Environment Kuznets Curve (EKC) Relationships between Pollutant Discharge Per Capita (PDC) of Domestic Wastewater and Income Indicators

Relationships between domestic wastewater pollutant discharges per capita (PDCs) and economic development indicators were discussed in this paper. Chronological relationships of PDCs (CODMn, TN and TP) with income indicators in the drainage area of Lakes Shinji and Nakaumi in 1955-93 showed statistically significant inverted U-shaped curve, namely environmental Kuznetz curve (EKC). CODMn discharge per capita (PDC-CODMn) in 47 prefectures in Japan in 2004 spatially had one-order relationship with an income index, which was regarded as the latter portion of the EKC. However, significant relationships were not observed for TN and TP discharges per capita (PDC-TN and PDC-TP), which should reflect area-specific regulations on the nutrients discharge. Graphical distribution of PDC-BOD and PPP-GNI per capita in developing countries in coastal areas in 2000±2 showed grouping of the coutries by each region. The relationship between BOD discharge per capita (PDC-BOD) and purchase power parity based gross national income (PPP-GNI) per capita showed that PDC-BOD were in wide range when PPP-GNI per capita was smaller and in narrow range when PPP-GNI per capita was larger. The relationship between PDC-BOD and newly introduced water, sanitation and economic parameter (WSEI) showed the same tendency. The transition levels were US$ 3,000-4,000 for PPP-GNI and 1.0 for WSEI. These relationships were similar to the original Kuznets relationship of economic growth and income inequality