Membrane Processes
• 두 마리의 토끼
– 소독에 내성이 강한 수인성 미생물의 제거
– 소독부산물 생성의 최소화
 고도정수처리의 도입
• 미국의 예
– 강화된 법령: LT2ESWTR
– Long Term 2 Enhanced Surface Water Treatment Rule (지표수
처리개선 장기 2차 규칙)
– 원수에 따라 강화된 크립토스포리디움 제거율 적용
– 막여과를 크립토스포리디움 제거를 위한 TT(treatment technology,
처리기술)로 규정
내염소성 원충: Giardia, Cryptosporidium
크립토스포리디움 - 1994년 밀워키 사건
Giardia
Cryptosporidium
막여과 기술 도입의 필요성
기존 정수처리공정의 병원성미생물 제어상 문제점
응집제
모래여과
응집
침전
Cl2
병원성 미생물에 대한 모래여과 공정의 개연성
소독제(염소)에 대한 원생동물의 내성
소독부산물에 대한 수질기준 강화
원생동물의 완벽한 제거
소독제 사용량 저감
Membrane Process
A thin film acting as a selective barrier
Microfiltration
0.1 to 10 m
Bacteria, Fine Solids
Ultrafiltration
0.01 to 0.1 m
Colloids, Macromolecules
Nanofiltration
0.001 to 0.01 m
Sugars, hardness, SOC, NOM
Reverse Osmosis
0.0001 to 0.001 m
Salts, metal ions
Water
Membrane Process
A thin film acting as a selective barrier
Pore size
(m)
정밀여과 0.01~10
한외여과
MWCO
(Da)
TMP(kPa)
<200
나노여과
1000300,000
350-1000
200~500
500~4000
역삼투막
~350
4000~100000
Membrane Process Application Guide
.001 m
.01 m
Dissolved
Organics
Salts
1.0 m
0.1 m
10 m
100  m
Bacteria
1,000 m
Sand
Viruses
Colloids
*Media Filtration (size
exclusion)
Microfiltration (size exclusion)
Ultrafiltration (size exclusion)
Nanofiltration (size and diffusion)
Reverse Osmosis (size and diffusion)
*Media filtration (not a membrane process) is shown for reference only.
*Electrodialysis removes only ionic species
Low-Pressure Membranes:
Microfiltration & Ultrafiltration
• Driving force: pressure difference between
membrane (TMP, transmembrane pressure)
•
•
•
•
Main removal mechanism: mechanical sieving
Pore size: 0.1 to 0.01 micron
Filtration of particles and some NOM
Disinfection by removal of microorganisms
막모듈의 분류
• 수납방식에 따라
– 가압식
– 침지식
• 모듈형태에 따라
– 중공사형, 평막형, 관형, 나권형
• 막여과방식에 따라
– Dead-end filtration(전량여과)
– Crossflow filtration(십자형여과)
Cased or immersed membrane system
•
Cased System
(Positive pressure)
•
Immersed System
(Vacuum pressure)
Membrane Modules
•
•
•
•
Plate and frame module
Hollow fiber module
Tubular
Spiral wound
Typical RO/NF
Spiral Wound
Configurations
Dead-end mode
Feed
Filtrate
Cross-flow mode
Feed
Concentrate
Filtrate
Typical MF/UF
Hollow Fiber
Configurations
Inside-out flow
Outside-in flow
Outside-in flow
Filtrate
Filtrate
Raw
Positive
pressure
Raw
Filtrate
Raw
Positive
pressure
Raw
Filtrate
Vacuum pressure
Filtrate
Typical MF/UF Membrane Process
Raw Water
Source
MF/UF
Filtered
Water
Type 1 : MF/UF - alone
Raw Water
Source
Coag/Floc
MF/UF
Filtered
Water
Type 2 : Pretreatment (Chemical Addition) + MF/UF
Raw Water
Source
Coag/Floc/Sed
MF/UF
Filtered
Water
Type 3 : Pretreatment (Chemical Addition w/ Sedimentation) + MF/UF
Raw Water
Source
MF/UF
RO/NF
or GAC
Type 4 : MF/UF + Post-treatment
Filtered
Water
Membrane Flux
• Definition
– Water permeability
– Darcy’s Law
초기의 깨끗한 막
P
Jo 
  Rm ( t)
운전이 진행된 후
P   k 
J
{Rm ( t)  Rc [ c ( t),]  R cp (D, J)}

Microfiltration
Pressure gauge
Coagulation reactor
Membrane Pressure
Konkuk University
Safety valve
Nitrogen gas Magnetic stirrer
=1.25psi
Data collection
Solution
reservoir
Permeate
Dead-end module

공극 0.2㎛, 막면적 32.17cm2, PS계열의 친수성 평막모듈

역세압: 2.5psi, 산세정: 0.1N HNO3, 염세정: 0.1M NaOH
Balance
Membrane Flux
P
Jo 
  Rm ( t)
예) TMP= 약 10 kPa, 초기 플럭스: 800 L/M2/h
물의 점성계수: 1.009*10-3 N-s/m2 (Pa-s)
 막자체 저항값은?
Membrane Operation
permeate flux (L/m2/hr)
1600
reversible
1400
irreversible
(fouling)
1200
1000
800
600
400
backwash
200
0
0
20
40
60
minutes
Source: Joel Mallevialle, Peter E. Odendaal, Mark R. Wiesner,
Water Treatment Membrane Process, McGraw Hill, 1996
80
Membrane operation
Concentrate
Macromolecules
Particle
Membrane
Pore
Permeate
Pore blocking
Concentration polarization layer
Cake formation layer
NOM adsorption
Fouling
•
•
•
•
Particle fouling
Organic fouling
Inorganic fouling
Biofouling
Membrane fouling
• Pore size: 100kD Molecular Weight Cut-Off (MWCO)
• Material: Polyethersulfone
Clean membrane
Fouled membrane
Inorganic Fouling - SEM
Precipitation
Problem Identification
• Fouling in membrane processes
Reduce water flux
Frequent shut down for cleaning
Termination of operation
• Major foulants
NOM
Particles
 Pretreatment
Integrity Test
• 막파손 가능
• 일반적인 분석방법(예, 탁도)으로는
수질변화는 미미함
• 문제가 생기기 전에 파손을 알아내는 방법
필요
• Direct:압력 변화 측정
• Indirect: 민감한 수질자료