Simultaneous Removal Of Ammonium And Phosphate By Mg-modified Zeolite

The growth of ammonium and phosphate is the leading cause of eutrophication. Eutrophication can result in the deterioration of water quality, damage to the balance of organisms present in the lakes and rivers increased the fish mortality, and the outbreak of harmful microalgae. As a result, simultaneous removing ammonium and phosphate from wastewater is important to control eutrophication。Previous researches have shown that biological treatment, chemistry precipitation and adsorption are the commonly used methods. Among the three methods, adsorption is more competitive over the other two methods, because of taking up relatively little space, relative simplicity of application and operation as well as environmentally friendly. Natural zeolite is a kind of low cost material, however, low selective toward ammonium and phosphate and low removal efficiency both need to be improved. Therefore, in this study, a new way to modify natural zeolite with MgCl2has been explored. Furthermore the characteristic of adsorption by modified zeolite and the LCA process of preparing modified zeolite also have been analyzed by software GaBi.The main conclusions are as follows:(1) Different methods were examined and the experiment indicated that impregnation with NaOH and MgCl2and without roasting was the best way to modify the natural zeolite, the concentration of NaOH solution was0.5mol/L, the concentration of MgCl2solution was1mol/L, the temperature of impregnation was80℃, and the temperature of drying was45℃. The adsorption capability of the best modified zeolite was greatly improved, the equilibrium adsorption capacity of NH4+-N and PO43-were7.90mg/g and2.17mg/g. The desorpton with NaCl solution was very high, and the efficiency of desorption for NH4+-N and PO43-were84.54%and59.35%.(2) Batch study for ammonium and phosphate removal using modified zeolite indicated that optimal NH4+-N and PO43-adsorption capability was achieved at pH7. Ammonium and phosphate adsorption equilibrium was reached in the initial1h. With the increase of initial NH4+-N and PO43-concentration, the adsorption capability increased. The higher the tempterature was, the greater the adsorption capability was. With the increase of zeolite loading, the removal efficiency increased but the removal capacity decreased.(3) The adsorption kinetic of ammonium and phosphate is of great importance to design the treatment systems. Five kinetic models were examined to fit the experimental data and to be proposed to elucidate the mechanism of adsorption. Adsorption kinetics was best approximated by the Pseudo second-order model. According to the Intraparticle diffusion model, the process of adsorption can be divided into two separate steps. The first step was the external surface adsorption and the second step was internal surface adsorption.(4) An adsorption isotherm can be characterized by certain contants, and three isotherms were tested in this paper. The experimental data were best fitted by the Langmuir and Freundlich model. The Tempkin parameters showed that NH4+-N were easier adopted than PO43-by modified zeolite.(5) The LCA report indicated that the greenhouse effect and the effect of eutrophication were contributed by the use of electric power in the process of modifying the natural zeolite. And the use of NaOH and MgCl2has made little contribution to the greenhouse and effect and eutrophication effect.