Regional footprints and interregional interactions of chemical oxygen demand discharges in China

Chemical Oxygen Demand (COD) is a key indicator of pollutants in waste water from the agricultural, industrial and household sectors and its abatement has become a key requirement in China. However, the distribution of COD discharge and fresh water resources varies throughout China. Understanding the spatial pattern and factors influencing regional COD discharge in China is vital to efforts in reducing regional discharges. Towards this end, using a multi-regional input-output model (MRIO), this research quantifies the domestic COD footprints (CODF) for individual regions and their interactions in 2010. Our results reveal that China's COD discharges were primarily from the agricultural sector, with a secondary contribution from the household sector. Of the 30 provinces studied, some eastern coastal provinces with large CODF, e.g., Shanghai, Tianjin and Jiangsu, were net interregional importers. The CODF per capita for the studied regions varied based on the final demand, lifestyle affluence, and availability of pollution-treatment infrastructure. The virtual COD flow patterns were divided into agricultural and industrial discharge, whereby the former flow transfers crossed long distances between the western and eastern regions of China. A comparison of the regional COD flows and their water resources characteristics suggests that Chinese policymakers should design and implement a holistic national plan to reduce the country's total COD discharge based on supply- and demand-side responsibilities − especially in net exporter regions that lack fresh water. Furthermore, a reduction in the demand for pollution-intensive products and an increase in the demand-side reuse and recycling of resources is vital.