Comparisons of the removal of Phosphate from domestic wastewater between blast oxygen furnace slag and Granular Ferric Hydroxide

• Main Authors: Chia-Wei Chu, 朱家偉
• Other Authors: 康世芳
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/98654116599118193415

碩士 === 淡江大學 === 水資源及環境工程學系碩士班 === 103 === 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.