Elsevier

Bioresource Technology

Volume 102, Issue 22, November 2011, Pages 10431-10435
Bioresource Technology

Use of inexpensive semicoke and activated carbon as biocathode in microbial fuel cells

https://doi.org/10.1016/j.biortech.2011.08.088Get rights and content

Abstract

In this study, two inexpensive semicoke and activated carbon packed bed biocathode were developed for oxygen reduction in microbial fuel cells (MFCs). These two materials were compared with two commonly used biocathode materials graphite and carbon felt in terms of material characteristic, power density, biomass density and price–performance ratio. MFCs with semicoke and activated carbon biocathode produced a maximum power density of 20.1 W/m3 (normalized liquid volume in cathodic compartment) and 24.3 W/m3, respectively, compared to 14.1 and 17.1 W/m3 obtained by MFCs with graphite and carbon felt biocathode, respectively. The bacteria attached on biocathode played a major role in oxygen reduction for all the materials investigated. The material cost per Watt produced for semicoke and activated carbon biocathode is only 2.8% and 22.7% of that for graphite biocathode, respectively. These two inexpensive carbon materials, especially semicoke, are very cost-effective biocathode materials for future large scale MFCs.

Highlights

► Inexpensive semicoke and activated carbon can be used as biocathode in MFCs. ► These two materials outperformed graphite and carbon felt in power generation. ► The bacteria attached on biocathode played a major role in oxygen reduction. ► These two materials are much more cost-effective than graphite and carbon felt.

Introduction

Microbial fuel cells (MFCs) are novel and promising future wastewater treatment technology for the generation of electricity from organic materials present in wastewater (Rozendal et al., 2008). In the past few years, higher power densities have been achieved by developing efficient materials, optimizing the reactor configuration and operation parameters (Cao et al., 2009, Logan et al., 2006, Oh et al., 2010). However, if it is to achieve practical application as a wastewater treatment technology, several important challenges need to be faced. Most of all, the capital costs of MFCs have to be significantly reduced so that MFCs can match the traditional wastewater treatment technology in terms of performance–cost ratio (Rozendal et al., 2008).

In most early studies, Pt catalysts were usually used for dissolved oxygen or open-air cathodes to increase the rate of oxygen reduction, but soon researchers realized that Pt was too expensive for application in MFCs (Cheng et al., 2006). To decrease the costs for the MFC, Clauwaert et al., 2007a, Clauwaert et al., 2007b developed biocathode MFC using bacteria as catalyst and achieved the reduction of oxygen and nitrite. Biocathodes have the important advantage of low cost, good stability and multiple functions for wastewater treatment. Thus it has become a rapidly emerging research topic within the MFC field (Huang et al., 2011). However, it is worthy to note that the cost of electrode material is still a pressing topic for biocathode MFCs. Currently, biocathode electrodes are mainly carbon-based materials like carbon felt, graphite granule, and graphite fiber, as well as stainless steel mesh. Taking graphite granule as an example, which was widely used in laboratory MFC and has a relatively low price, only the cost of electrode materials packed in a 1 m3 MFC reactor is several times that of conventional wastewater treatment systems with the same volume. Therefore, developing or looking for low-cost electrode materials and ensuring no loss of power generation performance remains an open challenge in the field of biocathode MFCs.

Material characteristics and configuration are two major factors affecting the performance of biocathode. The biocathode materials must have general characters of good conduction, good chemical stability, high mechanical strength, high surface roughness and good biocompatibility (Huang et al., 2011). To increase surface area for bacteria adhesion in per unit volume of MFC chamber, a three dimensional configuration, such as packed bed and brush structure, is preferable for biocathode. As packed bed biocathode provides wide range of choices in electrode materials, low-cost granular materials are expected to be one of the most practical options for future large scale MFCs.

Granular activated carbon (GAC) and granular semicoke (GS) are both commonly used carbon materials in filters or biofilm-driven water treatment processes. They both have characteristics of low cost, high specific area, good biocompatibility and moderate electrical conductivity, which basically meet the requirements of biocathode materials. At present, there have only been a few studies on MFCs using activated carbon as anode or air–cathode materials (Deng et al., 2010, Jiang and Li, 2009, Li et al., 2010, Zhang et al., 2009), but the performance of GAC and GS using as biocathode material is not clear.

In this study, we examined the use of GAC and GS as electrode materials of packed bed biocathode. These two materials were compared with commonly used biocathode materials, granular graphite (GG) and carbon felt cube (CFC), in terms of power generation performance and cost. It is known that the reduction of oxygen in biocathode is attributed to a combination of biological and chemical catalysis. In order to analyze the contribution of these two processes to oxygen reduction, the biomass density in cathode chamber and maximum power densities without bacteria attached on cathode (namely air–cathode) were also measured. At last, the performance–cost ratio of these biocathode materials was also assessed.

Section snippets

Cathodes characterization

Four granular carbon materials, including nut shell GAC (diameters between 2 and 5 mm, Beijing Chunqiudingsheng Environmental Science and Technology Co. Ltd., China), GS (diameters between 2 and 5 mm, China Electric Power Research Institute, China), GG (diameters between 2 and 5 mm, Sanye Carbon Co., Ltd, China) and CFC (1 cm on each side, Sanye Carbon Co., Ltd, China) were washed for 24 h in 20% HCl solution to remove metals from the surface. The washing process was repeated two times to eliminate

Electrode characterization

Elemental composition, specific area and total surface area of various carbon materials are shown in Table 1. XPS analysis showed that carbon and oxygen were two most abundant elements for these cathode materials. The mass fraction of carbon was above 80% for all these materials. GS have relatively low carbon content (81.61%). This is because semicoke is produced by incomplete carbonization and still contains some of volatile matters. The content of metal elements which may have catalytic

Conclusion

In this study, inexpensive GS and GAC were used as cathode materials in biocathode MFCs, which produced a maximum power density of 20.1 W/m3 and 24.3 W/m3, respectively, compared to 14.1 W/m3 with GG biocathode and 17.1 W/m3 with CFC biocathode. Biological catalytic processes play a major role for oxygen reduction in biocathode. The cost of GS and GAC biocathode per Watt produced were only 2.8% and 22.7% of that for graphite biocathode, respectively. Thus, these two inexpensive materials,

Acknowledgements

This research was supported by National High Technology Research and Development Program of China (863 Program) (No. 2009AA06Z306) and Shanghai Tongji Gao Tingyao Environmental Science & Technology Development Foundation (STGEF).

Cited by (58)

  • Cathode electrodes in MFCs

    2023, Biological Fuel Cells: Fundamental to Applications
  • Preparation of Ti<inf>3</inf>C<inf>2</inf>T<inf>x</inf> quantum dots/activated semi-coke composite and its electrocatalytic performance

    2022, Fuel
    Citation Excerpt :

    Thus, its conductivity was significantly improved. In addition, during the pore formation and activation process, the volatiles in semi-coke were removed to make the surface more conducive to the adhesion and electron transfer of pollutants [36]. Li et al. [37] used modified coal char materials as high-performance batteries.

  • Performance of different macrophytes in the decontamination of and electricity generation from swine wastewater via an integrated constructed wetland-microbial fuel cell process

    2020, Journal of Environmental Sciences (China)
    Citation Excerpt :

    To improve the electrical conductivity of the device, the anode adopted a high corrosion resistance stainless-steel wire mesh (20 cm × 20 cm × 10 cm) to wrap activated carbon particles buried in the downflow area (10–20 cm from the bottom), complying with the anodic conditions of the MFC, which was in an anaerobic condition (Oon et al., 2016). The high specific surface area made it an ideal medium for the attachment of microorganisms, and it exhibited characteristics of good activated carbon-like biocompatibility and moderate electrical conductivity (Wei et al., 2011). Carbon felt was used as the cathode (20 cm × 20 cm) and arranged on the upflow surface, and it could be combined with plant roots to promote oxygen transport and diffusion to create better aerobic conditions.

View all citing articles on Scopus
View full text