Resources Recycling (자원리싸이클링)

The Korean Institute of Resources Recycling (한국자원리싸이클링학회)
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Mechanisms on Struvite Production for Nitrogen and Phosphorus Recovery

질소/인 회수를 위한 Struvite 생성 메커니즘

  • Lee, Sang-hun (Dept. of Environmental Science, Keimyung University)
  • 이상훈 (계명대학교 환경학부 환경과학전공)
  • Received : 2019.04.08
  • Accepted : 2019.05.21
  • Published : 2019.06.30
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Abstract

The recovery of struvite using nitrogen and phosphorus in wastewaters is useful for prevention of eutrophication and use as fertilizer, but there are theoretical and technical issues to be resolved. Through the detailed literature review, this study discusses the possible reasonable prediction of struvite formation reaction by setting a feasible reaction equation with some theoretical considerations. In a technical aspect, the purity of struvite in solid precipitates can be promoted by excluding Ca in an effective way. As for the struvite reaction prediction issue, selection of proper equilibrium reaction as well as its reaction equilibrium coefficient is significant in the neutral and basic pH regions. The equilibrium reaction agrees well with the experimental batch test results. Considering the charge balance of the ions, the pH drop along struvite formation in a diluted solution can be predicted. Also, improvement of struvite purity through elimination of Ca can be expected by providing a highly concentrated ${NH_4}^+-N$ relative to ${HPO_4}^{2-}-P$ because ${NH_4}^+$ can enhance the thermodynamic driving force toward favorable struvite formation. Even though the phosphate reacts rapidly with Ca to form a solid precipitate, the thermodynamic driving force due to the high ${NH_4}^+$ activity can dissociate the phosphate-calcium precipitates and produce struvite.

폐수내 질소와 인을 이용한 struvite 회수는 수계 부영양화 방지 및 비료자원화에 효과적인 기술이나, 해결해야 할 이론 및 기술적 문제점이 있다. 본 연구에서는, 기존 문헌의 상세한 검토를 통하여, 이론적 측면에서 적절한 반응식 선정 및 이론적 고찰을 이용한 struvite 생성 반응예측 가능성을 논의하고, 기술적 측면에서는 struvite 생성의 대표적인 저해물질인 Ca의 배제를 통해 struvite 결정의 순도를 높일 수 있는 효과적인 방법을 소개하려 한다. 반응예측 측면에서는 중성~염기성 pH 영역에서 효과적인 struvite 반응식 및 반응계수를 이용, 정량적 모델을 구축할 수 있다. 이러한 모델은 실제 회분식 실험결과와 잘 일치하며 특히 이온들의 charge balance도 함께 고려하여 struvite 생성시 희석된 수용액에서 흔히 동반되는 pH 저하를 합리적으로 예측할 수 있다. 한편, Ca의 배제를 통한 struvite 순도 향상은 ${HPO_4}^{2-}-P$ 대비 고농도의 ${NH_4}^+-N$을 조성하여 해결할 수 있는데, 이는 고농도 암모늄 이온의 존재가 struvite 생성 관련 열역학적 구동력을 강화시켜 인산염이 Ca 대신 고농도 암모니아와 용이하게 반응하여 struvite 생성에 유리한 이온환경을 조성하기 때문이다. 즉 인산염이 $Ca^{2+}$과 빠르게 반응하여 이미 침전물이 형성하였을지라도, 고동도 암모늄으로 인한 열역학적 구동력으로 인산-칼슘 침전물이 재용해 되어 struvite를 생성시킬 수 있다.

Keywords

RSOCB3_2019_v28n3_15_f0001.png 이미지

Fig. 1. Schematic illustration of the reaction progress from T0 to T3; the Ca-phosphate precipitate is formed at T0 but Ca redissolution occurs by the thermodynamic driving force toward the struvite formation at the equilibrium at T3 (adapted from Lee, S.-H. et al. (2013))8).

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