Advances in Wastewater –
The Benefits to the GCC Region
Jonathan Bishop,
Middle East Unit
Water and Wastewater Process Manager
Introduction
• Odour Control
• Anaerobic Digestion
• Enhanced Treatment
– Nutrient removal
• Ammonia – standard in region
• Total Nitrate
• Phosphate
• Biological Nutrient Removal
• Recent Case Study
Odour Control
Odour
• Result of biological activity on proteins and other substances in
the wastewater in the absence of oxygen
• Odorants generated comprise volatile organic compounds and
gaseous inorganic compounds such as hydrogen sulphide (H2S)
and ammonia (NH3)
• Major sources of odour at typical wastewater treatment facilities
include:
– Pumped Sewers
– Inlet Works including screens
– Primary Settlement Tanks/Clarifiers
– Sludge and return liquor treatment areas
Odour- Analysis and Predictions
•
Dispersion models required to
convert measured or calculated
odour emission rates to
atmospheric odour
concentrations
•
2 popular models available –
AERMOD and ISC
•
AERMOD is recommended by
the US EPA
•
AERMOD requires terrain and
meteorological data for accurate
predictions.
Graphical Model Interface
Odour- Analysis and Predictions
•
Model outputs are in the form of diagrams showing likely (98 percentile)
atmospheric odour concentrations.
•
Wind roses show prevalent wind direction for the area under assessment.
Odour- Control, Treatment and Abatement
•
Dedicated Odour Control and
Abatement Equipment include:
– Dry absorbers such as carbon filters
– Bio-filters and Bio-scrubbers that
utilise biomass on a structured
media bed.
– Chemical Scrubbers that utilise
acids/alkalis and oxidants.
– Incinerators or thermal oxidisers that
oxidise odorants in foul air.
•
Masking Sprays may also be
used to mask
Odour- Control, Treatment and Abatement
Volumetric flow of gas (m 3/hr)
100,000
Incineration, Thermal Oxidation
10,000
Chemical Scrubbing
1,000
Biofilters and Bio-scrubbing
100
10
Dry Absorption
(Carbon Filters)
Low
Medium
High
3
Odour Concentration (OU/m )
Anaerobic Digestion
What is Anaerobic Digestion?
Conversion of organic matter to methane and carbon dioxide in the
absence of oxygen.
C5H702N+6H20
5CH4 + 2NH3 + 5CO2 + Biogas
Produces stabilised residual solids.
Biogas comprises approximately 60 to 65%CH4, 30 to 35%CO2 and
other gasses.
Typical AD system
• Effective gas mixing
• Effective external heat
exchangers
• 15 day retention
• Continuous feeding
Enhanced AD System
 Effective jet mixing
 Effective external heat
exchangers
 12 day retention
 Continuous feeding
Pre-treatment
What does Pre-treatment do?
• Increase pathogen destruction
– Compliance with microbial standards eg US EPA Class A
– Safe use of sludge in agriculture
– Applicable to wider range of crops
– Secure agricultural disposal route
• Increase solids destruction
– Increased Bio-Gas production
– Increased power generation through CHP
– Reduced amount of sludge requiring disposal
Reaction Steps in AD
Step 1: hydrolysis
slowest
starch  sugars
Step 2: acidification
sugars  VFAs
Step 3: acetogenesis
VFAs  acetates
Step 4: methanogenesis
acetates  biogas
step
Reaction Steps in AD with Pre-Treatment
AD
hydrolysis
hydrolysis
acidification
acidification
acetogenesis
methanogenesis
pH ~ 7.0 to 7.5
pH = 5.0 to 5.5
pre-treatment
Methods of Pre-treatment
• Biological
• Thermal
• Chemical
• Mechanical (high shear, grinding)
• Ultrasonic
Typical Biological System
cold water
raw sludge
55oC
42oC
42oC
42oC
Ht Ex 3
55oC
Ht Ex 1
Ht Ex 2
55oC
hot water
total retention =
2 days
pre-treated
sludge
to AD reactor
Case Study-Kings Lynn STC, United Kingdom
•
Sludge Throughput =
14,500 to 19,000tDS/year
•
Proportion of primary to
WAS = 50:50 to 35:65
•
Pre-treatment =
Biological
•
Volatile Solids
Destruction = 50 to 60%
Case Study-Kings Lynn STC, United Kingdom
Enough power
generated to
support the
Wastewater
Treatment
Plant and
export to the
grid
Why Adopt AD in the GCC?
•
Slow uptake of anaerobic technologies in the region.
WHY?
•
Cheap Energy - More expensive to recover energy from anaerobic digestion
than have energy supplied from the grid/other sources.
BUT
•
Landfill - There will eventually be constraints on space for landfills which is
currently the preferred disposal route for sludge solids
OTHER POSSIBLE DRIVERS
•
Fertiliser - Anaerobically digested sludge solids could be used as fertiliser if
appropriate legislation and regulations are in place.
•
Sustainable - Sustainable source of energy.
Nutrient Removal
Nutrient removal - Introduction
• Essential nutrients for plant growth:
– Nitrogen – Ammonia, Nitrate
– Phosphorous in the form of Orthophosphate
• Nutrients are usually limited in natural waters and hence
restrict plant and algae growth
• Free fertiliser where TSE is re-used to irrigate plants
Why use nutrient removal in GCC?
• Chlorine disinfection – Ammonia removal required
• Coastal discharges
• Prevention of eutrophication where:
– TSE is re-used for lakes and water features
– Storage in lagoons is primary disposal outlet for TSE.
Nutrient Removal – Ammonia
• Most plants in region are designed to meet re-use
standards
• Normally will also achieve ammonia removal as well
• Typically ammonia is converted to nitrate via nitrification
• Requirements for Nitrification:
– Typical Feed to Mass (F/M) Ratio = 0.15. This value increases with
temperature
Nutrient Removal - Nitrate
Ammonia
(NH3+)
Ammonia
Oxidising
Bacteria
(AOB)
Aerobic Cycle
(Air + Food)
Nitrite
(NO-)
Nitrite
Oxidising
Bacteria
(NOB)
Anoxic Cycle
Nitrogen
(N2)
(Food)
Nitrate
(NO2-)
Various Process Configurations
Biological Nutrient Removal
RAS
Johannesburg
Process
Anoxic
Anaerobic
Anoxic
Aer
Aer
Internal Recycle
RAS
5 stage Bardenpho
process
Anaerobic
Anoxic
Aer
Anoxic
Aer
Internal Recycle
RAS
Modified University
of Cape Town
(MUCT)
Anaerobic
Anoxic
Internal Recycle
Anoxic
Aer
Internal Recycle
Aer
Aer
TENDER DESIGN
Background
• Leightons Middle East were bidding major Watewater
Project in the Region
• Mott MacDonald were commissioned to provide a detailed
tender design covering all aspects of the project including:
–
–
–
–
–
Civil / Structural
Geo-technical
Process
Mechanical
Electrical and ICA
Detailed Tender Design
•
Close collaboration between all parties in the tendering team
•
Clearly defined extent of design responsibilities between all parties involved
•
Use of design examples / experience gained during execution of similar
project elsewhere within Mott MacDonald
•
A detailed tender design was produced making use of the skills of all parts
of the team
•
Good understanding of risks associated with the project and providing
greater cost certainty to contractor and ultimate client
•
Detailed tender stage work would facilitate rapid start following award.
•
Key Design aspects include:
– Carrying out engineering calculations for all structures and systems
– Preparation of 3D Modelling of key structures
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