Sewerage Systems Office

The Gravel Contact Aerated Oxidation Method was imported from Japan many years ago. In addition to absorbing organic pollutants by bio-membrane, gaps in the stacked gravel is another mechanism for removing pollutants. Suspended solids in the sewage are filtered off when flowing through gaps between gravels; turbid water is thereby clarified; a cleaning method learnt from nature.

In order to speed up the water quality improvement of Keelung River, Tamsui River and Xindian River, five on-site Gravel Contact Aerated Oxidation Facilities have been constructed using limited high marsh areas outside the riverbank of these rivers at the end of rainwater drainage systems for intercepting rainwater from urban areas; including 2 for Keelung River: Nanhu and Chengmei; 2 for Tamsui River: Guiyang and Zhongxiao; and 1 for Xindian River: Jingmei.

These facilities are constructed underground, mainly using natural gravels as the purification materials. They mainly consist of Intake Weir, Sedimentation Pool, Pumping Well and Sludge Tank; dense aeration tubes are provided inside the process tank, significantly benefiting odor removal. Sewage entering the facility is clarified by absorption and decomposing processes; it becomes so clear before being discharged into the river that no impurities can be seen. This is how the river water quality improves.

Since these facilities are built underground, their superstructure can be used for sport and leisure activities of citizens. Visitors are allowed to enter the central underground corridor, where environmental education can be achieved by letting people view from a short distance how sewage is purified by the gravel.

1. After entering the facilities, large solids in the diverted sewage are first removed by a Fine Bar Screen. Effluent from the Fine Bar Screen then enters Gravel Contact Aerated Oxidation Facility for removing organics.It is discharged into river. The sludge is discharged into the sludge storage tank and regularly transported to the location designated by the agency.
2. The purification mode of the contact aeration oxidation tank is that the sewage entering the treatment facility first passes through the aeration area through the biofilm adsorption and microbial decomposition of organic pollutants on the surface of the natural gravel, and then flows into the non-aeration area to remove suspended solids in the water. The gravel blocks sedimentation and turns the turbid water into clear water, which is a purification effect imitating nature.