The conventional process for removing nitrogen compounds from wastewater involves ammonia autotrophic-nitrification followed by heterotrophic-denitrification using organic material as electron donor. When the wastewater treatment involves the pre-treatment in an anaerobic reactor, the costs increase due to the need of adding organic-donors because the easily biodegradable organic matter is promptly consumed in anaerobic reactors. However, effluents from anaerobic reactors may contain mineral reduced compounds such as sulfide and also residual organic matter able to act as electron donors for denitrification. The aim of this research project is the evaluation of simultaneous autotrophic and heterotrophic denitrification processes in an anoxic reactor. In this project a pilot scale system consisting of two reactors (one anaerobic-anoxic and the other aerobic) will be used. This setup will be kept at room temperature, and fed with sewage. Sewage will undergo the anaerobic chamber; then it will be mixed with nitrified effluent, and undergo the anoxic chamber; effluent from this chamber will be nitrified in the aerobic reactor; part of this effluent will be returned to the anoxic chamber and the rest correspond to the final effluent. The up flow mode will be adopted in the anaerobic-anoxic reactor, whereas the aerobic reactor will be operated in a down flow mode. The hydraulic retention time (HRT) will be 8 h in the anaerobic chamber, 4-8 h in the anoxic chamber, and 5 h in the nitrifying chamber. The values of HRT and recycling flow rate from the nitrifying chamber to the anoxic chamber will be varied along the experiment to increase the system performance in removing organic matter and nitrogen.
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