Struvite-based phosphorus recovery from the concentrated bioeffluent by using HFO nanocomposite adsorption: Effect of solution chemistry

•Struvite-based phosphorus recovery from the concentrated bioeffluent was proposed.•The absence of Ca2+ due to Donnan effect favors quick formation of high-purity struvite.•DOM and high salinity lowers the saturation index of struvite.•DOM and high salinity favors the formation of struvite of large size.

Here we reported struvite-based phosphorous recovery from the concentrated desorption effluent of a proprietary hydrated ferric oxide (HFO) nanocomposite (HFO-201) system, and the effect of solution chemistry (alkalinity, salinity, and dissolved organic matter (DOM)) on struvite formation was particularly focused on. The optimum P recovery rate (∼97%) and high quality struvite was obtained at 25 °C, pH 9.0-9.5, and the molar Mg:NH4:P ratio of 1.4:4:1. The reaction reached equilibrium within ∼30 min, much faster than the reported high purity struvite formation at neutral pH (several days required). It largely relied on the absence of Ca2+ in the desorption effluent due to the Donnon co-ion effect exerted by HFO-201. Thermodynamic modelling with Stockholm humic model revealed that the presence of salinity and DOM resulted in a lower saturation index (SI) of struvite, thus inhibiting P recovery by struvite. Nevertheless, it is favorable to form struvite of large particle size. In addition, increasing the molar Mg:NH4:P ratio from 1:1:1 to 1.4:4:1 could significantly weaken the adverse effect of the high salinity and DOM. Direct addition of Ca2+ could also result in phosphorous recovery, but the P content of the resultant solid (∼4.4%) is much lower than the formed struvite (∼17%). The results indicated that struvite process is a very attractive option to recover P from the desorption effluent, and the effect of solution chemistry is crucial to optimize the process.

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