Mohita Sharma

Enhanced performance of sulfate reducing bacteria based biocathode using stainless steel mesh on activated carbon fabric electrode

An anoxic biocathode was developed using sulfate-reducing bacteria (SRB) consortium on activated carbon fabric (ACF) and the effect of stainless steel (SS) mesh as additional current collector was investigated. Improved performance of biocathode was observed with SS mesh leading to nearly five folds increase in power density (from 4.79 to 23.11 mW/m(2)) and threefolds increase in current density (from 75 to 250 mA/m(2)). Enhanced redox currents and lower Tafel slopes observed from cyclic voltammograms of ACF with SS mesh indicated the positive role of uniform electron collecting points. Differential pulse voltammetry technique was employed as an additional tool to assess the redox carriers involved in bioelectrochemical reactions. SRB biocathode was also tested for reduction of volatile fatty acids (VFA) present in the fermentation effluent stream and the results indicated the possibility of integration of this system with anaerobic fermentation for efficient product recovery.

Bioelectrochemical approaches for removal of sulfate, hydrocarbon and salinity from produced water.

Produced water (PW) is the largest liquid waste stream generated during the exploration and drilling process of both the conventional hydrocarbon based resources like crude oil and natural gas, as well as the new fossil resources like shale gas and coal bed methane. Resource management, efficient utilization of the water resources, and water purification protocols are the conventionally used treatment methods applied to either treat or utilize the generated PW. This review provides a comprehensive overview of these conventional PW treatment strategies with special emphasises on electrochemical treatment. Key considerations associated with these approaches for efficient treatment of PW are also discussed. After a thorough assessment of the salient features of these treatment platforms, we propose a new strategy of uniquely integrating bioelectrochemical processes with biological system for more effective PW treatment and management.

Influence of headspace composition on product diversity by sulphate reducing bacteria biocathode.

Mixed culture of sulphate reducing bacteria named TERI-MS-003 was used for development of biocathode on activated carbon fabric fastened to stainless steel mesh for conversion of volatile fatty acids to reduced organic compounds under chronoamperometric conditions of -0.85V vs. Ag/AgCl (3.5M KCl). A range of chemicals were bioelectrosynthesized, however the gases present in headspace environment of the bioelectrochemical reactor governed the product profile. Succinate, ethanol, hydrogen, glycerol and propionate were observed to be the predominant products when the reactor was hermetically sealed. On the other hand, acetone, propionate, isopropanol, propanol, isobutyrate, isovalerate and heptanoate were the predominant products when the reactor was continuously sparged with nitrogen. This study highlights the importance of head space composition in order to manoeuvre the final product profile desired during a microbial electro-synthesis operation and the need for simultaneously developing effective separation and recovery strategies from an economical and practical standpoint.

Optimization of electrochemical parameters for sulfate-reducing bacteria (SRB) based biocathode

This study focuses on the effect of operational and physiochemical factors on a stable sulfate reducing bacteria biocathode and their effect on the electrochemical response thereof. Two carbon-based electrode materials i.e. VITO CORE™ and Paxitech® electrodes were evaluated. The electrochemical performance was assessed by changing both organic and inorganic components of the synthetic feed, which included carbon substrates (acetic and butyric acid), ionic strength (concentration of sodium chloride) and weak electrolytes acting as buffering agents (potassium dihydrogen phosphate and ammonium chloride). The concentration of sodium chloride (0.34 M) and acetate (0.1 M) plays a crucial role in determining the performance as well as the bioelectrochemical mechanism of the sulfate reducing bacteria (SRB) biocathode. Butyrate did not significantly influence the performance of the biocathode but showed a synergistic effect when given along with acetate. The developed biocathode was also successfully tested for dark fermentation based effluent treatment application. Concentrations higher than 10% of effluent were found to be detrimental to the electrochemical performance of the biocathode. This study essentially highlights the significance of optimization studies on bioelectrochemical system (BES) at lab scale before its potential upscaling for industrial wastewater processing.

Electrochemical removal of sulfate from petroleum produced water

Petroleum produced water (PPW) is a waste-stream that entails huge cost on the petroleum industry. Along with other suspended and dissolved solids, it contains sulfate, which is a major hurdle for its alternative use intended toward enhanced oil recovery. This study proposes a two-step process for sulfate removal from PPW. A synthetic PPW was designed for the study using response surface methodology. During the first step, sulfate present in PPW was reduced to sulfide by anaerobic fermentation with 80% efficiency. In the second step, more than 70% of the accumulated sulfide was electrochemically oxidized. This integrated approach successfully removed sulfate from the synthetic wastewater indicating its applicability in the treatment of PPW and its subsequent applications in other oil field operations.

Separation of acetone and butyric acid for simultaneous analysis of sugars, volatile fatty acids, acetone and alcohols by HPLC using flow programming

This article deals with developing an efficient and economical method to quantify the major products of ABE fermentation (sugars, volatile fatty acids, acetone, ethanol and butanol) using HPLC. Other techniques based on a similar principle have poor resolution between peaks of butyric acid, acetone and ethanol. The advantage of our method was that the overlapping peaks of butyric acid, acetone and ethanol were separated and thus quantified simultaneously during analysis. Also, flow programming was used to reduce the analysis time, thereby saving energy. The maximum separation of all components was achieved using a water–sulfuric acid mixture (5 mM H2SO4 in water) as the mobile phase using flow programming with increasing flow rate from 0.6 ml to 0.9 ml within 21 min during analysis with a total run time of 26 min at a column temperature of 80 °C. A linear relationship over the analytical range of 10.0 to 0.01 g l−1 was observed. The robustness of the developed method was evaluated using parameters such as the capacity factor, selectivity, plate number and resolution. The applicability of this approach was validated by quantifying the substrates and products of ABE fermentation using lignocellulosic waste hydrolysate as a carbon source. The results of analysis proved that the method is reproducible, accurate, precise, and sensitive.