Question

what are the natural ways of sewage treatment​

Answer 1

Wastewater purification is becoming a more and more relevant problem due to the growth of wastewater collection systems, which brings more and more wastewater to treat. Technological progress allowed the realization of advanced wastewater treatment systems, which answer the very strict legislation imposed by EU  

In Italy e.g. small communities cannot afford the costs of these advanced and specialized systems, which require a trained and qualified staff as well. For this reason the development of very simple and cost effective natural wastewater treatment systems is particularly interesting. These treatments are called extensive, since they require long times and wide surface areas to become effective.