The cases of reconstruction of sewage treatment plants are increasing for such reasons as aging of facilities and to improve resistance against earthquakes. In order to formulate reconstruction plan, it is beneficial to utilize the accumulated operational data such as water quantity and quality by simulation. In this study, by using the simulators we developed, we compared three reconstruction scenarios of a virtual model sewage treatment plant, where half of the plant, currently the conventional activated sludge process(CAS), is replaced by 1)the Anaerobic Anoxic Oxic Process (A₂O), 2)the Membrane Bio-Reactor(MBR), or 3)the New Media Filtration. The results of the simulations were as follows, the introduction of the A₂O process or the MBR process improved the removal efficiency of nitrogen and phosphorus. However, the use of electrical energy increased by 2. 1 and 3. 1 times, respectively when compared with the CAS process due to the increase of air supply for nitrification. On the other hand, air supply was reduced, and electrical energy consumption can be depressed to less than 40％ of the CAS process when the NMF process was introduced. The effectiveness of the use of the sewage plant simulator was demonstrated and evaluated through the comparison with different reconstruction options from many aspects such as effluent quality, energy consumption/recovery, and maintenance cost for the reconstruction of sewage treatment plants.