D. Wild et al., P-FIXATION BY MG, CA AND ZEOLITE A DURING STABILIZATION OF EXCESS SLUDGE FROM ENHANCED BIOLOGICAL P-REMOVAL, Water science and technology, 34(1-2), 1996, pp. 391-398
Citations number
22
Categorie Soggetti
Water Resources","Environmental Sciences","Engineering, Civil
In anaerobic digestion of excess sludge originating from enhanced biol
ogical phosphorus removal (EBPR) a complete hydrolysis of polyphosphat
e occurs. Varying information exists about the resulting return flow o
f phosphorus to the activated sludge plant. Magnesium, calcium and zeo
lites from detergents are the main species involved in the refixation
of dissolved phosphate in the digester supernatant. Their interactions
and mechanisms of phosphate removal have been characterized and quant
ified in experiments. The precipitation of struvite (MgNH4PO4 . 6H(2)O
) evolves according to the equilibrium, whereas the fixation by calciu
m occurs kinetically controlled in the form of brushite (CaHPO4 . 2H(2
)O) or hydroxyapatite (Ca-5(PO4)(3)OH). Zeolites in digester sludge or
iginate mainly from detergents. They represent around 7% of total soli
ds entering the digester and their impact on digestion is given by 4 m
odes: The control of free cation concentrations as an exchanger, as a
source for calcium ions, as generator of aluminum phosphate precipitat
ion after being partly hydrolyzed and as a nucleus for crystallization
processes. With the current sludge composition phosphate fixation pro
cesses in anaerobic digesters avert serious recycle load problems. Cop
yright (C) 1996 IAWQ.