Co-precipitation of heavy metals with struvite from digested swine wastewater: Role of suspended solids

Struvite production can recover ammonia and phosphorous from digested wastewater as fertilizer. During struvite generation, most of the heavy metals was co-precipitated with ammonia and phosphorous into struvite. Understanding the precipitation behavior of heavy metals with suspended solids (SS) might provide the possible strategy for the control of co-precipitation. In this study, the distribution of heavy metals in SS and their role on the co-precipitation during struvite recovery from digested swine wastewater were investigated. The results showed that the concentration of heavy metal (including Mn, Zn, Cu, Ni, Cr, Pb and As) ranged from 0.05 to 17.05 mg/L in the digested swine wastewater. The distribution analysis showed that SS with particles > 50 μm harbored most of individual heavy metal (41.3–55.6%), followed by particles 0.45–50 μm (20.9–43.3%), and SS-removed filtrate (5.2–32.9%). During struvite generation, 56.9–80.3% of individual heavy metal was co-precipitated into struvite. The contributions of SS with particles > 50 μm, 0.45–50 μm, and SS-removed filtrate on the individual heavy metal co-precipitation were 40.9–64.3%, 25.3–48.3% and 1.9–22.9%, respectively. These finding provides potential way for controlling the co-precipitation of heavy metals in struvite.