Struvite Crystallization of Anaerobic Digestive Fluid of Swine Manure Containing Highly Concentrated Nitrogen

Abstract

In this study, the optimal operation factors for struvite crystallization for removing and recovering nitrogen and phosphorus from anaerobic digestive fluid of swine manure containing highly concentrated nitrogen was determined. Every experiment for the struvite crystallization reaction was conducted by placing 1,000 mL of digestion fluid in a 2,000 mL Erlenmeyer flask at various temperatures, pH, and mixing speed. Except for special circumstances, the digestion fluid was centrifuged (10,000 rpm, 10 min) and then the supernatant was used for the experiment at room temperature and 100 rpm. The optimal mole ratio of PO43−:Mg2+ was 1:1.5, and the pH effect ranging from 9 to 11 was similar, when mixed for 1 hour. Under this condition, the removal efficiency of NH4+-N and PO43−-P was 40% and 88.6%, respectively. X-shaped crystal was observed by light and scanning electron microscopy. In addition, struvite crystal structure was confirmed through X-ray diffraction analysis.

Struvite Precipitation for Sustainable Recovery of Nitrogen and Phosphorus from Anaerobic Digestion Effluents of Swine Manure

“…Owing to these advantages, some studies based on the recovery of NH 4 -N and PO 4 -P in AD effluents of livestock manure with struvite precipitation have been reported. Among those, it was proven that struvite was effectively recovered from AD effluent of swine manure through X-ray diffraction (XRD) or scanning electron microscopy (SEM) analysis [23,[27][28][29]. To date, these studies have mainly focused on the determination of key reaction parameters, including pH and stoichiometric Mg:NH 4 -N:PO 4 -P ratios, that affect the removal efficiency of NH 4 -N and PO 4 -P during struvite precipitation [23,[27][28][29][30][31][32][33][34][35][36].…”

“…Among those, it was proven that struvite was effectively recovered from AD effluent of swine manure through X-ray diffraction (XRD) or scanning electron microscopy (SEM) analysis [23,[27][28][29]. To date, these studies have mainly focused on the determination of key reaction parameters, including pH and stoichiometric Mg:NH 4 -N:PO 4 -P ratios, that affect the removal efficiency of NH 4 -N and PO 4 -P during struvite precipitation [23,[27][28][29][30][31][32][33][34][35][36]. In rare cases, the type of magnesium source added during struvite precipitation [30]; sequence of the chemical addition of Mg (magnesium source), P (phosphate source), and alkaline reagents [32,34]; optimal reaction time [23,27,34]; and mixing intensity [27] have been studied (Table 1).…”

“…First, according to the studies reported so far, the optimal conditions for reaction parameters that affect struvite precipitation of AD effluent obtained from livestock manure, such as pH and stoichiometric Mg:NH 4 -N:PO 4 -P ratios, differ significantly. The variations in the removal efficiency of NH 4 -N (40-97%) and PO 4 -P (6-100%) under optimal conditions have also been reported to be significantly large (Table 1) [23,[27][28][29][30][31][32][33][34][35][36][37][38]. Second, only a few studies have optimized the reaction time and mixing intensity in struvite precipitation of AD effluents (Table 1).…”

“…Therefore, it was determined that a final pH of 10 is most effective for maximizing the recovery rates of NH 4 -N and PO 4 -P and will save chemical costs during struvite precipitation from AD effluents. Several studies have reported that the removal rates of NH 4 -N and PO 4 -P increase as the pH increases during struvite precipitation experiments on AD effluents of animal manure [23,[27][28][29]31,34,36]. However, only the results of Gong et al [36] and Kwon et al [29] were consistent with those of this study in terms of the optimal pH conditions; in other studies, the optimal pH ranged from 8.5 to 9.5, which varies slightly from the results obtained in this study.…”

“…Considering the increase in energy costs due to the increase in mixing intensity, the optimal mixing intensity was determined to be 240 s −1 . To the best of our knowledge, Lee et al [27] has been the only study on the optimal mixing intensity in struvite precipitation of AD effluents. They reported that there was almost no change in the removal rate of NH 4 -N and PO 4 -P when the mixing intensity was increased from 100 to 200 revolutions per minute (rpm), which is similar to the result obtained in this study.…”