Biodegradation of 4-bromophenol by Arthrobacter chlorophenolicus A6T in a newly designed packed bed reactor

Facile synthesis of ZnO nanoparticles by Actinidia deliciosa fruit peel extract: Bactericidal, anticancer and detoxification properties

Synthesis of nanoparticles by eco-friendly method pulled an extensive concern worldwide due its biocompatibility and wide range of applications as catalysts, microbicidal agents, cancer treatment, sensors etc. Though different chemical methods available for preparation of ZnO nanoparticles, synthesis by utilizing plant material is an excellent substitute and green method as well. The present study describes preparation of ZnO nanoparticles by low-cost green synthetic way using Actinidia deliciosa (kiwi) fruit peel extract and its excellent biological and catalytic properties. The synthesized nanoparticles were well characterized by UV visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDAX). The bactericidal activity of the ZnO nanoparticles was determined by using Staphylococcus aureus (S. aureus), while mechanism of cell death was studied by SEM images. Superior anticancer activity was also observed in inhibiting the colon cancer cells (HCT116) by the ZnO nanoparticles. In addition, ZnO nanoparticles showed efficient photocatalytic activity towards degradation of p-bromophenol, about 96.3% within 120 min. Furthermore, phytotoxicity of the intermediate products was analyzed using Vigna radiata (V. radiata) as a model plant. About 8.0% of germination index (GI) was observed in pure p-BP while it increased to 82.3%, and exhibited that the detoxification of p-BP was attained after 120 min of degradation. Thus, the present study demonstrates ZnO nanoparticles prepared from simple, rapid, inexpensive, eco-friendly and efficient green method gives alternative root for biomedicine and wastewater treatment technologies.

Study on aerobic degradation of 2,4,6-trinitrotoluene (TNT) using Pseudarthrobacter chlorophenolicus collected from the contaminated site

2,4,6-trinitrotoluene or TNT, a commonly used explosive, can pollute soil and groundwater. Conventional remediation practices for the TNT-contaminated sites are neither eco-friendly nor cost-effective. However, exploring bacteria to biodegrade TNT into environment-friendly compound(s) is an interesting area to explore. In this study, an indigenous bacterium, Pseudarthrobacter chlorophenolicus, strain S5-TSA-26, isolated from explosive contaminated soil, was investigated for potential aerobic degradation of TNT for the first time. The isolated strain of P. chlorophenolicus was incubated in a minimal salt medium (MSM) containing 120 mg/L TNT for 25 days at specified conditions. TNT degradation pattern by the bacterium was monitored at regular interval using UV-Vis spectrophotometry, high-performance liquid chromatography, and liquid chromatography mass spectrophotometric, by estimating nitrate, nitrite, and ammonium ion concentration and other metabolites such as 2,4-dinitrotoluene (DNT), 2-amino-4,6-dinitrotoluene (2-ADNT), and 2,4-diamino-6-nitrotoluene (2-DANT). It was observed that, in the presence of TNT, there was no reduction in growth of the bacterium although it multiplied well in the presence of TNT along with no considerable morphological changes. Furthermore, it was found that TNT degraded completely within 15 days of incubation. Thus, from this study, it may be concluded that the bacterium has the potential for degrading TNT completely with the production of non-toxic by-products and might be an important bacterium for treating TNT (i.e., a nitro-aromatic compound)-contaminated sites.

A combined experimental and computational study on the oxidative degradation of bromophenols by Fe(VI) and the formation of self-coupling products

In this study, the degradation of eight bromophenols (BPs), including monobromophenols (2-BP, 3-BP, and 4-BP), dibromophenols (2,4-DBP, 2,6-DBP, and 3,5-DBP), a tribromophenol (2,4,6-TBP) and a pentabromophenol (PBP), by a Fe(VI) reaction process at a pH of 8.0 was systematically studied. It was concluded that their degradation rates increased with increasing Fe(VI) concentrations in solution. The removal of 2,4,6-TBP, 2-BP, and 2,6-DBP was faster than that of the other five BPs, which could be attributed to the position of the substituting Br atom. Moreover, the direct oxidation and coupling reactions greatly influenced the reactivity of the bromophenols with Fe(VI). The electron paramagnetic resonance (EPR) analysis confirmed the presence of hydroxyl radicals in present system. The oxidation reaction products of PBP and 2-BP were recognized by an electrospray time-of-flight mass spectrometer; hydroxylation, hydroxyl substitution, the cleavage of the C-C bond, direct oxidation and polymerization via an end linking mechanism were noticeably found in the reaction process, resulting in the formation of polymerization products and causing hydroxylation to occur. Theoretical calculations further determined the possible oxidation sites of 2-BP and PBP. This study may provide comprehensive and important information on the remediation of BPs by Fe(VI).

Enhanced detoxification of p-bromophenol by novel Zr/Ag-TiO2@rGO ternary composite: Degradation kinetics and phytotoxicity evolution studies

The toxicity and persistence of the halogenated aromatics, particularly brominated phenolic compounds have drawn serious concerns to the environment, emphasizing the potential effects on human health and ecosystems balance. Advanced oxidation process (AOP) has received much attention as an alternative for the conventional wastewater treatment methods to treat water contaminated with toxic pollutants. This study investigated the degradation and detoxification of p-bromophenol (p-BP) by a novel Zr/Ag-TiO₂@rGO photocatalyst under visible light. Upon 3 h of visible light irradiation over Zr/Ag-TiO₂@rGO, more than 95% of p-BP (15 mg/L) degradation was achieved at a rate of 0.23 min^-1. The degradation products were identified by GC-MS and possible degradation pathway was proposed. The phytotoxicity evolution of the degraded products was assessed on Vigna radiata (V. radiata), in which seeds treated with pure p-BP showed less germination (40%) compared to degradation products (100%). Furthermore, the germination index (GI) of p-BP was found to be 11.1% before degradation while it increased to 80.5% after 3 h of degradation indicated that this photodegradation process achieved detoxification of p-BP. Thus, this study demonstrated that p-BP elimination and detoxification could be simply achieved with Zr/Ag-TiO₂@rGO nanocomposite under visible light irradiation, which provides new solution for wastewater treatment and water reuse in crop irrigation.

Treatment of gaseous volatile organic compounds using a rotating biological filter

Rotating biological filter (RBF), which provides higher oxygen mass transfer has been developed for treating gaseous volatile organic compounds (VOCs) such as BTEX (Benzene, toluene, ethylbenzene and xylene) at higher concentrations. The screening of enriched cultures has been done initially to enhance the performance of RBF for treating xylene, toluene and xylene, and BTEX at various loading rates. The removal efficiency of BTEX was maximum (82%), higher than toluene and xylene (79%), and xylene (72%). The presence of xylene enhanced the removal of toluene in the mixture. In the BTEX, toluene was found to be highly biodegradable followed by ethylbenzene, benzene and xylene. The RBF also removed nutrients from wastewater along with VOCs. The stability study of RBF showed that supply of nutrient media influenced the RBF performance more. Further, the predominant strain identified in the mixed culture was Enterobacter cloacae SP4001, responsible for biodegradation of BTEX.

Catabolism of Phenol and Its Derivatives in Bacteria: Genes, Their Regulation, and Use in the Biodegradation of Toxic Pollutants

Phenol and its derivatives (alkylphenols, halogenated phenols, nitrophenols) are natural or man-made aromatic compounds that are ubiquitous in nature and in human-polluted environments. Many of these substances are toxic and/or suspected of mutagenic, carcinogenic, and teratogenic effects. Bioremediation of the polluted soil and water using various bacteria has proved to be a promising option for the removal of these compounds. In this review, we describe a number of peripheral pathways of aerobic and anaerobic catabolism of various natural and xenobiotic phenolic compounds, which funnel these substances into a smaller number of central catabolic pathways. Finally, the metabolites are used as carbon and energy sources in the citric acid cycle. We provide here the characteristics of the enzymes that convert the phenolic compounds and their catabolites, show their genes, and describe regulatory features. The genes, which encode these enzymes, are organized on chromosomes and plasmids of the natural bacterial degraders in various patterns. The accumulated data on similarities and the differences of the genes, their varied organization, and particularly, an astonishingly broad range of intricate regulatory mechanism may be read as an exciting adventurous book on divergent evolutionary processes and horizontal gene transfer events inscribed in the bacterial genomes. In the end, the use of this wealth of bacterial biodegradation potential and the manipulation of its genetic basis for purposes of bioremediation is exemplified. It is envisioned that the integrated high-throughput techniques and genome-level approaches will enable us to manipulate systems rather than separated genes, which will give birth to systems biotechnology.

Biodegradation of 4-bromophenol by Arthrobacter chlorophenolicus A6 in batch shake flasks and in a continuously operated packed bed reactor

The present study investigated growth and biodegradation of 4-bromophenol (4-BP) by Arthrobacter chlorophenolicus A6 in batch shake flasks as well as in a continuously operated packed bed reactor (PBR). Batch growth kinetics of A. chlorophenolicus A6 in presence of 4-BP followed substrate inhibition kinetics with the estimated biokinetic parameters value of μ max = 0.246 h(-1), K i = 111 mg L(-1), K s  = 30.77 mg L(-1) and K = 100 mg L(-1). In addition, variations in the observed and theoretical biomass yield coefficient and maintenance energy of the culture were investigated at different initial 4-BP concentration. Results indicates that the toxicity tolerance and the biomass yield of A. chlorophenolicus A6 towards 4-BP was found to be poor as the organism utilized the substrate mainly for its metabolic maintenance energy. Further, 4-BP biodegradation performance by the microorganism was evaluated in a continuously operated PBR by varying the influent concentration and hydraulic retention time in the ranges 400-1,200 mg L(-1) and 24-7.5 h, respectively. Complete removal of 4-BP was achieved in the PBR up to a loading rate of 2,276 mg L(-1) day(-1).