Total oxidation plants are used for the purification of waste water coming from small settlements. These biological purifiers are designed according to the characteristics of the wastewater to be treated and are sized to ensure that the limits of acceptability set by the law in force, for discharge of surface water, are discharged. The monolithic nature of the tanks, which are buried in an easy and quick way, ensures the absence of infiltration and loss of ground, giving absolute guarantee against hygienic problems.