MBRs: The lowdown on energy use and costs
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MBR basics have not changed in the last 10 years but the industry landscape is nearly unrecognizable. With so many manufacturers flooding the market what will 2025 look like?
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MBRs: The lowdown on energy use and costs
- 1. Professor Simon Judd MBRs: the low down www.cranfield.
- 4. 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
- 5. MBR process configurations Air In Out Membrane Out Bioreactor Recirculated stream Air In Pump Bioreactor Membrane immersed/submerged MBRsidestream MBR Really expensive Expensive? ?
- 6. MBR process configurations MBR technology Immersed Flat sheet Hollow fibre Sidestream Multitube/multichannel Pumped Classical Low energy Aerated Lift Injection Municipal MunicipalIndustrial memb- rane Industriall
- 7. MBR operational parameters • Key parameters are • operating flux flux = 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
- 8. OPERATIONDESIGN Clogging membrane channels aerator ports Fouling reversible irreversible Biomass characteristics Bulk characteristics • viscosity/rheology • hydrophobicity Feed characteristics Membrane module characteristics Configuration • 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
- 9. 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 and solids) • Key design parameter is • critical/ sustainable flux • There is a limit to how far the design flux can be pushed
- 11. Membrane process types Reverse osmosis ULTRAFILTRATION Nanofiltration MICROFILTRATION Depth filtration (to >1mm) 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 PesticidesDissolved 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
- 12. Material structure May be isotropic, but often anisotropic (symmetry in one direction)
- 14. 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
- 15. MBR membrane products – 70 off.Immersed (iMBR) Sidestream (sMBR) Flat sheet Hollow fibre Multi-tube/multi-channel, polymer A3/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, ceramic Ecologix - 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 sheet Lantian PeierCN Jie FuCN ROCHEM - Bio-FILTUS LiqTechDK KaiHongCN NovasepFR Martin - siClaroDE KejiCN MegaVisionCN Koch Membrane Systems - PURONUS Hollow fibre MeidenJP Kolon - CleanfilKR Polymem - IMMEMFR Mann+Humme/MICRODYN-NADIR – BIO-CELDE Litree - LH3CN newterra – MicroClearCA MEMOS - MEMSUBDE Flat disc Pure 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
- 16. 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
- 19. 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
- 20. MBR system suppliers FS • Ovivo • ADI • Busse • Kruger • Smith and Loveless • Sanitherm • Wigen • Hitachi • Memcon HF • Layne • Aquabio • Berghof • Dynatec • Triqua • Wehrle MT
- 23. Process components Category 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
- 24. Aeration AIR Nitrate-enriched sludge Feed Treated water fine bubble AIR coarse bubble
- 25. Membrane cleaning, UF/MF Chemical ACIDS Hydrochloric/sulphuric Citric/Oxalic BASE Causticsoda OXIDANT Hypochlorite Hydrogen peroxide Physical BACKFLUSHING • withair • without air RELAXATION CHEMICALLY ENHANCED BACKWASH CEB CIP
- 26. Fouling and cleaning Flocculant solids normally readily removed by physical cleaning Solutes and colloidal matter more tenacious Fouling exacerbated by: • high fluxes • low shear • infrequent cleaning
- 28. backflushY Y Bioreactor Clarification Membrane Feed Effluent backflush Bioreactor Membrane Feed Effluent CAS with polishing: MBR:
- 29. Removal data for 29 pharmas
- 30. Concentration data for 7 metals
- 32. Capital cost Young 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 < 20 BOD < 20 NH3-N < 1 Temp 12°C Peak 2X Case 1 & TN < 10 TSS < 10 BOD < 10 NH3-N < 1 TN < 10 TP < 0.2 Temp 12°C Peak 2X Case 3 with Primary Clarifier Case 3 with Tmin 25°C Case 3 with Peak 4X Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 by kind permission of GE
- 33. CAPEX, MBR vs. CAS, Germany Brepols et al, 2010
- 34. CAPEX, MBR vs oxidation ditch Itokawa 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] Constructioncost[103 JPY/(m3 /d)] MBR (whole plant) MBR (wastewater treatment) OD plant OD plant with sand filtration
- 35. Specific energy demand, Germany Brepols et al, 2010
- 36. 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 [%] Specificenergyconsumption[kWh/m3 ] Moryama intermittent operation
- 37. Moryama plant, JSWA Itokawa 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.
- 38. HF FS Specific energy demand, Ovivo
- 39. 0.00 0.50 1.00 1.50 2.00 2.50 0 20 40 60 80 100 120 SEDkWh/m3 % design flow Specific energy demand, Spain Gabarrón et al, 2014 HF FS
- 40. Operating cost Young 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 < 20 BOD < 20 NH3-N < 1 Temp 12°C Peak 2X Case 1 & TN < 10 TSS < 10 BOD < 10 NH3-N < 1 TN < 10 TP < 0.2 Temp 12°C Peak 2X Case 3 with Primary Clarifier Case 3 with Tmin 25°C Case 3 with Peak 4X Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 by kind permission of GE
- 41. 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 < 20 BOD < 20 NH3-N < 1 Temp 12°C Peak 2X Case 1 & TN < 10 TSS < 10 BOD < 10 NH3-N < 1 TN < 10 TP < 0.2 Temp 12°C Peak 2X Case 3 with Primary Clarifier Case 3 with Tmin 25°C Case 3 with Peak 4X Case 1 Case 2 Case 3 Case 4 Case 5 Case 6 by kind permission of GE
- 42. CAPEX & OPEX comparison
- 43. 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 4 3GE Water & Process Technologies
- 45. The MBR Survey (186 responses) • Q1What 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
- 46. The MBR Survey (186 responses) • Q1What is the main technical problem that prevents MBRs working as they should? 16% 10% 6%16% 4%8% 11% 12% 8% 5%4% Screening/pre-treatment Membrane/aerator clogging Overloading/under-design Membrane surface fouling Automation/control, or software Membrane chemical cleaning Energy demand
- 47. The MBR Survey, Q1 0% 5% 10% 15% 20% 25% Mar-10 Feb-12 Feb-15
- 48. The MBR Survey, Q2 • 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 cost fouling membrane materials automation & control potable/drinking robustness awareness/perception/acceptance nutrient pretreatment/screening/clogging
- 49. 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
- 50. 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
- 52. Past, present .. THAT WAS THEN: PORLOCK First municipal MBR (1997) • 1.9 MLD Manual aerator flushing No separate membrane tank • coarse-bubble aeration only Up to 14 years membrane life >2 kWh/m3 (MBR only) THIS IS NOW Bigger 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
- 53. … 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 removal Find out more (for free) at www.thembrsite.com