Qili Hu

Effect of electro-stimulation on activity of heterotrophic denitrifying bacteria and denitrification performance

The effects of electro-stimulation on heterotrophic denitrifying bacterial activity and nitrate removal were investigated using a bench-scale bio-electrochemical reactor in this study. Results showed that the maximum nitrate removal efficiency was 100% at the optimum current density of 200mA/m(2), at which low nitrite production and high ATP aggregate level were obtained. The activity of denitrifying bacteria was highest at the range densities of 200-250mA/m(2), although the terminative pH increased to 8.62 at 200mA/m(2) and 9.63 at 250mA/m(2). This demonstrates that suitable current densities could improve the activity of denitrifying bacteria. Therefore, this study provides a number of useful information to improve the bio-electrochemical reactor designs and promote the removal efficiency of pollutants.

The feasibility of an up-flow partially aerated biological filter (U-PABF) for nitrogen and COD removal from domestic wastewater

An up-flow partially aerated biological filter (U-PABF) was developed to study the removal of nitrogen and chemical oxygen demand (COD) from synthetic domestic wastewater. The removal of NH4(+)-N was primarily attributed to adsorption in the zeolite U-PABF and to bioprocesses in the ceramic U-PABF. When the hydraulic retention time (HRT) was 5.2h, the ceramic U-PABF achieved a good performance and the NH4(+)-N, total nitrogen (TN), and COD removal efficiency reached 99.08±8.79%, 72.83±0.68%, and 89.38±1.04%, respectively. The analysis of NH4(+)-N, NO3(-)-N, NO2(-)-N, and TN at different depths revealed the simultaneous existence of nitrification-denitrification, and anaerobic ammonium oxidation (anammox) in ceramic U-PABF. Illumina pyrosequencing confirmed the existence of Planctomycetes, which are responsible for anammox. The results indicated that the nitrification-denitrification and anammox all contributed to the high removal of NH4(+)-N, TN, and COD in the U-PABF.

Kinetic and isotherm studies of nitrate adsorption on granular Fe–Zr–chitosan complex and electrochemical reduction of nitrate from the spent regenerant solution

In this study, a granular Fe–Zr–chitosan complex was synthesized to remove nitrate from aqueous solution and an undivided cylindrical electrochemical cell was constructed to treat the spent regenerant solution, thus achieving separation and conversion. Adsorbent characterization was conducted by SEM, XRD, BET, FTIR and XPS. The effects of pH and co-existing anions on nitrate adsorption were investigated. The results indicated that nitrate adsorption on Fe–Zr–chitosan complex followed the first-order kinetic model and the two-site Langmuir isotherm model. The specific surface area of Fe–Zr–chitosan complex was 23.6 m2 g−1 and the maximum adsorption capacity reached 10.60 ± 0.74 mg g−1 (as N). The point of zero charge of Fe–Zr–chitosan complex occurred at a pH of 6.3. No significant changes in nitrate removal efficiency were observed over a wide pH range of 3.0–11.0. Sulphate and phosphate seriously interfered in nitrate removal. The developed electrochemical method might have a potential of practical application for the treatment of the spent regenerant solution.

Chemical regeneration mechanism of Fe-impregnated chitosan using ferric chloride

A process for the regeneration of spent Fe-impregnated chitosan (Fe-CTS) by continuous fluoride adsorption and chemical regeneration is described. Different concentrations of NaCl, FeCl3 and CaCl2 solutions were employed as regenerants. The regeneration efficiencies were valued using 100 mg L−1 fluoride adsorption on regenerated Fe-CTS. Results showed that the maximum adsorption capacity (qe) of 14.44 mg g−1 was obtained when the Fe3+ regenerant concentration was 150 mg L−1. Changes in F− and Cl− concentration were also measured. To examine the stability of regenerated Fe-CTS, Fe3+ leaching was observed in the fluoride solution after adsorption. Scanning electron microscopy with an electronic differential system and surface charge distribution were performed to elucidate the regeneration and adsorption mechanisms. Holes and cracks that emerged after regeneration accelerated the rate of internal diffusion. After regeneration, the FeCl3 solution pH was less than pHpzc (4.92), indicating that FeCl3 regenerated Fe-CTS (FeCl3-Fe-CTS) was positively charged. The change in the concentration of fluoride was consistently greater than that of chloride, indicating that other mechanisms except ion-exchange, such as electrostatic attraction, contributed to fluoride adsorption. After seven regeneration/adsorption cycles, the total adsorption capacity of FeCl3-Fe-CTS was found to be 74.04 mg g−1 without a significant loss in the adsorption ability.

Kinetic studies of nitrate removal from aqueous solution using granular chitosan-Fe(III) complex

In the present study, a granular chitosan-Fe(III) complex was prepared as a feasible adsorbent for the removal of nitrate from an aqueous solution. There was no significant change in terms of nitrate removal efficiency over a wide pH range of 3-11. Nitrate adsorption on the chitosan-Fe(III) complex followed the Langmuir-Freundlich isotherm model. In order to more accurately reflect adsorption and desorption behaviors at the solid/solution interface, kinetic model I and kinetic model II were proposed to simulate the interfacial process in a batch system. Nitrate adsorption on the chitosan-Fe(III) complex followed the pseudo-first-order kinetic model and kinetic model I. The proposed half-time could provide useful information for optimizing process design. Adsorption and desorption rate constants obtained from kinetic model I and kinetic model II were beneficial to understanding the interfacial process and the extent of adsorption reaction. Kinetic model I and kinetic model II implied that nitrate uptake exponentially approaches a limiting value.

Biological denitrification using rice washing drainage (RWD) as carbon source for removing nitrate from groundwater

AbstractTo investigate the feasibility of rice washing drainage (RWD) as carbon source for biological denitrification, the denitrification performance using RWD, maize stalks, poplar leaves, and sawdust as carbon sources was evaluated by batch experiments. Results showed that nitrate in synthetic groundwater could be removed effectively using RWD, maize stalks, and sawdust as carbon sources, and the nitrate removal efficiencies were 96, 98, and 96%, respectively, while using poplar leaves was 73%. Furthermore, RWD-based denitrification resulted in a favorable nitrate removal rate constant (2.649 d−1), higher than others (2.412 d−1 for maize stalk, 0.427 d−1 for poplar leaf, 0.363 d−1 for sawdust). The optimum ratio of RWD to synthetic groundwater was obtained to be 50/350 (v/v), at which the nitrate removal efficiency reached 100% with no nitrite accumulation and the COD removal efficiency reached 90%, indicated that the denitrification with RWD could not only efficiently remediate the nitrate contaminate...