Aleksey N. Pisarenko

Development of surrogate correlation models to predict trace organic contaminant oxidation and microbial inactivation during ozonation.

The performance of ozonation in wastewater depends on water quality and the ability to form hydroxyl radicals (·OH) to meet disinfection or contaminant transformation objectives. Since there are no on-line methods to assess ozone and ·OH exposure in wastewater, many agencies are now embracing indicator frameworks and surrogate monitoring for regulatory compliance. Two of the most promising surrogate parameters for ozone-based treatment of secondary and tertiary wastewater effluents are differential UV(254) absorbance (ΔUV(254)) and total fluorescence (ΔTF). In the current study, empirical correlations for ΔUV(254) and ΔTF were developed for the oxidation of 18 trace organic contaminants (TOrCs), including 1,4-dioxane, atenolol, atrazine, bisphenol A, carbamazepine, diclofenac, gemfibrozil, ibuprofen, meprobamate, naproxen, N,N-diethyl-meta-toluamide (DEET), para-chlorobenzoic acid (pCBA), phenytoin, primidone, sulfamethoxazole, triclosan, trimethoprim, and tris-(2-chloroethyl)-phosphate (TCEP) (R(2) = 0.50-0.83) and the inactivation of three microbial surrogates, including Escherichia coli, MS2, and Bacillus subtilis spores (R(2) = 0.46-0.78). Nine wastewaters were tested in laboratory systems, and eight wastewaters were evaluated at pilot- and full-scale. A predictive model for OH exposure based on ΔUV(254) or ΔTF was also proposed.

Effects of ozone and ozone/peroxide on trace organic contaminants and NDMA in drinking water and water reuse applications.

An ozone and ozone/peroxide oxidation process was evaluated at pilot scale for trace organic contaminant (TOrC) mitigation and NDMA formation in both drinking water and water reuse applications. A reverse osmosis (RO) pilot was also evaluated as part of the water reuse treatment train. Ozone/peroxide showed lower electrical energy per order of removal (EEO) values for TOrCs in surface water treatment, but the addition of hydrogen peroxide increased EEO values during wastewater treatment. TOrC oxidation was correlated to changes in UV(254) absorbance and fluorescence offering a surrogate model for predicting contaminant removal. A decrease in N-nitrosodimethylamine (NDMA) formation potential (after chloramination) was observed after treatment with ozone and ozone/peroxide. However, during spiking experiments with surface water, ozone/peroxide achieved limited destruction of NDMA, while in wastewaters net direct formation of NDMA of 6-33 ng/L was observed after either ozone or ozone/peroxide treatment. Once formed during ozonation, NDMA passed through the subsequent RO membranes, which highlights the significance of the potential for direct NDMA formation during oxidation in reuse applications.

Organic Contaminant Abatement in Reclaimed Water by UV/H2O2 and a Combined Process Consisting of O3/H2O2 Followed by UV/H2O2: Prediction of Abatement Efficiency, Energy Consumption, and Byproduct Formation

UV/H2O2 processes can be applied to improve the quality of effluents from municipal wastewater treatment plants by attenuating trace organic contaminants (micropollutants). This study presents a kinetic model based on UV photolysis parameters, including UV absorption rate and quantum yield, and hydroxyl radical (·OH) oxidation parameters, including second-order rate constants for ·OH reactions and steady-state ·OH concentrations, that can be used to predict micropollutant abatement in wastewater. The UV/H2O2 kinetic model successfully predicted the abatement efficiencies of 16 target micropollutants in bench-scale UV and UV/H2O2 experiments in 10 secondary wastewater effluents. The model was then used to calculate the electric energies required to achieve specific levels of micropollutant abatement in several advanced wastewater treatment scenarios using various combinations of ozone, UV, and H2O2. UV/H2O2 is more energy-intensive than ozonation for abatement of most micropollutants. Nevertheless, UV/H2O2 is not limited by the formation of N-nitrosodimethylamine (NDMA) and bromate whereas ozonation may produce significant concentrations of these oxidation byproducts, as observed in some of the tested wastewater effluents. The combined process of O3/H2O2 followed by UV/H2O2, which may be warranted in some potable reuse applications, can achieve superior micropollutant abatement with reduced energy consumption compared to UV/H2O2 and reduced oxidation byproduct formation (i.e., NDMA and/or bromate) compared to conventional ozonation.

Rapid analysis of perchlorate, chlorate and bromate ions in concentrated sodium hypochlorite solutions

A sensitive, rapid, and rugged liquid chromatography with tandem mass spectrometry (LC-MS/MS) method for measuring concentrations of perchlorate, chlorate, and bromate ions in concentrated sodium hypochlorite solutions is presented. The LC-MS/MS method offers a practical quantitation limit (PQL) of 0.05 microg L(-1) for ClO(4)(-), 0.2 microg L(-1) for BrO(3)(-), and 0.7 microg L(-1) for ClO(3)(-) and a sample analysis time of only 10 min. Additionally, an iodometric titration technique was compared with the LC-MS/MS method for measurement of chlorate ion at high concentration. The LC-MS/MS method was the most reproducible for chlorate concentrations below 0.025 M while the iodometric titration method employed was the most reproducible above 0.025 M. By using both methods, concentrations of chlorate can be measured over a wide range, from 0.7 microg L(-1) to 210 g L(-1) in hypochlorite ion solutions. Seven quenching agents were also evaluated for their ability to neutralize hypochlorite ion, thereby stopping formation of perchlorate ion in solution, without adversely impacting the other oxyhalide ions. Malonic acid was chosen as the quenching agent of choice, meeting all evaluation criteria outlined in this manuscript.

Preozonation Effects on the Reduction of Reverse Osmosis Membrane Fouling in Water Reuse

The purpose of this bench-top study was to demonstrate the feasibility and effect of applying ozone and ozone/peroxide upstream of reverse osmosis (RO) membranes as a means of controlling organic fouling during reuse applications. A series of ozone or ozone/peroxide doses was applied to surface water and a membrane bioreactor (MBR) filtrate using a HiPOx® reactor skid, with ozone-to-dissolved organic carbon ratios of approximately 0.25 to 1.75. Results from the flat-sheet testing indicate that both ozone- and ozone/peroxide-treated waters, even at the lowest ozone dose of 1.5 mg/L, fouled the membranes less than the MBR filtrate and surface control waters while both treated and control waters maintained consistent levels of salt rejection throughout the tests.

Detection of ozone gas using gold nanoislands and surface plasmon resonance

Gold nanoislands interact with gaseous ozone to produce a surface plasmon resonance shift, similarly to the interaction of ozone and gold nanoparticles in water. Gold nanoislands are produced by sputtering, which significantly simplifies the synthesis and produces controlled size for the gold nanoislands. The shift of surface plasmon resonance peak was monitored while gold nanoislands were exposed to variable concentration of gaseous ozone. The shift was then correlated with ozone concentration. Our current results indicate sensing gaseous ozone at concentration of as low as 20 microg/L is achievable. Gold nanoislands were reversed to their original wavelength and were able to cycle between the wavelengths as ozone was introduced and removed. Potentially, this system can be useful as a sensor that identifies the presence of ozone at low part-per-billion concentrations of ozone in gaseous media.

Investigation of the use of chlorine based advanced oxidation in surface water: Oxidation of natural organic matter and formation of disinfection byproducts

Abstract Disinfection byproduct (DBP) formation during the treatment of raw Colorado River Water (CRW) using aqueous chlorine and ultraviolet (UV) light advanced oxidation processes (AOPs) was investigated. Here, CRW was combined with aqueous chlorine from two distinct sources (electrochemically-generated Mixed Oxidant Solution (MOS) and commercial sodium hypochlorite) and then exposed to ultraviolet C (UV-C) and ultraviolet A (UV-A) light. The impact of the treatment process on the structure of (NOM) in the CRW was examined, as well as the resulting production of various halogenated organic Disinfection By-Products (DBPs). Both AOP conditions tested resulted in destruction of chromophoric components of the NOM, while formation of total amounts of haloacetic acids and trihalomethanes was far below the US EPA regulated maximum contaminant level values for these contaminants, even though the UV and chlorine doses used in these studies were much higher than the typical doses used in an actual treatment process.

Effects of molecular ozone and hydroxyl radical on formation of N-nitrosamines and perfluoroalkyl acids during ozonation of treated wastewaters

N-Nitrosamines—toxic disinfection byproducts commonly associated with chloramination—have recently been shown to increase after ozonation of some surface waters and treated wastewaters. In addition to five nitrosamines, two perfluoroalkyl acids (PFAAs) are included in the most recent U.S. EPA Contaminant Candidate List due to potential public health risks. In this manuscript, the potential roles of molecular ozone (O3) and hydroxyl radical (˙OH) were investigated in the formation of N-nitrosamines and PFAAs in treated wastewaters. The results herein are based on controlled bench-scale experiments designed to isolate the effects of O3 with the use of t-butanol as a ˙OH scavenger. Nitrous oxide gas saturated samples were exposed to gamma radiation to isolate the effects of ˙OH, and para-chlorobenzoic acid was used to assess ˙OH exposure. This study found that the presence of molecular ozone versus the hydroxyl radical promoted N-nitrosodimethylamine (NDMA) formation. Six other N-nitrosamines showed very little or no formation upon the ozonation of six treated wastewaters up to an O3 : TOC ratio of 1.0. For PFAAs, perfluorohexanoic acid (PFHxA) formed the highest and most consistently upon ozonation (up to an O3 : TOC ratio of 2.0) of the same six treated wastewaters. Presence of molecular ozone (more so than hydroxyl radical), appears to promote the formation of PFHxA and perfluorobutane sulfonic acid (PFBS). The effect of pH in the range of 6–8 upon the formation of NDMA and PFAAs was found to be minimal. These findings provide new understanding of the formation of oxidation byproducts during ozonation of reclaimed wastewaters. Depending on future regulatory determinations, NDMA and a few PFAAs could be of concern for potable reuse treatment systems that employ ozone.

Two New Methods of Synthesis for the Perbromate Ion: Chemistry and Determination by LC-MS/MS

Historically, the synthesis of perbromate ion through conventional oxidation routes has proven elusive. Herein, we report perbromate ion formation through the reaction of hypobromite and bromate ions in an alkaline sodium hypobromite solution. Formation was established via LC-MS/MS analysis of the bromate and perbromate ions in the reaction solutions over a 13-day period. Furthermore, it was discovered that the perbromate ion was also formed as a result of the electrospray ionization process. Selective reduction of the bromate ion prior to analysis was used to confirm the two formation pathways.