Persulfate for the Disinfection of Ballast Water Dani Miles CMOP Intern, Summer 2010 Mentor: Paul Tratnyek

Stability studies of persulfate in aqueous solutions: Project Overview: Purpose To 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. Objectives Stability 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. Stability studies of persulfate. The stability of persulfate in natural waters in various temperatures.

Background: 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.

Methods: 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. -Colorimetric: Reaction forms yellow product, so measure the color (absorbance) to reflect the amount of reagents. -Not selective, but not a concern for water types. (Calibration curve) Very dilute persulfate and large quantities of KI (strength of persulfate and limiting reagent) Efficient with Gilford Stasar III flow through spectrometer. Reaction and dilution takes time, but with this instrument, able to do 800 individual persulfate samples this summer! Temp studies: 54*9=486+redos=>500 Salinity: 9*9=81 Sulf: 6*9=54 River 2*9=18 Iron: 12*9=108 Processed about 800 persulfate samples. Figure 2. Calibration curves for DI, Instant Ocean and natural water samples.

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 -persulfate concentration naturally decreases in water. It oxidizes other species present and becomes the stable sulfate ion byproduct. -rate of disappearance varies with temp (higher temp=faster decay) -qualitative comparison of curves not enough. -Instead, fit curves with first order kinetics curve, extract rate constants for quantitative comparison. -Rate constants usually shown on Arrhenius plot (ln(k) vs. inverse temp) 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.

Results: Temperature Effects Observations: Faster decay at higher temperatures. Slower decay than predicted values. Slower decay in ionized waters, but reduced effect at high temperatures. Differentiation between initial persulfate concentrations at 60˚C. Saline waters with and without organic matter exhibit similar kinetics. -persulfate concentration naturally decreases in water. It oxidizes other species present and becomes the stable sulfate ion byproduct. -rate of disappearance varies with temp (higher temp=faster decay) -qualitative comparison of curves not enough. -Instead, fit curves with first order kinetics curve, extract rate constants for quantitative comparison. -Rate constants usually shown on Arrhenius plot (ln(k) vs. inverse temp) -With so much data stacked at each temp, Expanded out according to water type. Looking at graph: -Horizontal lines correspond to expected lit values for persulfate decay in DI water at each temperature, according to linear fit of an Arrhenius plot. (single values according to each temperature) -Color coded by temp (warmer color is warmer temperature) -Organized by water type -Each initial concentration is shown within temp and water type. Conclusions - Faster decay at higher temps (higher rate constant) Usually slower decay than lit values particularly interesting trend with DI water—questions previous results Saline and sulfate solutions always lower. Generally Slower decay in saline waters: DI versus all (not as much effect at higher temps) - Similar kinetics between InstO and NatO: saline waters, regardless of organic matter 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.

Conclusions: 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.

Examining effectiveness for disinfection: Future 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:

Special Thanks Paul Tratnyek Jim Nurmi Needoba Lab Marisa Frieder Tawyna Peterson Jason Righter Paul Lim Tratnyek Lab Needoba Lab Marisa Frieder Vanessa Green CMOP NSF-STARS