Bioelectrochemical systems for ammonium removal in contaminated water

Summary Nowadays, ammonium (NH4+) is a pollutant present in all kinds of water bodies, leading to multiple environmental and health issues. The current NH4+-removing technologies are very expensive, as they require a lot of energy. Microbial electrochemical technologies (METs) are a less energy-consuming alternative to the conventional ammonium removal methods. The doctoral thesis “Bioelectrochemical systems for ammonium removal in contaminated water” by Miguel Osset Álvarez aims to contribute to the development of the two main ammonium-removing METs: bioelectrochemical nitrification and the combination of aerobic nitrification with bioelectrochemical denitrification. Bioelectrochemical nitrification is a very promising technology for NH4+ removal. However, the mechanisms behind this process have not been fully unveiled. A nitrifying bioelectrochemical system (niBES) was built, operated and studied for 550 days. A nitrifier (Achromobacter sp.) was found as the dominant microorganism in the niBES, while hydroxylamine (NH2OH) and nitrite (NO2-), two nitrification intermediates, were revealed as electroactive compounds. Overall, these results suggest that ammonium was converted into dinitrogen gas (N2) by a process combining bioelectrochemical NH4+ oxidation, denitrification and, to a lesser extent, anammox. On the other hand, a new ammonium-removing bioelectrochemical system (BES), the e-biofilter, was built by integrating bioelectrochemical denitrification into a biotrickling filter. E-biofilters were used to transform the NH4+ in synthetic aquaculture wastewater into nitrate (NO3-) and N2, enabling the reuse of this water for hydroponic culture. Moreover, the e-biofilters were capable of removing most of the ammonium, organic matter and suspended solids present in the secondary effluent of an urban wastewater treatment plant (WWTP), showing that e-biofilters can provide holistic wastewater treatment ​
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