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Microbial Electrochemical Systems and Technologies: It Is Time To Report the Capital Costs Yifeng Zhang* and Irini Angelidaki
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Department of Environmental Engineering, Building 113, Technical University of Denmark, DK-2800 Lyngby, Denmark WHY ARE CAPITAL COSTS IMPORTANT? The lack of data on capital costs makes a comparison between different systems, materials or technologies difficult and may create a large gap between the technologies and markets. In many cases, the advantages of the new systems or materials over the conventional ones for the reduction of the capital costs are obvious. For example, several electrode catalysts have been fabricated and have been demonstrated to be promising alternatives to platinum.3 The determination of which one is the most cost-effective and what the cost savings are is impossible as important information is always missing from reports. Thus, merely listing the technical advantages of a new technology is far from sufficient. Technologies should be costeffective to meet market demands. “How much does your system/technology cost?” is a question that often arises from industrial partners and has motivated us to write this viewpoint.
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WHEN SHOULD COSTS BE REPORTED? More than 6000 scientific papers concerning METs have been published, a number that is continually growing. Among these studies, some publications are more concerned with fundamental issues and are not related to technical improvements for the reduction of capital costs. Thus, it is not expected that every paper about METs should describe the capital costs. Therefore, it is of utmost importance to develop criteria and recommendations that identify when it is important to report capital costs. It is highly recommended to report capital costs for research in the following fields. (1) Material studies including electrodes, electrode binders, catalysts, membranes, electron collectors, gas diffusers, and reactors. The materials not only affect the technical performance but also influence the economic viability of the METs, as they account for a large part of the capital costs. While more than one-third of MET studies concern fabrication and application of new materials, the capital or material costs are rarely reported. A systematic comparison of the costs from a practical point of view, which would be of value to both the scientific and industrial communities, is not yet available. (2) New reactor architecture. New reactor designs may change the material and construction costs and thus need to be considered. (3) New applications. Depending on the value of the product delivered by the technology, the relative profit would be different; new profitable applications would therefore permit higher construction costs. (4) Comparison of METs to other bioenergy or biotechnological technologies. Conversely, the capital costs could be less directly related for studies in which the focus is on the mechanisms of functions or
INTRODUCTION
Microbial electrochemical systems and technologies (METs) that can convert chemical energy stored in organic or inorganic matter into energy and/or to valuable chemicals have been studied extensively in the past decade.1 Generally, a MET reactor is composed of anodes and cathodes separated by membranes. Electrons are released from the microbial oxidation of substrate in the anode and are subsequently accepted by the cathode to complete a reduction reaction. After extensive fundamental studies to understand the electron transfer mechanisms, microbiology, reactor architecture and materials involved, METs are becoming a versatile technology platform for various applications such as wastewater treatment, bioremediation, environmental monitoring, and sustainable production of bioenergy and valuable chemicals.2 As examination of the technical viability continues, the economic feasibility and assessment aspects are being studied extensively, especially for METs that have come closer to being used in practical applications. The capital costs are one of the decisive economic factors for scale-up and commercialization of METs. Therefore, the reduction of material and construction costs has frequently been cited as the main objective in recent studies. However, the question remains as to whether the capital costs have been accurately reported for the METs that have been developed. Less than 10 out of several thousand publications have provided this information; thus, the answer is obvious. © XXXX American Chemical Society
Received: March 31, 2016
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DOI: 10.1021/acs.est.6b01601 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology
listing of capital costs is obviously beyond the objective of this work; the present figure is intended to elicit additional reporting of the capital costs by peers to advance METs toward large-scale application.
other fundamental research issues, such as studies of electron transfer mechanisms, microbiology, or substrates.
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IN WHAT FORM SHOULD COSTS BE REPORTED? Along with the development of METs, efforts have been made toward the standardization of procedures for reporting system performance such as power density.4 Standardized methods for reporting capital costs must be developed to incorporate the capital costs with the performance parameters in a systematic way. Rozendal et al. estimated the capital costs of microbial fuel cells and microbial electrolysis cells based on a specific electrode, membrane and reactor design.5 The estimated capital costs may not represent all of the METs due to the rapid development of materials, reactor architecture and applications, but the estimated costs do provide an indication for the evaluation of the economic viability of the technology. In connection with the performance parameters, we recommend normalizing the capital costs with the surface area (€/m2), reactor volume (€/m3) or treatment capacity (€/kg Chemical oxygen demand), which could be defined as the “capital density”. The nature of the different components of capital costs determines that different methods of data reporting may be applied for the purpose of the studies. For instance, the capital density normalized with surface area could provide more direct information for audiences interested in the economic load of different electrode materials. The capital density, in the units of €/kg Chemical oxygen demand, could be more useful for studies of wastewater treatment.
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AUTHOR INFORMATION
Corresponding Author
*Phone: (+45) 45251410; fax: (+45) 45933850; e-mail: yifz@ env.dtu.dk,
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The work was supported by The Danish Council for Independent Research (DFF-1335-00142) and DTU PoC Fond (31176).
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REFERENCES
(1) Logan, B. E.; Rabaey, K. Conversion of wastes into bioelectricity and chemicals by using microbial electrochemical technologies. Science 2012, 337 (6095), 686−690. (2) Logan, B. E.; Hamelers, B.; Rozendal, R.; Schroder, U.; Keller, J.; Freguia, S.; Aelterman, P.; Verstraete, W.; Rabaey, K. Microbial fuel cells: methodology and technology. Environ. Sci. Technol. 2006, 40 (17), 5181−5192. (3) Zhou, M.; Chi, M.; Luo, J.; He, H.; Jin, T. An overview of electrode materials in microbial fuel cells. J. Power Sources 2011, 196 (10), 4427−4435. (4) Logan, B. E. Essential data and techniques for conducting microbial fuel cell and other types of bioelectrochemical system experiments. ChemSusChem 2012, 5 (6), 988−994. (5) Rozendal, R. A.; Hamelers, H. V.; Rabaey, K.; Keller, J.; Buisman, C. J. Towards practical implementation of bioelectrochemical wastewater treatment. Trends Biotechnol. 2008, 26 (8), 450−459.
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CAPITAL DENSITY AS A POWERFUL TOOL: MORE EFFORTS ARE NEEDED With capital density, we can make a precise economic analysis that is an effective approach for interpreting observations, comparing systems, and identifying the drawbacks and merits of prototypes. The outcomes of the economic analysis will fill the gap between technology and market and shed light on the future development of the technology. Figure 1 shows the capital density of several typical METs that were investigated in our lab, according to the local market portfolio. A thorough
Figure 1. Capital density of selected METs. MFC: microbial fuel cell; MEC: microbial electrolysis cell; MDC: microbial desalination cell; MEDCC: microbial electrolysis desalination and chemical production cell; MREC: microbial reverse electrodialysis electrolysis cell; MRFC: microbial reverse electrodialysis fuel cell; MREEC: microbial reverse electrodialysis electrolysis and chemical production cell; SMFC: sediment MFC. B
DOI: 10.1021/acs.est.6b01601 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
