• Environmental Engineering Research
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• v.22 no.1
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• pp.12-18
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• 2017

Struvite precipitation has been proven to be an effective method in removing and recovering ammonia nitrogen (N) and phosphate phosphorus (P) from wastewater. In this study, effects of pH, molar ratios and pre-treatment of effluent of anaerobically digested swine wastewater were investigated to improve struvite crystallization. The magnesium : ammonium : phosphate ratio of 1.2 : 1.0 : 1.0 was found to be optimal, yet the molar ratio in the wastewater was 1 : 74.9 : 1.8. From the analysis, the optimum pH was between 8.0 and 9.0 for maximal phosphate P release and from 8.0 to 10.0 for maximal ammonia N and phosphate P removal from real wastewater. Analysis from Visual MINTEQ predicted the pH range of 7-11 for ammonia N and phosphate P removal and recovery as struvite. For pre-treatment, microwave pre-treatment was ineffective for phosphate P release but ultrasound pre-treatment showed up to 77.4% phosphate P release at 1,000 kJ/L of energy dose. Precipitates analysis showed that phosphorus and magnesium in the collected precipitate had almost same values as theoretical values, but the ammonia content was less than the theoretical value.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.8
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• pp.462-469
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• 2017

Eutrophication and shortage of phosphate ore raise the necessity of phosphate removal and recovery from wastewater treatment plants. Especially, a sludge treatment system containing highly concentrated phosphate should be targeted for phosphate removal and recovery. This study thus aimed to evaluate the capability of the struvite crystallization process for phosphate removal and recovery from a sludge treatment system of a wastewater treatment plant. Analysis on phosphate concentrations and masses in the sludge treatment system revealed that digested sludge and centrate have phosphate concentrations and masses, high enough to adopt the struvite crystallization process. Chemical equilibrium modeling indicated that the struvite crystallization reaction substantially occurred with pH higher than 8 and $Mg^{2+}$ concentration 1.2 times higher than its theoretical requirement. A series of batch tests with digested sludge and centrate indicated that the phosphate removal reaction by struvite crystallization followed a first-order kinetics and reached over 80% removal efficiency at equilibrium. Aeration in the batch tests was found to purge $CO_2$ in sludge or centrate and increase pH up to 8.7, without adding NaOH. Thus, we concluded that the struvite crystallization process could be an efficient and economical process for phosphate removal and recovery from a wastewater treatment plant.

• Journal of Korean Society on Water Environment
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• v.31 no.4
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• pp.387-391
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• 2015

This study was performed to evaluate the effect of pH (8-12) and molar ratio of magnesium and phosphate ($[Mg^{2+}]/[PO_4{^{3-}}]$) (0.6-1.4) on struvite crystallization of anaerobic digester supernatant using seawater as magnesium source. pH range of 9-10 is favorable for ammonium and phosphate recoveries. The recovery efficiency of ammonium was highest at $[Mg^{2+}]/[PO_4{^{3-}}]$ of 1.0 and pH 10. On the other hand, high phosphate recovery efficiency (> 99%) was achieved at ($[Mg^{2+}]/[PO_4{^{3-}}]$) of 1.4 and pH 10. The results demonstrated that seawater can be considered as low-cost magnesium source to recover phosphorus from anaerobic digester supernatant.

• Journal of Korean Society on Water Environment
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• v.32 no.4
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• pp.343-348
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• 2016

A chemical sequencing batch reactor was operated to test the feasibility of nutrient recovery from a biological livestock wastewater treatment plant. Both phosphate and ammonia could be successfully recovered as magnesium ammonium phosphate (MAP) crystals. The contents of TP and TN in the recovered MAP crystals were 26.2% and 4.0%, respectively. Zn, Cr and Ti were identified in the crystals, but the contents remained below the Korean standard for an organic fertilizer. Chemical analyses confirmed that the MAP crystals could be useful phosphate fertilizers. On the other hand, the results of physical analyses using an X-ray diffractometer and an energy dispersive X-ray spectrometer strongly suggested that crystalline materials like magnesium potassium phosphate (KMP) and hydroxyapatite (HAP) were also formed during the MAP crystallization, depending on the availability of K⁺ and Ca²⁺.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.3
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• pp.273-278
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• 2007

Modern society has moved from a phosphorus recycling loop, where animal manure and human wastes were spread on farming land to recycle nutrients, to a once-through system, where phosphates are extracted from mined, non-renewable phosphate rock and end up either in landfill(sewage sludge, incinerator ash) or in surface waters. In this research, crystallization of nitrogen and phosphate with natural sources of $Mg^{2+}$ in synthetic water was tested. The operational parameters of pH, mixing time, and the magnesium molar ratio were investigated to find optimal conditions of the MAP precipitation using synthetic wastewater. The removal efficiency of phosphate increased with pH up to 11. By MAP precipitaiton of the synthetic waste water, 94% of the phosphate were eliminated at pH 11. It was found that at least 10 minutes mixing time was required and 20 minutes mixing time was recommended for efficient phosphate removal. High efficiency removal of phosphate was possible when the magnesium molar ratio was 1.0~2.0. The comparative study of different magnesium sources showed that coagulants (PAC) was the more efficient sources than only magnesium. The result showed that 97% of phosphate removal. In conclusion, coagulants (PAC) induced crystallization of struvite and hydroxyapatite was shown to be a technically viable process that could prove cost effective for removing phosphate in wastewater.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.7
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• pp.515-520
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• 2009

This study investigated the influence of oxyanions (nitrate, carbonate, phosphate) on the attachment of bacteria (Bacillus subtilis) to Al-Fe bimetallic oxide-coated sand using column experiments. Results showed that bacterial attachment to the coated sand was independent of nitrate concentration. Bacterial mass recovery remained constant (10.9${\pm}$0.2%) with varying nitrate concentrations (0.1, 1, 10 mM). In case of carbonate, mass recovery increased from 25.6% to 39.0% with increasing carbonate concentration from 0.1 mM to 1 mM, and mass recovery also increased from 50.9% to 78.9% at the same concentration condition in case of phosphate. This phenomenon could be attributed to the hindrance effect of carbonate and phosphate to bacterial attachment to the coated sand. Meanwhile, with increasing carbonate/phosphate concentration from 1 mM to 10 mM, mass recovery decreased from 39.0% to 23.8% and from 78.9% to 52.6%, respectively. This phenomenon could be ascribed to the enhancement effect of free carbonate/phosphate ions present in solution phase due to increasing carbonate/phosphate concentration, which increase ionic strength and thus enhance bacterial attachment to the coated sand. In our experimental conditions, the effect of phosphate to bacterial attachment to the coated sand was the greatest among phosphate, carbonate, and nitrate.

• Journal of Korean Society of Water and Wastewater
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• v.33 no.4
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• pp.291-297
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• 2019

Phosphorus is a vital resource for sustaining agriculture and nutrition, but a limited non-renewable resource. Thus, the recovery of phosphorus from waste activated sludge(WAS) was attempted by microwave heating and magnesium ammonium phosphorus(MAP) crystallization. Polyphosphate-accumulating organisms(PAOs) in WAS release phosphate from the cell when they are exposed to high temperature environments. Microwave heating caused phosphorus and ammonia to release from WAS. The amount was increased with increasing temperature, showing that 88.5% of polyphosphate present in the cells were released in the form of phosphate at $80^{\circ}C$. A similar result was also observed in the release of ammonia. On the other hand, both phosphorus and ammonia were crystallized with magnesium, and then was harvested as MAP. Phosphorus recovery rate reached almost 97.8%, but the ammonia was about 13.4%. These results cleary indicate that phosphorus could be recovered from WAS using a physiological trait of PAOs. Heavy metal analyses also show that the MAP crystal is useful and safe as a phosphorus fertilizer.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.6
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• pp.616-620
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• 2008

The aim of this study was to investigate the influence of phosphate on the adhesion of Escherichia coli to porous media. Column experiments were performed to examine the effect of phosphate on bacterial adhesion to quartz sand and iron-coated sand. Results showed that bacterial mass recovery in quartz sand decreased from 74.5 to 35.4% as phosphate concentration increased from 0 to 16 mg/L. This indicated that bacterial adhesion to quartz sand was enhanced with increasing phosphate concentration. This phenomenon is due to the increase of ionic strength. In contrast, the mass recovery in the coated sand increased from 2.9 to 26.0% as phosphate concentration increased. This indicated that bacterial adhesion to the coated sand was reduced with increasing phosphate concentration, due to the preoccupation of favorable adsorption sites and competitive adsorption by phosphate.

• Journal of the Korea Organic Resources Recycling Association
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• v.30 no.1
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• pp.33-39
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• 2022

Batch experiments were conducted to find out the effects of various types of magnesium compounds on phosphorus recovery by magnesium ammonium phosphate (MAP) crystallization. The phosphorus recovery from the centrate of anaerobic digested sludge was performed using magnesium chloride, magnesium hydroxide and magnesium oxide under different pH (7.5, 8.0 and 8.5) and Mg/P molar ratio (1.0, 1.5, 2.0, 2.5) conditions. The phosphorus recovery rate increased with increasing pH and Mg/P molar ratio in all magnesium compounds. At pH 7.5, magnesium oxide showed the highest phosphorus recovery rate, followed by magnesium hydroxide and magnesium chloride. However, at pH 8.5, more than 90% of phosphorus recovery rate was obtained in all Mg/p molar ratios. Thus, it is expected that magnesium hydroxide and magnesium oxide are able to replace magnesium chloride as a magnesium source in terms of phosphorus recovery efficiency and cost.

• Environmental Engineering Research
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• v.24 no.3
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• pp.434-442
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• 2019

The present study investigated a novel calcium hydroxide-coated dairy manure-derived biochar (Ca-BC) for adsorption of phosphate from water and dairy wastewater. The Ca-BC showed much higher adsorption of phosphate than that of dairy manure-derived biochar. The Ca-BC possessed mainly the calcium hydroxide and various functional groups resulting in high reactivity between phosphate and calcium hydroxide in the Ca-BC. The adsorption of phosphate onto Ca-BC followed pseudo-second order kinetic and Freundlich isotherm models indicating chemisorptive interaction occurred on energetically heterogeneous surface of Ca-BC. The maximum adsorption capacity of the Ca-BC was higher than those of iron oxide and zinc oxide-coated biochars, but lower than those of CaO- and MgO-coated biochars. However, the Ca-BC showed high reactivity per surface area for adsorption of phosphate indicating importance of surface functionalization of biochar. On the other hand, the adsorption of phosphate in dairy wastewater on Ca-BC was lower than that in water owing to competition between other anions in wastewater and phosphate. Overall, the Ca-BC would be a low cost and effective adsorbent for recovery of phosphate from water and wastewater.