Advanced Treatment by Membrane Processes

Transcription

1 Advanced Treatment by Membrane Processes presented by Department of Hydraulic and Environmental Engineering 1

2 Fundamentals of membrane technology Definition: A membrane is a permselective barrier, or interface between two phases, and the separation process takes place due to a specific driving force transporting a compound through the membrane from the one phase to the other Phase 1: membrane Phase 2: Feed Permeate Mass transport: 1. Through phase 1 2. Across the membrane 3. Through phase 2 Driving force; C, P, T, E 2

3 Classifying membranes: Membrane Classes Hydrophilic Organic (Polymeric) Hydrophobic Inorganic (Ceramic, metal) Etc. Microporous Etc. Dense / composite "Liquid carrier" Biological Etc. Etc. Based on; material structure / morphology properties / characteristics 3

4 Membrane polymers: 4

5 Membrane definitions: Filtration Spectrum 5 (OSMONICS)

6 Membrane classification: RO NF UF MF Conventional filtration Angstroms Microns Ionic range Macromolecular range Micron particle Fine particle RO rejection of ions/solutes (< 20 Å pore size) NF rejection of ions/solutes (< Å) UF defined by MWCO ( Å) MF colloidal suspensions ( µm) 6

7 Separation characteristics: MF UF NF RO Suspended particles Macromolecules Sugars Divalent salts Dissociated acids Monovalent salts Undissociated acids Water 7

8 Typical membrane module configurations: Plate and Frame (sheets) Spiral wound Tubular Hollow fiber Fabrics 8

9 Mass transfer through a porous membrane: Flow through a theoretical cylindrical (Hagen-Poiseuille equation) 2 π P d q = 128 µ x P - pressure d - pore diamter µ - viscosity x - membrane thickness Flux: J = N p q A and N p A d J d 2 2 In general: J 2 ε rp P = 8 µτ x ε - porosity r p - pore radius τ - tortuosity 9

10 Defining flux:? porosity / tortuosity f (membrane properties) Symmetrical cylinders Packed bed of spheres Asymmetric / sponge like Resistance model: P J = R J ' where R = RC + Rm 10 R C R m

11 Modes of operation: Dead-end Crossflow P time R c J time J R c 11

12 Defining resistance to mass transfer: 1. Membrane resistance R M : - determined by clean water flux 2. Fouling resistance R F : - reversible / irreversible 3. Cake-layer resistance R C : - dead-end operation 4. Concentration polarization R G : - formation of a gel-layer 12 R= Rm + RF + RC + RG +... Intrinsic membrane resistance: J = R ' m R = R + R P +Φ P ' m m F

13 Typical performance results: RO NF UF MF Monovalent ions Divalent ions > 98 % > 99 % < 50 % > 90 % Microsolutes (MW > 100) Microsolutes (MW < 100) > 90 % 0-99 % > 50 % 0-59 % < 50 % Bacteria and viruses > 99.9 % (< 6 log) > 99.9 % (4-6 log) > 99.9 % (2-6 log) % (1-3 log) TSS mg/l Turbidity ND ND ND ND 100 % ND >98 % >99 % COD / BOD mg/l > 99 % > 98 % > 95 % > 90 % 13

14 Water reuse with membranes: Wastewater Potable Non-potable Direct Indirect Agriculture Landscape application of recycled water choice of membrane process Industrial 14

15 Conventional plant: AS Sludge treatment RO GAC Recarbonation Air stripping Sand filter 15 Many unit processes operational restraints high costs

16 AS MF/UF RO: Pre-treatment AS MF/UF Sludge treatment RO Combines conventional process with membranes pretreatment of effluent necessary fewer unit processes easier to operate 16

17 MBR RO Pre-treatment MBR RO Sludge treatment Hybrid solutions 3 rd generation ww treatment plants compact systems, less units high quality effluent easier to operate 17

18 Advanced treatment study: Investigate the potential of a hybrid process design for compact wastewater treatment plants by combining a highrate moving bed biofilm reactor with membrane separation of biomass, colloidal and particulate COD Primary Settling tank MBBR Membrane Filtration unit Influent Permeate Air Air Concentrate 18 Sludge

19 System components: System conditions: MBBR: - KMT biofilm reactor Load: 120±20 mgcod/l - volume: ~ 200 l ~ 40% SCOD - flow: ~ 2 l/min HRT ~ 100 min Membrane filtration unit: - membrane unit: ZW-10, Sub. module - configuration: Outside/ in hollow fibers - nominal surface area: 0,93 m 2 - process tank working volume: 190 l - flow extracted from MBBR: ~ 1 l/min 19

20 Influent wastewater characteristics: SS mg/l COD mg/l SCOD mg/l NH 4 -N mg/l DO mg/l ph Temp. C High-rate study 88±18 219±66 100± ± Membrane study 79±45 204±100 56±11 21± ±

21 Treatment principle: Raw wastewater High-rate MBB-M-R Biological reactor MBB: biodegradable COD efficient, rapid removal low HRT high loading rates Particle separation Membrane separation efficient removal of particulate COD Flux rates, fouling Treatment efficiencies 21

22 System performance: Wastewater characteristics: COD (mg/l) SS (mg/l) Turbidity (NTU) Temp ph Oxyg Influent MBBR Process tank Permate 0 Influent MBBR Process tank Permate Quality parameter SS (mg/l) Turbidity (NTU) COD (mg/l) SCOD (mg/l) Treatment efficiency (%) 99,5 99,5 84,0 24,6 22

23 Conclusions: Rapid removal of biodegradable COD achieved in a high-rate MBB high volumetric loading rates very short hydraulic retention times (HRT) Efficient removal of particulate COD achieved by membranes: consistent high quality effluent ( >99% removal of SS & turbidity, 80-90% removal of COD) high performance maintained (flux of 60 LMH) Concept: Coagulant Air 23 MBB-M-R

24 Reclamation and reuse of wastewater: Submerged unit External unit Membrane technology is the accepted solution and BAT for wastewater reclamation and reuse! 24