Ozone Disinfection Processes Research Articles

Modelling ozone disinfection of secondary effluents in presence of scavengers and metal catalyst: Synergistic effect and regrowth

The variation in the matrix composition can lead to the use of inadequate oxidant dose and disturb a correct ozone treatment. The aim of this study was to model the ozone disinfection process of secondary effluents in presence of carbonate and nitrate using metal ozonation catalysts. The biological indicator used was the Escherichia coli. The ROH,O3 concept was applied to quantify and compare the E. coli inactivation by the radical pathway. The metals Fe and Zn caused a significative improvement on ROH values (p < 0.05) even in the presence of the •OH radical scavengers (carbonate and nitrate). The modelling results based on ROH values demonstrate that E. coli inactivation can be predicted satisfactory (R2 > 0.94–0.99), being a useful tool for the generalized prediction of disinfection by ozone. The presence of metals inhibited significantly bacterial regrowth (p < 0.05) even in the scavengers presence.

Change of the Oxidation-Reduction Potential of Model and Natural Waters in the Ozone Disinfection Process

The successful use of ozonation for water disinfection and purification requires the determination of optimal treatment conditions, which is associated with a large amount of experiments. At the same time, traditional methods for controlling the process of inactivation of microorganisms, being quite laborious and time consuming, allow one to obtain data on the degree of water disinfection only after 18–48 h after the experiment and sampling. Given that ozone is an oxidizing reagent and its presence in the treated water causes a change in the oxidation-reduction potential (ORP) of the solution, this study is aimed at changing the ORP during ozone disinfection of water and at investigating the possibility of express control of this process. As objects of study, we have used model solutions containing 104–107 CFU/cm3 of Escherichia coli and various concentrations (0–20 mg/dm3) of humic acids (HA) in a 0.05 M phosphate buffer at pH 6.8, as well as real natural waters of the Dnieper and Desna Rivers. The ozone concentration in the ozone–air mixture varies in the range of 0.5–2.0 mg/dm3, depending on the particular object of study. It is shown that changes in the ORP of a solution reflect changes in the microbiological and chemical composition of water during ozonation, owing to which measurements of this indicator can serve as a preliminary control method for the process of disinfection, as well as water decoloration. The inflection point on the curve of dependence of ORP on ozonation time practically coincides with the inflection point on the curve of dependence of the degree of water disinfection on the treatment time. In the case of treatment of model waters that are free of organic impurities, a sufficient level of disinfection of the solution is evidenced by an increase in the ORP of the solution to about 440–550 mV. In case of treating natural surface waters (with a high content of natural organic impurities), a sufficient level of disinfection and decoloration of the solution is detected by a decrease in the ORP of the solution by about 30–40 mV.

Disinfection characteristics of the combined ultraviolet radiation and ozone process using Escherichia coli as a probe

In the present study, the characteristics of the combined ultraviolet (UV) and ozone disinfection process were investigated from kinetic and mechanistic viewpoints employing Escherichia coli (E. coli) as an indicator microorganism. Compared to individual unit processes, the combined UV/O3 tests produced excess hydroxyl radicals (HO•) and yielded synergistic inactivation of E. coli in the initial phase of reaction. The presence of O3 during UV exposure caused the destruction of cell structure, and then repressed bacteria regrowth after treatment. Moreover, the formation of malondialdehyde (MDA) showed that the improved generation of intermediate HO• via ozone photolysis accelerated the decomposition of bacterial cell surfaces, which was further confirmed by the leakage of intracellular potassium ions (K+). The results suggested that the synergistic bactericidal effect of combined UV/O3 owed mainly to the enhanced destruction of bacterial cell structure.

Changes in selected quality parameters during the treatment and distribution of water

The main goal of water treatment plants is water intake from water’s natural sources and its preparation for consumers. After the water treatment process, water has to meet requirements of legal standards regarding chemical and microbiological composition. The quality of water from water pipes depends on: its initial composition, the way of treatment, storage, the condition of water system, terminal, and plumbing. The choice of the technological process of water treatment depends on raw water quality, which is often different at the consumer’s tap from the one delivered to the distribution system since water undergoes complex physical, chemical, and biological processes. This results in, so-called, secondary water contamination in a distribution system. In this article, the value changes of selected chemical water quality parameters have been presented during both ozone and sodium hypochlorite disinfection. Water samples were collected from underground water intakes. The results showed that disinfection processes did not negatively affect water quality. The number and the extent of changes to the water quality parameters were similar in the case of both ozone and sodium hypochlorite disinfection processes. All examined water samples showed an increase in total hardness following the treatment process and a decrease in the TOC content in water in the distribution process.

Quantification of Helicobacter pylori in the viable but nonculturable state by quantitative PCR in water disinfected with ozone

Helicobacter pylori is a Gram-negative spiral-shaped bacterium that colonizes the gastric mucosa and is associated with gastric diseases. It may present a morphological adaptation when it is out of its natural environment, such as in water. The morphological adaptation is a coccoid form, which is a viable but non-culturable state (VNC) in which the DNA remains active and therefore infective. Due to the impossibility of culture by traditional methods in the VNC state, we developed a methodology that includes a molecular technique, quantitative polymerase chain reaction (qPCR), which is capable of measuring the bacteria in both forms (helical and coccoidal) and therefore is able to measure a disinfection process and to estimate the resistance of the bacteria to ozone. The methodology developed measures the efficiency of the ozone disinfection when bacteria are in a VNC state only. Bacterial culture at 9 × 10(8)CFU/mL diluted in 40 mL reaction volumes were exposed to a wide range of CT values (0.11-15 mg min/L). The results show a 3.92-log reduction when treated with 15 mg min/L. Our results demonstrate the feasibility of using qPCR for the quantification and detection of H. pylori, in coccoid form, in water systems treated with an ozone disinfection process.

Estimation of CO2 emission from water treatment plant – Model development and application

A comprehensive mathematical model developed for this study was used to compare estimates of on-site and off-site CO2 emissions, from conventional and advanced water treatment plants (WTPs). When 200,000 m3 of raw water at 10 NTU (Nepthelometric Turbidity Unit) was treated by a conventional WTP to 0.1 NTU using aluminum sulfate as a coagulant, the total CO2 emissions were estimated to be 790 ± 228 (on-site) and 69,596 ± 3950 (off-site) kg CO2e/d. The emissions from an advanced WTP containing micro-filtration (MF) membrane and ozone disinfection processes; treating the same raw water to 0.005 NTU, were estimated to be 395 ± 115 (on-site) and 38,197 ± 2922 (off-site) kg CO2e/d. The on-site CO2 emissions from the advanced WTP were half that from the conventional WTP due to much lower use of coagulant. On the other hand, off-site CO2 emissions due to consumption of electricity were 2.14 times higher for the advanced WTP, due to the demands for operation of the MF membrane and ozone disinfection processes. However, the lower use of chemicals in the advanced WTP decreased off-site CO2 emissions related to chemical production and transportation. Overall, total CO2 emissions from the conventional WTP were 1.82 times higher than that from the advanced WTP. A sensitivity analysis was performed for the advanced WTP to suggest tactics for simultaneously reducing CO2 emissions further and enhancing water quality.

A novel approach to modeling the reaction kinetics of tetracycline antibiotics with aqueous ozone

Tetracycline antibiotics represent one of the most successful classes of pharmaceuticals and are extensively used around the world for human and veterinary health. Ozone-based processes have emerged as a selective water treatment process for many pharmaceuticals. The primary objective of this study was to determine the reaction kinetics for transformation of five tetracycline antibiotics (i.e., chlortetracycline, doxycycline, oxytetracycline, rolitetracycline, and tetracycline) by ozone across the pH2 to 9 range. The apparent second-order rate constant for tetracycline was on the order of 1–6×104M−1s−1 at low pH, and 0.6–2.0×106M−1s−1 at near neutral pH. The apparent second-order rate constants did not fit a conventional pKa-based model, presumably due to the complex acid/base speciation of tetracycline antibiotics. A model that considers the net charge on tetracycline molecules in solution provided a nice fit to experimental data for all five tetracyclines. The five tetracycline antibiotics demonstrated similar reaction kinetics with ozone, and a cumulative analysis of all kinetics data provides a baseline model for other tetracycline compounds. The ozone exposure required for complete transformation of tetracycline antibiotics (10−5M−s) is well below that achieved during ozone disinfection processes (10−3M−s), indicating that ozone is an effective treatment for tetracycline antibiotics.

Degradation of Selected Acidic and Neutral Pharmaceutical Products in a Primary-Treated Wastewater by Disinfection Processes

Anti-inflammatory and anti-convulsive drugs are being detected in measurable quantities in municipal wastewaters. Some of these emerging substances undergo major transformation at the sewage treatment plant after biological and chemical treatments. The degradation of pharmaceutical products from high-quality treated wastewaters by disinfection processes is well documented. However, the effect of disinfection processes on these products in physicochemical primary-treated municipal effluents remains to be investigated. Pilot projects using ozone, performic acid and UV-radiation disinfection processes were carried out at the Montreal wastewater treatment plant. Residues of pharmaceutical products like salicylic acid, clofibric acid, ibuprofen, naproxen, triclosan, carbamazepine, diclofenac, and 2-hydroxy-ibuprofen were found in the treated wastewaters before disinfection at concentrations ranging from 42 to 2556 ng/L. Most of these substances were eliminated at a rate greater than 50% at an ozone dose of 10 mg/L. Higher removal rates (as high as 70%) were observed when 20 mg/L of ozone was used. Removal rates for UV radiation, on the other hand, were often below 10% among the substances studied. Limited removal rate was observed after UV radiation for diclofenac and triclosan (25 and 40% efficiency, respectively). The irradiation used here (25 mJ/cm2) for bacterial treatment appeared, as previously reported, to be too low to cause the significant breakdown of many of the pharmaceutical substances contained in these wastewaters. Poor reduction efficiencies (< 8%) were observed with the performic acid treatment. Further investigations on analytical methodologies are therefore needed to assess the potential impact of degradation by-products on the environment and on human health.

Application of a multiphase CFD modelling approach to improve ozone residual monitoring and tracer testing strategies for full-scale drinking water ozone disinfection processes

A multiphase computational fluid dynamics (CFD) model has been developed to address the major components of ozone disinfection processes: contactor hydraulics, ozone decay and mass transfer. The model was applied to simulate ozone profiles and tracer residence time distributions of ozone contactors at the DesBaillets Water Treatment Plant (WTP) in Montreal, Canada. The modelling results showed that ozone residuals at the cross-section of the outlet of each chamber in the ozone contactors were very sensitive to monitoring point selection. The optimum locations were significantly affected by multiple operational parameters including water/gas flow rates, ozone dosage and baffling conditions. The modelling results suggested that multiple monitoring points should be used to obtain more representative ozone residuals. The CFD model was also used to study the factors affecting tracer residence time distribution (RTD). It was observed that the method of tracer injection could slightly affect tracer RTD results while sampling location had a significant influence on tracer RTD prediction or measurement. Therefore, it is suggested that multiple sampling points should be employed during tracer tests if possible.

A Computational Fluid Dynamics Based Integrated Disinfection Design Approach for Improvement of Full-scale Ozone Contactor Performance

A three-dimensional multiphase computational fluid dynamics (CFD) model has been developed, to address all the major components of ozone disinfection processes at the Charles DesBaillets Water Treatment Plant in Montréal, Canada. Good agreement was observed between the numerical results and full-scale tracer data. The CFD predicted flow fields showed that recirculation zones and short circuiting existed in the DesBaillets contactors. Installation of four additional baffles in the second chamber would significantly improve contactor mixing performance. The modeling results also indicated that ozone residuals at the cross section of the outlet of each chamber were very sensitive to the locations of monitoring points.

A Multi-Channel Stopped-Flow Reactor for Measuring Ozone Decay Rate: Instrument Development and Application

The ability to accurately estimate ozone decay rate through empirical measurement is often fundamental to efficient reactor design and operation in ozone disinfection processes. Variations of ozone decay rates in natural waters and difficulty to estimate them through mechanistic approach highlight the need for reliable methodologies to measure these parameters. In this study, a novel, multi-channel stopped-flow reactor that allows for automatic, continuous analysis of ozone decay kinetics under controlled conditions was developed and verified. Data presented includes instrument design and operation parameter optimization, precision and accuracy verification, and applicability demonstrated with representative synthetic waters.

Market for Advanced Drinking Water Technologies Expected to Grow at 10.7% Annually

According to a technical market research report from BCC Research, the U.S. market for advanced drinking water technologies is estimated at about $1.3 billion in 2006 and is expected to grow at a combined average annual growth rate (AAGR) of 10.7% to 2011, reaching a total of $2.1 billion in 2011. The drinking water technologies included in the report include membrane filtration, ozone disinfection, ultraviolet (UV) irradiation, and novel oxidation processes. This article includes a table of the value of U.S. market for advanced municipal water treatments through 2011, and also a figure of the global market forecast for advanced municipal water treatment through 2011.

A Dynamic Model of Ozone Disinfection in a Bubble Column with Oxygen Mass Transfer

The dynamic process of disinfection with ozone in a bubble column is studied for model establishment. Bubble columns have been widely used for ozone disinfection in plants and laboratories. Ozone is produced by passing oxygen-enriched gas through an ozone generator, and introduced into the bottom of a column equipped with a gas-diffuser. There certainly exists a temporary and unsteady period before the ozone disinfection system reaches steady state. Available ozone disinfection models employed to describe dissolved ozone and surviving microorganism profiles have commonly been developed for steady state. Moreover, oxygen maxx transfer has usually been neglected in previous ozone disinfection models. However, this information is desirable for the proper operation of ozone disinfection in a bubble column. Thus, the objective of this study was to model and investigate the dynamic ozone disinfection process in a bubble column with oxygen mass transfer. A dynamic axial dispersion model is proposed and was employed to predict the variation of the ozone, microorganism and oxygen concentrations along the column. The results of prediction were obtained based on the conditions of Marinas et al. (1993). E. coli was chosen as the model microorganism. The dynamic model of ozone inactivation is useful for proper prediction of the variables of an ozone disinfection system in a bubble column.

Wastewater disinfection by low-pressure UV and ozone: a design approach based on water quality

Disinfection processes are known to be very sensitive to wastewater quality. This paper discusses the parameters that impact the UV light (UV) and ozone disinfection processes and the related mechanisms based on literature review. Low-pressure UV and ozone technologies were investigated on effluents that covered a wide range of water quality. The results are given in terms of design doses required to meet three major disinfection standards. Both processes were found eligible for the majority of effluents tested. Although cost-effectiveness is usually considered more favourable to UV, the ozone alternative should be examined in cases such as the disinfection of low-quality effluents or large treatment plants. Ozonation was also found capable of meeting the stringent Title 22 standard with no coagulation at a dose of 10 mg/l.

Start-Up and Optimization of the Ozone Disinfection Process At the Sebago Lake Water Treatment Facility

The purpose of the ozone process at the Sebago Lake Water Treatment Facility (SLWTF) is to meet the disinfection requirements of the Surface Water Treatment Rule with ozone and without filtration. The start-up experience is presented including initial operating strategies to meet disinfection requirements. An ozone system performance test conducted during the first month of plant operation is described and the results are reviewed. The initial and proposed activities of an ozone optimization project are discussed.

Evaluation of parameter estimation methods for ozone disinfection kinetics

Inactivation data with ozone in a CSTR system were analyzed using error-in-variables method (EVM), forced linearization and classical nonlinear regression. Their relative efficiency was compared statistically. The Monte Carlo simulations demonstrated that the EVM produces parameter estimates with the least bias and minimum variance of residuals from the regression. Although used traditionally, the forced linearization would give the biased parameter estimates of kinetics and lead to the potential of misinterpreting the type of inactivation. Requiring the ad hoc assumption of first order decay rate, the classical nonlinear regression is of little use in practice. Fitting the kinetic model to experimental data shows that the behavior of the bacteria and virus inactivation can be well described by predictions from EVM estimates. The resultant coefficient of dilution ( n), defined as equation (1) was found to be much higher than one, indicating that the ozone concentration is a dominant factor over the contact time in determining the efficiency of ozone disinfection processes.

Inactivation ofGiardia murisUsing Ozone and Ozone-Hydrogen Peroxide

Abstract The disinfection effects of the ozone molecule alone and that of ozone decomposition products when inactivating Giardia muris cysts were investigated at bench-scale using two different ozone demand-free laboratory buffer systems. The first water was a 0.05 M phosphate buffer with hydrogen peroxide added at a 10:1 weight ratio. The second water was a 0.05 M phosphate – 0.01 M bicarbonate buffer which quickly scavenged radical species from ozone decomposition. The C3H/HeN mouse model was used to assess the infectivity of ozone treated cysts. The phosphate-bicarbonate buffer system had significantly greater (P ≤ 0.05) inactivation of G. muris cysts than that observed in the phosphate buffer – peroxide system where ozone was completely decomposed in less than 120 s. Consequently, the design of ozone disinfection processes should maintain ozone residual for disinfection prior to the addition of hydrogen peroxide for the oxidation of other compounds.

Wastewater Disinfection With Ozone - Process Control And Operating Results

Abstract The City of Indianapolis, Indiana operates two 125 mgd advanced wastewater treatment plants with ozone disinfection. The rated capacity of the oxygen-fed ozone generators is 6,380 Ib/day, which is used to meet geometric mean weekly and monthly disinfection permit limits for decal conforms of 400 and 200 per 100 mL, respectively. Since 1989, a disciplined process monitoring and control program was initiated. Records indicate a significant effect on process performance due to wastewater flow, contactor influent fecal coliform concentration, and ozone demand. Previously, ozone demand information was unknown. Several tasks/studies were performed in order to better control the ozone disinfection process. These include the recent installation of a pilot-scale ozone contactor to allow the plant staff to measure ozone demand on a daily basis. Also, tracer tests were conducted to measure contactor short-circuiting potential. Results demonstrated a noticeable benefit of adding additional baffles. Results also indicated operating strategies that could maximize fecal coliform removal, such as reducing the number of contactors in service at low and moderate flow conditions.

Ozone Disinfection of Sewage in a Static Mixer Contacting Reactor System on a Plant Scale

Results of our earlier laboratory study on ozone contacting systems in a continuous flow mode identified that the ozone disinfection process is limited by the mass transfer rate (7). The main controlling factor is the mass transfer efficiency rather than the contact time of the contactor in determining the effect of disinfection. By applying these concepts, we suggested a new ozone disinfection technique of using a static mixer as the contactor to substitute for a conventional bubble column designed with contact time.

Water Disinfection: A Relationship Between Ozone and Aldehyde Production

Abstract In the water potabilization plant of Turin city (Italy), the oxidation process is carried out with ozone. Due to its well-known insufficient performance, it is necessary to add alternative oxidants (hypochlorite ion and chlorine dioxide). In this paper, we discuss the formation of linear carbonyl groups during surface water treatment in Turin. The results obtained in the field confirm the synthesis of some aliphatic carbonyl compounds of low molecular weight. This phenomenon happens preeminently during the ozone disinfection process and, secondarily, during the other disinfection processes. Experimental results show that, in this last event, chlorine reacts with organic substances, and in a second moment, after organics consumption, if chlorine is still in a sufficient concentration, oxidizing them.