Applied Ozone Dose Research Articles

Identification of Degradation By-Products of Selected Pesticides During Oxidation and Chlorination Processes

Abstract Advanced oxidation processes (AOPs) are considered to be one of the most effective methods for the decomposition of a wide range of hardly-biodegradable organic compounds, including pesticides. The implementation of such processes in the water streams treatment often leads to the formation of decomposition by-products of micropollutants occurring in water. These compounds, even in concentrations of a few ng/dm3, may negatively affect the water quality. Therefore, there is a need for detailed analyses that will allow to identify intermediates found in the AOP solutions and to assess their impact on the aquatic environment. The paper presents an attempt to identify by-products of three pesticides: triclosan, triallat and oxadiazon during ozonation, chlorination and UV irradiation of their water solutions. The identification of compounds was performed based on the results of the GC-MS analysis using the NIST v17 mass spectral library. It has been shown that during all of tested advanced oxidation processes, incomplete degradation of pesticides occurs. The number of micropollutant decomposition by-products increases with the increase of the applied ozone dose and UV exposure time. During the chlorination process Cl− atoms were added to the tested compound molecules. In the case of triclosan, it led to the generation of compounds containing four or five chlorine atoms in their structure. The toxicological analysis performed by the use of the Microtox® and Lemna sp. Growth Inhibition Test showed the toxic nature of post-process solutions. The decomposition by-products of triclosan and triallate, generated during the UV irradiation process, were highly toxic against the test organisms (toxic effect > 75 %). This makes it impossible to drain these solutions into the natural environment.

Natural fluorescence emission – an indirect measurement of applied ozone dosages to remove pharmaceuticals in biologically treated wastewater

ABSTRACT This study investigated the feasibility of UV-absorbance and fluorescence as monitoring tools for ozone dosages applied to effluents from wastewater treatment plans (WWTPs). Secondary treated effluents from five Swedish WWTPs underwent ozonation (at dosages ranging 0.5–12.0 mg O3/L) in bench-scale experiments. Correlations between ozone dosages and UV-absorbance at 254 and 272 nm were extrapolated with the first one being preferential for the wastewaters used because of its higher signal. UV-absorbance could detect differences in the applied ozone dosage as low as 1 mg/L, making it suitable to monitor effluent ozone treatment processes. Next, fluorescence was investigated at wavelength transitions that have being associated with humic-like fluorescents (Ex249Em450 and Ex335Em450) and protein-like fluorescents (Ex275Em340 and Ex231Em360 and Ex231Em315 and Ex275Em310). The Ex249Em450 transition was found to have the highest signal in all effluents and the best linear regression fitting with the ozone dosages over a wide range. However, low ozone dosages (0.5–3.0 mg O3/L), Ex335Em450 wavelength transition showed a more constant slope among the different domestic wastewater samples with slightly better R 2 values than the Ex249Em450 transition. Fluorescence removal via ozonation correlated with the pharmaceutical removal; however, the wellness of fitting was directly dependent on the pharmaceuticals’ reactivity with ozone. Pharmaceuticals with moderate reactivity towards ozone appeared to be linearly correlated with the Ex249Em450 transition, while very reactive or recalcitrant pharmaceuticals had an exponential or a parabolic dependency. This means that fluorescence can potentially be used as a qualitative tool for pharmaceutical removal. Abbreviations: APIs, Active Pharmaceutical Ingredients; DOM, Dissolved organic matter; WWTPs, wastewater treatment plans; NOM, Natural organic matter; UV, Ultra-Violet light; DOC, Dissolved organic carbon.

Disinfection of anaerobic/aerobic sanitary effluent using ozone: Formaldehyde formation.

The scarcity of natural resources supports the perspective of reusing treated effluents, mainly in agriculture, where the reduction in the demand of drinking water and the provision of alternative sources for nutrients are important. However, the process of disinfection, essential to the protection of human health, generates deleterious by-products to both humans and the environment. This research aimed to evaluate the use of ozone as a disinfectant for wastewater treated by anaerobic/aerobic baffled reactor for later agricultural reuse. Disinfection tests were conducted by applying ozone, in batch, with applied dosages of 5, 8, and 10mgO3 /L and contact time of 7min. All the tests led to formaldehyde formation, therefore within the standard suggested by the World Health Organization. For the indicators total coliforms and Escherichia coli, the ozone was considered effective, satisfying the criteria for agricultural reuse according to the World Health Organization of a dosage of 8mgO3 /L. PRACTITIONER POINTS: Proposal of decentralized system (anaerobic/aerobic baffled reactor+ozone disinfection) for effluent treatment for agricultural reuse. Formation of formaldehyde dependent on applied ozone dose. Demand of ozone consumed preferentially for the formation of by-products, with low removal of COD. High formaldehyde formation (high ozone demand) can impair the inactivation of pathogens. System promotes effluent that meets the standards established by the World Health Organization (WHO) for agricultural reuse.

Assessment of ozonation reactivity of aromatic and oxidized naphthenic acids species separated using a silver-ion solid phase extraction method

Owing to the complexity of naphthenic acids (NAs) in oil sands process water (OSPW), previous ozone-treatment studies mainly investigated the removal of classical NAs (aliphatic O2−NAs) and the understanding of ozonation reactivity of other NA species has been limited. This work utilized a silver-ion solid phase extraction (SPE) approach to separate individual NA species into 20 fractions before subsequent ozone treatment. The ozonation reactivity of aromatic and oxidized NA species in isolated fractions was studied for the first time. Untreated and ozone-treated SPE fractions were characterized using ultra performance liquid chromatography ion mobility time-of-flight mass spectrometry. The removals of aliphatic O2−NAs (Fraction 3), aromatic O2−NAs (Fraction 8), O3−NAs (Fraction 11), and O4−NAs (Fraction 17) with an applied ozone dosage of 16.8 mg L−1 were 97.2%, 94.7%, 59.4% and 44.7%, respectively. The results showed that aromatic and oxidized NAs with larger carbon number were favorably removed during ozonation treatment. Comparison of the ozone utilization efficiency for different NA species indicated that the degradation of oxidized NAs consumed more ozone in molar ratio than the degradation of classical and aromatic NAs. The reactivity of oxidized NAs was lower than that of classical NAs because the former consumed more ozone in molar ratio during reactions. Knowing the reactivity of different NA species is crucial for the design of ozonation systems targeting species with high toxicity. Moreover, the utilization of silver-ion SPE pre-separation approach has been demonstrated for future studies investigating the degradation mechanism of distinct NA species under other treatment conditions.

Coupling of electrocoagulation and ozone treatment for textile wastewater reuse

Industrial textile wastewater is usually characterized by high pH, intense color and extremely high salinity, especially in case of wastewater generated after dyeing. Due to the complex matrix of textile wastewater, the selection of an appropriate treatment method can be a challenge. This paper presents the advantages of coupling electrocoagulation (EC) and ozonation (O3) as one-step (EC + O3) and two-step (EC → O3) operations. The combination of EC and O3, which both worked well in salty environment, gave very good results in the case of aqueous solutions and real industrial wastewater containing Reactive Black 5 (RB5). Very high color removal, more than 95%, was achieved in a very short treatment time (less than 18 min, while ca. 60 min was required in the case of individual O3). At the same time the applied ozone dose was reduced from 1.69 g/L, when using O3 only, to less than 0.3 g/L for EC → O3. The results of color removal and mineralization analysis indicated the high efficiency of both the EC + O3 and EC → O3 processes; however, the cost evaluation revealed that the EC → O3 treatment was more advantageous. EC preformed as a single treatment resulted in an increase in toxicity, but coupling EC with O3 reduced this undesirable effect. Very promising results were obtained in recycling trials. The color difference (DEcmc, according to ISO 105-J03) of textiles dyed with purified wastewater (brine) were between 0.28 and 0.98 (below the limiting value of 1.5).

Pre-ozonation of source water: Assessment of efficacy against Giardia duodenalis cysts and effects on natural organic matter

The protozoan Giardia duodenalis is one of the parasites of primary concern in drinking water treatment plants, due to its resistance to chlorination. Another matter of concern regarding chlorination of drinking water is the formation of disinfection by-products in the presence of precursors such as natural organic matter (NOM). In this study, the effects of ozonation (5 mg L−1) on G. duodenalis cysts in raw surface water from a drinking water treatment plant were evaluated, and the presence and alteration of NOM were assessed, as an indicative of the potential to prevent total organic halogen (TOX) formation during post-chlorination. Following ozone treatment, the presence of damaged cysts was observed by direct immunofluorescence assay (IFA) and confirmed by the molecular approach propidium monoazide-polymerase chain reaction (PMA-PCR). Using an animal model, analysis of the intestinal tissues revealed that 80% of the animals inoculated with ozonated water were positive for trophozoites. This study shows that analysis of intestinal fragments is imperative to accurately assess animal infection following inoculation of treated cysts. More importantly, considering the low infective dose of Giardia cysts in susceptible hosts, an ozone dosage usually applied in drinking water treatment plants did not completely inactivate G. duodenalis cysts in surface water. Nonetheless, the results suggest that competitive reactions with NOM have occurred, and the applied ozone dosage has proven useful to remove NOM reactivity, and thus prevent halogenated DBP formation during post-chlorination.

Rotating packed bed as a novel disinfection contactor for the inactivation of E. coli by ozone

The intensification of mass transfer and mixing in ozone-based disinfection processes is very important in order to achieve a certain disinfection effect at a reasonable cost. This study employed rotating packed bed (RPB), an efficient process intensification device, as an ozone-disinfection contactor, and its performance on disinfection and mass transfer was evaluated by the inactivation of Escherichia coli (E. coli) and mass transfer coefficient (kLa). The ozone exposure (Ct value) and the log inactivation of E. coli in the RPB reached 0.0008–0.0014 min mg L−1 and 6.8–7.3 in phosphate buffered saline buffer, respectively. And the kLa in RPB rose from 0.030 to 0.186 s−1 with the increase of liquid flow rate from 10 to 60 L h−1. The increase of rotation speed of the RPB enhanced the log inactivation and kLa simultaneously. It was also noted that a higher gaseous ozone concentration at the identical applied ozone dosage is favorable for the inactivation of E. coli. The calculation of Hatta number indicated that the inactivation of E. coli in RPB is a diffusion-controlled process for which RPB is well suited. Compared to the conventional bubble reactor, the achievement of high disinfection efficacy at a low Ct value in RPB revealed that RPB is an efficient ozone disinfection contactor for the inactivation of microorganisms in water.

Kinetic study of colored species formation during paracetamol removal from water in a semicontinuous ozonation contactor

Paracetamol aqueous solutions, when ozonized, acquired a strong red coloration depending on the applied ozone dose and the initial pH of the aqueous solution. Then, this color loses intensity and turns to yellow. Color formation is favored when operating at initial pH0 = 12.0 and ozone flow-rate 4.2 mg/min. A mechanism describing color formation was proposed, being the main pathway involved an initial paracetamol hydroxylation to yield 3-hydroxyacetaminophen followed by the formation of 2-amino-5-hydroxyacetofenone. Then, these compounds are degraded to colored oxidation by-products. A model describing color evolution was also proposed, considering first-order kinetics for both color formation and degradation. The corresponding kinetic constant values were determined to be kf = 0.01 (1/min) and kd = 0.03 pH −0.055 (1/min), respectively. A relationship between aromaticity loss and color changes during the reaction has been estimated considering the parameter α=kA/kf, being α = 1.62 pH + 3.5 and the first-order rate constant for aromaticity loss given by kA = 0.0162 pH + 0.035 (1/min).

Antimicrobial activity and acute toxicity of ozonated lomefloxacin solution.

Lomefloxacin (LOM) is a synthetic antimicrobial from the fluoroquinolone family (FQ) used as a veterinary and human drug. Once in the environment, LOM may pose a risk to aquatic and terrestrial microorganisms due to its antimicrobial activity. This study evaluated the effect of ozonation of LOM (500μgL-1), the residual antimicrobial activity against Escherichia coli and acute toxicity against Vibrio fischeri. In addition, degradation products were investigated by UHPLC-MS/MS and proposed. Ozonation was carried out varying the applied ozone dose from 0 to 54.0mgL-1 O3 and pH values of 3, 7, and 11. Ozonation was most efficient at pH11 and led to 92.8% abatement of LOM in a 9-min reaction time (54.0mgL-1 O3 applied ozone dose). Ozonation at pH3 was able to degrade 80.4% of LOM. At pH7, 74.3% of LOM was degraded. Although the LOM concentration and the antimicrobial activity of the solution dropped as ozone dose increased (antimicrobial activity reduction of 95% at pH11), toxicity to V. fischeri increased for pH7 and 11 (i.e., 65% at pH7 and 75% at pH11). The reduction in antimicrobial activity may be related to the oxidation of piperazinyl and the quinolone moiety. The formation of intermediates depended on the oxidant (hydroxyl radicals or/and molecular O3) that acted the most in the process.

Influence of pH and ozone dose on sulfaquinoxaline ozonation

Sulfaquinoxaline (SQX) is an antimicrobial of the sulfonamides class. Usually employed in veterinary medicine, this contaminant of emerging concern has been found in superficial and groundwater and its consequences for the environment and human health are not completely known. In this study, SQX (C0 = 500 μg L−1, 1 L) degradation by an ozonation process at pH 3, 7, and 11 was evaluated. Ozonation was effective in degrading SQX: efficiency exceeding 99% was obtained applying an ozone dose of 2.8 mg L−1 at pH 3. Assays were performed according to a 22 design of experiments (DOE) with star points and three central points for statistical validity. Minimum and maximum levels were set at 3 and 11 for pH, and 0 and 11.5 mg L−1 for applied ozone dose. There was no significant interaction between these variables, and the pH value played the most important role in terms of contaminant degradation. In relation to toxicity, samples ozonated at pH 3 did not inhibit the luminescence of the bacteria, even though different intermediates were formed and identified by mass spectra. At pH 7, inhibition of luminescence remained almost constant (at around 30%) according to ozonation time or ozone dose. However, the hydroxyl radical, the major oxidant at pH 11, was responsible for the formation of toxic intermediates.

Ozonation of carbamazepine, diclofenac, sulfamethoxazole and trimethoprim and formation of major oxidation products

The degradation of four pharmaceuticals, carbamazepine (CBZ), diclofenac (DCF), sulfamethoxazole (SMX) and trimethoprim (TMP) by ozonation was studied under a range of experimental conditions, including ozone dosage and concentration of target compounds. The concentration profile of the pharmaceuticals and detection of any by-products formed was carried out using liquid chromatography mass spectrometry. CBZ, DCF, TMP and SMX at initial concentration of 5 mg/L each were degraded to below the method detection limit (1 μg/L) when they reacted with 1.6, 2.3, 2.8 and 4.5 mg/L of ozone, respectively. For each parent compound several by-products were detected after the ozone treatment. A number of these by-products have not been previously reported in the literature. Some of these by-products were founds to be quite resistant to ozone up to applied ozone dosages of 15 mg/L.

Evaluation of the removal of antiestrogens and antiandrogens via ozone and granular activated carbon using bioassay and fluorescent spectroscopy

Antiestrogens and antiandrogens are relatively rarely studied endocrine disrupting chemicals which can be found in un/treated wastewaters. Antiestrogens and antiandrogens in the wastewater treatment effluents could contribute to sexual disruption of organisms. In this study, to assess the removal of non-specific antiestrogens and antiandrogens by advanced treatment processes, ozonation and adsorption to granular activated carbon (GAC), the biological activities and excitation emission matrix fluorescence spectroscopy of wastewater were evaluated. As the applied ozone dose increased to 12 mg/L, the antiestrogenic activity dramatically decreased to 3.2 μg 4-hydroxytamoxifen equivalent (4HEQ)/L, with a removal efficiency of 84.8%, while the antiandrogenic activity was 23.1 μg flutamide equivalent (FEQ)/L, with a removal efficiency of 75.5%. The removal of antiestrogenic/antiandrogenic activity has high correlation with the removal of fulvic acid-like materials and humic acid-like organics, suggesting that they can be used as surrogates for antiestrogenic/antiandrogenic activity during ozonation. The adsorption kinetics of antiestrogenic activity and antiandrogenic activity were well described by pseudo-second-order kinetics models. The estimated equilibrium concentration of antiestrogenic activity is 7.9 μg 4HEQ/L with an effective removal efficiency of 70.5%, while the equilibrium concentration of antiandrogenic activity is 33.7 μg FEQ/L with a removal efficiency of 67.0%. Biological activity evaluation of wastewater effluents is an attractive way to assess the removal of endocrine disrupting chemicals by different treatment processes. Fluorescence spectroscopy can be used as a surrogate measure of bioassays during ozonation.

Coagulation and oxidation for controlling ultrafiltration membrane fouling in drinking water treatment: Application of ozone at low dose in submerged membrane tank

Coagulation prior to ultrafiltration (UF) is widely applied for treating contaminated surface water sources for potable supply. While beneficial, coagulation alone is unable to control membrane fouling effectively in many cases, and there is continuing interest in the use of additional, complementary methods such as oxidation in the pre-treatment of raw water prior to UF. In this study, the application of ozone at low dose in the membrane tank immediately following coagulation has been evaluated at laboratory-scale employing model raw water. In parallel tests with and without the application of ozone, the impact of applied ozone doses of 0.5 mg L−1 and 1.5 mg L−1 (approximately 0.18 mg L−1 and 0.54 mg L−1 consumed ozone, respectively) on the increase of trans-membrane pressure (TMP) was evaluated and correlated with the quantity and nature of membrane deposits, both as a cake layer and within membrane pores. The results showed that a dose of 0.5 mgO3 L−1 gave a membrane fouling rate that was substantially lower than without ozone addition, while a dose of 1.5 mgO3 L−1 was able to prevent fouling effects significantly (no increase in TMP). Ozone was found to decrease the concentration of bacteria (especially the concentration of bacteria per suspended solid) in the membrane tank, and to alter the nature of dissolved organic matter by increasing the proportion of hydrophilic substances. Ozone decreased the concentration of extracellular polymeric substances (EPS), such as polysaccharides and proteins, in the membrane cake layer; the reduced EPS and bacterial concentrations resulted in a much thinner cake layer, although the suspended solids concentration was much higher in the ozone added membrane tank. Ozone also decreased the accumulation and hydrophobicity of organic matter within the membrane pores, leading to minimal irreversible fouling. Therefore, the application of low-dose ozone within the UF membrane tank is a potentially important approach for fully mitigating membrane fouling.

UASB reactor effluent disinfection by ozone and chlorine

This research studied the sequential ozone and chlorine process with respect to, the inactivation of indicator bacteria and the formation of ozone disinfection byproducts in sanitary wastewater effluent. The applied ozone doses were 5, 8 and 10 mg.O3.L−1, followed by chlorine doses of 10, 20 and 30 mg.L−1, respectively. After the sequential ozone/chlorine process, the mean reduction in chemical oxygen demand ranged from 9 to 37%. Total coliform inactivation ranged from 1.59 to 3.73 log10, and E. coli was always <1 CFU 100 mL−1. Ozonation resulted in the formation of aldehydes, which were not significantly impacted by the subsequent chlorine dose (P ≤ 0.05).

Ozone Effects on Botrytis cinerea Conidia using a Bubble Column: Germination Inactivation and Membrane Phospholipids Oxidation

Ozone treatments were applied on conidia aqueous suspensions in order to determine the minimal applied ozone dose to limit conidia germination and to observe the mechanisms involved in the spores inactivation. Conidia germination was significantly reduced, bubbling for at least 0.5 min as a gas with a minimal ozone concentration of 1 g.m−3. The applied ozone doses induce the membrane phospholipids oxidation, determined by the malondialdehyde quantification. Membrane phospholipids oxidation and inactivation rate are correlated. So, lipid peroxidation and consequently the alteration of the membrane integrity are involved in the antifungal action of ozone.

Oestrogenicity assessment of s-triazines by-products during ozonation

The triazines are a group of herbicides with a wide range of uses. Atrazine is, in fact, one of the most used agricultural pesticides in the world. The terbuthylazine is applied as a substitute of atrazine in some countries of Europe since 2004, when the European Union announced a ban of atrazine because of ubiquitous water contamination. In this study, both atrazine and terbuthylazine were degraded by the ozone process to estimate the efficiency on pesticide removal in water, the intermediates formed and their potential oestrogenic activity using the yeast oestrogen screen (YES) test. Both pesticides were rapidly eliminated from the medium during ozonation (applied ozone dose 0.083 and 0.02 mmol O3 L−1, respectively). The results show that both compounds generated similar by-products from ozone degradation. Moreover, significant oestrogenic activity was detected for both atrazine and terbuthylazine intermediates, during the first minutes of ozonation. The YES assay used in this study proved to be a sensitive tool in assessing trace amounts of oestrogenic chemicals, which can represent critical issues influencing the experimental results in environmental applications.

Post-treatment of anaerobic effluent by ozone and ozone/UV of a kraft cellulose pulp mill.

Pulp and paper mill effluents represent a challenge when treatment technologies are considered, not only to reduce organic matter, but also to reduce the toxicological effects. Although anaerobic treatment has shown promising results, as well as advantages when compared with an aerobic system, this process alone is not sufficient to reduce recalcitrant compounds. Thus, an advanced oxidation process was applied. This experiment was performed to determine the effect of ozone and ozone/UV treating a horizontal anaerobic immobilized biomass reactor effluent from a kraft cellulose pulp mill for 306 days with an organic volumetric load of 2.33 kgCOD/m³/day. The removal of organic compounds was measured by the following parameters: adsorbable organically bound halogens (AOX), total phenols, chemical oxygen demand (COD), dissolved organic carbon and absorbance values in the UV-visible spectral region. Moreover, ecotoxicity and genotoxicity tests were conducted before and after treatment with ozone and ozone/UV. At an applied ozone dosage of 0.76 mgO₃/mgCOD and an applied UV dosage of 3.427 Wh/m(3), the organochlorine compounds measured as AOX reached removal efficiencies of 40%. Although the combination of ozone/UV showed better results in colour (79%) and total phenols (32%) compared with only ozone, the chronic toxicity and the genotoxicity that had already been removed in the anaerobic process were slightly increased.

Discfiltration and ozonation for reduction of nutrients and organic micro-pollutants from wastewater – a pilot study

The combination of coagulation/flocculation and discfiltration with ozonation to reduce nutrients and organic micro-pollutants in secondary effluent was studied in pilot scale at Lundåkraverket wastewater treatment plant in Landskrona, Sweden. With a chemical dose of 4 gAl3+/m3 and 1.5 g/m3 cationic polymer as active material effluent water quality with regards to total phosphorous (Tot-P), suspended solids and turbidity were 0.03, 2 mg/l and 0.5 Nephelometric Turbidity Units (NTU) in average. The effluent water quality was similar whether ozonation with an applied ozone dose of 2–9 gO3/m3 was performed prior to or after coagulation/flocculation/discfiltration. The results were corresponding to removal efficiencies for the coagulation/flocculation/discfiltration process of 94, 74 and 85% for Tot-P, suspended solids and turbidity, respectively. For organic micro-pollutants removal, it was found to be beneficial to perform coagulation/flocculation/discfiltration prior to ozonation as the ozone requirements were lowered for the dosing intervals applied. The removal was in the range of 38–98% depending on process configuration and ozone dose.

UV-C irradiation enhanced ozonation for the treatment of hazardous insecticide methomyl

Decomposition of hazardous methomyl via ozonation (OZ) and ultraviolet photolysis OZ (UV-OZ) processes was studied. The decomposition efficiencies of methomyl (ηmet) and total organic carbon (ηTOC) were determined to measure the oxidative destruction ability. In the OZ process with pH 7 and 10, methomyl can be decomposed completely at the applied ozone dosage per volume of liquid (mA,in) of 300 mg L−1. At mA,in of 3600 mg L−1 with pH values controlled at 2, 7 and 10, the ηTOC values are 13, 26 and 43%, respectively, showing the great influence of pH value on the ηTOC for the OZ process. Combining the UV-C radiation in the OZ process can promote the decomposition of O3 to form OH˙ radical which has higher oxidizing ability than O3 and can further decompose the acidic intermediates, thus increasing the ηTOC. At mA,in of 3600 mg L−1 and UV-C lamp irradiation power of 16 W with controlled pH values at 2, 7 and 10 in the UV-OZ process, the ηTOC values are close to that (72%) without controlling the pH value. The results indicate that the UV-C radiation can enhance the mineralization with insignificant effect of pH value.

Ozone inactivation of infectious prions in rendering plant and municipal wastewaters

Disposal of tissues and organs associated with prion accumulation and infectivity in infected animals (designated as Specified Risk Materials [SRM]) is strictly regulated by the Canadian Food Inspection Agency (CFIA); however, the contamination of wastewater from slaughterhouses that handle SRM still poses public concern. In this study, we examined for the first time the partitioning of infectious prions in rendering plant wastewater and found that a large proportion of infectious prions were partitioned into the scum layer formed at the top after gravity separation, while quite a few infectious prions still remained in the wastewater. Subsequently, we assessed the ozone inactivation of infectious prions in the raw, natural gravity-separated and dissolved air flotation (DAF)-treated (i.e., primary-treated) rendering plant wastewater, and in a municipal final effluent (i.e., secondary-treated municipal wastewater). At applied ozone doses of 43.4–44.6mg/L, ozone was instantaneously depleted in the raw rendering plant wastewater, while a greater than 4-log10 inactivation was achieved at a 5min exposure in the DAF-treated rendering plant wastewater. Prion inactivation in the municipal final effluent was conducted with two levels of applied ozone doses of 13.4 and 22.5mg/L, and a greater than 4-log10 inactivation was achieved at a 5min exposure with the higher ozone dose. Efficiency factor Hom (EFH) models were used to model (i.e., fit) the experimental data. The CT (disinfectant concentration multiplied by contact time) values were determined for 2- and 3-log10 inactivation in the municipal final effluent treated with an ozone dose of 13.4mg/L. Our results indicate that ozone could serve as a final barrier for prion inactivation in primary- and/or secondary-treated wastewaters.