Comparison of pollutant discharge per capita (PDC) and its relationships with economic development: An indicator for ambient water quality improvement as well as the Millennium Development Goals (MDGs) sanitation indicator

Regression analyses were conducted between water pollutants discharges per capita (PDC) and gross domestic production per capita (GDPC) of developing countries in seven international coastal and lakeside Regions. Regional groupings of PDCs and GDPC were identified with graphical analyses. The inverted-U shaped curve relationships, namely environmental Kuznets curve (EKC), were found for biological oxygen demand (BOD) discharge per capita (PDC-BOD) and total phosphorus (TP) discharge per capita (PDC-TP) with a peak at ca. US$5, 050 and US$11,200, respectively, besides lower significance for PDC-BOD. Total nitrogen (TN) discharge per capita (PDC-TN) decreased linearly with GDPC increase. Possible reasons for the different tendencies of PDC-BOD, PDC-TN and PDC-TP with GCP per capita are that nutrient removal is introduced after economic development to some extent, and main nitrogen source is blackwater especially urine in domestic wastewater. Pollutants discharges reduction should be targeted with the relevant indicators to improve the ambient water quality especially after the achievement of the sanitation millennium development goals (MDGs) because the sanitation MDGs indicator mainly targets infectious diseases, hygiene health and lifestyle improvement, and there are several kinds of domestic wastewater treatment methods in the world.