Can MBR Eliminate Additional Disinfection? A Case...
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Can MBR Eliminate Additional Disinfection? A Case Study Ufuk Erdal, PhD, PE, CH2M Jonathan Vorheis, PE, CH2M July 17, 2015
Transcript of Can MBR Eliminate Additional Disinfection? A Case...
Can MBR Eliminate Additional Disinfection? A Case Study
Ufuk Erdal, PhD, PE, CH2M
Jonathan Vorheis, PE, CH2M
July 17, 2015
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Acknowledgement
• We sincerely thank to co-authors for their valuable contribution to the study:
• Howard Analla - City of Henderson
• Priscilla Howell - City of Henderson
• We also thank to City of Henderson and SNWA laboratory staff for their meticulous effort on sampling and microbial analysis
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Background
• Title 22 defines “disinfected tertiary recycled water as:
• A disinfection process that, when combined with the filtration process, has been demonstrated to inactivate and/or remove 99.999% of MS2, or polio virus in the wastewater
• Title 22 focuses on 5 log polio virus reduction through filtration and disinfection rather than disinfection alone
• No credit for virus removal through filtration is mentioned in the NWRI UV guidelines
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Background
• Increasing number of non-potable reuse facilities using MBR followed by UV or other disinfection methods
• This combination provides two effective barriers for pathogen reduction
• Discharge limits for disinfection are based on bacterial levels
• “Implicit” standards for disinfection are often assumed, such as virus removal/inactivation
• Because MBR permeate is frequently free of coliform, reuse plant operators are asking why is there a requirement for a separate disinfection process following MBR
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Objectives of the Study
• Evaluate the Removal of Pathogens in a Full-Scale MBR-
UV Facility
• To obtain virus removal credit for MBR
• Develop operational treatment goals that protect public health and reduce energy and chemical use
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City of Henderson Southwest Water Reclamation (SWRF) Facility
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City of Henderson SWRF
Operations
Building
Influent
Pumping and
Headworks
Chemical
Building
Blower
FacilityBioreactor
Basins
Membrane
Tanks
Membrane
Equipment
Building
Disinfection
Facility
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Treatment Capacity
• Phase I capacity:
• 8.0 mgd at annual average daily flow rate (AADF)
• 13.6 mgd at peak hourly flow rate (PHF)
• Phase 2 capacity:
• 16.0 mgd at annual average daily flow rate (AADF)
• 27.2 mgd at peak hourly flow rate (PHF)
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SWRF UV Design Criteria
• UV disinfection system was designed according to National Water Research Institute Guidelines (NWRI, 2012).
• To meet 5-log inactivation of poliovirus when using membrane filtration
• Design UV Dose: 80 mJ/cm2 at Design UV Transmittance of 65%)
• Effluent fecal coliform requirements:
• 2.2 MPN/100 mL (30-day geometric mean)
• 23 MPN/100 mL (Daily maximum)
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Pathogen Removal Mechanisms in MBR Systems
1. Biodegradation, decay and predation
2. Sorption on to the MLSS sludge or membrane surface
3. Size exclusion
• Direct removal (large molecules exceeding pore size of the membranes are retained)
• Pore blocking (large molecules block the entry of small molecules)
• Pore clogging as a result of cake/gel and/or scale formation (cake/scale layer is formed on the membrane which reduces effective pore size)
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Study Phases and Approach
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Study Phases
Phase I - Initial
Screening
Objective: Identify
and select virus
species for the study
Phase II – Testing
Objective: Determine
MBR virus removal
capabilities under
different operating
conditions
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Sampling Locations
Bioreactor Membrane
Tank UV
Disinfection
Post
Chlorination
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543
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Chlorine
MBR
Feed
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RAS
Phase I – Initial Screening
• Samples were collected under normal operating conditions (i.e., flux, SRT, RAS rates, etc.) and for the following virus analysis:
• Human Adenovirus (HAdV)
• Norovirus G1 and G2
• F specific (MS-2) and Somatic Coliphage
• Enterovirus
• Hepatitis A
• Rotovirus
• Polio virus
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Membrane Pore Size vs. Virus Sizes
• Nominal Pore Size of Zeeweed 500 d Membranes = 40 nm
• Pore Size of the Selected Viruses:
• Human Adenovirus (HAdV) (80-100 nm)
• Norovirus G1 and G2 (27-38 nm)
• Male Specific Coliphage (MS-2) (24-28 nm)
• Somatic Coliphage (Head 28-32, Tail 100-400 nm)
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Phase II – Virus Removal/Rejection of the System
Sampling were performed under the four following operating conditions:
1. Clean Membranes (immediately after sodium hypochlorite maintenance clean)
2. Clean Membranes (immediately after citric acid maintenance clean)
3. Operating at Increased Flux
4. Normal Operating Conditions with Reduced UV Dose (40 mJ/cm2)
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Monitoring Parameters
• BOD (Bioreactor feed, MBR Effluent)
• MLSS (RAS Line or MBR tank)
• Turbidity (MBR effluent)
• TMP (MBR system)
• SRT (MBR system)
• MLSS and RAS recycle rates (MBR systems)
• Water temperature (any reported point)
• UV Dose (UV system)
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Study Results Phase I - Initial Screening
• Enterovirus
• Hepatitis A
• Rotovirus
• Polio virus
• Human Adenovirus (HAdV)
• Norovirus G1
• Norovirus G2
• Male specific (MS-2) Coliphage
• Somatic Coliphage
Not detected in the influent and any sampled locations
Were abundant in the MBR
influent. Therefore, they were
identified as the indicator
organisms
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Phase I Initial Screening (Normal Operating Cond.)
Influent Bioreactor
Tank
MBR
Permeate
Concentration
Limit in
Recycled Water
Additional Log
Removal
Requirement for
Disinfection
System
HAdV, Copies/1 L 665,377 292,385 ND (<5) NSL1
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Norovirus G1,
Copies/1 L8,049 1,729 ND (<5) NSL
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Norovirus G2,
Copies/1 L25,845 ND (<5) ND (<5) NSL
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MS2 Coliphage,
pfu/100 mL1,900 11 ND (<1) NSL
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Somatic Coliphage,
pfu/100 mL1,600 12 ND (<1) NSL
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1No Set Limit; conservatively assumed that it is equal to reported detection limit20
Phase II – Test 1 (Clean Membranes with Hypo)
Influent Bioreactor
Tank
MBR
Permeate
Concentration
Limit in Recycled
Water
Additional Log
Removal
Requirement for
Disinfection System
HAdV, Copies/1 L 37,572,276 332,247 1 NSL1
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Norovirus G1,
Copies/1 L1,038,037 80,608 ND (<1) NSL
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Norovirus G2,
Copies/1 L197,974 3,886 ND (<1) NSL
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MS2 Coliphage,
pfu/100 mL2,400 22 5 NSL
10.70
Somatic Coliphage,
pfu/100 mL1,900 16 3 NSL
10.48
Total Coliform,
cfu/100 mL13,000,000 1,700,000 ND (<2) NSL
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Fecal Coliform,
cfu/100 mL5,000,000 400,000 ND (<2) 2.2 0
1No Set Limit; conservatively assumed that it is equal to its reported detection limit21
Influent Bioreactor
Tank
MBR
Permeate
Concentration
Limit in Recycled
Water
Additional Log
Removal
Requirement for
Disinfection System
HAdV, Copies/1 L 2,016 5,823 ND (<1) NSL1
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Norovirus G1,
Copies/1 LND (<1) ND (<1) ND (<1) NSL
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Norovirus G2,
Copies/1 LND (<1) ND (<1) ND (<1) NSL
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MS2 Coliphage,
pfu/100 mL1,800 30 21 NSL
11.32
Somatic Coliphage,
pfu/100 mL1,500 17 7 NSL
10.85
Total Coliform,
cfu/100 mL11,000,000 1,100,000 ND (<2) NSL
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Fecal Coliform,
cfu/100 mL11,000,000 800,000 ND (<2) 2.2 0
1No Set Limit; conservatively assumed that it is equal to its reported detection limit22
Phase II – Test 2 (Clean Membranes with Citric Acid)
Phase II – Test 3 (Operating at Increased Flux)
Influent Bioreactor
Tank
MBR
Permeate
Concentration
Limit in Recycled
Water
Additional Log
Removal
Requirement for
Disinfection System
HAdV, Copies/1 L 338,555 66,095 ND (<1) NSL1
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Norovirus G1,
Copies/1 L13,063,946 927,348 ND (<1) NSL
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Norovirus G2,
Copies/1 L13,133 ND (<1) ND (<1) NSL
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MS2 Coliphage,
pfu/100 mL2,100 16 4 NSL
10.60
Somatic Coliphage,
pfu/100 mL2,300 13 ND (<1) NSL
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Total Coliform,
cfu/100 mL30,000,000 5,000,000 ND (<2) NSL
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Fecal Coliform,
cfu/100 mL11,000,000 1,700,000 ND (<2) 2.2 0
1No Set Limit; conservatively assumed that it is equal to its reported detection limit23
Influent Bioreactor
Tank
MBR
Permeate
Concentration
Limit in
Recycled
Water
Additional Log Removal
Requirement for Disinfection
System
HAdV, Copies/1 L 588 23,490 ND (<1) NSL1
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Norovirus G1, Copies/1
LND (<1) ND (<1) ND (<1) NSL
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Norovirus G2, Copies/1
LND (<1) ND (<1) ND (<1) NSL
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MS2 Coliphage,
pfu/100 mL4,400 45 ND (<1) NSL
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Somatic Coliphage,
pfu/100 mL6,200 53 ND (<1) NSL
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Total Coliform, cfu/100
mL17,000,000 8,000,000 ND (<2) 2.2 0
Fecal Coliform, cfu/100
mL3,000,000 700,000 ND (<2) NSL
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1No Set Limit; conservatively assumed that it is equal to its reported detection limit24
Phase II – Test 4 (Normal Operating with Reduced UV Dose)
Conclusions and Path Forward
• Influent virus concentrations showed great fluctuations (i.e., Norovirus G1 (<1 to 13,063,946 copies/L)
• Without disinfection, the MBR completely retained bacteria and was very effective for reducing virus and to very low levels (in most cases to ND levels)
• The lowest virus rejection by the MBR was observed for MS2 Coliphage and under clean membrane conditions
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Conclusions and Path Forward
• Under these conditions, the MBR permeate contained viruses and additional removal was required by the disinfection system (either UV disinfection or chlorine disinfection)
• NWRI and Title 22 recycled water regulations do not set numeric concentration limit for viruses in recycled water
• Conservatively assuming that recycled water contains non –detectable virus, the additional virus removal required by disinfection was 1.32 log removal
• Assumed 2-log removal is required by the disinfection
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Conclusions and Path Forward
• 2-log additional virus inactivation can be satisfied with a UV dose of approximately 40 mJ/cm2
• 2-log additional virus removal can also be satisfied with free chlorine CT of 3 mg/L*min
• At residual chlorine concentration of 0.3 mg/L, it requires a contact time of 10 minutes
• CT can be satisfied using the 2 mile pipeline that conveys recycled water to the reservoir
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Conclusions and Path Forward
• The virus study results supported the conclusion that the MBR alone provides a level of disinfection consistent with permit compliance
• Following completion of this study, the City of Henderson presented the results to the State of Nevada, with the recommendation to reduce or eliminate UV disinfection at the SWRF.
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State of Nevada’s Approval
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Conclusions and Path Forward
• The State of Nevada agreed that UV disinfection following membrane treatment was not necessary to properly treat the effluent water to reclaimed standards
• By eliminating UV disinfection, the City of Henderson will achieve significant cost savings in power (an annual saving of over 1.2 million kWh is expected), equipment (i.e., lamp replacement), and staff time.
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Questions
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Ufuk G. Erdal, PhD, P.E.
CH2M
Santa Ana, CA
Jonathan Vorheis, P.E.
CH2M
San Antonio, TX
