Long-term operation of a pilot-scale reactor for phosphorus recovery as struvite from source-separated urine

Abstract

BACKGROUND: The treatment of source separated urine allows for a more sustainable approach to nutrients recovery in actual wastewater treatment plants. Struvite precipitation from urine yields a slow-release fertilizer (struvite) with a high marketable value for agricultural use. Extensive research on struvite precipitation has been carried out at laboratory scale, but there is still a lack of specific knowledge about the operation and key parameters at larger scale and over the long term. The effectiveness of the struvite reactor was assessed, as well as the quality of the harvested struvite in terms of size and composition. RESULTS: The efficiency of recovery of P was maintained at 85-99% for 1 year of continuous operation. Phosphorus was recovered in the form of struvite with purity over 90%. Struvite was harvested as round pellets between 0.3 and 6 mm in diameter, with heavy metals concentration well below the legal limits for fertilizers in The Netherlands. The post-treatment of the reactor effluent yielded almost complete removal (>95%) of calcium and magnesium. A loss of 26 ± 5% of the influent chemical oxygen demand and 16 ± 1% of the NH 4 + -N occurred during the magnesium ammonium phosphate (MAP) precipitation and the post-treatment. CONCLUSION: This work shows how the treatment of source-separated urine by struvite precipitation in a fluidized bed reactor allows for efficient recovery of phosphorus in the form of a potential fertilizer.

Decentralized Valorization of Residual Flows as an Alternative to the Traditional Urban Waste Management System: The Case of Peñalolén in Santiago de Chile

“…The recommended operating pH range is 8.5-9.5. With struvite precipitation, 85% of the P can be recovered while N can be recovered with a molar ratio 1:1 NH 4 to PO 4 or 0.46 N to P [74,75]. Struvite obtained from urine is a clean fertilizer, does not contain any OM, and has a negligible concentration of micropollutants and metals [76].…”

Investigation of fluorapatite crystallization in a fluidized bed reactor for the removal of fluoride from groundwater

“…The saturation index (SI) was calculated according to Eqn (1): 27,28 where log IAP is the logarithm of the ion activity product calculated from the stoichiometry; Ks is the temperature-corrected thermodynamic solubility product; and SR is the supersaturation ratio. A SI greater than zero indicates that the solution is supersaturated, and a SI value 0 indicates the solution is in equilibrium or undersaturated.…”

“…A SI greater than zero indicates that the solution is supersaturated, and a SI value 0 indicates the solution is in equilibrium or undersaturated. 27 The SI at a fixed temperature of 25 ± 2 ∘ C was calculated based on Visual MINTEQ (ver. 3.1, Jon Petter Gustafsson, 2013).…”

On precipitation of struvite (MgNH4PO4.6H2O)

“…It was therefore concluded that for an effective removal of N from wastewater through struvite precipitation, Mg:NH4:PO4 should be at least unity (Rahaman et al, 2011). In most cases, agricultural wastewater is deficient in Mg, and consequently Mg must be added (Zamora et al, 2017;Kataki et al, 2016). MgCl2 is preferred since this chloride salt has higher solubility compared to other magnesium compounds such MgO and Mg(OH)2 (Zamora et al, 2017;Kataki et al, 2016).…”