Presentation Outline

Transcription

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2 Presentation Outline Background on ECCV Brackish Water RO Project Options Considered for Concentrate Disposal Evaluation of Brine Minimization Alternatives Pilot Testing Results Conclusions & Recommendations

3 Denver Has Limited Native Surface Water & Relies on Imported Water or Deep Non-Tributary GW

4 Design of the ECCV Northern Project Started in 2004 Twelve 100 ft Deep Alluvial Wells Classified GW Under the Direct Influence of SW Recharge from Barr Lake & S. Platte River 3 Pump Stations 38 mile, 48 Dia. Waterline 7 mgd RO + 4 mgd Blend Class I Injection Well

5 Selection of Water Treatment Process High hardness and TDS required blending or reduction Blending is not a long-term solution Reverse Osmosis selected Only effective process to consistently meet water quality goals Eliminates most potential COC from effluent dominated sources Challenge is brine disposal

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7 ECCV Northern Water System 47 MGD Ultimate Capacity

8 RO Concentrate Disposal Options 1. Discharge to Sanitary Sewer System or POTW Discharge 2. NPDES Surface Water Discharge 3. Deep Well Injection 4. Zero Liquid Discharge Using: a. thermal/mechanical concentrators b. enhanced evaporation system c. passive evaporation basins d. Selective salt recoveries

9 Potential Impacts of RO Concentrate on Wastewater Treatment Plant 1. Decreased hydraulic residence time could impact effluent BOD and TSS 2. Increase in effluent TDS 3. Potential increase in radionuclides, heavy metals, nitrates 4. Potential inhibit treatment biology if concentrate increases TDS > 5000 mg/l 5. Potential impact on WET tests 6. Potential impact on equipment corrosion

10 NPDES Permit Can Be Based on Discharge Standards or Non-Degradation Criteria TDS not a typically discharge standard because wastewater treatment plant can t remove it Nitrate, metals, radionuclides are concentrated by RO and can exceed discharge standards ECCV discharge permit to irrigation ditch was controlled by non-degradation of groundwater relative to fluoride, uranium and gross alpha Acute and chronic toxicity discharge standards can be impacted by common ion concentration and ratios

11 Zero Liquid Discharge (ZLD) Options Thermal/mechanical evaporation systems: vapor recompression, spray dryers, crystallizers Low tech evaporation processes: passive solar evaporation basins, enhanced evaporation basins, misters, undulating film evaporators Photo courtesy GE

12 Brine Injected Below Potable Water Aquifers Injection wells include outer casing and inner casing to create and annular space that can be monitored for leaks Corrosion resistant materials compatible with salty brines Chemical stability of brines during and after injection 12

13 Deep Injection Wells Can Be Used for Final Disposal of Concentrated Brine 23 operating injection wells in Adams and Weld Counties (47 permitted by the State O&G Div.) ECCV well - EPA permit for a Class 1 well Underground formations 9,000+ feet below drinking water aquifers Estimated injection rate of 200 to 400 gpm Estimated cost of $2.3 million per completed well + pipeline from plant to well

14 Deep Well Disposal Option Secondary concentration of RO concentrate using brine minimization to 3-6% 14 of flow treated to minimize water rights loss and # of deep disposal wells

15 Brine Minimization Alternatives Using Membranes Focused on Controlling Precipitation Chemistry Traditional LPRO concentrate softening: positives: mature technology negatives: large chemical doses, large quantity of residuals generated, extensive tanks and filters required Increase solubility or inhibit precipitation adjust ph to increase solubility utilize scale inhibitors remove ions that catalyze precipitation shift equilibrium to more soluble species

16 Evaluation of RO Pretreatment Technologies for Increasing Solubility of Sparingly Soluble Salts Technologies Controls Hardness Organics Colloids & SS Manages Silica Ion Exchange (SAC and WAC) Yes No Yes No High ph No No No Yes Low ph & Scale Inhibitors Lime/Soda Softening w/ MF Yes Yes No Partially Yes Yes Yes Yes

17 RO Brine Minimization Using both Weak Acid IX & Strong Acid IX (KIMKO Meta-Stable Silica Process) Spent Regeneration Brine w/ Ca & Mg Hardness Spent Regeneration Brine w/ Polyvalent Cations ppt TDS Brine Low Pressure RO Concentrate Strong Acid Cation IX Weak Acid Cation IX Reverse Osmosis High Purity Water 4-6% NaCl Brine 1% HCl Solution Removes Ions that: form Ca & Mg Scale form Sulfate Scales Iron Manganese Aluminum Brine Minimization RO ambient ph supersaturated silica recovery limited by ultimate osmotic pressure

18 RO & Nanofiltration Systems Can Concentrate Ions Above the Theoretical Saturation Limits Scale inhibitors disrupt the crystallization process that leads to scale deposits ph adjustment increases solubility of the potential scaling salts and minerals Removing or adding ions can shift the equilibrium to more soluble salts AMTA /SCMA

19 Theoretical Solubility 25 C) Silica Solubility vs ph ph

20 Scale Inhibitors and Kinetics Allow RO Systems to Operate above Theoretical Saturation Limits Salt Saturation Concentration (mg/l) Typical Saturation Index Calcium Carbonate (CaCO 3 ) 8 LSI < 1.8 Calcium Fluoride (CaF 2 ) % Calcium Orthophosphate (CaHPO 4 ) % Calcium Sulfate (CaSO 4 ) % Strontium Sulfate (SrSO 4 ) % Barium Sulfate (BaSO 4 ) % Silica, amorphous (SiO 2 ) %

21 Flow (gpm), Flux (gfd) Recovery ECCV Brine Minimization Pilot Test Stage 3 at 93.4 percent Overall Recovery Stage 3B Flow Trends 100% 90% 80% 70% Stage 3B Feed Stage 3B Permeate Stage 3B Concentrate Stage 3B Flux Stage 3B Recovery % 50% % 30% 20% 10% 0% Date

22 Flow (gpm), Flux (gfd) Recovery ECCV Brine Minimization Pilot Test Stage 96.4% Overall Recovery Stage 4 Flow Trends 100% Stage 4 Feed Stage 4 Permeate % 80% 70% Stage 4 Concentrate Stage 4 Flux Stage 4 Recovery % 50% 40% 30% 20% 10% 0% Date

23 Brine Stability at Different Recoveries and ph HPRO Feed ph Average Hydrochloric Acid Dose (mg/l)

24 Total Estimated ECCV Brine Disposal O&M costs per 1,000 gallons of net water production Secondary Recovery and Landfill of Dry Solids w/ Enhanced Evap. Deep Well Injection, No Secondary Recovery Deep Well Injection, With Secondary Recovery Brine Minimization $0.08 N/A $0.08 ZLD & Enhanced Evaporation and Landfill of Dry Solids $2.32 N/A N/A Deep Well Injection N/A $0.20 $0.10 Total O&M Cost $2.40 $0.20 $0.18

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26 Questions Phone: Thank you WRRI, City of Alamogordo, Bureau of Reclamation, ECCV and all New Water New Energy Conference participants