The nitrogen removal in systems of cultivated stream beds is between 25 and 80%. The removal of the match in humid lands very efficient does not have to the limited chances of contact between residual water and land. The plants and the land catch part of the match. 1.4Substrato of the system wetland the cultivated stream beds constructed consists of design correct of a bucket that contains water, substratum, and the majority normally, emergent plants. Small changes in the hidrologia can have important effect in a humid land and in the effectiveness of the treatment and because of the superficial area of the water and its little depth, a system strong acts reciprocal and with the atmosphere through rain and evapotranspirao. The density of the vegetation affects its hidrologia strong.

The substratum in constructed humid lands includes ground, sand, rock, organic materials. The vegetation remaining portions are very important, therefore they support good part of the living organisms in humid lands, the permeability of the substratum for affecting the movement of the water. In some saturated substrata, the water substitutes the atmospheric gases in the pores and the microbiano metabolism consumes the available oxygen. In accordance with the parameters analyzed in the system of wetland, regulated for the CONAMA, have the waited incomes: reduction of the DBO, nitrogen, of suspended solids, ammonia entrance and exit, removal of the match, metal removal and the removal of fecais coliformes. The secondary or tertiary treatment of sewers with ‘ ‘ wetlands’ ‘ constructed it has promoted effluent ends of good quality, becoming possible its launching in bodies d’ water or its reutilizao for ends not considered noble: restricted irrigation, for example.