Dan Chen

Functionalization of 4-aminothiophenol and 3-aminopropyltriethoxysilane with graphene oxide for potential dye and copper removal

In this work, 4-aminothiophenol and 3-aminopropyltriethoxysilane were firstly used to functionalize graphene oxide (GO) in order to promote the sorption efficiencies of methylene blue (MB) and copper (Cu(2+)). Characterization experiments illustrated that sulfydryl group (SH) and amino group (NH2) were existed onto 4-aminothiophenol modified GO (GO-SH) and 3-aminopropyltriethoxysilane modified GO (GO-N), respectively. Adsorption isotherm results showed that the maximum adsorption capacities of MB by GO-SH and GO-N were 763.30 and 676.22mg/g, which was much higher than original GO 455.95mg/g. For Cu(2+) adsorption, the maximum adsorption capacities by GO-SH and GO-N were 99.17 and 103.28mg/g, suggesting that the engineered GO exhibited greater Cu(2+) sorption ability than original GO 32.91mg/g. Both MB and Cu(2+) removal rates increased with pH and adsorbent dosage increased, while the sorption rates weakly reduced with increasing ionic strength. The modification by SH and NH2 would not only increase the sorption sites, but also cause chelation with heavy metals, and thus improving the sorption capacities of MB and Cu(2+).

Microbial community in a hydrogenotrophic denitrification reactor based on pyrosequencing

Effects of some key factors on hydrogenotrophic denitrification were investigated in lab-scale bioreactors. Results indicated that optimum biomass loading, pH value, temperature, nitrate loading, and C/N ratio in this study were optical density at 600xa0nm (OD600) of 0.173, 6.0∼7.0, 35xa0°C, 105xa0mgxa0L−1, and 30, respectively. To obtain a better understanding of microbial community in the bioreactors, the 454-pyrosequencing technology was used to characterize the 16S ribosomal RNA (16S rRNA) gene of bacteria in selected samples Y1 and Y2, in which a total of 62,559 effective sequences (36,445 in Y1 and 26,114 in Y2) were obtained. The taxonomic complexities in two samples were compared at phylum/class/genus levels. In total, 41 bacterial phyla, 43 bacterial classes, and 312 genera were detected, where phylum Firmicutes, class Clostridia were most abundant. Genus Proteiniclasticum was predominant among the top 100 genera. This work aims to add some novel insights into hydrogenotrophic denitrification process and its microbial community structures in bioreactors.

Autotrophic denitrification by nitrate-dependent Fe(II) oxidation in a continuous up-flow biofilter

A continuous-upflow biofilter packed with sponge iron was constructed for nitrate removal under an anaerobic atmosphere. Microbacterium sp. W5, a nitrate reducing and Fe(II) oxidizing strain, was added to the biofilter as an inoculum. The best results were achieved when NO3−-N concentration was 30xa0mg/L and Fe2+ was 800xa0mg/L. Nitrite in influent would inhibit nitrate removal and aqueous Fe2+ resulted in encrustation. Fe(II)EDTA would prevent cells from encrustation and the maximum nitrogen removal efficiency was about 90xa0% with Fe(II)EDTA level of 1100xa0mg/L. Nitrate reduction followed first-order reaction kinetics. Characteristics of biofilms were analyzed by X-ray fluorescence spectroscopy.

Nitrate removal from groundwater by hydrogen-fed autotrophic denitrification in a bio-ceramsite reactor

In this work, the denitrification performance of a bio-ceramsite reactor based on autohydrogenotrophic denitrification was investigated. The effects of various experimental parameters such as nitrate loading, carbon to nitrogen ratio (C/N), water temperature and pH were evaluated during the operation. The unique aspect of this research is that the bio-reactor uses ceramsite as a carrier, which can provide a habitat for autohydrogenotrophic biocoenoses to accrete and grow. The results indicated that the denitrification rate increased as nitrate loading (below 130 mg NO3(-)-N/L) increased. However, the activity of autohydrogenotrophic denitrifying bacteria was inhibited when nitrate loading was further increased to higher than 130 mg NO3(-)-N/L. Denitrification efficiency changed slightly with C/N, this system performed well if C/N was more than 0.9. The optimum temperature for the reactor was 25-35 °C. This denitrification system was positively related to pH, as a neutral or alkaline environment was more preferable for the reactor. During the operation, effluent nitrite levels were always maintained below 1.75 mg NO2(-)-N/L.

Cr(VI) removal by combined redox reactions and adsorption using pectin-stabilized nanoscale zero-valent iron for simulated chromium contaminated water

The synthetic pectin-stabilized nanoscale zero-valent iron was used to remove Cr(VI) from simulated chromium contaminated water. The Cr(VI) removal data were well fitted with the pseudo-first order kinetic equation. The observed pseudo-first order rate constant for Cr(VI) removal decreased from 0.0781 to 0.0413 min−1 when the pH increased from 3 to 9. When the initial Cr(VI) concentration increased from 20 to 80 mg L−1, the observed pseudo-first order rate constant decreased from 0.0645 to 0.0366 min−1. The Cr(VI) removal efficiency had obviously increased as the dose of pectin-stabilized nZVI increased from 0.02 to 0.10 g, and it increased from 0.0276 to 0.1159 min−1 as the temperature increased from 15 to 35 °C. The scanning electron microscopy (SEM) images proved that the presence of pectin successfully stabilized the nZVI particles and thus increased the BET specific surface area of nZVI. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses demonstrated that the mechanisms of Cr(VI) removal by pectin-stabilized nZVI were a combined process of redox reactions and adsorption.

Microbial community and metabolism activity in a bioelectrochemical denitrification system under long-term presence of p-nitrophenol

Bioelectrochemical denitrification system (BEDS) is a promising technology for nitrate removal from wastewaters. The hazards and effects concerning p-nitrophenol (PNP) towards BEDS lack enough investigations and possess great research prospects. This study investigated how PNP affected the nitrate removal efficiency, microbial communities, functional denitrifying genes abundances, nitrate and nitrite reductase activities, diffusible signal factors (DSF) release, and extracellular polymeric substances (EPS) production in the BEDS. Results indicated that nitrate removal efficiency decreased with initial PNP concentration increased from 0 to 100mg/L. Phylum Firmicutes and class Clostridia were the main contributors for denitrification process in this BEDS. The abundances of the denitrifying genes nirS, nirK, napA, and narG all presented decreased trends with increasing PNP. In addition, the concentrations of nitrate reductase (NR), nitrite reductase (NIR), and EPS obviously decreased, while the concentration of DSF increased with increasing PNP, which demonstrated that higher PNP would inhibit the biofilm formation.

Culture of denitrifying phosphorus removal granules with different influent wastewater

AbstractFed with three different kinds of influent, i.e. sodium acetate-based synthetic wastewater, synthetic wastewater with 10-mgxa0L−1 Ca2+ ions, and raw domestic wastewater, respectively, compact of different influent wastewater on aerobic granulation was investigated in three sequencing batch reactors (corresponding to R1–R3) operating in an alternating anaerobic/oxic/anoxic mode. As a result, denitrifying phosphorus removal granules with an average diameter above 600xa0μm were successfully cultivated within 42xa0d when inoculated with flocculent sludge. The granules showed some characteristics, e.g. low in moisture content, high in specific gravity, and specific oxygen uptake rate. Reactors’ performance throughout operation presented that effluent concentration of COD was always lower than 40-mgxa0L−1; TN, -N, and TP was often lower than 1-mgxa0L−1. In addition, cycle test displayed that efficiencies of COD, -N, TN, and TP removal in R1–R3 reached up to 90.25, 92.98, 92.96%; 99.29, 99.57, 91.70; 90.83, 92.80,...

High nitrate removal by autohydrogenotrophic bacteria in a biofilm-electrode reactor

AbstractA biofilm-electrode reactor has been developed to effectively treat high nitrate-polluted wastewater. The novelty of this system is that the biological degradation of -N (electron acceptor) was enhanced by the generation of H2 (electron donor) and direct immobilization of autohydrogenotrophic bacteria on the surface of the cathode. Nitrate degradation rate increased as current increased from 10 to 120u2009mA. When current was increased above 120u2009mA, the degradation rate was decreased. Meanwhile, nitrite accumulation decreased as current (below 120u2009mA) increased. If current was increased further to higher than 120u2009mA, nitrite was observed to accumulate again. Denitrification rate increased with initial nitrate loading below 350u2009mg -Nu2009L−1. However, the denitrification was found to be inhibited at high nitrate loading (350–500u2009mg -Nu2009L−1). Meanwhile, nitrite accumulation increased as nitrate loading increased and the highest accumulated nitrite level reached 16.07u2009mg -Nu2009L−1 at nitrate loading of 500u2009mg -N...

Response of a three dimensional bioelectrochemical denitrification system to the long-term presence of graphene oxide

In this study, a three dimensional bioelectrochemical denitrification system (3D-BEDS) was operated under long-term graphene oxide (GO) condition to treat high nitrate polluted water. When GO concentration increased from 0 to 100mgL(-1), nitrate removal efficiency slightly decreased from 99.52% to 94.81%. However, when GO concentration was further increased to 150mgL(-1), the denitrification efficiency dramatically decreased to 74.95%. Increasing GO concentration in this BEDS resulted in decreased community richness, and the abundances of the dominant bacterial communities presented obvious shift. The abundances of denitrifying genes napA, nirS, and nirK showed no obvious changes with GO concentration lower than 50mgL(-1). However, the abundances of the three genes decreased when GO concentration was further increased to higher than 100mgL(-1). The increased lactate dehydrogenase (LDH) release and reactive oxygen species (ROS) production demonstrated that long-term presence of GO caused chronic impacts onto microorganisms in this BEDS.

Removal of phosphate and hexavalent chromium from aqueous solutions by engineered waste eggshell

In this work, a novel adsorbent derived from waste eggshell (ES) was used for phosphate and hexavalent chromium adsorption. EDS, XRD, and FTIR analyses demonstrated that α-FeOOH was successfully loaded onto the eggshell, thus increasing the available sorption sites and facilitating the adsorption abilities of phosphate and hexavalent chromium. The maximum phosphate and hexavalent chromium adsorption capacities on α-FeOOH modified eggshell (F-ES) were 248.73 and 41.57 mg g−1, which were much greater than that of the original eggshell 89.74 and 11.81 mg g−1, indicating that the modification process significantly improved the phosphate and hexavalent chromium removal abilities. Besides, the kinetics data were both well fitted with pseudo-first-order, pseudo-second-order, and Richie kinetics models, which proved that the adsorption process onto the eggshell was controlled by multiple mechanisms. In addition, the removal rates of phosphate and hexavalent chromium increased with increasing adsorbent dosage. However, the removal rates showed downward trends with pH increased from 3 to 9 and ionic strength increased from 0 to 0.1 M.