G. Mohanakrishna

Bio-electrochemical treatment of distillery wastewater in microbial fuel cell facilitating decolorization and desalination along with power generation.

Microbial fuel cell (MFC; open-air cathode) was evaluated as bio-electrochemical treatment system for distillery wastewater during bioelectricity generation. MFC was operated at three substrate loading conditions in fed-batch mode under acidophilic (pH 6) condition using anaerobic consortia as anodic-biocatalyst. Current visualized marked improvement with increase in substrate load without any process inhibition (2.12-2.48mA). Apart from electricity generation, MFC documented efficient treatment of distillery wastewater and illustrated its function as an integrated wastewater treatment system by simultaneously removing multiple pollutants. Fuel cell operation yielded enhanced substrate degradation (COD, 72.84%) compared to the fermentation process ( approximately 29.5% improvement). Interestingly due to treatment in MFC, considerable reduction in color (31.67%) of distillery wastewater was also observed as against color intensification normally observed due to re-polymerization in corresponding anaerobic process. Good reduction in total dissolved solids (TDS, 23.96%) was also noticed due to fuel cell operation, which is generally not amenable in biological treatment. The simultaneous removal of multiple pollutants observed in distillery wastewater might be attributed to the biologically catalyzed electrochemical reactions occurring in the anodic chamber of MFC mediated by anaerobic substrate metabolism.

Acidogenic fermentation of vegetable based market waste to harness biohydrogen with simultaneous stabilization

Vegetable based market waste was evaluated as a fermentable substrate for hydrogen (H(2)) production with simultaneous stabilization by dark-fermentation process using selectively enriched acidogenic mixed consortia under acidophilic microenvironment. Experiments were performed at different substrate/organic loading conditions in concurrence with two types of feed compositions (with and without pulp). Study depicted the feasibility of H(2) production from vegetable waste stabilization process. H(2) production was found to be dependent on the concentration of the substrate and composition. Higher H(2) production and substrate degradation were observed in experiments performed without pulp (23.96 mmol/day (30.0 kg COD/m(3)); 13.96 mol/kg COD(R) (4.8 kg COD/m(3))) than with pulp (22.46 mmol/day (32.0 kg COD/m(3)); 12.24 mol/kg COD(R) (4.4 kg COD/m(3))). Generation of higher concentrations of acetic acid and butyric acid was observed in experiments performed without pulp. Data enveloping analysis (DEA) was employed to study the combined process efficiency of system by integrating H(2) production and substrate degradation.

Potential of mixed microalgae to harness biodiesel from ecological water-bodies with simultaneous treatment.

Biodiesel as an eco-friendly fuel is gaining much acceptance in recent years. This communication provides an overview on the possibility of using mixed microalgae existing in ecological water-bodies for harnessing biodiesel. Microalgal cultures from five water-bodies are cultivated in domestic wastewater in open-ponds and the harvested algal-biomass was processed through acid-catalyzed transesterification. Experiments evidenced the potential of using mixed microalgae for harnessing biodiesel. Presence of palmitic acid (C16:0) in higher fraction and physical properties of algal oil correlated well with the biodiesel properties. Functional characteristics of water-bodies showed to influence both species diversity and lipid accumulation. Microalgae from stagnant water-bodies receiving domestic discharges documented higher lipid accumulation. Algal-oil showed to consist 33 types of saturated and unsaturated fatty acids having wide food and fuel characteristics. Simultaneous wastewater treatment was also noticed due to the syntrophic association in the water-body microenvironment. Diversity studies visualized the composition of algae species known to accumulate higher lipids.

Evaluation of the potential of various aquatic eco-systems in harnessing bioelectricity through benthic fuel cell: Effect of electrode assembly and water characteristics

Six different types of ecological water bodies were evaluated to assess their potential to generate bioelectricity using benthic type fuel cell assemblies. Experiments were designed with various combinations of electrode assemblies, surface area of anode and anodic materials. Among the 32 experiments conducted, nine combinations evidenced stable electron-discharge/current. Nature, flow conditions and characteristics of water bodies showed significant influence on the power generation apart from electrode assemblies, surface area of anode and anodic material. Stagnant water bodies showed comparatively higher power output than the running water bodies. Placement of cathode on algal mat (as bio-cathode) documented several folds increment in power output. Electron-discharge started at 1000 Omega resistance in polluted water bodies (Nacaharam cheruvu, Hussain Sagar lake Musi river), whereas, in relatively less polluted water bodies (Uppal pond/stream, Godavari river) electron-discharge was observed at low resistances (500/750 Omega).

Composite vegetable waste as renewable resource for bioelectricity generation through non-catalyzed open-air cathode microbial fuel cell

Single chambered mediatorless microbial fuel cell (MFC; non-catalyzed electrodes) was operated to evaluate the potential of bioelectricity generation from the treatment of composite waste vegetables (EWV) extract under anaerobic microenvironment using mixed consortia as anodic biocatalyst. The system was operated with designed synthetic wastewater (DSW; 0.98 kg COD/m(3)-day) during adaptation phase and later shifted to EWV and operated at three substrate load conditions (2.08, 1.39 and 0.70 kg COD/m(3)-day). Experimental data illustrated the feasibility of bioelectricity generation through the utilization of EWV as substrate in MFC. Higher power output (57.38 mW/m(2)) was observed especially at lower substrate load. The performance of MFC was characterized based on the polarization behavior, cell potentials, cyclic voltammetric analysis and sustainable resistance. MFC operation also documented to stabilize the waste by effective removal of COD (62.86%), carbohydrates (79.84%) and turbidity (55.12%).

Sustainable power generation from floating macrophytes based ecological microenvironment through embedded fuel cells along with simultaneous wastewater treatment

Miniatured floating macrophyte based ecosystem (FME) designed with Eichornia as the major biota was evaluated for bioelectricity generation and wastewater treatment. Three fuel cell assemblies (non-catalyzed electrodes) embedded in FME were evaluated with domestic sewage and fermented distillery wastewater in continuous mode for 210 days. Fermented distillery effluents from biohydrogen production (dark-fermentation) process exhibited effective power generation with simultaneous waste remediation. Two fuel cell assemblies (A1 and A2) showed effective bioelectricity generation. Increasing the organic load of wastewater showed good correlation with both power generation (A1, 211.14 mA/m(2); A2, 224.93 mA/m(2)) and wastewater treatment (COD removal, 86.67% and VFA removal 72.32%). Combining A1 and A2 assemblies depicted stabilized performance with respect to current and voltage along with significant decrease in ohmic and activation losses. FME also exhibited effective removal of nitrates, colour and turbidity from wastewater. The studied miniatured ecological system facilitates both energy generation and wastewater treatment with a sustainable perspective.

Rhizosphere mediated electrogenesis with the function of anode placement for harnessing bioenergy through CO2 sequestration

The feasibility of power generation by non-destructive usage of rhizodeposits of Pennisetum setaceum plant formed mainly due to photosynthesis-carbon sequestration mechanism was studied in rhizosphere based microbial fuel-cell (R-MFC). Four fuel-cell assemblies (non-catalyzed graphite-plates; membrane-less operation; air-cathode) were evaluated for their electrogenic activity by varying anode distances from root in rhizosphere [A1 - 0; A2 - 8; A3 - 12 and A4 - 16 cm] at 2 cm depth from soil-layer and analyzed their electrogenic potential. The fuel-cell assembly near to the root zone showed maximum electrogenic-activity (R1, 1007 mV/4.52 mA) followed by R2 (780 mV/4.11 mA), R3 (720 mV/3.4 mA) and R4 (220 mV/1.2 mA). The observed maximum electrogenesis with R1 and minimum with R4 electrode-assemblies enumerated the critical role of root-exudates as substrates. All fuel-cell assemblies showed 10% higher electrogenic activity during day-time operation which can be directly attributed to plants photosynthetic activity. The study enumerated the potential of plant to harness power in a sustainable way by optimum placement of fuel-cell setup in their rhizosphere.

Ecologically engineered system (EES) designed to integrate floating, emergent and submerged macrophytes for the treatment of domestic sewage and acid rich fermented-distillery wastewater: Evaluation of long term performance.

An ecologically engineered system (EES) was designed to mimic the natural cleansing functions of wetlands to bring about wastewater treatment. EES consisted of three tanks containing diverse biota viz., aquatic macrophytes, submerged plants, emergent plants and filter feeders connected in series. The designed system was evaluated for 216days by operating in continuous mode (20l/day) to treat both sewage (DS) and fermented-distillery wastewater (FDW, from hydrogen producing bioreactor). Floating macrophyte system (Tank 1) was more effective in removing COD and nitrates. Submerged and emergent integrated macrophyte system (Tank 2) showed an effective removal of volatile fatty acids (VFAs) along with COD. Filter-feeding system (Tank 3) visualized the removal of COD, VFA, turbidity and color. On the whole the system can treat effectively DS (COD, 68.06%; nitrate, 22.41%; turbidity, 59.81%) and FDW (COD, 72.92%; nitrate, 23.15%; color, 46.0%). The designed EES can be considered as an economical approach for the treatment of both sewage and fermented wastewaters.

Evaluation of voltage sag-regain phases to understand the stability of bioelectrochemical system: Electro-kinetic analysis

Voltage sag, regain and their stabilization phases were evaluated with time across load (closed circuit) and absence of load (short circuit) to understand the stability of the bio-electrochemical system (BES) under varying organic loads (OL). Closed circuit operation showed good stability along with the electrogenic activity over short circuit operation during both the sag and regain phases due to the regulated electron flow in the closed circuit. Relative change in voltage with time (dV/dt) was observed to be decreasing with increasing OL in the zone of sag, while it was observed to be increasing with increase in OL during the zone of regain. However, the change in dV/dt was not proportional with increasing OL during both the sag and regain phases indicating the influence of OL on the biocatalytic activity. Bio-electrocatalytic evaluation through Tafel analysis showed a gradually decreasing reductive slope from OL1 (0.62 V/dec) to OL4 (0.516 V/dec) indicating higher electrocatalytic activity towards reduction. While, the oxidative slope increased from OL1 (0.085 V/dec) to OL2 and was almost similar with further increment in the OL (0.099 ± 0.002 V/dec) which indicates marginal change in the electrocatalytic activity during oxidation even with increasing OL. Exchange current density from Tafel analysis was also observed to increase with increase in OL (OL1, 7.86 mA m−2; OL2, 8.33 mA m−2; OL3, 9.59 mA m−2; OL4, 11.77 mA m−2). Polarization resistance showed a decreasing trend with increasing OL (OL1, 12.23 Ω to OL4, 9.8 Ω) resulting in higher electron transfer.

Biohydrogen Production from Industrial Effluents

Publisher Summary Hydrogen (H 2 ) has been considered as a sustainable energy carrier as it is clean (does not emit any toxic by-product or greenhouse gases), efficient, and renewable. Currently, H 2 is being produced mainly from fossil fuels, biomass, and water. H 2 production through biological routes is considered as one of the opportunistic and sustainable ways to meet the future energy demand and to prevent fossil fuel-based environmental impacts. Biological approaches for producing H 2 also facilitate the conversion of negative-value organic waste. Broadly, biological H 2 can be produced through two main mechanisms: photosynthesis and dark fermentation. Photosynthesis is a light-dependent process, while dark fermentation (anaerobic) is a light-independent catabolic process. Most of the biological H 2 production processes are operated at ambient temperatures and pressures regarded as less energy intensive and therefore considered as a potential alternative to the conventional physical/chemical methods usually opted for H 2 production. Biohydrogen can also be viewed as energy source and an intermediate towards the production of VFA (volatile fatty acids). VFA present in these effluents generated from H 2 producing reactor can be further transformed to PHAs or can be used for biohydrogenation of fatty acids into alcohols.