Abstract
This study reports an investigation of the concept, application and performance of a novel bioelectrochemical nitritation-anammox microbial desalination cell (MDC) for resource-efficient wastewater treatment and desalination. Two configurations of anammox MDCs (anaerobic-anammox cathode MDC (AnAmoxMDC) and nitration-anammox cathode MDC (NiAmoxMDC)) were compared with an air cathode MDC (CMDC), operated in fed-batch mode. Results from this study showed that the maximum power density produced by NiAmoxMDC (1,007 mW/m3) was higher than that of AnAmoxMDC (444 mW/m3) and CMDC (952 mW/m3). More than 92% of ammonium-nitrogen (NH4+-N) removal was achieved in NiAmoxMDC, significantly higher than AnAmoxMDC (84%) and CMDC (77%). The NiAmoxMDC performed better than CMDC and AnAmoxMDC in terms of power density, COD removal and salt removal in desalination chamber. In addition, cyclic voltammetry analysis of anammox cathode showed a redox peak centered at −140 mV Vs Ag/AgCl confirming the catalytic activity of anammox bacteria towards the electron transfer process. Further, net energy balance of the NiAmoxMDC was the highest (NiAmoxMDC-0.022 kWh/m3 >CMDC-0.019 kWh/m3 >AnAmoxMDC-0.021 kWh/m3) among the three configurations. This study demonstrated, for the first time, a N-E-W synergy for resource-efficient wastewater treatment using nitritation-anammox process.
Highlights
Water and wastewater infrastructure accounts for approximately 3–4 percent of national energy demand in the United States[1]
A possible reason for higher generation of power density in NiAmoxMDC could be due to the presence of two terminal electron acceptors in a single cathode compartment: one reduction of oxygen and another metabolic activity of anammox bacteria
Electrons generated by exoelectrogenic bacteria via bio-catalyzed reactions at the anode were transferred to the cathode through an external electric circuit, where protons are combined with the electrons and oxygen to www.nature.com/scientificreports produce water (Fig. 1)
Summary
Water and wastewater infrastructure accounts for approximately 3–4 percent of national energy demand in the United States[1]. More than 50 percent of the supplied energy is used to meet the aeration demands for carbon and nitrogen oxidation processes in wastewater treatment[2]. Strous et al.[4] described the physical purification of anammox bacteria, which oxidize ammonium to nitrogen gas anaerobically, with nitrite (NO2−) as an electron acceptor and fixed carbon from CO2 as a sole carbon source for the growth of anammox biomass (CH2O0.5N0.15), making the organism an autotroph (see reaction R1). This anaerobic oxidation reaction is thermodynamically more favorable than the aerobic ammonia oxidation reaction. Hydrazine undergoes oxidation to produce dinitrogen gas generating four electrons (reaction R3) equivalent for reducing nitrite to form hydroxylamine (NH2OH) at the cytoplasm of anammox bacteria[8]
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