Leachate from the landfills cannot be released to the receiving streams, since it usually brings significant pollutant load.  Objective of the study is to develop a new technology for reducing nitrogen load as an alternative measure of leachate treatment with more labor saving and minimum energy consumption.  The authors have carried out field and laboratory experiments for devising a new nitrification/denitrification technology consisting of two-step process.  The first step is conversion of ammonia to nitrate by using a "Micro-Bubble, MB" aeration.  The second step is denitrification, which is carried out by heterotrophic bacteria with aid of fatty acid compounds as hydrogen donors.  An ecological model was developed in order to analytically describe ecohydraulics in the nitrification/denitrification processes by taking the relating parameters such as dissolved oxygen, microorganisms, ammonia, nitrite, nitrate, phosphorus, organic carbon, etc. into consideration.  A simultaneous equation system regarding the ecological processes was formulated to describe quantitative balance among each water quality component in a hydraulically and biochemically equilibrium state.  The theoretical solutions for nitrification and denitrification rates and concentration of each nitrogen component after treatment were obtained for given conditions of leachate loading rate Q (m³/day), MB aeration discharge Q_O (m³/day), hydraulic retention time t (day) and amount of fatty acid compounds A (m²).  Assuming a prototype treatment plant consisting of a MB aeration tank being connected to a reactor container filled with the fatty acid compounds, an optimum operation condition that provides the best performance both of nitrification and denitrification was theoretically obtained.