Calcium-based seeded precipitation for simultaneous removal of fluoride and phosphate: Its optimization using BBD-RSM and defluoridation mechanism. (June 2022)

• Record Type: Journal Article
• Authors: Lacson, Carl Francis Zulueta; Lu, Ming-Chun; Huang, Yao-Hui
• Is Part Of: Journal of water process engineering. Volume 47(2022)
• Publication Date: 2022-06
• Subjects: Defluoridation -- Wastewater treatment -- Adsorption -- Design of experiments -- Calcite; Water-supply engineering -- Periodicals; Saline water conversion -- Periodicals; Seawater -- Distillation -- Periodicals; Sanitary engineering -- Periodicals; Sewage -- Purification -- Periodicals; 627
• DOI: 10.1016/j.jwpe.2022.102658
• Languages: English
• ISSNs: 2214-7144

Abstract

Abstract: This study aimed to optimize a seeded precipitation process using recovered CaCO3 for treating wastewater containing high concentrations of fluoride and co-anions. The simulated wastewater contained 4000 mg F − /L and 2000 mg/L of co-anions (i.e. NO3 −, PO4 3−, and SO4 2− ). Critical factors such as precipitant concentration (mM Ca 2+ ), seed dosage (g), and pH were subjected to Box-Behnken Design, a response surface methodology, to simultaneously model F − and PO4 3− removal efficiencies. Generally, the critical factors were all statistically significant with Ca 2+ concentration as the most significant parameter for both fluoride and phosphate removal. Even at extreme anion concentrations, the optimum condition (Ca 2+ = 105.0 mM, seed dosage = 5.0 g., and pH = 3.79 ± 0.13) still reached a high defluoridation efficiency about 98% with marginal error from predicted removal. Moreover, anionic species (i.e., PO4 3−, SO4 2−, and NO3 − ) had removal efficiencies of 75%, 40%, and 17%, respectively. The range of the prevailing acidic pH (2.0–6.0) presumably deterred the potential precipitation of Ca 2+ with other anions but still ensured CaF2 precipitation. In this study, the solid analysis of the recovered CaCO3 subjected to different conditions could demonstrate a complex defluoridation mechanism using seeded precipitation. Highlights: Precipitation with CaCO3 -seed leads to simultaneous removal of F − and PO4 3− . BBD-RSM was used to optimize precipitant concentration, seed dosage, and pH. High concentrations of co-anions cannot significantly affect seeded precipitation. Defluoridation using seeded precipitation has multiple and complex mechanisms.