Removal and recovery of N, P and K from urine via ammonia stripping and precipitations of struvite and struvite-K

Abstract

This study investigated the recovery of N, P and K from source-separated urine in laboratory-scale combined processes of air stripping and precipitation. Two operation scenarios were carried out to recover N/P (named partial scenario) and N/P/K (named complete scenario). Most of the nutrients were recovered (>70%) by optimising the operation parameters including the increase of air flow rate and more dosages of the sources of Mg and P. Absorbent rich in ammonium sulphate and solid precipitates including struvite, struvite-K, and struvite-Na was produced. The simultaneous recovery of P and K was the key process to determine the substance input. The ratio of substance input to nutrient recovered (PO and KO) was 4.14 in the partial scenario, whereas it increased to 10.61 in the complete scenario. The inevitable co-precipitation of struvite-Na mainly responded for the lower economic efficiency of the complete scenario.

Integrated, multi-process approach to total nutrient recovery from stored urine

“…However, due to the elemental composition of K-struvite additional chemical input of Mg 2+ and P is required for effective K recovery. 28,30 TAN recovery by ammonia stripping-acid absorption 32,34,35 and TP recovery by struvite precipitation 21,25,27,[36][37][38][39][40][41][42][43][44][45][46][47][48][49][50] have been studied extensively to recover a significant portion of N and P in urine. For example, major conclusions from previous research include >95% TP recovery using MgCl 2 and >90% TAN recovery by increasing the pH and temperature of the solution.…”

“…For example, major conclusions from previous research include >95% TP recovery using MgCl 2 and >90% TAN recovery by increasing the pH and temperature of the solution. The gap in knowledge lies in the few studies that combine N and P treatment in series to produce separate N and P products, 30,31,[51][52][53][54] and minimal research on treatment processes to recover N, P, and K at significant concentrations. 30,55,56 For example, major conclusions on treatment processes to recover N, P, and K include a lack of significant N and K recovery via precipitation without the equimolar addition of P and Mg 2+ to N or K + in solution.…”

“…However, the precipitation of K-struvite is not likely until N is depleted to concentrations below K from urine. [27][28][29][30] Consequently, a significant portion of N and K remain in the solution after the struvite precipitation process.…”

Membrane stripping enables effective electrochemical ammonia recovery from urine while retaining microorganisms and micropollutants

“…Most recovery technologies are based on stripping via volatilization of ammonia (NH3) from the liquid waste stream through an increase in pH and/or temperature (Arredondo et al 2017, Böhler et al 2015, Christiaens et al 2017, Vanotti et al 2017, Xu et al 2017)(SI Table A.1). In general, the higher the NH3 concentration, pH, and temperature, the more efficient the recovery technology will be.…”

“…In all these technologies, NH3 is often recovered in strong acidic absorbents (e.g. H2SO4 or HNO3) (Arredondo et al 2017, Bernal et al 2016, Böhler et al 2015, Christiaens et al 2017, Vanotti et al 2017, Xu et al 2017. This increases the pH gradient and thus vapor pressure gradient between the alkaline NH3 solution and the absorbent.…”