Ozone Decomposition Rate Research Articles

Mineralization of 4-methyl-1-cyclohexane carboxylic acid by heterogeneous catalytic ozonation

This work studied the mineralization of an aqueous solution of a naphthenic acid model compound, 4-methyl-1-cyclohexane carboxylic acid (4MCH), by heterogenous catalytic ozonation in a semi-batch reactor. A catalyst screening was first conducted by evaluating total organic compound (TOC) removal of Cu, Ce, and Mn (1 and 5 wt%) dispersed on γ-Al2O3, TiO2, ZrO2, and MgO supports. Cu containing catalysts showed the highest TOC removal with Cu/MgO having the best mineralization effectiveness. The Cu/MgO catalysts were characterized by ICP-OES, BET, XRD, XPS, SEM, and TEM. CuO and Cu2O particles were formed on MgO with the majority of them being smaller than 5 nm. pH = 8.5 was identified as the optimum pH for total oxidation of 4MCH due to the right balance between the 4MCH oxidation and ozone decomposition rates. Phosphate and bicarbonate buffers had a different effect on the TOC removal of the Cu/MgO catalysts with better activities in the presence of the phosphate buffer. Mg and Cu leaching was observed during the oxidation of 4MCH, accompanied with an increase in pH. The reusability tests of Cu/MgO (1 wt%) showed that the catalyst retained its activity over 5 cycles with an average Mg and Cu leaching of 44 and 3 mg/L, respectively. The energy consumption cost of the treatment of 4MCH by catalytic ozonation was estimated to be around $13 per cubic meter of the wastewater.

Decomposition and O<sub>3</sub>-Catalytic Oxidation of <i>n-</i>С<sub>4</sub>Н<sub>10</sub>

The activity of transition metal oxides (V, Cr, Mn, Fe, Co, Ni, Cu, Zn) deposited on γ-Al2O3 in the ozone decomposition reaction has been studied. The catalytic characteristics of samples with high (NiO/Al2O3), low (Cr2O3/Al2O3) and intermediate (MnOx/Al2O3) activity in ozone decomposition were studied in the process of ozone-catalytic oxidation (OZCO) of butane. The obtained results allow us to conclude that the optimal activity of transition metal oxide in the decomposition of O3 is of key importance in the OZCO process. At a low rate of ozone decomposition, the oxidation of hydrocarbons is limited by the rate of formation of atomic oxygen, in the case of too high - the conversion of hydrocarbons is reduced due to the “inappropriate” process of recombination of atomic oxygen. The best catalytic characteristics in the oxidation of h C4H10 have been established for a catalyst based on Mn oxide, which has optimal activity in the decomposition of O3.

폐수방류수 오존처리시 오존 및 OH 라디칼 노출량 기반 미량유기오염물질 제거 예측

Municipal wastewater is a major source of contaminants of emerging concern in aquatic environments. Many studies have proven the effectiveness of ozonation for the removal of micropollutants, though the composition of the wastewater matrix influences the oxidation potential during this process. The ozone decomposition rate consists of two stages: instantaneous ozone consumption and slower ozone decay. In particular, with instantaneous ozone consumption, 62.8-79.7% of the initial ozone injection concentration is consumed. Determining the appropriate ozone dosage for wastewater ozonation is complicated by the complexity of the wastewater matrix composition. The purpose of this study was to propose a chemical kinetic model for the prediction of micropollutant removal during the ozonation of wastewater effluent. A kinetics approach based on the measurement of ozone and hydroxyl radical(·OH) exposure was proposed to predict the micropollutant removal efficiency. In this study, a batch-type ozone reactor was set up to measure the ozone and OH radical exposure during wastewater ozonation. Ozone and OH radical exposure was proportional to the initial dose of ozone, while OH radical exposure was found to be proportional to ozone exposure, though the deviation was relatively high at 1.0 to 1.5 gO³/gDOC. The calculated OH radical exposure was 3.0×10^-10 to 5.3×10^-10M·s. Of the target micropollutants, acetaminophen, sulphamethoxazole, andnaproxen, which are highly reactive with ozone and OH radicals, exhibited a removal rate of more than 80% at an ozone injection rate of 0.75 gO³/gDOC.

Potassium ferrate enhances ozone treatment of pharmaceutical wastewaters: Oxidation and catalysis

This work verified the ability of potassium ferrate to catalyse ozone-driven oxidation of refractory organic matter in a secondary effluent of a wastewater treatment plant at a local pharmaceutical factory. The effect of potassium ferrate reduction products on ozone decomposition was investigated by evaluating the variation in ozone concentration in water. The mechanisms were revealed by separating residual potassium ferrate reduction products from solutions and analysing the dissolved organic carbon (DOC), ultraviolet absorption (UV254), and fluorescent organics. The results showed that (1) the decomposition rate of aqueous ozone was higher with the potassium ferrate reduction products than without them, implying the catalytic ability on ozone decomposition. (2) The reduction products of potassium ferrate during ozone treatment resulted in an increase of 14.9 % in the DOC removal rate and 29.03 % in the UV254 removal rate compared with the results of treatment with potassium ferrate alone. These results show that the reduction products of potassium ferrate can promote ozone oxidation of refractory organic compounds in secondary effluents, and a multistage oxidation system in which potassium ferrate combined with ozone is technically feasible. To the best of our knowledge, this is the first study to verify that the synergistic effect of ferrate (VI)–ozone is due to the catalytic effect of reduction products on ozone oxidation.

Ozone Ice as an Oxygen Release Reagent for Heap Leaching of Gold Ore

The issue of poor aeration efficiency and low oxygen transfer in the heap leaching of gold has gained considerable attention. In this study, ozone ice was studied as an oxygen release reagent in the cyanide heap leaching of gold at a low temperature of approximately 5 °C, owing to its effective oxidation and clean and green properties. Quartz Crystal Microbalance with Dissipation (QCM-D) was used to monitor the effect of different ratios of cyanide and oxygen concentrations on the gold leaching rate. The results showed that the leaching rate doubled when the dissolved oxygen (DO) was increased from 8.2 mg/L to 12 mg/L at a relatively high cyanide concentration of 60 mg/L. The release of oxygen during the process of ozone ice melting was analyzed by simulating the oxygen-deficient condition of the ore heap in column leaching. In the first stage of ice melting, the DO in the solution increased dramatically, and the rate of increase improved with increased initial ozone concentration in the ice. In the second stage of ice melting, the rate of increase in the DO of the solution was not significantly affected by the initial ozone concentration in the ice; this was consistent with the decomposition rate of ozone. The addition of ozone ice containing 300 mg/L ozone increased the gold extraction by 4.1% in the ore column leaching experiment, compared to a column with no ozone ice. However, continuously increasing the ozone concentration up to 600 mg/L had no further significant effect, because the dissolved oxygen in the leaching solution reached saturation. The results facilitate a better understanding of the decomposition law of ozone in the melting process of ozone ice and help to improve the oxygen deficit state in gold leaching heaps.

Fe-Mn doped powdered activated carbon pellet as ozone catalyst for cost-effective phenolic wastewater treatment: Mechanism studies and phenol by-products elimination

A novel bimetallic doped PAC (Fe-Mn/PAC) pellet was prepared with a facile sol-gel method and used as an ozone catalyst for phenolic wastewater (PWW) treatment. Adoption of Fe-Mn/PAC pellet in microbubble ozonation enhanced the 1-h chemical oxygen demand (COD) and phenol removal in PWW to 79% and 95%, respectively. With ozone dosage of 10 mg/L, 1 g/L Fe-Mn/PAC pellet exhibited ozone conversion of 92%. In comparison to microbubble ozonation process, Fe-Mn/PAC induced microbubble-catalytic ozonation process promoted ozone decomposition rate by 1.9 times. In terms of •OH production, Fe-Mn/PAC pellet enhanced •OH exposure by 10 times, with a Rct value of 2.92 × 10 -8. Rct kinetic model also suggested that Fe-Mn/PAC pellet obtained higher kinetic rate constants for initiating and promoting •OH generation. Usage of Fe-Mn/PAC pellet in microbubble ozonation for phenolic wastewater treatment also reduced the total ozone consumption by 70%. In Fe-Mn/PAC induced microbubble-catalytic ozonation process, the ratio between ozone consumption and COD removal (ΔO3/ΔCOD) was 0.91. Fe-Mn/PAC pellet characterization with X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared (FT-IR) and X-ray powder diffraction (XRD) analysis revealed successful doping of Fe-Mn on PAC substrate and larger numbers of carbon-oxygen/hydroxyl surface groups, which played key roles in ozone decomposition and •OH production.

A novel γ-like MnO2 catalyst for ozone decomposition in high humidity conditions

MnO2 catalysts have been widely studied for catalytic gaseous ozone decomposition. However, their poor moisture resistance often leads to undesirable catalytic effects in the presence of high humidity. In this study, a novel catalyst with γ-like MnO2 was synthesized using the selective dissolution method on LaMnO3 perovskites. The as-prepared catalyst exhibited quite stable ozone conversion of ~90% within 12 h under 75% relative humidity (400–800 ppm of ozone, 30 °C, 150 000 mL·g−1·h−1 of WHSV). In contrast, traditional γ-MnO2 catalyst showed deficient resistance to H2O and sensitivity to space velocity. Detailed characterizations showed that the larger number of oxygen vacancies induced by structure reconstruction of the γ-like MnO2 and residual La3+ cations facilitated ozone decomposition in humid atmosphere. Finally, the reaction rate of ozone decomposition was proposed by a kinetic study, which further proved that the amount and hydrophilicity of oxygen vacancies are the determinants of the first-order reaction rate constant.

Implications of bromate depression from H2O2 addition during ozonation of different bromide-bearing source waters

Minimizing bromate formation by adding H2O2 is one major option for bromide-containing source water when applying ozone in drinking water. However, difference in background water quality can have a significant influence on bromate depression. In this study, three bromide-bearing source waters (YZ, HR and HP) were selected to investigate bromate depression during the H2O2-ozonation process. The results showed that there was strong correlation between bromate formation and molecular ozone consumption during ozonation process for the three waters. Compared to YZ and HR, ozone was consumed quickly within about 10 min for HP water, inducing lower bromate formation during ozonation process. In the initial step of bromide oxidation, molecular ozone oxidation was responsible for more than 80% of oxidation, much higher than that by hydroxyl radicals. Specifically, 94% of the oxidation of bromide occurred with ozone for YZ water, which might be attributed to the low concentration of organic matter in the water. The residual molecular ozone would be a restrictive factor and affect the bromate formation significantly. For YZ and HP water, as H2O2/O3 (g/g) increased to 0.5, the ozone decomposition rate increased 61 times and 7.2 times respectively, which resulted in difference in bromate depression performance when applying H2O2. Humic acid and tyrosine in water were confirmed to have effects on bromate formation and depression after H2O2 addition. This study could elucidate the different bromate depression effects occurring in different source waters when adding H2O2, which will provide an informative guide for bromate control in drinking water treatment.

Thermal decomposition of ozone at high temperature leading to ozone zero phenomena

A gradual decrease in the concentration of ozone produced by the continuous operation of a large-scale dielectric barrier discharge-type ozone generator (OG) was observed under the supply of a constant discharge power and high-purity oxygen as the feed gas. This finding was named the ‘ozone zero phenomena’ on the basis of our experiments demonstrating that the ozone molecules disappeared at the surface of the electrodes in the OG, in which both the formation and decomposition of ozone occur simultaneously. To clarify the cause of the phenomena, we performed new experiments with an OG separated functionally into two parts to avoid the effects of the discharge, which also oxidizes stainless-steel and increases the temperature in the generator, although the discharge is indispensable for ozone generation. The first part was an OG supplying ozone to the following part. The second part was an ozone destructor that simulated an OG in which only the ozone zero phenomena occurred. The ozone destructor was an incubator with pipes made of stainless-steel or borosilicate glass in them and maintained at a constant temperature of up to 473 K. The generator and destructor were connected serially with a gas flow line. Ozone–oxygen mixtures with constant ozone concentrations produced by the first part were introduced into the ozone destructor, and the ozone concentrations at the inlet and outlet of the pipes were monitored simultaneously. Using the two ozone concentrations, the decomposition rate of ozone was evaluated as functions of time, the pipe material, the pipe temperature, and the concentration of ozone introduced into the pipe. We concluded that in this model experiment the ozone zero phenomena are induced by the thermal decomposition of ozone in the pipes which is installed in the heated incubator to provide ambient temperature conditions for the conversion of ozone molecules.

Solubilization and stabilization for prolonged reactivity of ozone using micro-nano bubbles and ozone-saturated solvent: A promising enhancement for ozonation

The enhanced ozonation treatment by a combination of micro-nano bubbles (MNBs) and ozone-saturated solvent (e.g. acetic acid (HAc)) was investigated. The solubility, decomposition rate of ozone, and reactive oxygen species (ROSs) in various concentrations of HAc with/without MNBs were examined, and these synergetic effects were verified by the enhanced removal of p-chlorophenol (4-CP). The results showed that MNBs promoted the solubility and mass transfer coefficient (KLa) of ozone in both deionized (DI) water and HAc solution by 2.03–2.26 and 2.30–3.68 times respectively compared with normal millibubbles. Addition of a certain amount (0.5–5%) of HAc can further benefit the ozonation process. The ozone solubility was about four times larger in 5% HAc solution compared with that in DI water (0%), while the former KLa was 3.91-fold higher. The average half-lives of ozone were prolonged by 1.39–3.52 times in 0.5–5% HAc solutions to water alone. This was attributed to the inhibited chain reaction by scavenging the hydroxyl radical (OH) in the presence of HAc and thus retarded OH-catalyzed ozonolysis. The detection of ROSs showed that the concentrations of hydrogen peroxide (H2O2) and OH were up to 39.53 ± 4.10 and 70.17 ± 3.09 μg/L in the hybrid system. The ROSs led to that 48.15–77.55% of 4-CP were removed by ozonation with MNBs in 30 min, and 9.50–29.40 percent improvements were achieved in the HAc solutions than in the DI water. These results indicate that the combination of ozone with MNBs and HAc could enhance the removal of 4-CP effectively. This study illustrated the solubilization and stabilization effect for prolonged reactivity of ozone using MNBs and ozone-saturated solvent together.

Role of Aqueous Aerosols in Ozone Decomposition in the Near-Surface Atmosphere

The effect of aqueous aerosol on the ozone concentration in atmospheric air is experimentally demonstrated. In field experiments, an abrupt decrease in the ozone concentration in the near-surface atmosphere was observed during a short-term shower rain in a megacity. Ozone decomposition in the presence of water was also studied under laboratory conditions in the reactive chamber. It is shown that ozone decomposition in air is enhanced at high relative humidity, and in the presence of aqueous aerosol. The ozone decomposition rate depends on the aerosol size; the smaller the particle, the higher the decomposition rate; this can indicate a significant role of heterogeneous bonding on the aerosol surface in the ozone decomposition.

Ozonation catalyzed by iron- and/or manganese-supported granular activated carbons for the treatment of phenol

Iron- and/or manganese-supported catalysts on granular activated carbons (Fe and/or Mn/GACs) were prepared, and their catalytic activities were evaluated by using them to treat phenol and secondary petrochemical effluent via ozonation. The presence of Fe and/or Mn/GACs significantly improved the degradation and degree of phenol mineralization. Changes in dissolved ozone concentrations and the effects of carbonate and tert-butyl alcohol (TBA) indicated that the prepared catalyst enhanced the decomposition of ozone into hydroxyl radicals (·OH), which was determined to be a key factor in catalyzing the ozonation of phenol. Typical intermediate products were identified by GC-MS and HPLC analysis, and a possible degradation pathway of phenol via catalytic ozonation was proposed. The results of XPS, CV, and other experimental data indicated that introducing Fe and/or Mn increased the rate of ozone decomposition into ·OH, and also enhanced the interfacial electron transfer by Fe2+-Fe3+ and Mn2+-Mn3+-Mn4+ redox cycles, resulting in higher catalytic activity. However, the Fe-Mn/GAC surface was shown to undergo galvanic corrosion between Fe3O4 and MnO2, decreasing the catalytic activity. In addition, catalytic ozonation was used to treat secondary petrochemical effluent. The results demonstrated that the Mn/GAC/O3 system significantly improved the quality of phenol-containing wastewater in terms of its COD, TOC, NH4+-N, water color, and ecotoxicity. This study gives a better understanding of the phenol treatment by catalytic ozonation using Fe and/or Mn/GAC.

Facile synthesis of alkaline-earth metal manganites for the efficient degradation of phenolic compounds via catalytic ozonation and evaluation of the reaction mechanism

In this paper, we demonstrate the facile and general synthesis of alkaline-earth metal manganites, denoted as A(Mg, Ca, Ba)MnxOy, for efficient degradation of high-concentration phenolic compounds via catalytic ozonation. The representative CaMnxOy oxides show a hierarchical spherical structure constructed by crystalline nanorods and numerous macropores. They possess mixed Mn4+/Mn3+ chemical valences and abundant surface hydroxyl (OH) groups. The ozone (O3) decomposition rate on the CaMnxOy catalysts is greatly accelerated and follows the first-order law. These catalysts are promising for the degradation of phenolic compounds via catalytic ozonation, exhibiting rapid pseudofirst-order degradation kinetics, a high total organic carbon (TOC) removal efficiency and an excellent stability. Under optimized conditions (a low O3 dosage of 1.5 mg/min and a catalyst dosage of 7.5 g/L), for the treatment of concentrated phenol (50–240 mg/L), the CaMnxOy catalysts show 100% degradation and 50–70% mineralization within 1.0 h. The Ca2+ ions are essential to create redox Mn4+/Mn3+ couples and to significantly reduce manganese leaching. High surface ratios of Mn4+/Mn3+ and OH/lattice oxygen (Olat) are beneficial for enhancing the catalytic performance. Superoxide anion free radicals (O2–) and singlet oxygen (1O2) are the predominant reactive species for the oxidation degradation. The O2– reaction pathway is proposed. Specifically, the surface OH sites activate O3, displaying highly enhanced decomposition rates. The generated O2– and 1O2 play a role in oxidation. The redox Mn4+/Mn3+ and the Olat/oxygen vacancy (Olat/Ovac) couples play important roles in electron transfer. The proposed mechanism is supported by active site probing, radical scavenging, spectroscopic studies, and the results in the degradation of substituted phenols.

Aqueous ozone decomposition kinetics in a rotating packed bed

Abstract The decomposition kinetics of aqueous ozone in a rotating packed bed (RPB) at 18 ± 2 °C and in the pH range 3.0–11.0 was firstly investigated. The decomposition rate of ozone increased with increasing pH value and rotor speed. Moreover, a reaction kinetic model for ozone decomposition in RPB was developed, which can be applied for an extended range of pHs from acidic to alkaline operating conditions. It was deduced that ozone decomposition was based on pseudo-first-order kinetics with respect to the ozone concentration. The degree of the chain reaction between ozone molecule and hydroxyl ion in RPB was found higher than that in batch reactor. Furthermore, experiments showed that NO3−, Cl−, HCO3− and CO32− ions could promote the self-decomposition of ozone to some extent and the promotion effect of CO32− ion was the largest.

Intensification of the O3/H2O2 advanced oxidation process using a continuous tubular reactor filled with static mixers: Proof of concept

An innovative implementation of the O3/H2O2 advanced oxidation process was proposed to intensify the hydroxyl radical generation. Natural or drinking waters, containing atrazine as a probe compound, were spiked with H2O2 and further continuously mixed to a pre-ozonated solution in a homogeneous tubular reactor filled with static mixers. Hydraulic residence times ranging from 10 to 140 s were set at different sampling ports. The experimental results confirmed a very high ozone decomposition rate, concomitant with a high hydroxyl radical exposure (Rct in the range from 10−7 to 10−6), especially during the initial ozone decomposition phase (between 10 and 20 s). Equimolar initial concentrations of hydrogen peroxide and ozone were optimal to maximize the hydroxyl radical generation and to minimize their relative consumptions. The influence of the water matrix on the ozone decomposition and the hydroxyl radical generation was limited. This study is a proof of concept that using a homogeneous tubular reactor would be more effective than a gas–liquid reactor to apply the peroxone process.

Photocatalytic decomposition of indoor ozone motivated by the white-light-emitting diode

TiO2 photocatalysis driven by ultraviolet (UV) light has been utilized to remove harmful indoor ozone in many previous studies. However, UV lamp is energy-consuming, and UV radiation has been classified as a carcinogen. For sustainability and health’s sake, we investigated the photocatalytic degradation of ozone driven by the white-light-emitting diode in the present study. Five different materials including nitrogen-doped TiO2 (TiO2-N), TiO2 hydrogenated at 300 and 350 °C (TiO2-H300 and TiO2-H350), P25 and Merck TiO2 were used as photocatalysts in the experiments. We also examined the effects of relative humidity (RH35-80%), ozone concentration (50–250 ppb) and air flow rate (2–8 Lpm) on the ozone removal efficiency. Because H2O could increase electron–hole recombination by inducing surface structural bending, the ozone removal efficiency of all the photocatalysts decreased with the increase in RH. Among the five photocatalysts, the nanotubular structure of TiO2-N created the largest surface area for the adsorption of ozone, and the nitrogen doping enhanced the visible-light absorbance. Therefore, TiO2-N exhibited the highest apparent reaction rate of ozone decomposition. However, the nanotubular structure of TiO2-N also generated a mass transfer barrier that obstructed the removal of ozone. Fortunately, there was no significant mass transfer limitation in the granular photocatalysts (P25 TiO2, TiO2-H300 and TiO2-H350). This study provides practical data for the implication of visible-light-driven photocatalytic degradation of ozone.

Catalytic ozonation of sulfamethazine antibiotics using Fe3O4/multiwalled carbon nanotubes

Antibiotics are ubiquitous pollutants which cannot be effectively removed by conventional wastewater treatment processes. In this paper, the catalytic ozonation of sulfamethazine (SMT) by Fe3O4/multiwalled carbon nanotubes (MWCNTs) was investigated, including the effect of pH on degradation kinetics, mineralization, mechanism of SMT degradation, and ozone utilization. The experimental results showed that Fe3O4/MWCNTs catalyzed ozonation could increase the degradation and mineralization of SMT compared with ozonation alone. Acid condition was more favorable to the degradation and mineralization of SMT than neutral or basic conditions. The adsorption of organic pollutants and ozone onto Fe3O4/MWCNTs was an important step for SMT degradation. The catalytic ozonation of SMT by Fe3O4/MWCNTs was dependent on SMT adsorption, ozone decomposition rate and Fe3O4 state. The possible degradation pathways for catalytic ozonation of SMT on the surface of Fe3O4/MWCNTs were tentatively proposed. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 678–685, 2018

Effect of graphene oxidation degree on the catalytic activity of graphene for ozone catalysis

The potential of graphene-based materials, including graphene oxide (GO), over-oxidized graphene oxide (oGO), and non-oxidized graphene (nOG), for catalytic ozonation was investigated, along with the mechanism of ozone catalysis. Increasing the extent of oxidation of graphene led to the formation of hydroxyl and carboxyl groups on the graphene surface, which then partially converted into epoxy groups. The catalytic efficiency of oGO was much higher than that of both GO and nOG. Graphene’s extent of oxidation might be a significant factor in catalytic ozonation. The hydroxyl radical exposure to ozone exposure ratio (Rct) of 25mgL−1 ozone/oGO was 75-fold higher than that of an ozone alone process. The ozone decomposition rate and para-chlorobenzoic acid removal efficiency were higher at pH 9 than at any other pH. The Rct of ozone/oGO at pH 9 was 2.35×10−5. Temperature affected ozone adsorption on the nOG surface. Ozone/graphene experiment with an excess of tert-butyl alcohol was proposed that hydroxyl radicals generated by GO and oGO existed mainly in the solution phase, while those generated by nOG existed in both solution and surface phases.

Improved photocatalytic ozone abatement over transition metal-grafted titanium dioxide

Photocatalysis can be an effective means to combat air pollution. Up to now, mainly direct NOx abatement has been studied, but ozone abatement could also contribute significantly to improved air quality. The ozone decomposition rates of different commercial titanium dioxide based photocatalysts grafted with copper, manganese or iron ions were studied both under UVA illumination and under dark conditions. Copper and manganese grafting were effective in significantly increasing the ozone decomposition rate of the photocatalysts. The procedure worked best when using low surface area pigmentary anatase rather than nanoparticulate photocatalysts. Manganese grafting also increased the ozone abatement under dark conditions, likely due to small MnOx clusters acting as catalysts. Iron grafting appears to be the most universal method of improving the photocatalytic ozone removal rate, as it worked for all four different photocatalysts studied. Extremely low iron grafting ratios of 0.002at.% were sufficient to dramatically improve the performance.

Effects of Joint-reaction Combined by Ozonation and Coagulation on Aquatic Organic Matters

Variations of residual ozone concentration in pure water and Al2(SO4)3 solution were studied. The spectral characteristics, contents of organic compounds and disinfection by products (DBPs) yields in preozonated, preozonated coagulated (POC) and ozonated combined coagulated (OC) waters were detected by differential absorbance(DA), three dimensional fluorescence excitation-emission matrix spectroscopy (3D-EEM), GC and TOC. The purpose of the work was to investigate the effects of ozonation combined with coagulation on their oxidation extents of organic matter and the production of DBPs. Studies showed that there were remarkable differences between the two processes, POC and OC, which proved the existence of joint interaction of ozone and coagulant. The joint interaction involved the following aspects. 1 Decomposition rate of ozone was improved; and the free radical production was increased during OC compared with POC. Comparing to ozone alone, 15.2% and 23.9% more radical capture with ozone 2mg·L-1, Al3+ 1 mg·L-1, 3 mg·L-1 were detected. 2 The difference of OC and POC was found in that organic matter removal of OC was lower than that of POC. The pathways of OC and POC showed difference, which resulted in differences of reaction between organic matter and disinfectant, as well as yields of DBPs. OC removed UV254 and DOC more efficiently than single ozonation or single coagulation; but less efficiently than POC. DCAAFP (Dichloroacetic acid formation potential) and TCAAFP (Trichloroacetic acid formation potential) were 47 μg·L-1 and 20.5 μg·L-1 respectively after treatment by POC with O3 1mg·L-1and Al3+1mg·L-1, and chloroform formation potential (CFFP) was 97.8 μg·L-1, which were 51%, 64.6% and 41.5% respectively lower than those in the raw water. Under the same dose conditions, DCAAFP, TCAAFP and CFFP after OC were 48.4 μg·L-1, 21.4 μg·L-1 and 117.3 μg·L-1, respectively, which were 49.6%, 63% and 29.5% lower than those in raw water. The difference between the efficiencies of POC and OC would be enlarged with increase of coagulant dose under the same ozone dose. Considering its safety and efficiency, the ozone dosage, adding spot and coagulant species must be taken into account when combined treatment of preozonation and coagulation is used; further investigations are also needed.