Nowadays the application of biological functions to the treatment of wastewater has been a popular technology for more than 10 decades history. However, with the advancement of civilization, the requirement for the treatment will become stringent year by year, not only in the standard of respective items such as BOD, nitrogenous and phosphorus compounds, etc., but also the addition of new items to be considered such as microbial strains, viruses, bacteriophages etc. The wastewater treatment technology staring at the future development is discussed by reviewing mostly the related researches of the authors.