Simultaneous removal of sulfide and bicarbonate from synthetic wastewater using an algae-assisted microbial fuel cell

The anaerobic digestion (AD) process is one of the most practiced technologies for the remediation of organic waste and maximization of energy recovery in terms of biogas or biomethane. The presence of other gaseous components in biogas, e.g. CO₂ and H₂S, often makes its direct application in engines and electricity production unsuitable. This work aimed to develop and utilize an algae-assisted microbial fuel cell (AMFC) for the purification of biogas by removing both CO₂ and H₂S and simultaneous bioelectricity generation. In addition to biogas clean-up, elemental sulfur recovery and CO₂ utilization for algae cultivation add value to the proposed AMFC process. Experiments were performed with both sulfide and bicarbonate in their dissolved form, in the respective anodic and cathodic chambers of the AMFC. The sulfide concentration was varied from 100 to 800 mg/l and the AMFC exhibited a sulfide removal efficiency exceeding 97% at all concentrations tested. The process efficiency dropped, however, at sulfide concentrations above 300 mg/l in terms of both sulfide removal and power output. The AMFC performed best at 400 mg/l sulfide by exhibiting a power density of 24.99 mW/m³ and sulfide removal efficiency of 98.87%. The system exhibited columbic efficiency (CE %) in the range of 7.85-80%. The total alkalinity representing CO₂, carbonate and bicarbonate levels in the algae-based system was reduced by 49.54%. The electrical energy recovered from the AMFC was 0.1 kWh/m³ and the total energy recovery, which is the sum of the electrical and algal lipid energy, amounted to 7.25 kWh/m³.