Professor Simon Judd

MBRs: the low down

www.cranfield.ac.uk

Bibliography2000

2003

2006

20112014

MBR principles

aeration

primarysedimentation

secondaryclarifier

screenedsewage

settled sewage

final effluen

t

raw/primarysludge

PRIMARYTREATMENT

SECONDARY TREATMENT(activated sludge)

TERTIARYTREATMENT(disinfection)

cellseparation

Conventional sewage treatmentclarified, largely disinfected product provided

small footprint plantlow sludge yield (0.35 – 0.6 Kg DS/Kg BOD)

bulking problems become less relevanthydraulic and solids retention time are uncoupledintensive biotreatment provided, esp. nitrification

Cl2

waste activatedsludge

return activated sludge

MBR process configurations

Air

InOut

Membrane

OutBioreactor

Recirculated stream

Air

In

PumpBioreactor

Membrane

immersed/submerged MBRsidestream MBR

Really expensive Expensive? ?

MBR process configurationsMBR technology

Immersed

Flat sheet Hollow fibre

Sidestream

Multitube/multichannel

Pumped

Classical Low energy

Aerated

Lift Injection

Municipal MunicipalIndustrial

mem

b-ra

ne

Industriall

MBR operational parametersKey parameters are

• operating fluxflux = permeate flow / membrane area

• transmembrane pressure (TMP)• permeability

• permeability = flux / TMP• membrane module aeration or crossflow velocity

• Specific aeration demand = aeration rate / membrane area

These are all inter-related and impact on cleaning

OPERATIONDE

SIGN

Cloggingmembranechannels

aeratorports

Foulingreversible irreversible

Biomass characteristicsBulk characteristics• viscosity/rheology• hydrophobicity

Feed characteristics

Membrane module characteristicsConfiguration• geometry• dimensions

Pore• size• shape

Surface characteristics• porosity• charge/hydrophobicity

Floc characteristics• size• structure

EPS• free• bound

Retention time• Hydraulic• Solids

Hydraulics• flux• TMP• Crossflow

Cleaning• physical• chemical

Aeration• design (port size)• mean flow rate• pulse rate

Hydraulics, hydrodynamics & fouling/cloggingAll interlinked:

• increasing flux increases fouling/clogging• increasing crossflow (promoting turbulence) increases flux

– but increases energy demandFouling also determined by:

• biomass characteristicsThis is in turn influenced by

• feedwater quality• retention times (hydraulic and solids)

Key design parameter is• critical/ sustainable flux• There is a limit to how far the design flux can be pushed

The membrane

Membrane process types

Reverse osmosis ULTRAFILTRATIONNanofiltration MICROFILTRATION

Depthfiltration(to >1mm)

10-10 10-9 10-8 10-7 10-6 10-5Scale in metres

Freeatoms

200 20,000 500,000Approximate Molecular Weight in Daltons

Smallorganic

monomers

Sugars

Herbicides

PesticidesDissolvedsalts

Endotoxins/pyrogens

Viruses

Colloids:Albumen proteinColloidal silica

Bacteria (to ~40µm)

Crypto-sporidia

Redbloodcells

Porous membranefiltration processes

Dense membraneprocesses

Electrodialysis

Material structureMay be isotropic, but often anisotropic (symmetry in one direction)

Membrane material

Membrane pore size trends• The seven PES membranes are offered exclusively as

FS and are all 150 kDa rated (~0.03 µm)• The two PE FS membranes are 0.4 µm and

hydrophilicised (by chemical oxidation)• The PP membranes are offered exclusively as HF and

have various pore sizes• The PVDF membranes cover a pore sizes of 0.01-0.4

µm and a range of HF diameters• Ceramic FS membranes are offered predominantly in

the 0.1-0.5 µm range

MBR membrane products – 70 off.Immersed (iMBR) Sidestream (sMBR)

Flat sheet Hollow fibre Multi-tube/multi-channel, polymerA3/MaxFlowDE Asahi Kasei - Microza JP Berghof - HyPerm-AE; HyperFluxDE

Alfa Laval - Hollow SheetSE CrefluxCN Pentair – CompactUS

Beijing IWHR - GyroreactorCN DehongCN MEMOS - MEMCROSSDE

BenenvCN Econity - KSMBRKR Xylem/PCI MembranesUS

Brightwater/Anua - MembrightIRL/PuraM® Evoqua - MemPulseUS

CerafloSG FeitianCN Multi-tube/multi-channel, ceramicEcologix - EcoPlateTN GE - ZeeWeed US Likuid NanotekSP

Huber - VRMDE H-Filtration - MRCN Veolia Water Systems – CeramemFR

ItNDE HinaCN SuntarCN

KorED, NeofilKR HinadaCN LiqTechDK

Kubota - ES/EKJP Hyflux - PorocepSG

Kubota - SPJP JiamiaoCN Flat sheetLantian PeierCN Jie FuCN ROCHEM - Bio-FILTUS

LiqTechDK KaiHongCN NovasepFR

Martin - siClaroDE KejiCN

MegaVisionCN Koch Membrane Systems - PURONUS Hollow fibreMeidenJP Kolon - CleanfilKR Polymem - IMMEMFR

Mann+Humme/MICRODYN-NADIR – BIO-CELDE Litree - LH3CN

newterra – MicroClearCA MEMOS - MEMSUBDE Flat discPure Envitech Co., Ltd. – ENVISKR Origin WaterCN Grundfos - BioBoosterDK

Pure Envitech Co., Ltd. – SBMKR United Envirotech/Memstar - SMMSG

QUA - EnviQUS MicronaCN

SINAPCN Mitsubishi Rayon - STERAPORE 5000JP

SupratecDE MohuaCN

Toray - MEMBRAYJP MotianCN

VinaCN Motimo - FP AIVCN

Ovivo - OVTM PhilosKR

Porous Fibers S.L. - Micronet SP

QiangshengCN

Sumitomo - Poreflon JP

Superstring MBR Tech. Co.Ltd - SuperUFCN

ZenaCZ

Flat sheet MBR membrane panels:• all vertically-oriented• almost all rectangular in shape• 1-1.5 m in height• 0.4-1 m in width• separated by 6-9 mm• single permeate extraction point

Membrane module dimensions:FS panels

FS stacks/cassettes/units

Alternative FS configurations

HF modules and cassettes

Hollow fibre MBR membranes are almost all:•vertically-oriented•outside diameter 0.4-2.8mm•predominantly PVDF•around 2 m high

MBR system suppliersFS• Ovivo • ADI• Busse• Kruger• Smith and Loveless• Sanitherm• Wigen• Hitachi• Memcon

HF• Layne

• Aquabio• Berghof• Dynatec• Triqua• Wehrle

MT

The process

Process components

Process componentsCategory Component(s) ID Description/purpose Tanks Raw water T1 Storage tank for inlet wastewater Primary sedimentation T2 Removal of gross, settleable solids Equalisation (EQ) T3 Equalisation of flow Anoxic (Ax) T4 Denitrification Aeration (Ae) T5 Nitrification and biological oxidation Membrane T6 Membrane separation Treated water T7 Storage of permeate water Sludge T8 Storage of wasted sludge Chemicals storage T9,10 Pumps Settled sludge transfer P1 Submerged, settled sludge to sludge storage

tank Feed P2 EQ tank through rotary screen Permeate P3 Self-priming, membrane suction filtration Sludge return/discharge P4 Submerged, sludge recirculation and excess Sludge transfer P5 WAS to dewatering Chemicals P6,7 Cleaning chemicals transfer to membrane, x2 Blower Process B1 Biological process aeration Membrane B2 Membrane scouring Mixer EQ tank mixer X1 High speed, equalisation tank Ax tank mixer X2 Low speed, anoxic tank Screen Rotary screen S1 Fine screening of feed Membrane Membrane module M1 FS membrane plus frame with built-in aerator Diffusers Fine bubble diffuser D1 Process aeration Coarse bubble diffuser D2 Membrane aeration

Aeration

AIRNitrate-enriched sludge

Feed Treated water

fine bubble

AIRcoarse bubble

Membrane cleaning, UF/MF

Chemical

ACIDSHydrochloric/sulphuric

Citric/Oxalic

BASECaustic soda

OXIDANTHypochlorite

Hydrogen peroxide

Physical

BACKFLUSHING•with air•without air

RELAXATION

CHEMICALLYENHANCED BACKWASH

CEBCIP

Fouling and cleaning

Flocculant solids normally readily removed by physical cleaningSolutes and colloidal matter more tenaciousFouling exacerbated by:

• high fluxes• low shear• infrequent cleaning

Reversible fouling and irreversible fouling

Irreversible fouling

New membrane Irrecoverable fouling

Initial filtration

Long-term filtration

Physical cleaning

Chem

ical cleaning

Sludge flocs Colloids Solutes

MBR vs CAS

backflushY Y

Bioreactor Clarification Membrane

Feed Effluent

backflushY

Bioreactor Membrane

Feed Effluent

CAS with polishing:

MBR:

Removal data for 29 pharmas

~HALF THE CONCENTRATION

FROM AN MBR CF. CAS

Concentration data for 7 metals

~HALF THE CONCENTRATIONFROM AN MBR CF. CAS

$$$

Capital costYoung et al, 2012

• MBR CAPEX lower for enhanced nutrient removal and water reuse applications

• Result is the same for cold climates, warm climates, with primary clarification, and for plants with high peaking factors

TSS < 20BOD < 20NH3-N < 1Temp 12°CPeak 2X

Case 1 &TN < 10

TSS < 10BOD < 10NH3-N < 1TN < 10TP < 0.2Temp 12°CPeak 2X

Case 3 withPrimary Clarifier

Case 3 withTmin 25°C

Case 3 withPeak 4X

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6

by kind permission of GE

CAPEX, MBR vs. CAS, Germany Brepols et al, 2010

CAPEX, MBR vs oxidation ditchItokawa et al, 2014 (Japanese Sewage Works Agency)

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

Design capacity [m3/d]

Con

stru

ctio

n co

st [1

03 JP

Y/(m

3 /d)]

MBR (whole plant)

MBR (wastewater treatment)

OD plant

OD plant with sand filtration

Specific energy demand, Germany Brepols et al, 2010

Specific energy demand, Japan Itokawa et al, 2014 (Japanese Sewage Works Agency)

0

1

2

3

4

5

6

7

8

9

10

0 10 20 30 40 50 60 70 80 90 100

Inflow/capacity ratio [%]

Spe

cific

ene

rgy

cons

umpt

ion

[kW

h/m

3 ]

Moryamaintermittentoperation

Moryama plant, JSWAItokawa et al, 2011*

• System configuration• UCT process with FS membrane units submerged in the aerobic tank.• Several energy saving measures incorporated.

*Original figure taken from “Guidelines for Introducing Membrane, Technology in Sewage Works: The 2nd Edition”, MLIT, 2011.

Membrane units for large-scale MBRs.

Siphon filtration

Air-lift pumps for internal circulation.

Low speed mixers.

HF FS

Specific energy demand, Ovivo

0 20 40 60 80 100 1200.00

0.50

1.00

1.50

2.00

2.50

% design flow

SED

kW

h/m

3Specific energy demand, SpainGabarrón et al, 2014

HF

FS

Operating costYoung et al, 2013

• MBR OPEX is higher for all cases

• Differences mostly attributed to power, chemical, and membrane replacement

• Membrane replacement is responsible for a relatively small portion of the NPV

TSS < 20BOD < 20NH3-N < 1Temp 12°CPeak 2X

Case 1 &TN < 10

TSS < 10BOD < 10NH3-N < 1TN < 10TP < 0.2Temp 12°CPeak 2X

Case 3 withPrimary Clarifier

Case 3 withTmin 25°C

Case 3 withPeak 4X

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6

by kind permission of GE

Life cycle cost (CAPEX + OPEX)Young et al, 2013

• Life cycle cost is lower for MBR compared to CAS for enhanced nutrient removal and water reuse applications

• Lower CAPEX for MBR is off-set by higher OPEX

TSS < 20BOD < 20NH3-N < 1Temp 12°CPeak 2X

Case 1 &TN < 10

TSS < 10BOD < 10NH3-N < 1TN < 10TP < 0.2Temp 12°CPeak 2X

Case 3 withPrimary Clarifier

Case 3 withTmin 25°C

Case 3 withPeak 4X

Case 1 Case 2 Case 3 Case 4 Case 5 Case 6

by kind permission of GE

CAPEX & OPEX comparison

Costs: summary• MBR can be more cost-effective than CAS

depending on design and treated water quality required.

• MBR is more cost-effective than CAS when tertiary treatment with membranes is required.

• Cost breakdown, based on same effluent WQ for published studies:• OPEX higher for MBR

• this isn’t always necessarily the case• CAPEX lower for MBR• Lower life cycle costs

• CAS usually more cost-effective than MBR if tertiary treatment is not required, depending on design

• Critical membrane life for cost neutrality for NPV analysis

43

GE Water & Process Technologies

Survey

The MBR Survey (186 responses)• Q1 What is the main technical problem that prevents MBRs

working as they should?

16%

16%

12%11%10%8%

8%

6%5% 5% 4%

Screening/pre-treatmentMembrane surface foulingOperator knowledgeEnergy demandMembrane/aerator cloggingSludge/mixed liquor qualityMembrane chemical cleaningOverloading/under-designUneven aerationOther/CommentsAutomation/control, or software

The MBR Survey (186 responses)• Q1 What is the main technical problem that prevents MBRs

working as they should?

16%10%

6%

16%

4%

8%11%

12%

8%5% 5%

Screening/pre-treatmentMembrane/aerator cloggingOverloading/under-designMembrane surface foulingAutomation/control, or softwareMembrane chemical cleaning

The MBR Survey, Q1

0%

5%

10%

15%

20%

25%

Mar-10 Feb-12 Feb-15

The MBR Survey, Q2• Q2 How will MBR

technology develop in the future?

energy/power

cost

fouling

membrane materials

automation & control

potable/drinking

robustness

awareness/perception/acceptance

nutrient

pretreatment/screening/clogging

0 5 10 15 20 25 30 35 40 45 5048

3227

1716

141313

1010

99

888

666

55

Survey of 214 plants (Ovivo)• Electrical 6• Membrane CIP 12• Mechanical piping/design 14• Fine screening 14• Control valves 26• Instrumentation 27• Ancillary equipment 103• Process condition 111• Integration and controls 187

possibly membranes related

95% of mbr issues do not relate to the membrane

An academic’s view• Word cloud of keywords of all published MBR wastewater papers, 1990-

2009• Analysis of the SCOPUS database using Wordle• Common/generic words excluded

Past, present ..

THAT WAS THEN: PORLOCKFirst municipal MBR (1997)

• 1.9 MLDManual aerator flushingNo separate membrane tank

• coarse-bubble aeration onlyUp to 14 years membrane life>2 kWh/m3 (MBR only)

THIS IS NOWBigger plants:

• 9 MBRs of >100 MLD peak daily flow capacity

Better plants• Improved membranes and

membrane technology• Effective pretreatment• More efficient membrane air

scouring• Smarter, more holistic design• <0.5 kWh/m3

… and future?Further improvements/cost reductions in design and operation:

• Aeration efficiencies improving• Continued smart design and operation

• automation, real time data capture and processing• Cinder blocks and ceramic membranes

Direct potable reuse• Technically possible and already happening in some places

Game changers:• Complete standardisation (as in RO and other crossflow systems) • Complete energy and resource recovery

• immersed anaerobic MBRs with nutrient removalFind out more (for free) at www.thembrsite.com