Validation approaches and
challenges with wastewater and
storm water in the UK
Christy White
Peter Loughran
Mike Newberry
Aknowledgements:
UKWIR
Environment Agency
Methodology for the design and permitting of UV
irradiation for wastewater disinfection
•
Identification of disinfection requirements on a site specific basis
•
Evaluation of the UV dose required to achieve the disinfection
requirements
•
Determination of the design (water quality) envelope for the design
This approach is underpinned by the use of validated UV irradiation
systems, combined with site specific data, to ensure that the target
level of disinfection can be achieved and demonstrated.
Disinfection for wastewater discharges
Crude
sewage
Wastewater treatment
(no disinfection)
E. coli
7
10 cfu/100ml
Final
Effluent
2 log
reduction
105
E. coli
cfu/100ml
Dilution /
dispersion
1 log
dilution
Receiving
Water
E. coli
104 cfu/100ml
Bathing Water targets:
Final effluent
discharges require
disinfection to
achieve Bathing
water and Shellfish
water quality
targets
E. coli: 80 cfu/100ml
(5.4 log reduction from crude)
Intestinal enterococci: 32 cfu/100ml
Enterovirus: 4.4 log reduction from crude
Shellfish targets
E. coli 110 cfu/100ml
(5.25 log reduction from crude)
Minimum pathogen (virus) reduction through
disinfection process: 1 log10
UK wastewater
disinfection
•
Sewage from over 9
million PE (7% of UK
population) requires
disinfection
•
Predominantly UV
irradiation
•
210 sites (approx.,
up to Amp3)
•
Annual operating
power of circa 60
GWh
•
Circa 30,000 tonnes
CO2e
The 10 largest sites
• Disinfect over 2,120 Ml/d (3 Million PE)
• Estimated annual opex circa £2-3 million
• >15,000 lamps, estimated replacement costs of circa £3-5M
every 3 years
CUMULATIVE OPEX OVER 15 YEARS
60
50
40
30
20
10
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Collaboration through UKWIR project WW17
•
No low carbon “silver bullet” alternative to UV
irradiation
•
Analysis of data highlighted:
•
an “over achievement” of dose in comparison
with the permitted condition
•
the need for a relationship between UV dose and
expected performance
•
the need for more effective dose control
•
the potential for site specific data to support use
of alternative values to EPR 7.01 defaults to
determine the target log inactivation
Drivers for change
Key factors in optimising power use in UV irradiation are:
•
Selection of the target / operational UV dose
•
Ability to control to the target dose (turn down /
response to changes in WQ, flowrate)
Drivers for change
1. Operating costs associated with continuous (final effluent) systems
Existing methodology UV dose set by “a dose calculator”, default values &
UV system was designed to deliver a “theoretical” (PSS) dose:
•
no direct relationship between UV dose (PSS) and performance
•
not appropriate for dose optimisation
Environment Agency
UV Disinfection - Spreadsheet for the Calculation of the UV Dose for Faecal Coliforms
Jun-04
Input data in the yellow boxes can be changed by user. Critical Output is highlighted in blue
No constants or coefficients should be changed without reference to Surfacewater Process, Environment Agency
Site:
2. Alternative stormwater management solutions
Output - Dose Computation
Effluent Characteristics
Comments
Faecal Coliform Conc.
(No/100 ml) in the influent
US EPA empirical equation designed on high UVT
wastewaters
•
Test
Input
Suspended Solids conc. (mg/l)
25
UV Intensity (mW/cm^2)
Received Dose (mWs/cm^2)
UV DIS
Faecal
Coliforms
Enteroviruses
30.70
70.68
5.00
Critical Dose (mWs/cm^2)
70.68
Contact Time (s)
14.14
Default value 5 mW/cm^2
Compute Log-Reductions Required
Faecal
Coliforms
Log reductions achieved by critical dose
(mWs/cm^2)
Enteroviruses
Log-reduction achieved by
critical dose
Total Required Reduction
5.40
5.40
Reduction achievable through
Primary + Secondary treatment
2.00
2.00
See table below for default
reductions, or use site-specific
values.
Initial Dilution or
1.00
1.00
Use minimum values. Use the
greater of Initial Dilution and
Secondary Dispersion
Total
3.00
3.00
2.40
2.40
0
Required by UV
Default values for log reductions through conventional
treatment
Faecal
EnteroColiforms
viruses
Primary + Activated Sludge
2.00
1.50
Primary + Oxidation Ditch
2.00
1.50
Primary + BAFF
1.50
1.00
Percolating Filter
1.50
0.30
4.58
2.40
4.63
4.33
Maximum Achievable Reductions
Maximum Log10 Reduction
Secondary Dispersion/Mixing
dose-response)
Consent 95%ile
UV Lamps
the existing design / permitting process was not
applicable to stormwater (water quality,
Required UV Doses for Indicators and Targets
2.00E+07 Geomean influent conc.
(default 20,000,000)
Overview of methodology
1. Site specific testing to determine:
• Disinfection requirement (i.e. log removal of target
organisms required to meet water quality targets)
• Design envelope (UV transmittance vs flow,
impact on dose response of various WQ
parameters, fouling potential)
• Dose-response relationship for target
organisms (collimated beam testing)
Dose response E.Coli
1.00E+08
E.Coli 5th July
E.Coli 4th July
1.00E+06
E.Coli 19th July
Geomean Ecoli
1.00E+05
Target
concentration /100ml
1.00E+07
1.00E+04
1.00E+03
1.00E+02
1.00E+01
1.00E+00
0
5
10
15
20
25
30
35 40 45 50 55
DOSE (RED) mJ/cm2
60
65
70
75
80
85
Dose-response example
Dose – response example
UV transmittance
Flow to Full Treatment Mean - Inlet Works (l/s)
Final Effluent Flow - EA - MEAN (l/s)
500
80
400
60
300
40
200
20
100
flowrate, l/s
UV TRANSMISSITY
UV CH2 TRANSMISSITY SENSOR
100
0
0
1-Mar-16 0:00:00
1-May-16 4:48:00
1-Jul-16 9:36:00
31-Aug-16 14:24:00
31-Oct-16 19:12:00
1-Jan-17 0:00:00
UV transmittance
• Stormwater: >15-20%
• Unfiltered final effluent: >30%
• Filtered final effluent: >40-50%
• Chemically assisted tertiary filtration: >50%
• Potential impact of biofilm sloughing (biofilter plants)
• Potential impact of trade components can be
significant for design UV transmittance and compliance
Overview of methodology
2. Specification of UV equipment where dose delivery /
performance has been validated
Based on achieving desired performance for all
target organisms at design conditions:
• max flow
• minimum UV transmittance
e.g
Organism
Sensitivity, mJ/cm2
per LRV
Minimum Validated
UV Dose, mJ/cm2
Target log
inactivation
E. coli
4.8
10.1
2.1
Enterococci
6.7
10.1
1.5
Virus*
20
20
1
*minimum requirement for enterovirus log inactivation for a disinfection process set by EPR 7.01
Overview of methodology
3. Audit reports to demonstrate:
• UV dose selection (validated dose permit
condition)
• dose delivery by selected UV irradiation equipment
across design envelope
• robust validation (assessment vs UVDGM criteria)
Summary
•
Greater certainty of achieving desired environmental outcome than
PSS dose (delivery of validated dose, based on site specific data, to
demonstrate performance)
•
Applicable to stormwater & final effluent discharges (select
equipment with appropriate validation envelope)
•
Opportunity to optimise power & carbon within the limits of
turndown of the system
•
Opportunity to target other specific organisms in the future
(e.g. Norovirus)
•
Provides a level playing field between suppliers / systems to
achieve the same performance
Considerations for drinking
water disinfection
Microbial reduction in drinking water
Raw
water
Water
treatment
Treated
water
Disinfection
Disitribution
• What are the challenge organisms in the raw water, how do we quantify
them?
groundwaters
surface waters (reservoirs & rivers)
• What level of reduction is provided by upstream treatment
processes (if any) ? (USEPA SWTR)
• What is the required level of inactivation through
disinfection for each organism)?
• How much of this can be provided most
effectively by UV irradiation / chlorine contact /
combination?
UV irradiation for potable water
• What are the key target organisms for UV
irradiation
DVGW vs UVDGM
• Determining required performance / inactivation
• Performance specification
• Impact of water quality (UV transmittance) on
sizing
Target pathogen
Hepatitis A Poliovirus
Coxsackie virus
Adenovirus
High
High
Moderate
Resistant
22 (4 log crypto)
34
2
1
<0.5
40 (2 log MS2)
>4
34
2
<1
58 (1 log Adenovirus)
>4
>4
>2
1
186 (4 log Adenovirus)
>4
>4
>4
4
Sensitivity to UV irradiation
Log10 inactivation through UV irradiationa
validated UV dose based on UVDGM
(2006) mJ/cm2
a
Log inactivation for Adenovirus is taken from UVDGM, for Hepatitus A virus, Poliovirus and Coxsackie virus the log inactivation given is approximate order of magnitude for comparison purposes only and will be reactor specific.
Pathogen
Decreasing
sensitivity to
UV
irradiation
Cryptosporidium
Poliovirus
Hepatitis A / Coxsackie virus
Human Adenovirus
Human Norovirus
Increasing
sensitivity to
chlorine
contact
What is the impact of UV transmittance on UV system sizing /
power / performance?
220
UVT = 90
200
180
UV dose, mJ/cm2
•
UVT = 92
160
UVT = 94
140
120
UVT = 96
100
80
UVT = 98
60
40
20
0
20
25
30
35
40
45
Flowrate
50
55
60
65
Summary
• Determining disinfection requirements
• What is the site specific pathogen challenge(site / catchment specific)
• What are the key target organisms
• What can be achieved economically using UV irradiation; is it enough?
• Specifying performance / UV dose consistently
• Organism & target log inactivation
• UVGDM / DVGW
• Understand impact of UV transmittance on design and
operation (e.g. turn down / by-product formation)
Design with Community in Mind