Yankai Guo

Biological catalyzed denitrification by a functional electropolymerization biocarrier modified by redox mediator

Electropolymerization biocarriers were prepared by the electropolymerization of polypyrrole (PPy) on an active carbon felt (ACF) electrode using doping anions anthraquinone-2-sulfonate (AQS) or Na(2)SO(4). The functional electropolymerization biocarrier (ACF/PPy/AQS) with AQS was used as an immobilized redox mediator for the denitrification process. The characteristics of the electropolymerization biocarriers were analyzed by scanning electron microscope, elemental analyses, Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. The results suggested that the denitrification efficiency increased nearly 1.5-fold with ACF/PPy/AQS (0.04 mmol L(-1) AQS) compared to the control. A linear correlation was found for the k value and the AQS concentration (C(AQS)), which was k=624.71C(AQS)+83.87 (R(2)=0.9893). The ORP value stabilized around -200 mV for the denitrification process with ACF/PPy/AQS, which was -25 mV lower than that with ACF/PPy/Na(2)SO(4). Repeated-batch operations indicated that the denitrification efficiency with ACF/PPy/AQS maintained over 90% of the original value and exhibited better catalytic activity and durability.

Study on a novel non-dissolved redox mediator catalyzing biological denitrification (RMBDN) technology

There are little literatures about the accelerating effect of redox mediators on the denitrification processes. In this paper, a novel non-dissolved redox mediator catalyzing biological denitrification (RMBDN) technology was first explored, and the accelerating effect of redox mediator on the denitrification processes was conducted with immobilized anthraquinone. Anthraquinone as a redox mediator was able to increase the denitrification rate, and was immobilized by entrapment in calcium alginate (CA). The results suggested that the artificial redox mediator anthraquinone was found to be capable of raising about 2-fold denitrification rate, and the stabilized oxidation-reduction potential (ORP) values with anthraquinone immobilization beads were lower around 20mV than the control without anthraquinone immobilization beads. The results of repeated-batch operations shown that anthraquinone immobilization beads appeared to exhibit good reusability. The study explored a great improvement of the redox mediator application and the new bio-treatment concept for the denitrification processes.

Redox activity and accelerating capacity of model redox mediators during biodenitrification

The aim of this study was to analyse different model redox mediatiors: anthraquinone-2,7-disulphonate (2,7-AQDS), anthraquinone-1-sulphonate (α-AQS), anthraquinone-2-sulphonate (AQS) and anthraquinone-2,6-disulphonate (AQDS), with regard to the structure–activity relationship indicated by their cyclic voltammograms, their chemical structure, their oxidation–reduction potential and their capacity to accelerate the denitrification reaction during denitrification. Compared to the control, the nitrate removal after 21 h of denitrification was enhanced by a factor of 1.94, 1.56, 1.56 and 1.3 by 2,7-AQDS, AQDS, AQS and α-AQS, respectively. The ranking of the mediators based on their reduction potential ( ) was 2,7-AQDS > AQDS ≥ AQS > α-AQS. was positively correlated with accelerating the denitrification in experiments using 0.024 mmol·L−1 redox mediator, 360 mg L−1 NO3−–N and 5.0 g L−1 of dry cell weight. Practical computational approaches (the frontier orbital theory and the atoms-in-molecules theory) and inductive and resonance effects were also used to explain and assess how the molecular structure and stability of the redox mediators affect the accelerating capacity during denitrification.

Isolation and Cr(VI) reduction characteristics of quinone respiration in Mangrovibacter plantisponsor strain CR1

A Cr(VI)‐reducing Mangrovibacter plantisponsor strain, CR1, was isolated from tannery effluent sludge and had quinone respiration characteristics. Its chromate (CrO42−) resistance, quinone respiration characteristics, and Cr(VI) reduction efficiencies were evaluated in detail. Strain CR1 exhibited a high Cr(VI) resistance with a minimal inhibitory concentration (MIC) of 32 mM in LB medium, and its quinone respiration could occur when an electron donor and strain CR1 both existed in the reaction system. Cr(VI) reduction by strain CR1 was significantly enhanced by a factor of 0.4–4.3 with five different quinone compounds: anthraquinone‐2,7‐disulfonate, anthraquinone‐1‐sulfonate, anthraquinone‐2‐sulfonate (AQS), anthraquinone‐2,6‐disulfonate, and anthraquinone‐1,5‐disulfonate. AQS was the best electron shuttle among them, and the greatest enhancement to the Cr(VI) bio‐reduction was achieved with 0.96 mM AQS. The correlation between the reaction constant k (mg Cr(VI) g−1 dry cell weight H−1) and thermodynamic temperature T (K) was expressed as an Arrhenius equation lnk=−7662.9/T+27.931(R2=0.9486) ; the activation energy Ea was 63.71 kJ mol−1, and the pre‐exponential factor A was 1.35 × 1012 mg Cr(VI) g−1 dry cell weight H−1. During the Cr(VI) reduction process, the pH tended to become neutral, and the oxidation–reduction potential decreased to −440 mV. The efficient reduction of Cr(VI) mediated by a quinone respiration strain shows potential for the rapid anaerobic removal of Cr(VI).

Study of the dynamics and material transformation characteristics of nitrite denitrification in UASB

Nitrite is known to accumulate in wastewater treatment plants and play an important role during the biological denitrogenation process. In this study, wastewater with high nitrite concentration was effectively treated, and the possible material transformation of nitrite and carbon by microorganisms is discussed herein. While inoculating pre-acclimatized floccular sludge, nitrite-denitrifying granular sludge was obtained after approximately 15 days of cultivation in a denitrifying upflow anaerobic sludge blanket (UASB) reactor. The nitrite removal efficiency ( (%)) was always greater than 98%. At the same time, the nitrite removal rate () reached 0.46 g N g VSS−1 d−1. The granular sludge taken from the reactor was characterized. The fluorescence in situ hybridization (FISH) result showed that the microbial community structure was also changed during the granular sludge formation process and that the nitrite denitrifying bacteria increased in population size. Based on the carbon balance, the stoichiometric equation of nitrite denitrification was obtained and a biomass yield value was calculated. The practical ratio of chemical oxygen demand (COD) and nitrite was 2:1, which was higher than the theoretical value. The measured effluent pH was negligibly different from the stoichiometric value.

Effect of thiosulfate on rapid start-up of sulfur-based reduction of high concentrated perchlorate: A study of kinetics, extracellular polymeric substances (EPS) and bacterial community structure

Perchlorate (ClO4-) contamination is more and more concerned due to the hazards to humans. Based on the common primary bacterium (Helicobacteraceae) of both thiosulfate-acclimated sludge (T-Acc) and sulfur-acclimated sludge (S-Acc) for perchlorate reduction, the rapid start-up of sulfur-based perchlorate reduction reactor (SBPRR) was hypothesized by inoculating T-Acc. Furthermore, the performance of SBPRR, the SO42- yield, kinetics of ClO4- reduction and the extracellular polymeric substances (EPS) of biofilm confirmed the hypothesis. The start-up time of R3 (reactor inoculating T-Acc) was 0.18 and 0.21 times that of R1 (control) and R2 (reactor with the influent containing thiosulfate), respectively. The SO42- yield of R3 was lower than that of R2 and R1 with perchlorate removal rate 166.7mg/(Lh). The kinetic study and EPS demonstrated that inoculating T-Acc was beneficial for the development of biofilm. Consequently, the present study indicated that SBPRR can be rapidly and successfully started-up via inoculation of T-Acc.

A study of the kinetics and the effect of trace elements on mixed anaerobic fermentative biogas production by ternary quadratic general rotary unitized design

ABSTRACT In this study the effect of trace elements on methanogenesis was investigated during mixed anaerobic fermentation using a single-factor experiment in the present study. The most effective concentrations of Fe0, Fe2+, Co2+ and Ni2+ that were added were 1500, 250, 0.3 and 0.6 mg/L, respectively. The optimal trace element combination was 0.58 mg/L Ni2+, 1200 mg/L Fe0 and 0.34 mg/L Co2+ by the ternary quadratic general rotary unitized design method. The degree of influence exerted by trace elements on the cumulative methane yields decreased in the order of Ni2+, Fe0 and Co2+, and the maximum CH4 yield was 241.6 mL/g volatile solids (VS), according to a regression equation. The non-dissolved organic carbon hydrolytic process showed a good fit with the first-order kinetic model. The maximum value of CH4 was 312.87 mL/g VS. Compared to the control, the bioconversion efficiencies of CH4 and CO2 production increased by 36.76% and 74.50%, respectively, at the optimal trace element combination. The obtained results provide new knowledge for improvements in the efficiency of anaerobic fermentation biogas production.

Enhanced electrochemical oxidation of Acid Red 3R wastewater with iron phosphomolybdate supported catalyst

Electrochemical oxidation of Acid Red 3R (AR3R) was investigated with the new catalyst of iron phosphomolybdate (FePMo12) supported on modified molecular sieves type 4 Å (4A) as packing materials in the reactor. The results of the Fourier transform infrared spectroscopy and X-ray diffraction indicated that the heteropolyanion had a Keggin structure. The optimal conditions for decolorization of simulated AR3R wastewater were as follows: current density 35 mA/cm², initial pH 4.0, airflow 0.08 m³/hour and inter-electrode distance 3.0 cm. With the addition of NaCl to the system, the decolorization efficiency increased. But Na₂SO₄had a negative effect on the decolorization efficiency, which was attributed to the negative salt effect. The degradation mechanisms of AR3R were also discussed in detail.

Degradation of Acid Red B by the combined technology of ozonation and High-voltage pulsed discharge

In this study, the optimum conditions, the decolorization rate and the possible degradation mechanism were explored for the degradation of Acid Red B by the combined technology of ozonation and high voltage pulsed discharge (HVPD). The results suggested that the decolorization rate of the Acid Red B fitted the pseudo-first-order kinetics with initial dye concentration. The optimum ozone dose and pH was 4.0 g h−1 and 8.0, respectively. Compared to ozone alone, the combination of ozone and HVPD enhanced 25% of the decolorization rate. At the same time, a proposed degradation mechanism was put forward according to the degraded intermediates, which were analyzed by gas chromatography and mass spectrometry for nitrobenzene and benzene sulfonamide acid and were detected by ion chromatography for nitrate and sulfate ions and formic, acetic and oxalic acids. Therefore, the combined technology was a very promoting technology in the wastewater treatment.

Preparation characteristics and accelerating denitrification effectiveness of polyamide 6 modified by AQS

In this study, the functional polymer biocarrier polyamide 6 (PA6) modified by anthraquinone-2-sulphonate (AQS) was synthesized by hydrolysis and sulphonation reactions. The optimal hydrolysis conditions of PA6 were 35 °C, 3 mol/L HCl and 72 h reaction time. The optimal sulphonation conditions of PA6 modified by AQS (PA6-AQS) were 30 °C and 6 h reaction time. The morphology and heat resistance of PA6-AQS were analysed by scanning electron microscopy, thermogravimetric analysis and differential scanning calorimetry. The AQS content of PA6-AQS, determined by an elemental analysis, was approximately 0.11 mmol/g. The denitrification efficiency was enhanced by 1.78-fold with PA6-AQS. Repeated-batch operations showed that the denitrification efficiency with PA6-AQS became stabilized above 80% of the original value and exhibited a better catalytic activity and durability.