Post on 16-Apr-2017
aeration
primary sedimentation
secondary clarifier
screened sewage
settled sewage
final effluent
raw/primary sludge
PRIMARY TREATMENT
SECONDARY TREATMENT (activated sludge)
TERTIARY TREATMENT (disinfection)
cell separation
Conventional sewage treatment clarified, largely disinfected product provided
small footprint plant low sludge yield (0.35 – 0.6 Kg DS/Kg BOD)
bulking problems become less relevant hydraulic and solids retention time are uncoupled intensive biotreatment provided, esp. nitrification
Cl2
waste activated sludge
return activated sludge
MBR process configurations
Air
In
Out
Membrane
Out
Bioreactor
Recirculated stream
Air
In
Pump
Bioreactor
Membrane
immersed/submerged MBR sidestream MBR
Really expensive Expensive ? ?
MBR process configurations
MBR technology
Immersed Flat
sheet Hollow fibre
Sidestream
Multitube/multichannel
Pumped
Classical Low energy
Aerated
Lift Injection
Municipal Municipal Industriall
mem
b-
rane
Industriall
QR
MBR operational parameters
Permeate flow (Q)
Area (A)
Flux Flow per unit area per unit time
L/m2/h, or LMH
P1
P2
Transmembrane pressure TMP (bar) = P1-P2
Permeability Flux per unit TMP
LMH/bar
Aeration (Qa)
Specific aeration demand SADp = Qa/Q
Q
Hydraulics, hydrodynamics & fouling/clogging
• All interlinked: • increasing flux increases fouling/clogging • increasing crossflow (promoting
turbulence) increases flux – but increases energy demand
• Fouling also determined by: • biomass characteristics
• This is in turn influenced by • feedwater quality • retention times (hydraulic/lids)
• Key design parameter is: • critical/ sustainable flux
• There is a limit to how high the flux can be pushed
Permeability loss
Permeability decline Fouling
Coating of membrane surface
Reversible Physically removed by backflushing or
relaxation
Irreversible Removed by
chemical cleaning
Clogging Agglomeration of solids
Sludging Filling of
membrane channels
Ragging/braiding Blocking of
membrane channel inlets
Membrane process types
10-10 10-9 10-8 10-7 10-6 10-5 Scale in metres
Free atoms
200 20,000 500,000 Approximate Molecular Weight in Daltons
Small organic
monomers
Sugars
Herbicides
Pesticides
Dissolved salts
Endotoxins/ pyrogens
Viruses
Colloids: Albumen protein Colloidal silica
Bacteria (to ~40µm)
Crypto- sporidia
Red blood cells
Porous membrane filtration processes
Dense membrane processes
Electrodialysis
MBR membrane configurations
Three types: flat sheet (FS) hollow fibre (HF) multitube (MT)
• multichannel
flat sheet
multitube hollow fibre
Sidestream MBRs: advantages
• Reduced membrane area requirement (higher fluxes) • Fouling controlled by crossflow velocity (CFV)
• between 2 and 4 m/s CFV applied in practice complete flexibility for both operation and CIP cycle • In-situ chemical cleaning of membranes possible without
any chemical risk to biomass. • Maintenance and plant downtime costs, particularly for
membrane module replacement, generally slightly lower: • modules readily accessible • can be replaced in ~30 minutes • can be readily brought on and off line according to
hydraulic loading • Operation at higher MLSS levels possible, cf. HF iMBRs. • Operation at slightly lower energy demand possible if
• CFV and TMP are reduced • Air-lift/injection is employed
The 2015 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% 4% 4% Screening/pre-treatment
Membrane surface fouling
Operator knowledge
Energy demand
Membrane/aerator clogging
Sludge/mixed liquor quality
Membrane chemical cleaning
Overloading/under-design
Uneven aeration
Other/Comments
Automation/control, or software
Q2 How will MBR technology develop in the future?
48 32
27 17
16 14
13 13
10 10
9 9
8 8 8
6 6 6
5 5
0 5 10 15 20 25 30 35 40 45 50
energy/power reuse/recycle
cost industrial
fouling footprint/compactness
membrane materials aeration/air scour
automation & control municipal
potable/drinking membrane life
robustness anaerobic
awareness/perception/acceptance decentralisation
nutrient optimisation
pretreatment/screening/clogging legislation/regulation
The 2015 MBR Survey (186 responses)