Effect of electrode in UASB-MFC reactor for nitrogen removal under anammox condition and its microbial community profile

Abstract

Nitrogen removal through anammox is well-known for its low cost and less CO2 emissions, in this process ammonium converted into nitrogen gas with the help of anammox. It is hypothesized that the presence of electrodes in upflow anaerobic sludge blanket-microbial fuel cell (UASB-MFC) might increase nitrogen removal. In order to check this, two experimental setup were used to remove ammonium with electrode (UASB-MFC) and without electrode (UASB), under anammox condition. Different parameters were analyzed including nitrate, nitrite, total nitrogen and voltage. After 164 days, the NH4+ concentration in effluent was 3.20 mg/L and 4.23 mg/L, total inorganic nitrogen was 11.9 mg/L and 8.45 mg/L in UASB and UASB-MFC effluent respectively. Bacterial growth rate was calculated through biokinetic modelling, indicating anammox growth rate 0.00294 g VSS/m3.d in UASB-MFC with maximum voltage production of 774 mV. Metagenomic study was performed through 16 S rRNA genome sequencing showed, Firmicutes phylum was high in both reactors, while Planctomycetes, abundance 2.8% showing anammox growth achievement only in UASB-MFC. Lower concentration of nitrate, nitrite and total inorganic nitrogen were found in the UASB-MFC effluent which suggested the higher conversion of ammonium into nitrogen gas. It is concluded that the presence of an electrode oxidizes more nitrogen; hence total nitrogen was removed much more than in the absence of an electrode.