| Power plant wastewater contains ammonia (400-600 mg NH4+/l) and nitrate (300 to 1,100 mg NO3-/l). As discharge norms for nitrogen become more severe (15 mg N/l), research for efficient technology that removes N is justified. The existing methods for degrading ammonia and nitrate ions are biological treatment, the reduction on metallic iron (for nitrate), stripping and oxidation on TiO2/Pt (for ammonia). Biological treatment is complex, requires careful monitoring and produces sludge. The use of metallic catalysts is not yet at a cost effective point for both ammonia and nitrate degradation from industrial wastewater. Recently, Laborelec and the University of Louvain-la-Neuve developed an innovative technology that simultaneously degrades ammonia and nitrate ions into N2. This technology implements an electrochemical cell with suitable electrodes that favour the desired reactions. The degradation of nitrate occurs first via reduction into ammonia; ammonia is then oxidized into N2. Reduction of nitrates and oxidation of ammonia are realized in the same cell and at the same time, thus benefiting from the use of the same electrons for oxidation and reduction. We studied the influence of the current density, the electrode types, composition of the solutions, and optimized the operating parameters during lab tests to get the highest performances.
Results on the laboratory scale showed degradation rates ranging from 70 to 80 g NO3-/h/m2 and from 30 to 70 g NH3/h/m2. Nitrate and ammonia could be degraded to very low levels (10 to 20 mg NO3-/l and < 5 mg NH4+/l, without detection of nitrite). Given the promising results obtained on the laboratory scale, Laborelec applied for financial support from the European Commission and received grants from a LIFE demonstration project (ELONITA) to test the technology on an industrial scale (2005-2006). The construction of the pilot installation (treatment capacity: 5 m3/d) was finished in March 2004. Tests for the process reliability at large scale are running. Information regarding economic aspects is also collected. Application for a patent was made in April 2004. |