Sanjukta Subudhi

Bioelectrochemical enhancement of direct interspecies electron transfer in upflow anaerobic reactor with effluent recirculation for acidic distillery wastewater

Methane production in the upflow anaerobic bioelectrochemical reactor (UABE) treating acidic distillery wastewater was compared to the upflow anaerobic sludge blanket reactor (UASB), and the electron transfer pathways for methane production were also evaluated in the effluent recirculation. The methane productions from reactors were influenced by the low pH of influent wastewater. However, the methane production rate and yield of the UABE were 2.08L/L.d and 320mL/g CODr, which were higher than the UASB. The effluent recirculation containing alkalinity neutralized the acidic influent and increased the upflow velocity in both reactors, and improved the direct interspecies electron transfer more in the UABE. When the effluent recirculation ratio was 3.0 in the UABE, the methane production rate and yield were reached up to 3.88L/L.d and 501.0mL/g CODr, respectively. The UABE requires electrode installation and electrical energy for operation, but the benefits from increased methane production are much higher.

Production of a non-cytotoxic bioflocculant by a bacterium utilizing a petroleum hydrocarbon source and its application in heavy metal removal

A bacterium isolated from the activated sludge of an oil refinery of Assam, India retained efficient bioflocculating activity through production of the bioflocculant when it was grown on a crude oil amended medium void of any other carbon source. The bioflocculating activity gained from the optimized medium broth was 86.2%, which could be enhanced up to 89.1% with the purified bioflocculant. During the course of the bioflocculant production, the bacterium utilized about 77% of the petroleum hydrocarbons after incubation for 168 h when the activity was found to be the highest. The bioflocculant was efficient in flocculating Ni2+, Zn2+, Cd2+, Cu2+ and Pb2+. The bioflocculant was characterized as a glycoprotein complex by biochemical tests, FT-IR, SEM-EDX and LC/MS analyses. The bioflocculant showed negligible cytotoxicity on testing with the L292 cell line indicating the tremendous possibility of its use in bioremediation.

Implication of composite electrode on the functioning of photo-bioelectrocatalytic fuel cell operated with heterotrophic-anoxygenic condition

Electrode materials play a vital role in biofilm formation and electron conduction for efficient functioning of fuel cells. In the present study, graphite polymer composite electrode (GPF) was evaluated as anode for photo-bioelectrocatalytic fuel cell (PhFC; biophotovoltaic system) and compared with much studied graphite electrode (Gc) with photosynthetic bacteria as biocatalyst under anoxygenic condition. The electrogenic activity noticed in GPF (584mV; 2.67mA) was slightly lower than Gc (604mV; 2.92mA; OL2/HRT2). Consequently, COD removal observed by GPF (87.3%) was lower than Gc (91.8%). The increase in bacterial chlorophyll pigment showed a positive influence on electrogenic activity for both the electrodes. The polarization resistance (OL2 and HRT2 condition) was significantly higher for GPF (330Ω) as compared to Gc (110Ω). It is interesting to note that the performance of GPF is slightly lower than Gc based PhFC. The findings have opened avenues for composite materials for PhFC.

Characterization of a Novel Polymeric Bioflocculant Produced from Bacterial Utilization of n-Hexadecane and Its Application in Removal of Heavy Metals

A novel polymeric bioflocculant was produced by a bacterium utilizing degradation of n-hexadecane as the energy source. The bioflocculant was produced with a bioflocculating activity of 87.8%. The hydrocarbon degradation was confirmed by gas chromatography-mass spectrometry analysis and was further supported with contact angle measurements for the changes in hydrophobic nature of the culture medium. A specific aerobic degradation pathway followed by the bacterium during the bioflocculant production and hydrocarbon utilization process has been proposed. FT-IR, SEM-EDX, LC/MS, and 1H NMR measurements indicated the presence of carbohydrates and proteins as the major components of the bioflocculant. The bioflocculant was characterized for its carbohydrate monomer constituents and its practical applicability was established for removing the heavy metals (Ni2+, Zn2+, Cd2+, Cu2+, and Pb2+) from aqueous solutions at concentrations of 1–50 mg L-1. The highest activity of the bioflocculant was observed with Ni2+ with 79.29 ± 0.12% bioflocculation efficiency.

Effect of electrode surface properties on enhanced electron transfer activity in microbial fuel cells

The influence of electrode surface chemistry over biofilm growth was evaluated for photo‐bioelectrocatalytic fuel cell. A consortium of photosynthetic bacteria was grown onto different electrodes designed with polyethylenimine (PEI) and multiwall carbon nanotubes as hydrophilic and hydrophobic modifier, respectively. The designed electrodes were loaded with 0.08, 0.17, and 0.33 μg/cm2 of PEI to change the hydrophilicity. However, 0.56, 0.72, and 0.83 mg/cm2 of multiwall carbon nanotubes were used to alter the hydrophobicity of the electrodes. The surface chemistry of electrode and bio‐interaction was evaluated as a function of contact angle and biofilm formation. The results were compared with those obtained with a carbon paper electrode. The contact angle on the untreated electrode (carbon paper) was 118°, whereas for hydrophobic and hydrophilic electrodes, the maximum and minimum contact angles were 170° and 0°, respectively. Interestingly, the maximum biofilm growth (0.2275 g, wet basis) was observed on highly hydrophobic surface; however, the maximum electrochemical performance (246 mV) was shown by the most hydrophilic electrode surface. PEI‐based electrode with good biofilm formation showed comparatively higher electrogenic activity.

Performance of Upflow Anaerobic Bioelectrochemical Reactor Compared to the Sludge Blanket Reactor for Acidic Distillery Wastewater Treatment

The performance of upflow anaerobic bioelectrochemical reactor (UABE), equipped with electrodes (anode and cathode) inside the upflow anaerobic reactor, was compared to that of upflow anaerobic sludge blanket (UASB) reactor for the treatment of acidic distillery wastewater. The UASB was stable in pH, alkalinity and VFAs until the organic loading rate (OLR) of 4.0 g COD/L.d, but it became unstable over 4.0 g COD/L.d. As a response to the abrupt doubling in OLR, the perturbation in the state variables for the UABE was smaller, compared to the UASB, and quickly recovered. The UABE stability was better than the UASB at higher OLR of 4.0-8.0 g COD/L.d, and the UABE showed better performance in specific methane production rate (2,076 mL CH4/L.d), methane content in biogas (66.8%), and COD removal efficiency (82.3%) at 8.0 g COD/L.d than the UASB. The maximum methane yield in UABE was about 407 mL/g CODr at 4.0 g COD/L.d, which was considerably higher than about 282 mL/g CODr in UASB. The rate limiting step for the bioelectrochemical reaction in UABE was the oxidation of organic matter on the anode surface, and the electrode reactions were considerably affected by the pH at 8.0 g COD/L.d of high OLR. The maximum energy efficiency of UABE was 99.5%, at 4.0 g COD/L.d of OLR. The UABE can be an advanced high rate anaerobic process for the treatment of acidic distillery wastewater.

Polarized electrode enhances biological direct interspecies electron transfer for methane production in upflow anaerobic bioelectrochemical reactor

The influence of polarized electrodes on the methane production, which depends on the sludge concentration, was investigated in upflow anaerobic bioelectrochemical (UABE) reactor. When the polarized electrode was placed in the bottom zone with a high sludge concentration, the methane production was 5.34 L/L.d, which was 53% higher than upflow anaerobic sludge blanket (UASB) reactor. However, the methane production was reduced to 4.34 L/L.d by placing the electrode in the upper zone of the UABE reactor with lower sludge concentration. In the UABE reactor, the methane production was mainly improved by the enhanced biological direct interspecies electron transfer (bDIET) pathway, and the methane production via the electrode was a minor fraction of less than 4% of total methane production. The polarized electrodes that placed in the bottom zone with a high sludge concentration enhance the bDIET for methane production in the UABE reactor and greatly improve the methane production.

Hydrogen Production Through Biological Route

Socioeconomic development of a nation primarily depends on energy as a vital input, and thus, the energy strategy of a nation targets at energy security as well as at energy efficiency for its economic development. Owing to the rising population, limited crude oil reserves due to fast depletion of conventional fossil fuel sources along with rising greenhouse gas (GHG) emissions, there has been a global concern for energy security and environmental protection. In view of these concerns, energy production especially from sustainable sources has become the most imperative concern for national as well as for international policies. In this perspective, hydrogen has gained substantial global attention as clean, sustainable, and versatile energy carrier. Existing hydrogen production technologies mainly rely on photochemical, thermochemical processes which are high energy intensive and make use of conventional fossil fuel sources as feedstock either directly or indirectly. On the contrary, hydrogen production processes through biological route are less energy intensive, can be generated from renewable sources from organic wastes, and thus are sustainable. Biologically, hydrogen can be produced by few of the unique microbes/algae though four distinct approaches: (a) biophotolysis of water using algae/cyanobacteria, (b) photodecomposition (photofermentation) of organic compounds using photosynthetic bacteria, (c) dark fermentative hydrogen production using anaerobic (or facultative anaerobic) bacteria, and (d) hybrid biological hydrogen production through integration of dark fermentation process with photofermentation process. This chapter highlights in prospects and limitations of biohydrogen production process including recent developments on this domain. In addition, this chapter also sheds light on economic feasibility of biohydrogen production processes and addresses the need for integration of these technologies with production of value-added bio-based products in a biorefinery approach.