Recovery Of Phosphorus From Waste Activated Sludge By Adsorption And Regeneration

Phosphorus (P) recycling happens nearly in a single direction (from mainland to water body). It is estimated that P resource from all over of the world will be used up in 100 years. However, there is potential to recycle P contained in wastewater and disposed activated sludge. The main purpose of this dissertation was to investigate P recycle. Firstly, P was released from disposed activated sludge to solution by heating and ultrasonic treatments. Then FeCl₃ was used to prepare Hydrous Iron Oxide (HIO) as an absorbent for P sorption and desorption. The performance of HIO as absorbent was investigated and P release conditions (by heating and ultrasonic treatments) were optimized.Results showed that most of the P released is phosphate; High heating temperature accelerates the equilibrating time but not the P release efficiency. With enough heating time, P release equilibrium percentage reaches 60% under different temperatures. By adding HCl to the heating system, as high as 90% of P release equilibrium percentage was obtained, and more fast release process was observed. Microscope observation showed that the microorganism cells are more completely broken up with addition of HCl than just with heating. Treated with ultrasonic vibration for 1 h, P release reaches equilibration. The higher the pH was, the easier the cells are broken and the more P is released. No evident influence of ultrasonic vibration time on P release percentage was found.HIO was used for sorption of P from sludge digestion solution. Results showed that thesorption capacity increased while the solution pH decreased. The sorption kinetics followed the second-order model, and the sorption isotherm fitted the Langmuir equation. 5% (m/v) NaOH solution was used for desorption of P from HIO, and the desorption rate reached over 98%. No relation was found between desorption rate and adsorption capacity. Summering results obtained from digestion as well as sorption-desorption processes, more than 80% of P was recovered from sludge. The same method was applied to recover P from the supernate of sludge thickener in a wastewater treatment plant of Dalian. Results showed a 90% of P recovery efficiency. Finally, an effective P removal-recovery system from municipal wastewater was put forward, which includes adsorption, desorption, regeneration processes,as well as P recovery from P-rich desorption solution.