Development of a novel fractal-like kinetic model for elucidating the effect of particle size on the mechanism of hydrolysis and biogas yield from ligno-cellulosic biomass

The effect of particle size on hydrolysis and biogas production kinetics from a typical ligno-cellulosic biomass was assessed by studying the anaerobic co-digestion of fixed amount of rice husk and cow dung mixture using a newly developed fractal-like kinetic model. British Standard (BS) sieves were used to obtain varying particles size fractions ranging from 0.150 to 0.212 mm, 0.212–0.300 mm, 0.300–0.600 mm, 0.600–1.000 mm and 1.000–1.700 mm from oven dried, milled rice husk and pulverized, dried cow dung respectively. These particle size fractions from both biomass were mixed in a ratio of 1:1 after which, they were loaded into batch reactors and digested anaerobically at ambient conditions for 75 days. Hydrolysis of ligno-cellulosic biomass was observed to depend on the fractal exponent (h), which indexed the presence of inaccessible regions in ligno-cellulosic biomass. Also, hydrolysis was observed to depend on two other intrinsic factors that comprised of the initial hydrolytic rate (XoYko′) and overall affinity constant (ko′So). Larger particlesize fractions were associated with higher affinity but lower initial hydrolysis rate while, smaller particle size fractions were associated with lower affinity but higher initial hydrolysis rate. In addition, the fractal model compared favorably with the popular modified Gompertz equation

Adsorption of pyrene from aqueous solutions onto sepiolite

Polycyclic aromatic hydrocarbons (PAHs) are commonly referred to a large class of organic compounds, which have been shown to be highly carcinogenic, and to have a significant persistence in an environment for many years. In this study, the adsorption of pyrene, which was chosen as a model PAH due to its specific volatility, miscibility, and relatively soluble properties, onto sepiolite (Turkish origin) was investigated in detail. Pyrene used as a model PAH due to its specific volatility and miscibility characteristics, relatively soluble yet hydrophobic to explore the potential of sepiolite (Turkish origin) to sorb hydrophobic organic compounds from aqueous solution. The microstructure and morphology of sepiolite were characterized by using Elemental analysis, X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscope (FE-SEM), and surface property evaluation by the BET method from nitrogen adsorption isotherms. The results for the adsorption isotherms were closely fitted with the Langmuir model, and the coefficient of determination (R2) was higher than 0.999. The results indicated that the high affinity of pyrene on sepiolite surfaces was dominated by structural channels and large number of Si-OH groups located at the basal surfaces. However, its intracrystalline interactions with pyrene were more favorable than the surface Si-OH groups which could react directly with pyrene to form compounds with true covalent bonds (chemical interactions) between sepiolite and pyrene. Finally, the FE-SEM images initially revealed that after loading with pyrene, fairly straight and rigid fiber arrangement (aggregation of laths to form rods) occurred due to increasing sorption of pyrene onto sepiolite

Adsorption of pyrene from aqueous solutions onto sepiolite

Polycyclic aromatic hydrocarbons (PAHs) are commonly referred to a large class of organic compounds, which have been shown to be highly carcinogenic, and to have a significant persistence in an environment for many years. In this study, the adsorption of pyrene, which was chosen as a model PAH due to its specific volatility, miscibility, and relatively soluble properties, onto sepiolite (Turkish origin) was investigated in detail. Pyrene used as a model PAH due to its specific volatility and miscibility characteristics, relatively soluble yet hydrophobic to explore the potential of sepiolite (Turkish origin) to sorb hydrophobic organic compounds from aqueous solution. The microstructure and morphology of sepiolite were characterized by using Elemental analysis, X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscope (FE-SEM), and surface property evaluation by the BET method from nitrogen adsorption isotherms. The results for the adsorption isotherms were closely fitted with the Langmuir model, and the coefficient of determination (R2) was higher than 0.999. The results indicated that the high affinity of pyrene on sepiolite surfaces was dominated by structural channels and large number of Si-OH groups located at the basal surfaces. However, its intracrystalline interactions with pyrene were more favorable than the surface Si-OH groups which could react directly with pyrene to form compounds with true covalent bonds (chemical interactions) between sepiolite and pyrene. Finally, the FE-SEM images initially revealed that after loading with pyrene, fairly straight and rigid fiber arrangement (aggregation of laths to form rods) occurred due to increasing sorption of pyrene onto sepiolite

Sepiolite and sepiolite-bound humic acid interactions in alkaline media and the mechanism of the formation of sepiolite-humic acid complexes

The surface-controlled reactions and interfaces of clays and/or clay minerals are strongly determined by the adsorption of dissolved humic substances which have surface active characters. Consequently, this may lead to an improved understanding of organo-clay complexes for remediation purposes of polluted areas. The interactions between sepiolite and sepiolite-bound humic acid (HA), and its influence on the mechanism of the formation of sepiolite-humic acid complexes were examined by characterizing the structure of sepiolite through UV/Vis spectroscopy, field emission scanning electron microscopy (SEM+FEG), specific surface area, pore size and volume, and Fourier transform infrared spectroscopy (FTIR). The UV-VIS spectral results of the raw sepiolite showed that there is no correlation between UV254 and the amount of humic substance released from sepiolite is dependent on increasing extraction time. The low values of humification index of the sepiolite confirmed the presence of HA with higher, and similar molecular weight, particle size, humification degree and aromaticy. Hence, it can be concluded that HA groups are presumably associated with the large quantity of silanol groups located on the sepiolite external surface preferentially through H-bonds and/or surface complexation interactions between the functional groups in HA and dissolved metal cations (Mn+). This finding is in good agreement with results from FTIR and SEM-FEG investigations. EDAX analysis of the HA-extracted sepiolite illustrated a strong decrease in Mg2+, Ca2+ and K+ content indicating that electrically charged sites on HA may form metal complexes of high stability through chelation

Sepiolite and sepiolite-bound humic acid interactions in alkaline media and the mechanism of the formation of sepiolite-humic acid complexes

The surface-controlled reactions and interfaces of clays and/or clay minerals are strongly determined by the adsorption of dissolved humic substances which have surface active characters. Consequently, this may lead to an improved understanding of organo-clay complexes for remediation purposes of polluted areas. The interactions between sepiolite and sepiolite-bound humic acid (HA), and its influence on the mechanism of the formation of sepiolite-humic acid complexes were examined by characterizing the structure of sepiolite through UV/Vis spectroscopy, field emission scanning electron microscopy (SEM+FEG), specific surface area, pore size and volume, and Fourier transform infrared spectroscopy (FTIR). The UV-VIS spectral results of the raw sepiolite showed that there is no correlation between UV254 and the amount of humic substance released from sepiolite is dependent on increasing extraction time. The low values of humification index of the sepiolite confirmed the presence of HA with higher, and similar molecular weight, particle size, humification degree and aromaticy. Hence, it can be concluded that HA groups are presumably associated with the large quantity of silanol groups located on the sepiolite external surface preferentially through H-bonds and/or surface complexation interactions between the functional groups in HA and dissolved metal cations (Mn+). This finding is in good agreement with results from FTIR and SEM-FEG investigations. EDAX analysis of the HA-extracted sepiolite illustrated a strong decrease in Mg2+, Ca2+ and K+ content indicating that electrically charged sites on HA may form metal complexes of high stability through chelation

Mechanistic insight into pyrene removal by natural sepiolites

This paper investigates the sorption characteristics and mechanisms of pyrene onto two types of natural sepiolite -brown (B-Sep) and white (W-Sep). The effects of relevant properties such as clay content, surface area, pore diameter and volume, divalent cations and organic carbon content were investigated by single component batch adsorption systems. The results suggest that pyrene has high affinity for both sepiolite and its sorption behaviour could be mainly affected by exchangeable strongly hydrated cations such as Ca2+ and H2O in the zeolite-like channels and by open channel defects (OCD) structures but no so much by the large number of Si-OH groups located on the sepiolite's basal surfaces. Mesoporosity rather than surface area largely controls the sorption capacity and intensity of both sepiolites. This is shown by the increase in pore volume that exhibited the greatest increase in BET surface area. Particle size and morphological changes of both sepiolites following pyrene adsorption determined by FE-SEM showed that the sepiolite fibers are much longer than their widths, which are only several laths (several nanometres). This is a result of growth, mostly along the c-axis, at the expense of the diffusion of pyrene molecules through aqueous solution. As a consequence, a significant fibrous morphology is produced following the adsorption of pyrene by both sepiolites

Comparison of modified montmorillonite adsorbents. Part I:Preparation, characterization and phenol adsorption

This study concerns with the development of modified montmorillonites as adsorbents for water treatment. Polymeric aluminium and iron intercalated forms of montmorillonites have been prepared in the absence and presence of an alkylammonium cationic surfactant (Hexdecyl-trimethyl-ammonium bromide, HDTMA). Montmorillonites intercalated with polymeric Al, Fe, Fe/Al (2:1 Fe to Al ratio in solution), possess large N2 Brunauer-Emmett-Teller (BET) surface areas. XRD data also shows trace amounts of illite and plagioclase within the clay materials. Montmorillonites intercalated with HDTMA, polymeric Fe/HDTMA, polymeric Al/HDTMA and polymeric Fe/Al/HDTMA (1:1 metal to surfactant molar ratio in solution) undergo some losses of N2 BET surface areas. Preliminary adsorption studies on phenol have shown that polymeric Al/HDTMA- and HDTMA-only-modified montmorillonites possess a good affinity for phenol, whereas the polymeric Al/Fe modified- and starting montmorillonites have little affinity for phenol adsorption

Effects of nanosized titanium dioxide (TiO2) and fullerene (C60) on wastewater microorganisms activity

This paper investigates the impact of nano-TiO2 and fullerene (C60) on the activity of micro-organisms present in wastewater treatment works (WWTWs). Results showed that low concentration levels of nano-TiO2 (10 μg.L-1 ) and fullerene (1 μg.L-1 ) has little effect on both gas production and the microorganisms’ morphology. However higher concentrations of nano-TiO2 (100 and 1,000 μg.L-1 ) and fullerene (10 and 100 μg.L-1 ) reduced or stopped completely gas production. SEM micrographs showed that addition of nanoparticles reduced the microorganisms count up to 30 min of exposure, followed by an increase of selected micro-organisms after a 360 minutes exposure to TiO2 and Fullerene. Overall, this study demonstrates that engineered nanoparticle concentration levels and exposure time play an important role in the toxicity of microbial communities present in WWTWs. It also shows that under stressed conditions, the micro-organisms appear to protect themselves via a spore forming mechanism that allows them to survive the environment