You can check some past conversations on the topic by typing "phosphorous" in the "Browse the Forum" bar or you can also learn more here:
There are three ways to remove phosphorus from wastewater: assimilative uptake, enhanced biological phosphorus removal (EBPR), and chemical precipitation. Assimilative uptake removes some phosphorus by growing new bacteria. When excess biomass is removed from the process, some phosphorus is removed too. EBPR cycles the MLSS through anaerobic and either anoxic or aerated zones to encourage the growth of some specialized bacteria called the Phosphate Accumulating Organisms (PAOs). The PAOs can absorb up to 40% of their weight as phosphorus. When these bacteria area wasted from the system, much more phosphorus is removed. Finally, you can add alum, or ferric, or lime to precipitate phosphorus chemically. Which one is best? Well, that depends on 1) what permit limit you have to meet, 2) your influent BOD to P ratio, and 3) whether or not it is possible to add an anaerobic zone / basin to your treatment train.
EBPR can reliably produce effluent total phosphorus concentrations below 1 mg/L as P and will often achieve concentrations as low as 0.3 mg/L as P. All you need is 1) an anaerobic basin that provides 30 to 90 minutes of detention time, 2) pumps to recycle MLSS between the aerated or anoxic zone and anaerobic zone, and 3) the right ratio of influent BOD to P - generally, a BOD to P of at least 10 to 1 is needed. It's not quite that simple, but you get the idea. Chemical P removal can get down as low as 0.03 mg/L TP, but this generates a lot of extra sludge and increases solids handling costs. Plus, you have to buy the chemical. To get down to 0.03 mg/L TP, you'll also need effluent filters to remove solids. So... you can see that there are a lot of factors at play. The "best" method depends on your situation.
For more information on EPBR, check out this paper by Sam J. https://pdfs.semanticscholar.org/c7de/bb5cd7a803bd88d879998489a0d7eca51659.pdf