The effects of chemical oxygen demand(COD)concentration in the influent on nitrous oxide(N_(2)O)emissions,together with the relationships between N_(2)O and water quality parameters in free water surface constructed wetlands,were investigated with laboratoryscale systems.N_(2)O emission and purification performance of wastewater were very strongly dependent on COD concentration in the influent,and the total N_(2)O emission in the system with middle COD influent concentration was the least.The relationships between N_(2)O and the chemical and physical water quality variables were studied by using principal component scores in multiple linear regression analysis to predict N_(2)O flux.The multiple linear regression model against principal components indicated that different water parameters affected N_(2)O flux with different COD concentrations in the influent,but nitrate nitrogen affected N_(2)O flux in all systems.
Activated carbon was prepared from cattail by H3PO4 activation. The effects influencing the surface area of the resulting activated carbon followed the sequence of activated temperature > activated time > impregnation ratio > impregnation time. The optimum condition was found at an impregnation ratio of 2.5, an impregnation time of 9 hr, an activated temperature of 500°C, and an activated time of 80 min. The Brunauer-Emmett-Teller surface area and average pore size of the activated carbon were 1279 m2/g and 5.585 nm, respectively. A heterogeneous structure in terms of both size and shape was highly developed and widely distributed on the carbon surface. Some groups containing oxygen and phosphorus were formed, and the carboxyl group was the major oxygen-containing functional group. An isotherm equilibrium study was carried out to investigate the adsorption capacity of the activated carbon. The data fit the Langmuir isotherm equation, with maximum monolayer adsorption capacities of 192.30 mg/g for Neutral Red and 196.08 mg/g for Malachite Green. Dye-exhausted carbon could be regenerated effectively by thermal treatment. The results indicated that cattail-derived activated carbon was a promising adsorbent for the removal of cationic dyes from aqueous solutions.
