Transferred Ozone Dose Research Articles

Heterogeneous Catalytic Ozonation of Pharmaceuticals: Optimization of the Process by Response Surface Methodology.

Batch heterogeneous catalytic ozonation experiments were performed using commercial and synthesized nanoparticles as catalysts in aqueous ozone. The transferred ozone dose (TOD) ranged from 0 to 150 μM, and nanoparticles were added in concentrations between 0 and 1.5 g L-1, with all experiments conducted at 20 °C and a total volume of 240 mL. A Ce-doped TiO2 catalyst (1% molar ratio of Ce/Ti) was synthesized via the sol-gel method. Response surface methodology (RSM) was applied to identify the most significant factors affecting the removal of selected pharmaceuticals, with TOD emerging as the most critical variable. Higher TOD resulted in greater removal efficiencies. Furthermore, it was found that the commercially available metal oxides α-Al2O3, Mn2O3, TiO2, and CeO2, as well as the synthesized CeTiOx, did not increase the catalytic activity of ozone during the degradation of ibuprofen (IBF) and para-chlorobenzoic acid (pCBA). Carbamazepine (CBZ) and diclofenac (DCF) are compounds susceptible to ozone oxidation, thus their complete degradation at 150 μM transferred ozone dose was attained. The limited catalytic effect was attributed to the rapid consumption of ozone within the first minute of reaction, as well as the saturation of catalyst active sites by water molecules, which inhibited effective ozone adsorption and subsequent hydroxyl radical generation (●OH).

The role of noble metals in TiO2 nanotubes for the abatement of parabens by photocatalysis, catalytic and photocatalytic ozonation

The role of modified TiO2 nanotubes (TNTs) with noble metals was studied for photocatalysis, catalytic and photocatalytic ozonation of a paraben’s mixture. The TNTs were obtained by anodization and were modified by photodeposition with 0.25 mol% of Au, Pt or Pd.Results showed that solar photocatalysis led to higher degradation than UVA radiation, and under UVA radiation, the use of 3 Pt-TNTs (3 TNTs plates modified with Pt) and 3 Pd-TNTs present the same effect as the use of 5 and 7 pristine-TNTs plates, respectively. The best parabens removal was achieved for Pd-TNTs under UVA radiation and pristine TNTs under solar radiation, with 43% and 81% removal in 120 min, respectively.All the catalytic and photocatalytic ozonation experiments led to less ozone consumption than single ozonation (transferred ozone dose (TOD) = 5.27 mgO3/L) with total parabens abatement. Catalytic ozonation experiments suggest that the presence of metals can promote the formation of oxidative radicals, with the Au-TNTs presenting best performance (TOD ≈ 3.59 mgO3/L) while pristine TNTs led to TOD = 4.98 mgO3/L. For photocatalytic ozonation, the pristine TNTs led to the lowest ozone consumption (TOD = 3.74 mgO3/L).Moreover, the use of hydroxyl radical scavenger showed that hydroxyl radical is formed during single and photocatalytic ozonation mechanism, which should be related to the natural and surface catalytic ozone decomposition.

Comparison of macro and micro-pollutants abatement from biotreated landfill leachate by single ozonation, O3/H2O2, and catalytic ozonation processes

Micropollutants (MPs) in landfill leachate have attracted increasing attention because they pose a potential threat to the aquatic environment and ecosystems once discharged into nearby aquifers without proper treatment. Although ozone-based oxidative techniques perform well for the removal of MPs in low-strength water streams, their role in leachate containing high dissolved organic matter (DOM) concentration requires further exploration. Moreover, it is unclear the mechanism of different ozone-based processes in advanced treatment for biotreated landfill leachate. This study compared the single ozonation and two ozone-based advanced oxidation processes (AOPs, heterogeneous catalytic ozonation and O3/H2O2 process) for polishing biotreated leachate. The mechanism of different ozone-based processes during leachate treatment was explored, which facilitates selecting of the appropriate process based on leachate quality and target treatment requirements. The removal efficiency and energy requirements of the macro and micro-pollutants were evaluated. The results revealed that the role of catalytic ozonation is mainly to enhance the direct ozone oxidation, whereas the O3/H2O2 process is to promote the indirect oxidation. The strengthening effect was most visible in the early stage (specific transferred ozone dose (STOD) < 2 gO3/gDOC) for catalytic ozonation, whereas it was more pronounced in the later stage for the O3/H2O2 process. The removal of UV-quenching substances correlated well with the elimination of MPs (R2 > 0.95), which provides a surrogate-based predictive model for the removal of MPs from high-strength leachate. Catalytic ozonation consumed the least amount of energy when the desired chemical oxygen demand (COD) removal was ≤ 35 %, otherwise, the O3/H2O2 process was the most energy-efficient. In any process, MPs with O3 or OH reactivity could achieve more than 90 % elimination when the COD removal exceeded 30 %.

Carbon nitride photoactivation evaluation and degradation of a mixture of parabens by ozone assistance

Graphitic carbon nitride was investigated as an efficient and cheap catalyst for the degradation of a mixture of parabens through photo-aided processes. The ozone and g-C3N4 system was explored to obtain lacking necessary information regarding this combination for the proposed contaminants. The influence of key parameters was investigated to better understand the behavior of system and optimize it. Ultraviolet-A radiation promoted a more efficient activation of g-C3N4 compared to visible light. The photocatalytic ozonation process achieved higher parabens degradation rates and lower ozone consumption than the single technologies, reducing its overall cost. Basic and neutral conditions (pH = 7–11) promoted a better interaction between catalysts and contaminants, and radicals' formation. A catalyst concentration of 500 mg L−1 and parabens concentration of 1 mg L−1 resulted in >95 % removal of the three parabens within 15 min and with a lower transferred ozone dose required. Toxicity towards Allivibrio fischeri bacteria demonstrated a significant decrease in its luminescence inhibition after photocatalytic ozonation treatment, resulting in a non-toxic solution.

Ozone Kinetic Studies Assessment for the PPCPs Abatement: Mixtures Relevance

The increasing consumption of pharmaceutical and personal care products (PPCPs) by humankind has been causing an accumulation of contaminants (commonly referred to as contaminants of emerging concern), in effluents and water resources. Ozonation can be used to improve the removal of these contaminants during water treatment to alleviate this burden. In this work, the degradation of methyl (MP), propylparaben (PP), paracetamol (PCT), sulfamethoxazole (SMX), and carbamazepine (CBZ) by ozonation was assessed both for individual compounds and for mixtures with increasing complexity (two to five compounds). Ozonation was performed at pH3 to gain an insight on the exclusive action of molecular ozone as oxidizing agent. The degradation of contaminants was described as a function of time and transferred ozone dose, and the corresponding pseudo-first order kinetic rate constants (k’) were determined. PPCPs were degraded individually within 1.5 to 10 min. CBZ was the most quickly degraded (k’ = 1.25 min−1) and MP the most resistant to ozone (k’ = 0.25 min−1). When in the mixture, the degradation rate of the contaminants was slower. For parabens, the increase of the number of compounds in the mixture led to an exponential decrease of the k’ values. Moreover, the presence of more PPCPs within the mixture increased energy consumption associated with the treatment, thereby reflecting higher economic costs.

Performance evaluation of ozonation for removal of antibiotic-resistant Escherichia coli and Pseudomonas aeruginosa and genes from hospital wastewater

The performance of ozonation for the removal of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) using Escherichia coli and Pseudomonas aeruginosa carrying ARGs from hospital wastewaters was evaluated in this study. Bacterial inactivation was determined using plate count methods and real time PCR for ARG damage (Sul1, blatem, blactx, blavim and qnrS). The reduction rate of bacterial cells and ARGs was increased by different amounts of transferred ozone dose from 11 to 45 mg/L. The concentration of 108 cfu/ml bacteria was reduced to an acceptable level by ozone treatment after a 5 min contact time, Although the removal rate was much higher for concentrations of 106 cfu/ml and 104 cfu/ml bacteria. Overall, the tendency of gene reduction by ozonation from more to less was 16S rRNA > sul1 > blatem > blactx > qnrS > blavim. Given that plasmid-borne ARGs can potentially be transferred to other bacteria even after the disinfection process, our results can provide important insights into the fate of ARGs during hospital wastewater ozonation.

Integrating biodegradation and ozone-catalysed oxidation for treatment and reuse of biomass gasification wastewater

Syngas purification via wet-scrubbing processes generates a relevant amount of wastewater, which requires proper treatments before its disposal or reuse. Integrating chemical with cost-saving biological approaches represent a valuable alternative to traditional chemical-physical treatments. This study investigated the effectiveness of the BIO&CHEM treatment scheme for the treatment and reuse of wastewater collected from a wet-scrubber unit (chemical oxygen demand, COD = 2600 mg/L) containing several hazardous pollutants such as phenol (110 mg/L) and xylene (64 mg/L). The BIO&CHEM system included a sequencing batch biofilter granular reactor (SBBGR) and an ozonation unit that were operated at different hydraulic retention times (HRTs, from 5 to 1 day) and transferred ozone doses (TODs, 400, 280 and 250 mg/Linf), respectively. When a 4 d-HRT was selected, biologically treated wastewater was characterized by a COD of 140 mg/L and its toxicity on Daphnia magna was decreased from 100% to 5%. The integration between the biological SBBGR-based treatment (HRT = 1.5 d) and the ozonation (TOD = 280 mg/Linf) lowered effluent COD to 33 mg/L and erased toxicity on Daphnia magna. This operating condition resulted the most sustainable enabling multiple wastewater reuse and a significant reduction of plant size comparing with the biological treatment. Furthermore, the investigated aromatic and polyaromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs; including benzene, toluene, xylene and phenol) were completely removed. The analysis of the reactor biomass, performed at the end of the experimental trial, excluded also their mere accumulation within the reactor due to absorption or adsorption on the sludge.

TiO2 nanotube catalysts for parabens mixture degradation by photocatalysis and ozone-based technologies

The evolution of the analytical techniques allowed the detection of pollutants so called contaminants of emerging concern (CEC). Water scarcity is a reality lived by some populations. Thus, water reuse is mandatory to minimize this problematic. This implies that wastewater treatments must be improved. The Advanced Oxidation Processes (AOP) such as photocatalysis and ozonation can be suitable solutions for CECs abatement. Also, TiO2 powder catalyst is an important material in this field. However, its powder form presents a huge obstacle for industrial application, and the solution may be to support this material.This work studies the degradation of a mixture of 3 parabens by photocatalysis, catalytic and photocatalytic ozonation using TiO2 nanotube arrays (NTs). The studied catalysts were produced using electrolyte solutions with different ages, so the nanotubes growth ocurred at 5 (NTs_5) and 20 (NTs_20) anodization cycles. The toxicological assessment for the initial mixture, final samples and along the reaction time was performed using the cress seeds Lepidium sativum and the bacteria Aliivibrio fischeri. The photocatalysis with UVA radiation led to 50 % and 35 % parabens removal for NTs_5 and NTs_20 catalysts. This can be related to the different dimensional characteristics of the nanotubes. Ozone technologies led to total parabens degradation with an improvement when catalytic ozonation was applied. The use of NTs as catalysts in ozonation also reduced the transferred ozone dose (TOD) required for total parabens abatement when compared to single ozonation. The main parabens degradation mechanism seems to be via direct pathway by molecular ozone. Regarding the toxicity assessment, the toxicity did not change significatively, which can be explained by the intermediate’s formation.

How does the pre-treatment of landfill leachate impact the performance of O3 and O3/UVC processes?

In this study, O3 and O3/UVC processes were evaluated for the treatment of landfill leachate after biological nitrification/denitrification, coagulation, or their combinations. The O3-driven stage efficiency was assessed by the removal of color, organic matter (dissolved organic carbon (DOC) and chemical oxygen demand (COD)), and biodegradability increase (Zahn-Wellens test). Also, fluorescence excitation-emission matrix (EEM) and size exclusion chromatography coupled with OC detector (SEC-OCD) analysis were carried out for each strategy. The bio-nitrified-leachate (LN) was not efficiently mineralized during the O3-driven processes since the high nitrites content consumed ozone rapidly. In turn, carbonate/bicarbonate ions impaired the oxidation of the bio-denitrified-leachate (LD), scavenging hydroxyl radicals (HO•) and inhibiting the O3 decomposition. For both bio-leachates, only O3/UVC significantly enhanced the effluent biodegradability (>70%), but COD legal compliance was not reached. EEM and SEC-OCD results revealed differences in the organic matter composition between the nitrified-coagulated-leachate (LNC) and denitrified-coagulated-leachate (LDC). Nonetheless, the amount of DOC and COD removed per gram of ozone was similar for both. Cost estimation indicates the O3-driven stage as the costliest among the treatment processes, while coagulation substantially reduced the cost of the following ozonation. Thus, the best treatment train strategy comprised LDC (with methanol addition for denitrification and coagulated with 300 mg Al3+/L, without pH adjustment), followed by O3/UVC (transferred ozone dose of 2.1 g O3/L and 12.2 kJUVC/L) and final biological oxidation, allowed legal compliance for direct discharge (for organic and nitrogen parameters) with an estimated cost of 8.9 €/m3 (O3/UVC stage counting for 6.9 €/m3).

Disinfection enhancement of single ozonation by combination with peroxymonosulfate salt

Controlling pathogens and undesired biofouling in aquaculture or shipping activities is important due to the related potential economic and public health impacts. Accordingly, the treatment of seawater has increased interest in the maritime industry. Advanced Oxidation Processes are promising techniques for the treatment of different aqueous matrices. In this context, sulfate radical-based AOPs appear to be a good alternative for seawater applications. Consequently, the goal of this study is to evaluate the disinfection efficacy of combining the peroxymonosulfate salt ([PMS] = 1 and 5 mg L−1) with an ozonation treatment. Different inactivation processes (O3, PMS, and O3/PMS) have been investigated with Vibrio alginolyticus as a target microorganism. In comparison with single ozonation, kinetic rates have been accelerated by 65 % and 123 % with the addition of 1 and 5 mg L−1 of PMS, respectively. It results in a synergistic effect for the O3/PMS combination. The transferred ozone dose is also notably reduced for reaching the 4 Log-removal value (O3: 1.53 mg O3 ·L−1; O3/PMS: 0.87 mg O3 ·L−1 (1 mg PMS·L−1), and 0.59 mg O3 ·L−1 (5 mg PMS·L−1)). O3/PMS treatment also presents a greater residual effect and higher acute toxicity of the treated effluent. Results obtained suggest the peroxymonosulfate as a good promoter of disinfection in the presence of O3, not only by increasing the inactivation rate but also in minimizing bacterial regrowth, which implies greater cell damage during treatment processes. Thus, the O3/HSO5- process deserves further research as an alternative to traditional techniques for water treatment.

N-doped titanium dioxide for mixture of parabens degradation based on ozone action and toxicity evaluation: Precursor of nitrogen and titanium effect

Degradation of a mixture of five parabens was evaluated using photocatalytic oxidation, photolytic ozonation and photocatalytic ozonation, being applied UVA radiation and N-TiO2 doped catalysts. Photocatalytic oxidation was not able to eliminate parabens, achieving less than 10 % of removal. The use of ozone and UVA radiation resulted in total contaminants abatement with a transferred ozone dose (TOD) of 46.2 mg L−1. Photocatalytic ozonation also totally removed parabens but with a considerable reduction of TOD required along with higher COD and TOC removals, up to 35.7 % and 34.1 %, respectively, for the best catalyst (ammonia-doped 10 % N-TiO2). Toxicity tests were conducted using three different species. Lepidium sativum seeds had higher growth indexes (GIs) when exposed to solutions treated by photocatalytic ozonation reactions. Nevertheless, Allivibrio fischeri and Corbicula fluminea demonstrated lower toxic responses to photolytic ozonation treated solution which may be related with the different by-products formed.

Photocatalytic ozonation of parabens mixture using 10% N-TiO2 and the effect of water matrix

Nitrogen-doped TiO2 was applied in photocatalytic ozonation reactions for the degradation of a mixture of five parabens under UVA radiation, being evaluated the influence of the reaction medium. The initial mixture parabens concentration considered in these experiments was 50 mg L−1. The parabens degradation rate was considerably enhanced under neutral pH, specially using a buffered solution, leading to a complete removal under 60 min and with transferred ozone dose (TOD) 36% lower compared to reaction under natural conditions. Isopropanol, known radical scavenger, impeded the complete contaminants removal, affecting the reaction route and by-products formation, but when KI was jointly added, total removal was achieved under 30 min and with a TOD of 25.9 mg L−1. Parabens depletion was also improved in the presence of Cl−, SO42− and HCO3−, commonly present in wastewaters. The use of river water (RW) and a secondary wastewater (SWW) as water matrices maintained the process efficiency with lower TOD required, and treated solutions presented lower phytotoxicity towards Lepidium sativum.

Characterization and fate of EfOM during ozonation applied for effective abatement of recalcitrant micropollutants

Alterations occurring in the effluent organic matter (EfOM) during ozonation could be detrimental depending on the final application of the treated effluent. In this work, the fate of EfOM in different ozonized wastewaters was assessed through the monitoring of general water quality parameters and organic fractions determined through size-exclusion chromatography combined with organic carbon detection (SEC-OCD) analysis. These different components of EfOM were distinguished based on relative molecular weights and assigned to fractions named as biopolymers, humic substances, building blocks and low molecular weight neutrals and acids. The significant abatement (60–90%) of an ozone-refractory micropollutant (MP) was employed as reference to simulate potential scenarios in which also the presence of these species is wanted to be attenuated. Ultraviolet absorbance at 254 nm (UVA254) and chemical oxygen demand (COD) reductions ranged from 40 to 80% and from 10 to 45%, respectively, for ozone doses between 0.6 and 1.0 mM, depending on the organic matter content (both dissolved and suspended) and alkalinity of the effluents. Dissolved organic carbon (DOC) analysis showed 21–27% reductions in Membrane bioreactor (MBR) effluents, whereas for conventional activated sludge (CAS) samples this value increased (6–35%) during the oxidative treatment. This was attributed to the continuous solubilization of humic substances, according to SEC-OCD results. Moreover, accumulation of lower molecular weight fractions such as building blocks or acids was observed in all the tested effluents, and attributed to the breakdown of largest EfOM fractions, mainly humic substances. Relationships proposed in this work between humic substances evolution, water quality (UVA254) and process parameters (immediate ozone demand (IOD), IOD-normalized hydroxyl radical exposure (∫[OH]dt/IOD) and transferred ozone dose (TOD)) might be useful for EfOM variations estimations along ozonation.

Comparison of radical-driven technologies applied for paraben mixture degradation: mechanism, biodegradability, toxicity and cost assessment

Parabens (esters of p-hydroxybenzoic acid) are xenobiosis belonging to endocrine disruptors and commonly used as a preservative in cosmetics, food, pharmaceutical, and personal care products. Their wide use is leading to their appearance in water and wastewater in the range from ng/L to mg/L. In fact, the toxicity of benzylparaben is comparable to bisphenol A. Therefore, it is important to find not only effective but also ecofriendly methods for their removal from aqueous environment since the traditional wastewater treatment approaches are ineffective. Herein, for the first time, such extended comparison of several radical-driven technologies for paraben mixture degradation is presented. The detailed evaluation included (1) comparison of ozone and hydroxyl peroxide processes; (2) comparison of catalytic and photocatalytic processes (including photocatalytic ozonation); (3) characterisation of catalysts using SEM, XRD, DRS, XPS techniques and BET isotherm; (4) mineralisation, biodegradability and toxicity assessment; and (5) cost assessment. O3, H2O2/Fe2+, H2O2/UVC, O3/H2O2, O3/UVA, O3/H2O2/UVA, UVA/catalyst, O3/catalyst and O3/UVA/catalyst were selected from advanced oxidation processes to degrade parabens as well as to decrease its toxicity towards Aliivibrio fischeri, Corbicula fluminea and Lepidium sativum. Research was focused on the photocatalytic process involving visible light (UVA and natural sunlight) and TiO2 catalysts modified by different metals (Ag, Pt, Pd, Au). Photocatalytic oxidation showed the lowest efficiency, while in combining ozone with catalysis and photocatalysis process, degradation efficiency and toxicity removal were improved. Photocatalytic ozonation slightly improved degradation efficiency but appreciably decreased transferred ozone dose (TOD). Results indicate that the degradation pathway is different, or different transformation products (TPs) could be formed, despite that the hydroxyl radicals are the main oxidant.Graphical abstract

Impact of catalyst load, chemical oxygen demand and nitrite on disinfection and removal of contaminants during catalytic ozonation of wastewater

Calcium-silicate mineral Polonite® and aluminum-based catalyst (AL-1010S), previously identified as promising materials for catalytic ozonation, were used as catalysts to investigate the impact of some operating conditions (ratio ozone feed concentration to catalyst load) and wastewater characteristics (chemical oxygen demand - COD and nitrite - NO2 concentration) on the disinfection and removal of contaminants of emerging concern (CECs) during catalytic ozonation of wastewater. Tests conducted in synthetic wastewater using two different ozone gas concentration (4 and 8 g (nm3)) and 6 different catalyst loads provided ratios of 0.08, 0.11, 0.16, and 0.32. Results from the experiments indicated that the ratio of 0.11 was optimal and reached residual disinfection below 2 MPN mL−1 from the initial concentration of 5 ± 2 × 105 MPN mL−1 and removal of atrazine (ATZ) above 80% from the initial concentration of 100 ± 10 μg L−1 for an ozone dose of 41–45 mg L−1. Catalytic ozonation with the selected materials enhanced disinfection and ATZ removal from synthetic wastewater (SWW) in comparison to non-catalytic ozonation by making the treatment performance less sensitive to increased chemical oxygen demand (COD) and nitrite (NO2) in the matrix. Validation of the results in real wastewater effluents confirmed that catalytic ozonation enhanced disinfection. Catalytic ozonation using Polonite® and AL-1010S provided residual bacteria level of 0.6 ± 0.42 MPN mL−1 and 0.29 ± 0.41 MPN mL−1, while non-catalytic ozonation lead to an average residual bacteria level of 1.26 ± 0.09 MPN mL−1 for the same range of transferred ozone dose. However, under the conditions tested, a limited number of CECs were extracted at levels above the limits of quantification and further validation work required to evaluate the performance of catalytic ozonation for the removal of CECs.

Study of the influence of the matrix characteristics over the photocatalytic ozonation of parabens using Ag-TiO2

Parabens are widely used as antimicrobial and preservative in pharmaceutical and personal products. Their presence has been detected in rivers and wastewater treatment plants. Photocatalytic ozonation process using a low amount of 0.1 wt% Ag-TiO2 proved to be efficient on the degradation of a mixture of five parabens using a low transferred ozone dose (TOD). The pH effect was analyzed under acidic and neutral conditions. Also, the effect of hydroxyl radical scavenger on parabens degradation and on by-products formation was discussed. Hydroxyl radical present a significant role over parabens degradation and also on by-products formation. The reaction mechanism was analyzed using municipal wastewater as a matrix to infer about the behavior of the process at actual conditions. Municipal wastewater as a matrix clearly enhanced the parabens degradation when compared with the case where ultrapure water was used. In fact, the TOD required for total parabens degradation is lowered 10–20 mg/L of TOD. Therefore, to understand the main responsible species for this improvement, the effects of several ions naturally present in wastewater (HCO3−, Cl− and SO42−) were tested. According to the results it seems that sulfate radical improves the process, while chloride and bicarbonate radicals decrease the process efficiency. In terms of toxicity the luminescence inhibition for Vibrio fischeri was analyzed. The inhibition significantly decreased for treated spiked municipal wastewater.

LuminoTox as a tool to optimize ozone doses for the removal of contaminants and their associated toxicity

New treatment technologies and quality monitoring tools are needed for Contaminants of Emerging Concern (CECs) in wastewater. The purpose of this work was to assess the LuminoTox as a monitoring tool for CEC-associated toxicity in municipal wastewater during ozone treatment, and to evaluate the impact of different ozone feed concentrations at equivalent ozone doses for removing toxicity. The LuminoTox was sensitive at monitoring changes in toxicity of atrazine (ATZ) in synthetic wastewater (SWW) and in a 14 CECs mix in secondary effluent (SE) during ozone treatment. In both experiments, a decrease in toxicity was observed with increasing transferred ozone dose, which corresponded to a decrease in CEC concentration. For ATZ in SWW, a 5 ppm ozone feed showed better toxicity removal, up to 25% and 35% inhibition for LuminoTox algae biosensors SAPS I and SAPS II, respectively, for statistically equivalent ozone dose pairs of 43 mg (5 ppm ozone feed) and 36 mg (15 ppm ozone feed). The opposite was true for the 14 CECs in SE; the 15 ppm ozone feed showed better toxicity removal, up to a reduction of 37% and 40% for SAPS I and SAPS II inhibition, respectively, for statistically equivalent ozone dose pairs of 42 mg (5 ppm ozone feed) and 42 mg (15 ppm ozone feed). Different feed applications had an impact on the efficiency of toxicity removal for equivalent ozone doses; this efficiency appears to depend on the type of contaminants and/or wastewater matrix.

Paraben degradation using catalytic ozonation over volcanic rocks.

Parabens are widely used as antimicrobial and preservatives in pharmaceutical and personal care products and are continuously reaching the water streams. Conventional wastewater treatments are proven inefficient on the removal of this kind of contaminants from wastewater. Therefore, catalytic ozonation appears as a suitable option, due to the oxidant power of ozone and its high capacity of hydroxyl radical generation in the presence of a suitable catalyst. The main drawback of catalytic ozonation is related with the choice of stable and active catalysts at low cost. On this way, two volcanic rocks were tested to enhance the removal of a mixture of parabens by ozonation, improving their degradation. Indeed, catalytic ozonation with volcanic rock allowed total paraben degradation using a transferred ozone dose (TOD) of 55mg/L which corresponds to a reduction of about threefold the amount of TOD comparatively with single ozonation (170mg/L of TOD). Due to the presence of semiconductors on volcanic rock composition, the effect of UVA irradiation on paraben degradation was analyzed. The neutral and basic conditions enhanced catalytic ozonation comparatively to acid conditions. Higher pH values allowed a total methylparaben degradation with 35mg O3/L, whereas for low pH values, 55mg O3/L was required. The use of a radical scavenger proven that hydroxyl radicals are the main responsible for paraben degradation with catalytic ozonation. This was confirmed through the analysis of the by-products, where 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid (3,4-diHBA), 2,4-dihydroxybenzoic acid, and hydroquinone were quantified.

Noble metal–TiO2 supported catalysts for the catalytic ozonation of parabens mixtures

Abstract Parabens are endocrine disrupting compounds (EDCs) used as antimicrobial and preservatives and are reaching natural water courses with dangerous consequences. The efficiency of several catalysts in catalytic ozonation compared to single ozonation was tested for a mixture of five parabens degradation. On catalytic ozonation noble metals (Pd, Pt, Ag, Au) supported on TiO 2 were used, and their activity was compared with TiO 2 . Single ozonation was able to totally oxidize the initial parabens mixture using a high transferred ozone dose (TOD) (around 170 mg/L). However, the COD reduction was very low (25%). The combination of ozonation with the catalysts tested improved the parabens degradation and COD removal using lower TOD values. For best catalysts, 0.5% Pt–TiO 2 and 0.5% Pd–TiO 2 , total degradation of parabens was achieved for a TOD of 70 mg/L, which represents an ozone dose decrease by a factor of almost 3 in comparison to single ozonation. Moreover, these catalytic systems led to a COD and TOC removal of 36% and 18% respectively. The toxicity of the parabens solutions before and after treatments was evaluated using four different biological preparations. The initial parabens mixture was very toxic, but after treatment with all the conditions proposed the Vibrio fischeri luminescence inhibition and Asian clam mortality decreased while the germination index of Lepidium sativum increased. The studies made in a mammalian neuronal preparation, Wistar rat brain slices, indicate that the parabens mixture treated using single or catalytic ozonation had no effect on the measured neuronal ROS signals, unlike the raw mixture. Although total COD and TOC removal was not achieved, indicating the presence of refractory compounds, the toxicity analysis indicates that the transformation products are less environmentally harmful than parabens. These results show that, even using low catalyst loads, noble metals (especially Pt and Pd) can truly enhance ozone action over pollutants.

A novel model simulating reclaimed water disinfection by ozonation

Abstract Ozonation is broadly used as a disinfection technique for inactivation of pathogens in drinking water or reclaimed water. The conventional Chick-Watson model (C-W model) considering ozone exposure is sub-optimal in predicting the inactivation performance by ozonation in reclaimed water. In this study, the Escherichia coli (E. coli) and the Bacillus subtilis (B. subtilis) spore were used as test microorganisms and ozonation experiments were carried out upon different systems. The relationship between experimental inactivation and TOD was found to follow an S-shape curve. A novel and practical empirical model (L-I model) was set up to simulate the inactivation performance in reclaimed waters, regarding the transferred ozone dose (TOD), the instantaneous ozone demand (IOD) and the microbial resistance to ozone as the main parameters. According to the data fitting results, the parameters for E. coli and B. subtilis spores were determined. With TOD in 0–20 mg L−1 and IOD in 2–5 mg L−1, the calculated inactivation rates of the two test microorganisms could successfully match the experimental data derived from the batch ozonation test and the semi-continuous ozonation test for reclaimed water disinfection. The squared correlation coefficients (R2) for different tests range from 0.86 to 0.96 and the average relative errors (δ) are 0.08–0.59. This result verified that the L-I model is a practical way to simulate performances of ozonation systems for reclaimed water disinfection. Based on the model, the effects of water quality (IOD) and microbial resistance on disinfection performance were also analyzed.