Bioresource Technology 109 (2012) 308–311

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Bioresource Technology

journal homepage: www.elsevier .com/locate /bior tech

Production of algal biomass (Chlorella vulgaris) using sediment microbial fuel cells

Hyeon Jin Jeon a, Kyu-won Seo a, Sang Hyun Lee a, Yung-Hun Yang a, Rangarajulu Senthil Kumaran a,Sunghyun Kim b, Seok Won Hong c, Yong Su Choi c, Hyung Joo Kim a,⇑a Department of Microbial Engineering, Konkuk University, Seoul 143-701, Republic of Koreab Department of Bioscience and Biotechnology, Konkuk University, Seoul 143-701, Republic of Koreac Water Environment Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Republic of Korea

a r t i c l e i n f o a b s t r a c t

Article history:Available online 16 June 2011

Keywords:Sediment microbial fuel cellAlgal cultivationChlorella vulgarisBioelectrochemical CO2 generationBioelectrochemical CH4 suppression

0960-8524/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.biortech.2011.06.039

⇑ Corresponding author. Tel.: +82 2 2049 6111; faxE-mail address: hyungkim@konkuk.ac.kr (H.J. Kim

In this study, a novel algal biomass production method using a sediment microbial fuel cell (SMFC) sys-tem was assessed. Under the experimental conditions, CO2 generation from the SMFC and its rate ofincrease were found to be dependent on the current generated from the SMFC. However, the CH4 produc-tion rate from the SMFC was inhibited by the generation of current. When Chlorella vulgaris was inocu-lated into the cathode compartment of the SMFC and current was generated under 10 X resistance,biomass production from the anode compartment was observed to be closely associated with the rateof current generation from the SMFC. The experimental results demonstrate that 420 mg/L of algae(dry cell weight) was produced when the current from the SMFC reached 48.5 mA/m2. Therefore, SMFCcould provide a means for producing algal biomass via CO2 generated by the oxidation of organics uponcurrent generation.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Recently, a significant amount of attention has been focusedon renewable energy sources that might help satisfy the ever-increasing demand for energy consumption and environmentalprotection (Choi et al., 2010; De Schamphelaire and Verstraete,2009). Among possible renewable energy sources, microalgaehave gained increased attention as they contain a significantquantity (e.g. 20–50% dry cell weight) of neutral lipids for bio-diesel production (Hu et al., 2008). Various methods for the cul-tivation of algae have been proposed ever since Harder and vonWitsch proposed the mass cultivation of diatoms to produce ur-gently needed fat during World War II (Liang et al., 2009). In re-cent years, significant efforts have expended toward thedevelopment of biological aspects (i.e. strain selection and/orimprovement, etc.) and non-biological aspects (i.e. light source,fermentor design, cultivation method, etc.) for use in algal pro-duction (Brennana and Owendea, 2010). Despite recent effortsto improve the production yield of algal biomass, there remainsome technological barriers to overcome before the economicproduction of a stable energy source becomes feasible. Amongthese technological barriers, CO2 is one of the critical factors inphotosynthesis, along with light, water, and nutrients. Particu-larly in the case of high-density cultures of algal biomass in a

ll rights reserved.

: +82 2 446 2677.).

bioreactor, effective CO2 supply is recognized as a crucial factor.In the case of open pond-type cultures such as raceway-typeponds or lakes, quality control, slow growth, and low CO2 partialpressure constitute major obstacles (Brennana and Owendea,2010).

Along with the problems listed above, the presence of organicbottom lake sediment is associated with the generation of CH4,which has serious greenhouse gas effects. To remove CH4 gener-ation from conventional lake or swamp sediment, a variety ofmethods, including ultrasonication, O2 feeding, heat treatment,and acid/base treatment, have been proposed for the treatmentof sediment (Elbeshbishya et al., 2010). In particular, it has beenreported that the addition of inorganic electron acceptors to sed-iment inhibits CH4 generation (Scholten and Stams, 1995). In aprevious study, a microbial fuel cell (MFC) using lake sedimentas an electron donor for electrochemically active bacteria wasexamined, and it was determined that this method could beused successfully to reduce the organic matter content of thesediment (Hong et al., 2008).

In the present study, we demonstrate a novel algal productionsystem using a sediment microbial fuel cell (SMFC) capable ofdecreasing CH4 generation capability of organic rich-lake sediment,which was divided into two parts. First, using organic-rich sedi-ment obtained from a natural lake, correlations between currentgeneration and gas (CO2 and CH4) production in the SMFC wereestablished. Secondly, the algal production capability of the SMFCand the applicability of algal culture for SMFC operation withoutany external oxidant were investigated.

H.J. Jeon et al. / Bioresource Technology 109 (2012) 308–311 309

2. Methods

2.1. Algal strain, medium, and sediment for SMFCs

The Chlorella vulgaris strain (KCTC AG10002) was provided bythe Korean Culture Type Collection (Daejun, Korea). The mediumfor cultivation of C. vulgaris was Bold’s Basal Medium (BBM, pH6.8) (Lima et al., 2010). The cells were grown in 250 ml Erlenmeyerflasks on an orbital shaker set at 150 rpm at 25 �C under constantflorescence light. Sediment for the construction of SMFCs was ob-tained from Ilgam lake, an artificial lake at Konkuk University,Seoul, and a typical hypereutrophic lake in Korea (collection date:June 2010). The average amounts of organic matter in the sedimentas measured by the loss on ignition (LOI) and readily oxidizable or-ganic matter (ROOM) methods were 10.4% LOI and 3.52% ROOM,respectively (Hong et al., 2008).

2.2. SMFC construction

Fig. 1 shows a schematic diagram of the sediment microbial fuelcell (SMFC) employed in this study. The SMFC consisted of an an-ode and cathode positioned at opposite sides of a poly-acrylic plas-tic cylindrical chamber (d = 110 mm, h = 250 mm, t = 2 mm). Boththe anode (d = 80 mm, t = 2 mm) and cathode (d = 90 mm,t = 2 mm) consisted of graphite felt (GF series, GEE graphite Ltd.,UK). Electrodes were connected externally with concealed copperwire. The sediment (775 g wet weight) was initially added to thechamber (ca. 50 mm in thickness), and the anode was placed inthe middle of the sediment layer. The sediment was then coveredwith sterilized sand (638 g wet weight). For direct collection of thegas generated from the anode compartment (i.e. sediment), a fun-nel type gas collector (d = 80 mm) was placed on the surface of thesediment of the SMFC and connected to a gas sample bag (232 ser-ies, SKC, USA). Four sets of the SMFC system were used in thisstudy.

2.3. SMFC operation

The SMFCs were operated in a fluorescence light (light intensityof 81 lmol/m2 s) incubator at constant temperature of 25 �C. Toinvestigate the effect of external resistance on current and gas gen-eration, the cathode compartment was initially filled with BBM,and the cathode was aerated at a rate of 200 ml/min. The connec-

Fig. 1. Schematic diagram of the alg

tion between the anode and cathode was made via external loadresistors. BBM containing 1% glucose (w/v) as a fuel for operationof the SMFCs was supplied to the system (0.04 ml/min) with a peri-staltic pump. When the system set-up was completed, the currentgenerated from each SMFC was monitored with a digital multime-ter (model 2000, Keithley, USA) (Choi et al., 2010). The gas gener-ated during operation (15 days) of the SMFCs was collected via thegas collector and stored in the sample bag. Sampling for bicarbon-ate analysis was made via the sampling port (Fig. 1).

For algae cultivation in the SMFCs, the gas collector in the cath-ode compartment was removed and the precultured algae inocu-lated (20% v/v) into the cathode compartment. During algalcultivation, aeration to the cathode was stopped. Cultivations werecarried out for 15 days in the SMFCs with different load resistors.To prevent bacterial contamination, the SMFCs were irradiatedwith UV light (kmax = 204 nm) eight times a day (10 s every 3 h at200 lmol/m2 s intensity) (Seo et al., 2009). All experiments wereconducted at least in duplicate.

2.4. Analysis

Gaseous CO2 and CH4 generated from the SMFCs were analyzedvia gas chromatography as described previously (Holland et al.,1999). CO2 dissolved in the cathode compartment was measuredvia the acid/base titration based on the bicarbonate concentration(Fresenius et al., 1988). The dry weight of the algal culture samplewas determined by drying 50 ml of the algal suspension at 80 �C ina drying oven for 24 h after filtration through pre-dried and pre-weighted 0.45 lm filter paper.

3. Results and discussion

3.1. Effect of external resistance on generation of current, CO2, and CH4

After the SMFCs with different external load resistors were setup, electrical current and gas generation from the SMFCs weremonitored. The current gradually increased over 15 days, uponwhich it achieved steady state. Fig. 2 shows the relationshipsamong electrical current generation, CO2 generation, and CH4 gen-eration from the SMFCs connected with different external loadresistors.

al culture system using SMFC.

External resistance (Ω)10 100 500 Open circuit

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CH4

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O3- ,

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Fig. 2. Effect of external resistance on the generation of CO2 and CH4 from theSMFCs. The data were evaluated after 15 days of SMFC operation with differentexternal load resistors.

Time (day)16 18 20 22

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50Awith algae, without air

without algae, with air

Fig. 3. Operation of SMFCs under various experimental conditions. (A) Comparisonof currents generated from SMFCs with and without algal cultivation. (B) Currentgeneration pattern from an SMFC with and without illumination (lights-on: 18 h,lights-off: 6 h, arrows indicate lights-off times).

310 H.J. Jeon et al. / Bioresource Technology 109 (2012) 308–311

Under open circuit conditions (i.e. no electrical current flewthrough the SMFC), about 1.78 mM CO2 (gaseous CO2 + bicarbon-ate) was obtained. When the electrodes were connected via a10 X external load resistor (current: 33 mA/m2), however, themaximum concentration of CO2 reached 8.83 mM. The experimen-tal results demonstrate that the amount of CO2 generated from theSMFC was related closely to the rate of current generation from theSMFC. Previous studies have shown that current generation from amicrobial fuel cell is completely dependent on carbon metabolismby the bacteria, and the anode of the microbial fuel cell acts as anelectron acceptor for electrochemically active bacteria (Kim et al.,2002). Therefore, the correlation between increased CO2 genera-tion and increased current generation from SMFCs with low levelexternal load resistors can be attributed to the increased metabolicspeed of the electrochemically active bacteria in the sediment. Inthe case of a high level of resistance (i.e. 500 X or open circuit),limited electron flow suppresses the metabolic activity of the elec-trochemically active bacteria, resulting in a low level of CO2

generation.Electrical current also changed the rate of CH4 generation from

the SMFC. A gradual decrease in the rate of CH4 generation oc-curred when the current from the SMFC was increased. Under opencircuit conditions, about 1.34 mM CH4 was produced. When theSMFC was connected to a 10 X external load resistor, the CH4 con-centration was reduced to 0.13 mM. Previous research using a MFCdemonstrated that electron loss is attributable to the activity of theanode (i.e. electron acceptor), as a low level external load resistorreduced the rate of CH4 generation (Hong et al., 2008). In thisexperiment, changes in the gas generation rate from the SMFCcan be attributed to the action of the anode in the sediment, withoxidation of the electron donor and subsequent variations in theactivity of related microorganisms (Aelterman et al., 2008). Takingthese observations into consideration, additional experimentswere conducted to investigate the possibility of algal cultivationin the SMFC using CO2 generated from the system (i.e. anode com-partment) as an inorganic carbon source.

3.2. Effect of external resistance on the growth of algae in the SMFC

To evaluate the algal culture capability of the SMFC, algae-inoc-ulated SMFCs connected with different external load resistors wereoperated. When the current generation and biomass concentrationin the SMFCs were monitored after 15 days of operation, we foundthat the connection of a low-level load resistor to the SMFC in-duced both higher values of current and biomass concentration.

The algal biomass density in the SMFC connected to a 10 X resistorwas about 420 mg/l, which is approximately 1.5-fold higher thanthat in a conventional bioreactor (315 mg/l at 23 days; Lianget al., 2009). In SMFCs with high-level load resistors (i.e. 500 X)or open circuit conditions, however, the biomass concentrationsin the cathode compartments of the SMFCs were lower (230 mg/lin 500 X and 120 mg/l in open circuit) compared to that observedin the 10 X resistance SMFC. In this experiment, the dependency ofalgal concentration on current generation from the SMFC may beattributed to the rate of CO2 generation based on bacterial activi-ties in the anode compartment. It should be noted that one ofthe weak points of algal cultivation is the requirement of an exter-nal CO2 supply. Therefore, the results of this study imply that thecultivation of algal species in an SMFC is indeed possible withoutthe external addition of CO2.

3.3. Operation of SMFC in the presence of algae culture

Continuous supplementation of an oxidant (such as oxygen) tothe cathode is essential to maintain the potential and current of aMFC (Choi et al., 2010). Under illumination, assuming that algae inthe cathode compartment generate oxygen, the rate of currentgeneration of an SMFC will be proportional to the algal oxygen-producing activity, if oxygen is rate-limiting. Fig. 3a shows the cur-rent generation pattern from the SMFC in the presence of the algalculture. As a control experiment, an SMFC without algal inocula-

H.J. Jeon et al. / Bioresource Technology 109 (2012) 308–311 311

tion was operated with air. In the control experiment, the generalform of the amperometric response to the connection of the circuitwas a rapid rise in current as a function of time, followed by expo-nential decay to a plateau value (ca. 33 mA/m2). In the case of thealgae-inoculated SMFC with continuous illumination and no airsupply, a relatively slow increase in current was observed duringthe early stage of operation (0–9 days). However, after 11 days ofoperation, the current from the SMFC increased at a high rateand reached a steady state (48 mA/m2). One possible reason forthis higher current is that the increased amount of O2 producedby the algae under illumination interacted with the SMFC cathode.As is shown in Fig. 3b, when illumination was subjected to an on–off cycle (light: 18 h, dark: 6 h), the rate of current generation fromthe SMFC also fluctuated. These results show that the oxygen gen-erated from the algae could be directly employed as an oxidant forthe SMFC cathode. Therefore, the application of algal cultivation toa MFC format has a synergistic effect on both algal growth andSMFC operation. In this study, the rapid reduction of oxygen atthe surface of the cathode may have induced a reduction in theconcentration of oxygen, which probably stimulated algal growthin the SMFC (Paerl and Pinckney, 1996). Current research by ourgroup is focused on the optimization of algal growth and algal lipidaccumulation/quantification for biodiesel production (Park et al.,2010).

4. Conclusions

C. vulgaris was successfully cultivated in an SMFC format with-out any further addition of CO2. It was determined that the amountof CO2 and CH4 production from the anode compartment wasdependent on current generation from the SMFC. When C. vulgariswas inoculated into the cathode compartment of the SMFC, in-creases in both current and algal concentration were observed.These findings show that the synergic interaction between algalculture and SMFC; in other words, CO2 generated by bacterialactivity is consumed by algal cultivation, and the O2 produced fromthe algae is consumed by the SMFC cathode for current generation.

Acknowledgement

This subject is supported by the Korea Ministry of Environmentas a ‘‘Converging Technology Project (201-101-007)’’.

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