Fluidisation behaviour of struvite recovered from wastewater

A comprehensive characterisation of struvite particles produced from the Edmonton, AB, Canada, wastewater treatment plant was performed. The characterisation of struvite particles included the determination of intrinsic static parameters such as size, density, shape and morphology, as well as the determination of their dynamic behaviour in relation to liquid flow; this included terminal settling velocity, minimum fluidisation velocity and bed expansion characteristics for both monosized and multiparticle systems. The different sizes of struvite particles possessed almost identical dry densities and a nearly spheroidal shape. A very good correlation between average experimental terminal velocities and those predicted by the existing correlations was observed. A correlation reported in the literature was found to provide conservative values of the minimum fluidisation velocity (U_mf) for all size groups, with an average deviation of 10%. The expansion characteristics of the monodispersed struvite particle bed were well represented by the Richardson–Zaki relationship, and the expansion index for the struvite particles could be correlated with the particle Reynolds number at terminal settling velocities. Finally, for a multiparticle system, the bed expansion behaviour for struvite particles was better predicted by the serial model than by the average model.