Long-term stability of an enhanced biological phosphorus removal system in a phosphorus recovery scenario

Phosphorus recovery is usually based on the chemical precipitation of struvite from the supernatant comming from anaerobic digestion of surplus sludge of wastewater treatment plants. However, the recovery of phosphorus from the mainstream would be very beneficial to the operation of the plant. This work represents a step forward in this challenge. The configuration of a sequencing batch reactor performing Enhanced Biological Phosphorus Removal (EBPR) was modified to include the extraction of a P-rich supernatant after a settling period. The liquid extracted after the anaerobic phase has the highest phosphorus concentration in all the reactor cycle and is therefore suitable for implementing P-recovery strategies. This is the first experimental system operated under this configuration and in a long-term basis (more than one year) under different influent COD/P ratios with good performance and stability. This work shows experimentally that up to 60% of the P could be extracted without a deleterious effect on EBPR. The system could even operate at high COD/P ratio (7.5) with high activity. Finally, anaerobic supernatant extraction was linked to anaerobic sludge purging and it was demonstrated that higher methane production (24.3%) was obtained compared to the default case with the sludge purged at the end of the aerobic phase.