| Constructed wetland is a recently developed technology of wastewater treatment. There are many advantages of this technology: high removal capacity, simple construction, low investment costs, low maintenance and operation costs, simple operation and maintenance, which is adapted to sewage treatment of village and small town absent of capital and technician. However, the current constructed wetlands have low hydraulic loading rate, low nitrogen and phosphorus removal efficiency, and occupy large ground area. The aim of this paper is to look for optimal hydraulic loading rates, simple operation and maintenance, and good substrate of constructed wetland to solute the above problems.In order to look for optimal hydraulic loading rates, two lab plants of vertical flow constructed wetland were tested to treat low concentration sewage at hydraulic loading rates of 8.5cm/d, 10.6 cm/d, 14.1 cm/d, 21.2 cm/d and 42.4 cm/d respectively. The wastewater was fed continuously. Test results indicated that CODcr and NH4+-N removal efficiency had no significant difference between multilayer substrate wetland and dual-substrate wetland, which the effluent CODcr and NH4+-N concentrations were below 30mg/L and 5mg/L, respectively. A strong function was found between CODcr removal rate and CODcr loading rate, the two parameters had significant correlativity (correlation coefficients R >0.98). Nitrogen removal mechanism analysis revealed that nitrogen in the influent was mainly eliminated through biological process via nitrification and denitrification, which were affected by water quality, hydraulic loading rate and temperature et al. There was positive correlation between TN removal efficiency and CODcr loading rate at the hydraulic loading rate of 14.1 cm/d. The ideal hydraulic loading rate of multilayer substrate wetland is 42.4 cm/d, and dual-substrate wetland 21.2 cm/d.Experimental data indicated that substrate structure and hydraulic loading rate affected TP removal at the early stage of experiment. TP removal efficiency of the dual-substrate wetland got up to 97.5% with the hydraulic loading rates of 8.5cm/d, 10.6cm/d, 14.1 cm/d and 21.2cm/d, multilayer substrate wetland 96.3% with the hydraulic rates of 8.5cm/d and 10.6cm/d. However, TP removal rates were 92.7%, 81.2% and 34.5%, respectively, with the hydraulic rates of 14.1cm/d, 21.2cm/d and 42.4cm/d, which declined following hydraulic rates rising. P-adsorption experiment results showed that P-adsorption quantity of substrate were very limited. P removalefficiency was satisfactory before substrate P-adsorption saturation, while got worse after its saturation of the two vertical flow constructed wetlands.In order to simple operation and maintenance, a small-scale plot of valveless vertical flow constructed wetland was designed, and sewage treatment experiment was taken by simulating the effluent characteristic of country sewage in winter. The experiment results indicated that valveless vertical flow constructed wetland of planted ryegrass had a significant effect on removal organic matter in winter, the removal rate of CODcr was 85% and the effluent CODcr concentration was less than 50 mg/L. The wetland system TN removal efficiency was stabilization in 50%. TP removal rate fluctuated form 93.5% to 54.2%, which declined with the extending of running period. Simple operation and maintenance of vertical flow constructed could implement.To find out the optimal substrate of constructed wetlands, equilibrium sorption experiments and kinetics sorption process of 6 substrates were carried out. The data obtained in this study were fitted to both Langmuir and Freundlich adsorption isotherms. The order of Langmuir adsorption maximum (g P/m3 substrate) was steel furnace slag(SFS) > cinder > sand > blast furnace slag(BFS) > tungsten gangue > gravel. SFS adsorption process was fast and adsorption capacity was large. But the adsorption capacity of cinder in low P concentration liquid was very weak, which was not adapted to act as the substrate of treatment sewage constructed wetlands...
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