only get better………
Local Councils prevented trade discharges to sewer because it “Spoilt”
the municipal effluent quality
1936 Public Health Act enabled traders to discharge to sewer but gave
them deemed consents – So no control except for new traders who
also were charged for discharge. However some councils only applied
a temperature limit (43 C)
1951 Rivers Prevention of Pollution Act – required consents for new
discharges (trade and municipal
1961 Public Health Act extended charges to deemed consents

12. ……..and better
1960’s Mogden Formula introduced for traders as a method of
controlling trade loads by charging
1961 Rivers Prevention of Pollution Act – extended this to all existing
discharges
1974 Control of Pollution Act – An enabling Act which was brought into
law by Statutory Instruments. Act covered discharges to air, water,
land and noise.
1977 – Pre 1937 discharges to sewer at last consented
From 1977 to present day most environmental law has been through
EC Directive although some of it has been included in 1991 Water Act
EC produced a black list of chemicals to be banned from discharges
Also a red list of Chemicals to be controlled in discharges e.g. toxic
metals

13. ……..and better
1990 & 1995- Environment Act and Environmental Protection Act
1998 UWWTD required wastewater treatment for all areas above
15,000 PE
River Quality Objective standards set to ensure rivers achieve required
classification. Standard dependant on available dilution in river and
upstream quality. Today standards are set by Stochastic models
(statistically based e.g Monte Carlo Models)
2005- UWWTD increased to cover all works >2000 PE
2007 Environmental Permitting Regulations introduced
2009 – First River Basin Asset Management Programmes for the
Water Framework Directive. Environmental Permits get tighter

14. Sewage Treatment
What is Sewage and how do we
treat it?

15. What is Sewage?
Screenings
Grit
Faecal matter
Urine
Water

16. What is Sewage?
Once all the screenings are
removed, the 0.5% that isn’t
water is:
The consent is usually centred
around
BOD
Ammonia
Solids
and sometimes
Phosphorus, organic chemicals
and metals

17. The Wastewater Treatment
Process
Preliminary Treatment
Primary Treatment
Secondary Treatment
Tertiary Treatment
Sludge Handling &
Treatment

18. So what does a
Sewage Treatment Works
look like?

21. Esholt WwTW
Treats a population of 487k
Treats 280 million litres a
day
Generates 33 tonnes of
sludge
Processes 51 tonnes of
sludge
Consumes 60,000 kWh
Generates 20,000 kWh

22. A little more detail…..

23. The Wastewater Treatment
Process
Preliminary Treatment

24. Preliminary Treatment
Inlet works
Coarse
Screens
(optional)
Grit
Removal
(optional)
Fine
Screens
Sewer Primary
treatment
Screenings
treatment
Screenings
treatment
Grit
treatment

25. What comes down the sewer?

26. Getting the big stuff out
Coarse Screens
Usually around 25mm bars to take the big stuff out

27. Taking out the fine stuff
Fine screens
Typically a function of the consent and are normally specified as 6mm in
2 dimensions

28. What comes off the screens?
Screenings Treatment
The washer/dryer of the sewage treatment world

29. Grit – Why’s it a problem?
• Problems with flow
measurement
• Erosion and wear of
downstream equipment,
pumps etc
• Settles and takes up
volume in sludge storage
• Reduces volume in
digesters – reduced
gas/energy production
Better here
Than here

30. How is Grit removed

31. What happens when preliminary
treatment goes wrong

32. And when it goes right

33. The Wastewater Treatment
Process
Preliminary Treatment
Primary Treatment

34. Primary Treatment
Settlement
Primary
Settlement
Secondary
Treatment
Sludge
Treatment
Preliminary
Treatment

35. Primary Settlement
• Rely on gravity to settle out lighter SS material
• Circular or Rectangular constructions
• Usual designs :
• minimum 2 hours retention at peak flow
• 30-50% removal of organic load and 60% of solids
• High calorific value removed and goes off to digesters to
produce energy

36. The Science
Stokes Law
In practice this means:
A residence time in the primary settlement stage of 2 hours
An upflow velocity of 1.2m3
/m2
/hr with all tanks in service

37. What tanks are there?
•Septic tanks
•Rectangular
•Dortmund
•Upflow (cone)
•Radial Flow

38. So what happens?
Fluid retention time of at
least 2 hours
Scraper bridge scrapes it
into the hopper
Sludge collects in the
bottom
Sludge removed by pump
periodically either manually,
by timer, solids mode or
level control

39. The Wastewater Treatment
Process
Preliminary Treatment
Primary Treatment
Secondary Treatment

40. Secondary Treatment
The engine room of wastewater treatment
Secondary
Treatment
Tertiary
Treatment/
Outfall
Sludge
Treatment
Primary
Treatment

41. Secondary Treatment
A Biological process
Soluble organic fraction removed by biological treatment typically by either
trickling filters or activated sludge plant (ASP) but could be something
else.

42. Trickling Filters
• Fixed film process meaning the
bacteria grows on the rocks and
settled sewage is applied to it
• The most common type of all
treatment work with excess of
50% of all treatment works in the
UK ranging from a few hundred
people to a hundreds of thousands
served
• Settled sewage is dosed onto the
filters using mechanical
distributors.
• Parts of the slime regularly break
away from the media surface and
final settlement in humus tanks is
required to produce a high quality
final effluent.

43. Trickling Filters
Filter Media
• The filter media provides a surface for the
biomass to grow upon and is generally made of
slag, stone or plastic.
• The biomass requires air to survive and this is
achieved through natural ventilation within the
filter. This relies on fresh air having a direct path
to the base of the filter which is achieved through
vent pipes, holes or open centre wells. It is
important that these are kept clear.
Recirculation
• To maintain good wetting of filters most sites
recirculate a flow of final effluent. This improves
performance by a mixture of dilution and better
distribution of flow throughout the filter

44. Trickling Filters
Advantages
• Simple and easy to operate
• Low or no power
• Relatively cheap to build
• Resilient and robust to change
and toxic shock
• Very good for small works
• Adaptable
Disadvantages
• Large land take
• Not as efficient a removal
process as suspended growth
• Not resistant to the cold
• Overgrowth and ponding

45. Activated Sludge (ASP)
Activated sludge consists of
a mass of micro-organisms
which feed on pollutants in
the sewage. The bacteria is
suspended in liquid and is
called “mixed liquor”, it is
mixed with sewage and
aerated in aeration basins
before passing to final
settlement tanks where it is
settled and the sludge
returned. The effluent
produced is of a high
quality.

46. Activated Sludge (ASP)
• Sewage enters the
aeration tank and mixes
with mixed liquor
• Bacteria eat the sewage
and need to be fed with
air
• More bacteria are bred
and old sludge needs to
be wasted to maintain a
balance
• Sludge recycled around
to ensure the mass of
bacteria is maintained.

47. ASP
Surplus Activated Sludge (SAS)
Return Activated Sludge (RAS)
Anoxic
Zone
Aeration Lane Grows
sludge on dissolved
organics
FSTSelector
Aeration adds O2
Nitrification
NH4  NO2  NO3
Denitrification
NO3 NO2 
N2
50% 50%

48. Activated Sludge (ASP)
Advantages
• Very efficient producing a high
quality effluent
• Common technique with a lot of
industry knowledge
• Very adaptable to increasing
loads
• Can be adapted for Nutrient
Removal
Disadvantages
• Energy intensive
• More complicated to operate than
fixed film processes
• Produces more sludge than fixed
film

49. Wait!…there’s more
Tertiary Treatment
As consents get tighter and
tighter or populations increase or
things change there is sometimes
the need for further treatment.
Typically this includes:
Sand Filters (RGF & COUF)
Drum filters
Nitrifying Trickling Filters
SAFs
HSAFs
BAFFs
and many others………..

50. So what happens to all the
sludge……..?

51. Sludge treatment…..
a whole world of its own

52. WHAT IS SLUDGE?

53. Sludge depending upon its looks,
colour, weight and nature
depending where its from. It can
range from a thin RAS sludge at
0.7% dry solids to dried pellets at
98% dried solids
WHAT DOES IT LOOK LIKE

54. WHAT IS SLUDGE?
Mainly water (up to 99%)
Dissolved solids
Settled and suspended solids
Faecal matter
Bacteria and other micro-organisms
Nutrients (N, P, K)
Metals
Energy

55. SLUDGE
PRODUCTION
Primary 50 to 60g ds/person/day
Secondary 18 to 29g ds/person/day
Typical total sludge per person 70g/day
PE x yield x 365 = mass (tds)
Mass / concentration = volume
mass
vol x conc

56. SLUDGE
PRODUCTION
Approx 1.2 million tonnes dry solids produced in
UK annually this 165kg per person per year
YWS production 150,000tds last year

57. So… what do we do with it all
In 2004
62% Agricultural Land
19% Incinerated
11% Land Reclamation
7% Other (including composting)
1% Landfill
Source: Water UK

58. SLUDGE
TERMINOLOGY
990L water
10kg solids
490L water
10kg solids
1% ds 2% ds
240L water
10kg solids
4% ds
“Tonnes dry solids”
“Percent dry solids”
Volume1m3

59. SOURCES OF
SLUDGE

60. Primary sludge
Bio
1º
2º
Tertiary
Typically 3% ds (up to 5%)
Primary cause of site odour
SOURCES OF
SLUDGE

61. Primary sludge
Bio
1º
2º
Secondary sludge
Tertiary
Humus typically 2% ds (1-3% )
SAS typically 0.6% ds (0.25-1.25% )
SOURCES OF
SLUDGE

62. Primary sludge
Bio
1º
2º
Secondary sludge
Co-settled sludge
Tertiary
Typically 2% ds
SOURCES OF
SLUDGE

63. Primary sludge
Bio
1º
2º
Secondary sludge
Co-settled sludge
Tertiary sludge
Tertiary
Normally returned as
backwash liquor
SOURCES OF
SLUDGE

64. OBJECTIVES OF
SLUDGE MANAGEMENT
Reduce volume (removal of water)
Reduce/remove odour
Stabilise organic material (BOD removal)
Remove pathogens
Reclaim useful by-products (biogas, soil
conditioners)
Safe/appropriate disposal & recycling

65. BIOSOLIDS

66. >600 Sewage Treatment
Works
50 Sludge Treatment Centres
Varying degrees of treatment
Varying costs of treatment
Varying capabilities (sludge
intake, sludge output, day

67. Naburn
Beverley
Hull
Sutton Selby
Blackburn Meadows
Calder Valley Incinerator
Esholt
Knostrop
Bridlington
Staveley
Old Whittington
Sandall
Woodhouse Mill
Aldwarke
Lundwood
Caldervale
Mitchell Laithes
Leeming Bar
Goole
Wombwell
Northallerton
Colburn
STC LOCATIONS

68. TYPICAL SITE
LAYOUTS

69. Main types of
treatment
Thickening
Digestion
Advanced Digestion
Dewatering
Conditioning
Phyto-conditioning
Incineration

70. Decreases volume of sludge by removing water to reduce
downstream process size
Gravity settlement (storage tanks, PFT)
Gravity belt thickener*
Drum thickener*
*Polymer added to improve separation
THICKENING

71. To achieve target dry solids with minimal solids loss in the
filtrate
Target solids is 6% ds – thicker sludge is difficult to pump
Filtrate is returned to the works and excessive solids can
cause compliance problems
THICKENING - aim

72. 1 Sludge is conditioned with polyelectrolyte
2 Conditioned sludge is fed onto moving belt, water
passes through the weave
Belt continuously washed by a high pressure jets to prevent
solids accumulation in the belt weave
Standard flow rates are between 10 and 50m3
per m belt
per hour
Be aware of the maximum solids load for the asset (ie the
thicker the feed sludge, the lower the allowable flow rate)
THICKENING - process

73. Thin sludge can be due to:
Sludge application rate too high
Belt speed too high
Incorrect polymer dose – excessive dose may blind the
belt
Sludge characteristics eg excessive FOG
Solids in filtrate can be due to:
Incorrect polymer dose
Solids running off the edge of the filter belt
Problems with belt tracking, lubrication, tension (AMBS)
Poly suppliers will provide support to determine optimum
polymer
THICKENING - problems

74. Gravity belt thickener
THICKENING - GBT

75. THICKENING - PFT

76. THICKENING - drum

77. POLYMER
Added to sludge prior to mechanical thickening and
dewatering
Poly adheres to sludge particles, causing the release of
surface water, neutralisation of charge and conglomeration
of small particles by bridging.
Many different types of polymer used eg cationic, ionic,
single chain, cross linked
Type used depends on characteristics of solids (eg pH, age,
source) type of mixing & dewatering device
pH, Alkalinity, water hardness, temperature, can affect
performance of polymers

78. Type of sludge is the primary factor affecting the type and
quantity of polymer required
Raw Primary sludge requires much less poly than SAS
Old sludge requires a higher poly dose than fresh sludge
Polymer concentration required for a sludge is determined in
the lab by jar tests
NB sludge feed will vary therefore poly dose will change
POLYMER

79. Mixing of sludge and polymer is essential for effective
conditioning
Good conditioning depends on polymer addition, retention
time and mixing
POLYMER - mixing

80. DIGESTION - requirements
Min 12d primary digestion
Min 32ºC
Min 14d secondary digestion
Code of Practice for the Agricultural Use of Sewage Sludge (1989)

81. DIGESTION - benefits
Reduced sludge mass
-conversion of solids to gases
Reduced odour
-conversion of volatile compounds
Production of methane
-a renewable energy source
sludge
inert
solids
volatile

82. Biogas
DIGESTION
Heat
exchanger
Feed
Treated
sludge
Compressor

83. DIGESTION - biology
Complex
organics
Volatile
acids
CH4, CO2
1. Acidogenesis
2. Methanogenesis
Clostridium
Bifidobacterium
Lactobacillus
Methanobaciterium
Methanobacillus
Methanococcus

84. 990L water
10kg solids
490L water
10kg solids
1% ds 2% ds
10kg solids
20% ds
DEWATERING
40L water
Thickening
Dewatering

85. DEWATERING
Sludge feed
Polymer
Dewatered cake
Centrate

86. DEWATERING
Sludge feed
Polymer
Dewatered cake
Filtrate

87. DEWATERING

88. Chains of molecules that stick sludge solids together to release water
Charge type
Charge density
Molecular weight
POLYMERS

89. Chains of molecules that stick sludge solids together to release water
Charge type
Charge density
Molecular weight
POLYMERS
Molecular structure

90. Jet Wet process WATER SUPPLY
LEVEL PROBES
STORAGE TANK
TRANSFER PUMP
MIXER
MIXING / AGEING
TANK
VENTURI
EDUCTOR
BLOWER
AIR
SCREWFEEDER
POWDER
POWDER
HOPPER AIR / POWDER
JET WET
HEAD
LEVEL
PROBES
DRY AREA

91. DEWATERING
Centrifuges
Feed
Bowl
Scroll
Beach
Weir plate

92. DEWATERING

93. CONDITIONING

94. Provides required secondary retention
Allows drainage of free water
Forms a stable, friable product
Promotes aerobic conditions
CONDITIONING - Aim

95. CONDITIONING

96. SPC

97. Transpiration
Predation
Competition
Root penetration:
enzymic degradation
& aerobic conversion
SPC

98. INCINERATION

99. Flue gas stack
Fluidising air fan
Caustic
scrubber
Ash to disposal
2 field
Electrostatic
precipitator
Heat recovery
section
Induced
draft fan
Fluidised bed
incinerator
Turbo
generator
Quench
scrubber
Fixed
bed
adsorber
Sludge feed
Filtrate
Belt presses
MP steam
MP steam
INCINERATION

100. Sewage sludge – The opportunities
• Methane Production from Advanced and Conventional
Digestion
• Energy recovery from incineration or pyrolysis
• Nutrient Recovery from sludge liquors
• Utilisation of sludge liquors in BNR Processes
• Biosolids to agricultural land
• Topsoil production from Sludge phytoconditioning

101. Energy from sludge
Maximising energy throughput from sludges
There are a number of options:
• Digestion and advanced digestion
• Incineration or pyrolysis
• Physical disintegration techniques
• CHP –v- gas turbines –v- biofuel

102. Sludge as a marketable product
Technology exists its how you produce it and how you
sell it
Sludge as a marketable product
Biofert production at 13,200 tDS/annum
Sludge phytoconditioning
Biogas as a biofuel or supply to the gas grid
Ringsend 50% of energy from biogas
Sludge liquors as a product
Pearl & Crystal Green

103. Sludge Treatment as a resource
Sludge liquors – PEARL Process
Process that produces fertilizer by
removing nitrogen and
phosphorus from sludge liquors
Works by adding magnesium and
caustic soda to phosphorus rich
sludge liquors and passing them
through an upflow column
The sludge liquors pass through
pellets of struvite that are re-
circulated around to act as seeds.
The pellet size is a function of
retention time in the reactor

104. Sludge Treatment as a resource
Sludge liquors – PEARL Process
The pellets when ready are
removed from the reactor and
dried
The pellets are then bought,
marketed and sold by OSTARA
who developed the process as a
fertiliser that they term
“Crystal Green”
This creates a marketable product
from waste

105. ANY
QUESTIONS??