Shantonu Roy

Continuous mode of carbon dioxide sequestration by C. sorokiniana and subsequent use of its biomass for hydrogen production by E. cloacae IIT-BT 08.

The present study investigated to find out the suitability of the CO2 sequestered algal biomass of Chlorella sorokiniana as substrate for the hydrogen production by Enterobacter cloacae IIT-BT 08. The maximum biomass productivity in continuous mode of operation in autotrophic condition was enhanced from 0.05 g L(-1) h(-1) in air to 0.11 g L(-1) h(-1) in 5% air-CO2 (v/v) gas mixture at an optimum dilution rate of 0.05 h(-1). Decrease in steady state biomass and productivity was less sensitive at higher dilution and found fitting with the model proposed by Eppley and Dyer (1965). Pretreated algal biomass of 10 g L(-1) with 2% (v/v) HCl-heat was found most suitable for hydrogen production yielding 9±2 mol H2 (kg COD reduced)(-1) and was found fitting with modified Gompertz equation. Further, hydrogen energy recovery in dark fermentation was significantly enhanced compared to earlier report of hydrogen production by biophotolysis of algae.

Electro-stimulated microbial factory for value added product synthesis

Interplay of charge between bacteria and electrode has led to emergence of bioelectrochemical systems which leads to applications such as production of electricity, wastewater treatment, bioremediation and production of value added products. Many electroactive bacteria have been identified that have unique external electron transport systems. Coupling of electron transport with carbon metabolism has opened a new approach of carbon dioxide sequestration. The electron transport mechanism involves various cellular and sub cellular molecules. The outer membrane cytochromes, Mtr-complex and Ech-complex are few key molecules involved in electron transport in many electrogenic bacteria. Few cytochrome independent acetogenic electroactive bacteria were also discovered using Rnf complex to transport electrons. For improved productivity, an efficient bioreactor design is mandatory. It should encompass all certain critical issues such as microbial cell retention, charge dissipation, separators and simultaneous product recovery.

Improvement of power generation using Shewanella putrefaciens mediated bioanode in a single chambered microbial fuel cell: Effect of different anodic operating conditions

Three different approaches were employed to improve single chambered microbial fuel cell (sMFC) performance using Shewanella putrefaciens as biocatalyst. Taguchi design was used to identify the key process parameter (anolyte concentration, CaCl₂ and initial anolyte pH) for maximization of volumetric power. Supplementation of CaCl₂ was found most significant and maximum power density of 4.92 W/m(3) was achieved. In subsequent approaches, effect on power output by riboflavin supplementation to anolyte and anode surface modification using nano-hematite (Fe₂O₃) was observed. Volumetric power density was increased by 44% with addition of 100 nM riboflavin to anolyte while with 0.8 mg/cm(2) nano-Fe₂O₃ impregnated anode power density and columbic efficiency increased by 40% and 33% respectively. Cyclic voltammetry revealed improvement in electrochemical activity of Shewanella with nano-Fe₂O₃ loading and electrochemical impedance depicted inverse relationship between charge transfer resistance and nano-Fe₂O₃ loading. This study suggests anodic improvement strategies for maximization of power output.

Improvement of the degradation of sulfate rich wastewater using sweetmeat waste (SMW) as nutrient supplement.

External dosing of sweetmeat waste (SMW) dosing into exhausted upflow packed bed bioreactor (PBR) resulted in prompt reactivation of SO4(2-) removal. Different SMW concentrations in terms of chemical oxygen demand (COD)/SO4(2-) ratios (1, 2, 4 and 8) were introduced into four identical PBR where process stability was found within 3 weeks of operation. SO4(2-) removal was proportional to COD/SO4(2-) ratios up to 4 at which maximum sulfate removal (99%) was achieved at a rate of 607 mg/d. The value of COD consumption:SO4(2-)removal was much higher at ratio 4 than 8 whereas, ratio 2 was preferred over all. Net effluent acetate concentration profile and total microbial population attached to the reactor matrices were corresponding to COD/SO4(2-) ratio as 4>8>2>>1. Sulfate reducing bacteria (SRB) population was found to be inversely proportional to COD/SO4(2-) ratio in which acetate oxidizing SRB and fermentative bacteria were the dominant.

Reduction of start-up time through bioaugmentation process in microbial fuel cells using an isolate from dark fermentative spent media fed anode

An electrochemically active bacteria Pseudomonas aeruginosa IIT BT SS1 was isolated from a dark fermentative spent media fed anode, and a bioaugmentation technique using the isolated strain was used to improve the start-up time of a microbial fuel cell (MFC). Higher volumetric current density and lower start-up time were observed with the augmented system MFC-PM (13.7 A/m(3)) when compared with mixed culture MFC-M (8.72 A/m(3)) during the initial phase. This enhanced performance in MFC-PM was possibly due to the improvement in electron transfer ability by the augmented strain. However, pure culture MFC-P showed maximum volumetric current density (17 A/m(3)) due to the inherent electrogenic properties of Pseudomonas sp. An electrochemical impedance spectroscopic (EIS) study, along with matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) analysis, supported the influence of isolated species in improving the MFC performance. The present study indicates that the bioaugmentation strategy using the isolated Pseudomonas sp. can be effectively utilized to decrease the start-up time of MFC.

Comparative evaluation of the hydrogen production by mixed consortium, synthetic co-culture and pure culture using distillery effluent

Wastewater comprises of various carbon sources. So, the use of microbial consortium may improve the hydrogen production and organic reduction. The present study deals with biohydrogen production by acidogenic mixed consortia (AMC), synthetic co-culture (Klebsiella pneumoniae IIT-BT 08 and Citrobacter freundii IIT-BT L139) and pure culture using distillery effluent (DE). Higher hydrogen yield was observed in case of AMC (9.17 mol/kg CODreduced) as compared to the synthetic co-culture and pure culture. PCR-DGGE analysis indicated that the consortium was predominated by species closely affiliated to Clostridium sp. The average hydrogen production rate was 267 mL/Lh. The maximum hydrogen production rate (Rm), hydrogen production potential (P) and lag time (λ) by AMC using DE were 507.2 mL/Lh, 3729 m/L and 2.04 h, respectively. Maximum gaseous energy recovery by AMC was found to be higher by 21.9% and 45.4% than that of using co-culture and pure culture respectively.

Enhancement in lipid content of Chlorella sp MJ 11/11 from the spent medium of thermophilic biohydrogen production process

The present study investigates the effect of spent media of acetogenic dark fermentation for mixotrophic algal cultivation for biodiesel production. Mixotrophic growth conditions were optimized in culture flask (250mL) using Chlorella sp. MJ 11/11. Maximum lipid accumulation (58% w/w) was observed under light intensity, pH, nitrate and phosphate concentration of 100μmolm-2s-1, 7, 2.7mM and 1.8mM, respectively. Air lift (1.4L) and flat panel (1.4L) reactors were considered for algal cultivation. Air lift showed significant improvement in biomass and lipid production as compared to flat panel reactor. The results could help in development of sustainable technology involving acetogenic hydrogen production integrated with sequential mitigation of spent media by algal cultivation for improved energy recovery.

Gaseous Fuels Production from Algal Biomass

The most abundant renewable energy available to us is solar energy. It provides 178,000 TW energy to the Earth per year (Rupprecht et al., Appl Microbiol Biotechnol 72:442–449, 2006). Entrapment of such consistent source of energy has been performed by photosynthetic organisms. The interest for microalgae is growing worldwide for their ability to harness solar energy and consequently providing biomass that can be used as feedstock for renewable energy generation. The rate of CO2 fixation was up to 6.24 kg m−3 day−1 (Cheng et al. 2006, Sep Purif Technol 50:324–329). The productivity of algae could be 10 times higher (50 ton dry weight (DW) per hectare per year) when compared with conventional agricultural crops (Murphy and Power, Appl Energy 86:25–36 2009; Wijffels, Trends Biotechnol 26:26–31, 2008).

Liquid Fuels Production from Algal Biomass

Energy crisis is looming the global economy and environment. The rate at which fossil fuels are depleting, a necessity of alternate fuel has been gaining importance. The use of fossil fuels for energy is unsustainable and causes build up of greenhouse gases in the atmosphere leading to global warming. Biofuels store energy chemically that can be harnessed easily. It can also be used in existing combustion engines after blending with petroleum diesel to various degrees. No separate transportation infrastructures would be required for such fuels (Amaro et al., Appl Energy 88:3402–3410, 2011). In biorefinery concept, every component of the biomass material would be used to produce commercially important products. At present, first generation biofuels are produced using sucrose and starch crops. Second generation biofuels are produced using lignocellulosic biomass. Lignocellulosic biomass gained importance because of their abundant availability but need of pretreatment and saccharification processes has hindered their usage as feedstock. Moreover, bioenergy production using agricultural crops or agricultural wastes as feedstock is disadvantageous as resources for water and agriculture lands are limited (Li et al., Appl Microbiol Biotechnol 81:629–636, 2008). Algal biomass has been considered as third generation feedstock for biofuel production (Metzger and Largeau, Appl Microbiol Biotechnol 66:486–496, 2005). Many algal species having high lipid content thus could be explored for oleo-fuel generation. Similarly, algal species having high carbohydrate content can be exploited for bioethanol or biogas production.

Microbial Electrochemical System

Abstract “Water and Energy” are the two most precious resources that would eventually shape the future of the future generation. In recent times, the emphasis on development technology encompassing the use of alternative energy resources and “waste to energy” concept has gained importance globally. The microbial electrochemical systems (MESs) has emerged as one of the promising wastewater treatment technologies which could provide clean water as well as green energy. The MESs are bioelectrochemical reactors which can harvest energy from the biodegradable substances present in wastewater by using microbes. In MESs, migration of ions during generation of electricity can be utilized for valuable chemical production, water desalination, and resource recovery. Unlike, any chemical fuel cell, whose application is marred with high cost maintenance, MESs could provide a low cost and low maintenance solution for energy generation. The present chapter elaborates the existing researches on different microbial fuel cell–adapted systems and identifies a few key factors involved in efficiency optimization.