G. Venkata Subhash

Bioaugmentation of an electrochemically active strain to enhance the electron discharge of mixed culture: process evaluation through electro-kinetic analysis

The functional role of electrochemically active bacteria (EAB), Shewanella haliotis ATCC 49138 as biocatalyst for bioaugmentation onto anodic native microflora (anaerobic) was evaluated to enhance the electrogenic activity of microbial fuel cell (MFC). Fuel cell operation with S. haliotis (MFC-S) alone as anodic biocatalyst showed relatively higher power output (295 mV; 2.13 mA at 100 Ω) than mixed culture (MFC-M; 233 mV; 1.35 mA at 100 Ω) which might be attributed to the higher electron discharge capability of the EAB. Cyclic voltammetry profiles and Tafel slope analysis documented significant variation in bio-electrochemical behaviour and electro-kinetic aspects of fuel cells with the function of anodic biocatalyst. Two-fold higher capacitance and exchange current was observed with MFC-S operation compared to MFC-M. Lower Tafel slope and polarisation resistance observed with MFC-S operation indicated higher electron discharge capability of S. haliotis over the mixed consortia operation. However, the extent of power generation period and substrate degradation efficiency was comparatively higher with mixed culture operation. After augmentation with S. haliotis (MFC-SA), anodic microflora showed rapid enhancement in the fuel cell performance in terms of power output (378 mV; 2.73 mA) and bio-electrochemical behaviour. After augmentation, fifteen-fold higher exchange current density, ten-fold lower electron transfer coefficient and hundred-fold lower polarization resistance was observed compared to MFC-M operation. The syntrophic association of S. haliotis with native anodic biocatalyst showed positive influence on the electron discharge capabilities due to reduction in the activation losses. The stable and high electron discharge pattern observed with augmented system throughout the operation indicates the system stability in current generation.

Biodiesel production from isolated oleaginous fungi Aspergillus sp. using corncob waste liquor as a substrate.

The study documented the potential of isolated filamentous fungus Aspergillus sp. as whole cell biocatalyst for biodiesel production using Sabourauds dextrose broth medium (SDBM) and corncob waste liquor (CWL) as substrates. SDBM showed improvement in both biomass production (13.6 g dry weight/1000 ml) and lipid productivity (23.3%) with time. Lipid extraction was performed by direct (DTE) and indirect (IDTE) transesterification methods. DTE showed higher transesterification efficiency with broad spectrum of fatty acids profile over IDTE. CWL as substrate showed good lipid productivity (22.1%; 2g dry biomass; 48 h) along with efficient substrate degradation. Lipids derived from both substrates depicted high fraction of saturated fatty acids than unsaturated ones. Physical characteristics of fungal based biodiesel correlated well with prescribed standards. CWL derived biodiesel showed relatively good fuel properties (acid number, 0.40 mg KOH/g of acid; iodine value, 11 g I₂/100 g oil; density, 0.8342 g/cm³) than SDBM derived biodiesel.

Fermentative effluents from hydrogen producing bioreactor as substrate for poly(β-OH) butyrate production with simultaneous treatment: An integrated approach

The feasibility of bioplastics production as poly(beta-OH)butyrate (PHB) was studied with individual volatile fatty acids (VFA) and acid-rich effluents from a biohydrogen producing reactor (HBR) as primary substrates employing aerobic consortia as biocatalyst under anoxic microenvironment. Butyrate as substrate showed higher PHB productivity (33%) followed by acetate (32%), acids mixture (16%) and propionate (11%) among synthetic VFA studied. Acid-rich effluents from HBR yielded higher PHB productivity (25%) especially at lower substrate loading conditions. Decrement observed in PHB production (from 25% to 6%) with increase in substrate load might be due to the presence of high concentration of residual carbon along with acid metabolites. Neutral redox operation showed effective PHB production compared to acidic and basic conditions due to associated higher metabolic activity of the biocatalyst. The integrated approach helped to treat additional COD from acid-rich HBR effluents apart from by-product recovery.

Mixotrophic operation of photo-bioelectrocatalytic fuel cell under anoxygenic microenvironment enhances the light dependent bioelectrogenic activity.

Electrogenic activity of photo-bioelectrocatalytic /photo-biological fuel cell (PhFC) was evaluated in a mixotrophic mode under anoxygenic microenvironment using photosynthetic consortia as biocatalyst. An acetate rich wastewater was used as anolyte for harnessing energy along with additional treatment. Mixotrophic operation facilitated good electrogenic activity and wastewater treatment associated with biomass growth. PhFC operation documented feasible microenvironment for the growth of photosynthetic bacteria compared to algae which was supported by pigment (total chlorophyll and bacteriochlorophyll) and diversity analysis. Pigment data also illustrated the association between bacterial and algal species. The synergistic interaction between anoxygenic and oxygenic photosynthesis was found to be suitable for PhFC operation. Light dependent deposition of electrons at electrode was relatively higher compared to dark dependent electron deposition under anoxygenic condition. PhFC documented for good volatile fatty acids removal by utilizing them as electron donor. Bioelectrochemical behavior of PhFC was evaluated by voltammetric and chronoamperometry analysis.

Bio-electrolytic conversion of acidogenic effluents to biohydrogen: An integration strategy for higher substrate conversion and product recovery

Feasibility of integrating Microbial electrolysis cell (MEC) process with dark-fermentation process for additional hydrogen recovery as well as substrate degradation was demonstrated in the present study. MEC was employed in order to utilize the residual organic fraction present in the acidogenic effluents of dark fermentation process as substrate for hydrogen production with input of small electric current. MEC was operated at volatile fatty acids (VFA) concentration of 3000 mg/l under different poised potentials (0.2, 0.5, 0.6, 0.8 and 1.0 V) using anaerobic consortia as biocatalyst. Maximum hydrogen production rate (HPR), cumulative hydrogen production (CHP) (0.53 mmol/h and 3.6 mmol), dehydrogenase activity (1.65 μg/ml) and VFA utilization (49.8%) was recorded at 0.6 V. Bio-electrochemical behavior of mixed consortia was evaluated using cyclic voltammetry and by Tafel slope analysis. Microbial diversity analysis using denaturing gradient gel electrophoresis confirmed the presence of γ-proteobacteria (50%), Bacilli (25%) and Clostridia (25%).

Temperature induced stress influence on biodiesel productivity during mixotrophic microalgae cultivation with wastewater

The role of operating temperature as a physical stress factor for enhancing lipid induction during microalgae cultivation with domestic wastewater was evaluated. Experiments were designed with dual mode microalgae cultivation viz., growth phase (GP) and temperature induced stress phase (25 °C, 30 °C and 35 °C). GP showed enhancement in biomass growth and carbohydrate accumulation while stress phase (SP) operation at 30 °C showed noticeable improvement in lipid productivities (total/neutral lipid, 24.5/10.2%). Maximum carbohydrate utilization was observed during SP at 30 °C operation (57.8%) compared to 25 °C (50.6%) and 35 °C (26.9%) correlating well with the lipid synthesis. Interestingly the neutral lipid content documented five-fold increment illustrating feasibility towards good biodiesel properties. Biodiesel profile at 30 °C temperature is well supported by higher saturated fatty acids (SFA) to unsaturated fatty acids (USFA) ratio. GP operation showed good COD and nutrient removal concomitant to the biomass growth.

Microalgae mediated bio-electrocatalytic fuel cell facilitates bioelectricity generation through oxygenic photomixotrophic mechanism

Electrogenic activity of oxygenic photo-bioelectrocatalytic fuel cell (PhFCOX) under mixotrophic mode was evaluated using atmospheric CO2 and domestic wastewater as carbon sources for harnessing bioelectricity with mixed microalgae as anodic biocatalyst. PhFCOX operation showed good electrogenic activity (3.55 μW/m(2)) associated with higher biomass growth (2.87 g/l) and chlorophyll content (5.12 mg/l). Electrogenic activity was relatively higher during the day time (46 mV; 0.6 mA) compared to the night (6 mV; 0.01 mA). Performance of PhFCOX undergoing oxygenic photosynthesis (DO; 3.5 mg/l) was compared with the mixotrophic fuel cell (PhFCAX) with photosynthetic bacteria as biocatalyst under anoxygenic conditions (DO; 0.45 mg/l). The dissolved oxygen produced during photolysis of water in oxygenic photosynthesis is a major limiting factor affecting the electrogenic activity. Voltammetric and amperometric analysis along with electron transfer kinetics (Tafel analysis) supported the bio-electrochemical behavior of PhFCOX and PhFCAX.

Algae Oils as Fuels

Abstract Biologically produced fuels are considered potential and viable alternatives to meet the world’s fuel requirements. In this context, algal-based oil is of significant importance due to its renewable and carbon-neutral nature. Biosynthesis of triglycerides by utilizing CO2 (by biofixation) or wastewater under stress conditions via photoautotrophic, heterotrophic (photo/dark), or mixotrophic mechanisms enumerates the potential of microalgae for generation of renewable biodiesel. In addition to the algal cultivation, the conversion of the accumulated lipids to biodiesel is gaining considerable interest. Though there exist some constraints, the process of harnessing biofuel from microalgae is both economically viable and environmentally sustainable compared to the other oil-producing terrestrial crops. This chapter explores biofuel production using microalgae. Concerted efforts are made in this chapter to discuss the biochemistry pertaining to algal lipid synthesis, nutritional modes of algae, cultivation systems used for algal oil production, and the cascade of steps involved, from biomass cultivation to transesterification of the fuel. The ability of microalgae to capture CO2 and its survivability in wastewater is also elaborated in the context of lipid synthesis.

Relative effect of different inorganic acids on selective enrichment of acidogenic biocatalyst for fermentative biohydrogen production from wastewater

The effect of different inorganic acids viz., HNO3, HCl, H2SO4 and H3PO4 on inoculum pretreatment to selectively enrich hydrogen (H2) producing acidogenic bacteria was evaluated in anaerobic sequencing batch bioreactors. Relative positive efficiency of HNO3 pretreated consortia in enhancing H2 production (11.85 mol H2/kg CODR) was noticed compared to other acids (HCl, 5.64 mol H2/kg CODR; H2SO4, 7.65 mol H2/kg CODR; H3PO4, 6.90 mol H2/kg CODR) and untreated-parent consortia (control, 6.80 mol H2/kg CODR). On the contrary, substrate degradation (COD removal) was higher with the control operation (ξCOD, 66.3%; substrate degradation rate (SDR), 1.42 kg CODR/m(3)-day) compared to pre-treated culture. HNO3 pre-treatment resulted in a shift in the fermentation pathway towards more acetic acid production, while other acid pretreatment and untreated culture showed mixed type fermentation (acetic, butyric, propionic acids). The bio-electrochemical analysis and dehydrogenase activity supported the biocatalyst performance after HNO3 pretreatment with specific enrichment of Firmicutes and Bacillus.

Closed circuitry operation influence on microbial electrofermentation: Proton/electron effluxes on electro-fuels productivity

A novel biocatalyzed electrofermentor (BEF) was designed which uncovers the intricate role of biocatalyst involved in cogeneration of electro-fuels (hydrogen and electricity). The specific role of external resistance (Rext, electrical load) on the performance of BEF was evaluated. Four BEFs were operated separately with different resistances (25, 50, 100 and 200 Ω) at an organic load of 5 g/L. Among the tested conditions, external resistance (R3) with 100 Ω revealed maximum power and cumulative H2 production (148 mW and 450 mL, respectively). The competence of closed circuitry comparatively excelled because it facilitates congenial ambiance for the enriched EAB (electroactive bacteria) resulting high rate of metabolic activity that paves way for higher substrate degradation and electro-fuel productivity. Probing of electron kinetics was studied using voltammetric analyses wherein electron transfer by redox proteins was noticed. The designed BEF is found to be sustainable system for harnessing renewable energy through wastewater treatment.