Struvite precipitation for ammonium removal from anaerobically treated effluents

• Struvite precipitation process in anaerobically treated effluents was investigated.
• Without pH adjustment, best sources were Na3PO4·12H2O, MgCl2·6H2O and MgSO4·7H2O.
• Struvite precipitation with an Mg:NH4:PO4 ratio of 1:1:1 removed 95% of NH4+ in 30 s.
• The residual NH4+ decreased linearly as the Mg:NH4:PO4 ratio increased.
• For a specific Mg:NH4:PO4 ratio, the NH4+ removed was similar for all effluents.

The main objective of this research was to study the struvite precipitation process in relation to ammonium removal from anaerobically treated effluents. For this purpose, we investigated how the process was affected by the source of PO43− and Mg2+, temperature, effluent solid content and Mg:NH4:PO4 molar ratio. Use of Na3PO4·12H2O and MgCl2·6H2O without pH adjustment, for an effluent initially containing 2500 mg NH4+ L−1 and an Mg:NH4:PO4 molar ratio of 1:1:1, 95% of the NH4+ was removed in only 30 s. The efficacy of the process was not significantly affected by temperature (4, 22 and 35 °C) or by prior centrifugation of the effluent. As the molar ratio of Mg:NH4:PO4 was increased, the residual NH4+ in the effluents decreased, and for a specific Mg:NH4:PO4 molar ratio, similar amounts of NH4+ were removed from all of the effluents studied. Thus, the amounts of Mg2+ and PO43− required to achieve a specific residual NH4+ content in the supernatant can be estimated for this type of anaerobically treated effluent if the initial NH4+ concentration is known.