Brackish Desalination: Zero Discharge Thomas F. Seacord, P.E. ewithlogo.pptx
Topics covered include Background Current Disposal Options Zero Discharge In Practice Case Studies Emerging Technologies 2
April 20, 2010 3
1 out of 8 people lack access to clean water 3.3 million die each year from water related health problems 83 million people are added to the world population each year Within 15 years 1.8 billion people will live in regions of severe water scarcity April 20, 2010 4
Business as usual approaches will not meet demand for water Billion AF 6.5 5.7 4.9 4.1 Demand with no productivity improvements Historical Improvements in water productivity Portion of Gap Percent 20% Remaining Gap 60% Increase in Supply under businessas-usual 20% 2.4 Today 2030 Existing accessible, reliable supply SOURCE: 2030 Water Resources Group Global Water Supply and Demand Model (A United Nations Water Working Group) 5
Saltwater (seawater and brackish water) is the most abundant water source on Earth Fresh Water 2.5% 0.3% Lakes and Rivers 0.7% Available Groundwater 29.3% Unavailable Groundwater 69% Glaciers and Icecaps Total Water Salt Water 97.5% SOURCE: Encyclopedia of Desalination and Water Resources 6
The State of Texas has estimated that there is 27billion 2.7-billion acre-feet of brackish groundwater LBG-Guyton, Brackish Groundwater Manual for Regional Water Planning Groups, 2003 7
Desalination is the only significant solution Unlimited supply Local source Provides back-up and redundancy Drought proof Frees freshwater for environmental uses Image courtesy NASA, provided by Visible Earth (http://visibleearth.nasa.gov) 8
Global desalination capacity has increased exponentially 20.0 17.5 ~ 14,500 Plants 15.0 Global Desalination Capacity (Billion gal/day) 12.5 10.0 7.5 5.0 2.5 SOURCE: Global Water Intelligence 0..................... 1990 1995 2000 2005 2008 2010 9
There are 44 Desalination Plants in Texas (Capacity > 0.023 023 mgd) Currently produce 116 mgd Surface Water 12 plants Capacity: 50 mgd Groundwater 32 plants Capacity: 66 mgd Source: Texas Water Development Board Desalination Plant Database, 2010 10
There are several perceived barriers to implementation Cost Power consumption Concentrate Management 11
Concentrate disposal is the tail that wags the dog on any desalination project Concentrate Management For seawater and brackish water desalination: Concentrate consists of dissolved constituents from natural waters in a more concentrated form Nomenclature: Concentrate By-product Brine 12
Concentrate Management Options Include Surface water Sewer Deep well injection Land application (irrigation, dust control, etc.) Concentrators Zero discharge technologies 13
Brine management options fall into distinct categories Brine Disposal Beneficial Reuse Brine Treatment Surface Water Cooling Water Volume Reduction Discharge 1 Sewer Disposal 1 Land Application Chemical Precipitation Brine Irrigation Concentrators Deep Well Injection Dust Control Zero Liquid Discharge Evaporation Ponds 1- Includes export pipelines/brine lines Wetlands Zero Liquid Discharge Crystallizers 14
Depending upon brine volume, several steps may be required leading to zero liquid discharge Initial Brine Volume Reduction Chemical Precipitation Softening followed by Secondary RO Intermediate Brine Concentration Thermal Brine Concentrator Vapor Compression Brine Concentrator Final Solidification (Zero Discharge) Crystallizers Evaporation Ponds Enhanced Evaporation using Solar Bee 15
Brine volume minimization uses intermediate treatment to recover more water from the brine 1. Chemical/physical h i l processes a. Chemical precipitation pretreatment for additional desalting 2. Thermal treatment a. Heat used to accelerate evaporation of brine 16
Chemical precipitation reduces the saturation of salts that would otherwise limit further recovery by RO 2-Stage Primary RO Secondary RO Chemical Precipitation Process Permeate Primary RO Brine Secondary RO Conc. 17
Two softening processes can be used for chemical brine treatment CONVENTIONAL SOFTENING An economic way of brine volume reduction proven at bench & pilot scale Low rate (1.75 gpm/sf) = large foot print Requires open tank = energy loss Residuals require drying ponds or mechanical dewatering PELLET SOFTENING Fluidized bed using sand & lime High rate (35 gpm/sf) = small footprint t Can be operated in a pressure vessel = save energy Residuals easily dewatered by gravity 18
Thermal brine minimization uses waste heat and/or electricity to evaporate concentrate 1. An example of a thermal process is a seeded-slurry, falling film vapor compression brine concentrator 19
Heated Brine De-Aerated to Reduce Scaling and Corrosion Concentrated Waste is Blown Down to Crystallizer or Evaporation Ponds Vapor is Heated With Compressor Transfers Heat to Falling Brine Causing Evaporation Vapor Condenses as Highly Pure Distillate and Is Collected Brine is Recirculated From Sump Through Vertical Tubes RO Brine Passes Through Heat Exchanger 20
Mechanical evaporators are last resort option due to cost and energy usage >100 ft tall 250 gpm capacity Up to 98% evaporation efficiency Blowdown is 175k-200k mg/l TDS and 5-7% solids Capital Cost = $10 million Requires 90 to 100 kw-hr per 1,000 gallons of brine Deuel Vocational Institution Tracy, CA
Crystallizers can be used as a final step in the ZLD process 1. Only used if evaporation ponds or other final disposal methods are not feasible 2. Produces a solid that is dewatered and disposed of 22
Crystallizers can be used as a final step in the ZLD process 65 to 75 ft tall Flows: 2 to 50 gpm About 80 to 120 kw-hr per 1,000 gallons of brine
Evaporation ponds can be used for concentrate disposal Permit Triple liner system and leachate collection and monitoring system Loading Rate Based on net precipitation and evaporation rate for each location Land intensive in non-desert areas Can be combined with brine minimization as final disposal option Evaporation Ponds Fences & Bird Netting
Evaporation rates can be enhanced Solar Bee Minimizes i i pond size by mixing i pond s thermocline to enhance evaporation Enhanced evaporation 1.6 x during day 1.8 x during night May not be applicable when using thermal concentrators due to blowdown temperature (>200 o F) Photos: Erik Jorgensen, USBR 25
Case Study #1: Chemical Precipitation Arlington Desalter Brine Minimization GAC Towers (Biofilters) Secondary RO Recovery = 70% Cartridge Filter RO System Pellet Softener & Media Filter 26
Case Study #1: Chemical Precipitation Arlington Desalter Location: Riverside, CA Size: 8.5-MGD Primary RO: 5-MGD Secondary RO: 1.1-MGD Brine: 0.5-MGD Overall Recovery: 94% Drivers Reach IV-B of SARI is hydraulically maxed out Alternatives New SARI Pipeline & Conventional RO Expansion
Case Study #1: Chemical Precipitation Arlington Desalter Project Cost (Brine Recovery) Capital: $16.9-mil O&M: $698/AF ($2.14/kgal) Energy Required (Entire Treatment Plant) 1,869 kw-hr/af (5.73 kw-hr/kgal)
Case Study #2: Hybrid Brine Concentrator/Crystallizer RO System Decarbonation Tower Cartridge Filter Finished Water Pumps Zero Liquid Discharge Crystallizer Brine Concentrator 29
Case Study #2: Hybrid Brine Concentrator/Crystallizer Location: Salt Lake City, Utah Size: 7-MGD RO: 4,028 gpm BC: 1,007 gpm Crystalizer: 30 gpm Project Drivers Discharge to adjacent Jordan River was objectionable to community (selenium) Alternatives 26-mile pipeline to Great Salt Lake
Case Study #2: Hybrid Brine Concentrator/Crystallizer Brine Concentrator / Crystallizer Project Costs Capital: $129.8-mil O&M: $783/AF ($2.39/kgal) Energy 7,033 kw-hr/af (21.5 kw-hr/kgal) Water Cost $1,910/AF ($5.84/kgal) 26-mile Pipeline to Great Salt Lake Project Cost Capital: $45.8-mil O&M: $224/AF ($0.68/kgal) Energy 2,197 kw-hr/af (6.7 kw-hr/kgal) Water Cost $621/AF ($1.90/kgal) 31
Emerging technologies may provide more viable concentrate management options Emerging technologies primarily focus on volume reduction: VSEP TWDB, 2007 Report Seeded precipitation (hollow fiber RO) - SPARRO USBR DWPR, 2008 Report 32
Brackish Desalination: Zero Discharge Thomas F. Seacord, P.E. Carollo Engineers, Inc.