Phosphates may be removed from wastewaters by the use of chemical precipitation as insoluble calcium phosphate, aluminum phosphate, and iron phosphate . The liming process has been discussed previously, lime being typically added as a slurry, and the system used is designed as either a single- or two-stage one. Polyelectrolytes have been employed in some plants to improve overall settling. Clarifier/flocculators or sludge-blanket clarifiers are used in a number of facilities . Alternatively, the dissolved air flotation (DAF) process is both technically and economically feasible for phosphate and fluoride removal, according to Wang et al. [39-43] and Krofta and Wang [44-48]. Both conventional biological sequencing batch reactors (SBR) and innovative physicochemical sequencing batch reactors (PC-SBR) have been proven to be highly efficient for phosphate and fluoride precipitation and removal [32,43].
A number of aluminum compounds, such as alum and sodium aluminate, have also been used by Layer and Wang  as phosphate precipitants at an optimum pH range of 5.5-6.5, as
have iron compounds such as ferrous sulfate, ferric sulfate, ferric chloride, and spent pickle liquor . The optimum pH range for the ferric salts is 4.5-5, and for the ferrous salts it is 7-8, although both aluminum and iron salts have a tendency to form hydroxyl and phosphate complexes. As reported by Ghokas , sludge solids produced by aluminum and iron salts precipitation of phosphates are generally less settleable and more voluminous than those produced by lime treatment.
Was this article helpful?
Stop Wasting Resources And Money And Finnally Learn Easy Ideas For Recycling Even If You’ve Tried Everything Before! I Easily Found Easy Solutions For Recycling Instead Of Buying New And Started Enjoying Savings As Well As Helping The Earth And I'll Show You How YOU Can, Too! Are you sick to death of living with the fact that you feel like you are wasting resources and money?