A 20-year shift in China's sewage sludge heavy metals and its feasibility of nutrient recovery in land use

Recycling resources from wastewater is even more important for developing a more sustainable society. Disposing sewage sludge, which accumulates most pollutants and resources in sewage, is the main challenge in wastewater pollution control and resource utilization. Heavy metals (HMs) are the greatest constraint limiting the application of sewage sludge to land as a sustainable use of this material. We conducted a meta-analysis of the concentrations of HMs in Chinese sewage sludge by combining data from studies published from 2000 to 2019 (N = 8477). Over this period, the reported concentrations of HMs in sewage sludge declined in three stages (a fluctuating stage, a slight decrease stage, and a rapid and stable decrease stage). The results revealed that economic development and environmental policy implementation were the main factors mitigating HM pollution in sewage sludge in China. Moreover, if environmental regulations were strengthened and HM pollution-mitigation strategies were made consistent, such that the proportion of sewage sludge applied to land in China could be increased from 18.6% to 48.0% (the proportion applied to land in the United States), the ecosystem services analysis showed that huge ecological-economic benefits could be realized (3.1 billion Chinese Yuan) and the use of fertilizers could be substantially reduced (the use of nitrogen fertilizers by 8.5% and the use of phosphate fertilizers by 18.1%). This review shows that China should formulate a unified policy and inter-departmental committee for sustainable application of sewage sludge to land and wastewater resource recycling management.