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The produced nitrogen oxides from the biological treatment of swine and dairy anaerobic supernatant are evaluated. The quantification of the emissions has been conducted in a continuous way and coupled with batch tests to determine the mechanisms of formation. Using a continuous monitoring system, N2O and NO forms are present in higher quantities than NO2. The elevated emissions are linked with the increment of the influent nitrogen load both in the daily variations and in the long period. The NH4-N and NO2-N accumulations are recognized as the main parameters which determine the great nitrogen oxide emissions even at dissolved oxygen concentration of around 2 mgL(-1). The nitrogen oxides' impacts are between 0.0034 and 0.0044N% for the N2O and between 0.0020 and 0.0026N% for NO. A strict dependence between the N2O and the oxidation reduction potential is found.

The biological solution proposed to reduce the wasted sludge production is based on a process of alternating phases realized in a specific reactor (alternate cycles in sludge line (ACSL)) where a quote of the recycle sludge is treated and sent back to the main activated sludge process. The ACSL process was applied in two urban wastewater treatment plants (WWTPs). The reduction was tested by changing the hydraulic retention time and the conditions of oxidation reduction potential. The main mechanism of the process is recognized in the metabolic uncoupling. In fact, an increase in the specific oxygen uptake rate in the biological reactors was recorded (up to 20 mg/g VSS/h), which was stimulated by the fasting condition in the ACSL. The process is able to reduce the observed sludge yield on average of 25-30% with final average values reaching 0.179 kg VSS/kg chemical oxygen demand (COD) for WWTP1 and 0.117 kg VSS/kg COD for WWTP2.