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.     

Hydroxyl Radical Oxidation Processes For The Removal Of Triazine From Natural Water

The purpose of this study was to point out processes that can provide triazine oxidation via hydroxyl radical production in a water treatment line. We focus our attention on:

- oxido-flocculation, using Fe²⁺, H₂O₂

- inter-oxidation, using O₃, H₂O₂ and eventually an heterogeneous catalyst.

- disinfection, using UV, O₃ and H₂O₂ combinations.

Results show that triazines can be removed by all these processes with different efficiencies. At full scale, the O₃/H₂O₂ process presents the best performances from an economical and technical point of view.     

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.     

The Use Of High Concentration Ozone For Water Treatment

The use of high concentration ozone (HCO) in potable water treatment has been examined at laboratory scale with a gaseous concentration of 19% w/w. This has been compared with conventionally generated ozone at 1.5% w/w. The results of the study have shown that greater transfer efficiencies and higher ozone residuals are possible with HCO. In addition, faster rates of atrazine removal and significantly greater reductions in color and trihalomethane formation potential (THMFP) were observed with HCO.     

The Effect Of Preozonation,Ozone/Hydrogen Peroxide Treatment,And Nanofiltration On The Removal Of Organic Matter From Drinking Water

Pilot scale experiments were performed to evaluate the ability of ozonation, ozone/hydrogen peroxide treatment and nanofiltration to reduce levels of organic matter, mutagenicity, total adsorbable halogens, color and turbidity from purified and bank-filtered surface water rich with humic material.

Ozonation and ozone/hydrogen peroxide decreased the amount of organic material from drinking water by about 20 percent measured as TOC and COD_Mn. Color and turbidity level reductions were 49 and 11 percent, respectively. Ozonation reduced the AOX concentrations formed during postchlorination from 150 μgL^?1 to 75 μgL^?1. The addition of hydrogen peroxide further improved the removal to 37 and 26 μgL^?1 depending on the ratio of H₂O₂/O₃. The mutagenicity reduction followed the same pattern: without ozonation the chlorination-derived mutagenicity was 1,450 net revertant L^?1 after the ozonation 700 and after the H₂O₂/O₃ treatment from <100 to 400 net revertant L^?1 depending on the H₂O₂/O₃ ratio. Nanofiltration appeared to be the most effective way to remove organic material. The removal of TOC was 68%, COD_M 72%, color 90%, turbidity 68%, AOX 88%, and mutagenicity 85%.     

Estimation Of The Relative Importance Of Free Radical Oxidation And Direct Ozonation/UV Radiation Rates Of Micropollutants In Water

The relative importance of free radical and direct ozonation/photolysis oxidation of micropollutants in water can be estimated from simple kinetics of aqueous ozonation reactions provided these reactions develop in the slow kinetic regime of absorption. Knowledge of kinetic expressions of free radical initiation reactions and direct ozone-micropollutant or UV radiation-micropollutant reactions (and corresponding parameters: reaction rate constants, quantum yields, etc.) allows an estimation of the reaction rate ratios for any micropollutant in the ozone alone and combined with hydrogen peroxide and/or UV radiation oxidation systems.     

Preozonation Related to Algae Removal A Case History : The Plant of Mont-Valérien

The plant of Mont-Valérien supplies drinking water to the western suburbs of Paris. The plant has been upgraded, including a preozonation step. The plant has been operated with different doses of ozone applied during the preozonation step, and with different doses of coagulant for clarification. The purpose of that field test was to determine the best operating conditions to obtain the minimum of algae cells in the treated water. The results show that the minimum of algae cell count is obtained when the coagulant dose nullifies the zeta potential, and with an optimum dose of ozone.     

The Development Of Ozone For Potable Water Treatment Within The United Kingdom

The historical development of the application of ozone to potable water treatment within the United Kingdom is reviewed up to 1990. The impact of privatization of the water utilities on the use of ozone is discussed and the process applications currently being considered are described. The paper concludes with a survey of water treatment plants which are using ozone in 1993, and those planned for completion by the year 2000.     

Removal Of Residual Organics From Drinking Water By Ozonation And Activated Carbon Filtration: A Pilot Plant Study

The effects of ozonation, granular (GAC) and biological activated carbon (BAC) in the removal of natural organic matter and precursors of disinfection byproducts from drinking water were studied on pilot scale. Ozonation was determined to be the best method to reduce concentrations of the precursors of AOX, chloroform and mutagenicity, whereas BAC removed organic matter the most effectively. Reductions in TA100 mutagenicity were an average 40%, 4%, 26% in ozonated, GAC and BAC filtered water, respectively. Average reductions of AOX levels were similar at 48%, 7% and 35%, respectively. The chloroform formation potential always increased after GAC filtration.     

Photocatalytic Oxidation Processes In The Presence Of Polymers

The objective of the study was to investigate the removal of synthetic organic compounds and THM precursors by two photocatalytic oxidation processes in the presence of synthetic polymers. H₂0₂/UV and O₃/UV processes were tested on solutions of nitrobenzene and aquatic fulvic substances in the absence and presence of Polyethylene Oxide (PEO) and a Betz Polymer. The presence of high concentrations of PEO reduced the removal rate of nitrobenzene by competing with it for hydroxyl radicals. The presence of low concentrations of PEO did not significantly alter the removal rate of nitrobenzene and THM precursors. Experimental results indicated that even in the presence of the polymers, decomposition rather than coupling was the favored reaction pathway.     

The Chemistry of Water Treatment Processes Involving Ozone,Hydrogen Peroxide and Ultraviolet Radiation

Advanced oxidation processes are defined as those which involve the generation of hydroxyl radicals in sufficient quantity to affect water purification. The theoretical and (practical yield of OH from O₃ at high pH, 0₃/H₂0₂, O₃/UV and H₂O₂/UV systems is reviewed. New data is presented which illustrates the importance of direct photolysis in the O₃/UV process, the effect of the H₂0₂:0₃ ratio in the O₃/H₂O₂ process, and the impact of the low extinction coefficient of H₂O₂ in the H₂0₂/UV process.     

Water Quality Improvements with the Use of Ozone at the Los Angeles Water Treatment Plant

At 600 mgd (2,270 ML/day), the recently completed Los Angeles Aqueduct Filtration Plant (LAAFP) is one of the world's largest water' treatment facilities utilizing ozone for pretreatment. The treatment process features direct filtration at rates of up to 13.5 gpm/ft² (33 m/h). Under the optimized full-scale operation, preozonation has resulted in significantly reduced THM levels and very low effluent turbidity with low operating costs.     

Modelisation Of Micropollutant Removal In Drinking Water Treatment By Ozonation Or Advanced Oxidation Processes (O3/H2O2)

A simulation program is described, tested and used, to predict micropollutant removal in an ozonation bubble tower with or without hydrogen peroxide addition. To compute the removal efficiency, we need to know the chemical reactivity between organic compounds and oxidant species (molecular ozone and hydroxyl radicals), the ozone mass transfer from the gaseous phase to the liquid phase (k_La) and the hydrodynamic model describing the reactor. In this case, we divide the reactor into three parts (water arrival, air arrival and intermediate zones). Each part is modelled using completely stirred tank reactors in series (CSTR).

In each CSTR, the calculation of oxidant concentrations (O₃, H₂O₂) is made through mass balance equations and a semi-empirical formula which gives hydroxyl radical concentrations as a function both of ozone concentration and the main characteristics of the water to be treated (pH, TOC, alkalinity). Another semi-empirical formula links ozone consumption to the same characteristics.     

The Installation of GAC and Ozone Surface Water Treatment Plants In Anglian Water,UK

The surface water treatment plants in Anglian Water are being upgraded in order to more reliably meet the requirements of the EEC Drinking Water Directive. Ozone and additional GAC filtration capacity are being installed at 11 waterworks treating river and reservoir water, with capacities ranging from 11 to 360 ML/d. The installations and reasons for the plant designs are discussed.     

Removal of Adsorbable Organic Halides from Water Containing Bromide Ions by Conventional and Advanced Oxidation

The article focuses on an assessment of adsorbable organic halides degradation during the process of conventional ozonation and advanced oxidation as far as the water containing bromides is concerned. The amount of AOX in the water examined varied from 59 to 105 μg Cl^?/L, and the bromides concentration exceeded 200 μg Br^?/L. The effects obtained by O₃ and O₃/UV methods were compared with the results achieved for the water which underwent only UV irradiation. The analysis of presented research results shows that out of the examined oxidation methods, in water of pH 6.8–9.5 and temperature of approximately 287 K, the highest degree of AOX decomposition, was achieved by UV irradiation of water, which was previously subjected to ozonation. However, when the ozone dose reached ≥ 0.3 mg O₃/mg C in an alkaline environment, bromates were formed in amounts exceeding the maximum contaminant level in both processes.     

The “Big Switch”: Los Angeles Aqueduct Filtration Plant Treatment Of California State Project Water

Plant-scale tests were run in October 1987 and October 1988 to evaluate the ability of the 26.3-m³/s (600-mgd) Los Angeles Aqueduct Filtration Plant (LAAFP) to treat one of the source waters -- California State project water (SPW) -- used by the Metropolitan Water District of Southern California and to determine CT^a values for its ozone contact basins. During the test period, a large amount of water quality and operating data was collected, providing insight into the effectiveness of the preozonation/direct filtration process (followed by chlorination or chloramination) on SPW. This paper describes the results of the full-scale testing.     

Advanced Oxidation Processes In The Degradation Of Cyanazine

The use of two Advanced Oxidation Processes, constituted by the combinations of ozone and UV radiation, and hydrogen peroxide and UV radiation, in the destruction of the herbicide cyanazine is presented. In both cases, the influence of the operating variables (initial herbicide concentration, ozone partial pressure or initial hydrogen peroxide concentration, temperature and pH) is discussed, and a comparison is made among the efficiencies of the different oxidizing agents used.     

Antimicrobial Contamination Removal from Environmentally Relevant Matrices: A Literature Review and a Comparison of Three Processes for Drinking Water Treatment

The effectiveness of conventional water treatment technology in preventing the dissemination of antimicrobial contamination has been questioned due to significant rates of antibiotic resistance elements found both in solid wastes and in effluents. This implies that preventive efforts must cover both solid waste quality and effluent quality monitoring. This article presents a review of the occurrence data for a number of antibiotics and antibiotic resistance carriers along with the effectiveness of conventional and advanced technologies in the removal of antimicrobial contamination from various matrices. Although the current literature suggests that the advanced oxidation processes are more promising, cost viable oxidant doses may not be sufficient to reach targeted removal efficiencies especially in biosolids and manure. As a result, antimicrobial contamination can inevitably reach natural waters and contaminate drinking water sources. In this context, a comparison of the effectiveness of three oxidation processes on the removal of a resistance carrier bacterial plasmid DNA was studied. The relative effectiveness of ozonation or heterogeneous photocatalysis over conventional chlorination was demonstrated.     

Operating Strategy To Meet SWTR Disinfection Regulations At The Los Angeles Aqueduct Filtration Plant

Preozonation facilities were installed at the Los Angeles Aqueduct Filtration Plant originally to enhance coagulation assistance (microflocculation). The Surface Water Treatment Rule will amend this primary purpose to meeting disinfection standards. Additional ozone generation equipment and a revised ozone system operating strategy will be required to accomplish these changed objectives. The topics discussed in this paper are the considerations surrounding the development of a successful, cost-effective operating strategy. The strategy proposed herein was based on data collected between January and July 1991. On-line process monitoring plans and automated system control logic are described.     

UV/H2O2 Treatment: A Practical Solution for Organic Contaminant Control and Primary Disinfection

PWN's water treatment plant Andijk was commissioned almost 40 years ago. It services water from the IJssel Lake by conventional surface water treatment. In view of taste and odor problems the plant was retrofitted with GAC filtration 25 years ago. The finished water quality still complies with all E.C. and Dutch drinking water standards. Nevertheless an upgrade is desired to avoid the use of chlorine and to extend the barriers against pathogenic micro-organisms and a broad range of organic micropollutants such as pesticides, rocket fuel by-products (NDMA), fuel oxygenates (MTBE), solvents (dioxane), endocrine disruptors, algae toxins, pharmaceuticals, etc. UV/H₂O₂ treatment was selected for both primary disinfection and organic contaminant control. The disinfection requirements were based on a 10^?4 health risk. The required 3 log inactivation for Giardia and Cryptosporidium was achieved by an UV dose lower than 20 mJ/cm². The highest UV dose, 105 mJ/cm², was needed for the inactivation of spores of Sulphite Reducing Clostridia. Reactivation of protozoa was established for UV doses up to 25 mJ/cm², for doses higher than 45 mJ/cm² no reactivation was observed. In view of the raw water concentrations the required organic contaminant degradation was set at 80%. Collimated beam and pilot-plant work showed that the required degradation can be achieved by the proper combination of electric energy and H₂O₂. In a UV reactor optimized for organic contaminant control, UV dose of 540 mJ/cm² (about 0.5 kWh/m³) and 6 mg/L H₂O₂ were needed. Under those conditions pesticides (atrazine), NDMA, MTBE, dioxane, endocrine disruptors (bisphenol A), microcystine and pharmaceuticals (diclofenac, ibuprofen) could be removed up to the required 80%. Bromate formation was absent while formation of primary metabolites was insignificant. The UV dose for organic contaminant control is about five times higher than the dose needed for disinfection. The UV/H₂O₂ process was implemented into the existing treatment train between the sand and GAC filters. In the GAC filters excess H₂O₂ is degraded, nitrite is converted into nitrate and biodegradable reaction products are consumed by bacteria. The full-scale installation with 3 streets of 4 Trojan Swift 16L30 reactors has been in operation since October 2004. Disinfection and organic contaminant control are as expected.