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 levels averaged 1-1.5 FTEs per mgd of capacity; 2) effluent quality was typically below limits for BOD, TSS, and coliform; and 3) pretreatment most often consisted of perforated screens 1-2 mm and secondary screening. The document recommends pilot testing, dual stage screening, and peak flow management.

1. © 2014 HDR, Inc., all rights reserved.
Patrick Roe, HDR Engineering
Gordon Culp, Smith Culp Consulting
September 10, 2019
A Survey of Operating Membrane
Bioreactor Facilities in North
America

2. MBR Survey Status
Report
Staffing
Treatment
Performance
Pretreatment
Flux Rates
Mixed Liquor
Concentrations
Membrane Life
Other Findings
Actual vs. Design
Flow Recommendations
Peak Flow
Management

3. MBR Survey Status
Report

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

9. Staffing

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

11. Treatment Performance

12. High Quality Effluent
MLSS 5,000 –
14,500 mg/L
Mixed Liquor Permeate
MLSS 5,000 –
14,500 mg/L
TSS < 1 mg/l
Turbidity < 0.2 NTU

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

14. Pretreatment

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

18. Actual versus Design
Flow

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

20. Peak Flow Management

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

22. Flux Rates

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

26. Mixed Liquor
Concentrations

27. MBRs Employ High Mixed Liquor Suspended Solids

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

30. Membrane Manufacturer
and Life

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

33. Other Findings

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

36. Recommendations

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