NoNitriNox – Planning and operation of resource and energy efficient sewage treatment facilities with simultaneous reduction of environmentally hazardous emissions

The operation of wastewater plants for advanced treatment involves considerable costs and resource use. Particularly the energy requirements (electric power) of wastewater treatment plants constitute a significant portion of the energy budgets of municipalities. Accordingly, great efforts have been undertaken in recent years to minimize the energy needs of treatment plants. These measures include:

• Flexible process design and operation management to maximize denitrification, and
• Adapted control concepts with the goal of minimizing aeration energy (reduction of the ideal oxygen level, optimization of oxygen profiles, ammonium-controlled aeration, and nitrate-controlled intermittent aeration).

Aerial photograph of the wastewater treatment plant in Dusslingen; Photo: Abwasserverband Steinlach-Wiesaz

In practice, these measures have demonstrated that with good planning and operationalization, significant potentials for the improvement of the energy efficiency of wastewater-treatment plants exist. However, the introduction of these methods also involves risks and disadvantages. In addition to the potential maximization of ammonium emissions and the deterioration of sludge stabilization, sedimentation behavior and the dehydration capacity of the sludge, there is also the danger of increased emissions of environmentally hazardous pollutants such as nitrite and laughing gas (N₂O). The project has two essential targets:

• The development of a planning tool for the design and optimization of wastewater treatment plants, which, in addition to complying with typical requirements (nitrogen, phosphorus and carbon elimination), and estimating energy use and energy generation, also explicitly takes into account a quantification and evaluation of the nitrite, laughing-gas and methane emissions (a calculation of CO₂ emissions is also included); and
• The development of intelligent controlling concepts which, in addition to the classical compliance with process requirements and the achievement of energy-use minimization, also reduce the risk of nitrite, laughing-gas and methane emissions.