This document summarizes the findings of a survey of 28 operating membrane bioreactor (MBR) facilities in North America with capacities over 1 mgd. Key findings include: 1) staffing at most plants was 1-1.5 FTEs per mgd, 2) effluent quality was typically <2 mg/L BOD and <1 mg/L TSS, and 3) dual stage screening with 1-2 mm perforated plates was most common. The survey is ongoing and more facilities are invited to participate.
4. MBRs are becoming a common
means for wastewater treatment, but
are still a relatively new technology
Previous papers have collected
trends from a few operating
installations
Objective was to collect information
from a larger cross-section to verify
trends identified in previous papers
Focus was on facilities with a
capacity of greater than 1 mgd
MBR Objectives
5. 28 Participating MBR Plants in
12 States and 1 Canadian
Province
o One-quarter were from the
Northwest
Capacities range from 1.4 mgd
to 39 mgd
Membrane types – Suez,
Evoqua, Kubota, Fibracast
Still open to more participants
Summarize findings to date
MBR Survey Status
6. Electronic format
o To facilitate responses
and consolidate
responses
Survey Process
7. 1. General Facility Information
2. Membrane Supplier
a. Manufacturer
b. Membrane Replacement History
3. Membrane Capacity
a. Number of Trains
b. Membrane Area
c. Flux Rates
d. Adequate Flux Capacity?
e. Operation at Design Flux Capacity?
f. Ability to Add Chemical to Achieve Design Flux
4. MBR Effluent Performance
a. BOD and TSS
b. Nutrients
c. Fecal Coliform
Survey Questions - 1
8. 5. Membrane Pretreatment
a. Primary Treatment, including coagulant addition
b. Number of Screen Sets
c. Perforated or Slotted Screens
d. Screen Opening Size
e. RAS Screening
6. Operation and Maintenance
a. Performed by Owner or Contracted?
b. Annual Cost
c. Number of Staff
d. Membrane Cleaning Method and Frequency
7. Membrane Control Network
a. Control System Type – Ethernet or Hard-wired?
b. Replacement or Modification Plans?
8. Membrane Air Scouring System
a. Air diffusers
b. Blower type
9. Additional Comments
Survey Questions - 2
10. Only one plant used contract
operations, the rest were owner
operated
Most of the plants had staffing of
1-1.5 FTEs per mgd of plant
annual average capacity
Staffing
13. Typical MBR effluent for
municipal wastewater
o <2 mg/L BOD
o < 1 mg/L TSS and
o <2.2 MPN coliform
When integrated with a properly
designed and operated
biological/chemical treatment
process,
o Low levels of ammonia (<0.1 mg/L)
o Total nitrogen (<5 mg/L)
o Phosphorus (<0.02 mg/L)
Performance
15. Debris can accumulate
around membrane fibers
Membrane flux, and
therefore plant capacity,
declines with membrane
fouling
Membranes Are Susceptible to Fouling from Debris
16. Perforated screens of 1-2 mm
opening are most often used
A few plants use 3 mm screen
openings
o All but one facility with 3 mm
screens used flat plate membranes
20 percent had the flexibility to
screen RAS
Twice as many plants had no
primary sedimentation
compared to those that did
Pretreatment
17. Single set of screens – 62
percent of facilities
Two sets of screens (in series) –
38 percent
Generally, larger facilities had two
sets of screens
o But two facilities with less than 2 mgd
of capacity also had two sets of
screens
Few facilities used slotted
screens
o Perforated screens predominated
Screening Configuration
19. Nearly all of the plants are
operating with actual flow
significantly less than design
flow
Actual flow averaged 69% of
design flow and were as low
as 38% of design flow
The two plants that are
operating near capacity
reported issues with achieving
the design flux rate
Actual Versus Design Flow
21. Flow equalization or flow
diversion is used by 75% of
the respondents
Flow equalization is the most
commonly used method of
managing peak flows
A few plants divert peak flows
to another treatment plant or
to another part of the MBR
plant
Peak Flow Management
23. Once the membrane is
fouled, more pressure
is required to push the
flow through the
membranes
Slope of flux versus
pressure is called
permeability
Relationship Between Flux, Transmembrane Pressure
and Permeability
When the membrane is fouled, it
takes more pressure to push equal
flow through the membrane.
Equal flow.
Greater pressure
stresses the
membrane and
reduces life.
24. The actual peak flux rate for the
surveyed plants averaged 16.9
gallons per day per square foot
(gfd)
The actual annual flux rate
averaged 12.0 gfd
These values are less than
typical manufacturers’
recommended design values
o Pilot tests are a prudent step to
determine the flux rates achievable
for a given wastewater
Flux Rates
25. Half the plants surveyed
had the capability to add
chemical to enhance flux
rate
Typical chemicals used
o Ferric chloride
o PAX 19
o Polymer
o MDE 50
Although several have
tested polymers to
improve flux rates, none
reported sustained
success
Chemical Addition to Enhance Flux Rate
28. Facilities designed to
operate at 5,000 to 13,000
mg/L MLSS
Most plants are operating
with 8,000-10,000 mg/L
MLSS
Most plants are using
laboratory filtration tests to
monitor membrane
loadings
Mixed Liquor Suspended Solids
29. Typical basis for
operation at 8,000 to
10,000 mg/L
o High MLSS in
membrane tank
detrimental to
membrane permeability
o Oxygen transfer
efficiency reduced
Integrated Membrane Bioreactor Process
31. Several of the plants had been
in operation for less than 7
years
o One was proceeding with
membrane replacement
Five plants had been in
operation for 10-12 years
without replacing membranes
At seven plants, membranes
were replaced after 7-10 years
Membrane Life
32. Spectrum of membrane
manufacturers
o Suez: 15
o Evoqua/Siemens: 3
o Kubota: 7
o Fibracast: 1
o Not identified: 2
At two facilities, the
original membranes
had been replaced with
another manufacturer’s
product
Replacement with an Alternate Membrane Type
34. An MBR is a complex
system with many moving
parts
Control Systems
o All but one respondent use
Ethernet-type control
systems
o A few respondents had
made changes to the control
systems
Control Systems
35. Membrane Scouring Diffusers
o Coarse bubble diffusers were
more common than fine-bubble
diffusers
o Most manufacturers are
recommending coarse-bubble
diffusers
Membrane Scouring Blowers
o Centrifugal was most common
o But positive displacement units
were also used, as were Turbo
blowers
Other Findings
37. Operator gain experience
with membranes
Collect information on
actual flux
Verify cold weather impacts
Confirm ability to operate
within membrane warranty
limits
Operator gain experience
with membranes
Conduct Pilot Test before Design of Full-Scale Facility
38. Use dual stage screening
o Perforated plate upstream
o Downstream screen can be
drum or traveling band
screen
• Needs seal at perimeter to
capture all debris
Screen openings
o 1 or 2 mm for tubular
membranes
o May be able to use 3 mm
screens for flat plate
membranes
Effective Screening Is Essential to Effective Membrane
Treatment
Perforated
Plate Screen
Drum Screen
39. Unlike most other wastewater
treatment plants, MBR facilities
have variable capacity
Factors affecting membrane
capacity
o Membrane age
o Wastewater temperature
o Potential stresses on organisms
o Presence of foulants, such as debris
Most large facilities have
equalization or flow diversion to
manage peak flow
Peak Flow Control Is Critical
40. This survey is a work in progress
We welcome other Utilities to
participate in the survey!
To respond, go to the link
o https://hdrinc.co1.qualtrics.com/jfe/form/SV
_cAxLxIZSCYdyivX
Or Contact
o Pat Roe: Pat.Roe@hdrinc.com
o Gordon Culp: gordon@smithculp.com
Your name will remain confidential and
we won’t share your name or contact
information
How to Participate