Renewable energy from ammoniumrich anaerobic wastewaters and liquid sludges

Abstract

The Italian adoption of the recent European legislation on nitrates has further restricted the parameters for the discharge of water containing ammonium. This adoption has prompted the operators of wastewater treatment plants to invest in abatement equipment for ammonia within the parameters set by the law. This situation is particularly problematic for the anaerobic digestion plants that often have wastewater discharge with concentrations of ammonia nitrogen which also exceeds 3000 ppm. The technologies currently considered for eliminating ammonia include biological processes (NITRO/DENITRO, ANAMMOX, SHARON, CANON) [1] (which are difficult to apply to concentrations larger than 700- 800 ppm) and stripping ammonia (that requires complex plants and the supply of large quantities of energy). To the end of introducing a technology providing a competitive removal of ammonium, an abatement process with energy recovery of ammonia (that is particularly effective for wastewater with high load of ammonium) has been developed and tested. From the energetic point of view the ammonia has a lower calorific value (18.6 MJ/kg) and contains 17.6% by weight of hydrogen. This is remarkable (it exceeds by 41% the hydrogen content (by weight) of liquid hydrogen) result and may turn the effluent ammonium into a renewable energy source.