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.

Integration of third generation biofuels with bio-electrochemical systems: Current status and future perspective.

Biofuels hold particular promise as these can replace fossil fuels. Algae, in particular, are envisioned as a sustainable source of third-generation biofuels. Algae also produce several low volume high-value products, which enhance their prospects of use in a biorefinery. Bio-electrochemical systems such as microbial fuel cell (MFC) can be used for algae cultivation and bioelectricity production. MFCs find applications in wastewater treatment, CO2 sequestration, heavy metal removal and bio-remediation. Oxidation of electron donor by microbial catalysts in the anodic chamber gives electrons (reducing the anode), CO2, and electrical energy. The electron acceptor at the cathode can be oxygen/NO3 -/NO2 -/metal ions. However, the need for a continuous supply of terminal electron acceptor in the cathode can be eliminated by growing algae in the cathodic chamber, as they produce enough oxygen through photosynthesis. On the other hand, conventional algae cultivation systems require periodic oxygen quenching, which involves further energy consumption and adds cost to the process. Therefore, the integration of algae cultivation and MFC technology can eliminate the need of oxygen quenching and external aeration in the MFC system and thus make the overall process sustainable and a net energy producer. In addition to this, the CO2 gas produced in the anodic chamber can promote the algal growth in the cathodic chamber. Hence, the energy and cost invested for CO2 transportation in an open pond system can be saved. In this context, the present review outlines the bottlenecks of first- and second-generation biofuels along with the conventional algae cultivation systems such as open ponds and photobioreactors. Furthermore, it discusses about the process sustainability and efficiency of integrating algae cultivation with MFC technology in detail.

Performance evaluation of algae assisted microbial fuel cell under outdoor conditions.

This study reports for the first time an operation of an outdoor algae assisted Microbial Fuel Cell (MFC). The MFC (10 L) comprised of low-cost materials like rock phosphate blended clayware & low-density polyethylene bags as anodic & cathodic chamber respectively. Algae biomass after lipid extraction at 2 g/l served as electron donor at the anode. Chlorella vulgaris at cathode provided oxygen as electron acceptor and served as lipid source. The MFCs performed well in all aspects namely energy recovery, algae productivity, and cost of operation. The 5% RP-MFCs gave 0.307 kg/m3d algal productivity, 0.09 kg/m3d lipid productivity, and 11.5318 kWh/m3 of net energy recovery (NER). Rock phosphate served as a slow and constant source of phosphorus supporting algae growth. Proteobacteria (45.14%) were the dominant phyla while Alicyliphilus (5.46%) and Dechloromonas (4.74%) were the dominant genera at the anode. The estimated cost of the system was $11.225 only.

Microbial fuel cell powered by lipid extracted algae: A promising system for algal lipids and power generation.

In this study, a promising microbial fuel cell (MFC) system has been developed, wherein algae is cultivated in the cathode chamber, algae biomass is harvested and lipids are extracted. The lipid extracted algal (LEA) biomass was then used asan electron donor substrate. The performance of MFCs fed with LEA biomass was compared with that of fruit waste fed MFCs (FP-MFCs), wherein LEA-fed MFC was superior in all aspects. Power density of 2.7Wm-3 was obtained by LEA-fed MFCs which is 145% and 260% higher than FP MFC and control MFC respectively. The volumetric algae productivity of 0.028kgm-3day-1 in cathode chamber was achieved. The system was able to generate 0.0136kWhKg-1CODday-1 of electric energy and 0.0782kWhm-3day-1 of algal oil energy. The proposed system is a net energy producer which does not rely heavily on the external supply of electron donor substrates.