Shou-Qing Ni

Effect of organic matter on the performance of granular anammox process

The presence of organic matter (OM) is considered to affect anammox process adversely, while practically wastewaters containing ammonia are not free from OM. In this study, the performance of anammox granules in presence of OM was evaluated under different COD to N ratios. Low OM concentration did not affect ammonia and nitrite removal significantly but improved the total nitrogen removal via denitrifiers. High OM could suppress anammox activity, resulting in a lower ammonia removal. PCR tests revealed that there was a reduction in the number of anammox bacteria and denitrifiers quantity increased when 400mg COD/L influent was applied. A COD to N threshold ratio for anammox inhibition, defined when ammonia removal dropped to 80%, was 3.1, higher than that of flocculent sludge. This study revealed that the coexistence of denitrification and anammox was an effective strategy to treat wastewaters containing high levels of nitrogen and OM.

Adsorption of phosphate from aqueous solutions onto modified wheat residue: Characteristics, kinetic and column studies

Kinetic and column adsorption of phosphate from aqueous solution using modified wheat residue (MWS) as an adsorbent were studied in a batch reactor. The respective characteristic rate constants and activation energy were presented after linear and non-linear fitting. In addition, the effects of influent concentration of phosphate and flow rates on the column adsorption were also investigated. The results showed that the adsorption process could reach equilibrium in 10-15 min, and the pseudo-second-order equation generated the best agreement with experimental data for adsorption systems. The activation energy was 3.39 kJ mol(-1) indicating that the synthesis process was a physical adsorption. In the column tests, the increase of influent concentration and flow rate both decreased the breakthrough time, and the MWS-packed column exhibited excellent phosphate removal from aqueous solution. These results provide strong evidence of the potential of MWS for the technological applications of phosphate removal from aqueous solutions.

Facile synthesis of N-acetyl-l-cysteine capped ZnS quantum dots as an eco-friendly fluorescence sensor for Hg2+

This paper described an investigation of a novel eco-friendly fluorescence sensor for Hg(2+) ions based on N-acetyl-l-cysteine (NAC)-capped ZnS quantum dots (QDs) in aqueous solution. By using safe and low-cost materials, ZnS QDs modified by NAC were easily synthesized in aqueous medium via a one-step method. The quantitative detection of Hg(2+) ions was developed based on fluorescence quenching of ZnS QDs with high sensitivity and selectivity. Under optimal conditions, its response was linearly proportional to the concentration of Hg(2+) ions in a range from 0 to 2.4 × 10(-6) mol L(-1) with a detection limit of 5.0 × 10(-9) mol L(-1). Most of common physiologically relevant cations and anions did not interfere with the detection of Hg(2+). The proposed method was applied to the trace determination of Hg(2+) ions in water samples. The possible quenching mechanism was also examined by fluorescence and UV-vis absorption spectra.

Fast start-up, performance and microbial community in a pilot-scale anammox reactor seeded with exotic mature granules

The possibility to introduce the exotic anammox sludge to seed the pilot-scale anammox granular reactor and its fast start-up for treating high nitrogen concentration wastewater were evaluated in this study. The reactor was started up successfully in two weeks; in addition, high nitrogen removal was achieved for a long period. Stoichiometry molar ratios of nitrite conversion and nitrate production to ammonium conversion were calculated to be 1.26±0.02:1 and 0.26±0.01:1, respectively. The Stover-Kincannon model which was first applied in granular anammox process indicated that the granular anammox reactor possessed high nitrogen removal potential of 27.8 kg/m(3)/d. The anammox granules in the reactor were characterized via microscope observation and fluorescence in situ hybridization technique. Moreover, the microbial community of the granules was quantified to be composed of 91.4-92.4% anammox bacteria by real-time polymerase chain reaction. This pilot study can elucidate further information for industrial granular anammox application.

Enrichment and biofilm formation of Anammox bacteria in a non-woven membrane reactor.

An innovative reactor configuration for Anammox enrichment by connecting a non-woven membrane module with an anaerobic reactor was developed in this study. The Anammox non-woven membrane reactor (ANMR) exhibited high biomass retention ability through the formation of aggregates in the reactor and biofilm on the interior surface of the non-woven membrane. No fouling problems occurred on the membrane after the development of mature biofilms. After 8 months of operation, the nitrogen loading rate (NLR) and nitrogen removal rate (NRR) reached 1263 mg N/l/d and 1047.5 mg N/l/d, respectively, with a maximum specific ammonium consumption (SAC) of 51 nmol/mg protein/min. At steady state, the average ammonium and nitrite removal efficiencies were 90.9% and 95.0%, respectively. Morphological observation of Anammox aggregates and biofilm showed a high degree of compactness. Also, enrichment of Anammox bacteria was quantified by real-time polymerase chain reaction (PCR) analysis as 97.7%.

The kinetics of nitrogen removal and biogas production in an anammox non-woven membrane reactor

The anammox non-woven membrane reactor (ANMR) is a novel reactor configuration to culture the slowly growing anammox bacteria. Different mathematical models were used to study the process kinetics of the nitrogen removal in the ANMR. The kinetics of nitrogen gas production of anammox process was first evaluated in this paper. For substrate removal kinetics, the modified Stover-Kincannon model and the Grau second-order model were more applicable to the ANMR than the first-order model and the Monod model. For nitrogen gas production kinetics, the Van der Meer and Heertjes model was more appropriate than the modified Stover-Kincannon model. Model evaluation was carried out by comparing experimental data with predicted values calculated from suitable models. Both model kinetics study and model testing showed that the Grau second-order model and the Van der Meer and Heertjes model seemed to be the best models to describe the nitrogen removal and nitrogen gas production in the ANMR, respectively.

Effect of magnetic nanoparticles on the performance of activated sludge treatment system

Both short-term and long-term exposure experiments were carried out to investigate the influence of magnetic nanoparticles (NPs) on activated sludge. The short-term presence of 50-200 mg/L of NPs decreased total nitrogen (TN) removal efficiencies, resulted from the acute toxicity of a shock load of NPs. However, long-term exposure of 50 mg/L magnetic NPs were observed to significantly improve TN removal efficiency, partially due to the self-repair function of activated sludge and magnetic-induced bio-effect. Sludge properties and extracellular polymer substrates secretion were affected. Additional investigations with enzyme and FISH assays indicated that short-term exposure of 50 mg/L magnetic NPs led to the abatement of nitrifying bacteria. However, the activities of the enzyme nitrite oxidoreductase and key denitrifying enzymes were increased after long-term exposure.

Interaction of anammox bacteria and inactive methanogenic granules under high nitrogen selective pressure.

Granular anammox reactors usually adopted anaerobic/aerobic granules as source sludge, in which the washout of other species and enrichment of anammox biomass were very slow because of the competition of the coexisting bacteria. In this study, inactive methanogenic granules were proved to be suitable for rapid anammox granulation under high nitrogen concentrations by investigating their interaction with anammox bacteria. The start-up nitrite concentration was significantly higher than the published toxic level for anammox bacteria and other lab-scale studies. The nitrogen loading rate increased from 141 to 480 mg/L/d in 120 days operation with a total nitrogen removal efficiency of 96.0+/-0.6%. Anammox granules with a diameter of 1.3+/-0.4mm were observed over the course of three months. Molecular analysis showed that over 67% of the cells in the anammox granules were anammox bacteria after 90 days. The accommodations and proliferations of anammox bacteria in the inactive methanogenic granules might be the main reason for the high anammox purity in a short period. The important role of the extracellular polymer in the granule structure was observed via morphological observation.

One pot synthesis of ultrathin boron nitride nanosheet-supported nanoscale zerovalent iron for rapid debromination of polybrominated diphenyl ethers

To minimize the aggregation and size effects of nanoscale zerovalent iron (nZVI), nZVI/boron nitride nanosheets (BNNSs) composites were fabricated via a one pot “autoclave route” on a gram-scale. BNNSs (1–6 nm) supported nZVI (4–40 nm) was prepared by heating NaBH4, FeCl3 and NaN3 at 400 °C. The BNNSs matrixes benefit the retention of the activity for nZVI. The high specific surface area (182 m2 g−1) and density of structural defects allows enrichment of the pollutants, leading to a relatively high conversion by the nearby supported nZVI. Meanwhile, the gram-scale bifunctional nZVI/BNNSs have both reductive and magnetic properties, which make them highly reactive towards the test polybromodiphenyl ethers (PBDEs) and also easy to separate. The reaction rate of nZVI/BNNSs is almost twice that of the nZVI made in our lab. This study indicates that gram-scale nZVI/BNNSs are highly efficient and effective materials that can be utilized to treat PBDEs-contaminated sites, followed by the sequential magnetic separation.

Synthesis and Photocatalytic Activity of One-Dimensional CdS@TiO2 Core-Shell Heterostructures

One-dimensional CdS@TiO2 core-shell heterostructures were fabricated via the hydrolysis of tetrabutyl titanate (TBT) on preformed CdS nanowires. The as-prepared products were characterized by X-ray diffraction, transmission electron microscopy, selected area electron diffraction and diffuse reflectance spectroscopy techniques. Results demonstrated that the hydrolysis of TBT had a great influence on the morphology of the coated TiO2 shell, resulting in the formation of TiO2 nanoparticles and nanolayer-modified CdS@TiO2 heterostructures. Degradation of methylene blue using CdS@TiO2 core-shell heterostructures as photocatalysts under visible light irradiation was investigated. Comparative photocatalytic tests showed that the TiO2 nanoparticles-modified heterostructure exhibited a superior activity due to the passivity of photogenerated charge carriers.