Intensification Of Groundwater Nitrate Removal With Electrical Stimulation From Microbial Fuel Cells

Nitrate contamination in groundwater was mainly caused by the extensive use of chemical fertilizers and improper treatment of industrial wastewater. High concentration of nitrate posed serious threats to human health and ecological environment. Nitrate could chronically exist in surface and ground water due to its high solubility and poor adsorption property, which increased difficulty of nitrate removal. Biological denitrification and ion exchange were the two widely used treatment methods, which produced large numbers of the excess sludge and the spent brine, respectively. Adsorption has attracted great research interest for the purification of industrial and municipal wastewaters because of its low cost, operation simplicity, availability and recyclability.In this study, granular chitosan-Fe(III) complex was used to remove nitrate from water and was characterized using a scanning electron Microscope(SEM), surface area analyzer(BET) and Fourier transform infrared spectrometer(FTIR). The effect of adsorbent dosage, initial nitrate concentration, pH and Co-existing ions on nitrate adsorption was investigated. Results indicated that the maximum adsorption capacity was 8.35 mg·g–1. Nitrate adsorption was most independent of pH and temperature and was a spontaneous exothermic process. Adsorption process followed the pseudo-second-order kinetic model and the Langmuir-Freundlich isotherm model. Granular chitosan-Fe(III) complex could be effectively regenerated by NaCl solution.To optimize nitrate adsorption process, an adsorbent with high mechanical strength and good acid-alkali resistance was prepared. The maximum adsorption capacity reached 8.58 mg·g–1. The nitrate adsorption mechanism was primarily dominated by ion exchange and electrostatic attraction on the adsorbent surface, accompanying with the intraparticle diffusion. Process optimization of nitrate adsorption by a full factorial design(including adsorbent dosage, initial nitrate concentration, pH and temperature) revealed the interaction between the response and the factors. The proposed specific rate constant eliminates the effect of adsorbent dosage on adsorption process, which was superior to the pseudo-first-order rate constant. Thus, it was more suitable to describe nitrate adsorption on granular chitosan-Fe(III)-Al(III) complex. The extended Freundlich isotherm was suitable for the description of competition effect between sulphate and nitrate.In order to better reflect adsorption and desorption behaviors at the solid/solution interface, the proposed kinetic model I and kinetic model II were to simulate interfacial process for nitrate adsorption on chitosan-Fe(III) complex based on the modification of the pseudo-first-order and pseudo-second-order kinetic models. The goodness of fit of kinetic models was reasonably evaluated through coefficient of determination and chi-square analysis. Results indicated that kinetic model I and kinetic model II could well describe nitrate adsorption on granular chitosan-Fe(III) complex and that the amount of nitrate uptake exponentially increased up to a limited value with time. The theoretical deviation revealed the relationship between kinetic model I and kinetic model II and the pseudo-first-order and pseudo-second-order kinetic models, respectively.