Speciation, mass loadings, and fate of phosphorus in the sewage sludge of China

Phosphorus (P) in sewage sludge (SS) has been a concern for decades. Sludge-borne P could exacerbate eutrophication problems once released to aquatic environments. Meanwhile, sludge-borne P would be a valuable alternative source to P minerals. A comprehensive understanding of the occurrence forms and fate of P in SS is required prior to the assessment of environmental implications of sludge-borne P. In the present study, we conducted a nationwide survey on speciation of phosphorus in the SS of China. The average concentration of total phosphorus (TP) in SS was 17.3 ± 5.1 g· kg−1, of which 67.1 ± 8.9% occurred as inorganic forms. Non-apatite inorganic phosphorus constituted the major component (77.6 ± 11.4%) of inorganic phosphorus, with the rest minor portion occurring as apatite phosphorus. Organic P accounted for 26.8 ± 7.9% of TP in SS, showing an average concentration of 4.5 ± 4.2 g· kg−1. Majority of phosphorus in the SS of China occurs as labile forms, suggesting that the environmental implications of SS disposal approaches should be assessed seriously. Sewage sludge produced by China contained 1.1 × 105 t of TP in 2016, and the amount accumulated to 1.0 × 106 t since 2001. Landfill sites are the single most important fate, receiving 8.1 × 105 t of sludge-borne TP since 2001. Land application and building materials are the other two fates of sludge-borne phosphorus. Spatial-temporal variations of phosphorus in the SS of China were also discussed.