I just saw this event advertised by the German wastwater and waste association (DWA). Sorry, it is only in German, but the topics of the presentations sound very interesting for anyone who understands German and who is interested in what can be done with sewage sludge, in particular to recover phosphorus and agricultural reuse from sewage sludge:

de.dwa.de/klaerschlammtage.html

If anyone from the forum is going to is, please give us feedback about it afterwards (I might even go there myself).

For me this is also interesting because I recently added a section on phosphorus recovery to the Wikipedia article on "sewage sludge treatment" and I had a little discussion on the talk page with another editor who felt that this was too much R&D only and not yet established at a large enough scale so that it would be worth taking about on Wikipedia:

en.wikipedia.org/wiki/Sewage_sludge_trea...#Phosphorus_recovery

This is what I wrote on Wikipedia (please feel free to add to it):

Sidestream treatment technologies

Sludge treatment technologies that are used for thickening or dewatering of sludge have two products: the thickened or dewatered sludge, and a liquid fraction which is called sludge treatment liquids, sludge dewatering streams, liquors, centrate (if it stems from a centrifuge), filtrate (if it stems from a belt filter press) or similar. This liquid requires further treatment as it is high in nitrogen and phosphorus, particuarly if the sludge has been anaerobically digested. The treatment can take place in the sewage treatment plant itself (by recylyling the liquid to the start of the treatment process) or as a separate process.

Phosphorus recovery

One method for treating sludge dewatering streams is by using a process that is also used for phosphorus recovery. Another benefit for sewage treatment plant operators of treating sludge dewatering streams for phosphorus recovery is that it reduces the formation of obstructive struvite scale in pipes, pumps and valves. Such obstructions can be a maintenance headache particularly for biological nutrient removal plants where the phosphorus content in the sewage sludge is elevated. For example, the Canadian company Ostara is marketing a process based on controlled chemical precipitation of phosphorus in a fluidized bed reactor that recovers struvite in the form of crystalline pellets from sludge dewatering streams. The resulting crystalline product is sold to golf courses and the general public as fertiliser under the trade name of Crystal Green.[5]

and

Emerging Technologies
Phosphorus recovery from sewage sludge or from sludge dewatering streams is receiving increased attention particularly in Sweden, Germany and Canada, as phosphorus is a limited resource (a concept also known as "peak phosphorus") and is needed as fertilizer to feed a growing world population.[13][14] Phosphorus recovery methods from wastewater or sludge can be categorized by the origin of the used matter (wastewater, sludge liquor, digested or non-digestedsludge, ash) or by the type of recovery processes (precipitation, wet-chemical extraction and precipitation, thermal treatment).[15] Research on phosphorus recovery methods from sewage sludge has been carried out in Sweden and Germany since around 2003, but the technologies currently under development are not yet cost effective, given the current price of phosphorus on the world market.[15][16]

Regards,
Elisabeth

P.S. It's been said that on this forum we don't provide enough space for technical discussions on centralised wastewater treatment systems. So this post is an example for the opposite.