Precipitation of Phosphates from Water with Ferrous Salts

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Title: Precipitation of Phosphates from Water with Ferrous Salts
Creators: Svanks, Karlis
Contributors: United States. Office of Water Resources Research; Ohio State University. Water Resources Center
Subjects (LCSH): Water -- Purification
Water -- Analysis
Issue Date: 1971-02
Publisher: Ohio State University. Water Resources Center
Series/Report no.: Project completion report (Ohio State University. Water Resources Center) ; no. 347X
Abstract: The use of ferrous sulfate for precipitating phosphate from water was investigated. Different phosphate containing solutions were evaluated: (1) pure orthophosphate, (2) secondary effluent from a waste treatment plant, and (3) precipitation of phosphate in a simulated activated sludge process. Studies were made to determine the effect of dissolved oxygen concentration, pH, and iron-to-phosphate ratio on the removal of phosphate. In addition, the relative effectiveness of calcium hydroxide and sodium hydroxide for control of pH and the use of microflotation and dissolved air flotation for separation of the phosphate precipitate were evaluated. In all cases, maximum phosphate removal (up to 97 percent) was obtained when the pH was 7 to 8, the molar iron to phosphate ratio greater than 1.5 and dissolved oxygen concentration equal to that required for complete oxidation of ferrous iron. Calcium hydroxide was found to be a more effective base since the optimal pH range was expanded and the coagulation and flocculation of the insolubilized phosphates were improved. Interferences from organic matter in secondary effluents on flotation operations were observed. Ferrous sulfate should be very effective for removing phosphate in the activated sludge process. The low dissolved oxygen concentration will control the oxidation of ferrous iron to optimal rates, and the sludge will increase the settling rate of the phosphate precipitate.
Other Identifiers: OCLC #630754 (print)
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