Influence of pH and Temperature on Struvite Purity and Recovery from Anaerobic Digestate

The precipitation of struvite (MgNH4PO4.6H2O) from wastewater streams simultaneosuly recovers nitrogen (N) and phosphorus (P) for reuse as fertilisers. Struvite crystallisation is controlled by pH, saturation index, temperature other ions in the solution (e.g., Ca2+, Mg2+ CO32?). This work studies effect pH on removal via quality resulting precipitate product (i.e., crystal size, morphology purity). was precipitated batch reactors supernatant produced during anaerobic sludge dewatering at a treatment works, under (8, 9 10) (25, 33 40 °C) conditions. optimal P struvite, reduction co-precipitation with Ca increase particle size precipitates were determined. results showed that temperatures °C are not recommended precipitation—i.e., purity lower, ammonia losses induced volatilisation. At all pH-tests, efficiency >93%, but highest phosphate content obtained 9.0. optimum formation large crystals (84 µm) high (>70%) 25 °C, respectively.