Removal of Low‐Concentration Phosphorus Using a Fluidized Raw Dolomite Bed

Abstract

Raw dolomite powder, obtained from dolomitic rocks, was evaluated for its efficiency in removing low concentrations of phosphate present in various water and wastewater matrices. A variety of experimental setups and process variables were tested, in an attempt to determine the optimal scheme (fluidized bed) that will be used to accomplish the objectives of the study. Test influents, including distilled water (DW), synthetic groundwater (SGW), tap water (TW), and sodium-hydroxide (NaOH)-alkalized wastewater treated with liquid bittern (STSE-B) and wastewater treated with lime (STSE-L) were used to assess the effect of influent parameters on the quality of the effluent generated. The adsorptive behavior of dolomite was described by fitting data generated from the study into the Freundlich and Langmuir isotherm models. Regeneration of the dolomite was attempted by the use of an acid (hydrochloric acid), DW, and an alkaline (NaOH). Test results indicate remarkable phosphate removal levels for DW and SGW. Removal levels of 100% were attained, for an average of 307 and 314 bed volumes at inflow concentration levels of 0.28 and 0.34 mg phosphate (PO4)/ L, respectively. Relative adsorption capacities were calculated to be 0.06 and 0.072 mg PO4/g of dolomite, respectively. For TW, STSE-L, and STSE-B, 100% removal before the start of the breakthrough was sustained for averages of 205, 94, and 28 bed volumes at phosphate dosages of 0.34, 0.56, and 0.6 mg PO4/L, respectively. The calculated adsorptive capacities were 0.05, 0.051, and 0.025, respectively. Zeta potential measurement resulted in values of -16.0 mV before treatment and +3.0 mV after complete exhaustion of the bed with PO4-jacked SGW influent, indicating an ionic adsorption of ions of opposite charge to that of the particle surface. Although both the Freundlich and Langmuir isotherms were found to fit the sorption curves, the Langmuir seems to better describe the sorption process in dolomite. Among the three attempted dolomite regeneration processes, the use of NaOH has shown to be the most successful.