Arsenic treatment the rest of the story
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Arsenic Treatment The rest of the story. Presented to:. Texas Commission on Environmental Quality October 25, 2005. Russell Fisher Turnstone Services The Woodlands, Texas (281) 419-0747. The Commercial Perspective. Locate prospects – anticipate the unmet need

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Arsenic treatment the rest of the story

Arsenic TreatmentThe rest of the story

Presented to:

Texas Commission on Environmental Quality

October 25, 2005

Russell Fisher

Turnstone Services

The Woodlands, Texas

(281) 419-0747


Arsenic treatment the rest of the story

The Commercial Perspective

  • Locate prospects – anticipate the unmet need

  • Qualify Prospects – gather data to understand need

  • Propose Solution - Satisfy customer’s need

Turnstone Services


Arsenic treatment the rest of the story

The Need - Arsenic Treatment Objectives

Achieve compliance

Conserve the water resource

Define the Need – Gather Information

Aquifer characteristics

Water Quality Data - TCEQ

Usage information - PWS

Develop Arsenic Treatment Strategy

Associated regulatory issues

Technology Constraints

Unanticipated Consequences

Turnstone Services


Arsenic treatment the rest of the story

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

Turnstone Services


Arsenic treatment the rest of the story

Understanding the Environment

Indicator Species

TDS - may require lowering of salt content

pH - activity of the hydrogen ion

Eh – electrode potential, activity of the electron

Ca/Mg – hardness, scale forming pH sensitive

Cl- – major contributor to TDS

HCO3- – contributes to TDS, limits F trmt

Turnstone Services


Arsenic treatment the rest of the story

The lesser know elements of water chemistry

Turnstone Services


Arsenic treatment the rest of the story

Common Redox Species In Ground Water

Oxidized Sand

Reduced Sand

Turnstone Services


Arsenic treatment the rest of the story

Groundwater Redox Front

O2

H2O

Fe2O3

UO2+2

MoS2

HAsO4-

As2O3

H3AsO3

As2S3

MoO4-2

UO2

FeS2

Turnstone Services


Arsenic treatment the rest of the story

Importance of redox potential

Redox state often dictates solubility

Fe(+III) insoluble, Fe(+II) low to moderate solubility

U(+IV) insoluble, U(+VI) highly soluble

Redox affects acid-base behavior, i.e. charge

H3AsO4 mild acid, H3AsO3 weak acid

HNO3 strong acid, HNO2 weak acid

Redox reactions affect pH

Ionization of weak acids: HCO3-1, H4SiO4

Turnstone Services


Arsenic treatment the rest of the story

Typical Treatment Strategies

Rule #1: Match the Solution to the Problem

Turnstone Services


Arsenic treatment the rest of the story

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

Turnstone Services


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