title: Modeling phosphorus removal and recovery from anaerobic digester supernatant through struvite crystallization in a fluidized bed reactor.
abstract: The cost associated with the disposal of phosphate-rich sludge, the stringent regulations to limit phosphate discharge into aquatic environments, and resource shortages resulting from limited phosphorus rock reserves, have diverted attention to phosphorus recovery in the form of struvite (MAP: MgNH4PO4·6H2O) crystals, which can essentially be used as a slow release fertilizer. Fluidized-bed crystallization is one of the most efficient unit processes used in struvite crystallization from wastewater. In this study, a comprehensive mathematical model, incorporating solution thermodynamics, struvite precipitation kinetics and reactor hydrodynamics, was developed to illustrate phosphorus depletion through struvite crystal growth in a continuous, fluidized-bed crystallizer. A thermodynamic equilibrium model for struvite precipitation was linked to the fluidized-bed reactor model. While the equilibrium model provided information on supersaturation generation, the reactor model captured the dynamic behavior of the crystal growth processes, as well as the effect of the reactor hydrodynamics on the overall process performance. The model was then used for performance evaluation of the reactor, in terms of removal efficiencies of struvite constituent species (Mg, NH4 and PO4), and the average product crystal sizes. The model also determined the variation of species concentration of struvite within the crystal bed height. The species concentrations at two extreme ends (inlet and outlet) were used to evaluate the reactor performance. The model predictions provided a reasonably good fit with the experimental results for PO4-P, NH4-N and Mg removals. Predicated average crystal sizes also matched fairly well with the experimental observations. Therefore, this model can be used as a tool for performance evaluation and process optimization of struvite crystallization in a fluidized-bed reactor.
authors.affiliation: Department of Building Civil and Environmental Engineering, Concordia University, 1455 de Maisonneuve Blvd, West, EV-6.139, Montreal, Quebec, Canada H3G 1M8. Electronic address: saifur.rahaman@concordia.ca.
authors.forename: Md Saifur
authors.initials: MS
authors.lastname: Rahaman
authors.affiliation: Pollution Control & Waste Management Group, Department of Civil Engineering, University of British Columbia (UBC), 2002-6250 Applied Science Lane, Vancouver, BC, Canada V6T 1Z4.
authors.forename: Donald S
authors.initials: DS
authors.lastname: Mavinic
authors.affiliation: Department of Building Civil and Environmental Engineering, Concordia University, 1455 de Maisonneuve Blvd, West, EV-6.139, Montreal, Quebec, Canada H3G 1M8.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Meikleham
authors.affiliation: Fluidization Research Centre, Department of Chemical & Biological Engineering, University of British Columbia (UBC), 227-2360 East Mall, Vancouver, BC, Canada V6T 1Z3.
authors.forename: Naoko
authors.initials: N
authors.lastname: Ellis
mesh_terms: D000693:Anaerobiosis; D019149:Bioreactors; D003460:Crystallization; D057446:Hydrodynamics; D007700:Kinetics; D017616:Magnesium Compounds / Q000302:isolation & purification*; D008954:Models, Biological; D010710:Phosphates / Q000302:isolation & purification*; D000069877:Struvite; D013816:Thermodynamics; D014865:Waste Disposal, Fluid / Q000295:instrumentation / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D018508:Water Purification / Q000295:instrumentation / Q000379:methods*
chemical_list: D017616:Magnesium Compounds; D010710:Phosphates; D014874:Water Pollutants, Chemical; D000069877:Struvite
keywords: Crystallization; Fluidized bed; Modeling; Phosphorus recovery; Struvite