Removal of volatile fatty acids and ammonia recovery from unstable anaerobic digesters with a microbial electrolysis cell

Abstract

Continuous assays with a microbial electrolysis cell (MEC) fed with digested pig slurry were performed to evaluate its stability and robustness to malfunction periods of an anaerobic digestion (AD) reactor and its feasibility as a strategy to recover ammonia. When performing punctual pulses of volatile fatty acids (VFA) in the anode compartment of the MEC, simulating a malfunction of the AD process, an increase in the current density was produced (up to 14 times, reaching values of 3500mAm(-2)) as a result of the added chemical oxygen demand (COD), especially when acetate was used. Furthermore, ammonium diffusion from the anode to the cathode compartment was enhanced and the removal efficiency achieved up to 60% during daily basis VFA pulses. An AD-MEC combined system has proven to be a robust and stable configuration to obtain a high quality effluent, with a lower organic and ammonium content.

Microbial fuel cells for polishing effluents of anaerobic digesters under inhibition, due to organic and nitrogen overloads

“…The pH of the bulk solution in the anode compartment remained in the range 7.3–8.8, thus being appropriate for microbial activity (Figure (b)). In a previous work using a MEC, current density increased in response to each VFA pulse . This behaviour agrees with the low coulombic efficiencies achieved when working with MFCs (1–4%) compared with those achieved in MEC mode (11–18%) .…”

“…However, MFC performance against AD destabilisation has not been studied in depth, nor has its influence on ammonia recovery. A previous study performed under microbial electrolysis cell (MEC) mode, thus applying a low amount of energy to the system to boost the process, has shown that VFA accumulation in pig slurry digestates can be removed in a MEC reactor while recovering ammonium at the same time . That study also showed that higher MEC performances were attained when the AD was in an unstable or inhibited state.…”

Stratified microbial structure and activity within anode biofilm during electrochemically assisted brewery wastewater treatment

“…Owing to the slow growth and high sensitivity of methanogens to various inhibitory compounds, the organic acids (acetic and propionic acids) produced through fermentation easily accumulate under a high organic load during the anaerobic digestion (Franke‐Whittle, Walter, Ebner, & Insam, 2014). In contrast, in polarized systems, organic matter can be rapidly depleted by exoelectrogens using an anode as an electron acceptor (Asensio, Fernandez‐Marchante, Lobato, Caňizares, & Rodrigo, 2016; Cerrillo, Viñas, & Bonmati, 2016). This is consistent with the higher removals of acetic acid and propionic acid in the polarized system than in the open‐circuit system investigated in this study (Figure 2).…”

Microbial electrolysis cell as an emerging versatile technology: a review on its potential application, advance and challenge

“…Integration of AD with BES can enrich exoelectrogens (anode) and hydrogenotrophic methanogens (cathode) . The degradation rate of recalcitrant compounds in wastewater is higher in the integrated MEC‐AD system, and the effluent has been found to have low organics and ammonium contents . Dou et al .…”

“…163 The degradation rate of recalcitrant compounds in wastewater is higher in the integrated MEC-AD system, 76 and the effluent has been found to have low organics and ammonium contents. 122 Dou et al 163 reported that an MEC-AD had higher resilience to shock organic loading, and a potential of 2 V resulted in water electrolysis and led to a higher CH 4 production rate (105 mL L −1 day −1 ) and biogas CH 4 content (88.5 + 1.4%).…”