In a microbial electrolysis cell (MEC), it is possible to conduct the two main reactions of anaerobic digestion (AD) in two physically separated chambers, by coupling COD oxidation into CO2 (in the bio-anode) to the CO2 removal and reduction into methane (in the bio-cathode), thanks to the transfer of reducing power by the electrical and ionic current. Moreover, AD and MEC can be integrated, by using the MEC to upgrade methane content of the AD biogas while also using residual COD from AD anaerobic digestate, so improving the overall energy efficiency and the quality of the products of conventional AD (Villano et al 2013). However, this approach has not been tested with real substrates yet and concerns also exist on possible fouling and poisoning effects on ionic membrane and/or electrodic material. Here, a continuous-flow 2-chamber MEC was operated under anodic potentiostatic control (at 0.2 vs SHE), to compare its performance by feeding the bio-anode with synthetic vs real substrates; both an anaerobic digestate (from methanogenic stage) and an acidogenic fermentate (from preliminary acidogenic stage) were tested and compared with a synthetic substrate mixture (as described in Zeppilli et al 2014). The MEC was equipped with a proton exchange membrane (PEM) and both electrodic beds made by graphite granules. The cathode chamber was fed by a continuous sparging of a gas mixture of N2/CO2 (70/30 v/v to simulate biogas), whereas a concentrated liquid stream was spilled to counterbalance osmotic water flow across PEM. The MEC performed poorly (23 ± 4 mA) when fed by the anaerobic digestate because its residual COD resulted to be poorly available for anodic oxidation, whereas the mixture of both first and second stage AD effluents gave slightly better performance than the synthetic mixture(60 ± 4 mA vs 50 ± 1 mA, respectively). The latter evidence was not only due to high VFA-content but also to high ammonia concentration. Being ammonia higher than in the synthetic mixture, the percentage of ionic current transported across the PEM by the ammonium instead of the proton was increased from 2 to 20 %. This eventually increased the net generation of the alkalinity in the cathodic chamber and thus bicarbonate concentration in the cathodic spill. Overall, by using the VFA-rich and ammonia-rich mixture of both real effluents, a nitrogen removal rate of 228 mg/Ld was obtained while an average CO2 removal of 3.4 g/Ld was observed in the cathode. Fouling phenomena were observed to decrease the MEC performance, likely due to the high content of suspended solids in both real substrates (in spite of preliminary filtration at around 0.2 mm cut off). However, adverse fouling effects were easily recovered by periodic backwashing of the bio-anode.
Two phase anaerobic digestion effluents as feedstocks to bioelectromethanogenesis sustenance / Zeppilli, Marco; Ilaria, Ceccarelli; Villano, Marianna; Majone, Mauro. - STAMPA. - (2016). (Intervento presentato al convegno 3rd European Meeting ISMET 2016 tenutosi a Chemical Department, University of Rome Sapienza nel 26-28 September 2016).
Two phase anaerobic digestion effluents as feedstocks to bioelectromethanogenesis sustenance
ZEPPILLI, MARCO;VILLANO, MARIANNA;MAJONE, Mauro
2016
Abstract
In a microbial electrolysis cell (MEC), it is possible to conduct the two main reactions of anaerobic digestion (AD) in two physically separated chambers, by coupling COD oxidation into CO2 (in the bio-anode) to the CO2 removal and reduction into methane (in the bio-cathode), thanks to the transfer of reducing power by the electrical and ionic current. Moreover, AD and MEC can be integrated, by using the MEC to upgrade methane content of the AD biogas while also using residual COD from AD anaerobic digestate, so improving the overall energy efficiency and the quality of the products of conventional AD (Villano et al 2013). However, this approach has not been tested with real substrates yet and concerns also exist on possible fouling and poisoning effects on ionic membrane and/or electrodic material. Here, a continuous-flow 2-chamber MEC was operated under anodic potentiostatic control (at 0.2 vs SHE), to compare its performance by feeding the bio-anode with synthetic vs real substrates; both an anaerobic digestate (from methanogenic stage) and an acidogenic fermentate (from preliminary acidogenic stage) were tested and compared with a synthetic substrate mixture (as described in Zeppilli et al 2014). The MEC was equipped with a proton exchange membrane (PEM) and both electrodic beds made by graphite granules. The cathode chamber was fed by a continuous sparging of a gas mixture of N2/CO2 (70/30 v/v to simulate biogas), whereas a concentrated liquid stream was spilled to counterbalance osmotic water flow across PEM. The MEC performed poorly (23 ± 4 mA) when fed by the anaerobic digestate because its residual COD resulted to be poorly available for anodic oxidation, whereas the mixture of both first and second stage AD effluents gave slightly better performance than the synthetic mixture(60 ± 4 mA vs 50 ± 1 mA, respectively). The latter evidence was not only due to high VFA-content but also to high ammonia concentration. Being ammonia higher than in the synthetic mixture, the percentage of ionic current transported across the PEM by the ammonium instead of the proton was increased from 2 to 20 %. This eventually increased the net generation of the alkalinity in the cathodic chamber and thus bicarbonate concentration in the cathodic spill. Overall, by using the VFA-rich and ammonia-rich mixture of both real effluents, a nitrogen removal rate of 228 mg/Ld was obtained while an average CO2 removal of 3.4 g/Ld was observed in the cathode. Fouling phenomena were observed to decrease the MEC performance, likely due to the high content of suspended solids in both real substrates (in spite of preliminary filtration at around 0.2 mm cut off). However, adverse fouling effects were easily recovered by periodic backwashing of the bio-anode.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.