Analysis on the effect of salinity in underwater wireless optical communication

Abstract

This article deals with the effect of salinity variation on underwater wireless optical communication (UWOC). Effect of different concentration of salt on underwater optical communication has been carried out experimentally in terms of received power at different link lengths. Based on the analysis of experimental data, a mathematical model has been proposed to describe the saline water channel. A simulation study is performed for different data rates and link lengths. It is seen that with increased salinity the attenuation is higher and the UWOC system performance degrades with higher data rate and increased link length.     

Enzymatic degradation of polyhydroxyalkanoate using lipase from <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

Polyhydroxyalkanoates (PHAs) are an important class of biodegradable polymers synthesized by a few bacteria under nutrient-limiting conditions. In this study, the lipase-catalysed degradation of PHA synthesized by Enterobacter sp. was monitored. For this, the lipase-encoding gene from Bacillus subtilis DI2 was PCR-amplified, cloned into a T vector system and sequenced. It was expressed in Escherichia coli DH5α cells, the recombinant enzyme was purified 24.25-fold, and its molecular weight was determined to be around 28 kDa. When PHA biodegradation studies were carried out with this enzyme, gel permeation chromatography showed 21.3 and 28.3 % molecular weight decrease and weight loss, respectively. Further, scanning electron micrographs revealed alterations in polymer surface morphology. Changes in molecular vibrations were noticed in the FTIR spectra. When the chemical shifts in NMR spectra were studied, a steep reduction in area under the peak at 1.57 ppm was observed. In the heating range of 30–930 °C employed during thermogravimetry analysis, the degraded sample showed a total of 45.82 % weight loss, as against 18.89 % for the native sample. The melting temperature (T _m) of the polymer was also brought down from 126.22 to 118.18 °C, as inferred from differential scanning calorimetry. Lipase-catalysed chain scission reactions could thus be used to generate low molecular weight functional biopolymers with wide-ranging pharmaceutical applications, such as in sustained drug release.     

Advanced approach for degradation of recalcitrant by nanophotocatalysis using nanocomposites and their future perspectives

Industrial effluents containing persistent pollutants play a significant role in environmental pollution. Classical techniques such as chlorination, coagulation, ion flotation, membrane process and sedimentation that have been used to decontaminate polluted water are incapable of efficient degradation due to the generation of secondary pollutants. Photocatalysis, an advanced oxidation process in which the photoreaction is accelerated by the irradiation of catalyst, has shown efficient degradation of recalcitrant in water system. Usage of nanoparticles as homogenous photocatalyst has become prevalent due to their improved properties such as large surface-to-volume ratio, controlled uniform particle size and its composition which enhances the degradation rate. The recombination of holes and electron pair which is considered to be the limitation in homogenous system can be overcome by nanocomposites or heterogeneous photocatalysts. This system decreases the rate of recombination, leading to effective degradation of individual pollutants because of their enhanced physicochemical and structural properties. In recent years, heterogeneous nanophotocatalytic processes employing titanium dioxide (TiO₂) and zinc oxide (ZnO) composites have gained immense research interest as an effective wastewater treatment method because of its efficacy in decomposing and mineralizing the hazardous organic and inorganic pollutants utilizing the UV and visible photons. This paper reviews about the process, synthesis and parameters influencing photocatalytic reaction and their kinetics with much emphasize on types of nanoparticles and nanocomposites and its application in wastewater treatment.     

Remediation of chromium contaminants using bacteria

Chromium contaminants emanating from industrial activities pose a significant threat to human??s well-being. Chromium (III) and Chromium (VI) are the forms in which they are commonly encountered, of which the trivalent form is relatively benign. Hence, biological reduction of hexavalent chromium has been widely explored by researchers, yielding fruitful outcomes, opening up exciting avenues and also throwing up new challenges. This article attempts to review this area of research. Microbes, especially bacteria capable of Chromium (VI) reduction, belonging to a heterogeneous group have been isolated from contaminated sites. They exhibit plasmid-mediated chromate resistance and the reduction is enzymatically mediated. Reduction studies have been carried out with free and immobilized enzymes as well as whole cells. Experiments have been carried out in specifically designed bioreactors operated in batch and continuous modes. Although significant progress has been made, much needs to be done for its successful in situ application as the organism may not withstand the Chromium concentration or may be impeded by the presence of other toxicants. With molecular engineering, it may be possible to derive strains with improved performance even under stressful field conditions.     

Production of polyhydroxyalkanoates from Ralstonia eutropha using paddy straw as cheap substrate

Polyhydroxyalkanoates are polyesters of natural origin accumulated in form of intracellular granules by a wide variety of bacterial strains as candidates for biodegradable polymers, possessing material properties similar to the synthetic thermoplastics and elastomers. Paddy straw (lignocellulosic substrate) after hydrolysis was used as the carbon source for the production of polyhydroxyalkanoates from the predominant polyhydroxyalkanoates producer Ralstonia eutropha MTCC 1472. The effect of hydrolysed straw in the modified mineral salt media on bacterial growth and polyhydroxyalkanoates accumulation was analysed. Fourier transform infrared spectroscopy, thermogravimetric analysis and differential scanning calorimetry were performed on the extracted polyhydroxyalkanoates sample. At a dry cell weight of 19.2 g/L, 37.55 % polyhydroxyalkanoates accumulation was achieved; thus, paddy straw can be efficiently used as a cheap carbon source for industrial production of the polyhydroxyalkanoates.     

Isolation of <Emphasis Type="Italic">Virgibacillus</Emphasis> sp. strain KU4 from agricultural soil as a potential degrader of endocrine disruptor bisphenol-A

Bisphenol-A is one of the highest volumes of chemicals produced worldwide and released into the atmosphere each year. Recent extensive literature has raised concerns about its possible endocrine-disrupting effect in animals and humans. A bacterium having high tolerance of bisphenol-A (1000 mg L^?1) was isolated from agriculture soil of Coimbatore District, Tamil Nadu, India, and identified as Virgibacillus sp. KU4 by 16S ribosomal RNA sequence analysis. Bisphenol-A removal efficiency of this strain was measured as greater than 92% at seventh day of incubation in a basal mineral medium supplemented with 1000 mg L^?1 at seventh day. Gas chromatography analysis showed that 1000 mg L^?1 BPA in distilled water was degraded by the Virgibacillus sp. KU4 in an efficient way. A 70 ± 3% bisphenol-A degradation was observed in the suspended cell pellet-mediated degradation study, where distilled water supplemented with 1000 mg L^?1 bisphenol-A was sole carbon and energy source for bacterial growth. Further, Virgibacillus sp. KU4 is expected to be a candidate as a biological cleaner of BPA in the environment.     

Surface layer temperature inversion in the Arabian Sea during winter

Surface layer temperature inversion in the south eastern Arabian Sea, during winter has been studied using Bathythermograph data collected from 1132 stations. It is found that the inversion in this area is a stable seasonal feature and the occurrence is limited to the coastal waters. The inversion layer is found to have thickness varying from 10 to 80 meters and gradient of 0.0–1.2°C. The causative factor for the inversion is identified to be the winter-time surface-advection of cold less saline Bay of Bengal water over the warm saline Arabian Sea water along the west coast of India. Finally, the possible forcing mechanism for such an advection was examined using a hydrographic section and wind observations along the west coast of India.     

Chromium(VI) adsorption by <Emphasis Type="Italic">Codium tomentosum</Emphasis>: evidence for adsorption by porous media from sigmoidal dose–response curve

Adsorption of Cr(VI) using native and chemically modified marine green macroalgae Codium tomentosum biomass and its adsorption kinetics were studied under specific conditions. Maximum Cr(VI) removal occurred at pH 2 for both untreated and acid-treated biomass. However, base-treated biomass exhibited maximum adsorption at pH 6 due to the hydrolysis of methyl esters present in the cellulose, hemicellulose and lignin molecules resulting in carboxyl groups (COO^?) on the surface. The effect of adsorbent dose revealed that untreated and acid-treated biomass follows Henry’s linear isotherm, while base-treated biomass exhibited sigmoidal curve indicating energetic heterogeneity on the adsorbing surface. The monolayer adsorption capacity of untreated, acid-treated and base-treated biomasses was 5.032 ± 0.644, 5.445 ± 0.947, 3.814 ± 0.559 mg g^?1, respectively. Adsorption was found to follow Ho and McKay’s pseudo-second-order kinetic model with decreasing pseudo-second-order rate constant (K ₂, g mg^?1 min^?1) of 0.088 ± 0.037 (acid-treated), 0.019 ± 0.003 (untreated) and 0.012 ± 0.003 (base-treated).