Policies on combined sewer overflows pollution control: A global perspective to inspire China and less developed countries

Combined sewer overflows (CSOs) are of major concern for urban water environment restoration that draws worldwide attention. The enaction of related policies, regulations, guidelines and criteria forms a crucial foundation for CSO control and management. Some developed countries, such as the US and European countries, are leading the CSO control and management worldwide and have developed a relatively completed legislative framework. Despite great efforts made worldwide, the existing combined sewer systems and severe illicit sanitary sewer connections to storm sewers still result in urban wet-weather flows (UWWF) pollution which is similar to or even more detrimental than CSOs, deteriorating receiving water bodies, particularly in developing countries. This article aims to review the history and evolution of CSO-related policies, regulations, permits, criteria, technical guidances and measures in typical developed countries to guide the UWWF pollution control and management in latecomers. It was found that the US has formed a complete system from national policies to states' control practices and proceeded to a green development stage. European countries have transitioned CSO control targets toward meeting water quality standards. In comparison, Japan and South Korea attach importance to end-of-pipe treatment and sewer management. On this basis, recommendations were proposed for long-term UWWF control and management in China. This is also expected to guide the enactment of related policies and regulations in less developed countries facing serious UWWF pollution.