# Presentation: 823046

## Edward T. Urbansky

**Edward T. Urbansky**

**U.S. Environmental Protection Agency**

- National Risk Management Research Laboratory

- Water Supply and Water Resources Division

- Cincinnati, Ohio 45268

## What techniques will work?

## Approach

## About Perchlorate

## Chlorine Species

## Chemical Reduction

## Perchlorate Lability

## Labile Reducing Agents

** **
** ****Titanium(III)         Methylrhenium dioxide, CH3ReO2 **
** ****Vanadium(II, III)  Dimolybdenum(III), Mo26+**
** ****Chromium(II)       Molybdenum(III)**
** ****Ruthenium(II)**

## Chemical Reduction: Problems

-  Slowness of reaction
-  Toxicity of by-products
-  Removal of by-products

## Electrochemical Reduction

## Tungsten carbide
 Ruthenium
 Platinum
 Aluminum
 Titanium
 Aluminum oxide
 Carbon (doped with Al2O3 or Cr2O3)

- Tungsten carbide
-  Ruthenium
-  Platinum
-  Aluminum
-  Titanium
-  Aluminum oxide
-  Carbon (doped with Al2O3 or Cr2O3)

- Electrochemistry:  Anodes

## Advantages
 Nontoxic by-products
 Well-known technique
 Disadvantages
 Construction/implementation expense
 Operation expense (electricity)
 Electrolysis of water
 Slowness (reaction and diffusion)
 Safety (high voltage)

**Advantages**
-  Nontoxic by-products
-  Well-known technique
-  **Disadvantages**
-  Construction/implementation expense
-  Operation expense (electricity)
-  Electrolysis of water
-  Slowness (reaction and diffusion)
-  Safety (high voltage)

## Biological Reduction

-    The use of biological organisms, especially bacteria, to chemically reduce perchlorate to other chemical species

- Perchlorate-reducing bacteria

**Ideonella dechloratans**
**Proteobacteria**
**Vibrio dechloraticans Cuzensove B-1168**
**Wolinella succinogenes HAP-1**

## Biological Reduction

**USAF, Tyndall AFB, Florida**

## Biological Reduction

**Advantages**
-  Nontoxic by-products
-  Versatility
-  Speed
** ****Disadvantages**
-  Acceptance
-  Regulatory barriers
-  Construction/implementation costs
-  Hardiness of bacteria

## Biochemical Reduction

- Bacteria use a biological catalyst or enzyme, called a reductase, to reduce perchlorate.
-  It may be possible to purify this enzyme and use it directly as a reactant for chemical reduction (addition or tethering).
-  Perchlorate reductases evolved from nitrate reductases used by nitrogen-fixing bacteria (e.g., those in legumes).

## Biochemical Reduction

**Advantages**
-  No toxic perchlorate by-products
-  Fast reaction time
-  High effectiveness
-  **Disadvantages**
-  High expense in producing enzyme
-  High maintenance
-  Difficult implementation
-  Enzyme by-products unstudied

## Physical Separation

**Anion exchange**
**Membrane processes**
-  Nanofiltration
-  Reverse osmosis
-  Electrodialysis

## Anion Exchange

**A positively charged resin is used to exchange the perchlorate ion for a harmless chloride ion.**

## Ion Exchange for Pertechnetate

## Ion Exchange for Nitrate

- Nitrate-selective resins already exist.
-  Perchlorate and nitrate have similar physical properties (charge, size, aquation).
-  Therefore, these resins are expected to be effective in removing perchlorate.
-  However, permissible nitrate concentrations are much higher than the perchlorate action level.

**Anion exchange is used to remove nitrate from water.**

## Anion Exchange

**Advantages**
-  Reasonable operating costs
-  Well-developed technique
-  Easy implementation
- Effectiveness
-  **Disadvantages**
-  Waste disposal from regeneration
-  Moderate selectivity
-  Distribution system effects
-  Resin lifetime

## Membrane Techniques

**  ****Reverse osmosis**
**  ****Nanofiltration**
**  ****Electrodialysis**

## Reverse Osmosis/Nanofiltration

## Electrodialysis

## Membrane Techniques

**Advantages**
-  High effectiveness
-  Low operating cost
-  High throughput
-  Easy implementation
** ****Disadvantages**
-  Low selectivity
-  Distribution system effects
-  Palatability
-  Waste effluent disposal

## Under Investigation

- Reverse Osmosis and Nanofiltration
-  Ozone/GAC (Chemical Reduction?)
-  Biological Reduction
-  Anion Exchange

## General Considerations

**Incomplete health effects studies**
**Success at reaching trace concentrations**
**Distribution system effects**

## General Considerations

**Effects on other treatment       processes**
**Effects from other treatment processes**
**Reliability**

## General Considerations

-  Palatability
-  Time
-  Expense

## Customization

**   ****The best solution for a specific situation is likely to be a combination of technologies.**

-  Anion exchange + bioremediation
-  Nanofiltration + blending

## Small Systems

-    Small systems may benefit from a number of techniques that will not work in large systems.

-  Reverse osmosis
-  Anion exchange

## Point of Use

- Some techniques lend themselves to point-of-use devices.
-  Both anion exchange and RO may be used at individual sites or for very small systems.
-  No standards presently exist for purification systems; however, that could be rectified fairly

## Directions

-     Congress has appropriated $2 million to the East Valley Water District for studies on perchlorate.

- The American Water Works Association Research Foundation has requested proposals.

- EPA anticipates an initiative in fiscal year 2000.

## Closing

**Perchlorate is unlike other contaminants already regulated.**
** ****Effective management will require long and short term responses.**
** ****The best solutions will **
**  ****only come about through **
**  ****continued cooperation**
**  ****among state, local, and**
**  ****federal agencies.**