Relationships between water pollutant discharges per capita (PDCs) and indicators of economic level, water supply and sanitation in developing countries

Water pollutant discharges per capita (PDCs) as indicators to evaluate quantitatively domestic wastewater pollutant discharges to the ambient water were applied to eight international coastal zones and lakeside regions. Statistical analyses were conducted to find the relationships between PDCs and water, sanitation and economic parameters including purchase power parity based gross national income (PPP-GNI) per capita, proportions of access to safe drinking water and appropriate sanitation, domestic water usage amount, and integrated parameters of water, sanitation and economic indicators (WSEI1, 2). Two of the important findings from the regression analyses results were PDC-BOD correlated with PPP-GNI per capita with 3rd-order regression, and PDC-TP correlated with WSEI1 positively with 10% significance, besides smaller adjusted regression coefficients. t-values of partial regression coefficients between PDC-TP and WSEI2 increased in the most analyses cases compared to those between PDC-TP and WSEI1, which showed improvement of the indices. Empirical estimations were also conducted based on the regression analyses results and distributions of PDCs and PPP-GNI per capita on the graphs. Six components generated by the principle component analysis (PCA) contributed 99% of the parameters. The first component represented access to sanitation, second one represented household connection of safe drinking water, third one represented areal equipment of water supply in urban area, fourth one represented domestic water usage amount, fifth one represented areal equipment of water supply, and sixth one represented income per capita and sanitation. Although some statistically significances of the multiple linear regression analysis were observed, the relationships between PDCs and the water supply parameters were considered as complicated in regards to areal equipment and household connection, and in whole country and in urban area. Possible chronological relationships between PDC-BOD and water supply equipment were considered based on the results of the multiple linear regression analyses and PCA. Based on the considerations of the water pollutant discharges and the economic related parameters relationships, domestic wastewater treatment facility deployments and improvements on pollutant discharges reduction for the water quality improvement in the receiving water bodies were recommended, which would lead the relationship curves between the water, sanitation and economic related indicators and PDCs to move downward.