P. Chiranjeevi

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.

Algal biocathode for in situ terminal electron acceptor (TEA) production: Synergetic association of bacteria–microalgae metabolism for the functioning of biofuel cell

Replacement of energy intensive mechanical aeration with sustainable oxygenic photosynthesis by microalgae at cathode was studied in dual-chambered microbial fuel cell (MFC). The synergistic association between bacterial fermentation at anode and the oxygenic photosynthesis of microalgae at cathode facilitated good power output as well as treatment efficiency. However, MFC operation during spring showed higher bioelectrogenic activity (57.0 mW/m(2)) over summer (1.1 mW/m(2)) due to the higher oxygenic photosynthetic activity of microalgae and respective dissolved oxygen (DO) levels. This can be attributed to RuBisCO inactivation under high temperatures and light intensity of summer, which prevented rich algal biomass growth as well as their photosynthetic activity. Unlike abiotic cathode, the algal cathode potential increased with operation time due to the algal biomass growth during spring but was negligible during summer. The catalytic currents on voltammetric signatures and the bioprocess parameters also corroborated well with the observed power output.

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.

Bioaugmentation of potent acidogenic isolates: a strategy for enhancing biohydrogen production at elevated organic load.

The efficiency of bioaugmentation strategy for enhancing biohydrogenesis at elevated organic load was successfully evaluated by augmenting native acidogenic microflora with three acidogenic bacterial isolates viz., Bacillus subtilis, Pseudomonas stutzeri and Lysinibacillus fusiformis related to phyla Firmicutes and Proteobacteria separately. Hydrogen production ceased at 50g COD/l operation due to feed-back inhibition. B. subtilis augmented system showed higher H2 production followed by L. fusiformis, P. stutzeri and control operations, indicating the efficacy of Firmicutes as bioaugmentation biocatalyst. Higher VFA production with acetic acid as a major fraction was specifically observed with B. subtilis augmented system. Shift in metabolic pathway towards acidogenesis favoured higher H2 production. FISH analysis confirmed survivability and persistence of augmented strains apart from improvement in process performance. Bio-electrochemical analysis depicted specific changes in the metabolic activity after augmentation which also facilitated enhanced electron transfer. P. stutzeri augmented system documented relatively higher COD removal.

Biohydrogen Production from Wastewater

Abstract Biohydrogen (H2) production from renewable wastewater signifies a sustainable alternative to a fossil fuel-based economy. H2 is deemed to be the futuristic energy carrier with a high-energy yield. This chapter specifically addresses H2 production through wastewater remediation. A comprehensive emphasis is made on the fermentative routes, namely, light-driven and light-independent processes, encompassing wastewater and mixed culture application as a focal point. Important process parameters that have critical roles on process efficiency are elaborated. Some of the persistent limitations encountered during the process operation are delineated. Stress is made on the pertinent discussion on biocatalyst pretreatment methods in the context of mixed culture wastewater usage. Reported strategies to overcome the limitations are discussed to make the process economically viable, especially for large-scale applications.

Waste derived bioeconomy in India: A perspective

Environmental and climatic change issues, population explosion, rapid urbanisation, depletion of fossil reserves, need for energy security, huge waste generation, etc. are some of the inherent issues associated with the fossil based linear economy which need greater attention. In this context, the world is gradually transforming from fossil-based economy to a sustainable circular bio-economy. The biogenic waste which is generated in enormous quanties in India can be considered as potential feedstock for structuring the bio-based economy. This communication depicts the need for developing waste derived bioeconomy in the Indian perspective. Waste is now being perceived as a resource with value and believed to supplement petroleum feedstock to a great extent if properly utilized. The necessity to introduce waste as the core element for the future economic models which also allows sustainable development is discussed. The review also establishes drivers for the bioeconomy and structures the waste derived bioeconomy in a sustainable format to address the futuristic needs, scope and opportunities envisaged in the business and economic realm. The enabling technologies/processes that can be applied for biogenic wastes valorisation are elaborated. Circularizing the economy in a waste biorefinery model for the production of biobased products including bioenergy is discussed.

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.

Optimizing the Critical Factors for Lipid Productivity during Stress Phased Heterotrophic Microalgae Cultivation

Microalgae-derived biodiesel/biofuel is one of the promising and sustainable processes. In order to study the influence of different factors viz., pH, temperature, salinity and carbon concentration that influences the microalgae lipids and carbohydrate productivity Taguchi orthogonal array (OA) experimental design (DOE) was used with variation at four levels (21×44). Experiments were performed with allegorical batch experimental matrix [16 experimental trails]. Salinity, temperature, carbon concentration and pH showed marked influence on lipid production whereas temperature and carbon concentration showed major influence on carbohydrate production. Higher lipid productivity (55%) was observed with experimental condition six (pH: 6; Salinity: 1 g/l; Temperature: 20 OC; Carbon concentration: 30 g/l). FAME analysis revealed the highest number of Saturated fatty acids (SFAs) (C12:0 to C24:0) was detected with experimental set up six and eight more favoring the biodiesel properties.

Diverse acidogenic effluents as feedstock for microalgae cultivation: Dual phase metabolic transition on biomass growth and lipid synthesis

In this study, a biorefinery process integrating dark fermentation with microalgae cultivation (dual phase metabolic transition) was demonstrated with real-field wastewater. Acid rich fermented effluents (distillery waste (FDW1); dairy waste (FDW2)) were used as feedstock for microalgae cultivation. Experiments were performed with FDW1 during growth phase (GP) in mixotrophic mode and FDW2 during stress phase (SP) in both mixotrophic and heterotrophic modes. Mixotrophic cultivation with FDW1 documented significantly higher biomass productivity (5.3g/l). Total lipid (TL) percentage was high in mixotrophic (34%) mode and neutral lipid (NL) was high in heterotrophic (13%) mode of cultivation during SP with FDW2. Overall, the microalgae growth is favoured with effluents containing high acetate, and low butyrate concentrations. Mixotrophic cultivation enhanced both biomass growth and lipid production along with simultaneous treatment.