Arsenic Treatment The rest of the story Texas Commission on Environmental Quality October 25, 2005...
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Arsenic Treatment The rest of the story Texas Commission on Environmental Quality October 25, 2005 Presented to: Russell Fisher Turnstone Services The Woodlands, Texas (281) 419-0747
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Transcript of Arsenic Treatment The rest of the story Texas Commission on Environmental Quality October 25, 2005...
Arsenic TreatmentThe rest of the story
Texas Commission on Environmental Quality
October 25, 2005
Presented to:
Russell FisherTurnstone Services
The Woodlands, Texas(281) 419-0747
The Commercial Perspective
• Locate prospects – anticipate the unmet need
• Qualify Prospects – gather data to understand need
• Propose Solution - Satisfy customer’s need
Turnstone Services
The Need - Arsenic Treatment ObjectivesAchieve complianceConserve the water resource
Develop Arsenic Treatment StrategyAssociated regulatory issuesTechnology Constraints
Unanticipated Consequences
Define the Need – Gather Information
Water Quality Data - TCEQ
Usage information - PWS
Turnstone Services
Aquifer characteristics
Turnstone Services
Texas Groundwater is a Dynamic System
• Sandstone Aquifers – highly variable over short dist
• Intermittent Recharge – year to year rainfall variance
• Regional climate variation – fluctuating water levels
• Coastal faulting and subsidence
• Geochemistry - the rock/water system
Understanding the Environment
pH - activity of the hydrogen ion
Eh – electrode potential, activity of the electron
Turnstone Services
Ca/Mg – hardness, scale forming pH sensitive
Indicator Species
TDS - may require lowering of salt content
Cl- – major contributor to TDS
HCO3- – contributes to TDS, limits F trmt
Arsenic (As) toxic regulated under the CWA
Iron (Fe) essential nutrient, contributes to color and taste
Manganese (Mn) contributes to color and taste
Sulfide (H2S) contributes to odor, toxic at high concentration
Uranium (U) radiation source, toxic
Silica (SiO2) non regulated, foulant for membrane processes
Fluoride (F) beneficial at low concentrations, regulated
The lesser know elements of water chemistry
Turnstone Services
Std E0
(Volts)
Oxidizedform
Reducedform
1.23 MnO2 Mn+2
1.15 SeO4-2 H2SeO3
0.94 NO3-1 HNO2
0.77 Fe+3 Fe+2
0.74 H2SeO3 Se
0.58 H3AsO4 HAsO2
0.48 H2MoO4 MoO2+1
0.34 VO+2 V+3
0.33 UO2+2 U+4
0.17 SO4-2 SO2
0.14 S H2S
Oxidized Sand
Reduced Sand
Turnstone Services
Common Redox Species In Ground Water
Fe2O3
FeS2
As2O3 As2S3
MoS2HAsO4-
MoO4-2
UO2
UO2+2
H3AsO3
H2OO2
Groundwater Redox Front
Turnstone Services
Turnstone Services
Importance of redox potential
Redox affects acid-base behavior, i.e. charge
Redox state often dictates solubility
Redox reactions affect pH
Fe(+III) insoluble, Fe(+II) low to moderate solubility
U(+IV) insoluble, U(+VI) highly soluble
H3AsO4 mild acid, H3AsO3 weak acid
Ionization of weak acids: HCO3-1, H4SiO4
HNO3 strong acid, HNO2 weak acid
Turnstone Services
Typical Treatment Strategies
As Absorption
As, TDS R/O or R/O + Absorption
Ratio dependent
As, Fe, Mn, S-2 Adsorption + Catalytic Oxidation
As, TDS, F R/O
Fe, Mn, S-2, U Catalytic Oxid + Adsorption
Rule #1: Match the Solution to the Problem
Turnstone Services
Summary
• Understand geological setting – aquifer type, mineralogy
• Analyze water sample for less known species
• Interpret water analysis in context of aquifer geochemistry
• Apply technologies that best address the problem
