Juanshan Du

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.

Possible causes of excess sludge reduction adding metabolic uncoupler, 3,3′,4′,5-tetrachlorosalicylanilide (TCS), in sequence batch reactors

Two parallel sequence batch reactors (SBRs) were operated, with and without TCS addition, to research the causes of sludge reduction by uncouplers. Three possible mechanisms of sludge reduction by TCS were studied: (1) occurrence of metabolic uncoupling, (2) consumption of more energy to resist the infection of TCS, (3) promotion of lysis-cryptic growth by TCS addition. Results showed the remarkable reduction of electronic transport system (ETS) activity and specific cellular ATP (SATP) in TCS reactor, which proved the occurrence of metabolic uncoupling. The increasing amounts of extracellular polymeric substances (EPS), as measured by chemical methods and excitation-emission matrix (EEM) fluorescence spectra, implied microorganisms consumed more energy to resist TCS. The similar DNA concentrations of the effluents in two reactors indicated sludge lysis was not intensified by TCS. Therefore, uncoupler might not only cause metabolic uncoupling but also induce more energy consumption in the production of some substances to resist uncoupler.

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.

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.

Degradation of sulfadiazine in water by a UV/O3 process: performance and degradation pathway

In this study, the performance of a combined UV/O3 process for aquatic sulfadiazine (SDZ) removal was investigated. By comparing with UV irradiation or ozonation, the UV/O3 process showed excellent performance for SDZ removal, particularly on the mineralization of SDZ. The degradation rate of SDZ by UV/O3 increased with the increment of O3 gas concentration and UV intensity. Meanwhile, initial solution pH also played an important role in the UV/O3 process. The pH increment of solutions (3.0–9.0) could promote the SDZ degradation rate which was mainly ascribed to the generation of ˙OH by O3 self-decomposition and the dissociation of SDZ. But this phenomenon was seriously reversed for the production of more free radical scavengers like CO32− as initial pH increased from 9.0 to 11.0. Two different degradation pathways of SDZ by UV/O3 were proposed based on the combination of theoretical calculations and experimental intermediate identification. Pathway I was initiated by hydroxyl radicals which involved oxidative cleavage of the S–N bond and pathway II was induced by direct UV irradiation which involved the opening of the pyrimidine ring. According to the results obtained in this work, UV/O3 was recommended as an effective method to remove SDZ.

Factors affecting p-nitrophenol removal by microscale zero-valent iron coupling with weak magnetic field (WMF)

The effect of WMF on the kinetics of p-nitrophenol (PNP) removal by six commercial zero-valent iron (ZVI) samples from different origins were studied at pH 4.0. The pseudo-first-order rate constant (kobs) of PNP removal by ZVI with WMF were 2.9–5.4-fold greater than those without WMF. The strong correlation between the specific reaction rate constants (kSA) of PNP removal by various ZVI samples and the specific rate constant of Fe(II) release (kFe(II) release SA) during these processes indicated that enhancement of PNP removal by ZVI in the presence of WMF was mainly ascribed to the improved Fe0 corrosion and Fe(II) generation. Effects of pH value (4.0–7.0), ZVI loading (100–1000 mg L−1), PNP concentration (5–100 μM), magnetization time (1–120 min), and various anions (at 1–50 μM concentration) on PNP removal by ZVI with and without the presence of WMF was investigated. The presence of WMF significantly accelerated PNP removal at pH 4.0–7.0, especially at neutral pH values. The kSA and kFe(II) release SA linearly increased with increasing ZVI loading, and the enhancement factor is stable with increasing ZVI loading. PNP concentration exhibited a very slight effect on PNP removal with and without WMF. The kobs of PNP removal increased with increased magnetization time and trended to be consistent for more than 5 min of magnetization by WMF. WMF exhibited a positive effect on PNP removal in the presence of sulfate, chlorate, and nitrate. Although perchlorate could inhibit PNP removal by ZVI, WMF decreased the negative effect of perchlorate on PNP removal by ZVI. Furthermore, the possible degradation pathway of PNP degradation by ZVI was proposed according to the detected intermediates.

Treatability study of 3,3',4',5-tetrachlorosalicylanilide (TCS) combined with 2,4,6-trichlorophenol (TCP) to reduce excess sludge production in a sequence batch reactor.

The present study investigated the synergistic effects of a novel combined uncoupler of TCS and TCP on excess activated sludge reduction during a 60-day operation using a sequence batch reactor (SBR). Response surface methodology (RSM) was employed to obtain the optimal dosage of the combined uncoupler. The results of 60-day operation demonstrated the combined uncoupler had effectively reduced the sludge yield by approximately 52%, without serious affecting the substrate removal efficiency. The high sludge reduction rate revealed that it was feasible and effective to utilize a combined uncoupler to limit excess activated sludge. The three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy analysis of activated sludge with different metabolic uncouplers indicated that tryptophan, tyrosine protein-like substances and tryptophan, tyrosine amino-like substances were reduced by adding a combined uncoupler. Moreover, the variation of sludge components provided a better understanding of the effects of uncouplers on activated sludge reduction.

Hydroxyl radical dominated degradation of aquatic sulfamethoxazole by Fe0/bisulfite/O2: Kinetics, mechanisms, and pathways

In this study, batch experiments were carried out to investigate the key factors on sulfamethoxazole (SMX) removal kinetics in a new AOPs based on the combination of zero valent iron (Fe0) and bisulfite (S(IV)). With the increase of Fe0 from 0.25 mM to 5 mM, the removal rate of SMX was linearly increased in the Fe0/S(IV)/O2 system by accelerating the activation of S(IV) and Fe0 corrosion to accelerate. In the first 10 min of reaction, the increasing concentration of S(IV) inhibited SMX removal after since the high S(IV) concentration quenched reactive oxidative species (ROS). Then SMX removal rate was accelerated with the increase of S(IV) concentration after S(IV) were consumed up. The optimal ratio of S(IV) concentrations to Fe0 concentration for SMX removal in the Fe0/S(IV)/O2 system was 1:1. With SMX concentrations increasing from 1 to 50 μM, SMX removal rate was inhibited for the limitation of ROS yields. Although the presence of SO4- and OH was confirmed by electron paramagnetic resonance (EPR) spectrum, OH was identified as the dominant ROS in the Fe0/S(IV)/O2 system by chemical quenching experiments. Besides, strong inhibitive effects of 1,10-phenanthroline on SMX degradation kinetics by Fe0/S(IV)/O2 proved that the generation of ROS was rely on the release of Fe(II) and Fe(III). The generation of SO4- was ascribed to the activation of S(IV) by Fe(II)/Fe(III) recycling and the activation of HSO5- by Fe(II). And OH was simultaneously transformed from SO4- and generated by Fe0/O2. Density functional theory (DFT) calculation was conducted to reveal special reactive sites on SMX for radicals attacking and predicted intermediates. Finally, four possible SMX degradation pathways were accordingly proposed in the Fe0/S(IV)/O2 system based on experimental methods and DFT calculation.

Biosorption of cadmium by a lipid extraction residue of lipid-rich microalgae

The present study investigates the performances and mechanisms of biosorption of cadmium (Cd) ions using a lipid extraction residue from three strains of lipid production microalgae. The adsorption performance was determined by batch biosorption experiments and kinetic modeling. The algae cell in the whole growth period and lipid extraction residue both exhibited desirable adsorption performance. The lipid extraction residue from the strain of Coelastrum sp. PTE-15 had the highest capacity of Cd sorption, which was 32.8 mg g−1. FTIR data suggested that the functional groups acting as binding sites on the microalgae surface which participate in biosorption were carboxylic, hydroxyl, and amino. The biosorption properties and maximum adsorption capacity of the lipid extraction residue from three microalgal strains were determined by equilibrium modeling. The adsorption process followed the Langmuir isotherm model with a high value of correlation coefficients (≥0.99) and biosorption capacity being estimated to be 36.1 mg g−1.