Combined Strategies to Prompt the Biological Reduction of Chlorinated Aliphatic Hydrocarbons: New Sustainable Options for Bioremediation Application

Groundwater remediation is one of the main objectives to minimize environmental impacts and health risks. Chlorinated aliphatic hydrocarbons contamination is prevalent and presents particularly challenging scenarios to manage with a single strategy. Different technologies can manage contamination sources and plumes, although they are usually energy-intensive processes. Interesting alternatives involve in-situ bioremediation strategies, which allow the chlorinated contaminant to be converted into non-toxic compounds by indigenous microbial activity. Despite several advantages offered by the bioremediation approaches, some limitations, like the relatively low reaction rates and the difficulty in the management and control of the microbial activity, can affect the effectiveness of a bioremediation approach. However, those issues can be addressed through coupling different strategies to increase the efficiency of the bioremediation strategy. This mini review describes different strategies to induce the reduction dechlorination reaction by the utilization of innovative strategies, which include the increase or the reduction of contaminant mobility as well as the use of innovative strategies of the reductive power supply. Subsequently, three future approaches for a greener and more sustainable intervention are proposed. In particular, two bio-based materials from renewable resources are intended as alternative, long-lasting electron-donor sources (e.g., polyhydroxyalkanoates from mixed microbial cultures) and a low-cost adsorbent (e.g., biochar from bio-waste). Finally, attention is drawn to novel bio-electrochemical systems that use electric current to stimulate biological reactions.

Nitrate removal during Fe(III) bio-reduction in microbial-mediated iron redox cycling systems

Fe(III) bio-reduction provides a prospect of applying the iron redox cycle to nitrate remediation in the aquatic environment. The objective of this study was to realize multiple nitrate removals in the system containing Shewanella oneidensis MR-1 (S. oneidensis MR-1) and ferrihydrite or magnetite. The results showed that with three periods of 30 mg·L−1 NO3−-N addition, all nitrate reduction was completed within 170 h. In the first period (0–30 h) of nitrate addition, the main contribution of nitrate removal was due to the biological reduction process by S. oneidensis MR-1, accompanied by the reduction of Fe(III). During the second (45–90 h) and third periods (100–170 h) of nitrate addition, oxidation of biogenic Fe(II) coupled with the reduction of nitrate took place. This redox reaction resulted in the production of gaseous nitrogen of 47.33% and 16.8% for ferrihydrite/S. oneidensis MR-1 and magnetite/S. oneidensis MR-1 systems, respectively. In addition, nitrite, as an intermediate product, accumulated and negatively affected nitrate removal after the third addition of nitrate. By comparing the patterns of X-ray diffraction of the iron minerals before and after the bio-reduction, it was found that ferrihydrite was transformed into magnetite, while magnetite kept its original crystal form.

A Multi-Sensor System for Sea Water Iodide Monitoring and Seafood Quality Assurance: Proof-of-Concept Study

Iodine is a trace chemical element fundamental for a healthy human organism. Iodine deficiency affects about 2 billion people worldwide causing from mild to severe neurological impairment, especially in children. Nevertheless, an adequate nutritional intake is considered the best approach to prevent such disorders. Iodine is present in seawater and seafood, and its common forms in the diet are iodide and iodate; most iodide in seawater is caused by the biological reduction of the thermodynamically stable iodate species. On this basis, a multisensor instrument which is able to perform a multidimensional assessment, evaluating iodide content in seawater and seafood (via an electrochemical sensor) and discriminating when the seafood is fresh or defrosted quality (via a Quartz Micro balance (QMB)-based volatile and gas sensor), is strategic for seafood quality assurance. Moreover, an electronic interface has been opportunely designed and simulated for a low-power portable release of the device, which should be able to identify seafood over or under an iodide threshold previously selected. The electrochemical sensor has been successfully calibrated in the range 10–640 μg/L, obtaining a root mean square error in cross validation (RMSECV) of only 1.6 μg/L. Fresh and defrosted samples of cod, sea bream and blue whiting fish have been correctly discriminated. This proof-of-concept work has demonstrated the feasibility of the proposed application which must be replicated in a real scenario.

Nitrite as a causal factor for nitrate-dependent anaerobic corrosion of metallic iron induced by Prolixibacter strains

Microbially influenced corrosion (MIC) may contribute significantly to overall corrosion risks, especially in the gas and petroleum industries. In this study, we isolated four Prolixibacter strains, which belong to the phylum Bacteroidetes, and examined their nitrate-respiration- and Fe0-corroding activities, together with two previously isolated Prolixibacter strains. Four of the six Prolixibacter strains reduced nitrate under anaerobic conditions, while the other two strains did not. The anaerobic growth of the four nitrate-reducing strains was enhanced by nitrate, which was not observed in the two nitrate-non-reducing strains. When the nitrate-reducing strains were grown anaerobically in the presence of Fe0 or carbon steel, the corrosion of the materials was enhanced by more than 20-fold compared to that in aseptic controls. This enhancement was not observed in cultures of the nitrate-non-reducing strains. The oxidation of Fe0 in the anaerobic cultures of nitrate-reducing strains occurred concomitantly with the reduction of nitrite. Since nitrite chemically oxidized Fe0 under anaerobic and aseptic conditions, the corrosion of Fe0- and carbon-steel by the nitrate-reducing Prolixibacter strains was deduced to be mainly enhanced via the biological reduction of nitrate to nitrite, followed by the chemical oxidation of Fe0 to Fe2+ and Fe3+ coupled to the reduction of nitrite.

Synthesis, Crystal Structure, Spectroscopic and Antimicrobial Properties of Ruthenium Complexes of Vinyl Imidazole and 4-Ethylaminomethyl Pyridine Ligands

Ruthenium complexes of vinylimidazole (VIMD) and 4-ethylaminomethyl pyridine (EMP) ligands were synthesized and characterized by XRD and spectroscopic methods. The binding of these Ru(IIII) complexes with calf thymus-DNA has been studied by UV-visible spectroscopic and electrochemical studies. A prominent increase in the intensity of fluorescence spectra of these complexes with CT-DNA was observed and a distinct UV-visible spectral shift in presence of CT-DNA is probably due to an interaction of these complexes with CT-DNA. The evidence of DNA binding has been found from the change in the intensity of fluorescence and UV visible spectra. Also, the electron transfer ability of these complexes is very important in order to rationalize their activity towards the biological system therefore, we have studied the electrochemical studies of these complexes by using cyclic voltammetry. From this study, it is possible to draw some ideas on electrochemical potentials of the complexes relevant to biological reduction possibly Ru(III)/Ru(II). Both complexes were also tested for antimicrobial activity against bacterial strain and responses well as antimicrobial agent.

Detoxification of Ciprofloxacin in an Anaerobic Bioprocess Supplemented with Magnetic Carbon Nanotubes: Contribution of Adsorption and Biodegradation Mechanisms

In anaerobic bioreactors, the electrons produced during the oxidation of organic matter can potentially be used for the biological reduction of pharmaceuticals in wastewaters. Common electron transfer limitations benefit from the acceleration of reactions through utilization of redox mediators (RM). This work explores the potential of carbon nanomaterials (CNM) as RM on the anaerobic removal of ciprofloxacin (CIP). Pristine and tailored carbon nanotubes (CNT) were first tested for chemical reduction of CIP, and pristine CNT was found as the best material, so it was further utilized in biological anaerobic assays with anaerobic granular sludge (GS). In addition, magnetic CNT were prepared and also tested in biological assays, as they are easier to be recovered and reused. In biological tests with CNM, approximately 99% CIP removal was achieved, and the reaction rates increased ≈1.5-fold relatively to the control without CNM. In these experiments, CIP adsorption onto GS and CNM was above 90%. Despite, after applying three successive cycles of CIP addition, the catalytic properties of magnetic CNT were maintained while adsorption decreased to 29 ± 3.2%, as the result of CNM overload by CIP. The results suggest the combined occurrence of different mechanisms for CIP removal: adsorption on GS and/or CNM, and biological reduction or oxidation, which can be accelerated by the presence of CNM. After biological treatment with CNM, toxicity towards Vibrio fischeri was evaluated, resulting in ≈ 46% detoxification of CIP solution, showing the advantages of combining biological treatment with CNM for CIP removal.