I read that phosphate reserves will exhaust in coming years wiki, why don't we extract it from sewage , is it really that difficult to extract phosphate ?
The idea has been proposed by several journal articles and Wikipedia suggests that it is being done already. In "Phosphate fertilizer from sewage sludge ash (SSA)", Franz proposes a method
whereby more than 90% of phosphorus can be extracted to make an adequate phosphate fertilizer
Also, the journal "Phosphorus recycling in sewage treatment plants with biological phosphorus removal" by Heinzman lists three processes:
- Krepo Process
- Seaborne Process
- Aqua Reci Process
In it Heinzman also mentions that
up to now no phosphorus recycling with a defrayal of costs is possible. The future importance of phosphorus recycling will depend on the market price for raw phosphate, the recycling costs and, furthermore, on the general political framework
So, it appears that it is cheaper to mine it than to recycle it. This may change in the future of course.