Different Matrix Vertical Flow Artificial Wetland Treatment Of Piggery Wastewater Applied Research

Three sets of vertical-flow constructed wetlands (VFCW) with different carriers were built for piggery wastewater treatment. Performances at start-up stage and seasonal running stage were investigated, and main reasons for the variations in NH₄⁺-N removal efficiencies among different VFCWs are discussed. Moreover an orthogonal experiment was conducted to determine the optimum parameters of VFCWs' operation.Zeolite was found to be the best carrier with the highest capability of NH4 -N adsorption compared with cinder and sand. The adsorption isotherms of NH₄⁺-N onto the zeolite fits the Langmuir isothermal formular, whereas the adsorption isotherms of NH₄⁺-N onto the cinder and sands fits the Freundlich isothermal formular. Zeolite can achieve better NH₄⁺-N adsorption in near neutral condition, whereas the adsorption capacity cinder and sand improved with the increase of pH. In comparison, the adsorption capacity of zeolite was lower in treating the actual piggery wastewater than that of the simulated wastewater. Zeolite can also contribute to the removal of organic matter in the piggery wastewater. After treated by zeolite, the pH of wastewater reached near neutral condition.VFCWs can adapt higher CODcr loading rate during the start-up stages (removal efficiency reached up to 60⁷0%). It indicated a good liner relationship between COD_Cr loading rate and COD_Cr removal rate (R²: 0.81⁰.95, n=14). Removal efficiencies of NH₄⁺-N in zeolite type and zeolite-cinder type wetlands were over 90% with tested loading rates. Total Nitrogen (TN) removal efficiencies of zeolite type and zeolite-cinder type wetlands under higher loading rate (27.3 g N/m²d) were 75.2% and 62.7%, respectively. The results indicated that zeolite type and zeolite-cinder type wetlands had relatively better capability of nitrification and denitrification in comparison to the conventional type. The sequence of the pollutant removal efficiency of the three systems is zeolite-cinder VFCW > zeolite VFCW > conventional VFCW.According to the results of orthogonal experiments, the conventional type VFCW is efficient with lower pollutant loading rate and lower hydraulic loading rate, hence the recommended running condition is A₂B₁C₂D₁. The recommended running condition for zeolite type VFCW is A3B2C2D2. While, A₂B₃C₂D₂ for the zeolite-cinder type VFCW. When it is considered as a single reactor, the best removal efficiency canbe achieved under the conditions of A₂B₁C₂D₂ for zeolite-cinder type wetland.There was no apparent seasonal difference in COD_Cr removal among three VFCW systems. Zeolite-cinder type VFCW had the best performance. First order rate models can be used to simulate the removal of organic matter in VFCWs. The NH₄⁺-N removal efficiency of conventional type remained considerably stable in different seasons(54.8% in autumn, 53.7% in winter, 47.6% in spring). Unlike the conventional type , the NH₄⁺-N removal efficiency of zeolite type and zeolite-cinder type wetlands decreased from 89.8%,and 93.4% in autumn to 64.2% and 73.5% in winter, respectively. With the increase of the temperature, the NH₄⁺-N removal efficiencies of all systems increased. In contrast, the zeolite-cinder type system showed the high capability of NH₄⁺-N removal in all seasons.As for TN removal efficiency of three systems, zeolite VFCW is the highest followed by that of zeolite-cinder VFCW and conventional VFCW. Nitrification activities at different layers of zeolite-cinder type system were all higher than the other two systems, and denitrification activities in zeolite type and zeolite-cinder type were higher than that in conventional type system, indicating that the TN removal capability can be improved by using the zeolite as carrier in VFCWs. No apparent seasonal differences in TP removal of the three VFCWs were observed.