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April 5, 2011, Madison WI

CSWEA Education Seminar

Key elements and bottlenecks of the membrane bioreactor (MBR) process for advanced wastewater treatment

Prof. TorOve Leiknes

TorOve Leiknes

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Outline: - Brief introduction to the history of MBRs - Market potentials and development – Global / Europe - Challenges and bottlenecks in MBR systems - Where is research heading today? - Future perspectives…

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Looking into membrane technology: Suspended matter

MF

Macromolecules

UF

Sugars' Divalent salts Dissociated acids Monovalent salts Undissociated acids

NF Fluks Trykk

RO

Water

Conventional filtration

MF UF NF RO

Angstroms 1 Microns 10-4

10 10-3 Ionic range

102 10-2

103 10-1

Macromolecular range

104 1

105 10 Micron particle

106 102 Fine particle

RO – rejection of ions/solutes (< 20 Å pore size) NF – rejection of ions/solutes (< 20 – 600 Å) UF – defined by MWCO (10-1000 Å) MF – colloidal suspensions (0.02 – 10 μm)

4 AS

Wastewater applications:

Sludge treatment

RO

2. Process optimization

Recarbonation Air stripping

GAC

Pre-treatment AS

Sand filter MF/UF

RO

1. For tertiary treatment

Sludge treatment

Pre-treatment

MBR

AS MF/UF

RO Sludge treatment

3. Replace conventional treatment

RO Sludge treatment

4. Membrane bioreactors 5. ……… ?

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Steps on the way to MBR…..

Application distinction: Municipal / industrial

End of 1960’s: - UF: for municipal wastewater, sludge separation in AS (1969) 1970’s and 1980’s: - MF/UF of industrial wastewater (f.ex. textile industry, oily wastewater, separation of metals, organic compounds) - In connection with separation in anaerobe digestion 1990’s: - Membrane bioreactor concepts

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MBR breakthrough… 1989: Prototype of current MBR solutions, Yamamoto et.al.

• Flux: ~ 3-9 LMH • Sludge: 10-11 kg/m3 • TMP: ΔP ~ 1.33 bar • Energy: 0.007 kWh/m3 • Treatment efficiencies: - 93 - 95% COD - 94 - 99% TOC - no SS

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Why the interest in MBRs?

(Gander et al., 2000)

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What has happened…..? ……… what is to be expected?

Yamamoto, 2009

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What drives MBRs R&D? Global water markets: $350 - $375 billion

• municipal sector ∼ $225 billion, • industrial segment ∼ $110 billion, • residential market ∼ $25 billion

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Water

Wastewater

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• Total value - 224 billion €

Billion EURO

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- AAGR 16-20%

100 80

• Drinking water

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– doubling of market value

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• Wastewater largest segment

20 0

1998

1999

2000

2005

2015

– 43 % growth rate

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Market drivers Investigations of market trends have highlighted:

“The driving factor for the growth of this market is waster stress…”

• • • • •

need to recycle and reuse wastewater stricter environmental regulations worldwide new applications in the industry and new developments biosolids management and energy recovery sustainable wastewater management

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Global trends

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Anticipated growth rates Stipulated average annual growth rates Large regional difference China and Middle East key future markets

Region N. America Middle East Europe Asia Pacific China Japan Total

Annual growth (% / year) 15 % 25 % 10 % 10 % 20 % 10 % 20 %

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Examples of large MBR projects WWTP name Jumeirah Golf Estates Palm Jebel Ali Brightwater Jebel Ali Free Zone International City Guangzhou Kunyu River Johns Creek Beixiaohe Al-Ansab Peoria Lusail Qinghe Syndial

Location Commissioning Dubai Dubai USA Dubai Dubai China China USA China Oman USA Qatar China Italy

2010 2010 2010 2007 2007 2010 2007 2007 2007 2006 2007 2007 2007 2007

Capacity (m3/d) 220 000 220 000 144 000 140 000 110 000 100 000 100 000 93 500 80 000 78 000 75 700 60 200 60 000 47 300

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European trends

65 new refs/year

Total Municipal in Europe About 2 millions e.p (0.5% population) 45 new refs/year

30 new refs/year

(Lesjean et.al. 2009)

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MBRs, a proven technology! • Competitive for tertiary treatment requirements • BAT for wastewater reuse / recycling

Large scale installations

MBR

Retrofitting / upgrading Package plants

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Comparison of CAS - MBR

Investment cost, new and retrofitted WWTPs 1989 - 2006

Specific cost, EUR per PE

2000 1800

CAS

1600

CAS with tertiary treatment

1400

MBR

Investment costs

Cost function (all WWTPs)

1200 1000 800 600 400 200 0 0

10

20

30

40

50

60

70

Treatment Capacity, MLD

Erftverband, Germany, 2009

Energy consumption

80

90

100

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MBR in a nutshell

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If only membranes were membranes….

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If only bacteria were bacteria….

Filamentous Protozoa

Rotifers

Nematodes

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Key elements of the MBR process Feed characteristics Membrane module Composition of feed Treatment requirements

- pore size / surface properties

Module configuration

- Geometry / dimensions

Biological process Membrane process Biomass characteristics: - Floc structure - EPS (free/bound)

Membrane fouling:

- reversible / irreversible

Clogging:

Bulk characteristics:

- membrane channels - aeration system

- viscosity

Aeration Aerobic phase Mass transfer

- Hydraulic (HRT) - Solids (SRT)

Air scouring Cleaning

Hydraulics

Flux / TMP Fouling Cleaning

Operating parameters

Operating parameters

- Nutrient removal - End use of treated water

Retention times:

Main “bottlenecks”:

Membrane characteristics

• Fouling / sludging • Aeration (biology & membrane) • Operation / monitoring • Complete process configuration • Energy demands • Costs – market acceptance

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Fowled membranes……???

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Bottleneck - 1: Clogging Fouling of membrane channels and aeration systems; → increased aeration? → improved modules design? → improved pretreatment?

“Improved” aeration

=€

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Impact of improving sludging • Pretreatment • Improved module design • Operating conditions

Before

After

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Trends in aeration demands: Energy for: - pumping - aeration (biology / membranes)

Consequence: → design of aerators → module designs → operating modes (GE Zenon)

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Bottleneck – 2: Aeration in MBRs: • Membrane module operation – air scouring • Bioprocess operation – oxygen for aerobic degradation

Pre-treated wastewater

Anoxic

Aerobic

Permeate Sludge recirculation

Air

• Coarse bubbles - membrane operation • Fine bubbles - bioprocess operation

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Biological vs. membrane operation Biological needs: • • • • • • • • •

Objective: Oxygen transfer for aerobic degradation Practice: Fine bubble diffusers Challenge: Change in fluid viscosity Poorer masstransfer efficiencies, more energy High operating costs Change in biomass characteristics?

Membrane needs: • Objective: • Generate crossflow hydrodynamic conditions • Generate high shear stress on surface • Remove deposition on membrane surface • Practice: • Continuous aeration for air scouring • Intermittent aeration (on/off cycles) • Relaxation techniques (no production during aeration) • Challenge: • High specific aeration demands • High operating costs

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Aeration for aerobic biological processes: - Same fundamental Monod kinetics apply - Process must be designed for oxygen necessary to degrade both organic matter and to convert NH4 to NO2/NO3 as required - Determines oxygen transfer rate (OTR)

Challenge: - Parameters in OTR equation affected by high SS concentrations - Particularly viscosity and the α-factor - Correlations have been proposed where

MBR: CAS:

µ is viscosity (kg/(m s)) x is the correlation exponential

MLSS of 12 g/L → α-value of 0.6 MLSS of 3-5 g/L → α-value of 0.8

Consequence → higher aeration demand

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Is the biomass different in an MBR? Floc size

Boimass denisty

EPS density

Oxidation tank

Large Medium Small

Frequently loose

Lower

Membrane

Large Medium

Compact and dense

Higher

FISH analysis: • using general phylogenetic probes • using probes for specific functional groups

Beta-proteobacteria other Bacteria

Gamma-proteobacteria other Bacteria

(IBET, Portugal – EUROMBRA project)

Alpha-proteobacteria other Bacteria

FISH probes targeting Alpha-, Beta- and Gamma-proteobacteria covered ≈ 60-75%

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Bottleneck - 3: Fouling control / mitigation

MBR foulants

• polysaccharides • proteins

• colloids • filterability

Challenges: • Understand interaction biology – membranes • Identify major foulants • Strategies for fouling mitigation and control • Optimize operating conditions for minimal fouling • Cleaning of fouled control

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Main mechanisms and types of membrane fouling 1. Membrane resistance: RM

4/6

5

3

1 2

R = Rm + RF + RC + RG + ...

2. Adsorption / scaling: RF - reversible / irreversible 3. Pore blocking / plugging: RP 4. Cake formation: RC - dead-end operation 5. Concentration polarization: RG - formation of gel-layer 6. Biofouling – biofilm/EPS: RB

∆P J= ' Rm + Φ ⋅ ∆P

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Illustration of fouling development by particles:

Clean membranes Start phase;

→ cake formation

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- Fouling of MBRs - “Types” of fouling, how it behaves

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• How does bio-fouling (biofilm growth / EPS) behave on the membrane surface?

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Study biofilm growth Study fouling development CLSM analysis of biofouling Characterization

- green: signal from the membrane - red: fluorescent light from the lectin WGA, bound to the polysaccharides Nacetyl-glucosamine in the biofilm

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Understanding MBR fouling and mitigation: Fundamentals of membrane fouling •

EPS issues; polysaccharides vs. proteins, colloids?

Data acquisition, monitoring techniques • • • •

Online monitoring systems Fouling control and SMP sensor DFU – filtration characterization unit Advanced control systems (VITO)

Modeling • • •

Biological models Sludge production models CFD modeling and process development

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Bottleneck - 4: sustainable flux, operation costs Flux = f( hydraulics, aeration, module design, operating mode, feed) → → → →

increased crossflow conditions (aeration) module designs and choice of membrane material backwash/relaxation, cleaning strategies/protocols monitoring/analysis of feed Module geometry and aeration: • • • •

Bi-phasic CFD model for optimization of modules and filtration reactors Impact of module geometry on short and long term fouling behavior and filtration performance Impact of flow pattern and aeration mode on performances Enhanced mass transfer characteristics Acoustic Doppler velocimeter

CFD modeling - module design - geometry

+ verification

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CFD modeling of submerged MBR - System definitions - Numerical models

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- Influence of aeration mode - Influence of module design

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- Example of modeling a full-scale plant - Impact on flow using alternative mixing strategies

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Optimization of process configurations MBR with or without primary sedimentation? Submerged modules externally or directly in aerated reactor? Dual MBR/CAS for plant retrofitting? Turn-key standardized range of MBR/filtration units? How to best tackle peaks? (biology & filtration) Integrated hydrodynamics of membrane / biological system? Models as predicting tools + pilot- & large-scale validation

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Process improvement / retrofitting “Dual“ technology (= MBR-CAS hybrid) for plant retrofiting Based on full-scale Schilde CAS/MBR plant Flow distribution ?

4 g/l

Dual1

Dual2

? ?

10 g/l 15 g/l

??

(modelling, case scenario, full scale demo) Settleability ? (pilot study)

4-6 g/l 15 g/l

Cost evaluation

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So why choose MBR? • • • • • • • • •

More stringent regulations Advanced wastewater treatment Water scarcity / reuse Suited for retrofitting Reduced investment costs Potential for energy reduction Potential for improved solid waste management Market confidence / acceptance Steps towards standardization

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BF-MBR concept Concept:

Biofilm process

SCOD

→

Membrane process

PCOD

Process:

• One-step biological degradation – biological reactor configuration • Can use various biological reactor designs and concepts • Design membrane reactor for enhanced particle removal • Potential to maximize the treatment steps • Enhanced performance, i.e. fouling control in membrane reactor

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Advantages of BF-MBR over AS-MBR Potentials of the BF-MBR: Very low suspended solids concentrations in BF-MBR Improved handling of the colloidal fraction Control of solids retention time (SRT) Resulting in: 1. Alternative designs / operation of membrane filtration unit 2. Enhanced fouling control by air scouring / hydrodynamics 3. Less problems with membrane clogging and plugging 4. Great flexibility for the process design: biological location and hydrodynamic arrangement etc. 5. Low viscosity: i.e. lower energy demand for aeration 6. Higher membrane packing densities possible – more compact 7. Potentially less overall energy demand

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Identification of dominant foulants in BF-MBR • polysaccharides • proteins

• what is significant? • what dominates? • colloids • filterability

In BF-MBR results indicate that; • suspended solids and particulates appear to dominate • particularly the colloidal fraction is seen to impact performance • EPS/SMP nature has significance

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BF-MBR applied to municipal wastewater Pilot plant setup: Pre-treatment

Operating conditions: Biofilm reactor

Membrane reactor

Municipal wastewater

• varying organic loading rates • varying suspended solids loads • flux range: 35-60 LMH • varying aeration intensities • recoveries > 95%

Permeate

Aeration

Retentate

Treatment efficiencies:

Membrane performance: operation time (days) 0

1

2

3

4

5

6

7

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10

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15

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transmembrane pressure

% removal

0 -0,1 -0,2 -0,3 -0,4 -0,5

HRT = 4h HRT = 0h HRT = 1h

HRT = 3h

-0,6 TMP after backwash for different HRT in the bioflim reactor

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Investigation of identified foulants in BF-MBR 1. Suspended particles – MLSS - range > 1.2 µm Flux 35 LMH

2. Colloidal particles – PSD number % - range 0.04 -1.2 µm

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Developement strategies for BF-MBR (1) Development of membrane module / filtration unit:

• alternative filtration unit design / operation • integrated designs for enhanced particle removal / solids control Completely mixed reactor (CM-MR) → CM with sludge hopper (SH-MR) → modified SH-MR (MSH-MR) ?

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Performance of alternative membrane reactors General: • Separation factor (Ks) increased; CM-MR → SH-MR → MSH-MR • Fouling rate decreased drastically

Operation: • TMP as expression of fouling rate; CM-MR → SH-MR → MSH-MR • Lowest fouling rate for MSH-MR • Why?

MSP-MR SP-MR

CM-MR

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Impact of colloidal fraction on membrane filtration

Example of PSD analysis: • Zones in MSH-MR unit

Inlet

Reduction in colloidal fraction correlates with improved performance!

Conclusions: 1. In a BF-MBR the membrane reactor should be designed as an enhanced particle separation unit (focus on colloidal material) 2. Reactor design will affect composition of water around the membrane and thus fouling rates and overall performance

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Conclusions BF-MBR Potentials of BF-MBR New and flexible process configurations possible • • • • • •

Alternative strategy for solids control and management Reduction of colloidal material in membrane filtration unit Lower suspended solids load on membrane Minimal clogging/sludging problems Enhanced membrane performance / less fouling Lower energy requirements (overall)

Challenges of BF-MBR Understanding membrane fouling Process control and optimization System complexity and interdependence

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Where are MBRs now?

How long will it take to get from here…..

……. to there?

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Where is MBR development headed • A better understanding of fouling • mechanisms • interactions (biology/membranes)

• Improved membrane module designs • novel solutions • enhanced by CFD analysis

• Integrated systems • AS-MBR, biofilm-MBR, anaerobic-MBR • hybrid solutions

• More energy efficient • Improved robustness and life-time • Steps towards standardization

?

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www.mbr-network.eu

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The pessimist complains about the wind, the optimist expects it to change, the realist adjusts the sails… William Arthur Ward (1921-1994)