Abstract
The bioelectric activity of two lab scale microbial fuel cell (MFC) designs, MFCI (1,500 cm3) and MFCII (12,000 cm3) were examined using old corrugated containerboard (OCC) discharge for simultaneous effective treatment with greater power production. The decrease of MFC internal resistance (MFC-Rin) resulted in increased generated power output. The different parameters used in MFC included electrode conducting area (ECA), cathodic redox solution (CRS), MFC volume capacity, and MFCs connections. The generated current densities (CD) and power densities output (PD) at variables of external resistances (Rex) that ranged from 10 Ω to 20,000 Ω were calculated to estimate the MFC-Rin. In MFCI, using potassium ferri-cyanide as CRS, the change of ECA from 16 cm2 to 64 cm2 decreased the MFCI-Rin from 130 Ω to 110 Ω, and it was further decreased to 65 Ω when manganese dioxide was used as the CRS. Using Rex 100 Ω, MFCII exhibited lower Rin 18.46%, enhanced voltage 37.5%, and greater chemical oxygen demand removal 4.77% compared with MFCI. Series and parallel connections between four MFCI increased the generated PD by 286% and 258%, respectively, compared with that obtained by single MFCI.
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Bioelectric Activity of Microbial Fuel Cell during Treatment of Old Corrugated Containerboard Discharges
ShuJie Fan,a,b M. S. Mahmoud,a, b, c,* Biao Wen,a, b ZhenHua Su,a,b and Yu Zhang a,b
The bioelectric activity of two lab scale microbial fuel cell (MFC) designs, MFCI (1,500 cm3) and MFCII (12,000 cm3) were examined using old corrugated containerboard (OCC) discharge for simultaneous effective treatment with greater power production. The decrease of MFC internal resistance (MFC-Rin) resulted in increased generated power output. The different parameters used in MFC included electrode conducting area (ECA), cathodic redox solution (CRS), MFC volume capacity, and MFCs connections. The generated current densities (CD) and power densities output (PD) at variables of external resistances (Rex) that ranged from 10 Ω to 20,000 Ω were calculated to estimate the MFC-Rin. In MFCI, using potassium ferri-cyanide as CRS, the change of ECA from 16 cm2 to 64 cm2 decreased the MFCI-Rin from 130 Ω to 110 Ω, and it was further decreased to 65 Ω when manganese dioxide was used as the CRS. Using Rex100 Ω, MFCII exhibited lower Rin 18.46%, enhanced voltage 37.5%, and greater chemical oxygen demand removal 4.77% compared with MFCI. Series and parallel connections between four MFCI increased the generated PD by 286% and 258%, respectively, compared with that obtained by single MFCI.
Keywords: Microbial fuel cell; Bio-electric energy; Pulp and paper effluent
Contact information: a: China National Pulp and Paper Research Institute, Beijing, P. O. Box 100102, China; b: National Engineering Lab for Pulp and Paper, Beijing, P. O. Box 100102, China; c: Sanitary and Environmental Institute (SEI), Housing and Building National Research Center (HBRC), P. O. Box 1770, Egypt; *Corresponding author: mphdmicro2012@yahoo.com
INTRODUCTION
Water and energy are two major concerns in global environmental protection. The size of the pulp and paper industries is increasing, and they generate high liquid effluent discharges with different characteristics. A main discharge in paper industries is old corrugated containerboard (OCC), which is widely used as recycled OCC fibers. This effluent has different chemical properties depending on the pulping process, rate of recycling, and contaminant contents. The most general characteristics of these discharges are color, pH, alkaloids, dissolved salts, suspended solids, lignin, cellulose, organic acids, soluble small fibers, fillers, coatings, plastic materials, wet strength agent, and halogenated organics (Du and He 2002). The re-use of pulp and paper liquid discharges is an important operating task because of its high water and chemical contents (Han 2003). Traditional treatment processes include alkali recovery (Ai et al. 2003), acid precipitation (Chen et al. 2002; Zhang 2003), ultrasonic treatment (Zhou et al. 2002), combustion (Yin et al. 2004), coagulation (Guo and Wang 2003; Xiong et al. 2004), chemical oxidation with ozone and photo-catalysis (Wu 1999), floatation (Zhang et al. 2002; Liu et al. 2002), flocculation (Lu et al. 2000), filtering (Yue 1997), membrane separation (Tang and He 2003), and electrochemical separation (Wang and Wang 2000; Jian and Wang 2002). Most of these techniques are either expensive or insufficient for organic elimination to match with environmental pollution control.
Aerobic or anaerobic biological treatment is an effective way for organic consumption needed for microbial survival and proliferation. The anaerobic biological techniques include: up-flow anaerobic sludge blanket (UASB), anaerobic filter bed method, anaerobic moving bed method, anaerobic expanded bed method, anaerobic rotating disc method, and anaerobic microbial fuel cell method (Bal and Dhagat 2001). Microbial fuel cell (MFC) treatment technology is advantageous for its environmental friendliness, economic return, and organic disposal especially for high organic loads discharges (Li and Li 2001).
The use of MFC for generating power density (PD) and achieving high organic removal rate from OCC discharges represent a new perspective technique in advanced research areas. Optimizations of MFC, which is required to magnify power output, include continuous development of biochemical reactions (Qiao et al. 2004; Ahmad et al. 2013). The biochemical oxidation and reduction reactions are described as follows.
Oxygen, ferric cyanide, and manganese dioxide are the most common cathodic redox solutions (CRS) in the cathode cell part and are characterized by their effective reduction reactions. Oxygen has limited activity due to low solubility, so the uses of ferric cyanide and manganese dioxide have better activities as of their independency on the solubility (Rhoads et al. 2005). Cathodic reactions are described as follows.
MFC can produce greater power output by modifying factors that can generate and receive high electron numbers leading to lower MFC-Rin (Logan 2004). The challenge is to study the bio-electrochemical behavior of MFC through definite key factors attributed to enhance performance by decreasing the MFC-Rin. OCC discharge was used as the anodic organic substrate. By using an Rex ranging from 10 Ω to 20,000 Ω in two MFCs lab-scale batch models, MFCI (1500 cm3) and MFCII (12000 cm3), the MFC-Rin was calculated. The key variable parameters were the electrode conducting area (ECA), cathodic redox solutions (CRS), and MFC volume capacity. This study also focused on the increase of power generation efficiencies through four MFCI connections in both series and parallel states. This study also estimated the organic consumption efficiencies in both studied MFC models.
EXPERIMENTAL
Analytical Equipment
A 5B-6 spectrophotometer was used for rapid determination of chemical oxygen demand (COD) at a λ value of 610 nm (Lian-hua Technology Ltd., Lanzhou, China). A computer multi-function voltage digital data acquisition collector card was used for online measurements of the MFC voltages (MPS-010602, Qichuang Mofei Electronic Technology Co., Ltd., Beijing, China).
Anaerobic Biofilm and OCC Collection
Anaerobic microbial biofilm samples were collected from an anaerobic reactor (Sun Paper Ltd., Shandong, China). Anaerobic biofilm was activated using basic nutrient media, including 5 g/L of glucose, 5 g/L of peptone, 1.5 g/L of beef extract, 1.5 g/L of yeast extract, and 100 g/L of granular activated carbon (GAC) (Mahmoud et al. 2018). This was incubated at 30 °C for 90 d under anaerobic conditions. Samples of OCC effluents were collected from Sun Paper Ltd. (Shandong, China), analyzed within 8 h, and stored at 4 °C for use. The physio-chemical analysis of both biofilm and OCC effluent are listed in Table 1.
Table 1. Physico-Chemical Analysis for Biofilm and OCC Samples
MFC Operation Setup
Two methyl methacrylate MFC lab-scale designs, MFCI (1500 cm3) and MFCII (12000 cm3), were used. Each one consists of two cell-parts separated by a cationic exchanger membrane. Variable external resistances (Rex) that ranged from 10 Ω to 20,000 Ω were used for each MFC operation study. Carbon cloth was used as a conducting electrode. In the cathode cell-part, two cathodic redox solutions were used: 50 mmol/L of K3[Fe(CN)6]-K2HPO4 and 0.2% manganese dioxide dissolved in sulfuric acid and hydrogen peroxide (30 %). In the anode cell-part, the pH was adjustment to a pH of 6.0 to 6.5 and the anaerobic biofilm was added to the OCC effluent by ratio 1:3 with mixed liquor suspended solids (MLSS) concentration of around 5000 mg/L (Mahmoud et al. 2018). The MFCs anaerobic conditions were controlled by supplying an adequate nitrogen gas capacity of 0.5 L/min. Online assessments of various parameters such as the obtained voltages, pH, DO, MLSS, TSS, COD, and BOD were monitored regularly under different hydraulic retention times (HRT).
Analytical Methods
All MFCs tests measurements were analyzed in triplicate according to the procedures described in the standard method (APHA 2005). The removal percentage was calculated as follows,
where C0 and Ce are initial and final concentrations (mg/L), respectively.
The power density (W. m-2), current density (A. m-2), and MFC resistance (Ω) were calculated by Eqs. 2, 3, and 4, respectively,
where U is the voltage output (V), R is the total resistance (Ω) used, and A is the electrode area (m2).
Each MFC-Rin was achieved by plotting the current density against power density at different external resistances (Rex) that ranged from 10 Ω to 20,000 Ω.
RESULTS AND DISCUSSION
Microbial fuel cell technology can be an affordable, reliable, clean source of energy and alternatives to waste disposal. To achieve high organic elimination and supplementary power generation, two MFCs lab scale designs, MFCI (1500 cm3) and MFCII (12000 cm3), were operated by feeding of enriched anaerobic microbial biomass with GAC and OCC effluent in the anode cell-part. The role of GAC is to increase electron transfer mechanism (Mahmoud et al. 2018). As the MFC generated power output depends on different induced reactions, this study focused on the change of the electrode conducting area (ECA), cathodic redox solutions (CRS), MFC volume capacity, and MFCs connections in both series and parallel states.
Electrode conducting area (ECA) is one of the most important reasons for electron transfer mechanisms in both MFC cell-parts that affect the MFC-Rin. In MFCI lab design, MFCIa and MFCIb potassium ferri-cyanide were used as a CRS with ECA of 16 cm2and 64 cm2, respectively. Results showed that there was an increase in the voltage output and a decrease in the Rin due to the increase of the electron transfer mechanisms. The achieved MFCIa-Rin was 130Ω, while the MFCIb-Rin was 110Ω. By using Rex 100Ω, results represented a significant increase in the obtained voltage from 0.185 V to 0.361 V, while a decrease in the generated power density was observed from 214.85 mW.m-2 to 203.84 mW.m-2 for both MFCIa and MFCIb, respectively, as drawn in Fig. 1. The increase of the obtained voltage resulted from the decrease of MFC-Rin, while the decrease of PD was due to increase of the electrode surface area (Shima 2017).
The cathode redox solutions (CRS) are of great importance in MFC power generation in which reduction reaction and attraction of electrons takes place. In MFCI lab design, MFCIc manganese dioxide was used as CRS with ECA of 64 cm2. Results showed increase in power output and decrease of Rin. The achieved MFCIc-Rin was 65 Ω. By using 100 Ω Rex, the obtained voltage was 0.480 V, the generated PD was 360.73 mW.m-2, and the obtained CD was 0.751 A.m-2, as shown in Fig. 2. This could be explained by high activity of electrons attracting and the high protons reducing activity (Rhoads et al. 2005; Li et al. 2010; Passos et al. 2016; Mahmoud et al. 2018).
To study the effect of MFC volume capacity on the MFC power output, MFC-Rin and organic removal at different hydraulic retention time (HRT), scale-up process takes place. In the MFCII lab design, manganese dioxide was used as CRS with ECA of 256 cm2. Results showed significant increase in both current output and organic removal by increasing the MFC volume capacity, as drawn in Fig. 2. The MFCII-Rin was 53 Ω. By using Rex 100 Ω, the obtained voltage was 0.660 V, the generated PD was 169.99 mW.m-2, and the obtained CD was 0.258 A.m-2. The decreases of both PD and CD by increasing MFC volume capacity are due to the reverse correlation with the electrode area (Passos et al. 2016; Mahmoud et al. 2018).
Fig. 1. Power output of MFCIa and MFCIb
Fig. 2. Power output of MFCIc and MFCII
For organic waste removal represented in the OCC chemical oxygen demand (COD) removal, it was noticed that the MFC consuming efficiency had proportional correlation with MFCs scale-up in both operational retention time and removal percentages. The results showed that the consumption of COD reached 88% and 92.2% after 8 d of operating MFCIc and MFCII, respectively, as shown in Fig. 3.
The rate of anaerobic granulation was expressed by the rate of biological growth in relation with the organic ratio (F/M) and formation of MLSS (Guo et al. 2017). The initial F/M ratio [COD/SS] for both MFCIc and MFCII was 1.2. The MFCII exhibited higher growth rate or sludge loading rate in the mixed liquor suspended solids (MLSS) in a shorter time of operation than MFCIc, as shown in Fig. 4. The F/M ratio highly decreased in case of MFCII with an effective start-up than MFCIc at the same time of operation, and this could be explained by extra competition between the anaerobic microbes and organic COD in case of MFCII.
The limitation of the F/M ratio along with retention time of operation for both MFCs, indicated that the OCC effluent had limited biodegradability, as the BOD/COD ratios that were in range from 0.25 to 0.43 (Durgesh and Akshay 2013; Yazdi et al.2015).
Fig. 3. Voltage output and COD removal of both MFCIc and MFCII
Fig. 4. F/M ratio and MLSS of both MFCIc and MFCII
The connections between four MFCIcs on the current production were studied in both series and parallel connections as shown in Fig. 5. In the series connection, the obtained voltage increased from 0.815 V to 3.14 V and the PD increased from 378 to 1461 for single and four connections of MFCIcs, respectively. In the parallel connections, there was no noticeable increase in the obtained voltages, while the PD increased from 378 mW.m-2 to 1355 mW.m-2 for both single and four connections of MFCIcs, respectively (Passos et al. 2016; Mahmoud et al. 2018).
Fig. 5. The power output for both single and connections of four MFCIcs in series and parallel states
CONCLUSIONS
- This study focused on microbial fuel cell (MFC) innovation and development using old corrugated container (OCC) effluent as bio-resources for sustainable energy production along with effective organic removal performance.
- For high MFC performance, lower internal resistance (MFC-Rin) should be achieved through increasing the electrode areas, using manganese dioxide as the cathodic redox solution (CRS), increasing the MFC volume capacity.
- For high power generation, multiple MFCs connections should be connected either in series or in parallel states.
- The decrease of MFC-Rin that results in accelerating the start-up time, which decreases the power losses and is better for power production.
ACKNOWLEDGMENTS
This project was funded by the China Science and Technology Exchange Center (Grant No. 2016YFE0114700).
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Article submitted: January 7, 2018; Peer review completed: March 11, 2018; Revised version received and accepted: March 12, 2018; Published: March 23, 2018.
DOI: 10.15376/biores.13.2.3545-3553