Overcoming organic and nitrogen overload in thermophilic anaerobic digestion of pig slurry by coupling a microbial electrolysis cell

Abstract

The combination of the anaerobic digestion (AD) process with a microbial electrolysis cell (MEC) coupled to an ammonia stripping unit as a post-treatment was assessed both in series operation, to improve the quality of the effluent, and in loop configuration recirculating the effluent, to increase the AD robustness. The MEC allowed maintaining the chemical oxygen demand removal of the whole system of 46±5% despite the AD destabilization after doubling the organic and nitrogen loads, while recovering 40±3% of ammonia. The AD-MEC system, in loop configuration, helped to recover the AD (55% increase in methane productivity) and attained a more stable and robust operation. The microbial population assessment revealed an enhancement of AD methanogenic archaea numbers and a shift in eubacterial population. The AD-MEC combined system is a promising strategy for stabilizing AD against organic and nitrogen overloads, while improving the quality of the effluent and recovering nutrients for their reutilization.

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

“…In Phase 1, the first block of experiments, the MFC was fed for 40 days with the digestate from a pig slurry mesophilic AD plant with a HRT of 40 days (Vila‐Sana, Lleida, Spain), diluted with tap water (1:2) to obtain the desired COD. The organic loading rate (OLR) of the MFC anode compartment was set at 18.22 g COD L ‐1 d ‐1 , similar to that of previous work in MEC mode . As a preliminary performance evaluation of the MFC at a sudden overload episode of the AD system, a series of pulses of pure and mixed VFAs were performed on the anode compartment (Table ).…”

“…The second block of experiments, Phases 2(a) and 2(b), started a week after the last pulse of Phase 1. To assess its performance with a real inhibited AD effluent, the MFC was fed for 142 days with the effluent from a 4 L lab‐scale thermophilic AD, described previously . This AD was fed with pig slurry with a HRT of 10 days.…”

“…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.…”

“…Therefore, microbial population evolution under these conditions is a field that needs an in‐depth study in order to gain insight on the stability of microbial biofilms established on the anode in bioelectrochemical system (BES) reactors. A previous study has shown a reduction in anode biodiversity when integrating pig slurry AD with a MEC system, but more data are needed to understand these changes with a MFC system when no additional energy is supplied to the BES.…”

Urine in Bioelectrochemical Systems: An Overall Review

“…More recently, Cerrillo et al [112] studied the combination of anaerobic digestion (AD) and MEC in order to improve the quality of the effluent and recover ammonia by coupling a stripping/absorption unit. The anaerobic digester consisted of a cylindrical glass reactor where the temperature was controlled.…”