The 2 main methods of P recovery from sewage  are chemical precipitation and biological methods (which are less reliable). However, there are other methods such as ion exchange, reverse osmosis, chemical coagulation, electrodialysis, absorption, use of chemical adsorbents.

Chemical precipitation is widely used in most treatment plants and involves addition of iron or aluminium or lime to form phosphorus precipitates which are removed as sludge.

Ther are some sustainable methods which involves encouragement of spps. that  accumulate and utilize phosphorus as energy source, but it is unreliable method and maybe limited by rainfall, temperature, nutrient availability

just to add that where biological method is employed, additional step can be added to the process to recover phosphate as struvite, which can act as a slow release fertilizer providing a good source of phosphate, Magnesium and Nitrogen to plants and help to reduce over exploitation of phosphate rocks

Beside the conventional biological and chemical phosphorous removal, a new method for simultaneous phosphorous removal and recovery is emerging. Crystallization is the separation of phosphorous in form of Magnesium ammonium phosphate hexahydrate (MgNH4PO4.6H2O) crystals also known as MAP or struvite. Being primarily perceived as a disturbance in wastewater treatment processes, struvite crystallization has now become an interesting approach to phosphorous removal since struvite has fertilizer properties and can be directly commercialized as fertilizer. 

Now I understand that some european countries are pursuing  the production of    

struvite from municipal  waste water. what is the magnitude and success of production of struvite   in different european countries ?  Also can countries like India  go for this technology in their cities   to recover valuable P source   ?                                        

I believe In japan struvite production from wastewater is being practiced in full scale successfully. It is a promising technology and some institutes are working on the pilot plants to overcome problems and make this process technically and economically feasible.

About India, I am not sure what technologies are currently being used for phosphorous removal. If phosphorous removal is not a common step in wastewater treatment, conventional chemical and biological treatments would be a better option and can be adjusted to the current treatment facilities.

I think since agriculture has an important place in India, the market for struvite as fertilizer will be good; therefor, it is worthwhile to investigate more about this process or similar ones.     

Thank you Sadaf   very much for your valuable  answer.Countries like India  need to 

note the experience of Europe and Japan and pursue research and technology efforts

for recovering P from all types of waste waters and urine of animal /human sources .

Also the municipalities need to upgrade their sewage  treatment systems to recover P from the  waters.They can recover part of their treatment cost by selling Struvite fertilizer.

We operated a  full-scale struvite crystallization system  in a municipal WWTP in Spain, in order to recover the P from the sidestream. The results are promising. However, the amount of struvite produced per year is quite low, and is difficult in this case to have a market for the produced fertilized.

There are several projects in different countries in europe, where the P is recovered from separated collected urine, using special toilets.

Regards

Conference Paper Enhancement Of Struvite Crystallization With Magnesium Hydro...

Article Recovery of N and P from Urine by Struvite Precipitation Fol...

Dear  Dr.Nicolas, thank you for the literature attached. I shall return back after going through the literature. I hope that one day struvite shall become a popular slow release P fertilizer in agriculture.

popular for a while, calcined Polish Opoka ore, has a high specificity for soluble phosphate in weak solutions such as biological waste streams ( see Sweden, BioPtech).  More advanced is NCLEAR (avoid searches for nuclear...) a company near Atlanta, GA, USA.  http://www.nclear.us/  Very specific and tailored nano-crystals to remove phosphate from sewage treatment, lakes and other bodies of water. 1-404-260-0164

Mr.Hebbard,Thank you for the information on struvite production technologies.I shall be waiting for somebody to a start a pilot plant in India in collaboration with some Municipality or Corporation of a big city.

A group of Korean researchers basing from experiments in university laboratory facilities has already suggested one of the P-recovery methods from sewage. 

Please refer to the three articles I wrote about HAP crystallization using converter slag as a seed crystal described below. 

I think economic feasibility for P recovery from sewage treatment is the most important factor. 

I am sure India has the following three promising aspects necessary for a feasible P recovery: big sewerage system, steel industry(converter slag), and excellent experts (policy influencer like you). 

To effect feasibility of P recovery, note that: 1) converter slag(by-product of steel production) is one of the most cost-effective seed material (see Ref.(1) below), 2) neutral pH region for making meta-stable zone when a highly concentrated phosphate (about 100 mgP/L) reaction condition exists and this finding may crucially reduce chemical-costs (see Ref.(2) below), and 3) the kinetics analysis for P-crystallization reaction helps to clear the fundamentals (see Ref. (3) below). 

Ref.(1): article(2004), A comparative study of seed crystals for the phosphorus crystallization process, S. Yim and E-H Kim, Environmental Technology, Vol.25, p741-750 

Ref.(2): article(2006), Hydroxyapatite crystallization from a highly concentrated phosphate solution using powdered converter slag as a seed material, Kim et. al, Journal of Hazardus Materials, Vol.136 issue 3, p690-697 

Ref.(3): article(2006), Recovery of phosphates from wastewater using converter slag: Kinetics analysis of a completely mixed phosphorus crystallization process, Kim et. al, Chemosphere, Vol.63 issue 2, p192-201 

At this stage, I propose that the EBPR(Enhanced Biological Phosphorus Removal) process be adopted followed by anaerobic sludge digestion which is an essential factor for realizing feasibility of P-recovery. It should also be noted that this is feasible only for large-scale sewage treatment plants.

 Dr.Kim,thank you for the relevant literature provided/suggested.I may further interact with you after going through literature.

Colleagues I have comeacross a very good review article on struvite crystallization from waste waters.The following reference provides the interesting details.

Production of slow release crystal fertlizer from wastewaters through struvite crystallization.By.Rahman,M.M. et al. Arabian Journal of Chemistry ,7(1):139-155(2014)

http://www.sciencedirect.com/science/article/pii/S187853521300347X

Hello Sir,

We have published two extensive review papers covering number of aspects of struvite recovery technologies. Hope these will give you some insight.

Thank you.

http://www.sciencedirect.com/science/article/pii/S0921344915301555

http://www.sciencedirect.com/science/article/pii/S0956053X16300022

 Dr.Sampriti,thank you very much for attaching the abstracts of two of your very valuable review articles on the topic  of my interest.I understand that your articles are very valuable scientific contribution.But I do not know the reach or accessibility to research community ,public in general and policy makers especially in India.As mentioned by me earlier we need some pilot plants at least in some metropolitan cities.Now in Europe a lot of importance is given to recovering and reusing P.Recently quality criteria is available for struvite fertilizer and  marketing  of the product is also being done.Now the recovering of P from municipal,farm and industrial waste waters as struvite should receive the attention of policy makers,administrative personnel and public at large.I request you to publish a comprehensive and concise review in Journals like Current Science for easy accessibility to Indian scientific community and also draw public attention.I also thank Drs.Nicolas and Kim for attaching very good /valuable publications for benefit of the followers and viewers of this discussion.

Yehh Rao Sir, I do agree with you, that's indeed a very good suggestion to make struvite recovery a commercially viable technology in Indian context.

Here you can find an overview of commercial technologies for P-recovery:

Article Sustainable Sewage Sludge Management: From Current Practices...

Thank you Mr.Sina Shaddel for the useful article provided

Maybe our recent published review is useful for answer your question Article Nitrogen and Phosphorus Recovery From Anaerobically Pretreat...

https://www.frontiersin.org/files/Articles/429470/fsufs-02-00091-HTML/image_m/fsufs-02-00091-t001.jpg