Analysis of material and energy flow in sewage treatment facilities in Japan

Energy consumption in sewage treatment facilities in Japan has increased due to increasing tap water consumption. To reduce the resource/energy consumption in sewage treatment facilities, measures such as the selection of optimum treatment processes and operating conditions should be considered. The objective of this study is to gather information necessary for the determination of optimum sewage treatment processes and optimum operating conditions. The energy consumption and material flow in sewage treatment facilities in Japan are analyzed using statistical data. In 1994, reuse rate of treated sewage outside the treatment facilities in Japan was 18% of the amount of domestic treated water. In this regard, reuse of water outside facilities should be encouraged. Average electric power consumption per unit volume of wastewater in sewage treatment facilities varies widely from facility to facility and closely correlates with the facility scale. For example, the smaller the facility scale, the larger the electric power consumption. Treatment volume of sewage in smaller facilities is much less than their capacity. 3.7 million t year-1 of dehydration cake is incinerated and 0.1 million t year-1 of it is converted by composting. The recycle rate of the cake was low. Developing a new sludge treatment process other than incineration is necessary.