Total organic carbon and total nitrogen removal and simultaneous electricity generation for nitrogen-containing wastewater based on the catalytic reactions of hydroxyl and chlorine radicals

The treatment of nitrogen-containing organic wastewater is a difficult problem because organic and nitrogen contents are hard to remove simultaneously for the common sewage disposal technologies. Here we propose a new method to efficiently remove total organic carbon and total nitrogen and generate electricity simultaneously for this wastewater. The key idea of design is that organics and ammonia nitrogen is converted into CO2 and N-2 by catalytic reacting with hydroxyl and chlorine radicals, respectively, while generating electricity concurrently in a self-biased wastewater fuel cell. Nitrate-N (including original or generated) was reduced on Pd/Cu modified Ni foam electrode with high selectivity toward N-2, realizing the completely removal of total nitrogen from the water. Moreover, self-bias voltage was generated by employing WO3 nanoplate array electrodes and silicon photovoltaic cells as a hybrid photoanode to enhance the charge separation. This system was also successful in extending the light harvest. A series of experiments were performed with nitrate-N (ammonium-N) and phenol and the results indicated the removal efficiency of nitrate-N (ammonium-N) was 98.7% (91.5%) in 90 min and total nitrogen was efficiently transformed to N-2 with extending time to 120 min. The system also showed a superior performance for phenol degradation (99.1% in 90 min). Combined with the analysis of ESR and free radical capture experiment, it was concluded that chlorine radical played an important role in the phenol and ammonia-N oxidation. In addition, maximum power density output of the system reached 1.23 mW cm(-2). This study offers a self-sustaining approach for simultaneous nitrogen-containing organic wastewater treatment and electricity production.