To reduce intra-plant nutrient cycling and recover phosphorus (P) fertilizers from nutrient-rich sidestreams, wastewater utilities increasingly elect to employ struvite precipitation processes without a clear understanding of the inherent tradeoffs associated with specific design and operating decisions. Specifically, the impact of reactor conditions on struvite crystallization rate and distribution between formation of fines particles and secondary growth onto large diameter seed crystals represent critical knowledge gaps limiting the predictive capabilities of existing process models. In this work, the relative impacts of initial supersaturation (S_i) and seed loading on P removal kinetics and struvite solids distribution were investigated. In experiments conducted at different levels of initial supersaturation (1.7–2.4) and seed loading (0–25 g L⁻¹), struvite fines represented the majority of phosphate solids formed in 10 of 12 conditions. While total P removal was dependent on S_i, and primarily attributed to formation of fines, the concentration of struvite seed granules had a significant impact on the rate of P removal. Struvite seed granules increased the rate of precipitation by reducing induction time of primary nucleation of struvite fines. Secondary crystal growth represented the majority of struvite solids formed at high seed loading and low S_i, but presented the tradeoff of low total removal and low rate of removal. To convey the significance of these findings on process modeling, we show how a prominent kinetic model with a first order dependency on solid struvite concentration over-predicts P removal rate when total mass is dominated by large diameter seeds (0.9 mm). This works reveals the critical role of struvite fines in P removal and highlights the need to account for their production and kinetic importance in struvite process design and operation.

为了减少植物内的养分循环并从富含养分的侧流中回收磷（P）肥料，污水处理厂越来越多地选择采用鸟粪石沉淀工艺，而没有清楚地了解与特定设计和操作决策相关的内在取舍。具体而言，反应器条件对鸟粪石结晶速率以及细粒形成与二次生长到大直径晶种之间的分布之间的影响代表了关键的知识差距，限制了现有工艺模型的预测能力。在这项工作中，初始过饱和的相对影响（S _i）和种子负荷对磷去除动力学和鸟粪石固体分布的影响。在不同的初始过饱和度（1.7–2.4）和种子装载量（0–25 g L ^-1）下进行的实验中，鸟粪石细粉代表了在12种条件中的10种条件下形成的大部分磷酸盐固体。尽管总磷的去除取决于S _i，并且主要归因于细粉的形成，鸟粪石种子颗粒的浓度对磷的去除率有显着影响。鸟粪石种子颗粒通过减少鸟粪石细粉初级成核的诱导时间而增加了沉淀速率。二次晶体的生长代表了在高种子负荷和低S _i下形成的鸟粪石固体的大部分。，但提出了较低的总清除量和较低的清除率的折衷方案。为了传达这些发现对过程建模的意义，我们显示了当总质量以大直径种子（0.9毫米）为主导时，对固态鸟粪石浓度具有一级依赖性的显着动力学模型如何预测磷的去除速率。这项工作揭示了鸟粪石细粉在磷去除中的关键作用，并强调了在鸟粪石工艺设计和操作中需要考虑其产量和动力学重要性的需求。