What material is the Topas WWTP made of and how is it manufactured?

Topas WWTPs are made from polypropylene (PP). This plastic is classified among thermoplastics, meaning it can be joined by melting and welding at appropriate temperatures. The material is stable, non-toxic (the same is used for drinking water pipes) and is only degraded by UV radiation, i.e., sunlight. Since the entire WWTP is buried, aging is minimal and the lid, which is exposed to the most degradation, is made of PP material with a UV filter thus having an extended lifespan even in direct sunlight.