Stenco has resolved on several occasions a frequent problem in the industry, which is the denitrification of effluents from small discharges and where sanitary waters predominate. It is usual to solve this problem to have compact biological plants, forgetting that these waters have high concentrations of ammoniacal compounds. Stenco has accommodated several plants of this type, creating an intermediate stage of anoxia, regulating the pH and adding carbon compounds if necessary, to achieve a denitrification of the residual effluent.