Dynamics Of Nitrogen Transportation And Transformation Of Field Applied With Digester Effluents

Anaerobic digestion is carried out by a consortium of microorganisms that converts biodegradable organic matter, such as manure, straw, and agricultural wastes, into carbon dioxide (CO2) and methane (CH4). A biologically stable and partially hygienic product, the effluent, is also generated during anaerobic digestion process. To apply effluent to field has some positive effects. It could amend soil conditions, improve soil fertility, as well as increase crop yield and improve product quality by participating the nutrients cycling of the agro-ecosystem. However, secondly pollution comes consequently, acting as a negative effect. Because of the limited absorb capacity of soil and crops, surplus nutrients would lapsed driven by water or emitted by gaseous. Thus, how to apply effluents to field scientifically and safely is essential to maintain an environment with high quality and ensure a sustainable agricultural production.To assess the fertilizing values and prevent contamination of soil and water better, it is essential to quantify the concentrations of nutrients and metals prior to the application of effluents. However, limited information about effluent characteristics is available and previous studies often reported strong variations among different manure digester effluents. The characteristics of nutrients and metals in effluents have been insufficiently studied. Samples of influent, effluent, liquid and solid fraction after separation were taken from three biogas plants every two months over14months. Samples were analyzed for nutrient and metal concentrations. Nitrogen runoff losses and distributions in soil profile caused by applying influents and effluents to field were analyzed under simulated rainfall. This research also used the Agricultural Policy/Environmental extender (APEX) model simulation to simulate and predict the nitrogen in runoff, soil and leachate. The differences of nitrogen losses under manure application and effluent application were compared. The main conclusions are as follows:Significant differences (P0.05) of the effluents from three digesters were largely affected by the types of influents. High variability of nutrient and metal concentrations in effluents was observed not only among three digesters, but also within each digester in different sampling months. It’s indicated that to adequately evaluate the performance of anaerobic digesters and their effects on nutrient and metal concentrations in effluent. It is necessary to analyze multiple samples for a sufficiently long duration. There was a164-463%increase of nitrogen and phosphrous in effluent solid fraction after separation; a10-19%decrease in effluent liquid fraction. The different nutrient characteristics of solid and liquid fraction would affect the corresponding transport and agricultural management.Under the same applied amounts of nitrogen (200kg ha-1N) and after30min of simulated rainfall, there were0.8%and14.3%of fertilizer N lost with runoff from manure and effluent treatments. There were10.7%and6.7%of fertilizer N remained in the soil profile. Along with the experimental time, the N in soil profile increased. A pencentage of21.3%and13.0%of fertilizer N remained in the soil profile1d after manure and effluent applications. There were84.0%and74.4%of fertilizer N remained in the soil profile28d after manure and effluent applications. So there would be a leaching risk of nitrate after the application of manure and effluents. It should be concerned in case of groundwater pollution.APEX model was calibrated and validated by USDA National Soil Erosion Research Lab. This study simulated the nitrogen loss from field applied with effluents during2014-2049. The annual nitrogen runoff loss of manure, effluent,2times application of manure, and2times application of effluent was76.4,37.2,141.8, and71.1kg ha"1. The annual nitrogen in leachate loss was17010.7,8107.6,34349.5, and16431.5kg ha’1. Nitrogen runoff and leachate loss from field under effluents application was much less than that of manure application. The nitrogen in soil profile showed an increasing treand along with the continuous application of manure and effluents. As the nitrogen and phosphrous application amount doubled, the nitrogen loss from field increased with it.