||Calcium Phosphate Precipitation in Wastewater Treatment.
Mena, Arnold B. ;
Jenkin, David ;
||California Univ., Berkeley. Sanitary Engineering Research Lab.
||SERL-72-6; EPA-WQO-17080-DAR; 06038,; R2-72-064
( Chemical removal(Sewage treatment) ;
( Precipitation(Chemistry) ;
( Sewage treatment ;
Chemical removal(Sewage treatment)) ;
Calcium phosphates ;
Magnesium hydroxides ;
Calcium carbonates ;
Crystal growth ;
Water pollution control
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Precipitation of calcium phosphate from both synthetically derived wastewater and from actual wastewater was investigated. An amorphous tricalcium phosphate was the steady state solid phase that controlled dissolved phosphate residuals. The solubility of this phase determined from chemically defined systems was used with success to predict dissolved phosphate residuals from both chemically defined systems and actual wastewaters. Suspension settling was enhanced by magnesium hydroxide precipitation but not by calcium carbonate precipitation. In wastewater of moderate alkalinity and hardness, a phosphate removal in excess of 80% was consistently achieved at pH 9.5 with lime doses of at the most 200 mg/l as calcium carbonate. The overall phosphate removal performance was dictated by the performance of the precipitation reactor and its ensuing sedimentation basin. Phosphate containing particles that escaped sedimentation could not be removed by filtration because they dissolved rapidly during the recarbonation process that necessarily precedes the filtration step.