Abstract
Anaerobic digestion process can be improved in combination with bioelectrochemical systems in order to recover energy and resources from digestates. An electromethanogenic microbial electrolysis cell (MEC) coupled to an ammonia recovery system based on hydrophobic membranes (ARS-HM) has been developed in order to recover ammonia, reduce organic matter content and upgrade biogas from digested pig slurry. A lab-scale dual-chamber MEC was equipped with a cation exchange membrane (CEM) and ARS with a hydrophobic membrane in the catholyte recirculation loop, to promote ammonia migration and absorption in an acidic solution. On the other hand, an electromethanogenic biofilm was developed in the biocathode to promote the transformation of CO2 into methane. The average nitrogen transference through the CEM was of 0.36 gN m−2 h−1 with a removal efficiency of 31%, with the ARS-HM in the catholyte recirculation loop. The removal of ammonia from the cathode compartment helped to maintain a lower pH value for the electromethanogenic biomass (7.69 with the ARS-HM, against 8.88 without ARS-HM) and boosted methane production from 50 L m−3 d−1 to 73 L m−3 d−1. Results have shown that the integration of an electromethanogenic MEC with an ARS-HM allows for the concomitant recovery of energy and ammonia from high strength wastewater digestates.
Highlights
The combination of the well-established anaerobic digestion technology with biolectrochemical systems (BES) has been subject of wide study in the last decade, since multiple configurations and objectives have been addressed [1,2,3]
BES have been proved to be a suitable technology for ammonia recovery, using dual chamber cells and cationic exchange membranes (CEM), either in the form of energy producing microbial fuel cells (MFC) or by introducing a small amount of energy to boost the process using microbial electrolysis cells (MEC) [16]
The aim of this study is to evaluate an electromethanogenic microbial electrolysis cell (MEC) coupled to an ammonia recovery system based on hydrophobic membranes (ARS-HM) in order to recover ammonia, reduce organic matter content and upgrade biogas from digested pig slurry
Summary
The combination of the well-established anaerobic digestion technology with biolectrochemical systems (BES) has been subject of wide study in the last decade, since multiple configurations and objectives have been addressed [1,2,3]. BES can help to overcome many of the drawbacks of anaerobic digestion, such as process instability [1,4,5], polishing of effluents and recovery of nutrients from the digestate [6,7,8,9,10], or biogas upgrading [11,12,13,14,15]. Anaerobic digestion of high organic and nitrogen strength wastewater, such as livestock manure, provides the possibility of being combined with BES in order to simultaneously recover ammonia from the digestate and to enhance energy recovery from the substrate, by converting the CO2 contained in the biogas into CH4 [11]. Present in the substrate fed into the anode compartment of the cell, migrates through the CEM towards de cathode compartment, concomitant to the electron movement from the anode to the cathode through the external circuit, in order to maintain the electroneutrality of the reactor [17,18]
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