Effect of Ozonation on the Chlorine Demand of a Treated Surface Water and Some Macromolecular Compounds

The study described in this paper was conducted to examine the effects of ozonation and ozone-GAC filtration treatment steps on chlorine consumption of the Seine river water treated in the Choisy-le-Roi drinking water works. Ozone-GAC combined treatment was found to significantly reduce both the initial chlorine demand and the long-term chlorine demand of waters, excepting for waters sampled during cold months of the year. The removal of the chlorine demand potential by ozonation alone was found to be limited for the studied waters and for solutions of macromolecular compounds even in the presence of carbonate species. Ozonation carried out in the absence of bicarbonate ion was found to increase reactive sites with chlorine treatment of an aquatic fulvic extracted from the Seine river water.     

Use Of Ozone And Flotation For The Treatment Of A Reservoir Water: The Dinan Case History

The plant of Dinan supplies water to the urban district of Dinan (Brittany-France). The raw water is a dam water, soft, containing iron and manganese, highly colored with a high content of organic carbon. The area providing water to the dam is rural country, so water also contains residues of agricultural practices such as pesticides and nitrates.

During summer, algae blooms may occur. The old plant (including prechlorination, coagulation, flocculation, settling and sand filtration) has been replaced with a treatment line including: remineralization, preozonation, flotation, ozonation and granular activated carbon. Nitrate removal will be considered in the future. The paper presents the results obtained in the plant, the optimization of the preozonation dose as well as comparison with laboratory tests. A special reference concerns algae removal.     

Ozonation at Wiggins Water Purification Works,Durban, South Africa

The post-ozone plant at Wiggins waterworks was commissioned during 1984. The main objective of the post–ozone plant was to ensure proper disinfection, including the elimination of viruses, whenever raw water for the works was pumped from the polluted lower Umgeni River. The main problems experienced with the post–ozone plant were poor ozone transfer efficiency in the contact tank and poisoning of the catalyst in the thermal-catalytic destructor.     

Ozonation at Belle Glade,Florida : A Case History

In October 1984, the city of Belle Glade, FL installed a two-stage ozonation process for the treatment of lake water high in organics (av TOC 30 mg/L; up to 75 mg/L), high in color (av 100 color units; up to 500), and high in THM concentrations, at times nearly 1,000 μ/L. The new treatment process applied 3 mg/L of ozone to the raw water ahead of the flash mix basin, lime softening, alum and polymer coagulation, clarification, recarbonation, and addition of 3 mg/L ozone prior to filtration. Post-chlorination then produced distribution system THM concentrations averaging 124 μg/L. Distribution of THMs shifted from 85% chloroform by the original process to 40% after adoption of ozonation, the balance comprising brominated species (but not bromoform).

In 1987, the treatment process was modified by adding chlorine and ammonia at the outlets of the pre- and intermediate-stages of ozonation and abandoning free chlorination. This has further reduced the distribution system THM levels to 20-30 μg/L. Filtered water turbidity and color have been improved. The use of chloramines after ozonation controls the nuisance aquatic growths in the clarifiers and recarbonation basins (caused by ozonation alone), and produces a combined chlorine residual which can be maintained throughout the distribution system. Periodic use of free chlorine in the distribution system is required to prevent elevated heterotrophic plate counts and the formation of excessive concentrations of nitrite ion due to biological regrowth and nitrification.     

Ozone in Water Treatment—The Designer's Role

This paper presents the designer's role in providing an efficient and reliable ozone system for use in water treatment. The 789 m3/h (5 mgd) regional water plant in Avon, Colorado, USA is used as a case study. In the process design, two alternatives were evaluated. The ozone alternative was selected based on its multiple benefits. These benefits included iron and manganese removal, taste and odor control, coagulation and disinfection. Each aspect of the ozone system design is reviewed.     

Rationales for Multiple Stage Ozonation in Drinking Water Treatment Plants

Starting in the early 1970s, the application of ozone for drinking water treatment began to evolve from primarily single-purpose, single-stage use for disinfection, taste and odor control or iron and manganese oxidation, to multipurpose uses of ozone. As a result, most of the newer drinking water treatment plants have installed two- and even three-stages of ozonation. in order to maximize the technological benefits of ozone and to minimize the costs involved.     

Study of the Catalytic Ozonation of Humic Substances in Water and Their Ozonation Byproducts

It is shown that using transition metals, especially Mn(II) and Ag(I), during ozonation of humic substances in water allows important reductions in the content of organic matter. Characterization of the organic compounds resulting from ozonation was made by concentrating the sample through liquid-liquid extraction or derivation with PFBOA.HCl, along with the GC/MS and GC/ECD techniques. In total, 110 different organic compounds were identified using GC/MS; mainly carboxylic acids, aromatics, hydrocarbons, aldehydes, ketones, and furan-carboxylic acids. The percentages of elimination or formation levels reached during ozonation are discussed.     

Comparison of Ozone Efficiency for Manganese Oxidation Between Raw and Settled Water

Ozone was tested at the Moores Bridges WTP as a replacement for chlorine for oxidizing dissolved manganese. Two points of ozone application were tested, raw and settled water. Dissolved manganese appeared to be much more readily oxidized with a lower ozone dose when ozone was applied to the settled water than when it was applied the raw water. Apparently the TOC concentration of the water affected ozone's ability to oxidize manganese by exerting an ozone demand which must be overcome. Because of the results of the pilot testing, a decision was made to ozonate settled water rather than raw water to oxidize the manganese.     

Iron and Manganese Removal with Ozonation in the Presence of Humic Substances

The conditions for the removal of iron and manganese contained in slightly mineralized water, rich in humic substances, were determined in a case where an intermediate oxidation was provided in a conventional potabilization line comprising a coagulationflocculation stage with iron salts.

The experiments were conducted both on a synthetic water, with or without addition of humic substances, and on raw water from the Moulin-Papon dam. While iron was easily removed by simply increasing the pH measurement from 8.2 to 8.5 without intermediate oxidation, ozonation applied to water with a pH of nearly 8.4 did not enable the manganese to be removed with a low ozone dose (about 1 mg/L) unless a significant amount of bicarbonates (120 to 130 mg/L as CaCO₃) were injected prior to the ozonation-filtration stage.

As it removes the manganese from the water, intermediate ozonation also removes the abatement of organics on the filters, and lowers the THM buildup potential.     

Formaldehyde Formation During Ozonation Of Drinking Water

Partial oxidation of natural organic material during ozonation produces oxygenated by-products of low molecular weight. Formaldehyde, being the most common oxygenated by-product of ozone, is considered to be a problematic compound by the water industry due to its potential adverse health effects. This research attempts to provide specific information on the effects of water quality parameters, specifically, pH and alkalinity, the structure of humic material, and the operational parameters, e.g., ozone dosage and contact time, on generation of formaldehyde. The results showed that ozonation caused almost an immediate formation of formaldehyde, which reached a peak value, and then started to decrease with continued ozonation. Ozonation of aqueous fulvic acid produced higher concentrations of formaldehyde compared to other types of humic material. Formaldehyde formation was suppressed by high bicarbonate levels, and enhanced at higher pH. Formaldehyde accumulation was more dramatic at low ozone dosages.     

Improvement of Ozone Oxidation and Disinfection Design

For a long timei the aim of ozonation has been the improvement of the organoleptic qualities of treated water. Disinfection! and particularly virus inactivationi also has been a reason for introducing ozonation steps in the treatment line of a potable water treatment plant. Other purposes of ozonation then have been developed in different fields of application, such as iron and manganese removal, micropollutants oxidation, urban wastewater disinfection! coagulant and flocculant aids, and improvement of biological treatment. During the last few years, numerous studies have been concerned either with the kinetics of ozonation reactions, or the modelling of contact systems. A better fit between these two factors should be found.     

Use Of Static Mixer For Oxidation And Disinfection By Ozone

Ozone is used in drinking water treatment as a biocide, as an oxidant and as a pretreatment in order to improve the performance of subsequent processes. Increasing concern over the quality of drinking water has led to a number of new stringent regulations in the control of chemical and microbiological contaminants. Disinfection deals with the concept of “CT”, which is the need to maintain a certain minimum concentration for a given time. Under ideal laboratory conditions, it is 0.4 mg O₃/L for 4 min. In practice, since the method for the CT determination has not been finalized by the EPA, “T” can be the minimum detention time of 90% of total flow, and “C” can be a measured ozone residual at the outlet of cells of the contactor. New standards for micropollutants in drinking water imply an optimization of the ozonation step, by improving the ozone transfer from gas to water, and the control of the detention time as well as ozone residual within the contactor.

All these considerations have led us to use static mixers to transfer ozone into water. This process enables us to control the ozone concentration in water and detention time. It is a very simple system, with very low maintenance requirements due to the lack of moving parts. Civil engineering is minimized. A pilot scale study is presented here. It took place at the Méry-sur-Oise water treatment plant, on a pilot plant working at 8-12 m³/h. It is composed of a static mixer for the transfer of ozone from gas to liquid, linked to an air lift to separate gas from liquid, providing ozonated water.

The optimization of transfer was achieved by studying the impact of water flow, gas flow and ozone concentration in the gas. It is possible to reach 90% of transfer in less than 15 s. Headloss (ΔP) across the mixer is a function of gas and water flows and remains economically very acceptable as 0.15 bar for 12 m³/h.

Atrazine removal was studied using a static mixer, an air lift and a contact pipe 80-m long, providing an optimum contact time phase, working as a plug flow reactor. Ozone and H₂O₂/O₃ treatments were compared. The maximum reduction of atrazine concentrations (e.g., for an infinite contact time) is a function of the amount of transferred ozone, but H₂O₂ influences the kinetics of the reaction. In the presence of H₂O₂ with a ratio of H₂O₂ to O₃ of 0.4 w/w, maximum elimination is reached in 2 min 30 s.

The effect of such treatments on environmental bacteria also was followed. A counting of total germs at 20°C showed a decrease of 1- to 3-logs 10 after 1 min 30 s of contact time for about 2 mg/L of transferred ozone. No significant difference between treatments with or without H₂O₂ was shown. The same conclusions were obtained from heterotrophic plate counts (37°C) and epifluorescence countings.     

Ozonation of Drinking Water: A Design Methodology

The formation of potentially carcinogenic organic halides has been shown to result from drinking water disinfection with chlorine. xidative treatment of organic halide precursors with ozone prior to chlorination has surfaced as an attractive technique for reducing the formation of these compounds. In addition to reduction of precursor levels, preozonation has been reported to effect other beneficial results in water treatment. This paper presents design methodologies to optimize the implementation of the ozonation process for water treatment applications. Pre-design considerations common to all ozonation design processes are discussed. Subsequently, design procedures for the ozone generation and contacting systems are reviewed.     

The Basic Principles of UV–Disinfection of Water

The disadvantage of chlorination of drinking water is the possible synthesis of toxic chlorinated fragments. In different cases UV can be an alternative to chlorination. The germicidal effectiveness of UV–radiation is in the 180–320 nm region with an optimum at 265 nm. Approximately 95% of the energy radiated by a low–pressure mercury arc is at the 253.7 nm line, so this source is the most effective one for germicidal applications. The germicidal effectiveness of a broadband source can be calculated. UV alone cannot decrease the concentrations of organic contaminants of the treated water. Quite promising are the systems where UV–radiation acts as a catalyst in oxidation reactions in order to decrease the organic contaminants.     

Principles of Ozone Oxidation and Disinfection Design

The efficiency of ozone for different purposes can be determined by different laboratory tests. It is necessary to use a specific test for each aim of ozonation. Consequently, the design of commercial ozone–water contact systems can be determined in relation with the purpose of ozonation: virucide effect, oxidation of pollutant, clarification improvement or wastewater disinfection.     

A Comparison of Objectives,Level of Development and Energy Consumption of Two New Hungarian Ozonation Plants

Basedon the success of the first Hungarian large capacity drinking water treatment ozonation plant of Budapest that was put into operation in 1984, a similar second plant was put into operation in 1988 in Debrecen with 150,000 inhabitants. This recently built plant solves taste and odor problems and water quality development of a surface water treatment plant with a capacity of 50,000 m³/day that is operative for a longer period of time. The experiences gained at the Budapest ozonizing plant were utilized during both planning and construction. Thus, for example, the method of ozone absorption had been modified.

The in-situ repair of the Frings turbines for ozone contacting placed at the Rackeve plant of the Budapest Waterworks will be introduced, as well as a concept of a newer kind of ozone mixing.     

Oxidation of Organic Pollutants of Water to Mineralization by Catalytic Ozonation

The oxidation of various organic compounds in aqueous solution was studied using catalytic ozonation (TOCCATA process) and conventional ozonation. The aim of the work is to assess catalytic ozonation efficiency for the mineralization of various organic compounds in order to envisage its application on real effluents. The selected organic compounds (about 30) are commonly found in industrial wastewaters. Comparative experiments were performed in batch mode at laboratory scale. Investigations were focused on ozone consumption rate, variations of total organic carbon, oxidation by-products and oxidation rate. Catalytic and conventional ozonation treatments were compared considering kinetic data, mineralization extent, and effect of organic functionalities. Catalytic ozonation system according to the TOCCATA process was able to convert organic compounds which were totally inert to ozone treatment and permitted considerably enhanced reaction rates when compounds were reactive to ozonation.     

Ozonation of Trace Organic Compounds: Model Predictions versus Experimental Data

This paper is focused on the use of ozone for the elimination of manmade organic micropollutants from drinking waters and waste effluents requiring advanced treatment. A mathematical model was developed to simulate the physical transport and chemical oxidation phenomena prevailing during the process of ozonation. A packed column reactor was constructed in order to test the aptness of the process model. After determining the fluid-dynamic and mass transfer properties of the reactor, stock water solutions spiked with toluene were brought into contact with gaseous O₂-O₃ mixtures. Toluene removal efficiencies observed under different experimental conditions then were compared with the model predictions.     

Cellular Toxicity and Mutagenicity Assays from On-Site Sampling of Drinking Water Treatment Plants Using Multistage Ozonation

Studies were carried out on-site in a potable water production plant utilizing ozonation treatment at three stages of the process. The quality of water in the treatment line was studied by chemical analysis, but also for toxicity to Hela cells after XAD resin concentration, and for mutagenesis to Salmonella Ames strains and mammalian cells V79 HGPRT system. With a sufficient dose of ozone and activated carbon adsorption, the initial cytotoxicity of the raw water and the mutagenic or promoter activity are destroyed.     

Removal of Natural Organic Matter from Groundwater Using Advanced Oxidation Processes at a Pilot Scale Drinking Water Treatment Plant in the Central Banat Region (Serbia)

To improve water quality, a pilot-scale evaluation into upgrading the conventional treatment process was conducted. By following DOC content, UV₂₅₄ absorbance, SUVA and by-products formation, three oxidative pre-treatments were evaluated: pre-ozonation (2.2 g O₃/m³); O₃/H₂O₂ process (2.2 g O₃/m³; H₂O₂:O₃ = 1:2) and O₃/H₂O₂ process (2.2 g O₃/m³; H₂O₂:O₃ = 2:1). The second pre-treatment gave the best results, with a final average DOC content of 0.9 mg C/L, UV₂₅₄ absorbance of 0.06 cm^?1 and the lowest THMFP of 130 μg/L. UV₂₅₄ absorbance can serve as a proper indicator for predicting THM and HAA formation, yielding a correlation coefficient ≥ 0.90.