The Potential of Membrane Bioreactors for The Potential of Membrane Bioreactors for

Wastewater TreatmentWastewater Treatment

11Laboratory of Sanitary EngineeringLaboratory of Sanitary EngineeringSchool of Civil Engineering School of Civil Engineering

National Technical University of AthensNational Technical University of Athens

11stst International Conference on Sustainable International Conference on Sustainable Urban Wastewater Treatment and Reuse Urban Wastewater Treatment and Reuse

Nicosia 15-16Nicosia 15-16thth September 2005 September 2005

S. MalamisS. Malamis11, A. Andreadakis, A. Andreadakis11 & D. Mamais & D. Mamais11

Presentation Aim & Layout Presentation Aim & Layout AimsAims

• To assess the feasibility of Membrane To assess the feasibility of Membrane Bioreactors (MBR) in GreeceBioreactors (MBR) in Greece

• To examine state-of-the-art research in the To examine state-of-the-art research in the field of secondary treatment of municipal field of secondary treatment of municipal wastewater using MBR technologywastewater using MBR technology

LayoutLayout• Basics on MBR for wastewater treatmentBasics on MBR for wastewater treatment• Examination of two full-scale MBR applicationsExamination of two full-scale MBR applications• Adoption of MBR technology in Greece Adoption of MBR technology in Greece • State-of-the-art research State-of-the-art research

Basics on MBR Basics on MBR Employ biological reactor and Employ biological reactor and

membrane filtration as a unified membrane filtration as a unified system for the secondary treatment system for the secondary treatment of wastewaterof wastewater

Membranes perform the separation Membranes perform the separation of the final effluent from the biomass of the final effluent from the biomass through filtration through filtration

Filtration takes place by the Filtration takes place by the application of a pressure gradient application of a pressure gradient

Process BasicsProcess Basics

SS

Deni NitriSS

SCT

discharge

conventional technologymembrane technology

NDN

effluentUF notSec. Clarif.

Process BasicsProcess Basics

membranewater

suction

dis. solids

sludge floc

viruses

bacteriakinet. energy

Re-circulation

Feed

SS

Submerged MBR SystemSubmerged MBR System

Cleaningchemicals

Module Back pulse

BP Tank

effluent

Permeate

ZeeWeedAeration

aeration

Assessment of MBR TechnologyAssessment of MBR Technology

AdvantagesAdvantages• High effluent quality High effluent quality • No sludge settling problems No sludge settling problems • Reduced volume requirements Reduced volume requirements

DisadvantagesDisadvantages• Membrane fouling Membrane fouling • Increased operational costsIncreased operational costs

Full-Scale WWTP in Germany (1)Full-Scale WWTP in Germany (1)

P.E. = 80,000 Largest P.E. = 80,000 Largest MBR full-scale MBR full-scale installation in the world installation in the world

4 parallel 4 parallel biological biological reactors:reactors:• Anoxic zoneAnoxic zone• Swing zoneSwing zone• Aerobic zone with Aerobic zone with

immersed membranesimmersed membranes SRT = 25 days SRT = 25 days MLSS = 10-15 g/lMLSS = 10-15 g/l 192 cassettes (8 192 cassettes (8

parallel trains) parallel trains) Total filtration area = Total filtration area =

84,480m84,480m22

Full-Scale WWTP in Germany (2)Full-Scale WWTP in Germany (2)

Parameter Parameter Final Effluent Final Effluent

SS (mg/l)SS (mg/l) Non detectable Non detectable

CODCOD (mg/l)(mg/l) 15-20 15-20

BODBOD55 (mg/l) (mg/l) <3 <3

NHNH44++-N (mg/l)-N (mg/l) <1<1

TN (mg/l)TN (mg/l) 5-105-10

TP (mg/l)TP (mg/l) 0.70.7

Total Coliforms / 100 ml Total Coliforms / 100 ml <100<100

Fecal Coliforms /2000 mlFecal Coliforms /2000 ml <500<500

Salmonella /1000 mlSalmonella /1000 ml 00

Final Effluent disposed to a sensitive river Final Effluent disposed to a sensitive river

Full-Scale WWTP in Italy (1)Full-Scale WWTP in Italy (1)

Consists of 3 parallel lines Consists of 3 parallel lines • Lines A & C: Conventional Lines Lines A & C: Conventional Lines • Line B: Upgraded from conventional to MBR system Line B: Upgraded from conventional to MBR system

Total P.E. = 380,000Total P.E. = 380,000 Upgrading of Line B to MBR increased its capacity from 12,200 mUpgrading of Line B to MBR increased its capacity from 12,200 m33/d to 42,000 m/d to 42,000 m33/d within the same /d within the same

space space MLSS = 6.5-10 g/l MLSS = 6.5-10 g/l SRT > 20 d SRT > 20 d

Full-Scale WWTP in Italy (2)Full-Scale WWTP in Italy (2)Parameter Parameter MBR EffluentMBR Effluent

mg/l (%)mg/l (%)Conventional Conventional

Effluent Effluent

mg/l (%)mg/l (%)

SS (mg/l)SS (mg/l) <2 (99)<2 (99) 25 (73.2)25 (73.2)

BODBOD5 5 (mg/l)(mg/l) 4 (95.8)4 (95.8) 19 (82.3)19 (82.3)

COD (mg/l)COD (mg/l) 27 (88.5)27 (88.5) 66 (77.2)66 (77.2)

TN (mg/l)TN (mg/l) 9.2 (73.7)9.2 (73.7) 15.9 (54.5)15.9 (54.5)

TP (mg/l)TP (mg/l) 2.4 (36.1)2.4 (36.1) 3.4 (8.6)3.4 (8.6)

Conclusions from the examination Conclusions from the examination of full-scale installations (1)of full-scale installations (1)

Full-scale MBR provide a superior effluent quality Full-scale MBR provide a superior effluent quality compared to conventional methodscompared to conventional methods

The final effluent can meet the requirements of the The final effluent can meet the requirements of the

Urban Wastewater Directive 91/271/EEC even for Urban Wastewater Directive 91/271/EEC even for P.E. >100,000 with disposal to sensitive recipients P.E. >100,000 with disposal to sensitive recipients (TN <10 mg/l, TP < 1mg/l)(TN <10 mg/l, TP < 1mg/l)

Final effluent conforms to the microbiological Final effluent conforms to the microbiological requirements for bathing waters (Directive requirements for bathing waters (Directive 76/160/EEC), without the need for further 76/160/EEC), without the need for further disinfection with chlorine or ozonedisinfection with chlorine or ozone

Conclusions from the examination Conclusions from the examination of full-scale installations (1)of full-scale installations (1)

Enhance reuse options of secondary Enhance reuse options of secondary effluent effluent

However:However: the stricter microbiological criteria for the stricter microbiological criteria for

agricultural reuse are not met and further agricultural reuse are not met and further disinfection is requireddisinfection is required

Main barrier to their wider full-scale Main barrier to their wider full-scale adoption is the high operational cost and adoption is the high operational cost and the lack of economies of scale the lack of economies of scale

Adoption of full-scale MBR in GreeceAdoption of full-scale MBR in Greece

Currently there is no full-scale MBR systemCurrently there is no full-scale MBR system

It is an attractive solution for arid and semi-It is an attractive solution for arid and semi-arid regions and islands characterized by:arid regions and islands characterized by:• Water scarcityWater scarcity• Small/Medium P.E.Small/Medium P.E.• Coastal zones and seas of high aesthetic value Coastal zones and seas of high aesthetic value • Limited land availability Limited land availability • Large seasonal changes in populations Large seasonal changes in populations

State-of-the-art Research State-of-the-art Research

MBR technology has resulted in MBR technology has resulted in multidiscipline research, since it multidiscipline research, since it brings together the topics of system brings together the topics of system design and construction, design and construction, hydrodynamics, chemistry and hydrodynamics, chemistry and microbiology.microbiology.

This work focuses on the topics of:This work focuses on the topics of:• Membrane foulingMembrane fouling• System microbiology System microbiology

Membrane Fouling (1) Membrane Fouling (1)

Biofouling is the dominant type of Biofouling is the dominant type of membrane fouling in MBRs membrane fouling in MBRs

Definition: Definition: the undesirable deposition the undesirable deposition and accumulation of microorganisms, and accumulation of microorganisms, EPS and cell debrisEPS and cell debris

Main operating problem impeding Main operating problem impeding the widespread adoption of MBR to the widespread adoption of MBR to full-scale plantsfull-scale plants

Membrane Fouling (2)Membrane Fouling (2) Biofilm develops due to the following Biofilm develops due to the following

mechanisms: mechanisms: • Adsorption of macromolecules Adsorption of macromolecules • Adhesion of micro-molecules which are Adhesion of micro-molecules which are

easily attached from the liquid under easily attached from the liquid under suspension to the membrane’s surfacesuspension to the membrane’s surface

• Creation of colonies and growth of Creation of colonies and growth of micro-organisms on and within the micro-organisms on and within the biofilm biofilm

• Detachment mechanisms attributed Detachment mechanisms attributed mainly to shear forcesmainly to shear forces

Main Parameters Influencing FoulingMain Parameters Influencing Fouling (3) (3) Membrane parameters Membrane parameters

• ConfigurationConfiguration• MaterialMaterial• Pore SizePore Size• HydrophobicityHydrophobicity

Operating Parameters Operating Parameters • HRT/SRTHRT/SRT• Aeration system Aeration system • TMP and flux TMP and flux

Biomass Biomass characteristics characteristics • EPS EPS • SMPSMP• MLSSMLSS

The degree of influence of The degree of influence of each biomass each biomass characteristic varies characteristic varies depending on the operating depending on the operating conditions and particularly conditions and particularly SRTSRT

Research is often Research is often contradictorycontradictory

No universally adopted No universally adopted relationships relating relationships relating fouling to its main fouling to its main influencing parameters influencing parameters

Promising research areas related to Promising research areas related to membrane fouling (4) membrane fouling (4)

Modeling the development of biofilm (determining Modeling the development of biofilm (determining thickness, concentration gradient of nutrients and thickness, concentration gradient of nutrients and DO etc)DO etc)

Derive relationships describing the degree of fouling Derive relationships describing the degree of fouling with respect to operating and biomass with respect to operating and biomass characteristics characteristics

The ultimate goal is to model long-term fouling The ultimate goal is to model long-term fouling

Examination of the influence of certain Examination of the influence of certain additives (alum, zeolite, activated carbon) additives (alum, zeolite, activated carbon) on foulingon fouling

System Microbiology (1)System Microbiology (1) Sludge FilterabilitySludge Filterability

• Impacts on filtration and fouling Impacts on filtration and fouling • Improved sludge filterability retards the Improved sludge filterability retards the

degree of fouling and thus prolongs the life of degree of fouling and thus prolongs the life of the membranethe membrane

Biomass characteristics Biomass characteristics • MBR produce 20-50% less sludge than MBR produce 20-50% less sludge than

conventional systems as they operate at higher conventional systems as they operate at higher SRTSRT

• Floc size depends on the SRT value and on the Floc size depends on the SRT value and on the MBR configurationMBR configuration

• Presence of small flocs, single cells and freePresence of small flocs, single cells and free--swimming bacteriaswimming bacteria

• Filamentous micro-organisms are favored Filamentous micro-organisms are favored (absence of FST, low F/M ratios)(absence of FST, low F/M ratios)

System Microbiology (2) System Microbiology (2)

Organic & nutrient removal Organic & nutrient removal • Examined extensively through pilot-Examined extensively through pilot-

plants and bench-scale experiments plants and bench-scale experiments • Innovative processes have been tested Innovative processes have been tested

(e.g. use of a single reactor for (e.g. use of a single reactor for simultaneous nitr-denitr by maintaining simultaneous nitr-denitr by maintaining the DO level at 1mg/l) the DO level at 1mg/l)

0

10

20

30

40

50

60

70

80

75-80 80-85 85-90 90-95 95-97,5 97,5-100Removal Efficiency (%)

Fre

quen

ncy

of O

ccur

renc

e (

%)

COD BOD5 NH4-N

0

5

10

15

20

25

30

35

50-60 60-70 70-80 80-85 85-90 90-95 95-100Removal Efficiency (%)

Fre

quen

cy o

f O

ccur

renc

e (

%)

TN ΤP

Promising research areas related to Promising research areas related to microbiology (4)microbiology (4)

Extensive analysis of the microbiology Extensive analysis of the microbiology and physiology of micro-organisms which and physiology of micro-organisms which develop both in the liquid under develop both in the liquid under suspension and on the membrane suspension and on the membrane surface. Examination of the differences in surface. Examination of the differences in the microbial populations the microbial populations

Determine the influence of certain Determine the influence of certain factors (e.g. pH, organic loading, SRT) on factors (e.g. pH, organic loading, SRT) on filterability filterability

Conclusions Conclusions

MBR technology is compatible with Greek MBR technology is compatible with Greek needs of wastewater treatment needs of wastewater treatment

Promising research themes: Promising research themes: • Develop model that will predict long-term Develop model that will predict long-term

fouling fouling • Find cost effective additives which can Find cost effective additives which can

reduce fouling reduce fouling • Determine the operating factors which affect Determine the operating factors which affect

filterability filterability • Extensive microscopic analysis of the Extensive microscopic analysis of the

biomass biomass