The biological treatment plant of Thasos was constructed for the treatment of waste and sewage of an equivalent population of 3.500 and 4.500 people for the winter and summer of a 20-year period, while there is a plan for the expansion of the project and the covering of the needs of 15.000 equivalent people for the winter of a 40-year period and 22.500 people for the summer of a 40-year period.

The treatment system applied is that of active sludge with prolonged ventilation and simultaneous biological removal of nitrogen and phosphorus (complete nitrification, high degree of de-nitrification and de-phosphorization ).