Wastewater Treatment Glossary: Initial Rainwater
If initial rainwater is discharged directly into natural receiving waters, it will cause very serious pollution. The early-stage rainwater must therefore be diverted and rejected. An initial-rainwater diversion and filtration device can be installed to divert the first flush of rainfall into the sewage pipeline. The later, less polluted rainwater, after suspended solids and solid particulate impurities have been intercepted by a trash-intercepting basket, can be discharged directly into natural receiving waters, effectively protecting our natural water environment.
At present the main works are complete and commissioning is about to begin. The minimum expected treatment targets for the demonstration project are a 75% reduction in the COD (chemical oxygen demand) pollutant index and 90% for suspended solids. The later-stage rainwater utilisation design takes the form of a Taihu-style landscape, embodying the expectation that water quality in the Taihu Basin will improve after initial-rainwater treatment. Once completed, the initial-rainwater demonstration project will reach a leading domestic level, and it is of typical and replicable significance for road rainwater treatment over large catchment areas in southern Jiangsu. [1]
As a demonstration project under a sub-topic of the National Major Water Pollution Control Programme of the 11th Five-Year Plan, initial-rainwater treatment attempts to solve the problem of non-point-source pollution from urban road rainwater runoff, making up for the long-standing neglect of non-point sources in favour of point sources, and creating a new highlight of the "Clear Water Project" through scientific and technological innovation. The initial-rainwater treatment demonstration project carried out by the Changzhou Drainage Authority together with Huazhong University of Science and Technology [2] has achieved initial results.
To address the bottlenecks common to domestic rainfall-runoff pollution control projects — large land footprint, relatively low efficiency, easy clogging and unstable operation — the demonstration project selected the Jinling Middle Road rainwater pumping station area on the Beitang River, collecting and treating on site the rainfall runoff from roughly 12,000 m² of the first 5 mm of rainfall on the ground along Jinling Middle Road. Small as it is, it is complete in every detail, and the design is highly ingenious. Road rainwater is collected through stormwater pipes into the Jinling rainwater pumping station and diverted to a 45 m³ initial-rainwater separation tank for storage; controlled by pumps, it is then conveyed to a purpose-built cyclone separator. After separation, the sewage is sent directly to the municipal sewage pipeline and on to the wastewater treatment plant for centralised treatment, while the rainwater enters a "stepless-speed" controllable rapid filtration system lined with quartz sand and pebbles for rapid filtration and deep adsorption. The final effluent flows into a constructed wetland, a Taihu-style landscape pond and an artificial cascade landscape, with research on the ecological use of rainwater carried out in parallel — making clever use of rainwater to realise resource recycling. [1]
Demonstration project for rainfall-runoff pollution control
