Characterization of morphology and component of struvite pellets crystallized from sludge dewatering liquor: Effects of total suspended solid and phosphate concentrations.

A lab-scale struvite pellet crystallization system was used to study phosphorus (P) removal and recovery from sludge dewatering liquor (SDL). Influences of total suspended solids (TSS) and phosphate concentrations on P removal as well as the size, morphology, purity, and components of struvite pellets were investigated. The increase in TSS concentration resulted in not only the decreases in phosphate removal efficiency and struvite purity but also the irregular pellet morphology and broken struvite crystals. Increasing inlet PO4-P concentration enhanced PO4-P removal, average struvite pellet diameter, purity and crystal volume growth rate. Amorphous calcium phosphate (ACP), calcite, brucite and magnesium phosphate were formed as co-precipitates with struvite. However, species and quantity of co-precipitates could be variable. More calcium precipitates were easily formed at lower PO4-P concentration (48mg/L), while brucite was the main co-precipitate at higher PO4-P concentration (151mg/L). Organic compounds were involved in struvite pellets along with suspended solids during the formation of struvite. Higher TSS concentration resulted in both more species and higher contents of organic compounds in struvite pellets. Therefore, it is essential to remove suspended solids in advance so as to obtain high P-removal and harvest high-quality struvite pellets.