Xian-Jiao Zhou

Sulfamethoxazole degradation by ultrasound/ozone oxidation process in water: kinetics, mechanisms, and pathways.

In this research, sulfamethoxazole (SMX) degradation was investigated using ultrasound (US), ozone (O3) and ultrasound/ozone oxidation process (UOOP). It was proved that ultrasound significantly enhanced SMX ozonation by assisting ozone in producing more hydroxyl radicals in UOOP. Ultrasound also made the rate constants improve by kinetics analysis. When ultrasound was added to the ozonation process, the reaction rate increased by 6-26% under different pH conditions. Moreover, main intermediates oxidized by US, O3 and UOOP system were identified. Although the main intermediates in ozonation and UOOP were similar, the introduction of ultrasound in UOOP had well improved the cleavage of S-N bond. In this condition SMX become much easier to be attacked, which led to enhanced SMX removal rate in UOOP compared to the other two examined processes. Finally, the SMX degradation pathways were proposed.

Optimization of operating parameters for sludge process reduction under alternating aerobic/oxygen-limited conditions by response surface methodology

Batch tests were employed to estimate the optimal conditions for excess sludge reduction under an alternating aerobic/oxygen-limited environment using response surface methodology. Three key operating parameters, initial mixed liquor suspended solids (initial MLSS), HRT (hydraulic retention time) and reaction temperature (T), were selected, and their interrelationships studied by the Box-Behnken design. The experimental data and ANOVA analysis showed that the coefficient of determination (R(2)) was 0.9956 and the adjR(2) was 0.9912, which demonstrates that the modified model was significant. The optimum conditions were predicted to give a maximal ΔMLSS yield of 226 mg/L at an initial MLSS of 10,021 ± 50 mg/L, an HRT of 9.1h and a reaction temperature of 29°C. The prediction was tested by triplicate experiments, where a ΔMLSS yield of 233 mg/L was achieved under the chosen optimal conditions. This excellent correlation between the predicted and measured values provides confidence in the model.

Ultrasonic-assisted ozone oxidation process of triphenylmethane dye degradation: evidence for the promotion effects of ultrasonic on malachite green decolorization and degradation mechanism.

This study aimed to prove the promotion effects of ultrasonic on malachite green (MG) decolorization in the ultrasonic-assisted ozone oxidation process (UAOOP), and propose the possible pathway of MG degradation. The decolorization of MG followed an apparent pseudo first-order kinetic law (initial MG concentration 100-1000 mg/L). When ultrasonic (US) was applied with ozone simultaneously, the apparent pseudo-first-order rate constant (K(app)) increased, and the time MG decolorized to the half of initial concentration (T(1/2)) shortened 185 s (1000 mg/L). Moreover, the stoichiometric ratio (Z(app)) between O(3) and MG was enhanced by US to 2.0 mol, saving 11% oxidant addition, comparing to individual ozone process. These results indicated that the application of US can reduce reaction time and dose of ozone addition. The possible pathway of MG degradation included three major approaches. And the result suggested that the reaction between MG and hydroxyl radical was substitution reaction rather than adduct reaction.

Characterizing the fluorescent products of waste activated sludge in dissolved organic matter following ultrasound assisted ozone pretreatments

This study investigated the effects of ozone and ultrasound (US) pretreatments, both individually and combined, on waste activated sludge reduction. Batch tests were conducted first to optimize the individual ozone and US pretreatments. Maximum sludge reduction ratios of 10.89% and 23% were obtained at 0.15g O3/g total solids ozone dose and 1.5W/mL US energy density, respectively. The combined ozone and US pretreatments were studied using response surface methodology. A maximum sludge reduction ratio of 40.14% was achieved by the combined ozone/US pretreatment with an ozone dose of 0.154g O3/g total solids and an US energy density of 1.445W/mL. The analysis of the dissolved organic matter by three-dimensional excitation-emission matrix fluorescence spectroscopy showed that the combined pretreatment was superior to the individual ozone and US pretreatments, and also demonstrated the synergetic effect of these two combined pretreatments.

Synergetic effects and flocculation behavior of anionic polyacrylamide and extracellular polymeric substrates extracted from Klebsiella sp. J1 on improving soluble cadmium removal.

The performance and flocs properties in removing soluble cadmium of the dual flocculant APAM-MFX (anionic polyacrylamide APAM used in combination with extracellular polymeric substrates extracted from Klebsiella sp. J1 MFX) were studied compared with the performance of using bioflocculant alone. In addition, adsorption isotherms and kinetic process for Cd(II) adsorption onto APAM-MFX were investigated. APAM-MFX synergistically improved the Cd(II) removal percentage by 82.68%. Characteristic flocs formed by APAM-MFX indicated the synergetic effects resulted from additional bridging bonds between APAM and MFX. Adsorption process was best described by the Freundlich isotherm and pseudo-second order kinetic model. The mean free energy E (8.39-8.57kJmol(-1)) and activation energy Ea (45.09kJmol(-1)) were determined. Based on the results, the main mechanism of Cd(II) removal by APAM-MFX could be chemical ion exchange, and the liquid-film diffusion step was the rate-limiting step.

A rapid and low energy consumption method to decolorize the high concentration triphenylmethane dye wastewater: Operational parameters optimization for the ultrasonic-assisted ozone oxidation process

This research set up an ultrasonic-assisted ozone oxidation process (UAOOP) to decolorize the triphenylmethane dyes wastewater. Five factors - temperature, initial pH, reaction time, ultrasonic power (low frequency 20 kHz), and ozone concentration - were investigated. Response surface methodology was used to find out the major factors influencing color removal rate and the interactions between these factors, and optimized the operating parameters as well. Under the experimental conditions: reaction temperature 39.81 °C, initial pH 5.29, ultrasonic power 60 W and ozone concentration 0.17 g/L, the highest color removals were achieved with 10 min reaction time and the initial concentration of the MG solution was 1000 mg/L. The optimal results indicated that the UAOOP was a rapid, efficient and low energy consumption technique to decolorize the high concentration MG wastewater. The predicted model was approximately in accordance with the experimental cases with correlation coefficients R(2) and R(adj)(2) of 0.9103 and 0.8386.

Thermophilic hydrogen production from sludge pretreated by thermophilic bacteria: Analysis of the advantages of microbial community and metabolism

In this study, the effects of thermophilic bacteria pretreatment and elevated fermentation temperature on hydrogen production from sludge were examined. The highest hydrogen yield of 19.9mlH2g(-1) VSS was achieved at 55°C by using pretreated sludge, which was 48.6% higher than raw sludge without pretreatment, and 28.39% higher than when fermented at 35°C. To explore the internal factors of this superior hydrogen production performance, the microbial community and the metabolism analysis were performed by using high-throughput sequencing and excitation-emission matrix. The pretreated sludge showed better utilization of dissolved organic matter and less inhibition of metabolism, especially at thermophilic condition. The 454 sequencing data indicated that microbial abundance was distinctly reduced and extremely high proportion of hydrogen-producing bacteria was found in the thermophilic community (Thermoanaerobacterium accounted for 93.75%). Thus, the pretreated sludge and thermophilic condition showed significant advantages in the hydrogen production using waste sludge as substrate.

Application of low frequency ultrasound to stimulate the bio-activity of activated sludge for use as an inoculum in enhanced hydrogen production

In order to increase hydrogen yield and shorten the lag time, low frequency ultrasonic (LFU) pretreatment was applied to stimulate the bio-activity of the seed bacteria, using waste activated sludge as the inoculum. A pretreated, sterilized sludge sample was seeded as the substrate for bio-hydrogen production. A Unisense microsensor multimeter with a hydrogen microelectrode was employed to examine the hydrogenase activities at different ultrasonic densities and exposure times. The optimum conditions were achieved at an ultrasonic density of 125 W L−1 and a reaction time of 10 s. A maximum hydrogen yield of 13.03 mL H2/g TS was obtained by LFU pretreatment under these optimal conditions, which was 18% higher than that obtained when seeding the raw sludge sample. To gain a better understanding of the end product distribution, three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy was performed to characterize the dissolved organic matter (DOM) and extracellular polymeric substances (EPS) in the sludge samples during the anaerobic fermentation process. Hydrogen production from NADH/NAD+ conversion was also proved by EEM.

Enhanced sulfamethoxazole ozonation by noble metal-free catalysis based on magnetic Fe3O4 nanoparticles: catalytic performance and degradation mechanism

In this research, Fe3O4 nanoparticles were prepared by a low-cost route free of other agents, and applied in the catalysis of sulfamethoxazole (SMX) ozonation. It was proven that Fe3O4 nanoparticles significantly enhance SMX ozonation. Using a kinetics analysis, when Fe3O4 particles were added to the ozonation process, the reaction rate constant increased by 51% when the pH was 5. Moreover, we also identified that Fe3O4 enhanced the SMX ozonation removal rate by changing the degradation pathway. It was found that addition of Fe3O4 improved the production of Lewis acid active sites in SMX. These kinds of site in SMX are much easier to attack, which leads to a higher SMX removal rate and lower operational costs for the Fe3O4-based catalytic ozonation process compared to an O3 oxidation process. Finally, the SMX degradation pathways were classified for the first time, based on ozone oxidation types to give a guide for the quick and direct oxidation of SMX and other pollutants.

Enhanced amoxicillin treatment using the electro-peroxone process: key factors and degradation mechanism

Amoxicillin (AMO) degradation was investigated using electrolysis, ozonation, and the electro-peroxone (E-peroxone) process. The E-peroxone process was found to be the most effective for AMO degradation. 67.8% total organic carbon (TOC) mineralization was obtained after 60 min by the E-peroxone process. In comparison, only 47.3% and 3.1% TOC mineralization were obtained using individual ozonation and electrolysis processes, respectively. It was found that hydroxyl radical production and O3 utilization were both enhanced in the E-peroxone process. The effect of pH on the E-peroxone process was investigated, and the highest AMO removal rate was obtained at pH = 9, indicating pH control was crucial in the E-peroxone process. In addition, more oxidation typical intermediates were identified in the E-peroxone process than the ozonation process using UPLC-MS/MS. Different pathways of AMO degradation were proposed, involving the hydroxylation of the benzoic ring and N, the four-membered β-lactamic ring opening, the oxidation of S, and other bond cleavage reactions. All these results above indicated that the introduction of electrolysis in ozonation has enhanced AMO cleavage and hence its degradation.