Selective release of phosphorus from waste-activated sludge by low-temperature thermal treatment: comparative study with ultrasonic treatment

Abstract

AbstractPhosphorus (P) is a limited and irreplaceable resource and its recovery has become critical for sustainable society. Waste-activated sludge (WAS) is an important source for P recovery. For selective release of P, thermal treatment at low temperature (50–80°C) was applied to WAS and the release characteristics of P, nitrogen (N), and organic compounds were investigated. Thermal treatment showed that P release is positively associated with temperature and treatment time. Thermal treatment of sludge at 50–80°C released 25–32% of total P (T-P) in 2 h. Inorganic phosphate (Pi) release was 19–22% of the T-P in the sludge, while polyphosphate (poly-P) release was 2–9% of the T-P at 50–80°C. Pi was the dominant P compound (85% of the released T-P) in the supernatant at 50°C and its proportion decreased to 56% at 80°C, while the proportion of poly-P in the supernatant increased at higher temperature. During the initial 30 min of thermal treatment at 50°C, the amount of released N exceeded that of P at 80°C...