The Effect of Ozonation and Filtration on AOC (Assimilable Organic Carbon) Value of Water from Eutrophic Lake

The effects of applying ozone into the source water of Cheng-Ching Lake Water Works (CCLWW) on the analysis of AOC (assimilable organic carbon) were compared in the laboratory and pilot-scale tests. CCLWW takes its raw water from an eutrophic lake. A pilot plant, established in CCLWW in southern Taiwan, was performed to improve the quality of water obtained by the former treatment processes. The direct application of ozone to the source water of CCLWW is called the pre-O₃ process. The post-O₃ process involves the treatment of effluent with ozone through a sand filter, following other treatments, including pre-O₃, coagulation and sedimentation. In a laboratory test, a 0.45 μm membrane filter was used to replace the facility of filtration for a sand filter. AOC_Total comprises AOC_P17 and AOC_NOX, which were determined using the P. fluorescens strain P17 and the Spirillum species strain NOX, respectively. During over 2 years' sampling in eutrophic lake, it revealed that AOC_P17 contributed substantially to AOC_Total. However, the filtrate from the source water obtained by filtering through a 0.45 μm membrane filter had an AOC_Total much lower than that of the source water, especially for the considerable decrease of AOC_P17. Also, the AOC value in source water is increased with algae number but not with NPDOC (non-purgeable dissolved organic carbon). This result indicated that algae numbers existing in the eutrophic lake might affect the analysis of AOC. Following the pre-O₃ process at the pilot-scale plant, the AOC_P17 was markedly lower than that of the source water, and AOC_NOX was slightly higher than that of the source water. However, when post-O₃ was added to the effluent from a sand filter at the pilot-scale plant, AOC_NOX exceeded that before post-O₃, while AOCP17 differed slightly from that before post-O₃. Apparently, this difference may be due to the algae number existing in the water samples. These results were verified by applying ozone to the source water, and to filtrate obtained by filtering through a 0.45 μm membrane filter in a lab-scale test, respectively.     

Effect of Ozone in UF-Membrane Flux and Dissolved Organic Matter of Secondary Effluent

The focus of this work was to determine the effect of ozone on the removal of dissolved organic matter (DOM) from a secondary effluent and its relation with the permeated flux behavior in an ultrafiltration membrane. To assess the ozone action, the DOM of the secondary effluent was fractionated into its hydrophobic, transphilic and hydrophilic fractions, using XAD-8 and XAD-4 resins. Ozone increased the hydrophilic fraction from 32% to 42%, and this percentage remained unchanged after ultrafiltration of the secondary effluent. Permeate flux dropped to 52% in the first hour of membrane operation, but when ozone was applied as a pretreatment, it could be maintained at 84% within the first hour.     

The Evaluation Of Ozonation and Chlorination On Disinfection By-Product Formation for a High-Bromide Water

High-bromide raw water was ozonated or chlorinated with and without hydrogen peroxide to study the effect of the disinfectants on the disinfection by-product (DBP) formation. Less bromate was formed when ozonation was made at the ambient pH of 5.8 as compared to ozonation at pH 7, showing the effectiveness of pH reduction in controlling the bromate formation. When chlorine dose was 1 mg/L instead of 2.3 mg/L, the trihalomethane formation was 50 μg/L instead of >100 μg/L, and the proportional distribution of the trihalomethanes was similar. The use of ozone for this water could provide good results in respect of the DBP formation.     

Production and Removal of Assimilable Organic Carbon Under Pilot-Plant Conditions Through the Use of Ozone and PEROXONE

Pilot-plant studies were conducted in two source waters to determine the effects of predisinfection with ozone alone and with a combination of hydrogen peroxide and ozone (PEROXONE) on the production of assimilable organic carbon (AOC) compounds. Colorado River water (CRW) and State project water (SPW) from Northern California were treated with ozone alone at applied dosages ranging from 1 to 4 mg/L and with PEROXONE at hydrogen peroxide/ozone (H₂O₂/O₃) ratios of 0.05, 0.10, 0.20, and 0.30. Ozonation of CRW with applied dosages of 1.0,2.0, and 4.0 mg/L increased AOC concentrations from 70μg C/L to 275, 350, and 224 μg C/L, respectively. Ozonation of SPW with an applied dosage of 4.0 mg/L elevated AOC concentrations from 70 to 522μg C/L.     

Modeling Bromate Formation During Ozonation

Bromate formation has been identified as a significant barrier in the application of ozone during water treatment for water sources that contain high levels of bromide. Bromate has been identified as a possible human carcinogen and bromate levels in drinking water are strictly controlled at 10 μg/L in most developed countries. Various models have been proposed to model bromate formation during ozonation based on raw water quality, ozone dose and contact time. Two main approaches for modeling have been used: an empirical regression modeling methodology and kinetic-based methodology. Currently, the benefit of the bromate models lies in their ability to show how process parameters may impact on the amount bromate formed.     

Formation Of Aldehydes During Ozonation

This study investigated the formation of aldehydes after ozonation of three real and three model waters reconstituted from hydrophobic organic material. The four main aldehyde species formaldehyde, acetaldehyde, glyoxal, and methyl glyoxal were analyzed. Formaldehyde was the dominant species formed as a result of ozonation. The different waters varied greatly with respect to aldehyde production under similar treatment conditions. Studies conducted with model waters allowed for exploring aldehyde formation as a function of various water quality parameters. Overall, the hydrophobic organic extracts appeared to have greater aldehyde formation potential than the hydrophilic organics. Aldehydes were formed in direct proportion to the total organic carbon (TOC) concentration of the water at a 1:1 ozone-to-TOC ratio. Greater aldehyde formation was observed at lower ozonation pH values. Bromide ion and inorganic carbon added to model waters appeared to have no effect on aldehyde production. Finally, Assimilable Organic Carbon (AOC) measurements exhibited a strong correlation between aldehyde production and AOC production.     

Impact of Ozone Treatment on Selected Microbiological Parameters

A pilot plant study was conducted to evaluate the effects of ozonation on the quality of Colorado River water delivered to the Phoenix (Arizona) Union Hills Water Treatment Plant through the Central Arizona Project canal. Raw and finished water were monitored for basic chemical water quality parameters and for microorganisms including total coliforms, heterotrophic plate count, enteric viruses, Giardia and Crvptosporidium cysts. Ozone, applied through diffusion contactors in dosages optimized to provide the required CT (concentration x contact time) value, was used as a primary disinfectant in two of the four 10 gpm (37.8 L/min) treatment trains.     

Ozonation of Dyestuffs and Intermediates and Further Decrease in Dissolved Organic Carbon by Post-Biodegradation

Four each of water-soluble dyestuffs, intermediates and reference compounds were examined to determine the effect of the combined use of ozonation and post-biodegradation on the decrease in the amount of dissolved organic carbon (DOC) and the synergistic effect induced by ozonation. The amount of DOC removed by ozonation was increased initially with increasing ozonation time, and showed a plateau thereafter. The amount of ozone required to remove 1 mg of DOC (ΔO₃/ΔDOC) ranged from 5.2 to 18.6 mgO₃/mgC for the dyestuffs and the intermediates. The DOC concentrations of all the ozonized solutions were decreased with incubation time. In the case of the dyestuffs and the intermediates, the total amounts of DOC removed were increased with increasing ozonation time and showed a plateau thereafter. The synergistic effect (the ozonation-induced increase in the amount of DOC removed by the biological process) was dependent on the initial biodegradability, and was observed in all the dyestuffs and the intermediates in the range of 0.2 to 42.7 mgDOC. On the other hand, no synergistic effect was observed in the reference compounds of high biodegradability.     

The Influence of the Removal of Specific NOM Compounds by Anion Exchange on Ozone Demand,Disinfection Capacity,and Bromate Formation

This research on a pilot scale focuses on the reaction of ozone with natural organic matter (NOM) for three water qualities with different dissolved organic carbon (DOC) concentrations and NOM compositions, obtained after several stages of an anion exchange process. It was shown that for the same ozone dosage per DOC, the ozone demand was higher, less bromate was formed and a lower disinfection capacity was reached for water containing mainly humic substances, than for water where the humic substances were partly removed. It can be concluded that NOM composition, specifically the humic substances, influences the ozone demand, disinfection capacity and bromate formation.     

Evaluating Magnetic Ion Exchange Resin (MIEX)® Pretreatment to Increase Ozone Disinfection and Reduce Bromate Formation

Magnetic ion exchange resin, known by its commercial name (MIEX®) provides one pretreatment alternative that could maximize ozonation disinfection while decreasing bromate formation in bromide-containing waters. During a 5-week pilot study, the MIEX® process removed up to 30 % of the dissolved organic carbon (DOC) and reduced ultraviolet absorbance at 254 nm (UV 254) by up to 60%. When MIEX® pretreated water was ozonated, ozone decay rates were reduced, increasing the CT achieved by 40% to 65%. The increased disinfection capability reduced the transferred ozone dosages required for Cryptosporidium inactivation by 15% to 25% and bromate formation by 35%.     

Mechanisms of Phenol Ozonation—Kinetics of Formation of Primary and Secondary Reaction Products

Organic acids are part of assimilable organic carbon (AOC) formed from natural organic matter (NOM) during ozonation for drinking water production. To elucidate the formation of organic acids, phenol as surrogate compound for NOM was ozonated while suppressing reactions of ^·OH radicals by addition of tert-butanol. Batch experiments show benzoquinone (40 and 18%), catechol (33 and 1%), cis,cis-muconic acid (6 and 3%), and hydroquinone (2 and 7%) to be the most abundant primary products at pH 7 and 3, respectively. The tertiary product oxalic acid was obtained in similar yields from phenol ozonation (0.8%) as during ozonation of lake water (1.6%). Together with other low molecular weight organic acids it was formed upon small ozone exposures, as was shown by time-dependent experiments in time ranges of 0.4–23 and 0.07–1.0 seconds for pH 3 and 7.25, respectively.     

UV Disinfection of E. coli Between Concentric Cylinders: Effects of the Boundary Layer and a Wavy Wall

UV inactivation of E. coli in a plug flow reactor between concentric cylinders was investigated. The concentration boundary layer thickness was computed for laminar, turbulent and Taylor-Couette flow in terms of the respective mass transfer Sherwood number. It is demonstrated that the concentration boundary layer is thin and that the mass transfer coefficient is large and comparable in size for both turbulent and laminar Taylor-Couette flow in contrast to laminar flow. Computation of the fluence distribution for each flow pattern indicate that turbulent and especially Taylor-Couette flow subject E. coli to an equal flux of photons corresponding to ideal plug flow. However, experiments with turbulent flow that require large axial velocities indicate that very long reactor lengths are necessary to inactivate E. coli. Finally, rotor wavy wall modifications are explored to increase the inactivation of microorganisms in Taylor-Couette flow.     

Reaction Mechanisms for DBPS Reduction in Humic Acid Ozonation

In this study, XAD-8 resins were used to extract the natural organic matter (NOM) from samples collected at the intake of Feng Yuan Water Treatment Plant (in central Taiwan) into five groups: humic acids, fulvic acids, hydrophobic neutrals, hydrophobic bases, and hydrophilic fractions. Quantitative results show that hydrophobic and hydrophilic fractions contribute 44.2% and 55.5% of NOM, individually. Ozonation processes will significantly reduce both disinfection by-products formation potential (DBPFP) and average molecular weight of the humic acid sample. Additionally, double carbon bonds are broken up so that hydrophobic fractions were converted to hydrophilic fractions by ozonation leading to the reduction of DBPFP.     

Bromate Control by Dosing Hydrogen Peroxide and Ammonia during Ozonation of the Yellow River Water

Ozonation of the downstream Yellow River water yields bromate with concentrations higher than China regulations. Bench tests demonstrated that dosing ammonia or hydrogen peroxide alone could not control the bromate concentration to below 10 μg/L. A pilot study showed that dosing hydrogen peroxide into the inherently ammonia-containing raw water at a dosage lower than 1.7 could effectively reduce the bromate concentration to below the detection limit when the ozone dosage was between 2 and 2.5 mg/L.     

Use of Ozone for Disinfection and Taste and Odor Control at Proposed Membrane Facility

Zone 7 of Alameda County Flood Control and Water Conservation District, in coordination with Black & Veatch, conducted a 9-month pilot study to determine preliminary design parameters for a new water treatment plant (WTP). The pilot study was performed to verify the performance of membrane filters and to establish preliminary design parameters for the submerged membrane process, followed by ozonation and biological granular activated carbon filtration. The pilot testing was conducted using water from the Patterson Pass WTP reservoir. The process included coagulation with either ferric chloride or polyaluminum chloride, flocculation, sedimentation, membrane filtration, ozonation, and filtration using biological granular activated carbon (BAC). The goals of the study were as follows:

1. Determine the potential effectiveness of ozone and BAC for removing geosmin and MIB.

2. Determine the impacts of different levels of pathogen inactivation, i.e., 0.5-log Giardia and 2-log virus inactivation.

3. Monitor the formation of bromate under various conditions of ozone oxidation for different levels of pathogen inactivation as well as for taste and odor control, and evaluate bromate mitigation strategies, if necessary.

The results of the study showed that the use of ozone achieved 2.0-log virus inactivation and 0.5-log Giardia inactivation. It also decreased the disinfection by-product formation and effectively controlled geosmin and removed a significant fraction of the MIB during a taste and odor event. Because the raw water bromide concentrations were low, bromate formation remained below the regulated level of 0.010 mg/L. However, in one instance, bromate mitigation was utilized by applying sulfuric acid to lower the pH to less than 7.1, which reduced bromate formation to less than 0.010 mg/L.     

Comparing Static Mixer Performances at Pilot and Full Scale for Ozonation,Inactivation of Bacillus subtilis,and Bromate Formation in Water Treatment

The potential benefits of using a static mixer for ozone dissolution was evaluated through comprehensive pilot- and full-scale studies under a variety of operating conditions and source waters. The static mixer pilot unit was operated side-by-side to a full-scale plant which also employed static mixers for ozonation. Based on the results obtained from this pilot study (and at other sites), it appears that an optimal ozone dose (≤0.5mgO₃/mgC) applied through a static mixer dissolution system integrated with a well-designed downstream contactor can result in enhanced microbial inactivation while keeping bromate formation below 10μg/L.     

Residence Time Distributions in Ozone Contactors

The hydraulics in ozone systems, characterized by the residence time distribution, are investigated numerically as well as experimentally. The complex geometry of the ozone contactors requires the application of computational fluid dynamics (CFD), which in combination with experimental results gives insight in the hydraulic processes. Particle tracking provides a distribution of CT-values (dissolved ozone concentration times residence time) to estimate disinfection precisely and points out dead zones that hamper disinfection. The CFD modeling predicts that small changes in geometry reducing the strength of the recirculation zone can significantly increase the inactivation of micro-organisms.