Phosphate recovery potential from wastewater by chemical precipitation at batch conditions

This study aimed to investigate the potential for phosphate recovery, instead of removal, from wastewater at conventional biological treatment processes. In the first part of this study, struvite and apatite phosphate-salts formation potential were investigated using artificially prepared solutions. In the second part, real municipal wastewater was subjected to batch-basis aerobic/anaerobic sequential order operation and supernatant of high phosphate-concentrations released into the liquid medium during the anaerobic phase were withdrawn and subjected to chemical precipitation tests. The formed mixed-liquor suspended solid suspensions were subjected to quiescent settling to ensure the separation of solids. Then, to form chemical bonds between calcium and phosphate ions, calcium was added to the withdrawn supernatants. The ability of apatite formation by itself as well as support-aided apatite formation was tested in supernatants. All the precipitation tests were carried out at orbital incubator at constant 20 degrees C and 25 degrees C temperature which were reported to be the range yielding the highest phosphate precipitation efficiency. In order to evaluate the solid-liquid separation ability of the chemical slurries, both centrifugation at 2000 rpm and membrane filtration at 100 mbar vacuum pressure were tested. The recovered solid phases as well as supernatants were analyzed for phosphate contents and it was revealed that the highest efficiency of phosphate precipitation was at pH of 9.50 for apatite and 9.40 for struvite. The results also suggested that struvite precipitation is more applicable for technical purposes while apatite precipitation is more applicable for economical reasons.