Effect of suspended solids and its role on struvite formation from digested manure

BACKGROUND: Phosphorus (P) resources are limited, and to assure its supply, efforts must be focused on P-recovery rather than its removal. In this sense, manure is a mining opportunity for nutrient recovery, for example, when recovered as struvite. However, manure treatment is challenging due to its characteristics, such as the solids content, one of the main hindrances to struvite formation. Many researchers have setablished a limit value of 1 g of total suspended solids (TSS)·L−1 to avoid interferences with struvite precipitation. Despite this, few studies have focused on the effect of solids on struvite formation. RESULTS: This study identified the role of solids in struvite nucleation and growth, and its interaction. The viability of struvite recovery from digested manure is ensured, even at high concentrations of solids (from 1 to 3 g TSS L−1), recovering more than 95% of the phosphorus as struvite. The results showed that solids not only did not interfere on struvite formation, but also played an important role during struvite crystallization, acting as nuclei favoring heterogeneous nucleation. CONCLUSIONS: Suspended particles favored the aggregation and/or agglomeration of struvite crystals, forming crystal nets and recovering bigger crystalline structures. The presence of solids on the recovered product might be beneficial for meeting crop demands and maintaining or restoring soil fertility, while applying an excellent slow-release fertilizer. .