Bacterial community structure of electrogenic biofilm developed on modified graphite anode in microbial fuel cell

Formation of electrogenic microbial biofilm on the electrode is critical for harvesting electrical power from wastewater in microbial biofuel cells (MFCs). Although the knowledge of bacterial community structures in the biofilm is vital for the rational design of MFC electrodes, an in-depth study on the subject is still awaiting. Herein, we attempt to address this issue by creating electrogenic biofilm on modified graphite anodes assembled in an air-cathode MFC. The modification was performed with reduced graphene oxide (rGO), polyaniline (PANI), and carbon nanotube (CNTs) separately. To accelerate the growth of the biofilm, soybean-potato composite (plant) powder was blended with these conductive materials during the fabrication of the anodes. The MFC fabricated with PANI-based anode delivered the current density of 324.2 mA cm-2, followed by CNTs (248.75 mA cm-2), rGO (193 mA cm-2), and blank (without coating) (151 mA cm-2) graphite electrodes. Likewise, the PANI-based anode supported a robust biofilm growth containing maximum bacterial cell densities with diverse shapes and sizes of the cells and broad metabolic functionality. The alpha diversity of the biofilm developed over the anode coated with PANI was the loftiest operational taxonomic unit (2058 OUT) and Shannon index (7.56), as disclosed from the high-throughput 16S rRNA sequence analysis. Further, within these taxonomic units, exoelectrogenic phyla comprising Proteobacteria, Firmicutes, and Bacteroidetes were maximum with their corresponding level (%) 45.5, 36.2, and 9.8. The relative abundance of Gammaproteobacteria, Clostridia, and Bacilli at the class level, while Pseudomonas, Clostridium, Enterococcus, and Bifidobacterium at the genus level were comparatively higher in the PANI-based anode.

Biosensing capabilities of bioelectrochemical systems towards sustainable water streams: Technological implications and future prospects

Bioelectrochemical systems (BESs) have been intensively investigated over the last decade owing to its wide-scale environmentally friendly applications, among which wastewater treatment, power generation and environmental monitoring for pollutants are prominent. Different variants of BES such as microbial fuel cell, microbial electrolysis cell, microbial desalination cell, enzymatic fuel cell, microbial solar cell, have been studied. These microbial bioelectrocatalytic systems have clear advantages over the existing analytical techniques for sustainable on-site application in wide environmental conditions with minimum human intervention, making the technology irrevocable and economically feasible. The key challenges to establish this technology are to achieve stable and efficient interaction between the electrode surface and microorganisms, reduction of time for start-up and toxic-shock recovery, sensitivity improvement in real-time conditions, device miniaturization and its long-term economically feasible commercial application. This review article summarizes the recent technical progress regarding bio-electrocatalytic processes and the implementation of BESs as a biosensor for determining various compositional characteristics of water and wastewater.

Extension of the intensive phase reduces relapse but not failure in a regimen with rifampicin throughout

SETTING

Damien Foundation tuberculosis (TB) control projects in Bangladesh.

OBJECTIVE

To assess the effectiveness of extending the intensive phase (P1) of treatment by 1 month for patients who are smear-positive after 2 months of a 6-month regimen containing rifampicin (RMP) throughout.

DESIGN

Prospective operational study randomising P1 extension for new smear-positive cases with any number of acid-fast bacilli in the 2-month smear (2M+). Smear-defined failures and relapses underwent culture and drug susceptibility testing in addition to DNA sequencing of the rpoB gene before and after treatment.

RESULTS

Of 16,708 patients evaluated, 12,967 were smear-negative at 2 months (2M-); 1871 and 1870 2M+ were randomised to no extension or extension. Respectively 0.3% (95%CI 0.2-0.4), 1.2% (95%CI 0.7-1.8) and 2.0% (95%CI 1.4-2.8) smear- and culture-positive failures, and 1.2% (95%CI 1.0-1.4), 2.6% (95%CI 1.9-3.4) and 0.9% (95%CI 0.5-1.4) relapses were detected. Extension significantly reversed the relative risk (RR) of relapse of 2M+ vs. 2M- patients from 2.2 (95%CI 1.6-3.0) to 0.7 (95%CI 0.4-1.2). The RR for failure remained high, at 7.3 (95%CI 4.7-11.5) with and 4.2 (95%CI 2.5-7.2) without extension. More multi-drug resistance was found after extension, but acquired RMP resistance was similar in all arms. The fair sensitivity of the 2-month smear for failure or relapse (40%) was offset by a very low positive predictive value (3%).

CONCLUSIONS

Extension of P1 is very inefficient with this 6-month regimen. Operational research should define appropriate algorithms allowing an earlier switch to the next higher regimen for those in need, using follow-up smears for screening.