Phosphatase activity in anaerobic bioreactors for wastewater treatment

Phosphatase (PO4ase) activity was investigated in continuous and fed-batch anaerobic bioreactors for wastewater treatment. PO4ase levels were high in continuously fed reactors (880–2632 μmol/L/h), compared to a fed-batch reactor (FBR) (540–1249 μmol/L/h). Alkaline and acid PO4ases were present in all the reactors, but in varying magnitudes and total PO4ase activity exhibited a 10–30% variation even at steady-state reactor conditions. The PO4ase activity was not affected by the inorganic phosphate (Pi) level in the reactors, but biomass level and wastewater type, including specific PO4ases (either alkaline or acid), strongly influenced the PO4ase activity in a reactor. Both flocculated and suspended cells produced PO4ase, and 60–65% of the enzyme was cell bound, remaining entrapped in the extracellular matrix and in cell-free form. Batch studies with anaerobic sludge showed a negative correlation between Pi and PO4ase activity. An increase in PO4ase activity was observed under starvation and higher salinity (above 15 g/L). Glucose and propionate (at 10 mM level) induced PO4ase activity, whereas acetate and butyrate (10 mM) addition had no response. This study also reveals that Archaea and bacteria contributed 45% and 55%, respectively, of total PO4ase activity in anaerobic sludge.