Improving fermentation industry sludge treatment as well as energy production with constructed dual chamber microbial fuel cell
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Microbial fuel cells offer a breakthrough for treatment of waste content coupled with energy generation. However, their applications are mostly limited to laboratories. Present research is focused on conducting the biological conversion of sludge originated from fermentation industry using microbial fuel cell (MFC). The efficiency of MFC was studied at different operating and nutritional conditions including pH, aeration rate and substrate concentration with biocatalyst Saccharomyces cerevisiae. The optimized conditions in terms of yielding maximum power density of 610 ± 30 mW/m2 were reported at substrate concentration of 60% at 160 ml/min aeration rate and pH of 6, corresponding to a current density of 994 ± 41 mA/m2. Results suggested that utilization of fermented sludge in MFC could give direction to handle the problem of fermentation industries and also to overcome a small fraction of energy crisis.
KeywordsFermented industry sludge Treatment of sludge Sustainable electricity Microbial fuel cell
Biological oxygen demand
Chemical oxygen demand
Total suspended solids
Volatile suspended solids
Due to continuous destruction of fossil fuels as well as uneconomical aspects of other non-renewable energy resources, world is heading towards the energy catastrophe [4, 5, 6, 7, 12]. However, fossil fuels’ consumption causes pollution which contributes in increasing global warming. Construction of a realistic globe requires the limited usage of such sources, ultimately to reduce the quantity of pollutants produced. Therefore, there is need to use an alternative energy source which can be regarded as economical, reusable and clean [8, 17, 18]. Microbial fuel cell (MFC) used to decompose organic waste and to generate energy simultaneously, presents the solution of above two problems [18, 19, 20, 32]. Potter observed the possibility of using bacteria for production of electrical energy in 1911 . However, adequate study was not conducted to advance this technology during 1911–1967. But in 1967, John Davis patented the first MFC technology, while a formal research in this area was begun later 1990′s [1, 3, 11, 21]. Most of the patents were issued in 2000’s. The MFC that handles the real fermentation, sludge can produce a power density of about 1884 mW/m2 equivalent to about 51.5% of the power density obtained from MFC (3664 mW/m2) using the same organic loading rate (OLR) of 1.92 g of acetate/L d. With gradual increase of OLR, the power density increased to 2981 mW/m3, OLR was 3.84 g/L d . Microbial fuel cells (MFCs) are basically a dual-chamber system consisting of anode and cathode chamber separated by a polymeric proton exchange membrane (PEM). In most MFCs, aqueous cathodes are used, where water is bubbled with air to provide dissolved oxygen to electrode. To increase energy output and reduce the cost of MFCs, we examined power generation in an air–cathode MFC containing carbon electrodes in the presence and absence of a polymeric proton exchange membrane. Power yield was enhanced as glucose concentration was increased according to saturation-type kinetics, with a half saturation constant of 79 mg/L with the PEM-MFC and 103 mg/L in the MFC without a PEM (1000 Ω resistor). Similar observations were reported for the influence of the PEM on power density using wastewater, where 28 ± 3 mW/m2 (0.7 ± 0.1 mW/L) (28% Columbic efficiency) was produced with the PEM, and 146 ± 8 mW/m2 (3.7 ± 0.2 mW/L) (20% Columbic efficiency) was produced when the PEM was removed . Preliminary tests using a two-chambered MFC with an aqueous cathode indicated that electricity could be generated from swine sludge containing 8320 ± 190 mg/L of soluble chemical oxygen demand (SCOD) (maximum power density of 45 mW/m2). Using a single-chambered air cathode MFC, maximum power density of 261 mW/m2 (200 Ω resistor) was yielded from the animal sludge and it was reported to be 79% higher than a previous report involving domestic sludge (146 ± 8 mW/m2) due to the higher concentration of organic matter in the swine sludge . A new highly scalable MFC design, comprising of a series of cassette electrodes (CE), was studied to improve the power generation from organic matter in wastewater. Power production was stable during this period, reaching maximum power densities of 129 W/m2 (anode volume) and 899 mW/m2 (anode projected area) . Single chamber air–cathode microbial fuel cells (MFCs) are used to ferment the primary fermented sludge. The maximum power density is 0.32 ± 0.01 W/m2, and only the primary effluent has a power density of 0.24 ± 0.03 W/m2. These results indicate that when fermented, the sludge can be effectively used for power generation and then diluted only with the primary effluent .
Industrial or domestic sludge are generally regarded as conductive substrates in the phenomenon of bioconversion in a bioreactor, whereby, highly concentrated organic (Sewage Sludge) contain higher chemical energy per unit volume as compared to that of present in the sludge. Therefore, sewage sludge being enriched with organic content is deemed as a suitable fuel for MFC operation in terms of electricity generation. In addition, domestic or municipal sludge which contains a multitude of organic compounds could be used as substrate. Adequate level of study is required for reporting the effects of various key parameters including aeration rate, substrate concentration, temperature and pH on performance MFC for voltage output [9, 24, 29, 30, 37]. This study is aimed to achieve the objectives of both the reduction in waste content of Fermentation industries as well as energy generation by using a rectangular dual chamber MFC. The efficiency of MFC is investigated by utilizing different substrate (sludge from fermentation) concentrations coupled with variation in above mentioned parameters.
2 Materials and methods
Sludge from feremneters characteristics
2.2 Growth medium
Growth medium for Saccharomyces cerivisae
Potassium di hydrogen phosphate
2.3 Construction and working principle of MFC
2.4 Measurement of electrical parameters
3 Results and discussion
Detailed analysis of different experiments
Aeration rate (ml/min)
Power density (mW/m2)
Current density (mA/m2)
3.1 Effect of air rate on cathode performance
3.2 Anodic pH impact on MFC performance
In MFC, the anodic reaction produces a proton that flows towards the cathode chamber and reacts with oxygen (or other reducing compound) to produces water. On the other hand, since the proton is continuously consumed by the oxygen, reduction reaction and the proton substitution due to the cationic oxidation reaction is lacking, alkalization is observed on the cathode side. Such phenomenon leads to a membrane pH concentration gradient that produces electrochemical/thermodynamic limitations of overall performance. Increased pH in the cathode chamber can immensely reduce the current generation because the potential of the oxygen reduction reaction increases with decreasing pH. In addition, the bacteria usually require a pH close to neutral to achieve their optimal growth, and the bacteria responds to changes in internal and external pH by adjusting their activity. Depending on the bacteria and growth conditions, variation in pH can causes to change several major physiological parameters such as ion concentration, membrane potential, proton motility and biofilm formation [16, 27].
3.3 Substrate concentration impact on electricity generation
3.4 Effect of current and power density on performance of microbial fuel cell
3.5 COD and BOD removal in MFC couple with current generation
The two-chamber microbial fuel cell was operated at initial COD concentration range from 310–350 mg/l. Volumetric flow rate couple with COD loading to microbial fuel cell was 0.18 kg COD/m3-d. After 18 days operation under unchanged condition, 88% COD and 87% BOD removal were achieved. The unsettled BOD and COD values observed in the effluent were 20.9 and 29.14 mg/l, respectively. BOD removal efficiency was higher than 78% removal reported by Gude  and Liu and Logan . The COD removal percentage in anode chamber was 46.3% and remaining COD was getting removed in the cathode chamber. For single chamber MFC, operated at HRT of 33 h, COD removal efficiency of 50–70% was reported by Liu and Logan . By comparing above discussion with Fig. 4. Figure 4 shows the BOD and COD removal with respect to time couple with current generation. Trend of COD and BOD decreasing as time passes couple with increasing in current generation, due to microorganism decomposing organic matter into electron and proton.
The sludge as a substrate was subjected into MFC in the presence of Saccharomyce cerevisiae biocatalyst. The maximum voltage obtained was 750 mV per liter of sludge when the anode and cathode chamber were maintained in batch and continuous mode respectively. These results have demonstrated the specificity of the mediator-microbial combination as well as the importance of developing a dual chamber MFC. This potential substrate was proved to produce a stable voltage in the feed batch at different initial sludge concentrations couple with aeration rate of 160 ml/min, pH 6 and 60% substrate concentration.
Authors are thankful to Chemical Engineering Department of Mehran university of Engineering and Technology and Dawood university of Engineering and Technology for providing the research facility. Special gratitude is paid to HEJ Karachi (University of Karachi) for their support to conduct sample analysis.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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