Yongdi Liu

The preparation, and applications of g-C3N4/TiO2 heterojunction catalysts-a review

In recent years, more and more attention has been paid in the research of heterojunction catalysts, due to their better catalytic ability than that of single component catalysts. Up to now, many kinds of heterojunction catalysts have been reported, such as Bi2O3/Bi2WO6, WO3/BiVO4, SnO2/TiO2, CdS/TiO2, Ta3N5/Pt/IrO2 and so on, among which the heterojunction catalyst composed of g-C3N4 and TiO2 has been studied tremendously recently, due to the high activity, high thermal and chemical stability, and well matched energy structure of them. Up to now, many methods have been explored for the synthesis of g-C3N4/TiO2 heterojunction catalysts, such as ball milling of g-C3N4 and TiO2, hydrothermal growth of TiO2 on g-C3N4 and so on. In this review, the recent researches on the synthesis of g-C3N4/TiO2 catalysts were summarized. Moreover, the applications of g-C3N4/TiO2 catalysts in the field of photocatalysis were detailedly introduced.

Effect of the chemical oxidation demand to sulfide ratio on sulfide oxidation in microbial fuel cells treating sulfide-rich wastewater.

This work focused on studying the effect of the chemical oxidation demand to sulfide ratio (COD/S) on power generation and sulfide oxidation in microbial fuel cells treating sulfide-rich wastewater containing organic contaminants. The maximum power density achieved was 20±1 W m −3 V Anode and the Coulombic yield was 20±2%. The COD/S of influent played an important role in elemental sulfur and sulfate production because of competition between acetate oxidation and element sulfur oxidation to sulfate in the anode. When the COD/S was 12.50/1, more than 74.0% of sulfide was converted into elemental sulfur after 24 hours of operation. The effect of the COD/S on power generation was negligible when the COD/S ranged between 4.85/1 and 18.53/1. After 24 hours, the COD removals were 110±6, 213±9, 375±8 and 410±10 mg l −1 when the COD/S was 4.85/1, 8.9/1, 12.5/1 and 18.53/1, respectively. The COD removal increased with the increasing COD of the influent, which fitted to the model of first-order reaction kinetics.

A control strategy for promoting the stability of denitrifying granular sludge in upflow sludge blankets

The nitrate removal rate of denitrifying granular sludge in an upflow sludge blanket reactor is very high and reaches up to 3.6 gNO3–N·gVSS−1 d−1 at a nitrate loading rate (NLR) of 32.0 gNO3–N L−1 d−1. However, the granular sludge exhibits flotation under high NLR conditions, where the granules become large in size (of approximately 3–5 mm), light, and easily adhere to gas bubbles. In order to decrease the flotation potentiality of granular sludge, three measures were taken as follows: reducing the size of the granules, increasing the density of the granules, and weakening the adhesion effect of sludge to bubbles. While, these measures did not completely eliminate the granular sludge flotation. The way to solve sludge flotation namely instability was to slow down the biomass growth rate. The main factors to reduce denitrifying bacteria growth rate were verified as relatively low operating temperature, carbon source with comparatively slow degradation rate, and low NLR. Therefore, controlling denitrifying biomass growth rate via reducing temperature, replacing methanol with glucose as carbon source, and decreasing NLR was able to improve the stability of the granular sludge.

Inhibitory effect of cyanide on nitrification process and its eliminating method in a suspended activated sludge process

Inhibition of nitrification by four typical pollutants (acrylonitrile, acrylic acid, acetonitrile and cyanide) in acrylonitrile wastewater was investigated. The inhibitory effect of cyanide on nitrification was strongest, with a 50% inhibitory concentration of 0.218 mg·gVSS-1 being observed in a municipal activated sludge system. However, the performance of nitrification was recovered when cyanide was completely degraded. The nitrification, which had been inhibited by 4.17 mg·gVSS-1 of free cyanide for 24 h, was recovered to greater than 95% of that without cyanide after 10 days of recovery. To overcome cyanide inhibition, cyanide-degrading bacteria were cultivated in a batch reactor by increasing the influent cyanide concentration in a stepwise manner, which resulted in an increase in the average cyanide degradation rate from 0.14 to 1.01 mg CN-·gVSS-1·h-1 over 20 days. The cultured cyanide-degrading bacteria were shaped like short rods, and the dominant cyanide-degrading bacteria strain was identified as Pseudomonas fluorescens NCIMB by PCR.

Diversity and degradation mechanism of an anaerobic bacterial community treating phenolic wastewater with sulfate as an electron acceptor

Petrochemical wastewater often contains high concentrations of phenol and sulfate that must be properly treated to meet discharge standards. This study acclimated anaerobic-activated sludge to treat saline phenolic wastewater with sulfate reduction and clarified the diversity and degradation mechanism of the microbial community. The active sludge in an upflow anaerobic sludge blanket (UASB) reactor could remove 90xa0% of phenol and maintain the effluent concentration of SO42− below 400xa0mg/L. Cloning and sequencing showed that Clostridium spp. and Desulfotomaculum spp. were major phenol-degrading bacteria. Phenol was probably degraded through the carboxylation pathway and sulfate reduction catalyzed by adenosine-5′-phosphosulfate (APS) reductase and dissimilatory sulfite reductase (DSR). A real-time polymerase chain reaction (RT-PCR) showed that as phenol concentration increased, the quantities of 16S rRNA gene, dsrB, and mcrA in the sludge all decreased. The relative abundance of dsrB dropped to 12.46xa0%, while that of mcrA increased to 56.18xa0%. The change in the electron flow ratio suggested that the chemical oxygen demand (COD) was removed mainly by sulfate-reducing bacteria under a phenol concentration of 420xa0mg/L, whereas it was removed mainly by methanogens above 630xa0mg/L.

Effect of Ozone on Removal of Dissolved Organic Matter and its Biodegradability and Adsorbability in Biotreated Textile Effluents

A study was conducted on the efficacy of ozonation in removing dissolved organic matter (DOM) in biotreated textile effluents and effects on its biodegradability and adsorbability. Results showed the efficient removal of color and fluorescence compounds were achieved through ozonation, due to increasing hydrophilicity and lowering molecular weight of DOM. A significant biodegradability improvement was also observed, and DOM adsorbability on activated carbon was highly dependent on ozone dosage. As the key parameter, consumed 3.8 g O3/u2009g TOC0 was the optimal dosage in the hybrid process combining ozonation with biological activated carbon (BAC) for wastewater reclamation.

Decrease of dissolved sulfide in sewage by powdered natural magnetite and hematite.

Natural magnetite and hematite were explored to decrease sulfide in sewage, compared with iron salts (FeCl3 and FeSO4). A particle size of magnetite and hematite ranging from 45 to 60μm was used. The results showed that 40mgL-1 of powdered magnetite and hematite addition decreased the sulfide in sewage by 79%and 70%, respectively. The achieved decrease of sulfide production capacities were 197.3, 210.6, 317.6 and 283.3mgSg-1Fe for magnetite, hematite, FeCl3 and FeSO4 at the optimal dosage of 40mgL-1, respectively. Magnetite and hematite provided a higher decrease of sulfide production since more iron ions are capable of being released from the solid phase, not because of adsorption capacity of per gram iron. Besides, the impact on pH and oxidation-reduction potential (ORP) of hematite addition was negligible; while magnetite addition resulted in slight increase of 0.3-0.5 on pH and 10-40mV on ORP. Powdered magnetite and hematite thus appear to be suitable for sulfide decrease in sewage, for their sparing solubility, sustained-release, long reactive time in sewage as well as cost-effectiveness, compared with iron salts. Further investigation over long time periods under practical conditions are needed to evaluate the possible settlement in sewers and unwanted (toxic) metal elements presenting as impurities.nnnCAPSULE ABSTRACTnPowdered magnetite and hematite were more cost-effective at only 30% costs of iron salts, such as FeCl3 and FeSO4 for decreasing sulfide production in sewage.

Simultaneous removal of nitrogen, phosphorus and COD in an integrated OCO reactor

An integrated OCO reactor with two side-ditch separators based on the anaerobic/anoxic/oxic (A2/O) process was developed for municipal wastewater treatment in this study. The effects of dissolved oxygen (DO) concentration, hydraulic retention time (HRT) and the ratio of chemical oxygen demand (COD) to total nitrogen (C/N) in the influent were investigated for optimization, in order to achieve the removal of total nitrogen (TN), total phosphorus (TP) and COD in the reactor simultaneously. When the DO concentration of 2.0 mg/L in the aerobic zone, HRT of 12 h and C/N ratio of 8:1 were applied in the reactor, the superior removal efficiencies of COD, TN and TP reached 96%, 81% and 92%, respectively. The modification in integrated OCO system was characterized by the mixing of the liquid refluxed from anoxic and aerobic zones with the influent in the anaerobic zone. And the risk of activated sludge bulking was decreased successfully by enhancing phosphorus removal without any chemical auxiliary methods. Quite precise prediction results with the correlation coefficients (R) of 0.9584–0.9948 were forecasted by the back-propagation neural network model. All the results indicated that the integrated OCO process is able to remove TN, TP and COD in a reactor simultaneously.

Removal and transformation of effluent organic matter (EfOM) in biotreated textile wastewater by GAC/O3 pre-oxidation and enhanced coagulation

GAC/O3 (ozonation in the presence of granular activated carbon) combined with enhanced coagulation was employed to process biotreated textile wastewater for possible reuse. The doses of ozone, GAC and coagulant were the variables studied for optimization. The effects of different treatment processes on effluent organic matter (EfOM) characteristics, including biodegradability, hydrophobic and hydrophilic nature, and apparent molecular weight (AMW) distribution were also investigated. Compared with ozonation, GAC/O3 not only presented a higher pre-oxidation efficiency, but also improved the treatability of hydrophobic and high molecular weight compounds by enhanced coagulation. After treatment by GAC/O3 pre-oxidation (0.6 mg O3·mg−1 COD and 20 g·L−1 GAC) and enhanced coagulation (25 mg·L−1 Al3+ at pH 5.5), the removal efficiencies of chemical oxygen demand (COD), dissolved organic carbon (DOC) and colour were higher than those for coagulation alone by 17.3%, 12.0% and 25.6%, respectively. Residual organic matter consisted mainly of hydrophobic acids and hydrophilic compounds of AMW<1 kDa, which were colourless and of limited biological availability. The combination of GAC/O3 and enhanced coagulation was proved to be a simple and effective treatment strategy for removing EfOM from biotreated textile wastewater.

Increasing power generation of microbial fuel cells with a nano-CeO2 modified anode

ABSTRACT Nano-CeO2 was used to modify the carbon felt anode in microbial fuel cell (MFC). The MFC with the modified anode obtained the higher closed circuit voltage resulting from the lower anode potential, the higher maximum power density (2.94 W m−2), and the lower internal resistance (77.1 Ω). Cyclic voltammetry (CV) results implied that the bioelectrochemical activity of exoelectrogens was promoted by nano-CeO2. Electrochemical impedance spectroscopy (EIS) results revealed that the anodic charge transfer resistance of the MFC decreased with modified anode. This study demonstrates that the nano-CeO2 can be an effective anodic catalyst for enhancing the power generation of MFC.