Strengthening aerobic granule by salt precipitation.

Structural stability of aerobic granules is generally poor during long-term operation. This study precipitated seven salts inside aerobic granules using supersaturated solutions of (NH 4 ) 3 PO 4 , CaCO 3 , CaSO 4 , MgCO 3 , Mg 3 (PO 4 ) 2 , Ca 3 (PO 4 ) 2 or SiO 2 to enhance their structural stability. All precipitated granules have higher interior strength at ultrasonic field and reveal minimal loss in organic matter degradation capability at 160-d sequential batch reactor tests. The strength enhancement followed: Mg 3 (PO 4 ) 2 = CaSO 4 > SiO 2 > (NH 4 ) 3 PO 4 > MgCO 3 > CaCO 3 = Ca 3 (PO 4 ) 2 > original. Also, the intra-granular solution environment can be buffered by the precipitate MgCO 3 to make the aerobic granules capable of degradation of organic matters at pH 3. Salt precipitation is confirmed a simple and cost-effective modification method to extend the applicability of aerobic granules for wastewater treatments. [ABSTRACT FROM AUTHOR]