1

Persulfate for the Disinfection of Ballast Water

Dani MilesCMOP Intern, Summer 2010

Mentor: Paul Tratnyek

2Project Overview:

PurposeTo test the effectiveness of a potentially new method to treat

ballast water for the prevention of spread and establishment of invasive species in coastal margins.

ObjectivesStability studies of persulfate in aqueous solutions:

Develop a quick and reliable method for determining persulfate concentrations.

Systematic observation of persulfate decay versus key variables.

Examine persulfate decay in natural water samples.

3Background: Ballast Water Treatments

Initiatives and Treatments Offshore Ballast Exchange (IMO). Physical: filtration, UV light, heat. Chemical: chlorine, hydrogen

peroxide, peracetic acid, and other oxidants.

Treatment Disadvantages Costly and harmful by-products.

Advantages of Persulfate Already applied to ground water. Potent oxidant. Inexpensive. Safe sulfate by-product.

4Methods: Persulfate Spectroscopy

Colorimetric Method: Established method for assays

of general oxidative activity. Oxidation of colorless iodide (I-)

forms yellow iodine (I2).

Effectiveness: Not selective to oxidants. Successful in many water types. Very dilute persulfate (μM). Requires large quantities of KI. Efficient with a flow-through

spectrometer, Gilford Stasar III.

Figure 1. Ultraviolet and visible absorption spectra of primary reagents.

Figure 2. Calibration curves for DI, Instant Ocean and natural water samples.

5 Results: Persulfate Decay

Water samples: Deionized water Instant Ocean (30 g/L salts) Natural sample (Newport) Sulfate solution (28 mM)

Simulation conditions: Temperatures:

60, 70, and 80˚ C

Initial Concentrations: 10, 5, and 1 mM persulfate

Figure 3. Persulfate decay curves in un-buffered aqueous solutions at 60˚ C. Water type is indicated by color, and initial concentrations are shown by marker shape. Curves are fit to data as first order decay.

6Results: Temperature Effects

Figure 4. Natural log of rate constants for first order decay of persulfate in un-buffered aqueous solutions. Temperature is indicated by color, solvent is shown on the bottom axis, and initial concentrations are given in the legend.

Observations: Faster decay at higher

temperatures. Slower decay than

predicted values. Slower decay in ionized

waters, but reduced effectat high temperatures.

Differentiation between initial persulfate concentrations at 60˚C.

Saline waters with and without organic matter exhibit similar kinetics.

7Conclusions: Persulfate

Completed Studies: Observation of temperature, water type and initial

concentration effects. Analyzing the influence of salinity and the sulfate ion. Comparing river and estuary water samples. Investigating solutions exposed to solid iron.

Summary: Temperature is the primary variable governing

persulfate stability. Increased salinity or ionic strength slows decay. Persulfate exhibits a long lifetime as an active oxidant

in aqueous solutions.

8Future Studies:

Examining effectiveness for disinfection: Fluorescent stains and flow cytometry. Observing persulfate at seawater temperatures. Determining optimal dose. The effect of metal ballast tanks. The effect of pH. Comparisons to current oxidative treatments

and regulations:

9Special Thanks

Paul Tratnyek Jim Nurmi Tawyna Peterson Jason Righter Paul Lim Tratnyek Lab

Needoba Lab Marisa Frieder Vanessa Green CMOP NSF-STARS