In situ and short-time anaerobic digestion coupled with alkalization and mechanical stirring to enhance sludge disintegration for phosphate recovery

In situ and short-time anaerobic digestion coupled with alkalization and mechanical stirring was studied to enhance sludge (especially high-inorganic sludge) disintegration for phosphate recovery. Anaerobic digestion batch experiments with varying conditions were carried out. It was observed that high initial pH values (e.g. 9, 10, 12 and 13) in conjunction with mechanical stirring resulted in effective sludge disintegration. Results showed that mechanical stirring mainly worked as the role of uniform mixing for better material exchange and bacteria contact, but without the function of vortex shear force for cell wall breaking. Bacterial effects contributed less and less to phosphate recovery from sludge as alkalization increased, indicating that chemical effects have a more significant role during operation. Meanwhile, almost all insoluble non-apatite inorganic phosphorus was dissolved back into the supernatant with alkalization and mechanical stirring. Therefore, compared with other sludge disintegration methods, in situ and short-time anaerobic digestion coupled with alkalization and mechanical stirring is economical and practical, requiring only 7 days for sludge disintegration, especially with optimum alkalinity (pH 9 & 10).