Table 141

Forms of Phosphorus in Activated Sludge

Form Percent of total P

Nucleotide-P, lipid-P, nucleic acid-P, protein-P 3128

Trichloroacetic acid-insoluble-P 13

poly-P (inorganic)29 RNA and protein (organic)30 Inorganic-P

poly-phosphate (poly-Pj) 32-4428

that process detrital organic-P or those involved in P regeneration (production of Pi from organic-P outside the cell). Little is known, for example, of the processes that depolymerize high molecular weight detrital organic-P compounds in wastewater or those that hydrolyze the phosphomonoesters to the organic subunits and Pi. These processes, however, are likely to influence overall P removal from wastewater streams.

14.3.2 Phosphatase Enzymes

PO4ase enzymes hydrolyze the P-O bond of phosphomonoesters. PO4ases are subdivided into alkaline and acid PO4ases, based on the pH at which optimum activity occurs. Alkaline PO4 function in the neutral and basic pH range, are induced at low external Pi concentrations, are localized at or near the cell surface, and hydrolyze phosphomonoester-containing organic compounds to provide cells with an alternative source of Pi. Alkaline PO4ases may also be induced under Pi-sufficient but carbon-limited conditions to meet metabolic requirements of bacterial cells. Acid PO4ases display maximum activity over the pH range of 4 to 6, are typically intracellular, and are not repressed by Pi. Alkaline PO4ase has been reported to hydrolyze inorganic poly-Pi, a P-containing storage product that accumulates in a variety of bacteria found in activated sludge.26,28,31-33 Alkaline PO4ases have been implicated in Pi release from intact bacterial cells containing poly-P storage products in anaerobic lake sediments.34 Alkaline PO4ases may participate in the degradation of cell-surface-associated poly-P, which represents a more transient but significant portion of the total poly-Pi accumulated by cells of Acinetobacter Iwoffii JW11.35 Since poly-Pi formation and degradation exerts significant control over enhanced P removal from wastewater,25,26 a better understanding of the role of extracellular bacterial PO4ases in poly-Pi degradation and detrital organic-P regeneration should lead to better control over and more efficient P removal in the activated sludge process of wastewater treatment systems.

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