Dandan Zhou

Preparation, characterization and performance of a novel visible light responsive spherical activated carbon-supported and Er3+:YFeO3-doped TiO2 photocatalyst

A novel spherical activated carbon (SAC) supported and Er(3+):YFeO(3)-doped TiO(2) visible-light responsive photocatalyst (Er(3+):YFeO(3)/TiO(2)-SAC) was synthesized by a modified sol-gel method with ultrasonic dispersion. It was characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDS), powder X-ray diffractometer (XRD) and UV-vis diffuse reflectance spectrophotometer (DRS). The photocatalytic activity of Er(3+):YFeO(3)/TiO(2)-SAC was evaluated for degradation of methyl orange (MO) under visible light irradiation. The effects of calcination temperature and irradiation time on its photocatalytic activity were examined. The experimental results indicated that Er(3+):YFeO(3) could function as an upconversion luminescence agent, enabling photocatalytic degradation of MO by TiO(2) under visible light. The Er(3+):YFeO(3)/TiO(2) calcinated at 700°C showed the highest photocatalytic capability compared to those calcinated at other temperatures. The photocatalytic degradation of MO followed the Langmuir-Hinshelwood kinetic model. Although the photocatalyst showed a good physical stability and could tolerate a shear force up to 25 × 10(-3)N/g, its photocatalytic activity decreased over a four-cycle of reuse in concentrated MO solution, indicating that the decreased activity was ascribed to the fouling of catalyst surface by MO during the degradation process. However, the fouled Er(3+):YFeO(3)/TiO(2)-SAC could be regenerated through water rinsing-calcination or acid rinsing-calcination treatment.

Microbial selection pressure is not a prerequisite for granulation: dynamic granulation and microbial community study in a complete mixing bioreactor.

Microbial selection pressure is traditionally supposed as a prerequisite for aerobic granulation. This work gives a different insight on this issue. Fluorescent microspheres were used to label the flocculent biomass granulation for a period of 47days in a continuous-flow bioreactor. Analysis of the distribution of fluorescent microspheres in granules revealed that the terminal phase of granulation is in a dynamic steady state, where bioflocs detach, collide and aggregate randomly. This revealed that the un-granulated biomass was the result of the dynamic aggregation and breakage, rather than the microbial species unable to be granulated. Furthermore, denaturing gradient gel electrophoresis (DGGE) profile and UPGMA dendrogram results showed similar microbial communities during the granulation. To sum up, microbial selection pressure was not a prerequisite for aerobic granulation from both of the dynamic granulation steps and molecular biology aspects.

Intimate Coupling of Photocatalysis and Biodegradation for Degrading Phenol Using Different Light Types: Visible Light vs UV Light

Intimate coupling of photocatalysis and biodegradation (ICPB) technology is attractive for phenolic wastewater treatment, but has only been investigated using UV light (called UPCB). We examined the intimate coupling of visible-light-induced photocatalysis and biodegradation (VPCB) for the first time. Our catalyst was prepared doping both of Er(3+) and YAlO3 into TiO2 which were supported on macroporous carriers. The macroporous carriers was used to support for the biofilms as well. 99.8% removal efficiency of phenol was achieved in the VPCB, and this was 32.6% higher than that in the UPCB. Mineralization capability of UPCB was even worse, due to less adsorbable intermediates and cell lysis induced soluble microbial products release. The lower phenol degradation in the UPCB was due to the serious detachment of the biofilms, and then the microbes responsible for phenol degradation were insufficient due to disinfection by UV irradiation. In contrast, microbial communities in the carriers were well protected under visible light irradiation and extracellular polymeric substances secretion was enhanced. Thus, we found that the photocatalytic reaction and biodegradation were intimately coupled in the VPCB, resulting in 64.0% removal of dissolved organic carbon. Therefore, we found visible light has some advantages over UV light in the ICPB technology.

Preparation of spherical activated carbon-supported and Er3+:YAlO3-doped TiO2 photocatalyst for methyl orange degradation under visible light

In order to develop the high photocatalytic activity of TiO2 under visible light as that under ultraviolet light and make it easy to be separated from treated liquor, a visible light response and spherical activated carbon (SAC) supported photocatalyst doped with upconversion luminescence agent Er3+:YAlO3 was prepared by immobilizing Er3+:YAlO3/TiO2, which was obtained by combination of Er3+:YAlO3 and TiO2 using sol-gel method, on the surface of SAC. The crystal phase composition, surface structure and element distribution, and light absorption of the new photocatalysts were examined by X-ray diffraction (XRD), energy dispersive X-ray spectra (EDS) analysis, scanning electron microscopy (SEM) and fluorescence spectra analysis (FSA). The photocatalytic oxidation activity of the photocatalysts was also evaluated by the photodegradation of methyl orange (MO) in aqueous solution under visible light irradiation from a LED lamp (λ>400 nm). The results showed that Er3+:YAlO3 could perform as the upconversion luminescence agent which converts the visible light up to ultraviolet light. The Er3+:YAlO3/TiO2 calcinated at 700 °C revealed the highest photocatalytic activity. The apparent reaction rate constant could reach 0.0197 min−1 under visible light irradiation.

Granulation of activated sludge in a continuous flow airlift reactor by strong drag force

Most aerobic granule cultivation has been based on the sequencing batch reactor (SBR) and then the factors that affect aerobic granulations were developed in the SBR. However, little work has been done to cultivate aerobic granules in a continuous-flow bioreactor with simple structure that is realistic for engineering. This work is the first to cultivate aerobic granules in a continuous flow airlift fluidized bed reactor (CAFB) possesses a very simple structure and without settling time and starvation time controlling. The configuration of CAFB was the simplest continuous-flow aerobic granular bioreactor reported by now. The majority of granules could be formatted in the CAFB after 12 days cultivation. The effluent COD concentration maintained at 50 ± 10 mg/L for the variable COD loading rate of 3.5 g COD/L/d and 4.8 g COD/L/d, which confirmed that the CAFB performed good anti-shock abilities. CAFB performed good nitrification ability, however, little denitrification was found under the operating conditions of this study. The shear stress acting on the solid phase were hundreds of times stronger in the CAFB than in the SBR at the same aeration strength. It seems CAFB is very efficient for granulation due to the strong shear-force exertion, which is promising for continuous-flow aerobic granular bioreactor. Protein, positive to the hydrophobicity, was predominant in extracellular polymeric substances in the granules, and favored the granules formation in the CAFB combined with the polysaccharides. However, filamentous bulking always happened in 35 days operation of the CAFB, thus further study on the stability of this bioreactor is urgently necessary.

Calcium accumulation characterization in the aerobic granules cultivated in a continuous-flow airlift bioreactor

Limited work has been done on the accumulation characterization of Ca2+ in aerobic granules that are cultivated in a continuous-flow bioreactor. In this work, the contribution of Ca2+ to the biogranulation in a continuous flow airlift fluidized bed (CAFB) reactor has been studied. The spatial distribution and form of calcium in the granules were investigated by scanning electron microscopy-mapping, energy dispersive X-ray and X-ray diffraction (XRD). Calcium was located throughout the Ca-rich granules, rather than accumulating in the center of the granules of the sequencing batch reactor. Furthermore, CaCO3 was detected as the main crystalline mineral form of the calcium. Calcium augmentation of the inflow promoted the accumulation of magnesium in the granules in the CAFB. The magnesium was presented as Ca7Mg2P6O24 according to XRD analyses.

Optimization of Chlorella vulgaris and bioflocculant-producing bacteria co-culture: enhancing microalgae harvesting and lipid content

Microalgae are a sustainable bioresource, and the biofuel they produce is widely considered to be an alternative to limited natural fuel resources. However, microalgae harvesting is a bottleneck in the development of technology. Axenic Chlorella vulgaris microalgae exhibit poor harvesting, as expressed by a flocculation efficiency of 0·2%. This work optimized the co‐culture conditions of C. vulgaris and bioflocculant‐producing bacteria in synthetic wastewater using response surface methodology (RSM), thus aiming to enhance C. vulgaris harvesting and lipid content. Three significant process variables— inoculation ratio of bacteria and microalgae, initial glucose concentration, and co‐culture time— were proposed in the RSM model. F‐values (3·98/8·46) and R2 values (0·7817/0·8711) both indicated a reasonable prediction by the RSM model. The results showed that C. vulgaris harvesting efficiency reached 45·0–50·0%, and the lipid content was over 21·0% when co‐cultured with bioflocculant‐producing bacteria under the optimized culture conditions of inoculation ratio of bacteria and microalgae of 0·20–0·25, initial glucose concentration of <1·5 kg m−3 and co‐culture time of 9–14 days. This work provided new insights into microalgae harvesting and cost‐effective microalgal bioproducts, and confirmed the promising prospect of introducing bioflocculant‐producing bacteria into microalgae bioenergy production.

Roles of an easily biodegradable co-substrate in enhancing tetracycline treatment in an intimately coupled photocatalytic-biological reactor

Intimately coupled photocatalysis and biodegradation (ICPB) was realized in a macroporous carrier in which a photocatalyst was present on the outer surface, while a biofilm accumulated inside the carrier. In ICPB, photocatalysis products are rapidly biodegraded by a protected biofilm, leading to mineralization of the refractory organics, such as antibiotics. However, mineralization in ICPB could be compromised if the photocatalysis products remain refractory or are inhibitory. To address this, we attempted to increase metabolic activity by providing a readily biodegradable co-substrate (acetate) that could act as a source of energy and electrons to improve biotransformation and mineralization of the refractory antibiotic tetracycline (TCH). When we added acetate during ICPB of TCH, TCH removal increased by ∼5%, mineralization increased by ∼20%, and almost all photocatalysis products disappeared. Acetate addition also led to an increase in active biomass, an increase in the biomasss respiratory activity, and evolution of the microbial community to having more members able to biodegrade photocatalysis and biotransformation intermediates. Thus, providing an easily biodegradable co-substrate was an effective means for enhancing TCH removal and mineralization with the ICPB technology.

Bioremoval of Cu2+ from CMP wastewater by a novel copper-resistant bacterium Cupriavidus gilardii CR3: characteristics and mechanisms

Bacteria of the genus Cupriavidus are known for the ability of resistance to various heavy metals and metal-binding capability. Herein, we investigated the bioremoval of Cu2+ from synthesized chemical–mechanical polishing (CMP) wastewater by living cells of Cupriavidus gilardii CR3, a novel copper-resistant bacterium isolated in our previous study. The surface topography changes of strain CR3 were observed by SEM-EDX, where images showed that binding took place on the bacterial cell surface. FTIR spectra provided evidence that carboxyl, hydroxyl, amino, and phosphate groups on the surface of strain CR3 could be available for characteristic coordination bonding with Cu2+. Zeta potential confirmed that electrostatic interaction was involved in Cu2+ binding. The biosorption and bioaccumulation of Cu2+ by strain CR3 was highly pH-dependent, and the optimum pH value was 5.0. The maximum binding capacity for Cu2+ was 18.33 mg g−1 and the bioremoval efficiency was 27% under optimal conditions. The Cu2+ binding process obeyed the Langmuir isotherm (R2 = 0.99). Kinetic data were properly fitted with both pseudo-second order kinetic model (R2 = 0.99) and an intraparticle diffusion model (R2 = 0.98). It can be concluded that living cells of C. gilardii CR3 have the potential to be utilized for the removal of Cu2+ from CMP wastewater.

Responses of the Microalga Chlorophyta sp. to Bacterial Quorum Sensing Molecules (N-Acylhomoserine Lactones): Aromatic Protein-Induced Self-Aggregation

Bacteria and microalgae often coexist during the recycling of microalgal bioresources in wastewater treatment processes. Although the bacteria may compete with the microalgae for nutrients, they could also facilitate microalgal harvesting by forming algal-bacterial aggregates. However, very little is known about interspecies interactions between bacteria and microalgae. In this study, we investigated the responses of a model microalga, Chlorophyta sp., to the typical quorum sensing (QS) molecules N-acylhomoserine lactones (AHLs) extracted from activated sludge bacteria. Chlorophyta sp. self-aggregated in 200 μm bioflocs by secreting 460-1000 kDa aromatic proteins upon interacting with AHLs, and the settling efficiency of Chlorophyta sp. reached as high as 41%. However, Chlorophyta sp. cells were essentially in a free suspension in the absence of AHLs. Fluorescence intensity of the aromatic proteins had significant (P < 0.05) relationship with the Chlorophyta sp. settleability, and showed a positive correlation, indicating that aromatic proteins helped aggregate microalga. Transcriptome results further revealed up-regulation of synthesis pathways for aromatic proteins from tyrosine and phenylalanine that was assisted by anthranilate accumulation. To the best of our knowledge, this is the first study to confirm that eukaryotic microorganisms can sense and respond to prokaryotic QS molecules.