Critical conditions of struvite growth and recovery using MgO in pilot scale crystallization plant

Abstract

The struvite crystallization process can recover struvite crystals as a valuable slow-release fertilizer from the side stream of wastewater treatment plants (WWTPs). The purpose of this study is to demonstrate the crystal growth characteristics and determine the appropriate recovery criteria for a struvite crystallization pilot plant. A pilot plant (8.6 m3/d) was designed with a feeding system of MgO (magnesium oxide), a pH controller, and a hydrocyclone for recovering struvite; the plant was operated for 42 hours at a pH range of 8.25–8.5. The removal efficiencies for PO4-P and NH4-N were 82.5–90.7% and 13.4–22.9%, respectively. The struvite recovered from the hydrocyclone was sifted using standard sieves and analyzed by SEM and XRD. The dry weight fraction of the precipitate in the 300–600 μm range increased gradually from 7% to 74% in 18 hours. The XRD analysis revealed that the crystalline structure of the precipitate in the 150–600 μm range indicates struvite without any peaks of MgO, Mg(OH)2, and MgCO3. This indicates that the critical conditions for recovering struvite from the side-stream of WWTPs are an operation period of 18 hours and a crystal size greater than 300 μm.

New Strategy to Maximize Phosphorus Utilization of Sewage Sludge Incineration Ash for Struvite Crystallization

“…Meanwhile, SEM-EDS data were not presented in this paper, since they overlapped with previous research results. Please refer to reference [4]. The sequential injection of the NaOH 1 N_eluate and (NaOH+H 2 SO 4 )_eluate afforded the experimental results presented in Figure 11.…”

“…Meanwhile, SEM-EDS data were not presented in this paper, since they overlapped with previous research results. Please refer to reference [4]. The removal efficiencies of PO 4 -P and NH 4 -N were 78.2-86.3% and 61.5-78.4%, respectively.…”

“…Meanwhile, SEM-EDS data were not presented in this paper, since they overlapped with previous research results. Please refer to reference [4]. The precipitates of each experiment (Mg:P:N = (1.0-1.5):1.0:1.0) were analyzed via XRD for the qualitative and quantitative analyses of crystals.…”

“…Several studies have been conducted to derive the optimal conditions for struvite crystallization from synthetic wastewater, digested sludge filtrate, and livestock manure on a laboratory scale, using K 2 HPO 4 or KH 2 PO 4 as phosphorus sources to compensate for insufficient phosphorus compared to ammonium [4][5][6][7][8][9]. In these studies, the Mg:P:N molar ratio and pH were considered the operating factors, and the PO 4 -P and NH 4 -N removal efficiencies exceeded 90%.…”

Treatment of emerging contaminants in simulated wastewaterviatandem photo-Fenton-like reaction and nutrient recovery

“…[13][14][15][16] Struvite is synthesized by adding an Mg 2+ source to NH 4 + and PO 4 3− containing wastewater, with many studies focusing on the use of magnesium chloride. Recent studies showed that insoluble Mg-minerals such as MgO, [17][18][19][20] MgCO 3 , 21 CaMg(CO 3 ) 2 (ref. [22][23][24] can also be used for struvite recovery as potentially more abundant and more sustainable sources, with PO 4 3− removal up to 94%.…”