Mengchun Gao

Effect of salinity on extracellular polymeric substances of activated sludge from an anoxic–aerobic sequencing batch reactor

The effect of salinity on extracellular polymeric substances (EPS) of activated sludge was investigated in an anoxic-aerobic sequencing batch reactor (SBR). The contents of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were positively correlated with the salinity. The polysaccharide (PS) and protein (PN) contents in both LB-EPS and TB-EPS increased with the increase of salinity. With the increase of salinity from 0.5% to 6%, the PN/PS ratios in LB-EPS and TB-EPS decreased from 4.8 to 0.9 and from 2.9 to 1.4, respectively. The four fluorescence peaks in both LB-EPS and TB-EPS identified by three-dimensional excitation-emission matrix fluorescence spectroscopy are attributed to PN-like substances and humic acid-like substances. The Fourier transform infrared spectra of the LB-EPS and TB-EPS appeared to be very similar, but the differences across the spectra were apparent in terms of the relative intensity of some bands with the increase of salinity. The sludge volume index showed a linear correlation with LB-EPS (R(2)=0.9479) and TB-EPS (R(2)=0.9355) at different salinities, respectively.

Long-term effects of ZnO nanoparticles on nitrogen and phosphorus removal, microbial activity and microbial community of a sequencing batch reactor

The performance, microbial activity, and microbial community of a sequencing batch reactor (SBR) were investigated under the long-term exposure of ZnO nanoparticles (ZnO NPs). Low ZnO NPs concentration (less than 5mg/L) had no obvious effect on the SBR performance, whereas the removals of COD, NH4(+)-N, and phosphorus were affected at 10-60mg/L ZnO NPs. The variation trend of nitrogen and phosphorus removal rate was similar to that of microbial enzymatic activity with the increase of ZnO NPs concentrations. The richness and diversity of microbial community showed obvious variations at different ZnO NPs concentrations. ZnO NPs appeared on the surface and cell interior of activated sludge, and the Zn contents in the effluent and activated sludge increased with the increase of ZnO NPS concentration. The present results provide use information to understand the effect of ZnO NPS on the performance of wastewater biological treatment systems.

Magnetic Fe3O4 nanoparticles induced effects on performance and microbial community of activated sludge from a sequencing batch reactor under long-term exposure

The performance and microbial community of activated sludge from a sequencing batch reactor (SBR) were investigated under long-term exposure of magnetic Fe3O4 nanoparticles (Fe3O4 NPs). The COD removal showed a slight decrease at 5-60mg/L Fe3O4 NPs compared to 0mg/L Fe3O4 NPs, whereas the NH4+-N removal had no obvious variation at 0-60mg/L Fe3O4 NPs. It was found that 10-60mg/L Fe3O4 NPs improved the denitrification process and phosphorus removal of activated sludge. The microbial enzymatic activities of activated sludge could be affected by Fe3O4 NPs, which had similar variation trends to the nitrogen and phosphorus removal rates of activated sludge. The reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release demonstrated that Fe3O4 NPs led to the toxicity to activated sludge and destroyed the integrity of microbial cytomembrane. High throughput sequencing indicated that Fe3O4 NPs could obviously affect the microbial richness and diversity of activated sludge.

Structural and functional properties of organic matters in extracellular polymeric substances (EPS) and dissolved organic matters (DOM) after heat pretreatment with waste sludge.

The effects of heat pretreatment on waste sludge hydrolysis were investigated in this study. Heat pretreatment was conducted at 65°C, 80°C, 100°C and 121°C for 5min, 10min, 15min, 20min, 25min and 30min. Not only analyzed the changes of SCOD (Soluble chemical oxygen demand), carbohydrate and protein, but also evaluated the structural and functional properties of organics in extracellular polymeric substances (EPS) and dissolved organic matters (DOM) by using three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy with fluorescence regional integration (FRI) analysis. The SCOD in DOM increased with pretreated temperatures. The optimal heat hydrolysis temperature and time were selected by further studying the biodegradable and non-biodegradable components. After treated at 80°C for 25min, the fluorescence intensity and percent fluorescence response (Pi,n) of easily biodegradable soluble microbial by-product substance were higher than others, and little non-biodegradable fulvic acid-like substance was accumulated.

Performance and microbial community of a sequencing batch biofilm reactor treating synthetic mariculture wastewater under long-term exposure to norfloxacin.

The performance and microbial community of a sequencing batch biofilm reactor (SBBR) treating synthetic mariculture wastewater were evaluated under long-term exposure to norfloxacin (NFX) due to the overuse of antibiotics during the mariculture. The COD and NH4+-N removals had no distinct change at 0-6mgL-1 NFX and were inhibited at 6-35mgL-1 NFX. The specific oxygen uptake rate (SOUR), specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR) and specific nitrate reduction rate (SNRR) of the biofilm kept a decreasing tendency with the increase of NFX concentration from 0 to 35mgL-1. The presence of NFX promoted the microorganisms to secrete more extracellular polymeric substances (EPS) and affected the chemical compositions of EPS. The microbial richness and diversity showed some obvious variations at different NFX concentrations. The present results demonstrated that NFX inhibited the SBBR performance and should decrease the NFX dosage in the mariculture.

Extracellular polymeric substances, microbial activity and microbial community of biofilm and suspended sludge at different divalent cadmium concentrations.

The differences between biofilm and suspended sludge (S-sludge) in extracellular polymeric substances (EPS), microbial activity, and microbial community in an anoxic-aerobic sequencing batch biofilm reactor (SBBR) at different concentrations of divalent cadmium (Cd(II)) were investigated. As the increase of Cd(II) concentration from 0 to 50mgL(-1), the specific ammonium oxidation rate (SAOR), specific nitrite oxidation rate (SNOR), and specific nitrate reduction rate (SNRR) of biofilm decreased from 4.85, 5.22 and 45mgNg(-1) VSSh(-1) to 1.54, 2.38 and 26mgNg(-1)VSSh(-1), respectively, and the SAOR, SNOR and SNRR of S-sludge decreased from 4.80, 5.02 and 34mgNg(-1)VSSh(-1) to 1.46, 2.20 and 17mgNg(-1)VSSh(-1), respectively. Biofilm had higher protein (PN) content in EPS than S-sludge. Contrast to S-sludge, biofilm could provide Nitrobacter vulgaris, beta proteobacterium INBAF015, and Pseudoxanthomonas mexicana with the favorable conditions of growth and reproduction.

Effects of hydraulic retention time (HRT) on denitrification using waste activated sludge thermal hydrolysis liquid and acidogenic liquid as carbon sources

Waste activated sludge (WAS) internal carbon source can efficiently and economically enhance denitrification, and hydraulic retention time (HRT) is one of the most important operational parameters for denitrification. The effects of HRT on denitrification were investigated with WAS thermal hydrolysis liquid and acidogenic liquid as carbon sources in this study. The optimal HRT was 12h for thermal hydrolysis liquid and 8h for acidogenic liquid, with NO3--N removal efficiency of 91.0% and 97.6%, respectively. In order to investigate the utilization of sludge carbon source by denitrifier, the changes of SCOD (Soluble chemical oxygen demand), proteins, carbohydrates, and VFAs (Volatile fatty acids) during denitrification process were analyzed and three-dimensional fluorescence excitation-emission matrix (EEM) spectroscopy with fluorescence regional integration (FRI) analysis was introduced. The kinetics parameters of denitrification rate (VDN), denitrification potential (PDN) and heterotroph anoxic yield (YH) were also investigated using sludge carbon source at different HRT.

Effect of C/N ratio on extracellular polymeric substances of activated sludge from an anoxic–aerobic sequencing batch reactor treating saline wastewater

The effect of C/N ratio on extracellular polymeric substances (EPS) of activated sludge was investigated in an anoxic–aerobic sequencing batch reactor (SBR) treating saline wastewater. The protein (PN) and protein/polysaccharide (PN/PS) ratio in the loosely bound EPS (LB-EPS) increased with the decrease of C/N ratio, whereas the PS in the LB-EPS decreased. The PS, PN and PN/PS ratio in the tightly bound EPS (TB-EPS) were independent of C/N ratio. Two fluorescence peaks in the LB-EPS and TB-EPS were identified at excitation/emission (Ex/Em) wavelengths of 275–280/335–340 nm and 220–225/330–340 nm by three-dimensional excitation–emission matrix (3D-EEM) fluorescence spectroscopy, respectively. These peaks in LB-EPS and TB-EPS were, respectively, associated with tryptophan protein-like substances and aromatic protein-like substances. The tryptophan protein-like fluorescence peaks in LB-EPS showed blue shift along the Ex axis and red shift along the Em axis with the decrease of C/N ratio. Fourier transform infrared spectra suggested that the variation of C/N ratio had more distinct effect on the functional groups of protein in the LB-EPS than those in the TB-EPS. The sludge volume index value decreased with the increase of LB-EPS, but there was no correlation between SVI and TB-EPS.

Impact of sulfadiazine on performance and microbial community of a sequencing batch biofilm reactor treating synthetic mariculture wastewater

The impact of sulfadiazine on the performance, microbial activity and microbial community of a sequencing batch biofilm reactor (SBBR) were evaluated in treating mariculture wastewater due to the application of sulfadiazine as an antibiotic in mariculture. The COD and nitrogen removals kept stable at 0-6mg/L sulfadiazine and were inhibited at 10-35mg/L sulfadiazine. The microbial activities related to organic matter and nitrogen removals reduced with an increase in sulfadiazine concentration. The presence of sulfadiazine could affect the production and chemical composition of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) in the biofilm. High-throughput sequencing demonstrated that sulfadiazine could impact on the microbial richness and diversity of SBBR treating mariculture wastewater. The relative abundances of Nitrosomonas, Nitrospira, Paracoccus, Hyphomicrobium, Rhodanobacter, Thauera and Steroidobacter decreased with an increase in sulfadiazine concentration, indicating that the presence of sulfadiazine decreased the relative abundance of some nitrifying and denitrifying bacteria.

Preparation of graphene/TiO2 nanotube array photoelectrodes and their photocatalytic activity for the degradation of alachlor

Graphene/TiO2 nanotube array (GR/TNA) photoelectrodes were fabricated by combining in situ anodization and an electro-deposition process. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-vis diffuse reflectance spectra (DRS), photopotential measurement, electrochemical impedance spectroscopy (EIS) and zeta-potential measurement were employed to characterize the as-prepared samples. The photocatalytic properties of the GR/TNA photoelectrodes were investigated using the degradation of alachlor as a model reaction. The introduction of GR had no obvious effect on the original crystallization of the TNAs, whereas the photoelectric property was significantly improved. The GR/TNA photoelectrodes exhibited higher photocatalytic activity for alachlor degradation than the bare TNA photoelectrodes. The degradation efficiency of alachlor by the GR/TNA photoelectrodes gradually decreased with the increase of initial alachlor concentration, initial pH and distance from illuminant. Some interfering anions (e.g. NO3− and SO42−) could improve the photocatalysis efficiency, whereas Cl− exhibited a slight inhibition effect on the alachlor degradation. Additionally, GR/TNA photoelectrodes possessed superb stability for maintaining a high alachlor degradation efficiency at more than 99.5% after 15 times of successive use with 60 min irradiation for each cycle.