|摘要: ||本研究探討轉爐石(BOF)與粒狀氫氧化鐵(GFH)去除家庭污水磷之比較，BOF與GFH分別取自於中國鋼鐵公司與市售吸附劑，含磷家庭污水取至淡水水資源回收中心之初沉池出流水，其磷濃度為2.26-5.43 mg/L。採等溫吸附實驗比較BOF與GFH去除家庭污水中磷之效能，實驗參數包括吸附劑添加量、接觸時間與pH。吸附實驗結果以Freundlich等溫吸附公式、Lagergern 擬二階(Pseudo-second-order)動力與內部孔隙擴散速率(Intraparticle diffusion model)模式評估吸附水中磷之動力。此外，並利用電子顯微鏡(SEM)與能量散佈分析儀(EDS)分析吸附劑之化學組成與表面顯微特性。|
研究結果顯示由於BOF化學成分組成鈣12.62 wt%，添加於廢水中會溶出鈣且pH會由7.3上升至約9.0，鈣與磷形成Ca5(PO4)3(OH) (s) (hydroxyapatite, HAP) 沉澱物以去除磷，去除磷機制含沉澱與吸附作用，且以沉澱作用為主；SEM顯示BOF表面有HAP沉澱物。相對地，GFH不含鈣但鐵佔68.17 wt%，GFH於水中無溶出鈣且pH些微變化約維持於7.2，去除磷機制以吸附作用為主。對同一吸附劑添加量且磷去除率達75 %時，BOF與GFH所需接觸時間約分別為2小時與8小時。BOF與GFH去除磷之最適pH分別為11與4，BOF去除磷速率為2.54 mg-P/g-hr，約為GFH去除磷速率(0.34 mg-P/g-hr)之7.5倍。此外，BOF及GFH對磷吸附遵循Freundlich等溫吸附，動力吸附則遵循Lagergren擬二階動力吸附與內部孔隙擴散模式，BOF之擬二階動力常數k2值皆大於GFH之k2值。BOF內部孔隙擴散速率(kid)值小於GFH之kid值，且磷於內部孔隙擴散主要於表面吸附去除。綜合結果顯示BOF去除磷速率與經濟性皆優於GFH。
This study compares the removal of phosphate from domestic wastewater between basic oxygen furnace steel slag (BOF) and granular ferric hydroxide (GFH). BOF is sampled from the China steel company and GFH is a commercial available adsorbent. The wastewater samples were taken from primary effluent of the Tamshui wastewater treatment plant. The phosphate concentration of primary effluent ranges from 2.26 to 5.43 mg/L. The operational parameters include dosage of adsorbent (BOF and GFH), contact time and pH. All experiments are conducted by the isotherm adsorption test. The adsorption kinetic of phosphate by adorbents are evaluated by the Freundlich isotherm, the Lagergern pseudo-second-order and Intraparticle diffusion models. Furthermore, the chemical composition and surface morphology of slags are examined by energy dispersive spectrum (EDS) and scanning electron microscopy (SEM), respectively.
The results show that due to chemical composition of BOF containing 12.6 of Ca (wt%), BOF could release Ca ions into solution to raise pH from 7.3 to about 9.0. The released Ca ions could react with P to form the precipitation of Ca5(PO4)3(OH) (s) (hydroxyapatite, HAP) to remove P. The mechanism for removal of P incudes precipitation and adsorption, however, it is predominated by precipitation. The SEM micrographs show that the precipitation of HAP on the BOF surface. In contrast, the chemical composition of GFH did not contain Ca but contain 68 of Fe (wt%). The pH of solution has slightly changed and kept about 7.2. The removal mechanism of P by GFH was predominant by adsorption onto GFH surface. To reach 75 % removal of P, the contact time for BOF and GFH is 2 hrs and 8 hrs, respectively. The optimum pH of p removal for BOF and GFH is at 11 and 4, respectively. The P removal rate of BOF is 2.54 mg-P/g-hr and it is about 7.5 times to GFH (0.34 mg-P/g-hr). The adsorption of P by BOF and DFH followed the Freundlich adsorption isotherm model. Moreover, the adsorption kinetic of P by BOF and GFH well follows pseudo-second-order and intraparticle diffusion models. The pseudo-second-order adsorption rate constant, k2 value of BOF is larger than that of GFH. In contrast, intraparticle diffusion rate constant, kid value of BOF is smaller than that of GFH. The P is mainly removed during surface diffusion stage. Overall, the removal mechanism of P by BOF and GFH is predominated by precipitation and adsorption, respectively. Based on the P removal rate and economic feasibility, BOF is a cost-effective adsorbent than GFH for the removal of P.