Application of WASP model and Gini coefficient in total mass control of water pollutants: a case study in Xicheng Canal, China

Abstract

The main objective of this study was to apply the water quality analysis simulation programme to develop total mass control of pollutant (TMCP) programmes by calculating the water assimilative capacities for chemical oxygen demand (COD) and ammonia nitrogen (NH₃-N) of a river that connects the Taihu Lake and the Yangtze River. Based on the distribution of water assimilative capacities, the geographical distribution of the pollutant permitted discharge load was validated by calculating the Gini coefficients for the economic, social and environmental efficiencies. According to the validation results, pollutant permitted discharge load was reallocated between townships and the rates of the reductions in pollutants for each township in the watershed were calculated. The water assimilative capacities of COD and NH₃-N of Xicheng Canal watershed were calculated as 4803 ton/yr and 186 ton/yr, respectively. The results for the reallocation of pollutant permitted discharge load between townships indicated that the reduction in COD was small, with only 11.2% reduction for Qingyang Town and 33.6% for Chengjiang Town. In contrast, the NH₃-N reductions of Yuecheng Town, Nanzha Town, Qingyang Town and Chengjiang Town were 52.9, 40.0, 61.4 and 54.5%, respectively, while the total reduction for Xicheng Canal watershed reached 53.5%. Based on the case, a new TMCP framework for allocating the pollutant permitted discharge loads in rivers was established, which not only combined the total mass of pollutant with the water quality but also took account for equity and efficiency in the allocation of pollutant permitted discharge loads.

Keywords:

• WASP
• Gini coefficient
• Water assimilative capacity
• Pollutant permitted discharge load
• Water quality

Acknowledgements

This work was supported by the project of science and technology of Zhejiang Province for environmental planning team building (2012F20018) and the National Key Science and Technology Project: Water Pollution Control and Treatment (No. 2012ZX07506-006).