Abstract
In this work, the feasibility of the Shortcut Biological Nitrogen Removal (SBNR) in the anodic chamber of a Microbial Fuel Cell (MFC) was investigated. Thirty day experiments were carried out using synthetic wastewaters with a Total Organic Carbon vs. nitrogen ratio (TOC/N) ranging from 0.1 to 1. Ammonium, nitrite, nitrate, pH, and TOC were daily monitored. Results showed that microaerobic conditions in the anodic chamber favored the development of nitritation reaction, due to oxygen transfer from the cathodic chamber through the membrane. Nitritation was found to depend on TOC/N ratio: at TOC/N equal to 0.1 an ammonium removal efficiency of up to 76% was observed. Once the oxygen supply to the cathodic chamber was stopped, denitritation occurred, favored by an increase of the TOC/N ratio: a nitrite removal of 80.3% was achieved at TOC/N equal to 0.75. The presence of nitrogen species strongly affected the potential of the electrochemical system: in the nitritation step, the Open Circuit Voltage (OCV) decreased from 180 mV to 21 mV with the decrease of the TOC/N ratio in the investigated range. Lower OCV values were observed in the denitritation steps since the organic carbon acted as the energy source for the conversion of nitrite to nitrogen gas. A kinetic analysis was also performed. Monod and Blackman models described the ammonium and the organic carbon removal processes well during the nitritation step, respectively, while Blackman-Blackman fitted experimental results of the denitritation step better.
Highlights
Nitrogen rich wastewaters are generated by several industrial and agricultural activities, as well, ammonium is one of the major pollutants in domestic wastewater
This study demonstrated that nitrogen cycle can be developed in an Microbial Fuel Cell (MFC) system, via the Shortcut Biological Nitrogen Removal (SBNR) pathway
High ammonium removal (76%) was observed for TOC/N = 0.1, whilst organic carbon removal was favored at higher TOC/N ratios and it was almost completed at TOC/N = 26
Summary
Nitrogen rich wastewaters are generated by several industrial and agricultural activities, as well, ammonium is one of the major pollutants in domestic wastewater. The uncontrolled release of such wastewater may favor eutrophication in rivers and lakes, and ammonium is a strong pollutant in aquatic ecosystems [1]. For this reason, the amount of ammonium discharged into the environment is limited by European Directive [2]. Nitrogen removal from wastewater is generally carried out through biological processes, called Biological Nutrient Removal (BNR), by a specific microbial pool [3]. The BNR process is characterized by two steps: ammonium oxidation (nitrification) followed by nitrogen gas development by nitrate reduction (denitrification). Nitrification, in turn, is carried out in two steps: ammonia is first converted into nitrite by Ammonia Oxidizing Bacteria (AOB, Equation (1))
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