| 摘要: | 磷 (P) 是所有生命體中重要的營養物質之一，磷礦短缺與磷資源損失使回收磷成為關注之議題，目前已有許多成熟磷回收技術從廢水和污泥回收磷，包含沉澱法、固定床結晶法、流體化床結晶法等，台灣正發展再生水廠，逆滲透(Reverse Osmosis, RO)濃排水之處理成為問題。
首先，探討實際與合成廢水結晶磷酸鹽之粒徑分布差異，實際廢水當中含有懸浮固體，因此無法準確透過粒徑判斷初始成核之pH，本研究認定粒徑分析找尋介穩定區不適用於實際廢水。
瓶杯實驗結果顯示最高磷去除率條件為Mg/P莫耳比 1和pH 10，磷去除率為87.7%，經Visual MINTEQ預測最佳磷酸銨鎂pH條件為9.5，羥基磷灰石pH條件為10，為滿足期望產物為磷酸銨鎂，因此本研究選擇pH 9.5為最佳條件，依鎂鈣去除量選擇Mg/P莫耳比 2為最佳條件。
流體化床因子實驗之啟動策略磷去除率皆高於 86.7%，最佳磷去除率條件為HRT 5分鐘及上流速度20 m/h，磷去除率為92.2 %；最佳磷結晶率條件為HRT 10分鐘及上流速度30 m/h，磷結晶率為15.4 %，且發現磷結晶率有負值產生，其原因為絮狀物累積於突擴區，使採樣口磷濃度較進流口磷濃度高所導致，在較低的上流速度及較高的HRT下，磷結晶率累積越嚴重。
長期實驗驗證因子實驗最佳條件，證實反應時間增長仍有污泥累積之情形，因此改變流體化床操作，增加成核階段後，再調整至因子實驗最佳條件，最佳迴流口及出流口殘留磷濃度為10.31 mg/L，獲得最高磷去除率以及磷結晶率74.5 %，且可承受0.29-0.34 kg/m2 h之磷截面負荷。
XRD分析結果顯示為羥基磷灰石，水質條件Ca/Mg莫耳比為2.45之條件所造成，說明高濃度競爭離子鈣抑制磷酸銨鎂生成，粒徑0.6-0.85 mm為最多，重量占比為68.4 %，含水率為9.9 %，視密度為1.396 g/cm3。
;Phosphorus (P) is one of the important nutrients for all forms of life. The phosphate rock depletion and the loss of phosphorus resources have made phosphorus recovery as high-profile issue. Currently, there are many mature phosphorus recovery technologies to recover phosphorus from wastewater and sludge, including chemical precipitation method , fixed bed crystallization method, fluidized bed crystallization method, and so on. Taiwan is developing reclaimed water plants, and the treatment of reverse osmosis (RO) rejected water has become a problem.
First, the difference in particle size distribution of crystallized phosphate in actual and synthetic wastewater was explored. Actual wastewater contains suspend solid, so it is impossible to accurately determine the pH of the primary nucleation through particle size. In this study, the particle size analysis cannot determine the metastable zone for actual wastewater.
The results of the jar-test experiment show that the highest phosphorus removal efficiency condition is Mg/P molar ratio 1 and pH 10, and the phosphorus removal efficiency is 87.7 %. Visual MINTEQ predicts that the optimal pH of magnesium ammonium phosphate crystallization is 9.5, and the optimal pH of the hydroxyapatite crystallization is 10. In this study, the expected product is magnesium ammonium phosphate, so the optimal condition selected pH 9.5. Mg/P molar ratio 2 as the optimal condition based on the magnesium and calcium removal quantity.
The phosphorus removal efficiency in the fluidized bed factor experiment are all higher than 86.7%. The optimal phosphorus removal efficiency condition is HRT 5 minutes and upflow velocity 20 m/h, and the phosphorus removal efficiency is 92.2%; the optimal phosphorus crystallization efficiency condition is HRT 10 minutes and The upflow velocity is 30 m/h, the phosphorus crystallization efficiency is 15.4%, and it is found that the phosphorus crystallization efficiency has a negative value. The reason is that colloid accumulates in the upper part, causing the phosphorus concentration of sample to be higher than the phosphorus concentration of inflow. The accumulation of phosphorus crystallization efficiency is significant at lower upflow velocity and higher HRT.
Long-term experiments verified the optimal conditions for the factor experiment and confirmed that sludge accumulation still occurred as the reaction time increased. Therefore, the fluidized bed operation was changed and the nucleation stage was added. Then, the optimal conditions were adjusted from the factor experiment. The residual phosphorus concentration of reflux and outflow is 10.31 mg/L, achieving the highest phosphorus removal rate and phosphorus crystallization rate of 74.5%.The system can withstand the phosphorus surface loading of 0.29-0.34 kg/m2h.
XRD analysis results show that it is hydroxyapatite, which is caused by the water quality condition of Ca/Mg molar ratio of 2.45, indicating that the high concentration of competitive ion calcium inhibits the formation of magnesium ammonium phosphate. The particle size of 0.6-0.85 mm accounts for the largest weight proportion, which is 68.4 %. The water content is 9.9 %, and the apparent density is 1.396 g/cm3. |
