Collaborative Development of Water Environment Quality Index in Japan

Abstract

Environmental Quality Standards (EQS) are established for water pollution control as target levels for water quality that are to be achieved and maintained in public water bodies under Basic Environment Law. The standards have two major goals: protection of human health and conservation of the living environment. The second goal is set for classified water bodies such as rivers, lakes, reservoirs, and coastal waters, based on water usage. The standard values for the living environment have been established for bio-chemical oxygen demand (BOD), chemical oxygen demand (COD), dissolved oxygen (DO), and other water parameters (Ministry of Environment, Japan; 2002). The attainment rate of the water quality standard has been the most commonly used method for evaluating water environments. Figure 11-1 shows the change of attainment rates in terms of BOD and COD as the organic pollution indicators from the first year of implementing EQS for water quality management. During the two decades of high economic growth from 1955 to 1975, the rapid spread of pollution in rivers and other bodies of water was clearly evident in urban areas. After this period, river water quality has been improved around the country through effective effluent regulation and the construction of sewerage systems with wastewater treatment plants. The increased attainment rate of BOD in rivers indicates that organic pollution has been mitigated (Ministry of Land, Infrastructure, Transport, and Tourism, Japan; 2007). Although the high attainment rate has been achieved in terms of BOD in rivers, we have realized that the state of water quality improvement and the