Factors Affecting the Crystal Size of Struvite-K Formed in Synthetic Urine Using a Stirred Reactor

Abstract

The crystallization of struvite-K (MgKPO4·6H2O) can simultaneously recover phosphate and potassium from source-separated urine. However, its crystal size has been rarely reported despite significantly affecting the crystallizer performance. Experimental results show that the average size of struvite-K was 15–63 μm in ammonium-depleted synthetic urine under the examined conditions with a stirred reactor. A low supersaturation ratio (S r) or the same S r induced by low pH and high Mg:P ratio resulted in large crystal size. Large crystals also formed at high agitation speed, small feed volume, or feeding close to the stirring impeller. The size distribution of struvite-K crystals was predicted using the coupling resolution of the population balance equation to on-site turbidity measurement. The estimated kinetic parameters quantitatively described the nucleation and crystal growth of struvite-K under different conditions of supersaturation, feeding, and mixing. This work proposes approaches to obtain large crystals while reducing fines of struvite-K.

Sustainable sanitation- how can we improve sanitation systems in the global south?

“…Struvite precipitation is the most concerned phosphorus recovery technology which can also simultaneously recover part of ammonium from urine (Krähenbühl et al, 2016;Zamora et al, 2017;Wei et al, 2018;Zheng et al, 2018;Aguado et al, 2019;Pinatha et al, 2020;Oztekin et al, 2022). The precipitation of struvite-K, an analogue of struvite, can simultaneously recover phosphate and potassium from ammonium-depleted urine (Xu et al, 2011;Xu et al, 2012;Xu K. et al, 2015;Xu et al, 2017;Zhang et al, 2017;Zhang et al, 2018;Huang et al, 2019). Furthermore, phosphate can also be recovered by the precipitation of calcium phosphate (Pradhan et al, 2017).…”

Pathogens inactivation in nutrient recovery from urine: A review

“…Struvite precipitation is the most concerned phosphorus recovery technology which can also simultaneously recover part of ammonium from urine (Krähenbühl et al, 2016;Zamora et al, 2017;Wei et al, 2018;Zheng et al, 2018;Aguado et al, 2019;Li P. et al, 2019;Pinatha et al, 2020;Oztekin et al, 2022). The precipitation of struvite-K, an analogue of struvite, can simultaneously recover phosphate and potassium from ammonium-depleted urine (Xu et al, 2011;Xu et al, 2012;Xu K. et al, 2015;Xu et al, 2017;Zhang et al, 2017;Zhang et al, 2018;Huang et al, 2019). Furthermore, phosphate can also be recovered by the precipitation of calcium phosphate (Pradhan et al, 2017).…”

Recovery of Phosphorus from Waste Water Profiting from Biological Nitrogen Treatment: Upstream, Concomitant or Downstream Precipitation Alternatives

“…The crystal size of the MPP formed is a critical aspect in view of its subsequent use. By optimising process operation parameters related to supersaturation, feeding, and mixing, larger crystals can be obtained [223,224]. Moreover, a downstream dewatering step can be advisable to prevent excess of fines in the water line, while improving the agglomeration of the precipitated material [81].…”