R. Kannaiah Goud

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.

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.

Saccharomyces cerevisiae as anodic biocatalyst for power generation in biofuel cell: Influence of redox condition and substrate load

Bio (microbial) fuel cell (microbial fuel cell) with Saccharomyces cerevisiae as anodic biocatalyst was evaluated in terms of power generation and substrate degradation at three redox conditions (5.0, 6.0 and 7.0). Fuel cell was operated in single chamber (open-air cathode) configuration without mediators using non-catalyzed graphite as electrodes. The performance was further studied with increasing loading rate (OLRI, 0.91 kg COD/m(3)-day; OLRII, 1.43 kg COD/m(3)). Higher current density was observed at pH6.0 [160.36 mA/m(2) (OLRI); 282.83 mA/m(2) (OLRII)] than pH5.0 (137.24 mA/m(2)) and pH 7.0 (129.25 mA/m(2)). Bio-electrochemical behavior of fuel cell was evaluated using cyclic voltammetry which showed the presence of redox mediators (NADH/NAD(+); FADH/FAD(+)). Higher electron discharge was observed at pH6.0, suggesting higher proton shuttling through the involvement of different redox mediators. The application of yeast based fuel cell can be extended to treat high strength wastewaters with simultaneous power generation.

Aerobic remediation of petroleum sludge through soil supplementation: Microbial community analysis

The effect of soil concentration on the aerobic degradation of real-field petroleum sludge was studied in slurry phase reactor. Total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAHs) showed effective removal but found to depend on the soil concentration. Aromatic fraction (48.12%) documented effective degradation compared to aliphatics (47.31%), NSO (28.69%) and asphaltenes (26.66%). PAHs profile showed efficient degradation of twelve individual aromatic compounds where lower ring compounds showed relatively higher degradation efficiency compared to the higher ring compounds. The redox behaviour and dehydrogenase activity showed a linear increment with the degradation pattern. Microbial community composition and changes during bioremediation were studied using denaturing gradient gel electrophoresis (DGGE). Among the 12 organisms identified, Proteobacteria was found to be dominant representing 50% of the total population (25% of γ-proteobacteria; 16.6% of β-proteobacteria; 8.3% of α-proteobacteria), while 33.3% were of uncultured bacteria and 16.6% were of firmicutes.

Acidic and alkaline shock pretreatment to enrich acidogenic biohydrogen producing mixed culture: long term synergetic evaluation of microbial inventory, dehydrogenase activity and bio-electro kinetics

Comprehensive experiments were designed to evaluate the function of acid-shock (pH 3; orthophosphoric acid; 24 h) and alkaline-shock (pH 11; NaOH; 24 h) pretreatment methods for the selective enrichment of an acidogenic culture to enhance H2 production efficiency of mixed anaerobic consortia. Long term (520 days) operation in suspended-batch mode bioreactors illustrated the relative efficiency and feasibility of redox pretreated cultures against an untreated parent culture in enhancing H2 production. Relatively higher H2 production was observed with an acid pretreated mixed culture (15.78 mol kg−1 CODR) over alkaline pretreated (9.8 mol kg−1 CODR) and untreated mixed cultures (3.31 mol kg−1 CODR). On the contrary, substrate degradation was higher with untreated culture (ξCOD, 62.86%; substrate degradation rate (SDR), 1.10 kg CODR/m3-day) and alkaline-shock pretreated mixed culture (ξCOD, 59.93%; SDR, 1.22 kg CODR/m3-day) compared to the acid-shock culture (ξCOD, 53.4%; SDR, 0.705 kg CODR/m3-day). Synergetics of microbial inventory, dehydrogenase activity and bio-electro kinetics in association with H2 production and substrate degradation were also evaluated in detail throughout the operation. Acid pretreatment of the parent culture has resulted in a shift in the fermentation pathway towards acetic acid production, while alkaline pretreatment showed a mixed type fermentation (acetic, butyric, propnoic acids) similar to an untreated parent mixed culture. Dehydrogenase activity of the biocatalyst showed a significant improvement after applying acid pretreatment indicating the increased redox inter-conversion reactions leading to the higher proton gradient in the cell that resulted in higher H2 production. The redox catalytic currents observed from the cyclic voltammograms (CV) and the output from the Tafel analysis also strongly supported the increased biocatalyst performance after pretreatment, especially at acid-shock. The shift in oxidative and reductive Tafel slopes towards a lower value after applying acid-shock treatment supports the redox inter-conversion reactions required for proton conservation. Microbial profiling revealed that the pretreatment method in the long term operation substantially affected the species composition of microbial communities. Dominance of Clostridia and Bacilli classes were observed in the pretreated culture and indicates their positive role in the H2 production process. This study shows the feasibility of controlling microbial metabolic functions by repeated application of the pretreatment to the reactor native microflora (in situ) during operation whenever required to regain or modify the process performances.

Prolonged applied potential to anode facilitate selective enrichment of bio-electrochemically active Proteobacteria for mediating electron transfer: Microbial dynamics and bio-catalytic analysis

Prolonged application of poised potential to anode was evaluated to understand the influence of applied potentials [500 mV (E500); 1000 mV (E1000); 2000 mV (E2000)] on bio-electrogenic activity of microbial fuel cell (MFC) and the resulting dynamics in microbial community in comparison to control operation. E1000 system documented higher electrogenic activity (309 mW/m(2)) followed by E500 (143 mW/m(2)), E2000 (112 mW/m(2)) and control (65 mW/m(2)) operations. The improved power output at optimum applied potential (1000mV) might be attributed to the enrichment of electrochemically active bacteria majorly belonging to the phylum Proteobacteria with less extent of Firmicutes which helped in effective electron (mediated) transfer through release of exogenous shuttlers. Improved bio-electrogenic activity due to enrichment at 1000mV applied potential also correlated well with the observed cyctochrome-c peaks on the voltamatogram, lower ion ohmic losses and bio-electro kinetic analysis. Electric-shock at higher applied potential (E2000) resulted in the survival of less number of microbial species leading to lower electrogenesis.

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.

Anoxic bio-electrochemical system for treatment of complex chemical wastewater with simultaneous bioelectricity generation.

Bioelectrochemical treatment system (BET) with anoxic anodic microenvironment was studied with chemical wastewater (CW) in comparison with anoxic treatment (AxT, sequencing batch reactor (SBR)) with same parent anaerobic consortia. BET system documented relatively higher treatment efficiency at higher organic load (5.0 kg COD/m(3)) accounting for COD removal efficiency of (90%) along with nitrate (48%), phosphate (51%), sulphates (68%), colour (63%) and turbidity (90%) removal, compared to AxT operation (COD, 47%; nitrate, 36%; phosphate, 32%; sulphate, 35%; colour, 45% and turbidity, 54%). The self-induced bio-potential developed due to the electrode assembly in BET resulted in effective treatment with simultaneous bioelectricity generation (631 mA/m(2)). AxT operation showed persistent reduction behaviour, while simultaneous redox behaviour was observed with BET indicating balanced electron transfer. BET operation illustrated higher wastewater toxicity reduction compared to the AxT system which documents the variation in bio-electrocatalytic behaviour of same consortia under different microenvironment.

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.

Spatiometabolic stratification of anoxic biofilm in prototype bioelectrogenic system

A prototype bio-catalyzed electrogenic system integrated with a biological treatment process (SBR-BET) was evaluated to study specific function of anoxic condition on the electrogenic activity. A multiphasic approach was employed, where the influence of DO on bio-electrogenic activity was optimized initially, later optimal anode to cathode inter-electrode distance was enumerated. Amongst the four electrode distances evaluated, 2cm showed higher power output. Bioelectrokinetics analysis was used to validate the system performance with the experimental variation studied. The redox behavior showed an increase in cathodic catalytic activity with an increase in the inter-electrode distance. Spatiometabolic distribution depicted the microbial stratification on the anode. Electrochemically active bacteria present on the anode surface (inner and outer layers of biofilms) showed relatively uniform diversity compared with the suspension culture.