When waste water treatment project becomes a successful project environmentally and energy-saving. Can you give an example of a project?

oui on peut résoudre beaucoup des problèmes dans le traitement des eaux usées par exemple quand en prend une eau usée et après l'étape de l'épuration nous pouvons passer à une étape de ultrafiltration et puis une autre étape de nano-filtration et enfin nous injecterons  les eaux dans des bassins d'infiltration ce-qui nous appelle  alimentation artificielle des nappes souterraines 

Of course first of all the WWTP must succesfully comply with the discharge requirement.

In fact, nowadays, WWTP technology is going towards energy generating plant, to become energy neutral (self sufficient), or even can provide surplus energy (example).  This is primarily done by anaerobic digestion of effluent, that produces methane gas that can be used as fuel.  There are many examples in the US, like EBMUD.  There is also research and pilot plant in south Korea.  .  I suppose on the contrary, aeration process is a major energy consumer.

Another possible way to produce energy is to burn the dried sludge and use energy generating devise cush as external combustion/sterling engine.  Also, it is possible to feed treated wastewater to algae farm that will later be used for bio-diesel production.  These two were projects I was involved in just before switching to the manufacturing sector.

Collect gas produced by bictaria from erasion basen and utalize for the production of steam.