DIRECT PURIFICATION OF RIVER WATER USING THE PURIFYING ACTION OF PLANTS

摘要

The city of Yokohama has actively promoted the construction of public seweragesystem ever since the first wastewater treatment plant was placed into operation in1962. As a result, some 98.6 percent of the city's entire population of 3.34 million isnow served by the public sewerage system. The construction also brought a dramaticimprovement in the water quality of public water areas.However, even today, when virtually all parts of the city have been sewered, thequality of water in rivers and other public water areas and the natural environments onthe neighborhood level are not completely satisfactory. Citizens are looking for a highqualitywater environment. The major tasks to this end are improvement in water quality,assurance of adequate flow, and creation of nature-rich waterside sections.As such, sewage works projects in Yokohama are in the process of entering a newphase characterized by expansion of advanced treatment and countermeasures fornon-point pollution sources.To supplement these measures, it has also become necessary to incorporatetechnology for direct purification of water in rivers and other public water areas. Thepaper presents the results of testing of one such method, i.e., vegetation-basedpurification, for quantitative determination of the purifying effect.The city views rivers as precious natural space within the urbanized environment, andis vigorously promoting river improvement projects including revival of river plant life inorder to restore the rich natural habitats that were lost due to development.The testing confirmed the presence of a certain purifying action and demonstratedthat the revival of plant life would also be effective for improving water quality.The city intends to improve the water quality of public water areas through appropriatecombinations of vegetation-based and other methods of direction purification.