Membrane Technology A Key Component in Water Reuse Systems

Transcription

1 Advanced Membrane Technologies Stanford University, May 07, 2008 Membrane Technology A Key Component in Water Reuse Systems Mehul Patel, P.E. Principal Process Engineer Orange County Water District One Day Seminar for Treating Brackish Groundwater, Seawater, and Reclaimed Water Stanford University May 7, 2008

2 Presentation Outline Common Reuse Applications of Membrane Technologies Historical Use of Membranes at OCWD Advantages, Disadvantages, and Recommendations for use of Membrane Technologies for Reuse Applications Examples of Reuse Applications: Water Factory 21 and the GWR System

3 Common Uses of Membrane Technology for Reuse MF/UF used as a tertiary treatment process to meet Title 22 recycled water criteria for irrigation or industrial process water (carpet dye, paper processing) RO downstream of MF/UF for indirect potable reuse including seawater intrusion and surface spreading for groundwater replenishment Single or Two-Pass RO for ultra pure industrial processes such as boiler feed or computer chip manufacturing Water quality requirements govern over process costs as conventional treatment capital costs are normally less

4 Background On Use of RO at OCWD RO used for Water Factory 21 since 1975 (RO for treatment of secondary effluent wastewater) Pilot scale polyamide TFC RO membranes tested downstream of MF/UF systems since 1994 Involvement in design and initial operation of Arlington Desalter, Chino Desalter, and Tustin Desalter (RO for desalination of brackish groundwater) GWR System contains the largest RO system in US (70 mgd) Partner for concept and planning of Irvine Desalter (RO for contaminated groundwater on former Tustin Marine Corps Air Base)

5 Background on RO Applied Research and Testing at OCWD Cellulose acetate (CA) RO membranes used in WF-21 since the late 1970 s Pilot scale polyamide TFC RO membranes tested downstream of MF/UF systems since 1994 Pilot scale tests using 4-inch diameter polyamide TFC elements showed lower operating pressure and higher rejection as compared with CA Testing also showed extended run time between cleaning due to MF/UF pre-treatment (tests also showed polyamide membranes not compatible with lime clarification pretreatment)

6 Conventional Versus Advanced Water Treatment (Membrane Technologies) Conventional treatment relies upon chemically enhanced settlement by gravity Disinfection is typically achieved solely through chemical addition Advanced treatment primarily relies upon physical separation by polymer based membranes Membranes offer two basic levels of treatment: particulate or dissolved contatminant removal (i.e. low pressure vs. high pressure membrane technology) Disinfection is achieved by chemical addition and/or altering the DNA of microorganisms

7 Advantages of Membrane Based Treatment Footprint is typically 4 to 6 times less than conventional clarification Level of treatment is far greater than conventional treatment processes Process upsets occur less often due to nature of the treatment process Removal by physical separation allows for treatment of a broad range of water quality Allows for a high level of automation to potentially save on labor costs

8 Advantages of Membranes for Municipal Reuse Most economical process for salinity reduction associated with secondary effluent (or other wastewater source) TDS levels Low Pressure membranes provide consistent water quality for nonpotable reuse regardless of feedwater particulate content Stringent California DPH Draft Recharge Criteria water quality requirements best met using RO technology Safeguard against future contaminants of concern (i.e. Pharmaceuticals, EDC s) Small footprint advantageous for areas where available land is at a premium

9 Disadvantages of Membrane Based Treatment Capital costs can be far greater than for conventional systems Current expertise of typical plant operators may not be up to level required Membrane replacement costs are high and must be budgeted for appropriately Proven track record at municipal scale is still being forged Concentrate and waste stream disposal issues

10 Roadblocks to Use of Membranes for Municipal Reuse High initial capital costs for process equipment O&M costs for membrane replacement Lack of large operator level knowledge base Post treatment or blending issues due to corrosive nature of product water More economical technologies exist depending upon desired level of treatment Energy intensive nature makes process expensive in areas where energy costs are high (i.e. California)

11 RO Is Not a Panacea: Low Molecular Weight Organic (LMWO) Rejection is not Absolute Not all LMWOs of concern are completely rejected by RO membranes Rejection of LMWOs is directly proportional to molecular weight and width of the compound NDMA is an example of a newly regulated compound not fully addressed by RO alone Approximately 35-40% of NDMA is rejected by PA TFC membranes; only 10-12% is rejected by CA membranes As lab methods improve more contaminants will be detected to far lower levels further demonstrating that RO capability to remove contaminants is not absolute

12 Must Haves if Membranes are to be Considered for Municipal Reuse Pilot testing on source water for an extended period of time (6 months minimum for full benefit) Pilot testing must help establish realistic O&M costs Thorough understanding of organic and inorganic make up of source water Proper pre-treatment (preferably low-pressure membrane technology) if RO is considered Strong membrane warranty language and technical support from chosen MF/UF and RO manufacturer

13 Recommendations for Use of RO Technology for Reuse Applications TDS and organics removal requirements typically drive the need for RO for reuse applications On-site pilot testing a must Level of pre-treatment determines the rate of O&M costs for RO State of CA water quality regulations for subsurface injection indirectly require the use of RO Newly regulated contaminants of concern (such as LMWOs) have shown that RO alone may not be enough A combination of low and high pressure membrane technology reduces cost of possible downstream oxidation treatment (UV/peroxide, UV/Ozone, Ozone)

14 Water Factory 21 - The First Municipal Facility to use RO for Reuse (1977 to 2004) Secondary treated wastewater flocculation carbon adsorption (10 mgd) AOP (5 mgd) (added later) filtration lime sludge clarification recarbonation reverse osmosis (5 mgd) CO 2 recycled lime (up to 75% recovery) Blending prior to use in seawater barrier transfer thickening recalcining

15 Water Factory 21 Conventional vs. MF/UF Treatment Prior to RO Water Factory 21 Conventional Pretreatment Lime Flocculation & Sedimentation Recarbonation Chlorination Filtration Reverse Osmosis GWR System Microfiltration Pretreatment NaOCl Microfiltration CA vs. PA

16 GWR System Advanced Water Treatment Facility (AWTF) Flow Diagram Enhanced Source Control Secondary Treatment 86 mgd Microfiltration (MF) 70 mgd 70 mgd Reverse Ultraviolet Osmosis Light (RO) (AOP) Lime addition Purified Water OCSD Secondary Effluent NaOCl addition Backwash OCSD Plant 1 Concentrate OCSD Outfall with hydrogen peroxide Surface Spreading & Seawater Intrusion Barrier

17 GWR System Components Kraemer Basin Fullerton Santa Ana River Pacific Ocean Huntington Beach Advanced Water Purification Facility Future Mid-Basin Injection/Recharge Seawater Intrusion Barrier Pumping OCWD Facilities OCSD Treatment Facilities Ocean Outfall GWR Pipeline Irvine Santiago Creek Groundwater Basin N

18 GWR System - Level of Treatment for Each Process MF removes suspended solids, bacteria, and protozoa MF pre-treatment increases efficiency of RO process RO removes salinity (TDS), virus, dissolved organics AOP process provides an additional barrier for disinfection AOP destructs low molecular weight organics Testing at OCWD has shown that the combination of RO and AOP is effective against emerging compounds such as: low molecular weight organics, pharmaceuticals, and endocrine disruptors

19 AWTF Process Flow Diagram

20 Microfiltration System 86 MGD Siemens CMF-S Microfiltration System (15,808 membrane modules) Removes bacteria, protozoa, and suspended solids 0.2 micron pore size In basin submersible membrane system Includes 2 CIP systems

21 MF System Design US Filter CMF-S system (immersed membrane) Flux Rate = 20.4 gallons per ft 2 per day 22 minute backwash interval using reverse flow and air agitation with complete drain of tank (cell) contents 26 cells with 608 membrane modules each 3 basins with 8 cells per basin (one additional basin with only two cells) 86 mgd total capacity 21 day cleaning interval

22 GWRS CMF-S MF System Design (86 mgd) Train D Basins Train A Basins Train E Basins Cell containing 684 MF modules Train B Basins Empty cells Membranes relocated from temporary system Punch - out wall for future expansion

23 GWRS Reverse Osmosis System 70 MGD Reverse Osmosis System (15, 5 mgd units) Hydranautics ESPA-2 Membranes Recovery Rate: 85% 3 stage array per unit in a 78:48:24 arrangement Removes salts, viruses, organics Pressure range: 150 psi 200 psi Includes 2 CIP systems

24 RO System Process Flow Mixer Flush System Reverse Osmosis MF Filtrate Pump Station Threshold Inhibitor System Sulfuric Acid System Cartridge Filters Feed Pump CIP System Drain Concentrate to Ocean Outfall To Post- Treatment

25 GWRS Ultraviolet Light /Advanced Oxidation System 70 MGD Trojan UVPhox System Low Pressure High Output lamp system Nine 8.75 mgd trains (3888 total lamps) Removes trace organics Uses Hydrogen Peroxide to form an Advanced Oxidation Process

26 Post Treatment Process Flow To Seawater Intrusion Barrier and Infiltration Basins Decarbonator Bypass UV Disinfection From RO System Decarbonators Barrier and Product Pump Stations Lime Addition (CaOH)

27 Stabilization and Storage Decarbonation and lime addition stabilize purified water GWR System water is pumped to seawater barrier and spreading basins Natural soil filtration and buffering provide final treatment prior to extraction after months of storage

28 Estimated Capital Cost Construction Contracts Escalated Cost ($M) Treatment Facilities Equipment Engineering Trailers Phase 1 GWR System & Site Power GWR Pipeline* Barrier Facilities Integrated Information System, Wells, Workshops & Insurance ELA & Contingency $65.3 *3 contracts Total $480.9

29 Estimated Annual O&M Cost Item Power Contract Maintenance Chemicals Plant Refurbishment Membrane Replacement UV Lamp Replacement Compliance Monitoring O&M Staff Sub - Total Metropolitan Water District Subsidy Total $ Million per Year (3.8) 25.8

30 Federal, State, and Local Funding Grants $ Million Environmental Protection Agency United States Bureau of Reclamation State Water Resources Control Board State Water Resources Control Board (Prop.13) Department of Water Resources (Prop. 13) Total Grants $92.5 Loans State Revolving Fund Loans $145.0

31 CA DPH Regulatory Criteria for Injection Subsurface Injection CDPH Proposed Criteria GWR System Total Suspended Solids Filtration <30 mg/l ND < 2 NTU 0.2 NTU Disinfection 4 log < 2.2 total per 100 ml ND Underground Retention Time Horizontal Separation Biochemical Oxygen Demand Total Nitrogen Total Organic Carbon > 12 months 24 months > 2,000 feet 3,120 feet < 30 mg/l ND < 5 mg/l 2.6 mg/l < 0.5 mg/l 0.26 mg/l Drinking Water Standards < MCLs < MCLs

32 Department of Public Health and Regional Board Approval Process DHS Public Hearing - February 2003 DHS Findings of Fact and Conditions RWQCB incorporated DHS Findings and Conditions into permit RWQCB Hearing March 2004 RWQCB issued requirements for both Interim WF-21 and GWR System GWR System 70 MGD - largest IPR project in the world

33 Additional Requirements for GWR System Buffer areas >500 ft for spreading >2000 ft for injection Retention time underground >6 months for spreading >1 year for injection Replacement water plan Initial blending 75% ramping up to 100% RWC Independent Advisory Panel (NWRI appointed) for OMMP review

34 Water Quality Requirements for GWR System Comply with Drinking Water Standards plus TOC and Total N Non-aggressive water to reduce leaching potential Testing for Notification Level compounds like NDMA, perchlorate and 1,4-dioxane Testing for selected pharmaceuticals and endocrine disruptors Monitoring in plant, blend water and groundwater along flowpath to production wells

35 Treatment Requirements for GWR System Enhanced Source Control by OCSD (Title 22, CCR, Division 4, Chapter 3. Recycling Criteria, Section General Requirements) Organics removal - <0.5 mg/l TOC Nitrogen removal - <5 mg/l Total N Disinfection UV system >4 logs virus inactivation UV photolysis for 1.2 log NDMA removal AOP for unknown organic contaminants

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37 For More Information Project Website: OCWD Website: