A thermochemical approach for struviteprecipitation modelling from wastewater

摘要

The cost of environmental protection and pollution prevention is increasing,above all because of stringent effluent quality standard. In that context, phosphate impacton water pollution plays a major role.This work addresses the problem of phosphorus recovery from wastewater byprecipitation of struvite which is chemically known as magnesium ammonium phosphatehexahydrate MgNH4 PO4 .6H2 O. A thermodynamic model for phosphate precipitation isproposed involving Davies activity coefficients.The model aims to determine the phosphate conversion rate and is based on numericalequilibrium prediction of the study system Mg-NH4 -PO4 -6H2 O. The parameters include thesolubility product of struvite.The mathematical problem is represented by a set of nonlinear equations that turns out tobe hard to solve, mainly due to the various order of magnitude of the involved variables.These equations have first been solved by a Genetic Algorithm strategy to perform apreliminary search in the solution space. The procedure helps to identify a good initializationpoint for the subsequent Newton-Raphson method.The model developed in this study will be used for validation and determination of processoperating conditions for struvite precipitation in an agitated reactor.