SENDAI -Towards a Disaster-Resilient and Environmentally-Friendly City

Before the disaster, the Minami-Gamo Wastewater Treatment Plant had been treating about 70% of Sendai’s sewage. On March 11, 2011, a tsunami of over 10 meters in height hit the plant and caused catastrophic damage with building structures broken, its machinery and electrical facilities submerged or swept away, and transmission towers collapsed, resulting in the shutdown of sewage treatment functions.

It was imperative to restore the plant promptly, since it was an indispensable to the everyday lives of the residents in Sendai. Along with removing debris from the tsunami and restoring the facilities and equipment at the plant, we held discussions on how to implement quick recovery. In September 2011, a restoration policy was decided to restore the plant with better functions than it had previously. It took one year to complete the design of a new plant. The plant was constructed in around three years while successfully reducing construction time from the average of ten years that are usually required to complete such projects.

A new plant with energy saving features and low environmental impact

The recovery of Minami-Gamo Wastewater Treatment Plant is
almost complete

Through installing the initial sedimentation basin and final sedimentation basin on two levels and adopting deep reactor tanks, the new facility is more compact than before; moreover, it has been built to withstand a tsunami of the size experienced in the Great East Japan Earthquake through elevating the facility to tsunami wave height T.P.+10.4m (※) and installing water-resistant doors.

Moreover, even if power is interrupted and the pumps cannot be used, a route for conducting the minimum treatment and discharge of sewage has been secured, and solar power generating equipment has also been installed. A micro-hydropower system has also been installed to limit use of electricity.

The Sendai Framework for Disaster Risk Reduction incorporates the principle of “Build Back Better”. This means that, when conducting recovery in the wake of disasters, rather than simply restoring facilities to the same state they were in before disaster, they are made even better in readiness for the next disaster. Minami-Gamo Wastewater Treatment Plant is a prime example of this principle being put into action.

※T.P. (Tokyo Peil) refers to Tokyo Bay mean sea level, which is the reference point for level surveying in Japan.

• Micro hydropower
• Solar power

Conceptual drawing of the completed wastewater treatment plant