Current Environmental Engineering - Volume 5, Issue 1, 2018

Background: Biodiesel is considered as an upcoming alternative to overcome the fossil fuel dependence. Much research has been aimed at conversion of biobased platform molecules into fuels and multiple commodity products. In this regard, biodiesel is of topical interest which is obtained by transesterification reaction of renewable triglycerides in which glycerol is a valuable by-product. Conversion of this bioglycerol to value added products such as 2,3-butanediol (2,3-BD) which is a starting material for 1,3-butadiene, by microbial route is of great importance in promoting biodiesel industrialisation on a larger scale. Bioconversions have distinct advantages of sustainability as well as biodegradability with respect to biocatalysts, substrates, intermediates, and most of the times, products and by-products. Methods: This review covers the literature on microorganisms mediated conversion of bioglycerol to 2,3 BD. This has been achieved by various strains of bacteria under aerobic, anaerobic conditions in batch as well as continuous modes of operation. Results: There are few reports on microbial mediated conversion of bioglycerol (C3 diol) to 2,3-BD which is a C4 diol. Although a variety of strains have been reported for this conversion, but Klebsiella sp. gives highest (131.5 g/L) 2,3-BD yield by mutational studies leading to a reduction of by-products. Conclusion: The review illustrates, the three stereoisomeric forms of (2,3-BD) produced by different bacterial strains along with pathway studies and their potent applications in various industries. Combination of strain improvement strategies will eventually lead in viable productivity of 2,3-BD production from biodiesel derived glycerol.

Background: To make the current chemicals production sustainable, new processes should be developed to produce chemicals from unused resources, such as organic wastes and biomass which could be also considered as supplementary resources. The new processes would also require that the raw materials and their by-products cause less stress to human being and to the environment, and that the production efficiency would be equal to or greater than the current petroleum-based system. In this manuscript, we report recent application of organic waste and biomass feedstock to produce valuable chemicals and gaseous fuels from by catalytic high-pressure and high-temperature reaction in water, which is the safest chemical for humans and the environment. Methods: This review covers the literature on chemicals production from organic wastes and biomass in high-temperature liquid water and supercritical water solvent. Results: The proposed processes shown in this review do not need dewatering pretreatment processes, which are energy-intesive. Conclusion: This review illustrates a recent application of catalytic transformation of organic wastes and biomass to produce commercially important chemicals and fuel gases in water solvent. The case studies presented here include (1) hydrolysis of polyethylene terephthalate to terephthalic acid and ethylene glycol in high-temperature liquid water, (2) hydrogenolysis of bio-glycerol to 1,2-propanediol over copper-aluminum in high-temperature liquid water, and (3) fuel gas production from organic wastes with supported ruthenium catalysts under supercritical water.

Objective: We develop a very efficient method for removal of aqueous heavy metal toxic ions by smart nanocomposite materials by adsorption. Background: Various methods such as ion exchange, nano-filtration, reverse osmosis, and coprecipitation that are used for the removal of aqueous toxic metal ions proved to be expensive, cumbersome and convoluted the condition. Both Graphene Family Materials (GFM) and Layered Double Hydroxides (LDH) have been extensively studied for environment protection for increased user acceptance, and improved overall performance. Methods: We review problems with noxious and recalcitrant heavy metals present in surface water. We contrast the approach of expensive and cumbersome methods to simple, low cost and eco-friendly ones. We put forward the various 2D-2D nano-composites recently used for effective removal of toxic metal ions substantiated due to anthropogenic activities. Results: On the basis of these analyses, we propose methods for supporting 2D-2D composites fabricated by surface altercation, crystal lattice defect substitution and intercalation modification by LDH with nanocarbons, carbon nanotubes, graphenic materials, polydopamine and polyaniline are frontrunners in well-organized, proficient and resourceful adsorbents. Finally, we describe the reasons, preparations and work done by LDH carbonaceous materials as fore-front adsorbents for removal of aqueous toxic metal ions from water. Conclusion: The chemical reactivity and positively charge of LDH and the electrical activity and negatively charge of carbonaceous materials synergistically contributed with large surface area, abundant active sites and compatibility made the sorbent a champion in water remediation. Application: The present scenario is urgently in need of innovative sorbents with 100% efficiency with fast removal of toxins from water to meet the scarcity of safe water in the coming decade.

Background: The treatment of sewage water is an important problem faced by many cities across India. Conventional methods are costly and require high space, therefore, there is a need to develop an eco-friendly and cost effective technique for the treatment of sewage water. Methods: The present work deals with the treatment of sewage water using three different microalgae cultures in combination with the Membrane Bioreactor (MBR). Open raceway pond was used to grow microalgae (three species) in presence of sunlight (12:12 h light-dark cycle) with continuous monitoring of nutrients and organic matter depletion for 5 days. Algal growth was measured using hemocytometer. Nutrients and organic matter uptake was measured using standard APHA & TOC analyzer respectively. The grown algal biomass was dewatered using three different membrane modules. Results: The effect of various operating parameters such as the concentration of microalgae, types of membranes (viz. ceramic, polysulfone and polyacrylonitrile (PAN)), and transmembrane pressure, on the quality of treated water was investigated in detail. During the operation, various process parameters such as nutrients uptake, pH and organic matters were monitored. It was found that at higher initial biomass concentration (5x106 cells/ml), the rate of the nutrients uptake was maximum for all the three cultures, and PAN membrane gave the highest permeate flux with less fouling compared to other membranes. Conclusion: Efficient biomass production and high quality permeate water was achieved together by the combination of microalgae and membrane bioreactor system.

Background: Dye molecules are non-biodegradable which leads to pollution of water. There it's important to treat these dye molecules prior to their discharge into water. There are various methods to treat the polluted water, but which has certain drawbacks with respect to their efficacy. The aim of this paper to introduce ultrasonically synthesized polymer hydrogel for removal of dye molecules from effluent. Methods: Polyacrylic acid based synthesis of hydrogel was carried out with the aid of acoustic cavitation. Encapsulation and uniform dispersion of cross linker (Halloysite nanoclay) has been efficiently carried due to ultrasonic irradiation produced by acoustic cavitation. Also Auramine O dye was considered for dye adsorption study. Results: The dye absorptivity of the synthesized hydrogel was analysed for removal of Auramine O dye. The adsorption study was carried out under various pH values for 5.5 hours. It was perceived that highest % removal of dye occurred at pH 11 with contact time of 5 hours. Conclusion: Prepared hydrogel was examined for its swelling capacity using deionized water. From swelling behavior data it has been observed that synthesized hydrogel has good swelling capacity and follows non-Fickian diffusion. From pH study it was observed that percentage removal of dye was increasing linearly with respect to pH up to 12.The optimum values for pH and contact time for highest dye removal (78.93%) are thus found out to be 11 and 5 hours respectively. The adsorption isotherm model study showed that Langmuir adsorption isotherm model well fitted with the experimental data.

Background: Personal care and pharmaceuticals products affect the ambient water quality when these materials enter the environment in the form of human and animal excreted metabolites or as effluents from hospitals, pharmacies, and chemical manufacturing facilities. The stated compounds are difficult to capture and pose a serious threat to the aquatic ecosystem, and human health. Photocatalytic Degradation (PCD) is seen to be an attractive and inexpensive method, when compared to the ones such as ozonation, photo-Fenton oxidation, sonolysis, and photolysis for the elimination of pharmaceutical compounds from the wastewater. Methods: Owing to the underlying complex nonlinear physicochemical phenomena, the design and construction of a “first principles” model for predicting the rate constant of the PCD is a timeconsuming and tedious process. To overcome the said difficulty, in this study, the stated mathematical models have been developed-for the first time-using an artificial intelligence (AI) based novel datadriven modeling method, namely, genetic programming (GP). The GP-based model predicting the rate constant of the PCD of pharmaceuticals uses following inputs: time of exposure of pharmaceutical pollutant to the solar radiation, pH of wastewater, concentration degraded during the measured time, and the ratio of concentration degraded to the initial concentration of the sample. In this study, PCD of three pharmaceutical pollutants, namely, Ciprofloxacin, Naproxen, and Paracetamol was studied and modeled using a single GP-based model. In the model's input space, the three pharmaceutical pollutants were differentiated using a number of attributes related to their molecular structures. Result: The GP-based model predicting the rate constant of the PCD, proposed in this study, exhibits an excellent prediction accuracy [correlation coefficient (CC) > 0.9] and generalization performance. Conclusion The GP-based modeling strategy introduced here can be fruitfully used in the development of models for a variety of other pharmaceutical degradation reactions.

Background: Glimepiride (GLM) is widely used for the treatment of type -II diabetes mellitus, one of the third generation sulfonylurea drugs having poor aqueous solubility, low oral bioavailability, and low elimination half life. Hence to improve its bioavailability, biodegradable chitosan nanoparticles containing GLM was developed. Methods: GLM loaded chitosan nanoparticles were prepared by ionic gelation method using 3-factor, 3- level Box-Behnken design. Response Surface Methodology (RSM) was used to optimize the independent variables like Polymer concentration (chitosan), Surfactant concentration (Tween 80) and cross linking agent (TPP) on dependent variables like Encapsulation Efficiency (EE) and in vitro drug release (DR). The developed GLM loaded chitosan nanoparticle were characterized for FTIR, DSC, XRD and Particle size. Result: The result of the RSM analysis shows that Chitosan and Tween 80 was significant for the EE (p < 0.0001) and DR (p<0.0001), whereas TPP is only significant for the EE (p = 0.0015). Statistical and Mathematical analysis of the design shows linear model was significant with correlation factor value (R2) of 0.9956 and 0.9925 to evaluate the EE and DR, respectively. The EE increases and DR decreases with increase in concentration of chitosan and was found in the range of 46.23% to 101.2%. In vitro drug release of GLM loaded chitosan nanoparticle shows sustained release up to 24 hours. Conclusion: From the study, we can conclude that response surface methodology seems to be promising approach for improving the oral bioavailability leading to improve patient compliance.

Background: Vast amounts of untapped natural gas are stored in the form of Natural Gas Hydrates (NGHs) which are encountered in nature in marine and permafrost settings. The global volume of natural gas trapped within NGH reserves is considered to be ranging around 1000-20,000 trillion cubic meters (TCM). India in particular is estimated to have around 1894 TCM of natural gas in the form of NGH reserves and even the possibility of harnessing 10% of the total energy present as this resource may fulfill the county's energy demand for the next 200 years. Methods: Taking into consideration the huge energy potential of NGHs, in the present work, experimental investigations have been conducted to study the kinetics of NGH formation and dissociation in simulated gas hydrate bearing sediments. The thermal stimulation method was used to decompose NGHs; hydrate dissociation was carried out at various dissociation temperatures and injection water flow rates. Results: For the hydrate formation experiments, higher water to hydrate conversion was observed with the unconsolidated sediment (silica sand + quartz mixture) as compared to the consolidated sediment (Berea sandstone) at the same initial water saturation. Water to hydrate conversion is also dependent on initial water saturation in the sediments. Higher water to hydrate conversion is observed in partially water saturated sediment as compared to completely water saturated sediment. The initial rate of water saturation also follows the same trend. For the hydrate dissociation experiments, it was observed that as the temperature of the injected water increases, the initial gas recovery along with its rate also increases which saturates and settles down after a certain period of time. The gas recovery (%) ratios obtained after say 10 minutes of hydrate dissociation, for the faster heating (high flow-rate) to slower heating (low flow-rate) systems were 2.08:1; 1.77:1; and 1:1 for the dissociation temperatures of 293 K, 288 K and 283 K respectively. Conclusion: The better hydrate saturation, gas uptake and hydrate growth kinetics obtained with the unconsolidated sediment may be down to a number of factors such as better gas-water contact, sediment porosity and spatial distribution of water in sediment while the partially water saturated sediment also leads to better dispersion of gas in the sediment along with the already present water thus resulting in higher hydrate formation rate. Gas recovery rate is directly dependent upon the temperature difference ( ΔT) between the injection water and the hydrate bearing zone (at the time of start of dissociation); at the dissociation temperature of 293 K, around 97% of gas recovery was achieved for the first 30 minutes of hydrate dissociation which is way better that the 67% and 43% achieved at 288 and 283 K respectively for the same time period. During thermal stimulation, the effect of the flow rate of injected water on the kinetics of hydrate dissociation becomes increasingly pronounced as the hydrate dissociation temperature (temperature of injected water) increases.