MBR Activated Sludge Truths:
The Real Information Concerning the
O&M Associated with MBR Activated
Sludge
OWEA State Conference
June 20, 2012
Presented by:
Ashley G. Williston
Terry M. Gellner, P.E.
When evaluating using the MBR process it
is important to look at the capital and o/m
costs for the WHOLE plant not just the
membranes.
Conventional Wastewater Plant
Tertiary
Treatment
Post Solids
Treatment Treatment
Primary
Clarifiers
Secondary Preliminary
Conventional Treatment
Clarifiers
Activated Sludge
Conventional Wastewater Plant
Preliminary
Treatment
Anaerobic Primary
Digesters Clarifiers
Conventional
Activated Post Treatment
Sludge
Secondary Clarifiers
MBR Wastewater Plant
Solids Handling MBR Activated Sludge
Post Treatment
Preliminary
Treatment
Definition of MBR
The membranes are submerged in the activated sludge
tanks to perform the critical solids separation process that
clarifiers and tertiary process units perform in conventional
treatment plants
Processes with an anoxic zone, aeration zone, and a
membrane zone. Sometimes an anaerobic zone if
biological nitrogen removal is required.
Conventional Plants MBR Plants
Influent Pumping Influent Pumping
Grit and Grease Grit and Grease
Fine Screens
Primary Settling
Conventional Activated Sludge MBR Activated Sludge
Secondary Clarifiers
Tertiary Filters
Disinfection Disinfection?
Solids Handling Solids Handling
MBR Plants have a SMALLER Footprint
MLSS is 3-4 times higher for MBR
facilities
Conventional: 2,000 – 4,000 mg/l
MBR: 8,000 – 12,000 mg/l
Membranes are submerged in the
Activated Sludge process
Expansion from 1.2 to 1.8 MGD; New Limits
Conventional Process
Flow EQ Basins
Digesters
MBR Process
McFarland Creek MBR vs Conventional Expansion
MBR Footprint Advantages
No impact to adjacent property value
Odors are negligible
Environmental impact and approvals
avoided
Excavation, erosion control, restoration
avoided
Land reclamation for other use
RAS Recycle Rate
Conventional: 0.5 - 1.5 Q
Return bugs back from
clarifiers to head of activated sludge
MBR: 2 - 4 Q
Return bugs back
Keeps basins in suspension
High RAS rates naturally increases nutrient removal
since bugs are fighting for more of the oxygen and food
SRT – Solids Retention Time
Conventional
Varies to suit effluent requirements (ammonia)
An ammonia limit requires a higher SRT
Ammonia limits require more power (need to increase
air demand)
MBR
Requires Higher SRT (2-3 times higher)
Ran higher to create a sludge that is less likely to stick
to the membranes
Side benefit is that the higher SRT causes ammonia
reduction
Permeate Quality
Benefits
Parameter Secondary Tertiary Treatment MBR
Treatment
CBOD (mg/l) 25 - 10 10 <5
TSS (mg/l) 30 - 12 12 <5
Fecal Coliform 1,000 1,000 <1
(CU/100 mL)
Metals Proportional to Same Less
TSS
Bio P without chemicals 3-1 2-1 0.5
(mg/l)
Need for Disinfection?
Does MBR treatment provide the same
level of public health protection from
microorganisms as that found for
conventional systems that use disinfection
after secondary treatment?
Samples were analyzed for...
Bacterial Indicators
E.coli, Fecal Coliform, Enterococi
Somatic and F-specific Coliphage
Enteric Viruses by qPCR
Enteroviruses, Noroviruses, Adenoviruses,
Rotaviruses, and Hepatitis A Virus
Culturable Viruses
Escherchia coli
100,000,000 100,000,000
MBR Plants Conventional Plants
4.2x106
Delphos (n = 6) 4.3x10 6 Aurora Shores (n = 4)
10,000,000 10,000,000
Dover (n = 5) Kent (n = 4)
3.5x106
Escherichia coli, in CFU/100 mL
1,000,000
Escherichia coli, in CFU/100 mL
1,000,000
3.4x106
100,000 100,000
8,200 6,100
1,700
10,000 10,000
1,000 Weekly Limit : 284 / 100 ml 1,000
100 100
2 6
10 10
1
Detection Limit <1 <1 <1 Detection Limit
1 1
Raw Post-MBR Post-Disinfection Raw Post-2º Post-Tertiary Post-Disinfection
(Median values are shown; CFU/100 mL, colony-forming units per 100 milliliters)
Conclusions of Study
Membranes remove fecal coliform and E.coli to
levels equivalent to conventional plants and after
disinfection
Membranes remove viruses to similar levels as
seen by conventional plants after disinfection
The removal amount of fecal coliform, E. coli, and
viruses by disinfection at MBR plants is
insignificant
Using Membranes for Disinfection
Eliminates additional Capital and O/M Costs
Reduces Environmental Impacts
Improves Plant Safety Conditions
Provides NPDES Permit Compliance
Provides comparable results for Fecal Coliform
and E.coli removal as existing BADCT disinfection
systems
Capital Costs UV O/M Costs
Electrical Power Cost
Bulb Replacement
Quartz Sleeve Replacement
Ballast Replacement
Wiper Ring Replacement
Chlorine O/M Costs
Sodium Hypochlorite ($0.65 - $1.10 per gallon)
Sodium Bisulfite ($1.50 per gallon)
Tank Replacement
Chemical Pump replacements
Effluent Quality – Water Reuse
Revenue possibilities
Sell to others
Industrial – make up, cooling, process
Use water to reduce other O/M costs for city
Any non potable water uses
Landscape Irrigation
Maintenance cleaning, sewer jetting
Toilet flushing
Fire protection
Sludge Production
MBR Plants have less sludge than Conventional
Plants – Use 20% Less for Studies
Union Rome used to dewater 4 days a week now only
4 days a month
Union Rome also has installed membrane thickening
for their sludge. Increases solids concentration from
1%-4%
Union Rome also increased the belt press from a 0.5
meter to a 1 meter
Union Rome Sludge Production Manpower Savings
Conventional Plant
Dewater: 4 days a week or 16 days a month
16 d/m* 12 m/yr *8 hr/day
Labor– 1,536 hours
MBR Plant
Dewater: 4 days a month
4 d/m* 12 m/yr**8 hr/day
Labor – 384 hours
An additional 1,152 hours per year (22 hours per week)
for the staff to be more productive
Capital Costs
Delphos WWTP $30 million project
Operational in 2006
Flow Rates Max Day 18 MGD; ADF 3.83 MGD
$7.50/gallon
Brand New Plant
Class A Biosolids
Included demolition of old plant
Capital Costs
Union Rome WWTP $20 million project
Operational in 2009
Flow Rates: Max Day 7 MGD, ADF 2 MGD
$10/gallon
Brand New Plant
Completely under roof
Odor Control
Increase of Capacity and New limits
Capital Costs
Carrolton WWTP $7.4 million project
Operational in May 2012
Flow Rates: Max Daily Flow 3.35 MGD, ADF 0.75 MGD
$9.85/gallon
New Headworks
New MBR structure
Retrofit for EQ and Digesters
New generator, site work, and drainage system
McFarland WWTP $6.8 million project
Operational in Spring 2006
Flow Rates: Max Daily Flow 4.5 MGD, ADF 1.8 MGD
$3.80/gallon
1.2 MGD to 1.8 MGD Expansion
MBR retrofit
Included Aerated Grit, UV Disinfection and Post
Aeration, Aerobic Digesters, Site Work, and Admin
Building Improvements
Capital Cost Conclusion
$2- $10 per gallon
Operation and Maintenance Factors
Power consumption
Chemical Consumption
Sludge Production
Capital Maintenance
MBR Replacement
Staffing Needs
McFarland Creek 1.8 MGD MBR Plant
Preconstruction 2004 cost converted to 2006
$14,060/month x 1.25 / 1.1 x 6.43 / 4.8 =
$21,400/month
Operation in 2006
$19,650/month
McFarland Creek Sludge Production 2004 vs 2006
Month Cubic Yards Dry Tons Avg. Percent Solids
2004 2006 2004 2006 2004 2006
June 422 200 63.01 33.13 17.6 19.5
July 330 222 54.34 33.99 19.35 17.92
August 284 96 43.57 17.16 18.24 20.98
September 255 174 37.08 25.03 17.06 17.02
October 420 232 59.58 37.53 16.63 19.01
November 372 308 50.74 49.13 15.99 18.68
Totals 2,083 1,232 308.32 195.97 17.48 18.85
Total Polymer Cost Total Disposal Fees
2004: $22,080 2004: $42,000
2006: $13,059 2006: $25,000
Difference: $9,021 Difference: $17,000
McFarland Creek Chemical Consumption
Ferrous vs. Alum – More expensive but using less
Less polymer used – Less sludge
Sodium Hypo/Hydrochloric Acid - New
$2,500/month increase
Capital Replacement –
MBR Replacement
Based on manufacturer recommendation
Either between years 5 and 10 or 10 and 15
Approximately $0.25 to $0.50 per square foot
Diffusers- 10-20 years
Pumps- 20 year
Staffing Demands
More automation
Less solids
Smaller footprint
Result has been that WWTP staff has had more
time to be proactive
Summary of MBR vs Conventional O&M
Power consumption is similar but should be
reviewed on a case by case basis
Chemical requirements are comparable but can be
less for MBR if nutrient limits are lowered
Sludge production is 20-30% less for MBR facilities
Equipment replacement Costs are comparable with
the exception of membrane replacement
Staffing needs are less for MBR facilities due to
automation and combined unit processes with
MBR
Final Comments
A cost analysis is appropriate – and it should be for
the whole plant
Based on a review of both captial and O/M costs
MBRs are often times a more cost effective
alternative
MBR is a system of multiple unit processes so the
design and operation is unlike conventional
treatment
Upgrading to MBR when building or expanding is a
worthwhile alternative to explore
Biologically Enhanced Treatment
Activated sludge process is the same
Traditional Recycle Rates are the same: 2-4Q
Both require internal recycle if needed
Both may require carbon source
Selector Processes required is the same
Oxygen demand required is the same
Biologically Enhanced Treatment
MLSS is still higher for MBR process
Footprint is 1/4 size for MBR process
Tertiary requirement for Conventional process
Disinfection?
Canton – Phosphorus and Total
Nitrogen Removal Plant Upgrade
Present Worth Costs Bio P & BNR MBR
Capital Cost 109,425,000 72,120,000
O&M Cost 45,355,979 43,332,085
Total Present Worth 154,780,979 115,452,085
Present Worth Cost Summary N=20 yrs
Canton - Total Equivalent Annual Costs
Bio P & BNR MBR
Annual Payment for Debt Service 7,086,216 4,777,020
Annual Payment For O&M 5,081,762 4,936,598
Total Annual Payment 12,167,978 9,713,618
MBR Basin Size
When first entering the market the trend was small
plant applications with uniform conditions
Now with improved systems manufacturers are
able to get more membranes into an area so the
membranes are more efficient for larger plant
applications
Typical Types of Membranes
Nozzle
Membrane Panel
Reinforced
Spacer
Structure
Membrane Sheet
Biomass
Effluent
Hollow
Fiber
Microstructure
Flat Plate Membranes Hollow Fiber Membranes
Pore Size: 0.4 µm Pore Size: 0.035 µm
Summary
More differences between membrane systems than there are
similarities
Flux rates are different based on the membrane type
Mixed liquor concentrations vary among membrane type
Some membranes can gravity permeate and others must
pump
Flux maintenance is different by membrane type
Systems that support the membrane process vary
Different types of membranes function differently on how they
permeate
Questions
