Muna A. Abu-Dalo

5-Cyano-2,3-ditolyl tetrazolium chloride (CTC) reduction in a mesophilic anaerobic digester: Measuring redox behavior, differentiating abiotic reduction, and comparing FISH response as an activity indicator

The tetrazolium salt 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) has been widely applied to assess microbiological activity in environmental samples. CTC reduction has previously been quantified in a variety of anaerobic systems (i.e., fermentative, nitrate reducing, sulfate reducing) using direct microscopy, solvent extraction, and flow cytometry. In this work, extracellular CTC reduction was observed and distinguished from its intercellular counterparts by the amorphous character and near uniform fluorescence of the resulting formazan precipitates (CTF). Fluorescence yielded by non-cellular-associated formazan precipitates bleached much more rapidly than CTF formed within cells under identical UV exposure (<2 min). Dehydrogenase activity assays and fluorescent in situ hybridization (FISH) were simultaneously carried out in microcosms containing active anaerobic digester biomass, propylene glycol, and settled sewage centrate for direct comparison. In substrate limited microcosms, quantitative FISH measurements remained well above their detection limit indicating sustained intercellular ribosomal RNA concentrations over a 5-day period, while dehydrogenase assays (CTC) decreased to background levels within 14 h of substrate limitation. Results from this work suggest that CTC reduction in cell-free samples may impede accurate enzyme activity measurements, particularly when quantification involves solvent extraction, flow cytometry, or software-aided counting. In addition, activity assessment in anaerobic digesters using FISH and CTC reduction assays may be comparable until substrate becomes limited.

Green Approach to Corrosion Inhibition of Mild Steel by Lignin Sulfonate in Acidic Media

The inhibition effect of lignin sulfonate against corrosion for mild steel in acidic solution has been examined by means of FTIR (fourier transform infrared spectroscopy), FAA (flame atomic absorption) spectroscopy, SEM (scanning electron microscope), EDS (energy dispersive X-ray spectroscopy), and mass loss techniques. The results revealed that lignin is a beneficial inhibitor for mild steel corrosion in acidic medium. It has been further found that Langmuir adsorption isotherm is obeyed by the tested lignin s adsorption over the surface of mild steel. The range of inhibition efficiency (IE) in 2 mol • L−1 HCl was found to be 75.88%–87.88% for Reax 88A, 40.72%–60.32% for Reax 88B, and 54.32% –63.03% for Reax 100M, after immersed at 298 K for 24 h time.