Impact Of Wastewater C: N Ratio On Nitrogen Transport And Transformation In Wastewater Irrigation System

Land disposal of wastewater can help for alleviating the situation of water resources scarcity and water pollution. Research on nitrogen transport and transformation processes in wastewater irrigation systems would have important scientific meaning and practical use for analyzing and forecasting nitrogen pollution, as well as increasing nitrogen-utilizing efficiency under the wastewater irrigation condition.To look at the effect of organic carbon content of wastewater on crop growth, nitrogen accumulation in and leaching from the soil, soil column experiments were carried out. A total of twelve columns were used. The twelve columns were divided into four treatments, and irrigated with wastewater of different organic carbon content (COD/TN=2.8, 7.5, 30, 75).The soil of the columns was collected from field of Daxing experimental station of IWHR, which can be classified to sandy loam. Alfalfa was grown in the columns. During the experiments, irrigation and drainage waters volumes of each irrigation cycle were monitored, crop height, dry matter yields and crop N uptake were measured, and samples collected for analysis of ammonium, nitrate, total nitrogen and COD. At the end of the experiments, soil moisture contents, ammonium and nitrate at different depths of the columns were measured.The main conclusions of the experiments are: (1) Application of wastewater amended with organic carbon can prolong drainage duration, increase cumulative drainage volume and cumulative leaching of ammonium, nitrate and total nitrogen. More cumulative leaching of nitrogen is collected from the treatment of the highest organic carbon content when compares with the one of the lowest organic carbon content. To some extent, the application of wastewaters with high organic carbon content can increase the cumulative leaching of nitrogen. (2) Application of wastewater amended with organic carbon decreases alfalfa height, dry matter yields and crop N uptake. These effects in the treatment of highest organic carbon content are more obvious than that of the treatment of lowest organic carbon content. The application of wastewaters with high organic carbon content affects the natural growth of alfalfa remarkably. (3) Analysis of soil samples at the end of the experiments shows that application of wastewater amended with organic carbon increases soil moisture above 30 cm and ammonium content of soil profile, decreases nitrate content above 30 cm, and these effects in the treatment of highest organic carbon content are more obvious than that in the treatment of lowest organic carbon content. These effects mentioned above will be wearing off with the soil drying process, differences of soil moisture between different treatments will be eliminated. The contents of ammonium and nitrate in the soil profile are also similar in different treatments except for the ammonium content in the subsoil layer is higher in the non amended treatment. (4) Nitrogen balance calculation suggested that as the organic carbon content of wastewater increase, ammonium, nitrate and organic nitrogen leaching loads and...