Influence of Process Parameters on the Characteristics of Struvite Pellets

Abstract

With an ever-increasing demand for phosphate-based fertilizer, new sustainable sources of phosphorus are warranted. Recent technologies have successfully demonstrated the possibility of recovering phosphorus from wastewater-treatment plants as struvite, which is also a ready-made, slow-release fertilizer. However, process parameters that influence the operation of crystallizers and production of good-quality struvite pellets have yet to be fully understood. This paper discusses the influence of process parameters on the characteristics of struvite pellets. Among the various process parameters, upflow velocity and flow patterns in the crystallizer were found to influence the size and shape of the pellets. In the range (1.5–7.1) tested, supersaturation ratio did not appear to influence the crushing strength of the pellets formed. Midsized pellets, in the 2.0–2.5-mm range, exhibited the highest crushing strengths. Higher magnesium concentration in the crystallizer was able to increase the crushing strength of struvite pellets by as much as 15–27%.